Monitoring the ecosystem service of forage production

IRISARRI, G.; OESTERHELD, M.; OYARZABAL, M.; PARUELO, J.M.; DURANTE, M.

Earth Observation of Ecosystem Services

CRC Taylor & Francis

Año: 2013; p. 87 - 100

Worldwide, 80% of the energy required by cattle to reach market weight is derived from rangelands and pastures (Wheeler et al. 1981; Oltjen and Beckett 1996). Managing these forage resources requires knowing their production. Forage production, also known as forage growth rate, is a portion of the aboveground net primary production (ANPP), a key ecosystem variable. At the individual level, ANPP represents the difference between photosynthesis and respiration (Chapin et al. 2002), whereas at the landscape level, ANPP represents the rate of biomass production per unit of area and time. At the ecosystem level, ANPP represents the rate of production of available energy for primary consumers. ANPP is an integrator of ecosystem functioning and determines the input level of many ecosystem services (Costanza et al. 1997). For example, the availability of information on ANPP for pastures and rangelands is critical to establish adequate stocking rates (Oesterheld et al. 1998) and to manage excesses or deficits of forage. Considering the high relevance of ANPP in rangeland management, few data on its spatial and temporal variation are available. This lack of information is due to the difficulty in estimating ANPP in the field and in extrapolating the few available data to other spatial or temporal situations. ANPP models derived from remote sensing data (Paruelo et al. 1997, 2000; Running et al. 2000; Piñeiro et al. 2006) can tackle this lack of information because they cover large areas and long periods. ANPP varies at different scales in space and time. Across wide resource gradients, ANPP consistently increases with precipitation (Lauenroth 1979; Sala et al. 1988). Within a landscape, ANPP widely varies with regard to topographic gradients (Knapp et al. 1993; Buono et al. 2010; Irisarri et al. 2012), edaphic differences (Aragón and Oesterheld 2008), or disturbance frequency (Knapp et al. 1993; Oesterheld et al. 1999). The interannual variation of ANPP of steppes, grasslands, or savannas is large and generates the greatest uncertainties for range management (Lauenroth and Sala 1992; Knapp and Smith 2001; Bai et al. 2008). The seasonal variation of ANPP is also large and restricts management. For example, in temperate areas of the Río de la Plata grasslands, spring ANPP is 10 times larger than winter?s (Sala et al. 1981; Oesterheld and León 1987; Altesor et al. 2005; Semmartin et al. 2007). The objectives of this chapter are (1) to introduce two approaches for ANPP estimations?the classic way through biomass harvests and a more recent practice based on remote sensing data, and (2) to describe a forage production monitoring system that routinely observes ranches of Argentina and Uruguay based on the second approach. In this chapter, we first describe the logic and difficulties involved in estimating ANPP through sequential biomass harvests. Second, we describe the logic of an approach based on remote sensing. Third, we discuss in some detail the estimation of radiation use efficiency (RUE). Finally, we present a monitoring system of forage production currently functioning in Argentina and Uruguay.