Trait variation along a regenerative chronosequence in the herb layer of submediterranean forests

The aim of this paper is to assess the functional shifts of the herb layer in the submediterranean Ostrya carpinifolia coppiced forests (central Italy) along a coppicing rotation cycle. More specifically, the following questions were addressed: i) is there a pattern in functional trait composition of the herb layer along a regeneration chronosequence?; ii) which traits states differentiate each regeneration stage?; iii) are patterns of trait state variation related to the change of the environmental conditions? Species cover percentage was recorded in 54 plots (20 m 20 m) with homogeneous ecological conditions. Relevés, ordered on the basis of the time since the last coppicing event and grouped into three age classes, were analysed with regard to trait variation, based on species absolute and relative abundance. Differences in light, temperature, soil moisture, and nutrients bioindicator values between consecutive regeneration stages were tested using the non-parametric ManneWhitney U-test. Multi-response permutation procedures (MRPP) revealed statistically significant separation between young and intermediate-aged stands with regard to most traits. Indicator species analysis (ISA) highlighted indicator trait states, which were filtered, along the chronosequence, by changes in environmental conditions. Redundancy analysis (RDA) revealed that light intensity had the greatest effect on traits states variation from the first to the second regeneration stage, while variation from the second to the third age classes was affected by temperature. Young stands were differentiated by short cycle species with acquisitive strategies that only propagated by sexual reproduction, with light seeds, summer green and overwintering green leaves, and a long flowering duration. Intermediate-aged and mature stands were characterized by traits associated with early leaf and flower production, high persistence in time, and showing retentive strategies aimed at resource storage (e.g., geophytes, spring green leaves, rhizomes, and mesomorphic/hygromorphic leaves).