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.
As the extensive pastures in the newly deforested zones of the Amazon basin have begun to age, it appears that they have begun to change in ecologically significant ways. Trees have begun to repopulate some of these pastures, creating silvopastures. To investigate the ecological dimensions of these changes and the socio-economic forces that appear to drive them, we studied pastures and silvopastures on 100 small scale cattle ranches in the upper reaches of the Amazon basin in southeastern Ecuador. Trees do appear to be repopulating pastures in this region without reducing the stocking rates for cattle. The growing number of trees in pastures has increased above ground biomass and carbon without changing the below ground accumulation of carbon in significant ways. About 1 to 1.5 more tons of carbon accumulate each year in the tree populated pastures compared with the treeless pastures. At current prices (~$7 per ton) for carbon credits, the extra carbon sequestered would entitle landowners to ~$10 of payments per hectare per year for the sequestered carbon. In this respect the tree populated pastures represent a 'win - win' scenario, good for the landowners and good for the environment. The emergence of these silvopastoral landscapes stems from deliberate management choices by farmers. They allow spontaneously germinated seedlings of commercially valuable tree species to grow in their fields. These management strategies are likely to be pursued by owner-operaters of small cattle ranches. The owners of these pastures welcome the emergence of the trees because the trees provide shade for cattle, protect watercourses, and become a source of income as lumber after the trees reach 15 years of age. These spontaneously generated silvopastoral landscapes do not emerge on rented lands, in part because renters who pasture their catttle on these fields do not profit from the emergence of the trees. Because Amerindians are much more likely to rent their land to others (usually mestizos), their pastures contained fewer sprouting trees than did the pastures of mestizos. In summary, this research shows that the environmental services provided by emerging silvopastoral landscapes in the tropics are sufficiently large that the owners of these lands could be compensated through the '+' portion of a REDD liek program of payments for environmental services. These payments could accelerate the emergence of silvopastoral landscapes in the Amazon basin and elsewhere.
