Plant trait variation along environmental indicators to infer global change impacts.
One of the key principles for modeling future impacts of anthropogenic and climate changes on vegetation is to identify clear patterns and trends between plant functional traits and ecological drivers. The global spectrum of plant form and function outlines the major axes of variation and coordination among plant traits. We hypothesized that inter-specific plant trait variation at the regional scale should match axes of plant adaptation highlighted by the global spectrum, and that plant trait-environmental associations should be evident over ranges of environmental indicators corresponding to key drivers of future climate and land use changes in Southern Europe. To test our hypotheses, we analyzed a sample of 1095 plant species from Northern Italy, also characteristic of Southern European vegetation. We analyzed trends for four plant traits (canopy height, leaf area, specific leaf area, leaf nitrogen content) along meso- (temperature, continentality) and micro-climatic (light) ranges, as well as along soil ranges (moisture, reaction and nutrient content), by means of Landolt's environmental indicators. At the regional scale, the inter-specific variation of mean plant traits over ranges of environmental indicators confirmed the main axes of plant adaptation emphasized by the plant global spectrum. Leaf area and specific leaf area showed the largest sensitivity over ranges of all environmental indicators, while canopy heights were the most responsive to temperature values. Temperature, light conditions and nutrients were associated with clear effects on plant traits, underlining that responses to changes in land use and increased soil nutrient loading (sudden and abrupt changes) could trigger and strengthen responses to climate alteration (gradual changes). Scenarios for the next few decades in Southern Europe indicate increased temperature, nutrient availability and forest coverage that, according to our findings, will favor more 'acquisitive and fast growing' plants, also represented by subtropical invasive species.