Lachuá National Park and Biotopo del Quetzal Administrations and staff are ..... The relationship between vegetation and pollen found in depository records, either ..... settlement took place in the region (Leyden, 2002), but emphasis has been ...
Natural and cultural landscape evolution during the Late Holocene in North Central Guatemalan Lowlands and Highlands
Carlos Enrique Avendaño Mendoza
A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Graduate Department of Geography University of Toronto
© Copyright by Carlos Enrique Avendaño Mendoza, 2012
Natural and cultural landscape evolution during the Late Holocene in North Central Guatemalan Lowlands and Highlands Doctor of Philosophy 2012 Carlos Enrique Avendaño Mendoza Graduate Department of Geography University of Toronto
Abstract Paleoecology has been only in recent decades applied to Mesoamerica; this thesis provides new records of paleoenvironmental changes in Guatemala. Paleoecological reconstructions are developed based mainly on pollen in the Lachuá lowlands and Purulhá highlands of the Las Verapaces Region. For the first time, quantitative vegetation and climate analyses are developed, and plant indicator taxa from vegetation belts are identified. Changes in vegetation are explained partially by elevation and climatic parameters, topography, drainage divides, and biogeography. Pollen rain and indicator plant taxa from vegetation belts were linked through a first modern pollen rain analysis based on bryophyte polsters and surface sediments. The latter contain fewer forestinterior plant taxa in both locations, and in the highlands, they contain higher local pollen content than in the lowlands. These calibrations aided vegetation reconstructions based on fossil pollen in sediment records from the Lachuá and Purulhá regions.
Reconstructions for the last ~2000 years before present (BP) were developed based on fossil pollen from cores P-4 on a floodplain in Purulhá, and L-3, a wetland in Lachuá.
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Core P-4 suggests that Mayan populations developed a system of agricultural terraces in a former paleolake-swamp environment, which was abandoned at the time of the Spanish Conquest (~400 BP). Core L-3 indicates the abandonment of Mayan “Forest Gardens” at the time of the early Postclassic. These gardens likely prevailed during the Classic period (~300-1100 yrs BP) at the outskirts of the ancient city of Salinas de los Nueve Cerros. Following abandonment, forest recovery took place for about 800 yrs. Cultural factors are found to be more important in determining vegetation dynamics in this region, since no clear evidence of climate forcing was found. The P-4 and L-3 cores provide likely evidence that Mayan populations were, contrary to other evidence, innovative landscape managers. Scenarios in the Las Verapaces Region have been drastically modified in recent times (e.g. after the European Conquest), as suggested by pollen evidence in the top of both P-4 and L-3 cores, possibly due mostly to modern large scale natural resources exploitation, which represent environmental threats greater than any seen in the last ca. 2000 years.
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Acknowledgments I deeply thank my supervisor Sharon Cowling for her sincere and wonderful support during the development of my Ph.D since the very first day I arrived to Canada. She was there waiting for me in the Toronto International Pearson Airport with a sign that had my name on, I can only say “Muchas gracias eternas”. Thanked is my co-supervisor Sarah Finkelstein for her marvellous support at the Paleoecology Laboratory of the Department of Geography. I had the honor to be at the start of her Laboratory and see the evolution to what today is: An excellent place to learn and grow.
I thank Prof. Tenley Conway and Prof. Anthony Davis for their helpful comments as part of my Ph.D. Academic Committee. Prof. Juan Carlos Berrio is greatly thanked for his valuable training in tropical paleoecology during field campaign in Guatemala and during my visits to his laboratory at the Department of Geography, Leicester University, England. I thank his wife Natalia de Berrio for her support too. I thank too the “Los Juanetes”, a Latin American rock band in the middle of England, for making my visit a nice one. I thank the Guatemalan team, “los COMPAI” and more, that supported me during my field campaign in Guatemala in 2006 and many many more things.
Lachuá National Park and Biotopo del Quetzal Administrations and staff are thanked for supporting my research. I am greatly thankful to forest guards at Lachuá National Park for their support in bryophyte polster and core sampling. I thank Santa Lucia Lachuá Municipality for support in collecting sediments from Salinas de los Nueve Cerros, especially to Major Pedro Oxom and Family Tun. San Cristobal Verapaz Municipality iv
Administration and staff are thanked for supporting our research. Fincas Villa Trinidad, Patal, Chisiguan, and Lesbia Mus and Yolanda Barahona are thanked for their support in collecting sediments.
I thank CONAP, Franklin Herrera, Escuela de Biología –at the Faculty of CCQQ and Pharmacy –USAC- for the support in acquiring collection and research licenses. As well I thank staff and members of Escuela de Biología, Faculty of CCQQ and Pharmacy, and USAC for their support during my Ph.D.
I thank Dr. Gerald Islebe for his support in pollen identification and feedback during my thesis development. Enric Aguilar and Melissa Gervais are thanked for obtaining Guatemalan climatic information. Joan Bunbury is greatly thanked for the support in creating maps and using CANOCO ©. Dr. Arnoud Boom is thanked for his support during my visit to Leicester University, England (as well, thanks for introducing me more into Asian Cinema). Grace Jeon is thanked for her support in developing Loss-on-ignition measurements for my core samples in the Paleoecology Lab, Department of Geography – UofT-. The Centre for Global Change Science and their staff, especially Ana Sousa, at the University of Toronto is greatly thanked for enhancing my Ph.D. experience. I thank Prof. Jock McAndrews and Charlie Turton for their support during my Ph.D.
I thank everybody at the Department of Geography who supported me during my Ph.D. years as a student, especially from the main office at Sidney Smith (esp. Marianne Ishibashi, Marika Maslej, and Jessica Finlayson). I am very grateful to the Physical
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Geography Building (PGB) community who supported and helped me, especially members of Cowling and Finkelstein’s research laboratories. Members of Chen’s, Diamond’s and Desloge’s laboratories are greatly thanked for their company and support. I am greatly grateful to Mircea Pilaf for his support since the first day I arrived to PGB and for the conversations in Romanian. I thank the “Geography soccer” community whom I shared many summer, fall, winter, and spring games. Thanked are Maria Johnson and Family for being my Guatemalan-“Chapina”-Canadian Family.
I am grateful to Claudia Avendaño and Knutt Eissermann for providing help and time in finding the source vegetation literature for this study. I am grateful to Maria Elena Hidalgo “mi Ague”, Carlos Avendaño E., Yolanda Mendoza de Avendaño, Gary Avendaño, and Hector Bol for providing help during field work. I thank my Family in Guatemala for their spiritual and moral support: Papa, Mama, Clada, Gary, Abue, Hector, Ti Lili, Dn. Enrique, Kennes ... This thesis is dedicated to my Family, which has supported me in my entire life in any possible path that I have taken … forever and ever.
Special dedication for Mateo and Belinda, who now have become my triangle of life, joy, and motivation to become a better being. Mateo: “No llegó la gota carmín, Llegó en su lugar la noticia de su visita, Certidumbres y rumbos no aleatorios, A esta edad, en este lugar, en esta vida… Semilla liberando indicios de luz, Transformando auras, metamorfosis interna, Milagro de la multiplicación de tu rostro en cada rostro, en el niño de la calle, en el abuelo de la esquina, en el rostro del espejo, Bien leí que en tradiciones ancestrales se entiende como la llegada de un maestro, En silencio quiero aprender de ti… Después de años de ser profecía, la epifanía llego esta mañana: reconocer al prójimo como a mi propio hijo… Traes polvo cósmico celestial, soplas tu aliento en mi oído y me revelas el universo”.
