Ecosystem carbon loss with woody plant invasion of grasslands

Abstract

The invasion of woody vegetation into deserts, grasslands and savannas is generally thought to lead to an increase in the amount of carbon stored in those ecosystems. For this reason, shrub and forest expansion (for example, into grasslands) is also suggested to be a substantial, if uncertain, component of the terrestrial carbon sink. Here we investigate woody plant invasion along a precipitation gradient (200 to 1,100 mm yr(-1)) by comparing carbon and nitrogen budgets and soil delta(13)C profiles between six pairs of adjacent grasslands, in which one of each pair was invaded by woody species 30 to 100 years ago. We found a clear negative relationship between precipitation and changes in soil organic carbon and nitrogen content when grasslands were invaded by woody vegetation, with drier sites gaining, and wetter sites losing, soil organic carbon. Losses of soil organic carbon at the wetter sites were substantial enough to offset increases in plant biomass carbon, suggesting that current land-based assessments may overestimate carbon sinks. Assessments relying on carbon stored from woody plant invasions to balance emissions may therefore be incorrect.

Soil moisture and vegetation controls on evapotranspiration in a heterogeneous Mediterranean ecosystem on Sardinia, Italy

“…[4] These Mediterranean ecosystems are commonly heterogeneous savanna-like ecosystems, with contrasting plant functional types (PFTs, e.g., grass, shrubs and trees) competing for the water use [Scholes and Archer, 1997;Ramirez-Sanz et al, 2000;Jackson et al, 2002;Baldocchi et al, 2004;Fernandez et al, 2004;Williams and Albertson, 2004]. Despite the attention these ecosystems are receiving, a general lack of knowledge persists about the relationship between ET and the plant survival strategies for the different PFTs under water stress [Baldocchi et al, 2004;Kurc and Small, 2004].…”

Complex facilitation and competition in a temperate grassland: loss of plant diversity and elevated CO2 have divergent and opposite effects on oak establishment

“…Species compositional shifts caused by woody encroachment into grasslands have important implications for community dynamics and ecosystem properties, such as carbon (C) storage and nitrogen (N) cycling (Post et al 1982;Reich et al 2001b;Jackson et al 2002;McCulley et al 2004;Knapp et al 2008;McKinley and Blair 2008;Barger et al 2011). While regional distributions of woody plants appear to be co-constrained by large-scale differences in precipitation and fire regimes (Staver et al 2011), local success of woody plants in grasslands is strongly associated with a change in disturbance regime that favors woody plants over herbaceous species, such as fire suppression (Van Auken 2000; Roques et al 2001;Silva et al 2001) or increased grazing pressures by cattle (Archer et al 1995;Brown and Archer 1999).…”

Soil aggregate fraction-based 14C analysis and its application in the study of soil organic carbon turnover under forests of different ages

“…Most previous studies concerning mechanisms of the SOC sequestration and emission in planted forest have focused on the SOC content and storage change [12,15], and there is no consensus on the changes in SOC pools following afforestation. Studies have reported accumulation [17][18][19], no net change [20][21][22], or loss [12,16,23] of SOC storage after afforestation. The disparity may be due to a number of factors, including sampling depth, regional climate, previous land use, tree species, and stand ages [23][24][25].…”

“…Studies have reported accumulation [17][18][19], no net change [20][21][22], or loss [12,16,23] of SOC storage after afforestation. The disparity may be due to a number of factors, including sampling depth, regional climate, previous land use, tree species, and stand ages [23][24][25]. SOC turnover time, as a parameter for estimating soil carbon flux, is important for understanding the dynamics of SOC [26][27][28], but little has been done to evaluate the soil carbon pool change based on the SOC turnover times for the soils under planted forests.…”