Regional scale relationships between ecosystem structure and functioning: the case of the Patagonian steppes

Abstract

Aims 1. To characterize ecosystem functioning by focusing on above-ground net primary production (ANPP), and 2. to relate the spatial heterogeneity of both functional and structural attributes of vegetation to environmental factors and landscape structure. We discuss the relationship between vegetation structure and functioning found in Patagonia in terms of the capabilities of remote sensing techniques to monitor and assess desertification.Location Western portion of the Patagonian steppes in Argentina (39 ° 30 ′ S to 45 ° 27 ′ S). MethodsWe used remotely-sensed data from Landsat TM and AVHRR /NOAA sensors to characterize vegetation structure (physiognomic units) and ecosystem functioning (ANPP and its seasonal and interannual variation). We combined the satellite information with floristic relevés and field estimates of ANPP. We built an empirical relationship between the Landsat TM-derived normalized difference vegetation index (NDVI) and field ANPP. Using stepwise regressions we explored the relationship between ANPP and both environmental variables (precipitation and temperature surrogates) and structural attributes of the landscape (proportion and diversity of different physiognomic classes (PCs)). ResultsPCs were quite heterogeneous in floristic terms, probably reflecting degradation processes. Regional estimates of ANPP showed differences of one order of magnitude among physiognomic classes. Fifty percent of the spatial variance in ANPP was accounted for by longitude, reflecting the dependency of ANPP on precipitation. The proportion of prairies and semideserts, latitude and, to a lesser extent, the number of PCs within an 8 × 8 km cell accounted for an additional 33% of the ANPP variability. ANPP spatial heterogeneity (calculated from Landsat TM data) within an 8 × 8 km cell was positively associated with the mean AVHRR/ NOAA NDVI and with the diversity of physiognomic classes. Main conclusionsOur results suggest that the spatial and temporal patterns of ecosystem functioning described from ANPP result not only from water availability and thermal conditions but also from landscape structure (proportion and diversity of different PCs). The structural classification performed using remotely-sensed data captured the spatial variability in physiognomy. Such capability will allow the use of spectral classifications to monitor desertification.

Animal Habitat Quality and Ecosystem Functioning: Exploring Seasonal Patterns Using Ndvi

“…It therefore would be desirable to investigate whether mechanistic links exist between the seasonal NDVI pattern and bear food items or fitness (Nielsen et al 2003). However, the correspondence between ecosystem functioning and vegetation structure is, in general, an open question, although it is often assumed (Paruelo et al 2004). …”

Thespieus maackisp. nov. (Lepidoptera: Hesperiidae, Hesperiini): A New Skipper from Southern Brazilian Páramos

“…At a finer grain, heterogeneity is due to altitude, slope, and exposure (Jobbágy et al 1996, Paruelo et al 2004). …”

“…Shrub encroachment is sometimes the final stage of grazing degradation of the grass steppes. Such changes reduce primary production (Paruelo et al, 2004) and modify water dynamics and herbivore biomass (Aguiar et al, 1996). In both vegetation units plant diversity is higher in ungrazed areas.…”

FENOLOGÍA Y PRODUCTIVIDAD PRIMARIA NETA AÉREA DE SISTEMAS PASTORILES DE Panicum maximun EN EL DPTO. MORENO, SANTIAGO DEL ESTERO, ARGENTINA, DERIVADA DEL NDVI MODIS

“…Por cuanto para los SP en este trabajo se tomó de bibliografía el valor de ε de Ruimy et al (1994), siendo el promedio anual de pasturas perennes igual a 0.23 g Ms/MJ (Field et al, 1995). Los valores considerados de α = 1.1 y β = 0.055, fueron determinados por Paruelo et al (2004) para Sudamérica en base a la metodología propuesta por Ruimy et al (1994). SINDVI es la estacionalidad integrada del NDVI (Reed & Brown, 2005 (Fensholt et al, 2004).…”