Aug 9, 2018 - Recovery Succession of Native Vegetation at Big Meadow Bog after .... stages on one Figure then decided the other solution Reviewer 1 ...
Wetlands Recovery Succession of Native Vegetation at Big Meadow Bog after Disturbance and Eutrophication from Herring Gulls --Manuscript Draft-Manuscript Number:
WELA-D-18-00070R1
Full Title:
Recovery Succession of Native Vegetation at Big Meadow Bog after Disturbance and Eutrophication from Herring Gulls
Article Type:
Wetlands Restoration
Section/Category:
Original Research
Keywords:
Big Meadow Bog; Peatland Eutrophication; Recovery Succession; Herring Gulls
Corresponding Author:
Nicholas Morison Hill, Ph.D Fern Hill Institute for Plant Conservation Berwick, NS CANADA
Corresponding Author Secondary Information: Corresponding Author's Institution:
Fern Hill Institute for Plant Conservation
Corresponding Author's Secondary Institution: First Author:
Nicholas Morison Hill, Ph.D
First Author Secondary Information: Order of Authors:
Nicholas Morison Hill, Ph.D Kristine Chinner, BSc Bradley Toms, BSc David Garbary, PhD
Order of Authors Secondary Information: Funding Information:
National Wetland Conservation Fund (GCXE16E064) Department of Natural Resources, Nova Scotia (1903396435)
Dr. Nicholas Morison Hill Dr. Nicholas Morison Hill
Abstract:
On Brier Island in eastern Canada, ditching of Big Meadow Bog resulted in predictable shifts in the plant community as shrubs and trees proliferated across the drained landscape. An unpredictable result, the attraction of the ditched bog to nesting gulls that daily foraged 35 km away at nutrient-enriched mink farms, caused larger impacts. Disruption of vegetation by gulls and recovery succession is retrospectively analyzed. Aerial photographs enabled a study of a shifting pattern of gull disturbance and subsequent community revegetation. Gull-bared peat was colonized in succession by exotic grasses (e.g. Holcus lanatus) and annuals; raspberry; Rubus spp. canes and biotically-dispersed Rosaceae shrubs; and wind-dispersed Ericaceae, ferns and trees (Picea mariana). There was no evidence of persistence of a bog species soil seed bank to aid post-gull revegetation nor evidence of interference in community regeneration by an exotic weed seed bank. Weed seed bank (six thousand seeds.m-2) declined to zero after 33 years (half-life = 3.6 years). In contrast, a secondary, native wetland seed bank (mainly Juncus spp.) of similar magnitude, persisted. The recovered plant community has swamp features (trees, ferns, tall shrubs). Whether the bog regains ombrotrophy will depend upon whether blocked ditches and reinstated water tables deter gull nesting.
Response to Reviewers:
Revisions made by Nick Hill with help from Brad Toms REVIEWER 1 #1 The Methods section starts with sub-heading Study Sites, but at line 114 shifts to air
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photo methods. A new sub-heading is needed after line 113. We have reorganized the Methods. Section One is now Study Site and Successional Stages within Big Meadow Bog. The successional stages are clearly laid out. The Reference Bog is described as the undisturbed, pristine control for the disturbed Big Meadow Bog. The gull activity is more thoroughly described. The Remnant Heath—we retain the name Heath to avoid confusion that it is actually a separate bog—is described and its area provided as requested. The three active gull phases are described (Perches, Gull Grass, Cane) with more clarity about how gulls relate to these phases and areas. The post-gull recovery stages are described. After this study site and succession methods, we insert a GIS Vegetation Analysis methods section. At line 126 and continuing through line 149, more information on vegetation phase changes begins. This does not really fit well in Methods. The information presented is important, but parts of it belong in the Introduction, and other parts perhaps in Study Site. At line 150, the paper goes back to Methods, then appropriate sub-heading are provided for Field Sampling and Vegetation Dynamics. Those sections are wellwritten, although the authors should be aware that taxonomists have renamed the genus Polygonum to Persicaria, with some species name changes also. We have consolidated the successional phases into the first methods section because it is directly applicable to sampling. We are aware of the newer nomenclature but we are following the nomenclature used in our region’s biodiversity authority, ACCDC (Atlantic Canada Conservation Data Centre). The Discussion does a good job of summarizing what has taken place at Big Meadow Bog and relating the importance of the results and trajectories. I did not understand the meaning of "this ecosystem engineer" on line 513, however. We have inserted the citation of Jones et al 1994 who explain this term and apply it to Sphagnum A few