Grazing exclusion reduces below‐ground biomass of temperate subhumid grasslands of South America: A meta‐analysis and a database

Abstract

AbstractThere are several plant below‐ground biomass databases for grasslands, but the contribution from the southern hemisphere is minimal. Particularly, no study has compiled the published values of plant below‐ground biomass for the temperate subhumid grasslands of South America. In these grasslands, called Río de la Plata grasslands, grazing is the most frequent disturbance. We set two objectives: (1) to compile and synthesize data of four variables: below‐ground biomass, fraction of total biomass allocated below‐ground, below‐ground net primary productivity and below‐ground biomass turnover rate; (2) to estimate the effect of grazing exclusion on below‐ground biomass by means of a meta‐analysis. There are 15 studies published on six out of eight regional sub‐divisions of the Río de la Plata grasslands. The most evaluated variable was below‐ground biomass, followed by below‐ground net primary productivity, while the other two variables were scarcely registered. Below‐ground biomass in the shallow portion of the soil (0–10 cm) was on average 877 g m−2. Below‐ground net primary productivity resulted in an average of 245 g m−2 year−1 (estimated using the ingrowth core method) or 560 g m−2 year−1 (core method). The fraction of total biomass allocated below‐ground was on average 0.75. Below‐ground biomass turnover rate presented an average of 2.5 years. On average, the effect of grazing exclusion on below‐ground biomass depended on exclusion time. When exclusion time was shorter than or equal to 3 years, grazing exclusion did not affect below‐ground biomass. In contrast, when exclusion time was longer than 3 years, grazing exclusion reduced below‐ground biomass by 62% (0–10 cm depth) and by 40% (total depth). Excluding South American grasslands from the global databases may introduce some biases in the observed patterns.