Trait-based representation of hydrological functional properties of plants in weather and ecosystem models

Land surface models and dynamic global vegetation models typically represent vegetation through coarse plant functional type groupings based on leaf form, phenology, and bioclimatic limits. Although these groupings were both feasible and functional for early model generations, in light of the pace at which our knowledge of functional ecology, ecosystem demographics, and vegetation-climate feedbacks has advanced and the ever growing demand for enhanced model performance, these groupings have become antiquated and are identified as a key source of model uncertainty. The newest wave of model development is centered on shifting the vegetation paradigm away from plant functional types(PFTs)and towards flexible trait-based representations. These models seek to improve errors in ecosystem fluxes that result from information loss due to over-aggregation of dissimilar species into the same functional class. We advocate the importance of the inclusion of plant hydraulic trait representation within the new paradigm through a framework of the whole-plant hydraulic strategy. Plant hydraulic strategy is known to play a critical role in the regulation of stomatal conductance and thus transpiration and latent heat flux. It is typical that coexisting plants employ opposing hydraulic strategies, and therefore have disparate patterns of water acquisition and use. Hydraulic traits are deterministic of drought resilience, response to disturbance, and other demographic processes. The addition of plant hydraulic properties in models may not only improve the simulation of carbon and water fluxes but also vegetation population distributions.

Strong restrictions on the trait range of co-occurring species in the newly created riparian zone of the three Gorges Reservoir Area, china

Aims community assembly links plant traits to particular environmental conditions.Numerous studies have adopted a trait-based approach to understand both community assembly processes and changes in plant functional traits along environmental gradients.In most cases these are long-established,natural or semi-natural environments.However,increasingly human activity has created,and continues to create,a range of new environmental conditions,and under-standing community assembly in these‘novel environments’will be increasingly important.Methods Built in 2006,the three Gorges Dam,largest hydraulic project in china,created a new riparian area of 384 km^(2),with massively al-tered hydrology.this large,newly created ecosystem is an ideal platform for understanding community assembly in a novel environment.We sampled environment variables and plant communities within 103 plots located in both the reservoir riparian zone(RRZ)and adjacent non-flooded and semi-natural upland(Upland)at the three Gorges Reservoir Area.We measured six traits from 168 plant species in order to calculate community-level distribution of trait values.We expected that the altered hydrology in RRZ would have a profound effect on the community assembly process for the local plants.Important Findingsconsistent with previous work on community assembly,the dis-tribution of trait values(range,variance,kurtosis and the standard deviation of the distribution neighbor distances)within all plots was significantly lower than those from random distributions,indicat-ing that both habitat filtering and limiting similarity simultaneously shaped the distributions of traits and the assembly of plant commu-nities.considering the newly created RRZ relative to nearby sites,community assembly was different in two main ways.First,there was a large shift in the mean trait values.compared to Upland commu-nities,plant communities in the RRZ had higher mean specific leaf area(SLA),higher nitrogen per unit leaf mass(Nmass),and lower max-imum height(MH).Second,in the RRZ compared to the Upland,for the percentage of individual plots whose characteristic of trait values was lower than null distributions,the reductions in the community-level range for SLA,Nmass,nitrogen per unit leaf area(Narea)and phos-phorus per unit leaf area(Parea)were much larger,suggesting that the habitat filter in this newly created riparian zone was much stronger compared to longer established semi-natural upland vegetation.this stronger filter,and the restriction to a subset of plants with very similar trait values,has implications for predicting riparian ecosystems’responses to the hydrological alterations and further understanding for human’s effect on plant diversity and plant floras.