Plant functional traits, herbivore selectivity and response to sheep grazing in Patagonian steppe grasslands
Article first published online: 21 DEC 2004
Journal of Applied Ecology
Volume 42, Issue 1, pages 50–59, February 2005
How to Cite
CINGOLANI, A. M., POSSE, G. and COLLANTES, M. B. (2005), Plant functional traits, herbivore selectivity and response to sheep grazing in Patagonian steppe grasslands. Journal of Applied Ecology, 42: 50–59. doi: 10.1111/j.1365-2664.2004.00978.x
- Issue published online: 22 FEB 2005
- Article first published online: 21 DEC 2004
- Received 9 December 2003; final copy received 3 August 2004
- diet selection;
- fertile steppes;
- forage quality;
- grazing tolerance;
- leaf toughness;
- resource availability;
- specific leaf area
- 1In some ecosystems there is a positive feedback between forage quality and grazing intensity. This involves three components of plant tolerance to grazing: functional traits, herbivore selectivity and response to grazing. We analysed the relationships between these components at species and community levels in Patagonian steppe grasslands.
- 2We measured plant functional traits [height, specific leaf area (SLA) and foliar toughness] and estimated sheep selectivity and grazing response indices for 35 plant species. Sheep selectivity indices were obtained from microhistological and species’ availability data, and grazing response indices from species’ abundances in sites with contrasting grazing intensities. We performed correlations and multiple regressions among the three types of variables across the pool of 35 species.
- 3To analyse data at the community level, we computed weighted averages of traits and sheep selectivity indices for 34 floristic samples taken from each side of 17 fence lines with contrasting grazing intensities. Correlations between mean trait values and sheep selectivity across the 34 samples, and paired comparisons of those variables between sides of the fences, were performed.
- 4Taller plants had leaves with lower SLA and/or higher toughness. Short species of intermediate toughness were selected more often by sheep, while SLA was not related to sheep selectivity. Short species with high SLA increased with grazing, while toughness and sheep selectivity were unrelated to grazing response.
- 5At the community level, short swards with high average SLA had high selectivity indices and were more abundant on the most intensively grazed sides of fence lines. Leaf toughness was unrelated to other traits or to sheep selectivity, and showed no significant response to grazing.
- 6Synthesis and applications. Intensive grazing can increase the forage value of grasslands by the creation of lawns dominated by tolerant species. However, results from this study showed that some plant species that were avoided by grazers also increased, indicating a potential risk of a shift in composition of grazing lawns towards states of low forage value. This suggests that periodic resting of lawns could be a good management strategy to favour palatable species, thereby minimizing the risk of undesirable shifts in the overall species composition.