Wood Loading in Headwater Neotropical Forest Streams

在温带地区的研究充分表明，木材对许多河流的地貌和生态过程具有重要影响。然而，人们对低纬度河流中木材的丰度或功能知之甚少，这些河流可能有广泛的森林覆盖。考虑到热带和温带河流之间已知的生态差异，简单地推断从温带河流到热带河流的木材生态动力学知识是不合适的，但基本上没有关于热带河流中木材负荷、停留时间或地貌功能的数据，从这些数据推断木材在这些系统中的生态影响。了解木材在热带河流中的作用的第一步是盘点不同热带地区和不同河流类型的木材负荷和停留时间。因此，拟议研究的主要目标是表征(i)木材负荷，（ii）与潜在控制变量相关的空间分布，以及（iii）木材在新热带水源排水网络中的停留时间。这样的基础研究将为研究热带溪流中木材的地貌和生态功能提供基础。实地研究将集中在1至4阶流通道。选定的场地位于哥斯达黎加的La Selva生物站和Braulio Carrillo国家公园，提供了一个从山地地形的高海拔一级排水的梯度，通过中等梯度的溪流和山坡过渡到加勒比海沿海平原。现场正在进行的数据收集提供了有关气候、水文和森林动态的信息，并建立了住宿的基础设施和通往溪流的小径网络。在现场工作的溪流生态学家的观察表明，至少在排水网络的某些部分存在大量的木材和碎片水坝。研究目标将通过围绕两个阶段组织的实地工作来解决；(1)绘制木材分布和河流特征图；(2)通过重复访问和间隔摄影，在选定的地图站点子集监测木材动态。研究还旨在检验关于木材引入渠道的不同过程的相对重要性以及在渠道网络的不同部分控制木材保留的过程的假设。该项目将持续三年，并将为一名博士候选人和至少两名本科生提供支持和培训。本研究首次对热带河流中木材的空间分布、木材负荷和停留时间进行了系统的研究，为理解热带河流的地貌和生态过程以及制定热带河流的管理指南提供了至关重要的基础。更广泛的影响：更广泛的影响包括五个组成部分：(1)首次提供了新热带水源排水中木材分布的空间格局以及木材保留率和过程的文件；(2)建立热带河流木材的基线知识，可用于制定管理准则，以尽量减少森林砍伐的影响；(3)培养研究生和本科生；(4)与溪流生态学家和热带研究站的其他工作人员建立跨学科的研究合作关系；(5)通过网站以及更传统的学科渠道传播研究成果。

Research in temperate regions has amply demonstrated that wood exerts a critical influence on geomorphic and ecological processes in many streams. However, very little is known of the abundance or function of wood in low-latitude streams, which are likely to have extensive forest cover. Given the known ecological differences between streams in tropical and temperate regions, it is inappropriate to simply extrapolate knowledge of the ecological dynamics of wood from temperate to tropical streams, yet there are essentially no data on wood loading, residence time, or geomorphic function of wood in tropical streams from which to infer the ecological influences of wood in these systems. The first step in understanding the function of wood in tropical streams is to inventory wood loading and residence time for different tropical regions and different stream types. Thus, the primary objectives of the proposed research are to characterize (i) wood loading, (ii) spatial distribution in relation to potential control variables, and (iii) residence time of wood across a neotropical headwater drainage network. Such fundamental research will then provide the basis for studies of the geomorphic and ecological functions of wood in tropical streams.Field research will focus on 1st to 4th order stream channels. The selected field site at La Selva Biological Station and Braulio Carrillo National Park in Costa Rica provides a gradient from high-elevation first-order drainages in mountainous terrain through moderate gradient streams and hillslopes that transition to the Caribbean coastal plain. Ongoing data collection at the site provides information on climate, hydrology, and forest dynamics, and an infrastructure of lodging and trail networks exists for accessing streams. Observations by stream ecologists working at the site indicate the presence of abundant wood and debris dams in at least some portions of the drainage network. The research objectives will be addressed with field work organized around two phases; (1) mapping wood distribution and stream characteristics, and (2) monitoring wood dynamics at a selected subset of mapped sites with repeat visits and interval photography. Research is also designed to test hypotheses regarding the relative importance of different processes of wood introduction to channels and the processes controlling wood retention within different portions of the channel network. The project will extend over three years, and will provide support and training for a PhD candidate, and at least two undergraduate students.Intellectual Merit: The research proposed here represents the first systematic investigation of spatial distribution, wood loading, and residence time of wood in tropical rivers, and as such will provide a critically important foundation for understanding geomorphic and ecological processes in tropical streams, as well as for setting management guidelines in these streams.Broader Impacts: Broader impacts include five components: (1) providing the first documentation of spatial patterns of wood distribution in neotropical headwater drainages and rates and processes of wood retention; (2) creating baseline knowledge of wood in tropical streams that can be used to develop management guidelines for minimizing the impacts of deforestation; (3) training graduate and undergraduate students; (4) establishing interdisciplinary research collaborations with stream ecologists and others working at the tropical research stations where field work will take place; and (5) disseminating the research results through a website, as well as through more traditional disciplinary outlets.