Influence of infrastructure development on the

J Coast Conserv DOI 10.1007/s11852-014-0307-2

Influence of infrastructure development on the vegetation community structure of coastal dunes: Jeffreys Bay, South Africa Serena Lucrezi & Melville Saayman & Peet van der Merwe

Received: 20 March 2013 / Revised: 17 January 2014 / Accepted: 17 January 2014 # Springer Science+Business Media Dordrecht 2014

Abstract Coastal dunes are increasingly at risk due to pressures deriving from global climate change, sea level rise, recreation and development. The consequences of the “coastal squeeze” in which dunes are placed, such as erosion and the loss of critical ecosystem services, are usually followed by expensive restoration and protection measures, many of which are unsuccessful. Due to the poor understanding and acknowledgement of the key attributes of coastal dunes in decision making processes, it is essential to provide scientific data on the impacts of human interference on coastal dunes so as to inform executives and guide them towards a sustainable management of the coastal zone. The aim of this study was to investigate the impact of five different levels of infrastructure development on the vegetation community structure of coastal dunes in Jeffreys Bay, South Africa. The effects of infrastructure development on dune vegetation were quantified by measuring the richness, diversity, cover, height and composition of plant species. With an increase in infrastructure development a significant decrease in dune width, average species richness and height of the plants occurred, accompanied by a shift in plant community composition. The foredunes that were backed immediately by infrastructure presented significantly greater species richness, diversity, cover and height compared with the foredunes abutted by primary dunes. This study demonstrated that coastal dunes are environments which are sensitive to varying levels of human impact. Informed and comprehensive management planning of these environments S. Lucrezi : M. Saayman : P. van der Merwe TREES—Tourism Research in Economic Environs and Society, North-West University, Locked Bag X6001, Potchefstroom 2520, North-West, South Africa S. Lucrezi (*) TREES, North-West University, Private Bag X6001, Potchefstroom 2531, North-West, South Africa e-mail: [email protected]

is therefore imperative for the restoration and maintenance of remnant dunes and for the conservation of undeveloped coastal dunes. Keywords Dunes . Infrastructure development . Vegetation . Foredunes . Primary dunes . Community structure

Introduction Coastal dunes are highly dynamic transitional ecosystems, connecting marine and terrestrial environments (Lubke 1998; Acosta et al. 2007). Their dynamic nature, shaped by the continuous changing of parameters such as wind, salt spray and wave regime, makes them exhibit sharp gradients of biotic (e.g., plant community composition) and abiotic (e.g., dune topography) properties, thus resulting in high levels of ecological diversity and environmental heterogeneity (Martínez et al. 2004; Acosta et al. 2007; Nordstrom et al. 2009). Coastal dunes provide a unique set of ecological services, including: protection from erosion, a barrier of defence against storms, water storage and filtration, nutrient recycling, linking marine and terrestrial ecotones, food and bait organisms, habitat, and social, cultural and economic services such as recreation and tourism (Lubke 1998; Schlacher et al. 2008; Defeo et al. 2009; Everard et al. 2010). The dynamism of coastal dunes renders them highly sensitive to human as well as environmental stressors, and over the last few decades dunes worldwide have been facing extreme pressures from various anthropogenic stressors (Defeo et al. 2009; Martínez et al. 2013). Aside from direct human use mostly related to coast-bound tourism, urban development and armouring on the landward side coupled with sea-level rise on the marine side place seashores and dunes in a socalled “coastal squeeze” (Schlacher et al. 2008). The negative implications of such a “squeeze” are profound, ranging from

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habitat destruction and erosion to biodiversity alterations (e.g., homogenisation of communities), extinctions of local species, introduction of alien species and the loss of key ecosystem functions (Acosta et al. 2000; Defeo et al. 2009; Nordstrom et al. 2009; Dugan and Hubbard 2010; El Mrini et al. 2012). Although in many countries ribbon development (continuous rows of beachfront resorts and urban stretches) along the coastline has already exerted irreversible negative impacts on coastal dunes, by causing either their complete loss or alterations in their topography and biodiversity, assessing the ecological state of coastal areas, whether developed or not, remains a critical component in the process of planning the management and conservation of coastal dunes and shores (Buffa et al. 2012). According to Dadon (1999, 2002), the increasing use of beaches and infrastructure development in the coastal zone generate an impact gradient. Along this gradient (i.e., from no infrastructure development to heavy infrastructure development), the composition of floral and faunal communities is expected to vary, reflecting the growing pressures associated with development and human use. This paradigm has been confirmed by a number of studies (McDonnell et al. 1997; Faggi et al. 2006; Faggi and Dadon 2010; Noriega et al. 2012). In South Africa over 80 % of the coastline is composed of sandy beaches and dunes (Tinley 1985), many of which have been subject to development including housing on the frontal dune system, without consideration for the mobile character of coastal dunes (Lubke and Sudgen 1990; Lubke 1998). Prior to the development of a new coastal policy advocated by the White Paper for Sustainable Coastal Development in South Africa (Department of Environmental Affairs and Tourism 2000), construction was allowed on the frontal dunes. The effects of such inappropriate development, exacerbated by an increasing use of coastal dunes and beaches for recreational purposes, have inevitably resulted in great economic expenditures in an effort to stabilise the dunes and prevent sand movement (Lubke and Sudgen 1990; Avis 1998). However, in certain parts of South Africa, ribbon development is still minimal and spatial variations occur in the degree of infrastructure development on beaches. This offers a good reason to evaluate the effects of different levels of infrastructure development on the communities of coastal dunes. The chief aim of this study was to investigate the role of infrastructure development in the variation of the dune vegetation structure at a well sought after coastal tourism spot in South Africa, namely Jeffreys Bay in the Eastern Cape. Dune vegetation structure here was characterised by the following variables: the total vegetation cover; the cover of various plant growth forms, community types, plant functional types (PFT), and invaders; vegetation height; species richness; and species diversity. The sub-set of objectives underlying the main aim of the study were to: i) assess the impact of varying degrees of

