Influence of precipitation and species composition on phytomass of a semi‐arid African grassland

Abstract

Summary 1The influence of botanical composition on annual phytomass production of a semiarid grassland in response to precipitation was tested with a 19-year experiment. Three compositional states reflecting good, medium and poor rangeland condition, whose basal cover increased from poor through to good, were created in 1978.2 Multiple regression models were developed for assessing whether phytomass was influenced by precipitation, composition, phytomass of the previous year, basal cover, abundance of individual species, or diversity. Composition and precipitation accounted for 66% of the variation in phytomass, but a separate model of basal cover by precipitation was equally successful. The linear effect of rainfall on phytomass was enhanced as composition improved from poor (0.076 g m -2 mm ) to good (0.277 g m -2 mm -1 ). Phytomass increased for low precipitation if it had been high the preceding year. Phytomass was more variable over time with deteriorating condition. 3 Species' complementarity ensured greater and more stable production. Setaria sphacelata , Eragrostis chloromelas and Digitaria eriantha increased phytomass on the good or medium condition grasslands during drier years, whereas Themeda triandra had this effect during wetter years. 4 Precipitation-use efficiency (PUE) was influenced mostly by composition and a linear and quadratic effect of precipitation (63% of variance). Optimum PUE of 0.308, 0.203 and 0.096 g m -2 mm -1 for the good, medium and poor condition grasslands, respectively, occurred at intermediate amounts ( ± 680 mm) of precipitation. PUE was increased if phytomass had been high the previous year. 5 Species' complementarity of PUE in response to precipitation was evident for all compositional states. Ten, mostly uncommon, species and their interaction with precipitation explained an extra 21-42% of the variance. Stability of production was related to PUE for medium and poor condition grassland. Uncommon species therefore ensured growth efficiency and stabilized production as condition deteriorated. 6 Diversity had no influence on phytomass or PUE except for a small to moderate effect, respectively, for the medium condition grassland. 7 Vegetation structure, through limiting runoff and promoting infiltration, is an important control on the amount and efficiency of plant production under variable precipitation, whilst composition further influences the amount and stability of production.

Photosynthetic Recovery of a Perennial GrassLeymus chinensisafter Different Periods of Soil Drought

“…in the recent decades (Zhou et al, 2002;Bai et al, 2004;Zhou et al, 2006). Many researches indicated that drought and the seasonal precipitation seriously affect the growth and the community composition of grasslands (Distel et al, 1996;O'connor et al, 2001;Kröpfl et al, 2002;Wang and Gao, 2003), and drought is particularly a problem, occurring episodically in many regions (Kang et al, 2002;Shah and Paulsen, 2003). The global climatic change may result in not only the change of total precipitation but also the occurrence of discontinuous drought.…”

Degradation of net primary production in a semiarid rangeland

“…approaches that seem reasonable but have severe limitations, particularly when applied to large areas: visual assessment of satellite imagery is entirely subjective and therefore unrepeatable; field surveys, such as the National Resources Inventory (Nusser and Goebel, 1997), are limited to small areas (Budde et al, 2004;O'Connor et al, 2001;Prince, 2004) that can be assessed by an evaluator on the ground; and process modeling of potential production followed by comparison with actual production (Bai et al, 2008;Boer and Puigdefabregas, 2005) suffers from the need for data and parameters that are generally not available (Prince, 2002).…”

The local impacts of climate change in the Ferlo, Western Sahel

“…As for most of Sub Saharan Africa's drylands, with the possible exception of South Africa (e.g. O'Connor et al 2001), there is a general lack of data required to model the impacts of climate change on the local dryland production system. These data constraints restrict the level of detail that can be incorporated in the model.…”

“…The right hand part of the equation shows how the long-term grazing pressure affects the rain-use efficiency by moving the curve towards a lower rain-use efficiency, while maintaining a quadratic relation (cf. O'Connor et al 2001). Further explanation of the function is provided in Hein and De Ridder (2006) and Hein and Weikard (2004).…”

“…The left-hand part of the equation is a simple quadratic function showing the relation between rain-use efficiency and rainfall without grazing (cf. O'Connor et al 2001;Hein and De Ridder 2006). The right hand part of the equation shows how the long-term grazing pressure affects the rain-use efficiency by moving the curve towards a lower rain-use efficiency, while maintaining a quadratic relation (cf.…”