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Table of Contents Abstract ............................................................................................................................... ii Acknowledgments...................................................................................................... iv List of Tables ............................................................................................................. ix List of Figures ............................................................................................................. x List of Appendices .................................................................................................... xii Chapter 1: Background Information ................................................................................... 1 1.1 Pollen as a Paleoecological Proxy ........................................................................ 1 1.2 Climate Variability Over the Holocene ................................................................ 4 1.3 Reconstructing vegetation and landscapes............................................................ 8 1.4 Reconstructing Cultural Landscapes................................................................... 10 1.5 Thesis Objectives and Research Questions......................................................... 13 1.6 Geomorphological and Vegetational Setting of Study Region........................... 15 1.7 Cultural History of Study Region ....................................................................... 20 Chapter 2 Vegetation Distribution along the Las Verapaces region in North Central Guatemala.... 27 2.1 Introduction......................................................................................................... 27 2.2 Methods............................................................................................................... 30 2.3 Results................................................................................................................. 35 2.4 Discussion ........................................................................................................... 47 2.5. Chapter summary ............................................................................................... 54 Chapter 3 Modern pollen rain in the north-central Guatemalan lowlands and highlands................. 56 3.1 Introduction......................................................................................................... 56 3.2 Methods............................................................................................................... 59 3.3 Results................................................................................................................. 64 3.4 Discussion ........................................................................................................... 85 3.5. Chapter summary ............................................................................................... 95 Chapter 4 Late-Holocene History of a Highland Floodplain in Las Verapaces, Guatemala............. 98 4.1 Introduction......................................................................................................... 98 4.2 Methods............................................................................................................... 99 4.3 Results............................................................................................................... 103 4.4 Discussion ......................................................................................................... 115 vii
4.5. Chapter Summary ............................................................................................ 132 Chapter 5 The Lachuá Lowlands Rain Forest in Guatemala: 2,000 yrs of forested landscape? ..... 134 5.1 Introduction....................................................................................................... 134 5.2 Methods............................................................................................................. 136 5.3 Results............................................................................................................... 139 5.4 Discussion ......................................................................................................... 149 5.5 Chapter summary .............................................................................................. 161 Chapter 6 Conclusions..................................................................................................................... 163 6.1 What are the factors that explain vegetation distribution along the Las Verapaces environmental gradient and what taxa can be used as "indicator species"? ........... 164 6.2 Can paleoecological calibrations for fossil pollen be constructed from a comparison of modern pollen rain from surface sediments and bryophyte polsters? ................................................................................................................................. 166 6.3 What are the major vegetation changes recorded in the highland core from the Las Verapaces region? ............................................................................................ 168 6.4 What are the major vegetation changes recorded in the lowland core from the Las Verapaces region? ............................................................................................ 170 6.5 What is the role of natural variability and cultural factors related to the Maya Civilization in the evolution of landscapes in the Las Verapaces Region? ............ 172 References....................................................................................................................... 174 Appendices...................................................................................................................... 196
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List of Tables Table 2.1. Sites included in the Las Verapaces Gradient, providing a total of 23 sampling units (SU) from 9 sites spanning an elevation gradient of 170 to 2532 m asl. Table 2.2. Indicator plant taxa for the three vegetation belts along the Las Verapaces Gradient, selected from DCA axis scores for species (see text for details). Table 2.3. Generalist plant taxa for the Las Verapaces Gradient, as determined by DCA axis scores for species (see text for details). Table 2.4. Disjunctive plant taxa distributed in Lowland Rain Forest and Montane Cloud Forest in the Las Verapaces Gradient generated from DCA axis scores for species (see text for details). Table 3.1. Pollen types and their % range for bryophyte polsters and surface sediments. Information about vegetation belt, plant habit, and pollen dispersal syndrome is provided. Table 3.2. Lachuá bryophyte polsters and surface sediments samples. Table 3.3. Purulhá bryophyte polsters and surface sediments samples. Table 3.4. Factor Analysis scores for pollen types with highest amount of variance. Table 4.1. P-4 core stratigraphic sequence. Table 4.2. Radiocarbon dates, calibrated age ranges from dated sediment from P-4 core of the Cahabón Floodplain, Purulhá Table 5.1. Radiocarbon dates, calibrated age ranges from dated sediment from P-4 core of the Cahabón Floodplain, Purulhá.
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List of Figures Figure 1.1. Temperature changes in the late Pleistocene and the Holocene inferred from oxygen-18 measurements in Greenland ice core (taken from Dergachev and van Geel, 2004). Figure 1.2. Location of Guatemala in Central America. Numbers indicate location of meteorological stations. Figure 1.3. Topographic map of the Las Verapaces Region in Guatemala. Figure 1.4. Topographic map of study sites in the Las Verapaces Region in Guatemala. Map I= Lachuá lowlands, Map II= Purulhá highlands. Figure 2.1. Detrended Correspondence Analysis diagram of Las Verapaces sites along the first two DCA axes. Figure 2.2. Linear regression of Detrended Correspondence Analysis (DCA) Axis 1 scores (raw scores) of indicator plant taxa (A) and sites (B) against elevation values per site of the Las Verapaces Gradient. Figure 2.3. Linear regression curves for temperature (°C) from meteorological stations from Central and Northern Guatemala. Figure 2.4. Detrended Correspondence Analysis diagram for the Las Verapaces Gradient sites and climatic variables. Figure 2.5. A) Indicator (in one vegetation belt) and B) generalist (across two vegetation belts) taxa separated according to their biogeographic origin along the Las Verapaces gradient vegetation belts Figure 3.1. Location of Guatemala in Central America. Las Verapaces Region is enclosed in rectangle. Figure 3.2. Pollen diagram from Lachuá and Purulhá based on bryophyte polsters and surface sediment samples. Figure 3.3. Lachuá pollen diagram based on bryophyte polsters and surface sediment samples. Figure 3.4. Lachuá DCA Q-mode diagrams of arboreal pollen data with Pinus removal. Figure 3.5. Purulhá pollen diagram based on bryophyte polster and surface sediment samples. x
Figure 3.6. Purulhá DCA Q-mode diagrams based on arboreal pollen and non-arboreal pollen data. Figure 3.7. Las Verapaces DCA Q-mode diagram AP shared data. Figure 4.1. P-4 core paleoecological diagram taken from Cahabón River Flooplain. Figure 4.2. Graph showing depth (cm) vs. calendar age (cal yrs BP) of sediments from core P-4 taken from the Cahabón River floodplain. Figure 4.3. Principal Component Analysis (PCA) of sampled levels from core P-4. Figure 4.4. Pollen percentage diagram of P-4 core from the Cahabón River floodplain. Figure 4.5. Location of the headwaters of the Cahabón River and the floodplain. Figure 4.6. Principal Component Analysis (PCA) of modern pollen rain samples from Purulhá highlands and fossil samples from core P-4. Figure 4.7. Principal Component Analysis (PCA) of modern pollen rain samples from Purulhá highlands and sampled levels from core P-4. Figure 4.8. Cahabón River and its floodplain. Series of 3 arrows indicate river flow direction. N= North, masl=meters above sea level. Taken by J.C. Berrio © 2006.
Figure 5.1. L-3 core paleoecological diagram taken from a wetland next to Lake Lachuá. Figure 5.2. Principal Component Analysis (PCA) of sampled levels from core L-3. Figure 5.3. Pollen percentage diagram of L-3 core from a wetland next to Lake Lachuá. Figure 5.4. Location of the ancient Mayan city of Salinas de los Nueve Cerros on the banks of the Chixoy River, Alta Verapaz, Guatemala. Figure 5.5. Principal Component Analysis (PCA) of modern pollen rain samples from Lachuá lowlands and fossil samples from core L-3.
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List of Appendices Appendix 2.1. Indicator, generalist, and disjunctive plant checklist. Appendix 3.1. Pollen types found in modern pollen calibrations and fossil pollen spectra from cores P-4 and L-3. Associated plant and uses by ancient Mayan populations are shown. Appendix 4.1. Pollen counts (raw) from P-4 core. Appendix 5.1. Pollen counts (raw) from L-3 core.
