CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, PR China.
Spatial Ecology Lab, School of Life Science, South China Normal University, Guangzhou 510631, Guangdong, China.
Sci Total Environ. 2018 Jul 15;630:422-431. doi: 10.1016/j.scitotenv.2018.02.125. Epub 2018 Feb 24.
Forests play an important role in regulating the global carbon cycle. Yet, how abiotic (i.e. soil nutrients) and biotic (i.e. tree diversity, stand structure and initial biomass) factors simultaneously contribute to aboveground biomass (coarse woody) productivity, and how the relative importance of these factors changes over succession remain poorly studied. Coarse woody productivity (CWP) was estimated as the annual aboveground biomass gain of stems using 10-year census data in old growth and secondary forests (25-ha and 4.8-ha, respectively) in northeast China. Boosted regression tree (BRT) model was used to evaluate the relative contribution of multiple metrics of tree diversity (taxonomic, functional and phylogenetic diversity and trait composition as well as stand structure attributes), stand initial biomass and soil nutrients on productivity in the studied forests. Our results showed that community-weighted mean of leaf phosphorus content, initial stand biomass and soil nutrients were the three most important individual predictors for CWP in secondary forest. Instead, initial stand biomass, rather than diversity and functional trait composition (vegetation quality) was the most parsimonious predictor of CWP in old growth forest. By comparing the results from secondary and old growth forest, the summed relative contribution of trait composition and soil nutrients on productivity decreased as those of diversity indices and initial biomass increased, suggesting the stronger effect of diversity and vegetation quantity over time. Vegetation quantity, rather than diversity and soil nutrients, is the main driver of forest productivity in temperate mixed forest. Our results imply that diversity effect for productivity in natural forests may not be so important as often suggested, at least not during the later stage of forest succession. This finding suggests that as a change of the importance of different divers of productivity, the environmentally driven filtering decreases and competitively driven niche differentiation increases with forest succession.
森林在调节全球碳循环方面发挥着重要作用。然而，非生物因素（即土壤养分）和生物因素（即树木多样性、林分结构和初始生物量）如何同时促进地上生物量（粗木质）生产力，以及这些因素的相对重要性如何随演替而变化，这些问题仍研究甚少。在中国东北，利用老林（25 公顷）和次生林（4.8 公顷）的 10 年普查数据，估计粗木质生产力（CWP）为每年地上生物量的增加。使用增强回归树（BRT）模型来评估树木多样性的多个指标（分类学、功能和系统发育多样性以及性状组成以及林分结构属性）、林分初始生物量和土壤养分对研究林分生产力的相对贡献。研究结果表明，群落加权平均叶片磷含量、初始林分生物量和土壤养分是次生林中 CWP 的三个最重要的个体预测因子。相反，初始林分生物量，而不是多样性和功能性状组成（植被质量）是老林 CWP 的最简约预测因子。通过比较次生林和老林的结果，随着多样性指数和初始生物量的增加，性状组成和土壤养分对生产力的综合相对贡献减少，这表明多样性和植被数量的作用随着时间的推移而增强。在温带混合林中，植被数量而不是多样性和土壤养分是森林生产力的主要驱动因素。研究结果表明，与通常所认为的相反，在自然森林中，多样性对生产力的影响可能并不那么重要，至少在森林演替的后期阶段不是这样。这一发现表明，随着生产力不同多样性重要性的变化，环境驱动的过滤作用减少，竞争驱动的生态位分化随着森林演替而增加。
