Two new papers from the global network of dryland sites we have gathered in the framework of the BIOCOM project have been accepted during the last weeks. They will be published online early during the next weeks/months, but here go the abstracts:
Ulrich, W., S. Soliveres, F. T. Maestre, R. Torices, N. J. Gotelli, J. L. Quero, M. Delgado-Baquerizo, V. Ochoa, B. Gozalo, E. Valencia, M. Berdugo, C. Escolar, M. García-Gómez, P. García-Palacios, A. Escudero, G. Alfonso, T. Arredondo, M. A. Bowker, D. Bran, O. Cabrera, A. Cea, M. Chaieb, A. A. Conceição, J. Contreras, M. Derak, D. J. Eldridge, C. I. Espinosa, A. Florentino, J. Gaitán, W. Ghiloufi, S. Gómez-González, J. R. Gutiérrez, E. Guzmán, R. M. Hernández, E. Huber-Sannwald, M. Jankju, R. L. Mau, M. Miriti, J. Monerris, M. Muchane, K. Naseri, A. Prina, E. Pucheta, D. A. Ramírez-Collantes, E. Raveh, R. Romão, D. Torres, C. Torres-Díaz, J. Val, J. P. Veiga, D. Wang, X. Yuan & E. Zaady. 2014.Variability in climate and soil attributes control plant species turnover in global drylands. Journal of Biogeography
Aim Geographic, climatic, and soil factors are major drivers of beta diversity, but their importance for dryland plant communities is poorly known. This study aims to: i) characterize patterns of plant beta diversity in global drylands, ii) detect common environmental drivers of beta diversity among different regions, and iii) test for thresholds in environmental conditions driving changes in plant composition.
Location 224 sites from 22 geographical regions in dryland communities from six continents.
Methods Beta diversity among sites within the regions was quantified with four complementary measures: the percentage of singletons (species occurring at only one site), Whittaker´s beta diversity b(W), a directional species turnover metric based on the correlation in species abundances among spatially contiguous sites (b(R2)), and a multivariate abundance-based metric b(MV). We used linear regression and regression trees to quantify the relationship between these metrics of beta diversity and geographic, climatic, and soil variables.
Results Soil fertility and variability in temperature and rainfall, and to a lesser extent latitude, were the most important environmental predictors of beta diversity. Metrics related to species identity (percentage of singletons and b(W)) were most sensitive to soil fertility, whereas those linked to environmental gradients and abundance ((b(R2)) and b(MV)) were more associated with climate variability. Statistical interactions among soil variables, climatic factors, and plant cover were not important determinants of beta diversity. Sites receiving less than 178 mm of annual rainfall differed sharply in species composition from more mesic sites.
Main conclusions Soil fertility and variability in temperature and rainfall are the most important drivers of plant beta diversity in global drylands, although they act independently. Our results suggest that those sites annually receiving ~ 178 mm of rainfall will be especially sensitive to future climate changes. These findings may help to define appropriate conservation strategies for mitigating effects of climate change on dryland vegetation.
Soliveres, S., F. T. Maestre, D. J. Eldridge, M. Delgado-Baquerizo, J. L. Quero, M.A. Bowker & A. Gallardo. 2014. Plant diversity and ecosystem multifunctionality peak at intermediate levels of woody cover in global drylands. Global Ecology and Biogeography
Aim The global spread of woody plants into grasslands is predicted to increase over the coming century. While there is general agreement regarding the anthropogenic causes of this phenomenon, its ecological consequences are less certain. We analyzed how woody vegetation of differing cover affects plant diversity (richness and evenness) and surrogates of multiple ecosystem processes (multifunctionality) in global drylands, and how this changes with aridity.
Location 224 dryland sites from all continents except Antarctica widely differing in their environmental conditions (from arid to dry-subhumid sites) and woody covers (from 0 to 100%).
Methods Using a standardized field survey, we measured the cover, richness and evenness of perennial vegetation. At each site, we measured 14 soil variables related to fertility and the build-up of nutrient pools. These variables are critical for maintaining ecosystem functioning in drylands.
Results Species richness and ecosystem multifunctionality were strongly influenced by woody vegetation, with both variables peaking at relative woody covers (RWC) of 41-60%. This relationship shifted with aridity. We observed linear positive effects of RWC in dry-subhumid sites. These positive trends shifted to hump-shaped RWC-diversity and multifunctionality relationships under semiarid environments. Finally, hump-shaped (richness, evenness) or linear negative (multifunctionality) effects of RWC were found under the most arid conditions.
Main conclusions Plant diversity and multifunctionality peaked at intermediate levels of woody cover, although this relationship became increasingly positive under wetter environments. This comprehensive study accounts for multiple ecosystem attributes across a range of woody covers and environmental conditions. Our results help us to reconcile contrasting views of woody encroachment found in current literature and can be used to improve predictions of the likely effects of encroachment on biodiversity and ecosystem services.