of the citations in the References section were out of order. The Reference section has been gone through thoroughly. The tables were ok, but Figures4 - 10 should use a non-serif font and Figures 8 and 9 seem out of order. The font has been changed to Arial So, where does the Results section fit in with this review? We have fixed the minor points raised by Reviewer 1. Thank-you. Now to the biggest problem. Through much of the Results section dealing with Figures 4 - 7, I found myself bouncing back and forth between 4 and 5 or between 6 and 7. The Figures were put together to make the vegetation and seed bank results more able to be followed. We did it both ways. I created landscape figures for vegetation and seed bank with all stages on one Figure then decided the other solution Reviewer 1 suggested, an A and a B figure on top of one another would be best. I can send the landscape versions if the journal prefers. Other than that, we redrafted all figures because of font or style or ease of following or for points brought up by Reviewer 2. REVIEWER 2 In particular, a summary of the ditch blocking activities and the hydrological monitoring work to date at this site was absent. The reader is left wondering if the ditch blocking was in the lagg or bog or both and whether it had restored the water table in the bog and lagg. This information is clearly available to the authors, and could easily be added to the Study Site section. Alternatively, simply leave out any mention of ditch blocking, since it’s not related to the results that are presented. We take Reviewer point about the lagg and the ditch blocking and the alternative approach of leaving out all mention to blocking and the lagg since a) the paper is not about the lagg and b) the paper is about a time (1978 to 2016) before the ditches were blocked. Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation
We have removed the reference to ditch blocking and to the conservation recovery effort in the Abstract and the Introduction so the reader can take this as a case of how do we regain a biological community and some wetland values (water filtration , carbon storage, berries, duck..and a suite of rare species) given the ditching and the attraction herring gulls have to the ditched system. A more general introduction on the subject of the article and a review of the relevant literature is needed. The last paragraph of the current Introduction could form part of this literature review. Since gull colonization of drained bogs seems like a rare study topic, it would be good to highlight the unique nature of this study. We have tried to put together an introduction that doesn’t go on about peatlands but which tackles the issue at hand. This reviewer helped us focus on eutrophication of peatlands. While gulls in peatlands may not be common, the problem is tied into the larger issue of nutrients from many sources..agriculture or atmospheric deposition..undermining high carbon, low nutrient systems. We bring this to light. We also use the issue of the rare plant (and rare plants in this peatland) to signal concern over the impact of nutrient cycle disruptions on biodiversity and suggest that rare species may be sentinels of the integrity of the biological communities they inhabit. It would be useful to add a table with the vegetation plot data for individual species, so the reader can review the results for themselves. This could help reduce some of the text about species cover in the Results and provide more information for the reader. We have done this now and have incorporated references throughout the results to Table 1. The title suggests that the authors will present data about eutrophication, but these data are not presented. There is mention of measured phosphorus concentrations in the Discussion (P18 L401-405), which is important information for the reader. It would be helpful to include a couple of sentences in the Study Site section summarizing what has been measured at the site in terms of eutrophication. The Discussion would also benefit from some consideration of how the vegetation results relate to site hydrology, as these two factors are closely interconnected in bogs. We have included these references in the study section, citing Kickbush and their data, and have discussed hydrology in the discussion, citing recent unpublished water levels as well as the online Kennedy et al 2014, hydrological study. Our present paper is timely at the study site because it is published just as the water table has been restored and there is keen interest in how the gulls will respond to water table changes and what the impact of the remaining nutrient in the system will be given the blocked ditches and gulls still present. We sum this up in the final paragraph. It would be better if the Abstract focused on the key points of the article, which are in my mind: 1) the lower water table as a resulting of ditching made the bog more attractive to nesting gulls, 2) gulls took over the bog and caused changes to vegetation and soil-water chemistry, and 3) vegetation starts to recover toward a bog plant community when the gulls abandon the site. We have revised the Abstract accordingly and have omitted mention of the Eastern Mt Avens and have instead focussed on gulls and vegetation, ending with the sentence that the fate of the bog now that hydrology is back will depend on gulls and nutrients. We do not go into Recovery strategy in the abstract as advised..and we agree. Specific questions: Reviewer 2
