Positive shrub-tree interactions facilitate woody encroachment in boreal peatlands

Boreal ecosystems are warming roughly twice as fast as the global average, resulting in woody expansion that could further speed up the climate warming. Boreal peatbogs are waterlogged systems that store more than 30% of the global soil carbon. Facilitative effects of shrubs and trees on the establishment of new individuals could increase tree cover with profound consequences for the structure and functioning of boreal peatbogs, carbon sequestration and climate.
We conducted two field experiments in boreal peatbogs to assess the mechanisms that explain tree seedling recruitment and to estimate the strength of positive feedbacks between shrubs and trees. We planted seeds and seedlings of Pinus sylvestris in microsites with contrasting water-tables and woody cover and manipulated both shrub canopy and root competition. We monitored seedling emergence, growth and survival for up to four growing seasons and assessed how seedling responses related to abiotic and biotic conditions.
We found...

北方生态系统（Boreal ecosystems）的升温速率约为全球平均水平的两倍，由此引发的木本植物扩张可能进一步加速气候变暖。北方泥炭沼泽（Boreal peatbogs）作为积水生态系统，其储存的土壤碳占全球土壤碳总量的30%以上。灌木与树木对新个体定植的促进效应，可提升区域树木覆盖度，并对北方泥炭沼泽的结构与功能、碳固存（carbon sequestration）以及全球气候产生深远影响。本研究在北方泥炭沼泽中开展了两项野外实验，旨在阐明树木幼苗定植的核心机制，并量化灌木与树木之间的正反馈强度。我们在地下水位与木本覆盖度存在差异的微生境中，种植了欧洲赤松（Pinus sylvestris）的种子与幼苗，并对灌木冠层及根系竞争进行了操控处理。我们对幼苗的出苗、生长与存活情况进行了长达四个生长季的监测，并分析了幼苗响应与非生物、生物环境条件的关联。本研究发现……