Dynesius Mats, Hylander Kristoffer, Nilsson Christer
Landscape Ecology Group, Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden.
Ecology. 2009 Apr;90(4):1042-54. doi: 10.1890/07-1822.1.
Landscape heterogeneity causes spatial variation in disturbance regimes and resilience. We asked whether the resilience of bryophyte (liverwort and moss) assemblages to clear-cutting differs between streamside and upland boreal forests in northern Sweden. We hypothesized that bryophyte survival and recolonization rates are higher in streamside areas, thus raising resilience. Conversely, disturbance-intolerant but also invading species should be more frequent here, potentially reducing resilience. In each of 18 sites, we compared two 0.1-ha plots (one streamside and one upland) located in old forest that had never been clear-cut with two matching plots in young stands established after clear-cutting of old forests 30-50 years earlier. We used the magnitude of the difference in assemblages between old and young stands as a measure of change and, therefore, resilience (large difference implying low resilience). Species assemblages were more resilient in streamside than in upland forests. Species composition changed significantly in upland but not in streamside forests. Reductions in species richness were more pronounced in upland forests for total richness and for eight subgroups of species. Two results indicated lower survival/recolonization in upland forests: (1) species had a stronger association with old stands in upland areas, and (2) among species present in both the old streamside and old upland plot in a site, fewer appeared in the young upland than in the corresponding streamside plot. Simultaneously, a higher proportion of species invaded streamside areas; 40 of the 262 species encountered in streamside forests increased their occupancy by two or more sites compared to only two of 134 species in uplands. We suggest that in boreal forests spatial variation in resilience of assemblages of forest organisms intolerant of canopy removal is related to factors governed mainly by topography. More generally, we argue that landscape-scale variation in resilience of assemblages is influenced by spatial variation in (1) stress and resource availability, (2) number of disturbance-intolerant species, and (3) magnitude of environmental changes brought about by a disturbance with a specific intensity. We also suggest that rapid recovery in the short term does not necessarily imply higher long-term ability to return to the pre-disturbance state.
景观异质性导致干扰格局和恢复力的空间变异。我们探究了瑞典北部溪边和高地寒温带森林中苔藓植物（叶苔和苔藓）群落对皆伐的恢复力是否存在差异。我们假设溪边区域苔藓植物的存活率和重新定殖率更高，从而提高恢复力。相反，不耐干扰但具有入侵性的物种在这里应该更常见，这可能会降低恢复力。在18个地点中的每一个，我们将位于从未被皆伐过的原始森林中的两个0.1公顷样地（一个溪边样地和一个高地样地）与30 - 50年前原始森林皆伐后建立的幼林中的两个匹配样地进行了比较。我们将原始林和幼林群落之间差异的大小作为变化的衡量指标，进而作为恢复力的衡量指标（差异大意味着恢复力低）。溪边森林中物种群落的恢复力高于高地森林。高地森林中的物种组成发生了显著变化，而溪边森林中没有。对于总物种丰富度和八个物种亚组来说，高地森林中物种丰富度的降低更为明显。有两个结果表明高地森林中的存活率/重新定殖率较低：（1）高地地区的物种与原始林的关联更强；（2）在一个地点的原始溪边样地和原始高地样地中都出现的物种中，出现在幼龄高地样地中的物种比出现在相应溪边样地中的物种更少。同时，更高比例的物种入侵了溪边区域；溪边森林中遇到的262个物种中有40个将其占据的地点增加了两个或更多，而高地的134个物种中只有两个如此。我们认为，在寒温带森林中，不耐树冠去除的森林生物群落恢复力的空间变异与主要由地形控制的因素有关。更普遍地说，我们认为群落恢复力的景观尺度变异受以下因素的空间变异影响：（1）压力和资源可用性；（2）不耐干扰物种的数量；（3）特定强度干扰所带来的环境变化的程度。我们还认为，短期内的快速恢复不一定意味着长期恢复到干扰前状态的能力更强。
