Data from: Functional diversity enhances silver fir growth resilience to an extreme drought

It is expected that extreme climate events such as droughts will increase both in severity and intensity as a consequence of forecasted climate change. Complementarity among tree species in resource acquisition strategy may reduce interspecific competition and increase the occurrence of facilitative interactions, resulting in an improved tree growth and resilience to extreme climatic events. However, the response of individual trees growing in more functionally diverse stands to extreme events is still under debate. We investigate the growth response of silver fir (Abies alba) to an extreme drought event which occurred in 1985-1986 in the central Spanish Pyrenees, and how the growth and resilience of trees relate to their neighbourhood functional diversity, stand heterogeneity, and to intraspecific and interspecific competition. Dendroecological methods were used to reconstruct radial growth. We recorded all tree species living around each sampled tree and calculated indices of intra- and interspecific competition among coexisting trees. Functional diversity around each focal tree was calculated by using the Rao quadratic entropy. Silver fir growth decreased significantly in response to the drought in the vast majority of trees, but most of them showed a growth recovery three years later. Despite most trees showed negative growth trends following the drought event (70%), those trees growing in more functionally diverse stands were more resilient, recovered more quickly and displayed greater growth and growth trends. Synthesis: The presented findings support the growing body of evidence that shows a positive impact of diversity on forest function. In addition, we provide a direct linkage between tree growth response to climate at the individual tree scale and a direct quantification of neighbourhood functional diversity and competition. An enhanced functional diversity facilitating a more efficient use of resources at the interspecific level and potentially increasing facilitative interactions contributes to lessening the negative impacts of extreme events as droughts on forest growth.

受预估气候变化影响，干旱等极端气候事件的严重程度与发生强度均将加剧。林木树种在资源获取策略上的生态位互补性，可降低种间竞争并提升促进性相互作用的发生概率，进而改善林木生长状况并增强其对极端气候事件的抗逆能力。然而，生长于功能多样性更高林分中的单木对极端气候事件的响应机制，目前仍存在学术争议。
本研究以西班牙比利牛斯山脉中部1985-1986年发生的极端干旱事件为研究背景，探究银冷杉（Abies alba）的生长响应特征，并解析林木生长与抗逆性与其邻体功能多样性、林分异质性以及种内、种间竞争的关联机制。本研究采用树木年代生态学方法（dendroecological methods）重建林木径向生长序列；对每株焦点树（focal tree）周边的所有林木树种进行调查记录，并计算共存林木间的种内与种间竞争指数；同时采用Rao二次熵（Rao quadratic entropy）计算每株焦点树周边的功能多样性水平。
研究结果显示，绝大多数银冷杉的生长在极端干旱事件后显著降低，但其中大部分个体在三年后实现了生长恢复。尽管70%的样木在干旱事件后呈现负生长趋势，但生长于功能多样性更高林分中的个体具有更强的抗逆性、更快的生长恢复速度，且表现出更优的生长水平与生长趋势。
综合分析：本研究结果为日益增多的相关研究证据提供了新支撑，证实了生物多样性对森林生态系统功能的正向调控作用。此外，本研究实现了单木尺度下林木生长对气候的响应与邻体功能多样性、竞争强度的直接量化关联。提升功能多样性可促进种间资源的高效利用，并潜在增强促进性相互作用，进而缓解干旱等极端气候事件对森林生长的不利影响。