ABSTRACT

Numerous temperate peatlands are currently experiencing an accelerated process of woody encroachment. Such encroachment may have harmful impacts on peatland biodiversity and functions. Our objective was to investigate the recent history of woody encroachment in a temperate bog using plant macrofossil, testate amoeba, aerial photograph analyses, and plant inventories. We also explored some plausible triggering drivers of the phenomenon and its impacts on plant richness, composition, and beta diversity. We showed that the recent woody encroachment was mainly associated with the native Betula populifolia and the exotic Frangula alnus. It began in the 1960s at the bog margins following a decrease in the water table and recurrent fire events, both likely associated with agricultural activities in the surrounding catchment. We found an increase in species richness with tree cover and basal area, but no effect of tree encroachment on beta diversity. Still, we found a significant compositional turnover from light-demanding bog specialists to terrestrial, exotic or ruderal species with tree basal area. It seems unlikely that the bog will naturally come back to its previous unforested state on a human life’s timescale as the observed changes are related to regional factors rather than in situ disturbance.

摘要

许多温带泥炭地目前正在经历加速的木本侵占过程。这种侵占可能对泥炭地生物多样性和功能产生有害影响。我们的目标是使用植物大型化石、遗嘱变形虫、航空照片分析和植物清单调查温带沼泽中木本侵占的近期历史。我们还探讨了该现象的一些可能触发因素及其对植物丰富度、组成和 Beta 多样性的影响。我们表明，最近的木本侵占主要与本土桦木和外来的Frangula alnus 相关. 它始于 1960 年代的沼泽边缘，因为地下水位下降和火灾反复发生，这两者都可能与周围集水区的农业活动有关。我们发现物种丰富度随树木覆盖和基底面积的增加而增加，但树木侵占对 beta 多样性没有影响。尽管如此，我们还是发现了从要求光照的沼泽专家到具有树基面积的陆生、外来或粗野物种的显着组成变化。沼泽似乎不太可能在人类生命的时间尺度上自然地恢复到以前的未森林状态，因为观察到的变化与区域因素有关，而不是与 原地干扰有关。