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Chapter 1: Background Information 1.1 Pollen as a Paleoecological Proxy One of the main objectives of paleoecological research is to reconstruct environmental changes occuring at different scales of resolution, from global to local scales (Bennington et al., 2009; Birks, 2005; Hunter, 1998; Willis and Birks, 2006). Many Holocene examples can be cited that demonstrate how natural and cultural factors influence the evolution of landscapes and regions (Berrio et al., 2001; Lorimer, 2001; Muñoz and Gajewski, 2010; Ye et al., 2010). The likely reason for the emphasis on separating natural from cultural factors relates to our understanding of whether current global environmental trends are due to natural variability, cultural factors, or some combination (Harris, 2003; Cao et al., 2010).
Vegetation is a fundamental component of ecosystems, landscapes and regions, and has been used widely as a paleoecological indicator (Markgraf et al., 2009; Valsecchi et al., 2010; Cheng, 2011). Vegetation was chosen as a proxy for landscape evolution because of its intimate relationship with climatic and topographic variability (Clark, 2007; Davidar et al., 2005; Simona et al., 2009). Vegetation reflects the environmental and/or cultural regimes that control landscapes and regions at different spatio-temporal ranges.
The chosen proxy for vegetation reconstruction is pollen because of its taxonomic specificity and because it reflects processes related to vegetation dynamics (i.e. pollination), in addition to the fact that it has been studied thoroughly and used often for
2 different applications in biogeography, climate change, biome reconstructions, and archaeology (Berrio et al., 2001; Birks and Birks, 2003.; Graham, 2006; Marchant et al., 2009). The relationship between vegetation and pollen found in depository records, either superficial or sedimentary, is not 1:1 because of the multiple factors that are involved in pollen release, transportation, deposition and preservation (Brown et al., 2007; Bunting et al., 2004; Campbell, 1999; Fægri and Iversen, 1989). It is necessary to understand the relationship between vegetation and pollen collected from depositories, in order to understand pollen representation at modern or past times for a determined landscape and region. Therefore the concept of uniformitarism underlies palynological research: it is assumed that the chosen proxy has had a response in the past similar to its responses to present-day natural and cultural changes (Bradley, 1999).
Vegetation has been closely linked to human history and activities (e.g. agriculture and forestry) because vegetation provides a resource source for multiple needs: timber, fuelwood, medicine, food, and resins (Fuller et al., 2010; Innes et al., 2009; Rokaya et al., 2010; Weiser and Lepofsky, 2009). Complementary use of archaeological methods helps to broaden our ability to understand human impact on landscapes (Li et al., 2010; McKey et al., 2010; Weiss and Brunner, 2010). Pollen grains (i.e. as micro-botanical remains or microfossils) have been widely used in paleoecology and have become relevant proxies to reveal natural and cultural factors in landscape evolution (Lozano-García et al., 2010; Scharf, 2010). Changes in pollen composition, pollen abundance, and information related to the presence or absence of specific taxa provide the foundation for paleoecological reconstructions of past environmental change.
3 Modern pollen spectra have been studied from bryophyte polsters (e.g. mosses and liverworts) and are collected mostly from the interior of non-disturbed forests (Domínguez-Vázquez et al., 2004). These studies are important in understanding the conditions under which the pollen is deposited; these studies are also necessary for comparisons (i.e. in presence, absence and abundance) between observed pollen signal and surrounding plant taxa. This modern-day calibration process is necessary for the best possible interpretation of the fossil pollen record.
Topography affects energy distribution in landscapes, such as water and wind flows where pollen transportation occurs (Schueler and Schluenzen, 2006; Vogler et al., 2009). The role of topography in affecting pollen transport, however, is not entirely understood (Higgins et al., 2003). These processes have mostly studied with respect to maize pollen in terms of cross-pollination in agricultural fields (Klein et al., 2003). On its own, elevation above sea level has an influence on pollen dispersal and deposition because of orographic effects related to patterns of wind circulation (Fægri and Iversen, 1989). Regionally-dispersed pollen is sensitive to atmospheric conditions, for example, because surface convection (i.e. air turbulence from heating) can raise pollen above the canopylevel, causing long-distance, horizontal transfer until the air parcel eventually cools and descends (Murray et al., 2007), or it encounters a “disturbance” in flow such as a lake basin causing pollen to fall out of the atmosphere (Sugita 1993). Provenance of pollen may also be a source of bias in interpreting paleoecological signals because where sediment is deposited (i.e. lakes, rivers, oceans) and how it is transported (i.e. by wind, water, terrestrial and aquatic animals) is important (Traverse, 1994; Nielsen, 2005). Once
4 pollen grains land on a surface, they will respond to the physical, chemical, and biological processes occurring on the surface, that in turn determine sedimentation and preservation of pollen samples. The understanding of taphonomy and pollen-environment relationship is determinant in pollen analysis, since an important assumption is that the pollen assemblage recorded from a sediment sample is the same as the originally deposited (Twiddle and Bunting, 2010).
The wide ranging applications of pollen analysis in paleoecology have increased the research scope to conservation biology and biogeography. For example, conservation efforts have been directed where plant communities in riparian environments have been identified as relicts (i.e. early Holocene), after studying pollen spectra in sedimentary records found in floodplains (Southgate, 2010). At the geological scale, pollen records have been the basis to explain the evolution of biomes coupled to tectonic processes (e.g. orogeny) based on pollen spectra collected in lakes sediments in the Andes (Hooghiemstra et al., 2006).
1.2 Climate Variability Over the Holocene Reconstucting past climate changes is important for explaining roles of external and internal forcings on the climate system and for predicting future trends. External forcings on the climate system include changes in orbital parameters of the Earth, and solar variability; internal forcings, by contrast, are related to processes that occur within the Earth system (e.g. volcanic activity) (Beniston, 2005). The Milankovitch Cycles are important variations in Earth’s orbit, known mostly for their role in promoting the
5 Pleistocene Ice Ages (Lisiecki, 2010). The parameter of eccentricity (the measure of the shape of the Earth's orbit around the sun) varies on a timescale of ~ 100,000 yrs and contributes to glacial-interglacial cycling (Berger, 1989). The other two Milankovitch parameters are: obliquity (measure of the Earth’s rotation tilt from 22 to 24.8° every 41 ky) that is responsible for the definition of tropical and circum-polar latitudes, and precession of the equinoxes (which cycles on a scale of 19 to 26 ky), which is related to solar insolation variability as a function of the Earth-Sun distance at the moment of the vernal equinox. The interaction of the three Milankovitch parameters is consistent with recorded climatic variability at the multi-millenial timescale, by producing a complex pattern of solar radiation reception on Earth’s atmosphere (Mendoza, 2005). Large-scale biotic processes such as migration and colonization have been affected by these cycles and modern day biogeography has been greatly influenced by the glacial – interglacial cycling of the Quaternary (Erwin, 2009; Kerhoulas and Arbogast, 2010).
At a much smaller time scale, solar variability as evidenced through the sunspot cycles of 11, 22 and 240 years, result in changes in the amount of short wave radiation reaching the Earth (Rapp, 2010). Decreased occurrence of sunspots is believed to be one of the factors explaining reductions of global temperature (see Little Ice Age below) (Haase-Schramm et al., 2005).
Internal forcing of climate is related to volcanic activity (i.e. tectonics), ocean circulation, and critical changes in the biosphere (marine and terrestrial) and cryosphere (Beniston, 2005). Volcanic activity cools the climate because particulate matter emitted from the
6 eruption changes the Earth's albedo, increasing solar energy reflectance. Ocean circulation patterns affect the climate, such as the associated drop in global temperatures due to a weakening of the thermohaline circulation during the Younger Dryas (ca. 11,000 yrs BP) and Little Ice Age (ca. 300 yrs BP) (Bradley and England, 2008; Helama et al., 2009). Variability in other circulations could have more regional effects at decadal time scales such as El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) (Seager et al., 2010). The former is associated to the contraction and expansion of warm waters in the west Pacific, and the latter is believed to account for ca. 50% of variability in sea level pressure on both sides of the Atlantic Ocean. The internal forcing factors have in common that they operate at a sub-millenial time scale.
