Centre of Ecological Research and Forestry Applications (CREAF), Bellaterra, Spain.
University Autònoma de Barcelona, Bellaterra, Spain.
Glob Chang Biol. 2021 May;27(10):2113-2127. doi: 10.1111/gcb.15529. Epub 2021 Feb 19.
Many temperate forests are changing in composition due to a combination of changes in land-use, management and climate-related disturbances. Previous research has shown that in some regions these changes frequently favour drought-tolerant tree species. However, the effects of these changes in composition on forest functioning (e.g. productivity) are unclear. We studied 25 years of change in individual tree biomass growth, ingrowth and mortality, and community composition and total plot biomass across 2663 permanent forest plots in Catalonia (NE Spain) comprising 85,220 trees of 59 species. We focused on the relationship between community-level forest productivity and drought tolerance (DT), which was estimated using hydraulic traits as well as biogeographic indicators. We found that there was a small increase (1.6%-3.2% on average) in community-mean DT (DTcwm) during the study period, concurrent with a strong increase (12.4%-19.4% on average) in DT richness (DTric; i.e. trait range). Most importantly, we found that the mean DT was negatively related to forest productivity, which was explained because drought-tolerant tree species have lower tree-level growth. In contrast, DT richness was strongly and positively related to forest productivity, probably because it allowed for a more stable production along wet and dry periods. These results suggest a negative impact of ongoing climate change on forest productivity mediated by functional composition shifts (i.e. selection of drought-tolerant species), and a positive effect of increased DT richness as a consequence of land-use legacies. Such a trend towards functional diversification, although temporary, would increase forests' capacity to resist drought and place them in a better position to face the expected change in climate.
许多温带森林的组成正在发生变化，这是土地利用、管理和与气候相关的干扰变化共同作用的结果。先前的研究表明，在一些地区，这些变化经常有利于耐旱树种。然而，组成变化对森林功能（例如生产力）的影响尚不清楚。我们研究了 25 年来个体树木生物量生长、生长和死亡、群落组成和总样地生物量在加泰罗尼亚（西班牙东北部）的 2663 个永久性森林样地中的变化情况，这些样地共有 59 个物种的 85220 棵树木。我们专注于群落水平森林生产力与耐旱性（DT）之间的关系，DT 是通过水力特性以及生物地理指标来估计的。我们发现，在研究期间，群落平均 DT（DTcwm）略有增加（平均增加 1.6%-3.2%），同时 DT 丰富度（DTric；即性状范围）也大幅增加（平均增加 12.4%-19.4%）。最重要的是，我们发现平均 DT 与森林生产力呈负相关，这是因为耐旱树种的树木生长较低。相比之下，DT 丰富度与森林生产力呈强烈正相关，这可能是因为它允许在干湿期更稳定地生产。这些结果表明，由于功能组成变化（即耐旱物种的选择），正在进行的气候变化对森林生产力产生负面影响，而由于土地利用遗产，DT 丰富度的增加则产生积极影响。这种功能多样化的趋势虽然是暂时的，但会增加森林抵御干旱的能力，使它们更能应对预期的气候变化。
