INITIAL RESPONSES OF FOREST UNDERSTORIES TO VARYING LEVELS AND PATTERNS OF GREEN-TREE RETENTION
INITIAL RESPONSES OF FOREST UNDERSTORIES TO VARYING LEVELS AND PATTERNS OF GREEN-TREE RETENTION
复制标题
森林林下植物对不同水平和绿树保留模式的初步反应
DOI：
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发表时间：
2005
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影响因子：
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通讯作者：
D. Maguire
中科院分区：
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作者：
Charles B. Halpern;D. McKenzie;Shelley A. Evans;D. Maguire
许多温带和北方森林生态系统已采用保留“绿树”的木材采伐方式，反映出人们日益重视管理森林的生态价值。在太平洋西北部的联邦林地上，已通过了保留绿树的标准和准则，但尚未对生态系统的反应进行系统的评估。我们研究了初始（1-2年）的反应，在西部俄勒冈州和华盛顿的六个地点（块）的血管林下群落的绿树保留，使用析因设计保留在对比水平（15%与40%的初始断面积）和空间格局（树木分散与聚集在1公顷补丁）。成分变化的方向（表示在排序空间）是相似的治疗在每个区块内，但变化的幅度始终大于在15%，而不是在40%的保留;保留模式对成分变化的影响不大。尽管植被结构的重大变化，早期seral（杂草）草本植物的贡献不大，植物的丰度和丰富度在大多数治疗。对于许多森林林下群体，在丰富度或丰富度的下降显着大于在15%的保留。然而，模式的保留有令人惊讶的影响不大的治疗水平的反应，虽然森林聚集体内的变化很小，在邻近地区的收获下降一般大于相应的分散治疗。晚系列的草药特别敏感，这些影响，更频繁地从地块内的收获部分的聚集治疗比分散治疗的根除。收获后，林下植物丰富度和丰富度的地块间变化增加，但保留水平和模式对这种变化的幅度影响不大。我们怀疑，最初的森林林下植被的绿树保留的反应是中介，在很大程度上，由相关的模式的干扰和削减积累，保留的水平和模式显着不同。由于这些代表了短期响应，未来的采样将是必要的，以了解结构保留收获的更广泛的影响。我们预测，随着干扰的影响随着时间的推移而减少，冠层结构的影响将越来越多地塑造林下植物的组成和结构发展模式。
Timber harvest with 'green-tree' retention has been adopted in many tem- perate and boreal forest ecosystems, reflecting growing appreciation for the ecological values of managed forests. On federal forest lands in the Pacific Northwest, standards and guidelines for green-tree retention have been adopted, but systematic assessments of eco- system response have not been undertaken. We studied initial (1-2 yr) responses of vascular understory communities to green-tree retention at six locations (blocks) in western Oregon and Washington, using a factorial design with retention at contrasting levels (15% vs. 40% of initial basal area) and spatial patterns (trees dispersed vs. aggregated in 1-ha patches). Direction of compositional change (expressed in ordination space) was similar among treatments within each block, but the magnitude of change was consistently larger at 15% than at 40% retention; pattern of retention had little effect on compositional change. Despite major changes in vegetation structure, early-seral (ruderal) herbs contributed little to plant abundance and richness in most treatments. For many forest understory groups, declines in abundance or richness were significantly greater at 15% than at 40% retention. However, pattern of retention had surprisingly little effect on treatment-level response; although changes within forest aggregates were small, declines in adjacent areas of harvest were generally greater than those in corresponding dispersed treatments. Late-seral herbs were particularly sensitive to these effects, with more frequent extirpations from plots within the harvested portions of aggregated treatments than from dispersed treatments. Plot-to- plot variation in understory abundance and richness within treatments increased after har- vest, but level and pattern of retention had little effect on the magnitude of this change. We suspect that the initial responses of forest understories to green-tree retention are me- diated, in large part, by associated patterns of disturbance and slash accumulation that differ significantly with level and pattern of retention. Because these represent short-term re- sponses, future sampling will be necessary to understand the broader implications of struc- tural retention harvests. We predict that, as effects of disturbance diminish with time, effects of canopy structure will increasingly shape patterns of compositional and structural de- velopment in the understory.