Species-area relationships and the impact of deer-browse in the complex phytogeography of the Haida Gwaii archipelago (Queen Charlotte Islands), British Columbia

Gaston, Anthony J.; Stockton, Stephen A.; Smith, Joanna L.

doi:10.2980/1195-6860(2006)13[511:sratio]2.0.co;2

Cited by 12 publications

(12 citation statements)

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“…There were many losers in this process but no real winners (McKinney and Lockwood 1999). Our results contrast with what has been shown to occur in many nonforest ecosystems (Keddy 2005), perhaps because human alteration to these insular systems have been small and, in particular they lack a diverse pool of non native species (Gaston et al 2006). The lack of positive effects of browsing on diversity could result from a high instantaneous rate of biomass removal by deer that prevents the recovery of the preferred plant species once they are affected, and from limited initial gains by the least preferred species.…”

Section: Herbivory and Plant Resistancecontrasting

confidence: 85%

“…The islands with the longest browsing history were the largest and least isolated of the study islands so, all else being equal, might be expected to have higher species richness than the other islands (MacArthur and Wilson 1967). However, in contrast with these expectations, plant species richness was highest on the smallest and most isolated islands (Stockton et al 2005;Gaston et al 2006), which were also those without deer. Overall geology, soils and topography were similar among the islands studied.…”

Section: Study Areacontrasting

confidence: 80%

“…One species, Nootka reedgrass, followed a guild II pattern but had substantially higher cover in the 0-50 cm vegetation layer on islands with deer \20 years. The low cover on the islands with deer [50 years may partly reflect habitat availability, as Nootka reedgrass is associated with lightly-wooded, exposed areas (Gaston et al 2006), which are less prevalent on these islands.…”

Section: Grassesmentioning

confidence: 99%

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Top-down and bottom-up consequences of unchecked ungulate browsing on plant and animal diversity in temperate forests: lessons from a deer introduction

et al. 2009

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Debate on the relative importance of competition for resources and trophic interactions in shaping the biological diversity of living communities remains unsettled after almost a century. Recently, dramatic increases in ungulate populations have provided a useful quasi-experiment on the effects of unrestrained ungulates on forest ecology. The islands of Haida Gwaii (Canada) offer a unique situation to investigate the potential of large herbivores to control temperate forest community structure and diversity. Black-tailed deer Odocoileus hemionus Merriam, native to adjacent mainland areas of British Columbia, were introduced in 1878 and spread to all but a few islands. Because deer were not native to the archipelago, islands that still lack deer provide a rare instance of temperate forest vegetation and fauna that developed in the absence of large herbivores. The colonisation of different islands at different times, and the absence of significant predation allow us to assess whether and how a large herbivore can exert ''topdown'' control on vegetation and its associated fauna. We studied plant communities in forest interior and shoreline, on seven small islands of varying browse history. Three islands were untouched by deer, deer had been resident for about 15 years on two, and on another two deer had been present for more than 50 years. Without deer, vegetation in the understorey and/or shrub layer was dense or very dense. Structure and composition varied markedly within and between shoreline and interior communities. Without deer, shoreline communities were dominated by species absent from islands with deer. Where deer had been present for less than 20 years most plant species characteristic of shorelines on islands without deer were already absent or scarce, but in the forest interior species richness was less affected and extensive shrub thickets remained. On islands where deer had been present for[50 years vegetation below the browse line was extremely simplified, converging in both forest interior and shoreline towards an open assemblage of a few deer-tolerant species, basically two coniferous trees. This top down effect on the plant community reflected up the food chain so that understorey invertebrate and shrub-dependent songbird communities became simplified. In contrast, species litter arthropods (especially weevils and millipedes) were highest where deer were present for [50 years. Canopy birds were unaffected by deer presence. In the absence of predators, major climatic stress or other means to control the herbivore, deer browsing created greatly simplified plant and animal communities.

