Collaborative Research: Vulnerability of Semi-arid Grasslands to Encroachment by Woody Plants: the Role of Grass Invasions, Seasonal Precipitation, and Soil Type

在过去的100年里，美国西南部的许多草原在不经意间变成了茂密的木本植物灌木丛，包括多刺的灌木麦斯奎特。这些转变对人类活动、生物多样性、养分循环和野火制度产生了重要影响。然而，许多以梅斯奎特为主的草原最近本身就受到了一种非洲草--莱曼牧草的入侵。这种草的入侵可能会改变土壤中水分和养分的可获得性，从而将梅斯奎特灌丛重新转向草原。然而，这些草原将由一种非原生草主导，其对生态系统的影响可以说比梅斯奎特对以前草原的影响更大。在预测西南牧场如何应对草本植物和木本植物的入侵时，还必须考虑土壤特性(例如粘粒含量)和潜在的气候变化(例如降雨量变化)如何影响草本植物和灌木的相对表现和最终比例。通过在亚利桑那州南部进行野外实验，研究人员将检验这样一个假设，即草的入侵将与土壤类型和季节性降水相互作用，影响在该栖息地成功建立麦斯奎特。将麦斯奎特作为种子引入试验田的反应将被用来衡量该物种对不同环境的潜在反应。同时对这些地块内二氧化碳和水的循环和储存进行研究，将有助于我们理解水、土壤类型和植被之间的相互作用。这项研究明确考虑了气候变化和生物入侵，每一种入侵都将继续影响自然生态系统及其为人类社会提供的商品和服务。研究将促进科学家、土地管理人员和几个机构的学生之间的合作，并将促进土壤科学、建模、生态学和大气科学等子学科的交叉。该项目包括为学生提供培训机会，包括那些参加教师培训计划的学生和代表人数不足的群体。

Within the last 100 years, many grasslands throughout the southwestern United States have been inadvertently converted to dense thickets of woody plants, including the thorny shrub mesquite. These conversions have had important impacts on human activities, biological diversity, nutrient cycling, and wildfire regimes. However, many mesquite-dominated grasslands have themselves been recently invaded by an African grass, Lehmann lovegrass. Invasions by this grass may change the availability of water and nutrients in the soil, and thus shift mesquite shrublands back towards grassland. However, these grasslands would be dominated by a non-native grass with arguably greater impacts on ecological systems than mesquite has had on former grasslands. When predicting how southwestern rangelands might respond to invasions by grasses and woody plants, one must also consider how soil characteristics (e.g., clay content) and potential changes in climate (e.g., changes in precipitation) affect the relative performance, and the ultimate ratio, of grasses to shrubs. By conducting a field experiment in southern Arizona, the investigators will test the hypothesis that grass invasions will interact with soil type and seasonal precipitation to affect the successful establishment of mesquite in this habitat. The response of mesquite introduced as seeds into experimental plots will be used to gauge the potential response of this species to different environments. Concurrent investigations of the cycling and storage of carbon dioxide and water within these plots will facilitate our understanding of interactions between water, soil type, and plant cover. This research explicitly considers both climate change and biological invasions, each of which will continue to affect natural ecological systems and the goods and services that they provide to human society. Research will foster collaborations between scientists, land managers, and students from several institutions, and will promote interdigitation of subdisciplines including soil science, modeling, ecology and atmospheric sciences. The project includes training opportunities for students, including those in teacher training programs and in underrepresented groups.