The role of animals in desertification: Herbivory patterns in degraded grassland

TitleThe role of animals in desertification: Herbivory patterns in degraded grassland
Publication TypeConference Paper
Year of Publication2004
AuthorsRoth G.A., Whitford WG, Steinberger Y.
Conference Name89th Annual Meeting, Ecological Society of America
Date PublishedAugust 1, 2004
Conference LocationPortland, OR
ARIS Log Number168827
Keywordsdesert grassland ecosystems, desertification, herbivory patterns, role of animals
AbstractWe examined the contribution herbivores make to the resistance and resilience of desert grassland ecosystems following a desertification process. The study took place in the Jornada Experimental Range, New Mexico, where, historically, desert grassland has gone through the desertification process during the past century. We monitored browsing signs on snakeweed (Gutierrezia sarothrae), the dominant sub-shrub in the landscape, and on all perennial grass species. Snakeweed was monitored for browsing on a monthly basis over a period of a year, while grasses were evaluated for herbivory in a single assessment at the end of their growing season. Plots grazed by livestock for 3 subsequent years were compared with undisturbed ones. Domestic animals grazing ceased in 1998, hence all herbivory documented is related to wild rabbits and rodents. Results show clear spatial and temporal herbivory patterns on snakeweed. The animals browsed in patchy patterns and have shown significant tendency for repeated browsing on specific plants, which indicates a nonrandom feeding behavior. Relatively high browsing frequency and biomass intake were documented between November and March, which forms the dry season in the northern Chihuahuan Desert. A significant decrease in snakeweed browsing was detected with the appearance of annuals and ceased almost completelywith the availability of perennial grasses. Despite the temporal pattern detected, plant-water content failed to explain the herbivore spatial feeding preferences. Grasses had much lower initial abundance and biomass compared to snakeweed. This resulted in a significantly higher relative percentage of grass biomass consumed by herbivory. That effect strongly intensified in formerly grazed plots where initial grass cover was the lowest. By the end of their growing season almost no grass flowering tillers survived which caused insufficient seed reservoir. Our findings show that herbivores contribute to the resistance and resilience of degraded grasslands by reducing the reestablishment of grasses.