José M. Paruelo

The value of the world's ecosystem services and natural capital

This article provides a crude initial estimate of the value of ecosystem services to the economy. Using data from previous published studies and a few original calculations the current economic value of 17 ecosystem services for 16 biomes was estimated. The services of ecological systems and the natural capital stocks that produce them are critical to the functioning of the Earths life-support system. They contribute to human welfare both directly and indirectly and therefore represent part of the total economic value of the planet. It was estimated that for the entire biosphere the value (most of which is outside the market) ranges US

Relative Abundance of Plant Functional Types in Grasslands and Shrublands of North America

16-54 trillion/year with an average of US

Grassland Precipitation-Use Efficiency Varies Across a Resource Gradient

33 trillion/year. Due to the nature of uncertainties this must be considered a minimum estimate. In addition the global gross national product total is around US

PATTERNS AND CONTROLS OF PRIMARY PRODUCTION IN THE PATAGONIAN STEPPE: A REMOTE SENSING APPROACH

18 trillion/year.

The value of ecosystem services: putting the issues in perspective

We analyzed the geographic distribution and climatic controls of the distri- bution of plant functional types (PFT) in temperate grasslands and shrublands of North America. It has been widely accepted that temperature is the principal control on the distribution of C3 and C4 species. Our results show that precipitation and its seasonal distribution are also important. C4 grass distribution was positively related to three climatic variables: mean annual precipitation, mean annual temperature, and the proportion of the precipitation falling in summer. These variables accounted for 66% of the total variability of this functional type. C3 grass abundance decreased with mean annual temperature and increased with the proportion of the precipitation falling during winter (r2 = 0.37). Sixty- two percent of the variability in the relative abundance of shrubs was explained by mean annual precipitation and the proportion of winter precipitation. Latitude and longitude explained a substantial portion of the variability of the distri- bution of the relative abundance of shrubs, C3 grasses, and C4 grasses (53, 46, and 61%, respectively). Along a given longitude, C3 grasses increased with latitude. As one moves westward, C4 grasses are replaced by shrubs. The relative abundance of C4 grasses reached a maximum at southern latitudes and eastern longitudes. Succulents showed a marginal decreasing trend with latitude. No relationship with geographic variables was detected for forbs.

Pathways of Grazing Effects on Soil Organic Carbon and Nitrogen

ABSTRACT Aboveground net primary production (ANPP) is positively related to mean annual precipitation, an estimate of water availability. This relationship is fundamental to our understanding and management of grassland ecosystems. However, the slope of the relationship between ANPP and precipitation (precipitation-use efficiency, PUE) has been shown to be different for temporal compared with spatial precipitation series. When ANPP and precipitation are averaged over a number of years for different sites, PUE is similar for grasslands all over the world. Studies for two US Long Term Ecological Research Sites have shown that PUE derived from a long-term dataset (temporal model) has a significantly lower slope than the value derived for sites distributed across the US central grassland region (spatial model). PUE differences between the temporal model and the spatial model may be associated with both vegetational and biogeochemical constraints. Here we use two independent datasets, one derived from field estimates of ANPP and the other from remote sensing, to show that the PUE is low at both the dry end and the wet end of the annual precipitation gradient typical of grassland areas (200–1200 mm), and peaks around 475 mm. The intermediate peak may be related to relatively low levels of both vegetational and biogeochemical constraints at this level of resource availability.

Land cover classification in the Argentine Pampas using multi-temporal Landsat TM data

We took advantage of regional gradients to study the spatial relationships between aboveground net primary production (ANPP) and climate in the Patagonian steppe of South America. We explored the same relationships through time, considering the natural variations of ANPP and climate for 11 yr. Based on NOAA/AVHRR satellite normalized difference vegetation index (NDVI) data, we evaluated the effects of climate on annual and seasonal ANPP across regional gradients of precipitation (100-500 mm/yr) and tem- perature (218-98C of annual mean). We studied ANPP climatic controls through time at four sites using NDVI and meteorological data. We used annual NDVI integral as a surrogate of annual ANPP. Annual NDVI integral increased linearly along regional gradients of precipitation, and its annual variability de- creased exponentially. Annual NDVI integral was, in most cases, unrelated to precipitation through time. We described the seasonality of ANPP using four variables derived from seasonal NDVI curves: the dates of growing season start and end, the date of maximum NDVI, and the length of the growing season. The growing season started later toward the cold extreme of the regional temperature gradients and, within a given site through time, during the coldest years. The dates of maximum NDVI and end of the growing season occurred later toward the humid or cold extremes of the regional gradients, whereas the length of the growing season was positively affected by precipitation and temperature along these gradients. These variables were not associated with climate through time. The response of the start of the growing season to temperature was greater in time, following the natural climatic fluctuations, than in space, accompanying regional temperature gradients. This difference probably resulted because the time required for shifts in community composition and plant adaptation is longer than one year. Climatic determinants of ANPP shifted from precipitation alone to precipitation plus temperature when the temporal scale of analysis changed from annual to seasonal. Our results indicate the feasibility of forecasting forage availability a few months prior to the beginning of the growing season, but not during the whole year. Longer term data sets and manipulative experiments are required to forecast annual ANPP and predict its response to climate change.

