Which plant traits determine abundance under long‐term shifts in soil resource availability and grazing intensity?

Abstract

Summary1. Soil resource availability and disturbance are widely recognized as key drivers of plant community structure. However, the relative importance of different plant traits in determining species abundance following shifts in soil resource availability and disturbance remains little studied, particularly in long-term experiments. 2. We studied trait-based plant community assembly in a 27-year grassland experiment where 25 plant species were sown into resident vegetation, after which annual manipulations of soil resource availability (five levels of superphosphate fertilizer; the highest level was also irrigated) and disturbance (three 'mob-grazed' sheep grazing intensity levels: lax, moderate, hard) were applied. We used community assembly through trait selection (CATS) models based on entropy maximization to predict species relative abundances and to quantify the relative importance of each trait in determining abundance. 3. Plant species were primarily differentiated along a trade-off axis corresponding to traits promoting rapid growth (e.g. high leaf [N] and specific leaf area [SLA]) vs. those promoting long leaf life span. Using 12 traits, the CATS model predicted >80% of the variation in the relative abundances of 51 species, suggesting that trait-based filtering was important. 4. Species with leaf attributes that reduce nutrient losses held a long-term advantage under the lowest soil resource availability, whereas those associated with a rapid growth rate became dominant under soil resource addition. Species with thinner leaves were also favoured under greater soil resource availability, which may reflect a strategy to maximize SLA without sacrificing leaf density and thus maintain leaf structural defences under grazing disturbance. Greater leaf [S] and the ability to symbiotically fix atmospheric N were favoured under greater soil resource availability. Greater plant height, thinner leaves and higher leaf [N] were favoured under lower grazing intensity. 5. Synthesis. Our results highlight the importance of species functional differences to understand how plant communities react to increases in soil resource availability and disturbance, two important and inseparable components of land-use change in grasslands world-wide.

Long-term Protection from Heavy Livestock Grazing Affects Ponderosa Pine Understory Composition and Functional Traits

“…These species can be characterized as slow-growing perennial species that allocate a relatively small proportion of their energy to reproduction and produce litter that decomposes slowly (Reich et al, 1997;Wright et al, 2004). These findings contribute to a growing body of evidence that there are consistent shifts in community-level leaf traits under a variety of grazing regimens around the world (Louault et al, 2005;Laliberté et al, 2012;Wesuls et al, 2012;Moreno García et al, 2014). Species with low SLA are at a competitive advantage when protected from heavy grazing because they are able to reduce resource availability.…”

“…Vegetative height has long been a key functional trait thought to reflect a mechanism of grazing avoidance, with increased levels of grazing intensity consistently favoring shorter plants (Dyksterhuis, 1949;Arnold, 1955;Díaz et al, 2001;Díaz et al, 2006). Seed mass, SLA, foliar N mass , LDMC, and leaf toughness have been used to understand and predict the impact of grazing because these traits are thought to reflect a general trade-off in growth versus defense (Moles and Westoby, 2004;Adler et al, 2004;Cingolani et al, 2005;Louault et al, 2005;Laliberté et al, 2012;Wesuls et al, 2012;Moreno García et al, 2014). Some researchers suggest that generalizations of grazing impacts described by plant traits may be difficult (Vesk and Westoby, 2001), whereas others suggest that plant species' responses to herbivory might be idiosyncratic with regard to LHS traits (Butterfield and Callaway, 2012).…”

The intrinsic dimensionality of plant traits and its relevance to community assembly

“…In the fynbos of South Africa, leaf traits, stem traits and flowering phenology were most important (Merow, Latimer & Silander 2011). In the tussock grasslands of New Zealand, leaf traits, root traits, height and life-history traits were most important (Lalibert e et al 2012). In upland rangelands of France, leaf traits, height, seed traits and flowering phenology were most important (Sonnier et al 2012).…”

Grass strategies and grassland community responses to environmental drivers: a review

“…It uses a matrix of species trait means and a vector of predicted communityweighted mean traits as input to obtain the most even probability distribution of species relative abundance. It has been shown in several studies how significant variation in species abundances can be explained (Sonnier et al 2010;Merow et al 2011;Laliberté et al 2012). The second model, entitled "Traitspace", has been proposed by Laughlin (Laughlin et al 2012;Laughlin and Laughlin 2013;Laughlin 2014).…”