P2 L15: Please specify where Brier Island is located, e.g. Nova Scotia or eastern Canada, for those not familiar with the area. OK, done P2 L17: If keeping the text about the Recovery Strategy (but see comments on Abstract above), it would help to specify for non-Canadians what this is, e.g. the federal endangered species Recovery Strategy. We no longer refer to the recovery strategy but do bring out the Action Plan of the Recovery Team. We fully reference what this is and that this is a federal listing and Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation
program in Canada. P2 L18-19: Either remove the text about ditch blocking from the Abstract (see comments on Abstract above), or clarify here that the vegetation analysis took place prior to ditch blocking in 2017. removed P2 L19: Because of the earlier mention of the lagg and Geum peckii, it’s not clear whether the gulls damaged the bog or lagg or both. The reader should not have to refer to the main text for the answer. lagg reference removed from Abstract..agree, this is clearer P2 L20: It would help to include the reason why gulls abandoned their nesting sites, if this is known. The earlier mention of ditch blocking suggests it was due to a higher water table, but it becomes clear later that abandonment pre-dated ditch blocking. We no longer have this issue. We only refer to a shifting pattern of gull occupation of the bog. P2 L27: The “recovered plant community” (presumably post-gull abandonment, but not clear) has “swamp features”. Does that mean it is part of the lagg or that the swamp is taking over the bog? In my experience, drained bogs often contain trees, ferns, and tall shrubs. I don’t think that means that the drained bog has become a swamp. Why is it no longer ombrotrophic? Because of the nutrient additions by the gulls? I believe ombrotrophic refers to the source of water, while oligotrophic refers to nutrient levels. Could the bog still be ombrotrophic even with nutrient additions by gulls? It would be beneficial to include a brief discussion of the definitions of these terms and how they relate to what has occurred in the bog. Again, we have not mentioned the lagg. There is no space here in the Abstract to get into ombrotrophy and we do precisely say that it is the plant community..not the ecosystem..that has swamp like features in the vegetation. P3 L43: This sentence could use a source reference. sentence on headwaters and bogs was omitted from the revised MS P3 L53 to P4 L75: This information would be better integrated into the Study Sites section, as some of it repeats what is already in Study Sites. This Big Meadow Bog background has been largely removed from the Introduction in this version and the Study Site has all the background. P3 L58: Is the Spooner et al. 2017 reference for the part about the historic vegetation succession or the part about the lagg and Geum peckii (or both)? “These values were lost after the bog was ditched and a suite of rare species in the marginal fens, including the globally imperiled Eastern Mountain Avens (Geum peckii), were further undermined as thousands of nesting Herring Gulls were attracted to the bog by the lowered water table conditions (Keddy 1986, Spooner et al 2017).” The study site section of the Spooner paper and the report by Cathy Keddy 86 discuss how the ditching and the gulls threatened the avens in the lagg of the Big Meadow Bog. P3 L58-60: Can you add a brief explanation as to why an increase in woody species would provide nesting conditions for gulls? Do they use trees or shrubs? Any woody species in particular? We now have added to our understanding of Herring Gulls as we revised. This section is excerpted from the Study Site which goes into the history of gulls. This also fits with what we see in the bog, gulls nest in the driest places but there is usually an adjacency between open and refuge (the woody) conditions. The Burger and Shisler paper cited explains this. “Prior to ditching, no Herring Gull nests were recorded in Big Meadow Bog. There was a nesting population in a bog southwest of the Reference Bog (Figure 1) in the early 1970s (Joyce DeVries, Personal Communication August 5, 2018) and small population known