Department of Biology and Florida Museum of Natural History, University of Florida, Gainesville, Florida, 32611, USA.
College of Science and Engineering, James Cook University, Cairns, Queensland, Australia.
Ecology. 2020 May;101(5):e02996. doi: 10.1002/ecy.2996. Epub 2020 Mar 9.
We took advantage of two natural experiments to investigate processes that regulate tree recruitment in gaps. In the first, we examined the recruitment of small and large saplings and trees into 31 gaps resulting from treefalls occurring between 1984 and 2015 in the 2.25-ha core area of a 4-ha tree plot at Cocha Cashu in Perú. In the second, we identified the tallest saplings recruiting into 69 gaps created during a violent wind storm in February 2000. In the established tree plot, we were able to compare the composition of saplings in the disturbance zones of gaps prior to, during, and subsequent to the period of gap formation. Recruitment in gaps was compared with that in "nofall" zones, areas within the plot that had not experienced a treefall at least since the early 1980s. Our results confirmed earlier findings that a consistently high proportion (~60%) of established saplings survived gap formation. Light demanding species, as proxied by mortality rates, recruited under all conditions, but preferentially during periods of gap formation, a pattern that was especially strong among gap pioneers. Similar results were noted, separately, for small and large saplings and trees recruiting at ≥10 cm dbh. One hundred percent of previously untagged trees recruiting into gaps in the first post-disturbance census were gap pioneers, suggesting rapid development. This conclusion was strongly supported in a follow-up survey taken of 69 gaps 19 months after they had been synchronously created in a wind storm. Ten species of gap pioneers, eight of which are not normally present in the advance regeneration, had attained heights of 6-10 m in 19 months. The 10 gap pioneers were dispersed, variously, by primates, bats, birds, and wind and reached maximum frequency in different-sized gaps (range <100 m to >1,000 m ). Both gap size and limited dispersal of zoochorous species into gaps serve as filters for establishment, creating a complex mosaic of conditions that enhances species diversity.
我们利用两个自然实验来研究调节林隙中树木更新的过程。在第一个实验中，我们研究了 1984 年至 2015 年间，在秘鲁科恰卡舒 4 公顷树木样地中 2.25 公顷核心区域的 31 个因树木倒伏而形成的林隙中，小树和大树的更新情况。在第二个实验中，我们确定了在 2000 年 2 月强烈风暴期间形成的 69 个林隙中，生长最快的幼树。在已建立的树木样地中，我们能够比较林隙干扰带内树木幼树的组成，包括在林隙形成之前、期间和之后。我们将林隙更新与“无倒木”区（至少自 20 世纪 80 年代初以来未经历过树木倒伏的样地内的区域）进行了比较。研究结果证实了先前的发现，即稳定的高比例（~60%）已建立的幼树在林隙形成过程中得以存活。对光有需求的物种（以死亡率为指标）在所有条件下都有更新，但在林隙形成期间更新更为优先，这种模式在林隙先驱者中尤为明显。对于在 dbh≥10cm 处更新的小树、大树，分别单独进行研究，也得到了类似的结果。在第一次林隙干扰后普查中，100%的新出现的树木都是林隙先驱者，这表明它们的快速发展。这一结论在对 19 个月前因风暴同步形成的 69 个林隙进行的后续调查中得到了有力支持。在 19 个月内，有 10 种林隙先驱者物种（其中 8 种在早期更新中通常不存在）达到了 6-10 米的高度。这 10 种林隙先驱者物种以各种方式被灵长类动物、蝙蝠、鸟类和风力传播，并在不同大小的林隙中达到最大频率（范围<100 米至>1000 米）。林隙的大小和动物传播的局限都会对物种的建立起到过滤作用，形成一个复杂的、能增强物种多样性的条件镶嵌体。
