Table Of Contents
- Comparison between semiarid systems in North and South America
- Regional analyses of the structure and function of grassland and shrubland ecosystems
- Collaboration between Hungarian and LTER scientists
Comparison between semiarid systems in North and South America:
During the last 15 years, the LTERCPER project has maintained a fruitful relationship with the Department of Ecology in the School of Agronomy, University of Buenos Aires. This relationship has grown in the last years through several projects of comparison between the shortgrass steppe ecosystem with the Patagonian steppe in South America. Currently, studies involve a comparison of grazing as an important driving force in the two systems. The shortgrass steppe has evolved under the impact of grazing, while the Patagonian steppe lacks a long evolutionary history of grazing. The consequence of this is that grazing has large impacts on plant communities in the Patagonian steppe. We studied the consequences of these vegetation changes for the Patagonian steppe ecosystem.
Grazing promotes changes in the plant functional type composition of the Patagonian steppe, grasses are replaced by shrubs. This modification promotes differences in the soil water dynamics, through changes in the seasonality of the water losses through transpiration. Evaporation was maximum in intermediate situations where neither grasses nor shrubs dominate the community. We evaluated the primary and secondary production along the grazing gradient. Overgrazed systems, dominated by shrubs, had less primary and secondary production than ungrazed ecosystems dominated by grasses. We also studied the changes that occur in the albedo and roughness, two key parameters for predicting the feedbacks of the ecosystem to the atmosphere.
References: Aguiar et al. in press
Regional analyses of the structure and function of grassland and shrubland ecosystems:We performed an analysis of the climatic patterns of the temperate zones in North and South America using a global database of monthly precipitation and temperature. Three synthetic variables, identified by a Principal Component Analysis of the monthly data, were used: mean annual precipitation, mean annual temperature and the proportion of the precipitation falling during summer. We displayed the spatial gradient of the three variables by constructing a composite color raster image. We used a parallepepid classification algorithm to locate areas in both continents that are climatically similar to five North American Long Term Ecological Research sites and to two South American long term ecological research sites. The same algorithm was used to identify areas in South America which are climatically similar to some of the major grassland and shrubland types of North America.
There is substantial overlap between the climates of North and South America. Most of the climatic patterns found in South America are well represented in North America. However, there are certain climates in North America that are not found in South America. An example is a climate with relatively low mean annual temperature and high summer precipitation. The climatic signatures of three North American LTER sites (Cedar Creek, CPER and Sevilleta) were not found in South America. The climatic signatures of two LTER sites (Konza and Jornada) had some representation in South America. Two South American research sites (Rio Mayo and Las Chilcas) were well represented climatically in North America. The climates of six out of seven selected North American grassland and shrubland types were represented in South America. The northern mixed prairie type was not represented climatically in South America. Our analysis suggests that comparisons of North and South America can provide a powerful test of climatic control over vegetation.
References:
Collaboration between Hungarian and LTER scientists:As part of a project funded by NSF International Programs to Diana Freckman and Debra Coffin, we are investigating areas of collaboration between Hungarian scientists and LTER scientists with a focus on longterm biodiversity research.
02/08/01