The recovery of plant community composition following passive restoration across spatial scales, Cedar Creek Ecosystem Science Reserve, 1983-2016

1. Human impacts have led to dramatic biodiversity change which can be highly scale-dependent across space and time. A primary means to manage these changes is via passive (here, the removal of disturbance) or active (management interventions) ecological restoration. The recovery of biodiversity, following the removal of disturbance is often incomplete relative to some kind of reference target. The magnitude of recovery of ecological systems following disturbance depend on the landscape matrix, as well as the temporal and spatial scales at which biodiversity is measured. 2. We measured the recovery of biodiversity and species composition over 27 years in 17 temperate grasslands abandoned after agriculture at different points in time, collectively forming a chronosequence since abandonment from one to eighty years. We compare these abandoned sites with known agricultural land-use histories to never-disturbed sites as relative benchmarks. We specifically measured aspects of diversity at the local plot-scale (α-scale, 0.5m2) and site-scale (γ-scale, 10m2), as well as the within-site heterogeneity (β-diversity) and among-site variation in species composition (turnover and nestedness). 3. At our α-scale, sites recovering after agricultural abandonment only had 70% of the plant species richness (and ~30% of the evenness), compared to never-ploughed sites. Within-site β-diversity recovered following agricultural abandonment to around 90% after 80 years. This effect, however, was not enough to lead to recovery at our γ-scale. Richness in recovering sites was ~65% of that in remnant never-ploughed sites. The presence of species characteristic of the never disturbed sites increased in the recovering sites through time. Forb and legume cover declines in years since abandonment, relative to graminoid cover across sites. 4. Synthesis. We found that, during the 80 years after agricultural abandonment, old-fields did not recover to the level of biodiversity in remnant never-ploughed sites at any scale. β-diversity recovered more than α-scale or γ-scales. Plant species composition recovered, but not completely, over time, and some species groups increased their cover more than others. Patterns of ecological recovery in degraded ecosystems across space and long-time-scales can inform targeted active restoration interventions and perhaps, lead to better outcomes.

1. 人类活动已引发剧烈的生物多样性变化，此类变化在空间与时间维度上均呈现显著的尺度依赖性。管控此类变化的核心手段之一，是通过被动（本研究中指移除干扰）或主动（即管理干预）的生态修复手段。相较于各类参照目标，干扰移除后生物多样性的恢复往往并不完全。干扰后生态系统的恢复程度，取决于景观基质以及测定生物多样性时所采用的时间与空间尺度。
2. 本研究对17处因农业活动弃耕的温带草原展开了长达27年的跟踪监测，这些样地的弃耕时间各不相同，共同构成了弃耕年限1至80年的时间序列样地（chronosequence）。我们将这些拥有明确农业土地利用历史的弃耕样地，与未受干扰的原始样地作为相对参照基准进行对比。研究重点测定了两种尺度下的多样性指标：样地局部尺度（α尺度，α-scale，0.5㎡）与样地整体尺度（γ尺度，γ-scale，10㎡），同时也测定了样内异质性（β多样性，β-diversity）以及物种组成的样间差异（周转与嵌套性，turnover and nestedness）。
3. 在α尺度下，相较于未翻耕的原始样地，农业弃耕后的恢复样地仅拥有70%的植物物种丰富度（均匀度仅约为原始样地的30%）。弃耕80年后，样内β多样性恢复至原始水平的约90%，但这一恢复程度仍不足以使γ尺度下的生物多样性得到完全恢复。恢复样地的物种丰富度仅约为原始未翻耕样地的65%。随着恢复时间推移，恢复样地中出现的原始未受干扰样地特有物种数量逐渐增加。相较于样地内禾本科草本植物（graminoid）的盖度，杂类草（forb）与豆科植物（legume）的盖度会随弃耕年限增加而下降。
4. 综合分析。本研究发现，在农业弃耕后的80年间，弃耕地（old-fields）在任一尺度下均未能恢复至原始未翻耕样地的生物多样性水平。β多样性的恢复程度优于α尺度与γ尺度。植物物种组成随时间推移逐步恢复，但并未完全达成；不同功能群植物的盖度恢复幅度存在差异。跨空间与长期时间尺度的退化生态系统恢复模式，可为针对性的主动修复干预提供科学依据，或有助于提升生态修复的实际效果。