from grassland at Hog Yard Cove (Fig. 1, Robicheau, R. Personal Communication December 20, 2016). Herring gull nesting preferences may be determined by a combination of the need to reduce the risk of nest flooding and of finding patches of vegetation that provide refuge from predators (Burger and Shisler 1978). Both of these requirements would have been met at Big Meadow Bog after ditching lowered water tables allowing for increased woody growth throughout but particularly on spoil piles.” P3 L60: Please specify who the “multipartners” were. We do not refer to this now. P3 L63: Were the drainage ditches in the bog or lagg or both? Where were the dams installed? A figure showing the ditch and dam locations in relation to the bog, lagg, and swamp zones would be very helpful. Were the peat barriers installed by hand or with Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation
machinery? When did ditch blocking occur? The date is mentioned later in the Discussion, but should be in Study Sites as well. Alternatively, leave out any mention of ditch blocking, as the results of ditch blocking are not presented. We have inserted this short paragraph for clarity at the end of he study section: “In 2017, the central and eastern lagg ditches were plugged at 30 m intervals using deep catotelmic peat excavated and contoured using a mini-excavator. The present study is a retrospective of changes that occurred along the western half of the bog (Figure 3) between 1978 and 2016 when the bog was still freely draining through central and eastern lagg ditches.” P4 L64: Was the ditch blocking only because of the Action Plan for Geum peckii, or also because bog restoration was desired? This discussion is no longer in the Introduction P4 L71-75: This might fit better under Methods. yes, done P4 L78: Please add something like “after gull occupation has declined/ceased” to end of this sentence, if that is what is meant. “1. Does the gull transformed vegetation succeed to a native wetland community after gulls abandon sites? 2. Does the soil seed bank facilitate or interfere with the post-gull recovery of native vegetation?” these changes include the desired clarity of the above and next point. P4 L79: Might “after gull abandonment” belong at the end of this sentence? see above please. P5 L99: Please show the “lagg zone of fen” on Figure 1 or a new figure. We have made changes to all figures but this will have to wait for Dr Garbary to return from conferences if it is key. Our text throughout underscores where the lagg is in relation to the bog but please advise. P5 L100: It is not clear to the reader that the bog is surrounded by swamp, and one might think that swamp refers to another part of the lagg rather than the larger surrounding ecosystem. in the revision, we did not include the swamp reference. P5 L108: Do gulls use the spoil piles because they are higher and drier? Not clear. We have now made this clear and we address this above in reference to lines 58-60 P5 L109 to P6 L110: It would be preferable to place the Latin name of the plants directly after each common name. we now do this. P6 L114: The following three paragraphs appear to be a new section about GIS. I recommend putting a new section heading here called “GIS Vegetation Analysis” or something similar. This text is about the method of analysis, not information about the study site. Yes, done P6 L126: Can delete “have” from “we have analyzed”. since we rearranged the Methods, this phrasing is gone. P6 L131: It’s not mentioned until the following paragraph that Remnant Bog is actually part of Big Meadow Bog. Please make this clear at the first mention of Remnant Bog. It would also be helpful to state how large the Remnant Bog area is in relation to the entire Big Meadow Bog area. Was the Remnant Bog area drained? A figure showing the location of the Remnant Bog in relation to the ditches and lagg would help to clear this up. This has been done in text and Remnant Heath is in Figure 3. “Seven stages were identified in Big Meadow Bog and these included a non-gull disturbed Remnant Heath, three active gull disturbance stages and three post-gull abandonment recovery stages (successional schema: Figure 2). The Remnant Heath is a one hectare area at the north end of Big Meadow dominated by heath plants (Kalmia angustifolia, Ledum groenlandicum and Gaylussacia dumosa) with scattered tussocks of club sedge, Trichophorum cespitosum (Figure 3, bottom right panel).” pg 6 to 7 There are several references to Remnant Heath: that it is north of Big Meadow, that it is Big Meadow and ditched, that it is non-gulled in its matrix though contains localized patches of perch disturbance, that it is a small area (25 ppm in bog
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water, Kickbush et al 2018) corresponding to the area of most recent gull occupation (Figure 3).
