Complex plant community responses to modifications of disturbance and nutrient availability in productive permanent grasslands

Abstract

Question Do the effects of grazing and fertilization on taxonomic and functional diversity follow the dynamic equilibrium model? Location Long‐term permanent upland grasslands, Massif‐central, France. Methods Over 8 yr, we monitored vegetation changes in 24 experimental plots in two productive grasslands after modification of grazing intensity (including abandonment) or fertilization regime (including cessation of fertilization). Botanical surveys and plant trait measurements (LDMC, SLA and reproductive plant height) were performed within each plot. We analysed taxonomic responses using PRC and functional responses from observed temporal changes of CWM traits and Rao index. Results Grazing abandonment led to significant reductions in species richness and functional convergence toward taller plants with higher LDMC in both grasslands. Intermediate and high grazing pressure did not differ but showed strong variations in taxonomic diversity between years. Changes in functional vegetation structure were mostly driven by species turnover and weakly influenced by intraspecific trait variability. Community responses to modified fertilization regime were more complex, with strong differences between the two mown grasslands. Species richness did not change significantly although species evenness decreased in the highly fertilized treatments (NPK), particularly in the most productive grassland. Here, functional changes were largely driven by intraspecific trait variability. Both functional divergence and convergence were found for different traits. In NPK, grassland assemblages converged toward taller plants while SLA diverged. Conclusions In our upland study system the different components of grassland diversity responded differently, in terms of direction or rate of change and mostly under extreme modifications of management. Following abandonment, the observed patterns suggest a prominent and consistent role of competitive exclusion, as expected under the DEM. However, our findings also suggest the role of additional processes, especially the importance of niche differentiation, for our mown grassland under NPK. Timing and net effects of these combined assembly drivers were sensitive to even slight differences in initial productivity and species composition.

Disentangling the processes driving plant assemblages in mountain grasslands across spatial scales and environmental gradients

“…However, mountain grasslands are often used as grazing grounds for livestock, with intensity varying in relation to elevation. In previous studies, added fertilisation and mowing has led to observed trait convergence and divergence depending on the attribute examined and the type/intensity of treatment (Bloor & Pottier, 2014;Louault et al, 2017;Mason et al, 2011).…”

Mechanisms of seed mass variation along resource gradients

“…; Louault et al . ). Nonetheless, the extraordinary growth of available data has left many empirical patterns of trait variation unexplained (Moles ).…”

“…During the last two decades several theoretical frameworks were developed for improving the theoretical basis of trait-based ecology (Westoby et al 2002;Grime 2006;Enquist et al 2007;Shipley 2010). Following the historical development of classical plant ecology (Whittaker 1967;Austin & Austin 1980), much research in this field has focused on the response of plant traits, particularly CWM and CWV, to soil resource gradients (Pakeman et al 2008;Cornwell & Ackerly 2009;Laliberte et al 2012;Louault et al 2017). Nonetheless, the extraordinary growth of available data has left many empirical patterns of trait variation unexplained (Moles 2018).…”

Intra and inter-annual climatic conditions have stronger effect than grazing intensity on root growth of permanent grasslands

“…Ten years of contrasted management had strongly modified the functional diversity and aboveground production of this fertile upland grassland (Herfurth et al 2015;Louault et al 2017).…”

“…The local climate is semi-continental with oceanic influences (mean annual temperature 8.5 °C, mean annual precipitation 784 mm, Table 1). The site supports mesotrophic multi-specific permanent grassland, dominated by species with high Ellenberg indicator values for N (Schaffers and Sykora 2000), indicating a high level of fertility for the site (Table S1; Louault et al 2017). The soil is a cambisol with a sandy loam texture, developed on granitic bedrock.…”