CNH: Spontaneous Silviopastoral Landscapes: Origins, Extent, and Ecological Significance in the Ecuadorian Amazon

随着全球热带森林面积的持续减少，农业景观现在覆盖了大约50%的热带生物群系。了解和影响热带生物多样性的能力在很大程度上取决于对积极管理的景观的基本了解。由于牧场覆盖了中美洲和南美洲新热带地区的大部分农业用地，因此其生物多样性的重大变化，如更多树木的出现，代表了一个潜在的重要发展。在过去的二十年里，厄瓜多尔亚马逊盆地牧场上的树木数量似乎有所增加。这些森林景观是自发形成的，没有人为的努力。这个跨学科的研究项目将调查这种变化与生态和人类的关系。靠近森林遗迹、土壤质量和物种特征对树木在牧场的传播起着重要作用，管理措施似乎也很重要。通过对不同树木数量的牧场的深入研究，研究种子雨、土壤肥力、树种和觅食如何影响树木在牧场的传播，以及随着树木数量的增加，生物多样性、碳储量和生物地球化学循环如何变化。通过与牧场所有者的访谈，调查人员将评估这样一种假设，即意图实现经济多样化的小农容忍牧场中有更多的树木，因为他们没有劳动力来做其他事情。小农并不是因为养牛的收入太重要而不能放弃养牛，而是因为他们现在有了非农业的追求，他们没有时间像全职养牛时那样彻底地“清理”牧场上的幼苗。由于中年男性离开家到其他地方工作，女性户主现在管理着更多的牧场，她们以一种尖锐的方式面临着这些困境。由于没有男性居民或土地的完全所有权，妇女担心土地被入侵，因此她们通过在土地上放牧来保持“存在”。与此同时，为了维持生计，妇女们一边照顾孩子，一边在家做针线活，因此她们没有时间清理牧场上的幼苗。一旦建立起来，树木就会创造微环境，让其他树木发芽。调查人员将根据厄瓜多尔亚马逊地区90个牧场的生态调查、对农民的采访、航空照片和卫星图像来评估这些假设。利用来自这些来源的数据和信息，他们将建立一个模型，其中社会和生态变化产生自发的森林景观。在新热带地区的一大片原森林地区出现了一条通往森林景观的自然路径。这种“自然”历史可能对促进森林景观的长期但相对不成功的努力具有重要意义。在政治家们考虑将支付环境服务费用作为更大的国际热带森林碳封存努力的一部分的背景下，概述小农如何在阴凉的牧场中封存碳的研究可以展示如何加速这种景观变化并使贫困农民受益。本项目由美国国家科学基金会自然与人类系统耦合动力学（CNH）计划和美国国家科学基金会国际科学与工程办公室支持。

With the continuing decline in the global extent of tropical forests, agricultural landscapes now cover roughly 50 percent of the tropical biome. Capabilities to understand and influence tropical biodiversity depend in large part on basic understanding of actively managed landscapes. Because pastures cover most agricultural lands in the neotropics of Central and South America, significant changes in their biodiversity, such as the emergence of more trees, represent a potentially important development. The numbers of trees in pastures in the Ecuadorian Amazon basin appear to have increased during the past two decades. These silvopastoral landscapes have emerged spontaneously, without efforts by people to create them. This interdisciplinary research project will investigate the ecological and human correlates of this change. Proximity to forest remnants, soil quality, and species characteristics play important roles in the spread of trees in pastures, with management practices also appearing to be important. Through intensive study of pastures with variable numbers of trees, the investigators will examine how seed rain, soil fertility, tree species, and foraging influence the spread of trees in pastures as well as how biodiversity, carbon storage, and biogeochemical cycling change with more trees in pastures. Through interviews with owners of the pastures, the investigators will assess the hypothesis that small farmers intent on economic diversification tolerate more trees in pastures because they do not have the labor to do otherwise. Small farmers do not abandon cattle ranching because income from cattle is too important to forego, but because they now have non-farm pursuits, they do not have time to "clean" pastures of seedlings as thoroughly as they did when they worked full time with cattle. Because middle-aged men have left home to work elsewhere, female household heads now manage more pastures, and they face these dilemmas in an acute way. Without resident males or full titles to land, women worry about land invasions, so they maintain a "presence" on the land by grazing cattle on it. At the same time, women combine child care with needlework at home to earn a livelihood, so they do not have time to clean pastures of seedlings. Once established, the trees create micro-environments that allow other trees to sprout. The investigators will evaluate these hypotheses with evidence from ecological inventories of pastures, interviews with farmers, aerial photos, and satellite images of 90 cattle ranches in the Ecuadorian Amazon. Using data and information from these sources, they will build a model in which social and ecological changes generate spontaneous silvopastoral landscapes.A spontaneous path to silvopastoral landscapes has emerged in a large, formerly forested area of the neotropics. This "natural" history may have important implications for the long-standing but relatively unsuccessful efforts to promote silvopastoral landscapes. In a context in which politicians consider paying for environmental services as part of a larger, international effort to sequester carbon in tropical forests, research that outlines how small farmers are sequestering carbon in shaded pastures can demonstrate how to expedite this landscape change and benefit poor farmers. This project is supported by the NSF Dynamics of Coupled Natural and Human Systems (CNH) Program and by the NSF Office of International Science and Engineering.