Washington State Department of Natural Resources, Forest Resources Division, 1111 Washington Street SE, Olympia, WA, 98504-7014, USA.
U.S. Department of Agriculture Forest Service, PNW Research Station, Forestry Sciences Laboratory, 3625 93rd Avenue SW, Olympia, WA, 98512-9193, USA.
Environ Manage. 2019 May;63(5):673-690. doi: 10.1007/s00267-019-01146-x. Epub 2019 Feb 18.
Many of the ecological processes in the riparian forests and streams across the Pacific Northwest have become impaired through production forestry practices common prior to the 1990s. Some of these practices included forest harvest without stream buffers, removal of instream wood, road construction and use, and harvesting large proportions of watersheds. Passive ecological restoration (the use of natural processes of succession and disturbance to alleviate anthropogenic impacts over time) is a common practice used in the management of riparian forests previously subjected to production forestry. Eighteen years after the implementation of passive restoration of riparian forests, we used four common stream indicators (stream temperature, canopy closure, instream wood, and salmonid densities) to assess the effects of restoration in small fish-bearing streams. Summer stream temperatures have decreased below unmanaged reference levels, whereas riparian forest canopy closure has increased beyond that in reference watersheds. Instream wood and age-1 or older salmonids appear to be either stable at reduced levels or declining, compared with production forestry and unmanaged reference watersheds. Overall, second-growth riparian forests need more time to develop allowing more light into streams (increasing primary productivity), while also allowing for the continuous recruitment of larger pieces of instream wood (improving habitat for salmonids). Using only passive restoration, stream conditions in second-growth forests are unlikely to increase salmonid production in the near future.
在 20 世纪 90 年代之前，太平洋西北地区的河岸森林和溪流中的许多生态过程都因常见的林业生产实践而受到损害。其中一些做法包括在没有溪流缓冲区的情况下进行森林采伐、清除溪流中的木材、道路建设和使用，以及采伐大部分流域。被动生态恢复（利用自然演替和干扰过程来缓解人为影响）是以前进行生产性林业管理的河岸森林管理中常用的做法。在实施河岸森林被动恢复 18 年后，我们使用了四个常见的溪流指标（溪流温度、林冠覆盖率、溪流内木材和鲑鱼密度）来评估恢复对小鱼溪流的影响。夏季溪流温度已降至未管理的参考水平以下，而河岸林冠覆盖率已超过参考流域。与生产性林业和未管理的参考流域相比，溪流内的木材和 1 龄或以上的鲑鱼似乎要么稳定在较低水平，要么下降。总体而言，次生河岸林需要更多的时间来发展，以便更多的光线进入溪流（增加初级生产力），同时也允许更多较大的溪流内木材不断补充（改善鲑鱼的栖息地）。仅采用被动恢复，在不久的将来，次生林的溪流状况不太可能增加鲑鱼的产量。
