Forest demographic dynamics are a key process in forest restoration, but how multiple variables may affect forest demography remains unclear. With data from 1,399 permanent forest plots containing 125 species and 103,773 individual trees in the Eastern Qinghai-Tibet Plateau, we examined the patterns of forest demography from 1979 to 2017 as affected by climate, functional traits and forest structure. We found that forest stand age, tree density and wood density (WD) all had strong negative effects on demographic rates. Additionally, climate factors and leaf functional traits indirectly affected growth rate (GR) and recruitment rate (RR) via tree density and specific leaf area (SLA). Tree turnover (recruitment and death) was faster in places with higher temperatures, with species in these places tending to be replaced by the species with higher SLA. Moreover, relationships between demographic rates and functional traits were modulated by site climate and forest structure. GR-SLA relationships varied with tree density, becoming more negative at higher density sites. There was no effect of WD on RR at colder sites, but the relationships were increasingly negative at warmer sites and at higher tree density. This suggests that forest quality could be improved via adjusting the composition of forest species with different functional traits, or via adjustments to tree density, or stand age. We propose that forest improvement projects can be optimised by 1) thinning the species with high SLA in sites with high tree density, increasing the RR of species with high WD in the Eastern Qinghai-Tibet Plateau; and 2) prioritizing species with high SLA in warm sites, and species with higher WD for growth and RR in cool sites.

中文翻译：

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青藏高原东部地区森林人口特征取决于林分结构、功能特征和气候


森林人口动态是森林恢复的关键过程，但多个变量如何影响森林人口仍不清楚。利用青藏高原东部 1,399 个永久林地（包含 125 个物种、103,773 株单株树木）的数据，研究了 1979 年至 2017 年森林人口特征受气候、功能性状和森林结构影响的变化。我们发现森林林龄、树木密度和木材密度 (WD) 都对人口比率产生强烈的负面影响。此外，气候因素和叶子功能性状通过树木密度和比叶面积（SLA）间接影响生长率（GR）和补充率（RR）。在温度较高的地方，树木的周转（补充和死亡）更快，这些地方的树种往往会被 SLA 较高的树种所取代。此外，人口比率和功能特征之间的关系受到场地气候和森林结构的调节。 GR-SLA 关系随树木密度而变化，在密度较高的地点变得更加负面。在较冷的地点，WD 对 RR 没有影响，但在较温暖的地点和树木密度较高的情况下，这种关系越来越负。这表明可以通过调整具有不同功能性状的森林物种的组成，或者通过调整树木密度或林龄来改善森林质量。我们建议，森林改良项目可以通过以下方式进行优化：1）在树木密度高的地点间伐高SLA树种，提高青藏高原东部高WD树种的RR； 2) 优先考虑在温暖地区具有高 SLA 的物种，以及在凉爽地区具有较高 WD 和 RR 的物种。