Collaborative Research: The Sustainability of Riparian Forests in Expanding Amazonian Agricultural Landscapes

亚马逊森林的大面积植被转变为集约化作物生产是塑造地球的主要力量之一。河流沿岸的河岸森林缓冲层可以通过拦截营养物质、提供遮荫以降低温度和保护河道，减少森林砍伐对河流水质和河流栖息地的潜在负面影响。该项目调查了森林砍伐、农田扩张和集约化以及化肥使用增加如何影响河岸森林的结构和可持续性，并最终影响其阻止养分径流进入河流的能力。研究将在亚马逊河流域的马托格罗索州进行，这里是巴西全球森林砍伐的热点地区，在过去20年里，大豆种植迅速扩大。该地区的生产者现在正从单季大豆转向双季大豆和玉米，这大大增加了肥料投入。该项目解决了如何在热带地区保护和维持水质和水生资源这一具有全球重要性的问题，在热带地区，森林砍伐和农田迅速扩张日益普遍。通过提高对河岸森林变化的轨迹和原因的认识，并预测氮在河岸带的运动，这些结果将为管理热带农业集约化的负面影响提供依据。项目组将通过举办两次关于河岸森林管理和保护的科学基础的研讨会，向巴西和美国的决策者和农民传达研究结果。该项目将调查农田中的河岸森林碎片是否长期保持其植被结构，以及这种结构如何受到农田典型的流域水文和小气候变化的影响。研究人员将确定农田溪流附近的河岸森林是否会拦截并清除流域中的氮，以及这种氮清除功能是否足以防止过量的氮进入高肥料投入的农田流域的溪流。该项目将量化农田河岸森林结构的变化如何改变河流温度、新陈代谢、养分吸收和下游养分输出。这将通过比较完整的热带森林、纯大豆农田和大豆玉米农田内复制流域的河岸森林来实现。本研究的重点是以下三个假设：(1)农田流域的河岸林比森林流域的高地林或河岸林具有更高的树木死亡率、更低的树木生长和更开阔的树冠。(2)与森林流域相比，农田流域的蒸散量更低，径流和养分输出更大，地下水位更高，河流侧坡更湿润，但河岸带的反硝化作用不足以阻止过量的氮进入双季流域的河流。(3)农田滨水林冠层越开阔，河流温度和代谢水平越高。该项目将为理解森林砍伐、农田扩张和农业集约化如何影响热带河岸森林和溪流创造一个新的概念框架。

The conversion of large areas of Amazon forest vegetation for intensive crop production is one of the major forces shaping the Earth. Riparian forest buffers along streams can reduce the potential negative effects of forest clearing on stream water quality and stream habitat by intercepting nutrients, providing shade to reduce temperature and protecting stream channels. This project investigates how deforestation, cropland expansion and intensification, and increased fertilizer use influence the structure and sustainability of riparian forests, and ultimately affect their capacity to keep nutrient runoff from reaching streams. Research will take place in the Amazon state of Mato Grosso, Brazil's global hotspot of deforestation where soybean cultivation has expanded rapidly in the last two decades. Producers in the region are now shifting from single-cropped soybeans to double-cropped soybeans and corn, which greatly increases fertilizer inputs. This project addresses the globally important issue of how to protect and sustain water quality and aquatic resources in tropical regions, where high deforestation and rapid cropland expansion are increasingly common. By improving understanding of the trajectories and causes of riparian forest change and predicting the movement of nitrogen through riparian zones, these results will provide a basis for managing the negative impacts of tropical agricultural intensification. The project team will convey findings to policymakers and farmers in Brazil and the US by conducting two workshops on the scientific basis for riparian forest management and conservation. This project will investigate whether riparian forest fragments in cropland maintain their vegetation structure over time and how that structure is influenced by alterations to watershed hydrology and microclimate that are typical of cropland areas. Investigators will determine whether riparian forests bordering streams in croplands intercept and remove nitrogen from watersheds and whether this nitrogen removal function is sufficient to prevent excess nitrogen from reaching streams in cropland watersheds with high fertilizer inputs. The project will quantify how changes to riparian forest structure in croplands alter stream temperature, metabolism, nutrient uptake and downstream nutrient export. This will be accomplished by comparing riparian forests in replicated watersheds within intact tropical forest, soybean-only cropland and soybean-corn cropland. The project focuses on the following three hypotheses: (1) Riparian forests in cropland watersheds have higher tree mortality, lower tree growth and a more open canopy than either upland forests or riparian forests in forested watersheds. (2) Cropland watersheds have lower evapotranspiration, greater runoff and nutrient export, higher water tables, and wetter stream side slopes than forest watersheds but denitrification in riparian zones is insufficient to prevent excess nitrogen from reaching streams in double-cropped watersheds. (3) More open canopies in cropland riparian forest will increase stream temperature and metabolism. This project will create a new conceptual framework for understanding how deforestation, cropland expansion, and agricultural intensification influence tropical riparian forests and streams.