Determinants of grassland primary production in seasonally-dry silvopastoral systems in Central America

Abstract

Grassland primary productivity is the function that underpins the majority of the fodder production in cattle-rearing silvopastoral farms. Hence, understanding the factors that determine grassland productivity is critical for the design and management of silvpastoral systems. We studied the effect of two factors with documented impact on grassland productivity in seasonally dry silvopastures of Nicaragua, rainfall and trees. We assessed the effects of three species that differed in crown size and phenology, one evergreen, Cassia grandis, and two deciduous species, Guazuma ulmifolia and Tabebuia rosea. Overall, grassland ANPP had a quadratic response to rainfall, with a decline at high rainfall that coincided with peak standing biomass and grassland cover. Trees had a predominately negative effect on grassland productivity, and the effect was concentrated in the rainy season at peak productivity. The effect of the trees corresponded with the tree crown area, but not with crown density. Trees reduced the standing biomass of graminoids and increased forb biomass; thus, the effect of trees on grassland ANPP appears in part to respond to changes in grassland composition. We also found higher levels of soil moisture content below the tree canopy, particularly at the peak of the rainy season when soils tend to become waterlogged. The evergreen species, C. grandis, affected grassland ANPP more strongly than the deciduous species.

Trees enhance soil carbon sequestration and nutrient cycling in a silvopastoral system in south-western Nicaragua

“…This land use type is usually the result of forest conversion to neotropical pasture with the preservation of selected trees (Guevara et al 1986;Harvey and Haber 1998). Next to pasture for cattle raising, the scattered isolated trees provide shade to cattle, firewood, wood for construction, and fodder and fruits that are important to cattle in the dry season when grassland production stops (Manning et al 2006;Ospina et al 2012;Rusch et al 2014). In addition, SPS may be a component of the terrestrial carbon sink by fixing CO 2 through photosynthesis into organic matter and the subsequent sequestration of organic matter in soil (Andrade et al 2008;Ballantyne et al 2012).…”

Community aggregated traits disclose functional responses to seasonal resource fluctuations and spatial heterogeneity

“…; Rusch et al. ). Differences in the relative composition of major plant life forms among sites could also have been important in determining the differences in trait averages observed among plots.…”

“…Although we used common indicators of soil fertility (mineral concentrations and soil texture), other soil factors may be better predictors of growth conditions. In particular, the soils in the area of the study have generally high clay content, low hydraulic conductivity and a tendency to seasonal water-logging, conditions which may override the importance of nutrient content as a limiting factor (Ospina et al 2012;Rusch et al 2014). Differences in the relative composition of major plant life forms among sites could also have been important in determining the differences in trait averages observed among plots.…”

“…; Rusch et al. ). There is also evidence of different species attaining dominance at different times of the growing period in similar savanna systems (Sarmiento , ).…”

“…The particular functional traits of individuals and populations can be scaled up to communities and ecosystems (D ıaz et al 2004;Violle et al 2007) through communityweighted mean values of a trait (henceforth, CWM) or the community aggregated trait, representing the dominant trait values in a community (Violle et al 2007), and which is a good indicator of trait-environment relationships (Schellberg & Pontes 2012). Our case study area is dominated by Neotropical savannas and grasslands that experience pronounced rainfall seasonality; the temporal pattern of rainfall is the most important cause of resource supply variation in these systems, which is reflected in the pattern of herbaceous above-ground primary productivity in the area (Ospina et al 2012;Rusch et al 2014). There is also evidence of different species attaining dominance at different times of the growing period in similar savanna systems (Sarmiento 1984(Sarmiento , 1992.…”