Data for: Comparing the effect of landscape context on vascular plant and bryophyte communities in a human-dominated landscape

AbstractAims: It is important to understand the effect of landscape context on biological communities to predict how biodiversity will be affected on human-dominated landscapes. While many studies have tested the effects of landscape context on the species richness and composition of vascular plants, few have compared the responses of vascular plants and bryophytes on the same landscape. We sampled non-epiphytic bryophytes and vascular plants in 184 plots to test whether three landscape context factors measured four years or four decades previously could predict bryophyte or vascular plant species richness and composition after accounting for local factors. Location: Temperate forests and oak savannahs, Vancouver Island, British Columbia, Canada. Methods: We used model selection and comparisons to test the effects of surrounding road density, total amount of forest, and distance to the nearest forest edge on species richness, species richness of non-disturbance-associated species, and community composition after controlling for important local predictors including substrate availability and topography. Results: The species richness of non-disturbance-associated vascular plants was lower in plots with greater surrounding historical road density, and perennial stayer bryophyte richness declined with increasing historical road density and lower historical forest amount, suggesting a potential extinction debt. Landscape context significantly affected total species richness and community composition of vascular plants, but not bryophytes. Conclusion: While bryophytes appear to be less sensitive overall to landscape context than vascular plants, disturbance-intolerant perennial stayer bryophytes may decline in the future in response to the increased road density and loss of forest cover that has occurred over the past four decades.
MethodsWe sampled 184 20m x 20m relevé plots on the Saanich Peninsula, a region of approximately 330 km2 in 2009. In each plot, we identified all vascular plants and estimated the percent cover of each. We also identified all bryophyte species occurring on soil, rock, or decomposing wood, and estimated the percent cover of each. If a species was estimated to cover less than 1% of the plot, we entered “0.5” in the data, and if it covered much less than 1%, we entered “0.1”. We did not survey epiphytic bryophytes on living trees. We also measured the slope and aspect of each plot, and estimated the percent cover of soil, exposed rock, and decomposing wood substrate. We then used a Geographical Information System (GIS) to measure the total amount of natural vegetated area within a 500m buffer of each plot, the total length of roads within the same distance of each plot, and the distance in metres from the plot to the nearest edge between natural and non-natural vegetation.

摘要 研究目的：明确景观背景对生物群落的影响，对于预测人类主导景观下生物多样性的变化趋势至关重要。现有诸多研究已探讨了景观背景对维管植物（vascular plants）物种丰富度与群落组成的影响，但鲜有研究在同一景观背景下同时对比维管植物与苔藓植物（bryophytes）的响应差异。本研究于184个样地中对非附生苔藓植物与维管植物进行采样，旨在验证：在控制局域环境因子的前提下，4年前或40年前测定的三类景观背景因子，能否预测后续的苔藓植物或维管植物物种丰富度与群落组成。
研究区域：加拿大不列颠哥伦比亚省温哥华岛的温带森林与橡木稀树草原。
研究方法（摘要版）：我们通过模型选择与对比分析，检验了周边道路密度、森林总面积以及到最近林缘的距离对物种丰富度、无干扰关联物种丰富度以及群落组成的影响，同时控制了底物可用性与地形等关键局域预测变量。
研究结果：无干扰关联维管植物的物种丰富度随周边历史道路密度的升高而降低；多年生定殖型苔藓植物的物种丰富度则随历史道路密度升高、历史森林面积减少而下降，这提示存在潜在的灭绝债务（extinction debt）。景观背景对维管植物的总物种丰富度与群落组成具有显著影响，但对苔藓植物并无显著作用。
研究结论：尽管整体而言苔藓植物对景观背景的敏感性低于维管植物，但在过去四十年间道路密度增加与森林覆盖减少的背景下，对干扰敏感的多年生定殖型苔藓植物未来可能出现种群衰退。

详细研究方法：2009年，我们在面积约330平方千米的萨尼奇半岛布设了184个20米×20米的植被样方（relevé plots）。在每个样方内，我们对所有维管植物进行物种鉴定，并估算其盖度百分比；同时对生长于土壤、岩石或腐木上的所有苔藓植物进行物种鉴定，并估算其盖度百分比。若某物种的盖度预估小于1%，则在数据中记为“0.5”；若盖度远小于1%，则记为“0.1”。本研究未调查活树上的附生苔藓植物。此外，我们测定了每个样方的坡度与坡向，并估算了样方内土壤、裸露岩石与腐木底物的盖度百分比。随后，我们借助地理信息系统（Geographical Information System, GIS）测定了每个样方500米缓冲区内的自然植被总面积、相同缓冲范围内的道路总长度，以及该样方到最近的自然与非自然植被边界的距离（单位：米）。