Responses of southern European forest understorey species to macro and microclimatic variations

Forests can mitigate climate change effects on understorey plants by maintaining microclimatic conditions which create local refugia for many species under ongoing climate warming. However, these microrefugia are today reduced and threatened by increasing forest fragmentation, land use change and anthropogenic or natural modification of the canopy cover, reducing the temperature buffering capacity of forests and exacerbating the negative effects of climate change on plants. Especially for species with a narrow ecological niche, such as forest specialist plants, their ability to respond to climate change through habitat tracking remains questionable, particularly in highly fragmented forest landscapes. Here, we assessed the functional trait responses of eight understorey plant species from southern Europe through a multi-factorial experiment performed in two deciduous forest types (thermophilous and mesophilous forests in Italy and Belgium, respectively) and along macro and microclimatic gradients (in open vs dense forests and at the forest edge vs forest interior). A total of 576 individuals were transplanted within their range (Italy) and beyond their northern range limit (Belgium): 288 individuals derived from lowland forests and 288 from highland forests. Individuals of all species were sourced from Italian forest sites as seedlings, bulbs or rhizomes collected from local native populations and grown in nurseries for one year. Specifically, during two growing seasons, we investigated the individual responses in terms of survival, number of flowers, ground cover percentage, number of leaves, plant height, SLA and LMA. This allowed us to estimate infraspecific trait plasticity for all species along the experimental gradients. Preliminary results showed strong effects of forest structure and edge vs interior position on plant growth and performance with significant interactions between the two regions for most species, i.e., in contrasting ways depending on macroclimate.