Friday, August 7, 2009

PS 83-88: Mapping ecosystem services within a Mexican watershed

Maria Jose Martinez and Patricia Balvanera. Universidad Nacional Autónoma de México


The current rate of transformation of ecosystems and its consequences on the provision of benefits or Ecosystem Services (ES) make necessary the need for information on the quantification of their provision and identifying areas with the most capacity to provide ES. The main goal of this study is to develop a method to locally measure four ES (forage, timber, firewood and carbon storage) provided by plant diversity and to explore which biophysical variables can predict the services at larger scales in order to map ES provision for a whole watershed. The study was undertaken in the Cuitzmala watershed (1082 km2), located in the pacific coast of Mexico. To quantify the ES contrasting study sites with respect to their environmental and management conditions were selected. Local provision of services was estimated through structural data of the tree community and aboveground biomass measurements for the herbaceous community within 20X20m plots. These values were used as response variables in multiple regression models employing biophysical data obtained from geographical information systems (elevation, slope, aspect, radiation and distances to streams, roads and towns) as well as from remote sensed data (normalized vegetation index and normalized infrared index for wet and dry season, and a canopy closure index) as independent variables.


The most explicative model for forage (r²=70%) was explained mainly for the canopy closure index, slope, elevation and distance to stream variables. The best model for timber (r²=50%) was explained for the canopy closure, normalized vegetation index for the wet season, normalized infrared index for the dry season, distance to road, to towns and to streams.  The model for the firewood (r²=62%) was explained for canopy closure, normalized vegetation index for both seasons, normalized infrared index for the dry season and slope.  The best model for the carbon storage (r²=65%), was explained for the canopy closure, normalized vegetation indexes for both seasons, slope and distance to stream. These models were used to extrapolate the ES values to the watershed and finally map the services. The resulting forage map showed a higher provision in the middle part of the watershed, while the timber, firewood and carbon storage maps showed higher values in the lower and upper parts of the watershed. These maps can be used jointly with biodiversity maps to establish conservation priorities in the watershed.