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Section: Herbivory and Plant Resistancecontrasting

confidence: 85%

Section: Study Areacontrasting

confidence: 80%

Section: Grassesmentioning

confidence: 99%

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Top-down and bottom-up consequences of unchecked ungulate browsing on plant and animal diversity in temperate forests: lessons from a deer introduction

et al. 2009

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“…To date, only one study has examined this possibility. Gaston et al (2006) found that species composition on islands uninvaded by deer exhibited higher similarity than invaded islands, suggesting that deer drive biotic differentiation rather than biotic homogenization.…”

Section: Introductionmentioning

confidence: 96%

High white-tailed deer densities benefit graminoids and contribute to biotic homogenization of forest ground-layer vegetation

2008

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Biotic homogenization, with its emphasis on invasions, extinctions, and convergence in taxonomic similarity, provides an important framework for investigating changes in biodiversity across scales. Through their selective foraging, large populations of white-tailed deer are altering population sizes, driving extirpations, and facilitating invasions of plants throughout the eastern United States. I hypothesize that deer can drive biotic homogenization in forest understory communities by shifting species composition to one dominated by grasses, sedges, and ferns (all wind-pollinated plants). I report the effects of 16 years of deer exclusion in a hemlock-northern hardwood stand in N Wisconsin using a block design. Species composition showed greater convergence in control plots than exclosure plots, indicating deer can drive biotic homogenization at the stand level. Total percent cover is nearly 4 times greater in exclosure plots. Percent cover by woody plants, broadleaf herbs, and ferns is 150, 63, and 20 times greater in exclosure plots, respectively, while cover by sedges and grasses is 3.8 and 2.2 times greater in control plots. Cover by species with showy, insect-pollinated flowers is 79 times greater in exclosures. Graminoid-dominated control plots represent a novel state not observed fifty years ago, and could reflect the emergence of a grazing lawn. The increase in graminoids at this study area and throughout the region could under some global change scenarios be an early stage of conversion from forest to savanna or wood pasture.

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“…Islands may also have lower levels of native species propagule pressure than larger and less-isolated mainland sites (MacArthur and Wilson 1963). Larger islands or mainland sites may be better able to mitigate species turnover from disturbances such as human visitation (Lonsdale 1999), deer browsing (Gaston et al 2006) or earthworm invasions, and we are not aware of any other large-scale biotic disturbances that would have varied across both mainland and island sites.…”

Section: Discussionmentioning

confidence: 96%

Diversity–invasibility relationships across multiple scales in disturbed forest understoreys

2009

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Non-native plant species richness may be either negatively or positively correlated with native species due to differences in resource availability, propagule pressure or the scale of vegetation sampling. We investigated the relationships between these factors and both native and non-native plant species at 12 mainland and island forested sites in southeastern Ontario, Canada. In general, the presence of non-native species was limited: \20% of all species at a site were non-native and non-native species cover was \4% m -2 at 11 of the 12 sites. Non-native species were always positively correlated with native species, regardless of spatial scale and whether islands were sampled. Additionally, islands had a greater abundance of non-native species. Nonnative species richness across mainland sites was significantly negatively correlated with mean shape index, a measure of the ratio of forest edge to area, and positively correlated with the mean distance to the nearest forest patch. Other factors associated with disturbance and propagule pressure in northeastern North America forests, including human land use, white-tailed deer populations, understorey light, and soil nitrogen, did not explain non-native richness nor cover better than the null models. Our results suggest that management strategies for controlling non-native plant invasions should aim to reduce the propagule pressure associated with human activities, and maximize the connectivity of forest habitats to benefit more poorly dispersed native species.

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Species-area relationships and the impact of deer-browse in the complex phytogeography of the Haida Gwaii archipelago (Queen Charlotte Islands), British Columbia

Cited by 12 publications

References 1 publication

Top-down and bottom-up consequences of unchecked ungulate browsing on plant and animal diversity in temperate forests: lessons from a deer introduction

Top-down and bottom-up consequences of unchecked ungulate browsing on plant and animal diversity in temperate forests: lessons from a deer introduction

High white-tailed deer densities benefit graminoids and contribute to biotic homogenization of forest ground-layer vegetation

Diversity–invasibility relationships across multiple scales in disturbed forest understoreys

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