Department of Biosystems, "Luiz de Queiroz" College of Agriculture, University of São Paulo, Piracicaba, SP, Brazil.
Environ Manage. 2011 Oct;48(4):750-63. doi: 10.1007/s00267-011-9730-4. Epub 2011 Aug 7.
Riparian forests are important for the structure and functioning of stream ecosystems, providing structural components such as large woody debris (LWD). Changes in these forests will cause modifications in the LWD input to streams, affecting their structure. In order to assess the influence of riparian forests changes in LWD supply, 15 catchments (third and fourth order) with riparian forests at different conservation levels were selected for sampling. In each catchment we quantified the abundance, volume and diameter of LWD in stream channels; the number, area and volume of pools formed by LWD and basal area and tree diameter of riparian forest. We found that riparian forests were at a secondary successional stage with predominantly young trees (diameter at breast height <10 cm) in all studied streams. Results showed that basal area and diameter of riparian forest differed between the stream groups (forested and non-forested), but tree density did not differ between groups. Differences were also observed in LWD abundance, volume, frequency of LWD pools with subunits and area and volume of LWD pools. LWD diameter, LWD that form pools diameter and frequency of LWD pools without subunits did not differ between stream groups. Regression analyses showed that LWD abundance and volume, and frequency of LWD pools (with and without subunits) were positively related with the proportion of riparian forest. LWD diameter was not correlated to riparian tree diameter. The frequency of LWD pools was correlated to the abundance and volume of LWD, but characteristics of these pools (area and volume) were not correlated to the diameter of LWD that formed the pools. These results show that alterations in riparian forest cause modifications in the LWD abundance and volume in the stream channel, affecting mainly the structural complexity of these ecosystems (reduction in the number and structural characteristics of LWD pools). Our results also demonstrate that riparian forest conservation actions must consider not only its extension, but also successional stage to guarantee the quantity and quality of LWD necessary to enable the structuring of stream channels.
河岸林对于溪流生态系统的结构和功能非常重要，为溪流提供了大型木质残体（LWD）等结构组成部分。这些森林的变化会导致流入溪流的 LWD 输入发生变化，从而影响其结构。为了评估河岸林变化对 LWD 供应的影响，选择了 15 个具有不同保护水平的河岸林的流域（第三和第四级）进行采样。在每个流域中，我们量化了溪流中 LWD 的丰度、体积和直径；由 LWD 形成的池的数量、面积和体积；以及河岸林的基面积和树木直径。我们发现，所有研究溪流中的河岸林都处于次生演替阶段，主要是胸径小于 10cm 的幼树。结果表明，河岸林的基面积和直径在溪流群（有林和无林）之间存在差异，但树木密度在群间没有差异。LWD 的丰度、体积、有亚单位的 LWD 池的频率以及 LWD 池的面积和体积也存在差异。LWD 直径、形成池的 LWD 直径以及无亚单位的 LWD 池的频率在溪流群之间没有差异。回归分析表明，LWD 的丰度和体积以及有和无亚单位的 LWD 池的频率与河岸林的比例呈正相关。LWD 直径与河岸林树木直径不相关。LWD 池的频率与 LWD 的丰度和体积相关，但这些池的特征（面积和体积）与形成池的 LWD 直径不相关。这些结果表明，河岸林的变化会导致溪流中 LWD 的丰度和体积发生变化，主要影响这些生态系统的结构复杂性（减少 LWD 池的数量和结构特征）。我们的结果还表明，河岸林保护措施不仅要考虑其延伸范围，还要考虑演替阶段，以保证必要的 LWD 数量和质量，从而实现溪流的结构构建。
