Defoliation increased above-ground productivity in a semi-arid grassland

• Published in: Rangeland ecology & management 2004-09, Vol.57 (5), p.442-447
• Main Authors: LOESER, MATTHEW R., CREWS, TIMOTHY E., SISK, THOMAS D.
• Format: Article
• Language: English
• Subjects: Elymus elymoides
• ISSN: 1551-5028; 1550-7424; 1551-5028
• DOI: 10.2111/1551-5028(2004)057\[0442:DIAPIA\]2.0.CO;2

In light of the continuing debate regarding overcompensation we studied the responses of above-ground biomass in a high-elevation, semi-arid grassland to defoliation, defoliation history, and livestock grazing. The above-ground annual net primary productivity (ANPP) was measured over 2 years in one-hundred twenty, 1-m super(2) plots that were exposed to single- and multi-year defoliation and grazing treatments. Plant communities showed an average increase in ANPP of 31%-45% due to a single defoliation event. The most conservative estimate of average ANPP of defoliated subplots was 29.4 g m super(-2) greater than the non-defoliated controls. A history of defoliation, due to clipping or grazing, lessened the magnitude of the compensatory response, but above-ground overcompensation of biomass was still observed, ranging on average from 17% to 26%. One dominant species, squirreltail grass [Elymus elymoides (Raf.) Swezeyi], accounted for nearly one-third of the community-level increases in ANPP. In contrast to above-ground patterns, below-ground root production of squirreltail did not increase in response to defoliation events. These results suggest that the above-ground production of high-elevation, semi-arid grasslands in the American Southwest may be temporarily increased through certain grazing events, and may help explain shifts in species dominance in grasslands exposed to long-term grazing by livestock.Original Abstract: A raiz del debate continuo respecto a la sobrecompensacion estudiamos las respuestas de la biomasa aerea a la defoliacion en una elevacion alta de un pastizal semi-arido, al historial de defoliacion y al apacentamiento por ganado. La productividad primaria neta anual aerea (ANPP) se midio en dos anos en 120 parcelas de 1 m super(-2) que fueron expuestas tratamientos de una sola defoliacion y defoliaciones multiples por ano y tratamientos de apacentamiento. Las comunidades vegetales mostraron un incremento promedio en la ANPP del 31 al 45% debido a un solo evento de defoliacion. La estimacion mas conservadora de la ANPP promedio de las subparcelas defoliadas fue 29.4 g m super(-2) mayor que las parcelas control no defoliadas. Un historial de defoliacion debido a cortes o apacentamiento redujo la magnitud de la respuesta compensatoria, pero la sobrecompensacion de la biomasa aerea aun se observo, variando en promedio de 17% a 26%. Una de las especies dominantes, 'Squirreltail grass' [Elymus elymoides (Raf.) Swezeyi], aporto casi un tercio