Plant functional traits, herbivore selectivity and response to sheep grazing in Patagonian steppe grasslands

Abstract

Summary 1.In 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. 2. We 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. 3. To 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. 4. Taller 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. 5. At 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. 6. Synthesis 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.

Perennial grasses traits as functional markers of grazing intensity in basaltic grasslands of Uruguay

“…These patterns of response represent a functional trade-off linked with the species strategies of resource-use and plant growth in different environments (Díaz and Cabido, 1997;Weiher et al, 1999). A conservative strategy was associated with low stocking rate, characterized by the increase in species with a low SLA, in agreement with reports of Cingolani et al (2005) and Leoni et al (2009), and high LDMC. Our results were consistent with findings of Cruz et al (2010) that reported LDMC and SLA as the traits that best described the response associated with the stocking rate increase.…”

“…The main changes related to grazing intensity were consistent with previous studies that reported the decrease of tall cool-season grasses with the increase in grazing intensity in North American mixed-grass prairies (Manley et al, 1997;Derner and Hart, 2007), in Uruguayan grasslands (Rodríguez et al, 2003;Altesor et al, 2005) and a decrease in all perennial grasses in Australia (Lavorel et al, 1997;McIntyre and Lavorel, 2001). The tall grasses are better adapted to capture resources at low grazing intensities, but are less grazing resistant under high grazing intensities (Cingolani et al, 2005). This can be explained because tall cool-season grasses have less leaf area index after grazing, less reserve organs and their growing points are more exposed to damage comparing with prostrate grasses.…”

Bases ecológicas para implementar un sistema de uso silvopastoral en la región patagónica de Aysén, Chile

“…La respuesta de las comunidades de pastizal al pastoreo ha dado lugar a un cuerpo teórico y empírico considerable que pretende identificar las características morfológicas y funcionales más relevantes relacionadas con esta actividad (McIntyre et al 1999), así como los atributos (estados posibles de esas características que representa cada especie) afectados positiva o negativamente por la misma (Montalvo et al 1991, Díaz et al 2001, Cingolani et al 2005b, de Bello et al 2005, Díaz et al 2007, Kahmen y Poschlod 2008. La interpretación de la respuesta del conjunto de atributos que se expresan en cada especie da lugar a diferentes estrategias (o síndromes de respuesta) para defenderse o tolerar el pastoreo (Grime et al 1997, Lavorel et al 1997, Westoby 1998, Kahmen y Poschold 2004, de Miguel et al 2010.…”

Capitulum and rosette leaf avoidance from grazing by large herbivores in Taraxacum

“…Although tolerance of herbivore damage reduces the fitness consequences through post-damage regrowth and reproduction (Briske 1991;Strauss and Agrawal 1999;Dı´az et al 2001;Cingolani et al 2005;Evju et al 2009), plant resistance reduces the extent of herbivore damage (Tiffin 2000). Resistance can be divided into antibiosis, which reduces herbivore performance, and avoidance, which allows plants to escape from herbivory.…”