The explanation of the Holocene climatic variability requires understanding the coupled effects of external and internal forcings. During the last 10,000-12,000 years the Holocene stands as an epoch of warmth and steady climate, characterized by centennial and millennial-scale alternating of cold and warm periods, superimposed over a longterm trend of first warming and then cooling (Bjune et al., 2004). The onset of the Holocene climate has been shaped by the cyclical transition from a glacial to an interglacial where the maximum insolation was experienced (~10 ky BP) (Solanki et al., 2004) (Figure 1.1.). Thereafter four warming maxima, alternated by cold stages, have been deducted from paleoecological data during the intervals: 6700-5700, 4500-3200, 2300-1600, and during 1150-900 yrs BP (the Medieval Climatic Optimum) (Dergachev and van Geel, 2004). Cold Heinrich events (stadials) and Dansgaard-Oeschger warm stages (interstadials) are important factors that are believed to play a role determining
7 climatic shifts at the millennial scale (Merkel et al., 2010). Millennial to centennial natural variability modifies macro-regional climatic regimes and therefore more localized dynamics such as forest humidity and temperature (Jouzel et al., 2007; Popescu et al., 2010).
Although global climatic synchronicities have been recognized, regional variations play a critical role in understanding biogeographical patterns found at smaller spatio-temporal scales (Viau and Gajewski, 2009). Variability in the location of the Intertropical Convergence Zone (Chiang and Bitz, 2005; Holbourn et al., 2010) and cyclicity of ENSO (Merkel et al., 2010) are of major importance to understanding climatic variability at more regional scales in Mesoamerica. Evidence of climatic variability in the Yucatán Peninsula, is derived from the 206-year period oscillations of oxygen isotopes and gypsum precipitation from Lake Chicancanab, and possibly related to variation in solar radiation (Hodell et al., 2001). Similar paleoclimatic patterns have been gathered from
Figure 1.1 Temperature changes along the late Pleistocene and the Holocene inferred from oxygen-18 measurements in Greenland ice core (taken from Dergachev and van Geel, 2004).
8 the Circum-Caribbean, Lake Valencia and the Cariaco Basin in Venezuela, and when combined with the Chicancanab data, aligns with critical processes along major cultural periods (Alley et al., 2003; Hodell et al., 1991; Peterson et al., 1991). Arid events have been associated with cyclic events and include observed droughts between 150 and 250 AD (Pre-Classic abandonment), 750-1050 AD (Terminal Classic Collapse) and 1450 AD (Post-Classic) (Hodell et al., 2007).
The climate system is currently understood as the product of the coupled interactions between the atmosphere, hydrosphere, lithosphere, cryosphere, and biosphere. Information provided by paleoclimatic studies provide scientific basis for hypothesis testing of climatic variability in determined locations under different temporal scales of resolution.
1.3 Reconstructing vegetation and landscapes A large number of vegetation reconstructions based on pollen have been conducted around the world, spanning time periods from hundred to millions of years ago, and have provided important information to determine the roles of natural factors in landscape evolution. Based on changes in pollen composition, it has been possible to identify a high correlation between tectonic processes of the Andean orogeny of the last 3 million years (Mya) with altitudinal changes in North Andean biomes (Hooghiemstra and Van der Hammen, 2004; Torres et al., 2005). In coastal environments, sea level changes at the multi-millenial scale have been analyzed based on regressive and transgressive phases
9 reconstructed from sedimentary sequences, and have been used in conjunction with pollen information to show an inland-to-coast migration of vegetation (Torrescano and Islebe, 2006; Gabriel et al., 2009). Milankovitch cycles affect the retreat and advance of glacial ice caps, events that can be recognized in pollen diagrams showing latitudinal tree line oscillations (Kramer et al., 2010). Other periods of natural climatic variability such as the Younger Dryas stadial (cold event) (Kokorowski et al., 2008) and solar cycles are evident in pollen diagrams (Morner, 2010). Pollen from the Arctic specialist Dryas octopetala is used as an indicator of the Younger Dryas because of the increase in distribution and abundance of D. octopetala at this stadial (Joosten, 1995).
In places such as the Mexican Central Highlands and the Lacandon rain forest in Chiapas, evidence of the Maya Terminal Classic (800-900 century AD) drought event has been interpreted based on the increase of Pinus pollen (Almeida et al., 2005; DomínguezVázquez and Islebe, 2008). In contrast, reconstructions from neighboring regions such as the Mexican Sierra Madre Oriental (East-Central Mexico) (Conserva and Byrne, 2002) and Sierra de Los Tuxtlas (Lozano-García et al., 2010) show no evidence of drought and actually indicate slightly moister conditions. Geographical variability in precipitation may be because of orographic effects in topographically complex regions, which creates climatic envelopes at the regional scale. For example, Wendt (1989) proposed the existence of a wet belt across the Gulf of Mexico, Southeast of Mexico, Central Guatemala, and the Izabal province (Caribbean Guatemalan Coast), which possibly allowed the permanence of hypothesized tropical rain forests pleistocenic refuges.
10 Data from Los Tuxtlas show evidence of the Little Ice Age (LIA) in the Gulf of Mexico; multi-proxy records indicate wetter conditions around 1500 to 1700 AD (e.g. increased lake levels and increased accumulation rates of pollen of lowland or highland forest taxa) (Lozano-García et al., 2007; Lozano-García et al., 2010). In contrast, reconstructions based on oxygen isotopes and titanium content from the Yucatán peninsula (Aguada X’caamal) and the Cariaco basin (respectively) show lower precipitation between 1500 and 1800 AD (Hodell et al., 2005). Climate proxies and the presence of Zea pollen from Lake Tzib at Quintana Roo, Mexico (Carrillo-Bastos et al., 2010) likely indicate higher precipitation around 1200 AD contrary to what would be expected during the time of the Medieval Warm Period (MWP) (just before the LIA).
1.4 Reconstructing Cultural Landscapes Pollen can also be used to reconstruct anthropogenic impacts on landscapes during different cultural periods, for example, during the early Holocene phase of hunters-andgatherers (Kunes et al., 2008). Cultural impacts on the environment are of greater interest for more recent times, including the transition from nomadic human populations to fully sedentary communities (Rowley-Conwy, 2009). It is when human groups started to remain in one area for longer periods of time that we can see a clear anthropogenic signal in the paleo-record, reflecting the evolution of agriculture as an important modifier of landscapes.
In different culturally important regions around the globe (the Near East, Ganges Delta, Yellow River watershed), the origins and development of agriculture have been
11 reconstructed based on the first appearance of cereal pollen cultigens. In the case of Mesoamerica, corn pollen (Zea mays L.) is traced (Zizumbo-Villarreal and ColungaGarcía, 2010) whereas in China, the initial presence of rice pollen (Oryza sativa) is used to signify the beginning of agriculture (Fuller et al., 2009). The reconstruction of landscapes histories based on architectural and ceramic remains (i.e. archaeological methods) is complemented with the use of pollen because it can tell a more complete story about an area, including information on landscape management, levels of disturbance, and conservation efforts (Bettis III et al., 2008; Dambrine et al., 2007; Delhon et al., 2009; Mercuri, 2008).
The magnitude to which anthropogenic activities influence landscapes is a topic of much discussion between researchers (Horrocks et al., 2007; Williams et al., 2010; Yu et al., 2010; Zhao et al., 2010). Numerous scholarly theories have been derived depending on the type of evidence collected (i.e. paleoecological versus archaeological) and the cultural context in which that evidence is found. On the one hand, ancient cultures have been considered responsible for major modifications to landscapes; involving activities that generally bring upon detrimental societal consequences as a result of natural factors such as soil erosion and resource depletion (Diamond, 2009; McWethy et al., 2009). It has been suggested that anthropogenic activities (particularly changes in land-use) can alter regional climate, such as precipitation (Shaw, 2003; Gill et al., 2007) and therefore could play an interactive role in prolonging periods of drought and/or deepening the magnitude of water stress. From this perspective, anthropogenic activities are considered the critical trigger in the collapse of past societies (Diamond, 2005).