FUNCTIONAL AND STRUCTURAL CONVERGENCE OF TEMPERATE GRASSLAND AND SHRUBLAND ECOSYSTEMS

a Department of Zoology, Center for En6ironmental Science, Uni6ersity of Maryland, Box 38, Solomons, MD 20688, USA b Institute for Ecological Economics, Uni6ersity of Maryland, PO Box 38, Solomons, MD 20688, USA c Department of Economics (emeritus), Uni6ersity of Wyoming, Laramie, WY, 82070, USA d Center for En6ironment and Climate Studies, Wageningen Agricultural Uni6ersity, PO Box 9101, 6700 HB Wageningen, The Netherlands e Graduate School of Public and International Affairs, Uni6ersity of Pittsburgh, Pittsburgh, PA 15260, USA f Institute for Ecological Economics, Uni6ersity of Maryland, PO Box 38, Solomons, MD 20688, USA g Department of Geography, Uni6ersity of Illinois, Urbana, IL 61801, USA h NCSA, Uni6ersity of Illinois, Urbana, IL 61801, USA i Institute of Ecosystem Studies, Millbrook, NY, USA j Department of Ecology, E6olution and Beha6ior, Uni6ersity of Minnesota, St. Paul, MN 55108, USA k En6ironmental Sciences Di6ision, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA l Department of Ecology, Faculty of Agronomy, Uni6ersity of Buenos Aires, A6. San Martin 4453, 1417 Buenos Aires, Argentina m Jet Propulsion Laboratory, Pasadena, CA 91109, USA n Department of Geography, National Center for Geographic Information and Analysis, Uni6ersity of California at Santa Barbara, Santa Barbara, CA 93106, USA o Ecological Economics Research and Applications, PO Box 1589, Solomons, MD 20688, USA

REGIONAL PATTERNS OF NORMALIZED DIFFERENCE VEGETATION INDEX IN NORTH AMERICAN SHRUBLANDS AND GRASSLANDS

Abstract Grazing modifies the structure and function of ecosystems, affecting soil organic carbon (SOC) storage. Although grazing effects on some ecosystem attributes have been thoroughly reviewed, current literature on grazing effects on SOC needs to be synthesized. Our objective was to synthesize the effects of grazing on SOC stocks in grasslands, establishing the major mechanistic pathways involved. Additionally, and because of its importance for carbon (C) biogeochemistry, we discuss the controls of soil organic nitrogen (N) stocks. We reviewed articles analyzing grazing effects on soil organic matter (SOM) stocks by comparing grazed vs. ungrazed sites, including 67 paired comparisons. SOC increased, decreased, or remained unchanged under contrasting grazing conditions across temperature and precipitation gradients, which suggests that grazing influences the factors that control SOC accumulation in a complex way. However, our review also revealed some general patterns such as 1) root contents (a primary control of SOC formation) were higher in grazed than in their ungrazed counterparts at the driest and wettest sites, but were lower at sites with intermediate precipitation (∼400 mm to 850 mm); 2) SOM C∶N ratios frequently increased under grazing conditions, which suggests potential N limitations for SOM formation under grazing; and 3) bulk density either increased or did not change in grazed sites. Nearly all sites located in the intermediate precipitation range showed decreases or no changes in SOC. We grouped previously proposed mechanisms of grazing control over SOC into three major pathways that can operate simultaneously: 1) changes in net primary production (NPP pathway), 2) changes in nitrogen stocks (nitrogen pathway), and 3) changes in organic matter decomposition (decomposition pathway). The relative importance of the three pathways may generate variable responses of SOC to grazing. Our conceptual model suggests that rangeland productivity and soil carbon sequestration can be simultaneously increased by management practices aimed at increasing N retention at the landscape level.

Ecosystem responses to changes in plant functional type composition: An example from the Patagonian steppe

The objective of this study was to explore the use of multi-temporal Landsat TM data from the same growing season for the classification of land cover types in the south-western portion of the Argentine Pampas. Investigations were made on how many dates are necessary to obtain an accurate classification and, given a fixed number of dates, which is the particular combination of dates that yield the best results. Additionally, the effect of using the NDVI instead of all the bands available on the classification accuracy and the use of a moving window filter over the classified image were tested. Scenes acquired in spring, early summer, late summer and early fall of the 1996-1997 growing season were used. Land cover information for the same period was collected from farms and ranches and this information was included in a GIS. Supervised classifications were performed using all the 15 possible ways to combine the four dates. At least two scenes are needed for a satisfactory classification. These scenes must embrace the shift between winter and summer crops (i.e. one spring and one summer image). Using the NDVI instead of Landsat TM bands 3, 4 and 5 increased the biological interpretability of the results but caused a decrease in accuracy.