Data from: Species-area curve and distance-decay relationship indicate habitat thresholds of ectomycorrhizal fungi in an old-growth Pseudotsuga menziesii landscape

Aim: Ectomycorrhizal fungi (EMF) are a diverse and essential biota of forests that are vulnerable to species loss through reductions in late-seral habitat. We examined how the spatial ecology of this biota, particularly distance-decay and species-area relationships, could better inform habitat thresholds for EMF conservation planning. Location: Southeast Vancouver Island near Victoria, British Columbia, Canada.
Methods: Using a stratified sampling design, 11 plots (0.15 ha in size) were established at 0.05 to 17.5 km apart across 2800 ha of mesic old-growth Pseudotsuga menziesii var. menziesii and Tsuga heterophylla forests. EMF communities were compiled through molecular analysis of root tips and sporocarps. Results: The EMF community was comprised of many Cortinarius, Piloderma, Russula and Tricholoma species typical of mesotrophic habitat. A total of 238 EMF species were observed, of which 86 species were detected only once. The ratio of average species richness per plot (84 taxa) to total richness was low at 0.35, and inherent stochasticity of the EMF community was estimated to be 31% community dissimilarity for species incidence. Distance decay of EMF communities was nonlinear, with an estimated slope break at 2.6 km, followed by a largely unchanging trend in β-diversity. Accumulated species-area curves were fitted best by the cumulative Weibull sigmoid model, and the asymptote (367 species) at approx. 50 ha was consistent with non-parametric estimates of γ diversity (342-362 spp.). Main conclusions: Old-growth forests host an impressive amount of EMF diversity, and many of the Ramaria, Inocybe and Russula species are likely to be endemic to the Pacific Northwest. Both niche- and neutral-based processes influenced EMF community composition, resulting in a minimum threshold of 50 ha (1.8% of the sample area) for capturing γ diversity. These spatial patterns will help design and evaluate conservation efforts, such as retention forestry, to sustain fully diverse EMF communities over managed landscapes.

研究目的：外生菌根真菌（Ectomycorrhizal fungi, EMF）是森林中多样且不可或缺的生物类群，其易因晚演替生境缩减而面临物种丧失风险。本研究探讨该类群的空间生态学特征——尤其是距离衰减效应与种-面积关系——如何能为EMF保护规划提供更精准的生境阈值参考。
研究区域：加拿大不列颠哥伦比亚省维多利亚市附近的温哥华岛东南部区域。
研究方法：本研究采用分层抽样设计，在2800公顷的湿润老龄花旗松原变种（Pseudotsuga menziesii var. menziesii）与西部铁杉（Tsuga heterophylla）林中，设置了11个面积为0.15公顷的样地，样地间距介于0.05至17.5千米之间。通过对植物根尖与子实体的分子分析，获取EMF群落组成数据。
研究结果：EMF群落由大量见于中营养生境的丝膜菌属（Cortinarius）、皮膜菌属（Piloderma）、红菇属（Russula）以及口蘑属（Tricholoma）物种构成。本研究共观测到238种EMF，其中86种仅被单次检出。单样地平均物种丰富度（84个类群）与总物种丰富度的比值仅为0.35，处于较低水平；经估算，基于物种出现率的EMF群落固有随机性可造成31%的群落相异度。EMF群落的距离衰减效应呈非线性特征，在2.6千米处出现斜率拐点，此后β多样性（β-diversity）基本保持稳定。累积种-面积曲线经最优拟合后符合累积威布尔Sigmoid模型，在约50公顷处达到的物种丰富度渐近值（367种）与γ多样性（γ diversity）的非参数估算值（342~362种）相一致。
主要结论：老龄林蕴含极为丰富的EMF多样性，诸多枝瑚菌属（Ramaria）、丝盖伞属（Inocybe）与红菇属物种大概率为太平洋西北地区特有种。生态位过程与中性过程共同塑造了EMF群落组成，据此得出维持完整γ多样性所需的最小生境阈值为50公顷（占样区总面积的1.8%）。上述空间格局将有助于设计与评估诸如保留林业等保护措施，以在经营景观中维持完整多样的EMF群落。