Long-term dynamics of a semiarid grass steppe under stochastic climate and different grazing regimes: A simulation analysis.

PARUELO J.M.,PUTZ, S., G. WEBER, BERTILLER, M., GOLLUSCIO, R.A., AGUIAR, M.R., WIEGAND , T

JOURNAL OF ARID ENVIRONMENTS

Elsevier Ltd

Año: 2008 vol. 72 p. 2211 - 2231

0140-1963

We built a grid-based spatial explicit stochastic model that simulates grazing events andbasic processes like seedling establishment, growth or mortality of the dominantspecies in the grass steppes of Patagonia. After evaluating the model with field data, weperformed simulation experiments aimed to explore the interaction of precipitation andgrazing regimes on vegetation dynamics. Grazing generated a reduction in tussockdensity which results in a decline in aboveground net primary production (ANPP). Bothresponse variables presented a non-linear behavior including high temporal variabilityand delay effects, which may prolong for decades. There was a clear threshold in theresponse of the variables to stock density, though changes become evident only when ahighly selective grazing scenario was used. Under high stock density conditions,precipitation use efficiency (PUE) was 82% lower than the values for non-grazed runs.The inter-annual variability of precipitation was more important than the grazingregime in explaining differences in tussock density. Simulation results highlightimportant issues regarding rangeland management: grazing regime might be asimportant as stocking density as a degradation agent, temporal lags might obscuredegradation processes for decades, the definition of monitoring variables need toconsider their response time constants.