infrastructure development on dune vegetation structure; ii) determine the extent to which dune vegetation structure differs across the sea-land gradient, specifically between the foredunes (i.e., the first clearly distinguishable vegetated dune formations on the shore, landward of the water) and the primary dunes abutting them (i.e., the dune ridge just landward of the foredunes); and iii) assess how the presence or absence (due to replacement with infrastructure) of primary dunes abutting the foredunes affects vegetation community structure on the foredunes. By answering these questions, this study aimed to provide insights on how different degrees of coastal development can affect dune ecosystems and what implications there are in terms of proper planning and management, so that sustainable development in coastal areas can be achieved.

Materials and methods Study area Jeffreys Bay (34°03′33″S, 24°91′67″E) is the largest coastal town of St Francis Bay in the Eastern Cape Province, South Africa (Fig. 1a). This half-heart bay is bounded to the northeast by Cape Recife and the large city of Port Elizabeth and to the south-west by Cape St Francis (Fig. 1a). The wave direction here tends to be north-easterly, while the wind pattern is dominated by westerly to south-westerly winds for most of the year alternated by inshore easterly winds in the summer months (Stone et al. 1998). These conditions present coastal dunes in the area with a typical transversely oriented shape with respect to the wind (Lubke 1998). According to Tinley (1985), these dunes are classified as transverse barchanoid (simple, compound or complex) and in Jeffreys Bay they make up a foredune backed by a primary dune ridge (Fig. 2a), unless it has been replaced with infrastructure (Fig. 2b). Jeffreys Bay falls under the Albany thickets biome or ecoregion, which is mainly characterised by dense woody shrubs and trees. The dunes here are dominated by pioneer communities of coastal dunes and dune scrub or thicket, but there are many species representative of rocky cliffs and promontories, coastal forest, coastal grasslands and dune fynbos (Lubke and van Wijk 1998). The latter, which is particular to South Africa, is characterised by shrubby species from the Cape (proteaceous plants, restios and heaths) growing on nutrientpoor calcareous dune sands along the coast, mostly in winter rainfall areas (Lubke and van Wijk 1998). The area in and around Jeffreys Bay acquired conservation importance due to the occurrence of endangered species such as the African black oystercatcher Haematopus moquini and the establishment of the Kabeljous, the Seekoei River, the Cape St Francis and the Gamtoos Mouth Nature Reserves (Southwood 1998).

Influence of infrastructure on coastal dune vegetation

Fig. 1 Geographic location of the study, Jeffreys Bay, Eastern Cape, South Africa (a). Spatial layout of the study (b). Vegetation was sampled along 7 km of coast, which was divided into 56 transects (excluding the retaining seawall area where vegetation was absent). For each transect (10 m width×100 m length), the total area covered by infrastructure was

calculated. Separately for the foredune and the primary dune (where present), five 0.5 m2 quadrats were randomly placed and photographed for further analysis in the laboratory. Finally, in each quadrat, vegetation height was measured using a line-intercept method

Jeffreys Bay is a major coastal tourism attraction in South Africa (CNN 2013). Most of the development in Jeffreys Bay and St Francis Bay consists of holiday resort facilities, private beach houses and holiday homes (Watling and Watling 1983). Some of the infrastructure is inappropriately located on the frontal dune system and, although minimal, some ribbon development is present along the coast in the bay, leaving a narrow strip of dunes (Avis 1998). This strip is evidently closed to human trampling except for designated access areas

(various notice boards on the beach clearly prohibit pedestrian access to the dunes). Some small portions of the dune stretch which are tentatively being restored are fenced, while other portions are owned by the private properties immediately backing the dunes. Based on the level of infrastructure development, the ecological status of Jeffreys Bay is regarded as being “fair” (that is the natural environment has been disturbed with a moderate impact and some ecosystem functions have been disrupted) (Avis 1998).