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The Reference Bog (Figure 1) is a 15 ha peatland to the west of the Brier Island member
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basalt ridge (Kontak and Webster 2010) that contains Big Meadow Bog to the east (see above),
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however there no major ridge containing the western edge of Reference Bog. The eastern margin
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of Reference Bog features a long fen (1100m) and a raised bog (400m x 150m) dominated by
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ericaceous shrub (primarily crowberry, Empetrum nigrum), and cloudberry (Rubus
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chamaemorus), has developed west of the fen.
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The Reference Bog, an undisturbed intact bog, is the control system compared with
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successional stages within the ditched Big Meadow Bog. Seven stages were identified in Big
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Meadow Bog and these included a non-gull disturbed Remnant Heath, three active gull
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disturbance stages and three post-gull abandonment recovery stages (successional schema:
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Figure 2). The Remnant Heath is a one hectare area at the north end of Big Meadow dominated
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by heath plants (Kalmia angustifolia, Ledum groenlandicum and Gaylussacia dumosa) with
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scattered tussocks of club sedge, Trichophorum cespitosum (Figure 3, bottom right panel).While
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it is remnant in terms of its heath (Ericaceae) composition, other aspects of its vegetation (low
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frequency of Sphagnum spp) reflect the impact of ditching. The first gull disturbance stage, the
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Perch zone, occurred around tussocks of T. cespitosum in the Remnant Heath that were used as
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perches. The Perch zone included the central damaged or dead sedge and the immediate bare
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area (1m radius) that surrounded the sedge perch. The second active gull stage, Gull Grass, was
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identified as the grassy areas where Herring Gulls congregated that were dominated by the exotic
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velvet grass, Holcus lanatus. This stage in vegetation succession was always adjacent to the third
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active gull stage, the Cane zone that was dominated by tall (2m) canes of raspberry (Rubus
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idaeus). This area was used for gull nesting and was a refuge for gull chicks. Three post-gull
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recovery stages were identified using a series of dated, geo-referenced aerial photographs and by
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tracking individual Gull Grass areas after its abandonment by gulls for ten, twenty and thirty
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years (see GIS Methods). Figure 3 shows that Herring Gull colonies were confined to the south
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of Big Meadow in 1978 and 1988 and that the nesting colony shifted to the north of the bog in
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the third and fourth decade (2001, 2011 and 2015 aerial photographs). Most of the area of Big
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Meadow Bog has been colonized by gulls with the exception of a small area, the Remnant Heath
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at the northern end (Figure 3).
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In 2017, the central and eastern lagg ditches were plugged at 30 m intervals using deep
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catotelmic peat excavated and contoured using a mini-excavator (East Coast Aquatics 2018). The
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present study is a retrospective of changes that occurred along the western half of the bog (Figure
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3) between 1978 and 2016 when the bog was still freely draining through central and eastern
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lagg ditches.
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7
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GIS Vegetation Analysis The Gull Grass areas were recognizable on aerial photos. There was close
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correspondence between the zones observed on the 2015 aerial photograph and on the ground
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observations in 2016 as there was between field mapped gull zones by Keddy (1986) and the
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1988 aerial photograph. A series of geo-referenced aerial photos (1928, 1945, 1955, 1967, 1978,
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1988, 2001, 2011 and 2015) were investigated and the gull vegetation polygons were outlined
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manually in ArcMap to create “areas of assumed occupation” (Toms, 2015). No occupied areas
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(areas of assumed occupation) could be identified in the four earliest photos but areas were
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mapped for all subsequent aerial photos. To understand post-gull vegetation recovery, areas of
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gull abandonment were identified and mapped on aerials for each flight date. For each of the
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mapped zones on aerials from 1978, 1988 and 2001, the occupied zones of subsequent flights
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were overlain on the earlier image to show the gull abandoned areas. Using the ‘Erase’ tool in
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ArcMap 10.2, the areas occupied at the later date were erased to reveal the areas that the gulls
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had abandoned. The time of abandonment was calculated from the average of the date when gull
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colonies were documented on aerials and the date of the subsequent aerial when no trace of gull
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activity was evident. This calculation for gull occupied areas on 1978, 1988 and 2001 aerials that
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were abandoned thereafter to the study (2016) resulted in three abandonment time classes (10,
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21.5 and 33 years) that were rounded to 10, 20 and 30 years. These areas are referred to as the
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10, 20 and 30 year Recovery Stages of succession.