12 In contrast, past societies can be viewed from the perspective of practicing sustainability of resources in their everyday activities, such as the planting of trees to prevent largescale erosion of highlands (Smith and Demarest, 2001; Aimers, 2007). From this second point of view, the “collapse” of an ancient civilization has foundations in multi-factorial processes, both anthropogenic and natural (e.g. biotic, abiotic) (Demarest et al., 2004; Demarest, 2009).
Regardless of how human activity is viewed within ecosystem dynamics, evidence shows an increasing effect of changes in greenhouse gas concentrations in the atmosphere, since the onset of agricultural activities, the introduction of large-scale herding of grazers, and most recently due to the burning of fossil fuels (Olofsson and Hickler, 2008; Brook, 2009). The "Anthropocene", a controversial naming of the latter period of the Holocene, has been defined by the period of over-arching effects of humans on climatic, hydrologic and edaphic cycles (Ruddiman, 2003; Crutzen, 2006).
13
1.5 Thesis Objectives and Research Questions
1.5.1. Rationale. The role of natural and cultural factors in the evolution of landscapes within the Las Verapaces region of north-central Guatemala is the focus of this thesis. Natural and cultural factors can intermingle or act independently at different spatio-temporal scales (Clark, 2007; Díaz and Stahle, 2007; Partel et al., 2007; Sarmiento et al., 2008; Wainwright, 2008). The separation of past cultural and natural processes by using paleoecological methodology is needed to help provide a solid scientific basis to assess modern-day impacts of human activities at the global, regional and landscape scales. This thesis is developed in the Lachuá lowlands and the Purulhá highlands of the Las Verapaces region, an important location in the Mesoamerican context due to its high biological and cultural diversity, which nevertheless lacks exploration in paleoecological terms.
1.5.2. Approach. My approach involves paleovegetation reconstructions of the Lachuá lowlands and the Purulhá highlands in the Las Verapaces Region from the Preclassic to modern-day times, covering the past two millennia. To develop paleo-vegetation reconstructions for the Las Verapaces Region, it was necessary to first determine the taxonomic composition of vegetation communities and the altitudinal distribution of vegetation types, including explanations for their geographical variation (Chapter 2). Since the relationship between the abundance of pollen grains and the abundance of corresponding vegetation is not 1:1,
14 it was necessary to develop the first calibration study of the region by comparing pollen sources such as lake sediments and bryophyte polsters and analyzing the modern pollen rain (Chapter 3). Paleoecological reconstructions were developed based on fossil pollen spectra collected from a core (P-4) from the Cahabón River floodplain at the Purulhá highlands spanning the last ~2390 years (Chapter 4) and a wetland core (L-3), taken adjacent to Lachuá Lake, within the Lachuá lowlands (Chapter 5) spanning the last ~2000 years.
Research Questions. The main research questions addressed in this thesis include:
a) What are the factors that explain vegetation distribution along the Las Verapaces environmental gradient and what taxa can be used as "indicators"?
b) Can paleoecological calibrations for fossil pollen be constructed from a comparison of modern pollen rain from surface sediments and bryophyte polsters?
c) What are the major vegetation changes recorded in the two (lowland, highland) cores from the Las Verapaces region?
d) What is the role of natural variability and cultural factors related to the Maya Civilization in the evolution of landscapes in the Las Verapaces Region?
15
1.6 Geomorphological and Vegetational Setting of Study Region The Las Verapaces region is located in north central Guatemala, encompassing sharp environmental gradients from the Lachuá lowlands (~170 masl) to the Purulhá highlands (~2500 masl) (Figure 1.2). In addition to being characterized by environmental gradients, I also selected the region because of the absence of paleoecological research (Islebe and Leyden, 2006) despite its importance in both natural and historical cultural diversity. Las Verapaces is distributed across two Guatemalan provinces: Alta Verapaz and Baja Verapaz (Figure 1.2 and 1.3). The geological structure of the area is primarily karstic terrain of Cretaceous and Tertiary origin (Alta Verapaz), with metamorphic regions dating from the Lower Paleozoic (Baja Verapaz and Alta Verapaz) (Ortega-Gutiérrez et al., 2007).
1.6.1 Lachuá Lowlands The Lachuá lowlands are located in a transitional zone between the Petén Lowlands and the Cordilleran central highlands (Weyl, 1980) and contain one of the last remnants of Lowland Rain Forest remaining in Guatemala (Figure 1.3) (for vegetation belt description see results Chapter 2). The site has a protected area, the Lachuá Lake National Park, which covers approximately 14,500 ha in addition to a surrounding buffer zone of approximately 28,000 ha (Monzón, 1999). An inventory of Lachuá’s forest species (as well as other vegetation types) was undertaken within the past 10 years (García, 2001; Ávila, 2004; Cajas, 2009; Castañeda, 1997), and more recently, a modern pollen reference collection of the thirty most abundant plant species has been collated (Barrientos, 2006). There is a Lowland Rain Forest remnant (~300 ha) northeast of
16 Lachuá Lake National Park located in the top of a hill 285 masl in elevation with a series of small ponds known as Tortugas (Tun personal communication, 2006). The remnant is known as Salinas de los Nueve Cerros Regional Park, where an archaeological site of the same name is located.
Geomorphologically, the area contains undulated karstic hills and varied landforms ranging from low- to mid-elevations (170-600 masl) (Avendaño et al. 2007). The Lachuá Lake is found at the Lachuá Lake National Park; a circular depression (400 hectares) with a depth of 200 m, draining into the lower sedimentary basin of the Chixoy River (Granados, 2001). Moisture-laden winds from the northwest and east originate from within the Caribbean Sea, creating a mean annual precipitation of approximately 20002499 mm. The rainy season occurs between May and October, with mean annual temperatures between 25.5–28°C (Monzón, 1999).
1.6.2 Purulhá highlands The Purulhá highlands cover the Cahabón River headwaters, and the Polochic and Chixoy upper basins, ranging in elevation from 1560-2300 masl (Figure 1.3). Purulhá contains a main remnant of cloud forest (1044 ha) that is protected under the jurisdiction of “Biotopo Universitario para la Conservación del Quetzal” (BUCQ) (CONAP, 2000). This site is underlain by the metamorphic and karstic system of the Sierra Chuacús mountain range (Weyl, 1980). Moisture-laden Caribbean winds from the east, northeast, and northwest result in mean annual precipitation around 2092 mm and mean annual
17
Figure 1.2. Location of Guatemala in Central America. Circle encloses location of the Las Verapaces Region. Numbers indicate locations of meteorological stations. 1= Flores, 2= Puerto Barrios, 3= Las Vegas, 4= Panzos, 5= Cahabón, 6=Papalhá, 7= Cobán, 8= Suiza Continental.
Gulf of Mexico
México
Caribbean Sea
1
Belize 2
Guatemala
7
5
6 4
3
Honduras
8
El Salvador
Nicaragua
Costa Rica
Pacific Ocean Panama
18
Figure 1.3. Topographic map of the Las Verapaces Region in Guatemala. Encircled numbers indicate study sites. 1= Lachuá lowlands, 2=Sierra Chinajá, 3= Rio Tinajas, 4= Chelemhá, 5=Tucurú, 6= Tamahú, 7=Purulhá (BUCQ)-, 8= Tactic, 9= Santa Cruz Verapaz. Locations #6 to #9 are part of the Purulhá highlands. Watershed names are indicated in italics. México
2 La Pasión
1
Chixoy
1800 m 1000 m 200 m Chinaja Watershed boundary
Cahabón
4
9 8
6
Polochic
5 3
7
19 temperatures between 13.9–20.4°C (García, 1998). The rainy and dry seasons occur between June and September and January and April, respectively. The Cahabón River headwaters are located in the municipality of Purulhá town, province of Baja Verapaz, at an elevation of approximately 1570 masl. The Cahabón River floodplain is characterized by the presence of entisols and inceptisols in the low valley sections, surrounded by andisols and ultisols in the surrounding mountains (MAGA, 2001). The floodplain is located close to the upper limit of the Lower Montane Rain Forest (1000-1800 masl), surrounded by valley slopes covered by Montane Cloud Forest (1800-2500 masl in my study region) (for vegetation belts description see results Chapter 2). Local inhabitants from Purulhá town have mentioned of the possible existence in the past of a lake in the environs of the town (Vázquez C. personal communication 2011).
