Data from: From the individual to the landscape and back: Time-varying effects of climate and herbivory on tree sapling growth at distribution limits

1. As herbivory can modulate climate-induced shifts in species distribution, disentangling the relative importance of herbivory and climate on plant growth can help to predict and manage future changes in vegetation, such as those occurring at treeline areas. 2. An individual-based hierarchical Bayesian time-series model (Individual-Based Model; IBM) was developed to estimate the time-varying impact of climate and herbivory on individual pine-sapling height growth in woodland and treeline ecosystems of Southern Europe during a 16-year period. The performance of the IBM was compared to a Linear Mixed-Effects (LME) model to test for potential inferential effects when individual variability is marginalized. Time-varying models were also compared to constant parameter approaches. 3. Model fitting and posterior predictive checking suggests a better statistical performance of individual-scale, time-varying inference. LME modeling overestimated herbivory effects and underestimated environmental stochastic effects, and model validation indeed suggested severe overfitting in the LME model relative to the IBM strategy. These results reveal a potential failure of common aggregation strategies to correctly resolve the effects of climate and herbivory variability at the individual scale. Moreover, ignoring the time-varying nature of the effects may preclude the correct estimation of the temporal scale of climate and herbivory impacts. 4. In general, we found stronger individual- and time-averaged effects of summer precipitation relative to the effects of herbivory, particularly at the treelines. Also, individual pines responses showed effects of the same sign more consistently in the case of precipitation. This suggests that precipitation is more pervasive at the population level, while herbivory act as a spatially aggregating force through individual-level damage. 5. Synthesis. Our results suggest that accounting for individual and temporal variability in ecological inference greatly improve the assessment of the relative importance of climate and herbivory on species distribution shifts. Strong effects of precipitation at the treeline could allow tree upward expansion, although increasing ungulate populations and associated browsing damages might limit positive climatic responses of pine-saplings in the near future. In this context, the spatially heterogeneous effect exerted by herbivory could result in diverse vegetation structures in ecotones, adding a new dimension to the predictions on climate-driven vegetation shifts.

1. 植食作用（herbivory）可调控气候诱导的物种分布偏移，厘清植食作用与气候对植物生长的相对重要性，有助于预测并管理未来植被变化，例如林线（treeline）区域发生的植被动态。2. 本研究构建了基于个体的分层贝叶斯时间序列模型（Individual-Based Model; IBM），用以估算16年间南欧林地与林线生态系统中，气候与植食作用对松树幼株高生长的时变影响。将该个体基模型的性能与线性混合效应模型（Linear Mixed-Effects, LME）进行对比，以检验当个体变异性被边际化时可能存在的推断偏差；同时还将时变模型与固定参数方法进行了对比。3. 模型拟合与后验预测检验（posterior predictive checking）结果表明，个体尺度的时变推断具备更优的统计性能。线性混合效应模型高估了植食作用的影响，同时低估了环境随机效应的作用；模型验证结果亦证实，相较于个体基模型框架，线性混合效应模型存在严重的过拟合问题。上述结果揭示，常见的聚合策略可能无法正确解析个体尺度下气候与植食作用变异性的影响。此外，忽略效应的时变属性，可能会导致无法正确估算气候与植食作用影响的时间尺度。4. 总体而言，相较于植食作用的影响，夏季降水在个体与时间平均层面展现出更强的效应，这一现象在林线区域尤为显著。同时，松树个体对降水的响应符号更为一致。这表明降水在种群层面的影响更为普遍，而植食作用则通过个体层面的取食损伤，形成空间聚集性的调控力量。5. 综合分析。本研究结果表明，在生态推断中纳入个体与时间变异性，可大幅提升对气候与植食作用影响物种分布偏移相对重要性的评估精度。林线区域降水的强效应可能推动树木向上扩张，但有蹄类（ungulate）种群数量的增加及其伴随的啃食损伤，可能在未来限制松树幼株的正向气候响应。在此背景下，植食作用所产生的空间异质性效应，可能导致生态交错带（ecotones）形成多样的植被结构，为气候驱动的植被变化预测增添了新的维度。