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Vegetation Assessment and Seed Bank Determination
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Plant cover assessment and soil collection for seed bank analysis was carried out for the
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two Intact systems (Reference Bog and Remnant Heath of Big Meadow), the three Active Gull
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stages (Perch, Gull Grass and Cane) and three post-gull abandonment, Recovery stages (10, 20
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and 30 years abandoned). For all except the 30 Year Recovery, vegetation and seed bank
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analyses were carried out on three patches; only two patches were large enough to locate with
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certainty for the 30 Year Recovery Stage using the 1978 aerial. The outline of each patch for the
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three Recovery Stages (on 1978, 1988 and 2001 aerial photos) was located in the field using a
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Garmin GPS unit. For other sites, the largest expanses of particular habitat types (e.g. Gull Grass,
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Cane, Perch, Remnant Heath) were selected. Sampling was confined to the west side of Big
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Meadow Bog to match the availability of geographically limited abandoned patches in 1978 and
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1988. Three soil and vegetation sampling sites were established per patch at the midpoint of
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transects radiating from the center at 120o to the patch margin. The vegetation of the Reference
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Bog was relatively homogenous and three patch centers were obtained by running a 300m line
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transect through the raised bog area and establishing patch centers at successive 100m distances.
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The cover vascular plants and mosses was estimated in a 4 m2 quadrat area for each of the three
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sampling sites per patch and the combined cover values were averaged. Vegetation data
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presented in Figures are means and standard errors obtained using patch averages. Species
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nomenclature followed the regional biodiversity monitoring organization, the Atlantic Canada
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Conservation Data Centre (http://www.accdc.com/en/ranks.html). Three soil cores were taken
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using a bulb planter (core diameter 5.5 cm, depth 10cm) aided by a sharp knife, within each
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quadrat area. This was repeated at each of the three radiating transects per patch.
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The reserve of seeds or fern spores—the seed bank and spore bank—was estimated using
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the emergence method (Simpson et al. 1989). Soil (peats) samples were collected over a ten day
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period (June 7 to 17, 2016). The samples were well mixed and litter and large rhizomes were
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removed. Each sample was placed on top of a 2.5 cm layer of commercial sand over a 70 cm2
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plastic liner. Ten plastic liners with samples and a control of sand and potting soil, were fitted
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into 20 x 50 cm plastic trays, and these were maintained over summer at ambient temperature
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outside in two small cold-frames (1.75 m x 0.75 m x 0.30 m) on Brier Island. In September 2016,
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samples were transferred to the St. Francis Xavier University greenhouse that was maintained at
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22°C with a natural light/ dark cycle. Soils were kept moist by water cans as needed. Once
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seedlings were identified, they were recorded and removed. Representatives of each seedling
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type were transplanted and grown on in potting soil. Seedling emergence was followed until
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November 27th 2016.
206 207
Analysis of Vegetation and Seed Bank Dynamics
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Vegetation Guilds
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Vegetation cover and seed banks were examined for ten guilds: five herbs, one cane
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(Rubus), three shrubs and one tree. Herbs included Ferns, Bog and Swamp Herbs (Facultative
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Wetland and Obligate, Lichvar 2016), Weeds (exotics and annuals) and Upland. Shrubs were
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Heath (Ericaceae), Rose (Rosaceae) and Other (Adoxaceae, Aquifoliaceae and Myricaceae). All
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woody species (shrubs and trees) were also separated by seed dispersal mode into
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endozoochorous (fleshy fruited), wind, and flotation groupings.
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Species richness was enumerated for thirteen guilds that included five dispersal shrub
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groups (Table 2). A score of diversity for vegetation phases was calculated using the Shannon
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Index to rate evenness between the thirteen guilds.