1.6.3. Geographical setting and study design Vegetation sampling (Chapter 2) of lowland sites took place in separate watersheds: (1) the Chixoy watershed which is composed of mainly Cretaceous-Tertiary marine sediments and Quaternary alluvium, and (2) the Polochic watershed located over a pullapart type basin containing Quaternary alluvium (Fourcade et al., 1999). Highland sites are located in the upland portions of the Cahabón and Polochic watersheds, which are underlain by Pennsylvanian to Permian eclogitic rocks and gneisses (Ortega-Gutiérrez et al., 2007). Rio Tinajas vegetation sampling sites are located in a sub-watershed that drains into the Polochic Watershed (Tot, 2000).
20 Modern pollen samples for palynological calibration (Chapter 3) and core samples (Chapter 4 and 5) were collected in two sites located at both ends of the Las Verapaces elevational gradient (Figure 1.3): (1) Lowland Rain Forests at the Lachuá lowlands in Alta Verapaz (~ 170 masl), and (2) the Montane Cloud Forest and the transitional vegetation belt at the lower limit at the Purulhá highlands and its environs in Alta and Baja Verapaz (~ 1400-2000 masl). The Purulhá highlands in our study region represent the highest geographical point.
1.7 Cultural History of Study Region According to the cultural succession and temporal differentiation for Mesoamerican civilizations such as Olmec, Maya and Aztec (Chase et al., 2009), standardized periods have been defined as the following: 1) Pre-Classic (3000 BC-300 AD), 2) Classic (300 900 AD), and 3) Post-Classic (900~1500 AD). These periods are delineated based on critical changes to the political, economic and ceremonial development of Mesoamerican civilizations. The most studied transition includes the end of the Classic Period of the Maya Lowlands, known as the Terminal Classic Period (Demarest et al., 2004; Demarest, 2006).
Paleoecological studies in the Guatemalan Northern Petén Lowlands (Figure 1.2) have reconstructed environmental changes dating back to the Last Glacial before any human settlement took place in the region (Leyden, 2002), but emphasis has been placed on Mayan cities that flourished mostly during the Classic Cultural period (300-900 AD) (Islebe and Leyden, 2006). The heightened interest in this time period occurs mostly
21 because the majority of Classical cities underwent a regional transformation process at the time of the Terminal Classic, largely known as Classic Mayan collapse (Aimers, 2007). Conclusions from some authors indicate that environmental anomalies, such as droughts (Diamond, 2005; Gill et al., 2007), have played a critical role in determining the fate of human societies, sometimes enhanced by human disturbances, which brought together social instability and revolts due to natural resource demise. Contrasting research approaches have concluded that environmental variability could have played more of a secondary role on the transformation of societies, and that intrinsic societal characteristics have a more relevant role in societal collapse (Demarest et al., 2004). This latter approach emphasizes the idea that societies like the Mayan are able to cope with extrinsic disturbances such as environmental extreme events, even when facing intrinsic instabilities that requires substantial societal transformations.
Mesoamerican paleoecological research has provided explanations regarding the role of environmental and societal factors on the shaping of landscapes along both highlands and lowlands. Based on different fossil proxy evidence found in sedimentary records, some lowland locations indicate the occurrence of drastic droughts, which are believed to have had a dramatic impact on the transition between the Classic and Postclassic (900-1000 AD) . On the other hand, at some other locations experiencing possible arid events, there were relatively few cultural changes or negative anthropogenic environmental impacts even when human populations were highest. The Classic-Postclassic transition is delineated mostly as a socio-political and religious transformation, that in some locations promoted total or temporary abandonment of cities, semi-destruction due to warfare,
22 while in other locations, cultural flourishment took place (Demarest, 2009). Evidence indicates that the most dramatic changes to all aspects of the Mayan Culture and the environment occurred during the Spanish Conquest and Colonization (Elliot et al. 2010). The Spanish settlers brought new diseases that contributed in part to the Mayan population demise, and ultimately the introduction of new economic, political, sociological, and religious systems (Van Buren 2010).
There is an obvious void in the Mesoamerican paleoecological record that must be filled due to the contextual importance of the Las Verapaces region. The Las Verapaces lowlands represent an important geographical transition from the Northern Petén region to the Las Verapaces Highlands, and Southern Maya Area (i.e. Kaminal Juyu, Copán, and Takalik Abaj) (Rice et al., 1985; Fowler et al., 1989). The lack of paleoecological information for the Las Verapaces Region places this thesis as critical for providing information about the landscape evolution of the last two millennia. Natural and cultural factors have been explored in this thesis to provide a baseline for continuing paleoecological research in this region as well as in neighboring regions in Mesoamerica.
The Lachuá lowlands are located east of the neighboring Petexbatún cultural region where important cities were developed along the Pasión and Chixoy rivers banks (Demarest, 2006). The Petexbatún region had different political elites that established a succession of Kingdoms, where military control was critical to maintain privileged economic riverine routes. Cancuen, located approximately 60 km east of Lachuá, was an important city since the late Pre-Classic until its abandonment during the Late Classic
23 (Aimers, 2007). Paleoecological and paleoagronomic evidence from the Petexbatún lowlands indicate that sustainable agriculture and forestry were practiced in succession (Demarest, 1997). Sustainable management practices likely involved soil conservation to mitigate environmental deterioration with time (Beach and Dunning, 1995; Beach et al., 2008; Dunning et al., 1997).
At the Lachuá lowlands, the ancient city of Salinas de los Nueve Cerros was established as an important salt producing center along the Chixoy river banks (Figure 1.4) (Dillon, 1977; 1990; Garrido, 2009). There is no direct evidence describing landscape management practices, but it is possible that similar soil ammendment measures observed in the Petexbatún region were also occuring in Salinas de los Nueve Cerros. Archaeological studies indicate that the economic importance of the Mayan site of Salinas de los Nueve Cerros was salt production practiced from the Preclassic to PostClassic times. At present, population pressure in the Lachuá Region is beginning to encroach on the Lachuá Lake National Park and Salinas de los Nueve Cerros; over the past 50 years, 50% of the forest has been lost to anthropogenic land-use change (Avendaño et al, 2007). The population generally consists of people from the q’eqchi’ ethnic group who mostly ended up in the region as a result of territorial displacement and colonization projects following the Civil War (Hurtado, 2008).
In order to better understand the cultural processes that were taking place in the Maya Lowlands, it is critical to concomitantly address the environmental and cultural history of the Maya Highlands. The scarcity of lakes on the one hand explains why highlands (i.e.
24
Figure 1.4. Topographic map of study sites in the Las Verapaces Region in Guatemala. Map I= Lachuá lowlands, Map II= Purulhá highlands. Bryophyte polsters are indicated in letters and surface sediments in numbers. 1= L1, 2= L2, 3= L3, 4= Sa2 (Salinas de los Nueve Cerros archaeological site and natural reserve), 5=J1, 6= T1, 7= P4, 8= P1, A=samples Ca-Ce, B= samples Ra-Re. Both A and B are located at the Lachuá Lake National Park. C= Samples N1-N10 (“Biotopo Universitario para la Conservación del Quetzal”). Highland archaeological sites: VP=Valpraiso, CH= Chican, CX= Cerro Xucaneb, S= Sulin. National parks are represented as dark grey polygons. Rivers are irregular black thick lines. Lachuá Lake is represented as light gray polygon in map I. Chichoj Lake is represented as light gray polygon in map II. Samples 6-8 are located in the Cahabón River Floodplains. Isolines every 50 m in Map I (lowest point 150 masl, highest point 700 masl). Isolines every 100 m in Map II (lowest point 1400 masl, highest point 2300 masl).
