Interactive Effects of Drought and Grazing on Northern Great Plains Rangelands

Abstract

Drought is common in rangeland environments and an understanding of its impacts on the structure and function of rangeland ecosystems is paramount for developing effective management strategies. This research was the second of a series of studies investigating the impacts of varying seasonal droughts on northern Great Plains rangelands. Research was conducted on native rangeland during the 1998 through 2001 growing seasons. Study plots were twelve 5 3 10 m nonweighing lysimeters. An automated rainout shelter was used to establish drought conditions on 6 lysimeters during April, May, and June of 1998 and 1999. Single-day, flash grazing events were imposed at the beginning of May, June, and July. Grazing treatments were 1) graze during the 2 years of drought and the year after; 2) graze during the 2 years of drought and rest the year after; and 3) rest all years. Results showed that the intense spring drought reduced soil water content in the upper 30 cm of the soil profile and subsequently reduced total herbage production 20% to 40%; cool-season perennial grasses were the primary contributor to the reduction and cool-season annual grasses were secondary. Periodic grazing during drought had minimal impact on herbage production, whereas impacts on nondrought plots ranged from moderate enhancement to moderate suppression, with effects varying depending on functional group. Results also showed that substantial recovery occurred during the 1st postdrought year, with near full recovery realized within 2 years. ResumenLa sequía es comú n en los ambientes de pastizal y entender sus impactos en la estructura y funció n de estos ecosistemas es primordial para desarrollar estrategias efectivas de manejo. Esta investigació n fue la segunda de una serie de estudios para investigar los impactos de variar sequías estacionales en los pastizales de las Grandes Planicies del norte. La investigació n se condujo en un pastizal nativo durante las estaciones de crecimiento de 1998 al 2001. Las parcelas de estudio fueron 12 lisímetros que no se pesan de 5 3 10 m. Se uso un protector de lluvia automatizado para establecer las condicionas de sequía en 6 de los lisímetros durante Abril, Mayo y Junio de 1998 y 1999. A inicios de Mayo, Junio y Julio se impusieron eventos relá mpago de apacentamiento de un solo día. Los tratamientos de apacentamiento fueron: 1) apacentamiento durante los dos añ os de sequía y el añ o posteriora ellos; 2) apacentamiento durante los 2 añ os de sequía y descanso en el añ o posterior a ellos y 3) descansar todos los añ os. Los resultados mostraron que la sequía intensa en primavera redujo el contenido de agua del suelo en los 30 cm superiores del perfil del suelo lo que redujo entre 20 y 40% la producció n total de forraje, siendo los zacates perennes de estació n fría los principales contribuyentes de la reducció n y los zacates anuales de estació n fría la segunda causa. El apacentamiento perió dico durante la sequía tuvo un impacto mínimo en la producció n de forraje mientras que los impactos en las p...

Combined effects of warming and drought on plant biomass depend on plant woodiness and community type: a meta-analysis

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