Evaluating the Impact of Abrupt Changes in Forest Policy and Management Practices on Landscape Dynamics: Analysis of a Landsat Image Time Series in the Atlantic Northern Forest
Evaluating the Impact of Abrupt Changes in Forest Policy and Management Practices on Landscape Dynamics: Analysis of a Landsat Image Time Series in the Atlantic Northern Forest
复制标题
评估森林政策和管理实践突然变化对景观动态的影响：大西洋北部森林陆地卫星图像时间序列分析
作者：
Kasey Legaard;S. Sader;Erin Simons
可持续森林管理的基础是管理行动、景观条件和森林价值之间的功能关系。管理实践的变化从根本上使研究这些关系变得更加困难，因为当前实践的影响很难与过去实践的持续影响分开。在美国缅因州的大西洋北方森林中，森林政策和管理做法在1990年代初突然改变。在20世纪70年代至80年代，一场严重的昆虫爆发刺激了对大片云冷杉森林的抢救性皆伐。在1991年明确规定之后，管理做法突然转变为几乎完全依赖部分采伐。利用Landsat卫星图像的时间序列（1973-2010年），我们评估了这些非常不同的管理制度造成的累积景观变化。我们建模的主要时间模式的收获和分割一个大的研究区域成组的景观单元具有类似的收获历史。时间序列的景观组成和配置指标平均组内显示的差异，在管理历史的差异所造成的景观动态。在某些组（24%的景观单位），抢救造成快速损失和细分的完整成熟的森林。大面积抢救性皆伐（通常平均超过100公顷）和云冷杉林转变为落叶林和混交林造成了持续的景观变化。在组的影响不大抢救（56%的景观单位），当代部分采伐造成损失和细分的完整成熟的森林，甚至更大的速度。斑块形状的复杂性和边缘密度达到较高的水平，即使累积收获面积相对较低。当代的做法引入了更多和更小的林分替代干扰斑块（通常平均<15公顷）和相应的大量边缘。管理制度对不同地区产生不同程度的影响，产生不同的地貌变化轨迹，在研究政策和管理做法对森林生态的影响时应认识到这一点。
Sustainable forest management is based on functional relationships between management actions, landscape conditions, and forest values. Changes in management practices make it fundamentally more difficult to study these relationships because the impacts of current practices are difficult to disentangle from the persistent influences of past practices. Within the Atlantic Northern Forest of Maine, U.S.A., forest policy and management practices changed abruptly in the early 1990s. During the 1970s-1980s, a severe insect outbreak stimulated salvage clearcutting of large contiguous tracts of spruce-fir forest. Following clearcut regulation in 1991, management practices shifted abruptly to near complete dependence on partial harvesting. Using a time series of Landsat satellite imagery (1973-2010) we assessed cumulative landscape change caused by these very different management regimes. We modeled predominant temporal patterns of harvesting and segmented a large study area into groups of landscape units with similar harvest histories. Time series of landscape composition and configuration metrics averaged within groups revealed differences in landscape dynamics caused by differences in management history. In some groups (24% of landscape units), salvage caused rapid loss and subdivision of intact mature forest. Persistent landscape change was created by large salvage clearcuts (often averaging > 100 ha) and conversion of spruce-fir to deciduous and mixed forest. In groups that were little affected by salvage (56% of landscape units), contemporary partial harvesting caused loss and subdivision of intact mature forest at even greater rates. Patch shape complexity and edge density reached high levels even where cumulative harvest area was relatively low. Contemporary practices introduced more numerous and much smaller patches of stand-replacing disturbance (typically averaging <15 ha) and a correspondingly large amount of edge. Management regimes impacted different areas to different degrees, producing different trajectories of landscape change that should be recognized when studying the impact of policy and management practices on forest ecology.