25 Las Verapaces) paleoecological research lags behind its lowlands counterpart. But on the other hand, this scarcity is related to the main interest of researchers in wanting analyze paleoenvironmental records related to archaeological findings from major Classic Maya centers which were distributed mostly in Mesoamerican lowlands (Anselmetti et al., 2006; Hillesheim et al., 2005; Wahl et al., 2007). This trend has dominated despite of the importance that the multi-factorial interaction (i.e. political, economical, ceremonial, etc.) lowlands-highlands had for the development of the Maya Civilization during the last 3000 years (Freidel et al., 1993). Nevertheless, recently there has been an increase in addressing paleoecological questions related to highlands environments in Mesoamerica (Almeida et al., 2005).
There is scarce paleoecological information about highlands landscape management practices, but archaeological investigations indicate that relatively high gradient environmental (e.g. topographic) boundaries promoted the evolution of relatively small (regional) and well-bounded cultural systems (Sharer and Sedat, 1987). In the Purulhá highlands, there are many minor archaeological sites that range from the Pre-Classic to the Post-Classic, including such sites as Cerro Xucaneb, Chican, Sulin, and Valparaiso (Figure 1.4) (Arnauld, 1978, 1987; Ichon et al., 1996). In contrast to the lowlands, expansion and alliances of these highland cultural entities was limited in part to constrained communication over mountainous landscapes, and not strictly to economic, social, political and ideological factors (Ichon et al., 1996). Natural trade routes have been traced between lowland and highland archaeological sites that cross mountain ridges and valleys, therefore indicating that commerce and cultural interregional exchange were
26 occurring at this time (Andrews, 1984). It is precisely the connection between disparate regions that was important for the development of the Maya Civilization (Arnauld, 1997). It is the exchange of socio-political, cosmological and ceremonial knowledge, in addition to landscape management practices, that unifies the Mayan cultural region. Little has been discussed about the Mayan Highlands terminal Classic and the occurrence of citycenter collapse (Demarest, 2009). There is need for further investigation about what causes some cities to be abandoned while others to be founded and flourished.
Land-use at the Purulhá highlands during the late-19th century was dominated by coffee plantations, whereas today the area is dominated by a complex mosaic of cattle fields, agricultural crops (mainly corn), and ornamental species. Population density in this highland area (primarily comprising achi, poqomchi’, q’eqchi’, and ladino ethnic groups) is steadily increasing, and has created an ever heightening demand for land for agriculture and urbanization (CONAP, 2000). Following European conquest (ca. 500 yrs BP) socioeconomic and political pressures led to dramatic changes in (1) land-use patterns (i.e. introduction of cash crops and plantations), (2) foreign investment, and (3) displacement of indigenous populations (Van Buren, 2010). More recently, anthropogenic disturbances associated with civil war, strong military rule, colonization, deforestation and pollution related to natural resource extraction (i.e. mining) have contributed to the character of the landscape in the Las Verapaces Region (Hurtado, 2008).
27
Chapter 2: Vegetation Distribution along the Las Verapaces region in North Central Guatemala 2.1 Introduction Understanding the controls on vegetation distribution in the tropics will improve predictions of responses to future climate change (Freycon et al., 2010) and help to better determine factors behind centers of high biological diversity ("biodiversity"). Climate is usually considered a first-order control on vegetation type and distribution (Tietjen et al., 2010); however, other factors such as watershed topography (Bertoldi et al., 2010) and evolutionary history (Vanderpoorten et al., 2010) can also play critical roles in shaping biogeography. Guatemala currently does not have a formal protocol for describing vegetation types or belts based on floristic and environmental criteria, however, the following approaches have been used in the past: (1) qualitative integrations of flora with physiographic and geomorphologic factors (Villar, 1998), (2) quantitative local adaptations of Holdridge Life Zones (De La Cruz, 1982), or (3) qualitative adaptations of classifications from neighboring regions like Mexico (Rzedowski, 2006). More formalized vegetation identification surveys are needed, particularly in light of the fact that Guatemala is located in Nuclear Central America and is home to the Mesoamerican Tropical Forest Hotspot (Harvey et al., 2008). The Mesoamerican hotspot is renowned for its high vegetation diversity (Knapp and Davidse, 2006), despite being located in an area influenced by humans for over the past 7,000 years (Chinchilla, 1984). Guatemala’s rich
28 biological and cultural complexity highlight the necessity for better understanding the roles of natural and cultural factors in vegetation distribution.
The first research objective is to identify changes in vegetation communities and to delineate boundaries between vegetation belts along an elevational gradient located in the Purulhá highlands and the Lachuá lowlands of the Las Verapaces region in north central Guatemala. The names of the vegetation belts applied for Las Verapaces region were adapted and integrated from different vegetation regional studies (Breedlove, 1981; de la Cruz, 1982; Kappelle et al., 1995; Kappelle, 1996; Domínguez-Vázquez et al., 2004) (Table 2.1): (a) Lowland Rain Forest below 1000 masl, (b) Lower Montane Rain Forest between 1000 and 1800 masl and (c) Montane Cloud Forest above 1800 masl up to approximately 2500-3000 masl. Other vegetation belts found in neighbouring regions include (de la Cruz, 1982; Islebe and Kappelle, 1994; Islebe and Velázquez, 1994; Islebe et al., 1995) (Table 2.1): (d) Lowland Humid Forest, with less precipitation than the Lowland Rain Forest, such as in the northern Petén region; (e) Montane Mixed Forest, where the endemic tree Abies guatemalensis is found; (f) Sub-Alpine Forest, being the tree line limit in Guatemalan forests; and (g) Páramo (Alpine bunchgrassland), in the Sierra de los Cuchumatanes and in the Western Volcanic Chain.
In order to achieve the first research objective a meta-data analysis of different local literature sources has been created, where the distribution of plant taxa within one site or among different sites in the elevation gradient is included. The existence of plant taxa with discrete elevational distributions is responsible for the delineation of vegetation
29 Table 2.1 Description of vegetation belts found in the Las Verapaces region* and neighbouring regions in Guatemala.
Vegetation Belt
Elevation range (masl)
Mean annual precipitation (mm)
Associated plant taxa
Lowland Humid Forest
~ 0 to 4100
Hedyosmum mexicanum, Quercus, Podocarpus oleifolius.
Mixed Montane Forest
~ 2500 to 3000-3100
~2500
Abies guatemalensis, Alnus, Pinus ayacahuite, P. montezumae, Quercus.
Sub-Alpine Forest
~ 3100 to 3800
~1100-1800
Alnus, Buddleja, Juniperus, Pinus hartwegii.
Páramo (Alpine bunchgrassland)
~ >3800
~1275
Cardamine, Poa venosa, Senecio, (Sierra de los Cuchumatanes); Calamagrostris, Luzula, Halencia, Oxylobus, Poa tacanae (Western Volcanic Chain).
30 belts; alternatively, plant taxa that have more continuous distribution create landscape continuums (Kessler, 2000; Hemp, 2006).
The second objective is to evaluate the factors responsible for vegetation distribution and turnover of plant communities along the Las Verapaces region. Three key deriving factors will be examined: (1) elevation and associated changes in climate (i.e. environmental lapse rate), (2) landscape position and topography in drainage divides, and (3) biogeographic origin (i.e. over geological timescales). The findings from this analysis will also provide a critical baseline from which to conduct palaeoecological research because we can relate fossil pollen spectra to indicator taxa from modern-day vegetation belts. Ultimately, by studying the natural (biotic, abiotic) factors influencing vegetation I can begin to tease apart complex interactions between the natural environment and anthropogenic processes.