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Seed bank dynamics
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The time of site abandonment was calculated by taking the difference between the date
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when gull colonies were documented on aerials and the date of the subsequent aerial when no
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trace of gull activity was evident. This value was divided by two and then the time from the
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subsequent aerial to the study date (2016) was added. This resulted in three abandonment time
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classes (10, 21.5 and 33 years—rounded to 10, 20 and 30 on vegetation figures) that are used as
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estimates for the time of seed bank development of Swamp Herbs and for the seed bank decline
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of Weeds. Both sets of successional time-dependent data had moderate values for kurtosis (1.1-
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1.2) and skewness (0.8-1.4). The Swamp Herbs are those wetland species not present in the
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vegetation of either intact bog (Reference Bog or Remnant Heath). Their seed bank increase and
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decline was analysed as for the above Weed decline except it employed polynomial regression.
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The seed bank decline of weeds (i.e. Bidens frondosa, Epilobium ciliatum, Impatiens capensis,
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Sagina procumbens) and introduced (Holcus lanatus, Poa annua, Polygonum hydopiper, P.
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persicaria, Potentilla norvegica, Rumex acetosella, and Stellaria media) analysed by linear
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regression, best fitted a logarithmic model.
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Ordination of Communities
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The 23 sites representing 8 successional stages (n=3 except n= 2 for 30 year Recovery)
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were ordinated using species richness variation among vegetation guilds (main matrix). The seed
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bank data for the 7 guilds that had sufficient germinants (all except Upland, Other Shrub and
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Tree) was a secondary matrix imported to run non-metric multidimensional scaling (NMS) using
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the Sorensen distance measure as set up in PC-ORD 6.08 (McCune and Mefford 2011). Six axes
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had initial p values < 0.001 (250 runs to determine stress related to dimensionality with real and
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with randomized data using a Monte Carlo test, McCune and Mefford 2011) but only two were
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accepted into the ordination; these accounted for 93% of the variation.
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Results
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Vegetation and Seed Bank Changes
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There were large shifts in the species composition in the vegetation between the intact systems,
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the undisturbed and ungulled Reference Bog and the Remnant Heath, and between each of the
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stages of succession examined in Big Meadow (Table 1). These species were categorized into
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functional groups to focus the analysis and relate changes to vegetation types and properties.
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The vegetation of the intact systems (Reference and Remnant Heaths) consisted mainly of Bog
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Herbs and Heath (Ericaceae) Family shrubs (Figure 4A). While cover of these groups dominated
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(combined covers = 67 and 55% of Reference and Remnant Heaths) the intact systems, it had
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greatly declined (15%) in the Perch zone (gull incursions around tussocks of Trichophorum
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cespitosum) and was scant in the later two active gull areas, the Gull Grass and Cane phases.
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Conversely, while the intact systems had no Weed cover, the Perch zone had minor cover of
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(3%) Weeds which increased greatly in the Gull Grass phase (Figure 4b). This phase was mainly
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Weeds dominated (97%) by the exotic grass, Holcus lanatus , with small amounts of Upland
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herbs and the Cane, Rubus idaeus (2.3 and 0.6% respectively, Figure 4b). The Cane phase had
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large cover of Rubus spp, (70% R. idaeus, 10% R. setosus), Weeds and Upland Herbs (10 and
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11% respectively, Figure 4b).
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Cover of the Bog Herbs and Heath was regained in the Recovery stages (Table 1 and
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Figure 4a). Both the 10 Year and the later Recovery stages have guilds noted for the Cane phase
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(Upland herbs, Rubus spp) as well as novel guilds, Swamp Herbs and Ferns, scarcely represented
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in intact or gull phases (Figure 4). The Recovering stages had the greatest cover of Rose family
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and Other shrubs. Trees were dominant (>35%) in the late Recovery but absent from all other
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stages (Figure 4a).
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There was little representation in the seed bank of the Bog Herbs or Heath (Figure 5),
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They had minor representation in the Reference, Remnant and Perch stages (germinants.m-2 for
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Heath and Bog Herbs respectively = 80 and 0 for Reference Bog, 125 and 90 for Remnant Heath,
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and 78 and 33 for Perch). There was no seed bank of either bog guild in the Gull Grass, Cane or
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the 10 Year Recovery stage but there were small banks in the combined 20-30 Year Recovery
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(for Heath and Bog Herb respectively = 37 and 19 germinants.m-2). Seed banks were scant ( 0.26, Pearson’s r > 0.34 for p
