Sachser Frederik, Pesendorfer Mario, Gratzer Georg, Nopp-Mayr Ursula
Department of Forest- and Soil Sciences Institute of Forest Ecology University of Natural Resources and Life Sciences Vienna Austria.
Department of Integrative Biology and Biodiversity Research Institute of Wildlife Biology and Game Management University of Natural Resources and Life Sciences Vienna Austria.
Ecol Evol. 2021 Aug 13;11(17):11890-11902. doi: 10.1002/ece3.7955. eCollection 2021 Sep.
Mast seeding, the synchronized interannual variation in seed production of trees, is a well-known bottom-up driver for population densities of granivorous forest rodents. Such demographic effects also affect habitat preferences of the animals: After large seed production events, reduced habitat selectivity can lead to spillover from forest patches into adjacent alpine meadows or clear-cuts, as has been reported for human-impacted forests. In unmanaged, primeval forests, however, gaps created by natural disturbances are typical elements, yet it is unclear whether the same spillover dynamics occur under natural conditions. To determine whether annual variation in seed production drives spillover effects in naturally formed gaps, we used 14 years of small mammal trapping data combined with seed trap data to estimate population densities of spp. mice and bank voles () on 5 forest sites with differing disturbance history. The study sites, located in a forest dominated by European beech (), Norway spruce (), and silver fir (), consisted of two primeval forest sites with small canopy gaps, two sites with larger gaps (after an avalanche event and a windthrow event), and a managed forest stand with closed canopy as a control. Hierarchical Bayesian N-mixture models revealed a strong influence of seed rain on small rodent abundance, which were site-specific for but not for spp. Following years of moderate or low seed crop, avoided open habitat patches but colonized those habitats in large numbers after full mast events, suggesting that spillover events also occur in unmanaged forests, but not in all small rodents. The species- and site-specific characteristics of local density responding to food availability have potentially long-lasting effects on forest gap regeneration dynamics and should be addressed in future studies.
大年结实，即树木种子产量的同步年际变化，是食谷森林啮齿动物种群密度的一个众所周知的自下而上的驱动因素。这种种群动态效应也会影响动物的栖息地偏好：在大量种子生产事件之后，栖息地选择性降低会导致动物从森林斑块扩散到相邻的高山草甸或皆伐地，就像在受人类影响的森林中所报道的那样。然而，在未受管理的原始森林中，自然干扰形成的林窗是典型的组成部分，但尚不清楚在自然条件下是否会发生同样的扩散动态。为了确定种子产量的年变化是否会在自然形成的林窗中驱动扩散效应，我们使用了14年的小型哺乳动物诱捕数据，并结合种子陷阱数据，来估计5个具有不同干扰历史的森林地点的小鼠和小林姬鼠种群密度。研究地点位于以欧洲山毛榉、挪威云杉和银枞为主的森林中，包括两个有小冠层林窗的原始森林地点、两个有较大林窗的地点（一次雪崩事件和一次风倒事件之后），以及一个树冠封闭的人工林作为对照。分层贝叶斯N混合模型显示种子雨对小型啮齿动物数量有强烈影响，对小林姬鼠来说这种影响具有地点特异性，但对小鼠来说则不然。在经历了数年中等或低种子产量之后，小林姬鼠避开开阔栖息地斑块，但在大年结实事件之后大量迁入这些栖息地，这表明扩散事件也发生在未受管理的森林中，但并非所有小型啮齿动物都会如此。当地密度对食物可利用性的物种和地点特异性特征可能对森林林窗更新动态有长期影响，应在未来研究中加以探讨。
