Buttressing a Biosphere Buffer Zone

Trees increase landscape complexity and may conserve biodiversity

by Suzanna Engman

The people of the ejido in Chiapas, Mexico call her “La Güerita.” To them she is the blonde girl from Puerto Rico who comes to study their land and live with them intermittently. The ejido, or communally owned property, of the Los Ángeles community is part of the La Sepultura Biosphere Reserve. “La Güerita” is Colibrí Sanfiorenzo-Barnhard, a biology graduate student at the University of Puerto Rico, Río Piedras Campus. Sanfiorenzo-Barnhard’s research will contribute to the knowledge base of agroforestry and silvopastoral systems as well as help develop a participatory silvopastoral research project for the people of Los Ángeles. Her research focuses on integrating trees into agricultural and cattle lands. Previous studies suggest that trees enhance biodiversity by providing suitable habitat for organisms, one goal of biosphere reserves.

Sanfiorenzo-Barnhard began her research in Mexico as a URP, RP undergraduate after she was awarded the Strategies for Ecology, Education, Development and Sustainability (SEEDS) fellowship for independent research. She conducted a preliminary exploratory analysis of the ejido vegetation and found patches of homogeneous areas dominated by oak species and heterogeneous areas dominated by deciduous species. “In the heterogeneous landscape I found a higher density of tree recruitment. So my preliminary work suggests that higher heterogeneity in the landscape could contribute to higher natural tree recruitment.”

A biosphere reserve is comprised of a core area that harbors high biodiversity and a buffer zone, intended to diminish anthropogenic impact on the core area. Core areas are protected from logging, hunting, cattle grazing, and agriculture. But in the buffer zone, points out Sanfiorenzo-Barnhard, these activities are permitted, with some restrictions. “Anthropogenic activities,”whe explains, “tend to encroach on the core area of the reserve. The landscape is an inter-related dynamic system. Agricultural matrices should behave as agro-ecological matrices that are permeable to organisms. The agricultural matrices need to become more similar to what you find in the core area, and one way to do this is to increase spatial heterogeneity in the landscape.”

Spatial heterogeneity can be increased by the presence of trees in agricultural fields and cattle pastures. Sanfiorenzo-Barnhard’s graduate research will investigate whether natural tree recruitment is associated with the vegetation structure and composition of the Los Angeles ejido rangelands. Studies suggest that spatial heterogeneity of the landscape could promote natural tree establishment by creating, among other things, favorable microclimate conditions.

Sanfiorenzo-Barnhard explains that live fences are important. “They would add to the heterogeneity of the rangelands. Instead of using just a piece of wood with barbed wire for a fence, you would have a row of trees. A number of studies say that live fences increase certain biodiversity, such as birds, because they use the live fences as perches and migration corridors. In addition, certain live fences can be used as food for cattle while keeping the farm animals inside the tree line. Live fences serve multiple purposes: they create a fence, produce food for the cattle, and last much longer than conventional ‘dead’ fences.”

The methodology for Sanfiorenzo-Barnhard’s research is still being developed but will require both high-tech laboratory work and rigorous field work. She will analyze the vegetation on the scale of both a patch and landscape. At the patch scale she will establish plots to measure structure, for example, foliage layers, percentage of canopy cover, and plant height, as well as flora composition. She will also measure soil fertility and slope. “The hardest things to identify are saplings. You can’t take them out. You have to identify them on site,” she says. Using IKONOS pictures, which are satellite images of high resolution that can be read to about four meters, she will construct a vegetation map for the area. “To create my vegetation map I will need to have at least two hundred points, one hundred to create the map and one hundred to corroborate the vegetation map.”

Sanfiorenzo-Barnhard’s results will be used in a larger project led by Luis García-Barrios, a professor at El Colegio de la Frontera Sur (ECOSUR). The Mexican university, based in San Cristobel de las Casas, is gathering data for a participatory silvopastoral research project in the Los Ángeles ejido.