2.2 Methods
2.2.1 Compilation of the vegetation database For areas with few published records, forest inventory databases and unpublished academic theses provide a rich source from which to better understand the biotic and abiotic factors influencing vegetation trends observed across modern-day landscapes (Kitahara et al., 2009; Veen et al., 2010). Data on vegetation community composition, plant species identification and abundance were collected from multiple sources including silvicultural, ecological and landscape research reports (Table 2.2). Five out of
31 ten of the sources report ecological data using traditional experimental design, including large sample sizes and multiple replicates. Dissertation research conducted by University students in Guatemala was invaluable to the collation of the database. These sources included: (1) four undergraduate theses from Lachuá (Ávila, 2004; Cajas, 2009), Purulhá (García, 1998), and Chelemhá (López, 2009.), (2) one Master of Science thesis from Sierra Chinajá (Bonham, 2006), and (3) forestry inventories extracted from undergraduate theses for Tucurú (Paz, 2001), Tamahú (Alonso, 1999), Santa Cruz (Palala, 2000), Tactic (Mollinedo, 2002), and Rio Tinajas (Tot, 2000).
Because six studies only presented qualitative data (presence/absence), sources that had quantitative data (abundances) were transformed to presence/absence to standardize my database. Taxonomic nomenclature was also standardized when necessary and updated (Gentry, 1982; Smith et al., 2004). In some cases, standardization required retention of genus-level information only, correction of spelling, and revision of taxonomic synonymies. The end result is a matrix showing distributions (presence/absence) of 794 angiosperm taxa across 23 sampling units.
Although I recognize the ecological, biogeographic and economic importance of gymnosperms, I am not incorporating them in my study because in Guatemala little information on their distributions is available outside of a plantation/forestry context. Therefore, my analysis focuses on exclusively angiosperms.
32
2.2.2 Creation of climate databases To create a regional climate database for sites along our selected gradient, I used information from eight meteorological stations located in Central and Northern Guatemala (Figure 1.1). Data from seven stations at different elevations were collected directly from INSIVUMEH (Volcanology, Meteorology, and Hydrology National Institute) in Guatemala City, each having temporal coverage from the years 1990-2005 inclusive. From a longer climate database (42 years; 1961-2003) (Aguilar et al., 2005), data from Flores (123 masl) was used for my analysis. Of all meteorological variables available, I selected three temperature variables that best represent both extremes and average indicators of regional climate. The chosen variables include: (1) maximum absolute temperature (TXx) defined as the recorded annual maximum value of daily maximum temperature, (2) minimum absolute temperature (TNn) defined as the recorded annual minimum value of daily minimum temperature, and (3) mean annual temperature (MAT). Temperature parameters such as MAT have been used to estimate upper limits of low-elevation taxa (Latorre et al., 2006), and TNn and TXx are useful to estimate physiological barriers for plants survival (e.g. drop of temperatures close to overnight frosting and dessication stress related high temperatures, respectively).
2.2.3 Statistical Analysis A multivariate analysis was run on a total of 794 angiosperm plant taxa from nine sites with a total of 23 sampling units (presence/absence data), to determine the degree of similarity between sites and the relationships between taxonomic assemblages and climate variables. Through a detrended correspondence analysis (DCA) sites were
33 arranged in a diagram along ordination axes to indirectly identify possible underlying environmental gradients (Jongman et al., 1995). The presented DCA diagram presents axis scores transformed into percentages to help visualize the data variability (McCune and Mefford, 2006). I created dendrograms through hierarchical cluster analysis (HCA) (relative Euclidean distance and Unweighted Pair Group Method Algorithm; UPGMA) of sites with similar taxonomic composition, which were of aid to establish groups of sites in the DCA diagram (Jongman et al., 1995). Where consistent agglomeration of sites was observed through ordination axes and cluster analysis, a vegetation belt was delineated as a correlation of elevation and species composition (Axis scores). The software PC-Ord was used to conduct all statistical analyses (McCune and Mefford, 2006). Plant taxon that presented a unique DCA Axis 1 score were chosen as representative of a particular distribution pattern along the altitudinal gradient, instead of utilizing a group of taxa with the same Axis 1 score. Species scores are known to represent a particular site or groups of sites, as DCA Mode-Q analysis indicates that sites are “centroids” for an assemblage or array of determined species (Jongman et al., 1995). Species and sites scores are known to be illustrative of each other (Chase et al. 2000).
As mentioned earlier, the names of the vegetation belts and their elevation limits were established a priori (Table 2.1): (a) Lowland Rain Forest below 1000 masl, (b) Lower Montane Rain Forest between 1000 and 1800 masl and (c) Montane Cloud Forest between above 1800 and 2500 masl.
Indicator taxa were defined as those found
exclusively inside a vegetation belt (i.e. in a discrete elevation range like 1000-1800 masl) whereas generalist taxa are those with a wide distribution that span across one or
34
Table 2.2. Sites included in the vegetation database of the Las Verapaces region, providing a total of 23 sampling units (SU) from 10 studies spanning an elevation gradient of 170 to 2532 masl. Where indicated, elevation ranges used to calculate average elevations are shown in parentheses. If researchers pooled sampling units (SU) of a site into one vegetation data set, the average elevation was calculated for the site. When sampling units of one site were not pooled, their elevations and corresponding vegetation data were entered directly into our database. If elevation ranges for sampling units were given, the average elevation was calculated. For data type, Q indicates studies that used abundance as measurement and C indicates studies that used presence/absence as measurement. Source
Ávila (2004) and Cajas (2009)
Bonham (2006)
Paz (2001)
Alonso (1999)
Palala (2000)
Mollinedo (2002)
Tot (2000)
García (1998)
López (2009)
Sites
Lachuá (n=1)
Tucurú (n=3)
Tamahú (n=1)
Santa Cruz (n=1)
Tactic (n=1)
Rio Tinajas (n=6)
Purulhá (n=5)
Chelemhá (n=4)
SU codes (in bold)
Lach
Sierra Chinajá (n=1) Chin
Tam
Scruz
Tac
Tin1 Tin2 Tin3 Tin4 Tin5 Tin6
Pur1 Pur2 Pur3 Pur4 Pur5
Che1 Che2 Che3 Che4
Elevation (m asl)
170
Buena Vista (Bvta) Cumbre de Florida, (Flo) Chelemá (Che) 1200 1100 1260
1048
1500
1650
200 (0-400) 600 (400-800) 1000 (800-1200) 1400 (1200-1600) 1800 (1600-2000) 2200 (2000-2400)
1800 1900 2000 2100 2200
C Cahabón
C Tinajas/ Polochic
1900 (18002000) 2100 (20002200) 2300 (22002400) 2466 (24002532) Q Cahabón / Polochic
Data Watershed (see Fig. 1.3)
Q Chixoy
400 (200600)
C Chixoy
C Polochic
C Polochic
C Cahabón
Q Cahabón / Polochic
35 two neighboring vegetation belts (i.e. from 400 to 1800 masl). I defined disjunctive taxa as those found at two discrete vegetation belts but not in three (i.e. 400 and 1800 masl). Disjunctive taxa were considered when they were distributed in two non-neighboring elevation belts. I created my plant checklist based on taxa from these three different categories (indicator, generalist, and disjunctive). DCA Axis 1 scores were used as representative of vegetation composition at each of the sites and Axis 1 scores were regressed against elevation.
Indicator, generalist and disjunctive plant taxa were allocated to one of Gentry’s (1982) four paleogeographic categories: (1) Laurasian, (2) Amazonian-centered, (3) Andeancentered, and (4) Miscellaneous. A chi-square contingency table test was run to analyze the relationship between these categories and their corresponding vegetation belts. Equations were constructed to describe the relationship between elevation and temperature (temporal average for each meteorological station) to determine the lapse rate. To predict the value of the chosen parameters for our study sites according to their elevation, an interpolation was performed for sites located between 2 masl (Puerto Barrios) and 2100 masl (Suiza Continental) in elevation, and an extrapolation was performed for sites with elevations higher than Suiza Continental.
2.3 Results 2.3.1 Ordination and grouping of sites and plant taxa A linear regression of the DCA Axis 1 scores of sites and their elevation showed a significant correlation (r2=0.53, p
