Long-term data suggest jarrah-forest establishment at restored mine sites is resistant to climate variability

1. Global climate change is projected to increase the frequency and intensity of drought in dry regions due to warming temperatures and declining rainfall. Severe drought can trigger tree mortality and drive persistent vegetation change.
2. To date, most empirical studies have focused on drought-induced mortality of adult trees, but this needs to be matched by similar efforts to understand drought impacts on seedling establishment if we are to understand the resilience of the world's forests to projected climate change.
3. The Eucalyptus marginata (jarrah)-forest ecoregion of south-western Australia has experienced a 17% reduction in mean annual rainfall from 1975 to 2011 compared with mean rainfall from 1900 to 1974. Drought-induced mortality of adult trees has been documented for jarrah forest, but there is limited understanding of its capacity to recover, making it difficult to predict the likelihood of persistent effects.
4. Long-term records of jarrah-forest restoration following bauxite mining are available for the 19-year period between 1992 and 2010. Records include annual data on seedling establishment in restored mine sites for 587 species in 1938 plots during a period of climatic variability.
5. We built a structural equation model to discriminate the relative effects of climate, restoration practice, and their interactive effects on three response variables including species richness of the restored plant assemblages. Climate variability had a significant negative effect on richness, but the effect size was relatively small, being less than half that of varying restoration practice. We suggest this is due, in part, to the reliability of rainfall (i.e. no change in the coefficient of variation, seasonality or evenness, between recent and historical climates) despite a threefold difference in the absolute amount of wet-season rainfall. Importantly, there was no evidence that restoration practices were compromised by interacting effects of increased climate variability.
6. Synthesis. Jarrah-forest establishment in a restoration context appears resistant to recent changes in climate. Our research highlights the importance of deriving multiple metrics of climate change to understand community responses. In particular, rainfall reliability should be a focus of future research to determine its broader significance to seedling establishment in forests subject to a drying climate.

1. 据预测，受气温升高与降雨量减少影响，全球气候变化将提升干旱的发生频率并增强其强度，在干旱区域尤为显著。严重干旱可引发树木死亡，并推动植被发生持续性转变。
2. 迄今为止，多数实证研究均聚焦于干旱诱导的成年树木死亡现象，但若要理解全球森林对预测中气候变化的恢复能力，还需开展同等量级的研究，以探明干旱对幼苗建植的影响。
3. 澳大利亚西南部的贾拉木（Eucalyptus marginata）林生态区，1975年至2011年的年均降雨量相较1900年至1974年的均值下降了17%。目前已有文献记录了贾拉木林内干旱诱导的成年树木死亡事件，但学界对其恢复能力的认知仍较为有限，因此难以预测其产生持续性影响的可能性。
4. 1992年至2010年这19年间，存有贾拉木林在铝土矿开采后开展修复的长期监测记录。该记录涵盖气候波动期内，1938个样地中587个物种的幼苗建植年度监测数据，监测范围覆盖修复后的矿区样地。
5. 本研究构建了结构方程模型（structural equation model），以区分气候、修复措施及其交互作用对三类响应变量的相对影响，其中包括修复后植物群落的物种丰富度。结果显示，气候波动对物种丰富度具有显著负向影响，但效应量相对较小，仅为修复措施变动影响的一半以下。我们推测，这一现象部分源于降雨的可靠性——尽管湿季降雨量的绝对数值相差三倍，但近期与历史气候的变异系数、季节性及均匀度均未发生变化。值得注意的是，并无证据表明气候波动加剧的交互作用会对修复措施产生负面影响。
6. 研究总结：修复场景下的贾拉木林建植过程，似乎能够耐受近期的气候变化。本研究强调，需构建多维度的气候变化指标以探明群落对气候变化的响应机制。尤为关键的是，未来研究应聚焦降雨可靠性，以明确其对气候干旱化背景下森林幼苗建植的更广泛影响。