Strategie adattive delle piante nella diversità oscura della vegetazione forestale in provincia di Varese (Lombardia) = Plant adaptive strategies in the dark diversity of forest vegetation in the province of Varese (Lombardy)

Background and Aims – Biodiversity has long been at the center of ecological research, however there is still no clear understanding of why some species are absent in a given location, although they could be potentially present. This undetectable component of biodiversity is defined as «dark diversity», and its study can provide insights into the missing functions of an ecosystem. Methods – We carried out 47 relevés distributed randomly within a study area of 10 km radius in the province of Varese (Lombardy, Northern Italy), and representative of eight types of broad-leaved deciduous forest vegetation: speciespoor and species-rich acidophilic beech forests (Luzulo-Fagion), basophilic beech forests (Aremonio-Fagion), neutrophilic beech forests (Asperulo-Fagetum), oak and birch forests (Querco-Betuletum s.l.), oak and ash tree forests (Querco-Fraxinetum s.l.), mixed ravine and slope forests (Tilio-Acerion) and mixed recolonization forests (Corylo-Fraxinetalia). For each relief, we calculated the community weighted mean of observed and dark diversity of three plant functional traits (LA, LDMC and SLA) and Grime’s CSR ecological strategies. Results – The highest probability of dark diversity was identified for mixed recolonization forests (mean value = 0.54), while the lowest was evident in both species-poor and speciesrich acidophilic beech forests (mean value = 0.42). In general, dark diversity exhibited a high degree of ruderality (R) as opposed to a selection towards more competitive (C) strategies in the observed diversity (p < 0.001 for both R and C). Conclusions – We hypothesized that the balance of competitiveness and ruderality between observed and dark diversity could be the basis of the properties of broad-leaved forest plant communities respectively linked to resistance and resilience.