Positive response of tree productivity to warming is reversed by increased tree density at the Arctic tundra-taiga ecotone
Positive response of tree productivity to warming is reversed by increased tree density at the Arctic tundra-taiga ecotone
复制标题
北极苔原-针叶林交错带树木密度的增加逆转了树木生产力对变暖的积极反应
DOI：
10.1139/cjfr-2020-0466
复制
发表时间：
2021
影响因子：
2.2
通讯作者：
Mack, Michelle C.
中科院分区：
文献类型：
--
作者：
Walker, Xanthe;Alexander, Heather D.;Berner, Logan;Boyd, Melissa A;Loranty, Michael M.;Natali, Sue;Mack, Michelle C.
北部北方森林和北极冻土带之间的过渡地带，被称为冻土带-针叶林过渡带（TTE），近几十年来经历了快速变暖。作为对这种变暖的响应，树木密度、生长和林分生产力预计会增加。树木密度的增加有可能通过减少活性层和增加竞争相互作用来抵消变暖对树木生长的积极影响。研究了树木密度对东北西伯利亚地区落叶松（Larix cajanderiMayr.）树木生长和气候生长响应的影响，以及对归一化植被指数（NDVI）变化趋势的影响。我们调查了19个成熟林分，这些林分都是在1940年的一场火灾之后建立起来的，树密度在300 ~ 37000茎·ha−1之间。活性层较浅的高密度林分比活性层较深的低密度林分生长量更低，林分生产力更高，生长季节温度负响应更强。landsat衍生的NDVI没有捕捉到林分生产力在密度梯度上的变化，但NDVI确实捕捉到了林分生产力的年变化。我们的研究结果表明，TTE火灾后树木密度的预期增加可能会有效地限制树木的生长，并且NDVI不太可能捕捉到与树木密度变化相关的生产力增加。
The transition zone between the northern boreal forest and the Arctic tundra, known as the tundra–taiga ecotone (TTE) has undergone rapid warming in recent decades. In response to this warming, tree density, growth, and stand productivity are expected to increase. Increases in tree density have the potential to negate the positive impacts of warming on tree growth through a reduction in the active layer and an increase in competitive interactions. We assessed the effects of tree density on tree growth and climate–growth responses of Cajander larch (Larix cajanderiMayr.) and on trends in the normalized difference vegetation index (NDVI) in the TTE of Northeast Siberia. We examined 19 mature forest stands that all established after a fire in 1940 and ranged in tree density from 300 to 37 000 stems·ha−1. High-density stands with shallow active layers had lower tree growth, higher stand productivity, and more negative growth responses to growing season temperatures compared with low-density stands with deep active layers. Variation in stand productivity across the density gradient was not captured by Landsat-derived NDVI, but NDVI did capture annual variations in stand productivity. Our results suggest that the expected increases in tree density following fires at the TTE may effectively limit tree growth and that NDVI is unlikely to capture increasing productivity associated with changes in tree density.