S. Lucrezi et al. Fig. 2 Diagram representing cross sections of the dunes at the study site, which was characterised either by a foredune abutted by a primary dune (a), or by a foredune abutted by infrastructure only (b)

Dune sectioning and classification according to infrastructure development level For the purpose of this study, the coastline stretching for approximately 7 km from Pellsrus (south-west) to the Kabeljous Lagoon (north-east), including Jeffreys Bay, was sampled where the dunes were present (Fig. 1b). A site along the coastline forming part of Dolphin Beach (approximately 190 m length) was not sampled, due to the complete replacement of the vegetated dune front with a concrete seawall (Fig. 1b). The remainder of the coastal stretch was divided into 56 transects (Fig. 1b). Field surveys were undertaken during the second week of October 2012. To avoid sampling bias, the entire site selection process was completed on Google Earth before the fieldwork commenced. Each transect comprised a rectangle measuring 10 m at the base, which was parallel to the shore, and extending from the base of the foredune inland perpendicular to the shore for 100 m (Fig. 1b). Thus, the area of each transect was 1 000 m2. The distance between the end of one transect and the beginning of the next transect was 150 m (Fig. 1b). For each transect, the total area cover (m2) and percentage cover (%) of infrastructure were measured. Each transect was classified into five infrastructure development classes according to the following criteria: No Development (no

infrastructure present); Little Development (25 % or less infrastructure cover); Moderate Development (26–50 % infrastructure cover); Heavy Development (51–75 % infrastructure cover); and Very Heavy Development (>75 % infrastructure cover). To test the validity of this classification scheme, the variance in infrastructure cover (m2) amongst the five classes was partitioned using a General Linear Model (GLM), with “infrastructure development level” as the fixed factor. The GLM was followed by a Fisher’s Least Significant Difference (LSD) post hoc test to observe significant interactions between the classes. The test confirmed the validity of the classification scheme, for each class had significantly higher infrastructure cover (m2) compared with the previous ones (Fisher’s LSD, P15 cm Thick spreading or deep, or thin and shallow Thick spreading or deep Present or absent Present

Indifferent Thick spreading or deep Present

Absent Absent Stable

Present Absent Moderately unstable

via non-parametric (Spearman rs) correlations. All statistical analyses were performed using ‘Statsoft Statistica’ (Version 10), ‘GraphPad Prism’ (Version 5) and ‘Primer-e’ (Version 6).

Results Dune vegetation Forty-one plant species were identified as inhabiting the dunes of the study site (Table 2). The most speciose plant growth form was that of shrubs (14 species), followed by herbs (ten species), grasses and sedges (six species), succulents (five species), creepers (four species) and trees (two species) (Table 2). The most common species was the succulent Tetragonia decumbens, occurring on both the foredunes and the primary dunes at all levels of infrastructure development (Table 2) and covering on average 14 % of the dune surface. The shrubs Chrysanthemoides monilifera and Helichrysum teretifolium were second and third most common species respectively, covering over 15 % of the dunes in total. Examples of the rarest species include the invader Agave, the succulent Plectranthus neochilus, the tree Sideroxylon inerme and the herb Silene primuliflora, with 0.15 % cover or less per species. A total of four invaders were identified (Table 2). The vegetation of the study area was confirmed to be typical of the coastal dune thicket of the Eastern Cape, with representatives from pioneer communities of coastal dunes, dune scrub or thicket, communities of rocky cliffs and promontories, coastal forest, coastal grassland and dune fynbos (Table 2). The most speciose community type in this case was dune scrub or thicket, with 21 representative species and with the greatest vegetation cover (x = 50.04±2.89 %; Table 2). This community was strongly associated with shrubs and succulents (Table 3). The second most speciose community was that of coastal dune pioneers, with 20 representative species and an average cover of 37.08±2.15 % (Table 2). This

Present Present Unstable

PFT3

community was strongly associated with succulents, grasses and sedges (Table 3). PFT1 included 12 species, mostly herbs; PFT2 comprised 15 species, a mixture of the various plant growth forms excluding trees; and PFT3 consisted of 14 species, mainly shrubs, also including trees (Table 2). PFT2 presented the greatest cover (x = 38.82±2.51 %), followed by PFT3 (x = 28.69±2.19 %) and PFT1 (x = 5.73±1.17 %). While plants of PFT1 are associated with relatively stable soils (less mobile and less prone to erosion by wind and water), species of PFT2 and PFT3 are associated to more unstable soils (more mobile and more prone to erosion by wind and water; Table 1). Variation in vegetation composition across infrastructure development levels There was a progressive reduction in average dune width with increasing infrastructure development (from x = 156±22 m width in the No Development level to just over x = 12±1.5 m in the Very Heavy Development level; Table 3; Fig. 3). The null-hypothesis 1 (H10) was not confirmed, since there was a considerable variation in the composition of vegetation across the five infrastructure development levels. Overall, 32 plant species occurred at the Moderate Development level followed by 31 at the Very Heavy Development level, 29 at the Heavy Development level, 27 at the Little Development Level, and 26 at the No Development level (Table 2). However, the species richness per transect was greatest at the No Development level (x = 9±1) and decreased progressively with increasing infrastructure development (Tables 3 and 4; Fig. 3). Post hoc test results confirmed that species richness was significantly greater at the No Development level compared with the Moderate Development (Fisher’s LSD, P=0.03), Heavy Development (Fisher’s LSD, P=0.01) and Very Heavy Development (Fisher’s LSD, P