Italy is among the European countries with the greatest plant diversity due to both a great environmental heterogeneity and a long history of man-environment interactions. Trait-based approaches to ecological studies have developed greatly over recent decades worldwide, although several issues concerning the relationships between plant functional traits and the environment still lack sufficient empirical evaluation. In order to draw insights on the association between plant functional traits and direct and indirect human and natural pressures on the environmental drivers, here we summarize the existing knowledge on this topic by reviewing the results of studies performed in Italy adopting a functional trait approach on vascular plants, briophytes and lichens. Although we recorded trait measurements for 1418 taxa, our review highlighted some major gaps in plant traits knowledge: Mediterranean ecosystems are poorly represented; traits related to belowground organs are still overlooked; traits measurements for bryophytes and lichens are lacking. Finally, intraspecific variation has been little studied at community level so far. We conclude highlighting the need of approaches evaluating trait-environment relationship at large spatial and temporal scales and the need of a more effective contribution to online databases to tie more firmly Italian researchers to international scientific networks on plant traits.

40The study of plant trait-environment links is rarely focused on traits that inform on space occupancy 41 and resprouting (both affecting plant persistence), especially in forest understories. Traits that can 42 effectively capture such key functions are associated with clonality and bud banks. We hypothesized 43 that: 1) climate is the main driver of clonal and bud bank traits, 2) traits related to space occupancy 44 (e.g., greater lateral spread) are more important in more mesic, richer soils forests, and 3) traits 45 related to resprouting ability (e.g., larger bud bank) are more important in more intensively and 46 recently managed forests. We addressed these hypotheses by analysing a unique dataset that is 47 statistically representative of Italian forests heterogeneity and includes three biogeographic regions 48 (Alpine, Continental, Mediterranean). We recorded data for sixteen climatic, soil and management 49 variables. We calculated community weighted mean (CWM) values of seven clonal and bud bank 50 traits for the forest understory vegetation. We used i) redundancy analysis to assess trait-51 environment relations, and ii) variance partitioning analyses to identifying the relative role of 52 different groups of abiotic variables on CWM variation of all traits combined together, as well as 53 clonal and bud bank traits taken separately. Climate alone had a pervasive effect in determining 54 patterns of clonal and bud bank traits in Italian forest understories, mainly related to the effects of 55 temperature extremes and seasonality. Unexpectedly, soil and management factors alone showed 56 marginal effects on clonal and bud bank traits. However, soil features influenced trait patterns when 57 joined with climate. Our results confirmed that, at the biogeographic scale, climate played a lion-58 share role in determining persistence-related traits of forest-floor plants. At the local-scale, other 59 interplaying factors (e.g., management, soil variables) may come into play in shaping patterns of the 60 studied plant traits. This study stressed the importance of examining functional trait patterns along 61 complex environmental gradients. 62 63 64

Question In functional biogeography studies, generalizable patterns in the relationship between plant traits and the environment have yet to emerge. Local drivers (i.e., soil, land use, vegetation structure) can increase our understanding of the trait–environment relationship. What is the role of climate and local drivers in shaping abundance‐weighted trait patterns of forest understories at biogeographic scales? Location Italian forests. Methods We selected 201 sites that are statistically representative for the heterogeneity of Italian forests across three biogeographic regions (alpine, continental, and mediterranean). Understorey vegetation was recorded for each site on an area of 400 m2, together with 25 environmental variables related to climate, soil, land use and forest structure. Specific leaf area (SLA), plant height (H) and seed mass (SM) were obtained from databases. Community‐weighted mean (CWM) values were calculated. Variance partitioning was used to identify the relative role of groups of environmental variables on the CWM of traits. Generalized Additive Models were used to assess the relationship between traits and single variables. Results Climate alone and climate–soil interactions explained the largest proportion of the variation of all the traits (13.7% to 22.8%). Temperature‐related factors as well as soil N and P availability were the climatic and edaphic explanatory variables most correlated to trait variation. Forest structure and land use accounted for a smaller percentage of the variation in traits. Land‐use factors alone were important in explaining only SLA variation. Conclusions While climate plays a major role in trait–environment relationships in forest understories, our results highlighted the need to integrate at least soil properties as local drivers of trait variation in broad scale functional biogeography studies of these systems.

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