Multifaceted diversity changes reveal community assembly mechanisms during early stages of post-logging forest succession

Abstract

Plant succession is a fundamental process of vegetation recovery on disturbed sites. Elucidating its mechanisms remains a challenge as succession is influenced by stochastic and deterministic processes related to abiotic and biotic filters. Here, we use a multifaceted diversity approach to reveal mechanisms of successional changes in European oak-hornbeam forests during the first 10 years after selective logging. As the mechanisms controlling succession may depend upon initial abiotic conditions and colonization potential of the surrounding vegetation, we compare changes in taxonomic, functional, and phylogenetic diversity between clearings connected with open habitats and those isolated inside forests. Despite fewer dispersal barriers and higher biomass production in connected clearings, similar mechanisms initially governed succession in post-logging sites. Both clearings had low taxonomic and functional diversity in the first year of succession, as evidenced by significant trait convergence, caused by the legacy of interactions between overstory and understory vegetation in pre-disturbance closed-canopy forests. Colonization by short-lived and light-demanding species in the second and third years after logging has markedly increased the overall taxonomic and functional diversity, as evidenced by significant trait divergence. Connected clearings had higher functional but lower taxonomic and phylogenetic diversity than isolated clearings from the fourth to ten years of succession, probably due to intense competition in more productive habitats. All diversity facets markedly decreased in the last years due to increasing asymmetric competition from regenerating trees. The successional processes were largely deterministic, driven by species’ life-history strategies and biotic interactions (competition) rather than abiotic constraints and stochastic events.

Biodiversity change in light of succession theory

“…Note that the above scenario is only one of many possibles – for example, plant diversity could drop in mid‐succession due to competition while productivity is high (e.g. in temperate forest secondary successions; Hilmers et al 2018, Lanta et al 2023), or diversity could increase asymptotically while productivity declines (e.g. in tropical forest secondary successions; Magnabosco Marra et al 2018, Rozendaal et al 2019), leading to a similar decoupling of changes in diversity and functioning.…”

Impact of Coppicing on Microclimate and Understorey Vegetation Diversity in an Ancient Mediterranean Oak Forest

“…Converging evidence was provided by the PD.ses and MNTD.ses indices which pointed to a decrease of phylogenetic diversity and evenness in the coppice understory. Phylogenetic clustering in forest plant communities often results from the pressure of environmental filters that select related species adapted to the local constraints (Selvi et al, 2016;Aldana et al, 2017;Ottaviani et al, 2019;Lazzaro et al, 2020;Lanta et al, 2023). If adaptations to selective environments involve complex traits, these are more likely to be shared by related co-occurring species than expected under neutral evolution, leading to a phylogenetic signal of these traits (Crisp and Cook, 2012).…”

“…Examining ecosystem responses to habitat changes and disturbances should always consider the multifaceted nature of biodiversity because facets can be affected in different ways . In temperate forests, for example, understory species richness is usually positively affected by light availability at the forest floor (Suding, 2001;Hamřík et al, 2023), while harsher environmental conditions may lead to a reduction of phylogenetic and functional diversity (Ottaviani et al, 2019;Lanta et al, 2023). Overall, we know little on how coppicing in thermophilous deciduous forests impacts on these understory diversity facets, despite the extent of this forest type in Europe (40 % of the ICP Forests Level I plots in Italy; International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests; Barbati et al, 2007), its rich flora and vulnerability to increasing heat and drought (Pollastrini et al, 2019;Iacopetti et al, 2021).…”

“…For a deeper understanding of the effects of coppicing we focused on all the three major dimensions of diversity, taxonomic, phylogenetic and functional, as these often respond differently to environmental changes and ecological factors . Accounting for stand structure, light and soil conditions, we could therefore test the following hypotheses: i) air and soil temperature buffering is lower in coppice stands because of lower canopy density; ii) coppicing positively affects understorey taxonomic diversity by increasing species richness (SR) due to a greater proportion of generalist and thermophilous plants; iii) understorey phylogenetic and functional diversity are lower in coppice stands, since more phylogenetically and functionally diverse communities commonly develop in more favourable conditions (Lanta et al, 2023).…”