Tropical Grasslands (2007) Volume 41, 50–54

The role of grasslands and forests as carbon stores

L.’t MANNETJE

Eekhoornlaan 14, 6705 CH, Wageningen, The Netherlands

Abstract

Carbon storage by forests is often mentioned as the only or the best way to reduce the CO2 concentration in the atmosphere. This paper presents evidence that grasslands are as important in this regard as forests.
Grasslands play a positive role in C storage, but a negative one in terms of CH4 emission, when grazed by ruminants. While extensively managed grasslands have negligible emissions of N2O and NH3, intensively managed grasslands, as in western Europe, can produce significant levels of harmful nitrogenous outputs. Grasslands release C to the atmosphere through respiration, decomposition of litter, burning and fermentation of feed in the rumen. However, photosynthesis of the regrowth can compensate for C losses from respiration, decomposition and burning.
Studies in Latin America have shown that improved, well managed, tropical grasslands store high rates of C (220–260 t/ha). Grass-legume mixtures store C at higher rates than pure grass swards. Grazed grasslands store more C than mown ones. Deep-rooted Brachiaria species and Andropogon gayanus deposit C at depths of up to 1 m. The deeper the C is deposited, the longer is its turn-over time. Estimates of C storage in well managed fertilised temperate grasslands are much lower (65–70 t/ha in 100 years). Conservation practices that conserve soil and increase vegetation cover increase C storage.
Forests accumulate C mostly in roots, trunks, leaves and litter. However, mature trees with little new net growth will assimilate only as much C as they lose in respiration. Both temperate and tropical old forests have been shown to do little to reduce CO2 levels in the atmosphere.

Download full article (68 KB PDF)  

  Return to Contributed Articles