Impact of climate change on forest reproduction and regeneration – FOREPRO

The lack of robust understanding of the determinants of tree reproduction and forest regeneration has restricted the effectiveness of forest management practices in many countries worldwide. Masting, a highly variable seed production over years and synchronized within populations, occurs in many forest tree species and has dramatic impact on the demographic of seed consumers and forest regeneration. Providing robust projections of forest dynamics in the future requires predicting how climate change and societal decisions will affect not only masting, but also the demography of seed-consumers and their effect on forest regeneration. In this project, we will study tree reproduction in oak species, that are of major ecological and economic importance. We will focus on three species in contrasted environments (the temperate deciduous pedunculate and sessile oaks and the Mediterranean holm oak) and on their interaction with acorn specialist insects (four weevil sibling species) that negatively impact seed germination and hence, early stages of forest regeneration. FOREPRO aims at quantifying the impact of societal decisions on seed production and forest regeneration and providing guidance to sustainable forest management in the context of climate change through acquiring sound knowledge and accurate tools for regeneration policies. The research program of FOREPRO is organized along three work packages:
(1) The physiological and climatic determinants of oak masting will be identified (i) by assessing the effects of tree resource availability on reproduction and growth, (ii) by measuring the relative weight of pollen limitation and weather vetoes on massive fruiting failure and fruiting synchrony and (iii) by assessing the environmental and genetic determinism of seed production. In addition, we will analyze the impact of forest management practices (i.e., plantation density, soil fertilization) on seed production.
(2) After evaluating the impact of seeding intensity on regeneration success, we will analyze how the different components of masting make oaks efficient at controlling the dynamics of acorn parasitic insect communities, including species with greatly diverse life history traits.
(3) We will develop new mechanistic models of masting that implement well-established ecophysiological processes, make projections about the future of masting and regeneration potential of oak forests, and provide avenues for forest management innovation.
This program will provide forest managers with knowledge about mechanisms of masting and decision support tools for optimizing oak forest regeneration strategies in the context of climate change. To address this challenge, FOREPRO will develop a new integrative approach based on complementary investigations : (i) field experiments (tree density and fertilizer use, partial rain exclusion, fruit removal, hand pollination associated with DNA metabarcoding); (ii) the analysis and collection of consistent data on spatially extended network of field sites (individually-based monitoring of male and female flowering, fruiting, growth and phenology, the airborne pollen amount, insect community dynamics and regeneration success), (iii) biochemical assays (nitrogen and carbon content of flowers and fruits), and finally (iv) the development of four inter-connected models (two ecophysiological models, CASTANEA, PHENOFIT, one Resource Budget Model for simulating masting and one community stochastic dynamic model for insects).
FOREPRO is at the interface between research and public action and should bring significant progress in our understanding and management of oak forest regeneration. It was built and will be developed thanks to the strong complementarity of partners from research and management fields (four research labs: LBBE -Lyon-, BioGeCo -Bordeaux-, CEFE -Montpellier-, ESE –Orsay-, and a management agency : ONF).