Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI, United States of America.
Weyerhaeuser, Springfield, OR, United States of America.
PLoS One. 2022 Aug 31;17(8):e0273630. doi: 10.1371/journal.pone.0273630. eCollection 2022.
Retention forestry is a common practice for biodiversity conservation in forests managed for wood production. Retention forestry often leaves unharvested patches of trees that vary in size and spatial pattern but experiments evaluating the effects of different retention patch configurations at a constant level of retention are lacking for many regions and taxonomic groups. We implemented an experimental study in clearcut conifer stands with retention across the U.S. Pacific Northwest region. The study consisted of five stand-level (11-55 ha) experimental treatments each replicated 10 times within a randomized complete block design, resulting in 50 treated stands. Retained tree density was comparable across treatments but size, number, and location (upland or riparian) of patches within stands varied among the five treatments. Within experimental treatments, we measured small mammal (<1kg) species and functional trait (i.e., body size, diet, activity stratum) richness in retention patches, surrounding harvested portions of stands, and nearby unharvested stands. We evaluated species and functional trait richness by treatment using generalized linear mixed-effects models and species-specific responses to retention placement using a community occupancy model. We obtained repeat captures of 21 species of small mammals but found limited evidence of a treatment effect on species richness, and no differences in functional trait richness. Species richness was highest where all retained trees were aggregated into one patch placed adjacent to a forested riparian buffer (mean = 6.6 species, 95% CI = 5.7-7.5), and lowest in the treatment containing one retention patch in the upland portion of a harvested stand (mean = 4.7 species, 95% CI = 3.8-5.6). Furthermore, estimates of species richness within retention patches of harvested stands (i.e., not considering species in harvested areas) did not differ among treatments, indicating that the slightly elevated species richness in riparian-associated retention results from 1-2 species in these patches that do not occur in adjacent harvested portions of each treated stand. Patch occupancy of several species was higher in riparian patches than harvested portions of the treated stands, and fewer species had higher occupancy in upland patches compared to harvested portions of treated stands. Our results indicated that at retention densities currently required in Oregon and Washington, the location of retention patches had a small influence on stand-scale measures of small mammal diversity, but local increases in species richness may be obtained by retaining trees adjacent to riparian buffers.
保留森林是森林管理中用于生物多样性保护的常见做法，这些森林的主要目的是木材生产。保留森林通常会留下未经采伐的树木斑块，这些斑块在大小和空间模式上存在差异，但对于许多地区和分类群，缺乏在恒定保留水平下评估不同保留斑块配置效果的实验。我们在美国太平洋西北地区的皆伐针叶林地上实施了一项实验研究。该研究包括五个林分水平（11-55 公顷）的实验处理，每个处理在随机完全区组设计中重复 10 次，共 50 个处理林分。保留的树木密度在处理间相当，但林分中斑块的大小、数量和位置（高地或河岸）在五个处理间存在差异。在实验处理中，我们测量了保留斑块、采伐林分内剩余部分和附近未采伐林分内小型哺乳动物（<1kg）物种和功能特征（即体型、食性、活动层）的丰富度。我们使用广义线性混合效应模型评估处理对物种和功能特征丰富度的影响，并使用群落占据模型评估对保留斑块位置的物种特定响应。我们对 21 种小型哺乳动物进行了重复捕获，但发现处理对物种丰富度的影响证据有限，且功能特征丰富度无差异。所有保留树木聚集在一个毗邻森林河岸缓冲区的斑块中的处理（平均值=6.6 种，95%置信区间=5.7-7.5）的物种丰富度最高，而在收获林分内有一个保留斑块的处理（平均值=4.7 种，95%置信区间=3.8-5.6）的物种丰富度最低。此外，收获林分内保留斑块内的物种丰富度估计值（即，不考虑收获区域内的物种）在处理间没有差异，这表明河岸相关保留中略微升高的物种丰富度是由于这些斑块中存在的 1-2 种不在每个处理林分内相邻收获部分出现的物种造成的。几种物种在河岸斑块中的占据性高于处理林分内的收获部分，而在高地斑块中占据性较高的物种比处理林分内的收获部分较少。我们的研究结果表明，在俄勒冈州和华盛顿州目前要求的保留密度下，保留斑块的位置对小型哺乳动物多样性的林分尺度测量影响较小，但通过将树木保留在河岸缓冲区旁边，可以获得局部物种丰富度的增加。
