Trait-based recovery of insect functional diversity following pine removal in a shrubland biodiversity hotspot

Abstract

Introduction: A primary goal of habitat restoration is the return of both taxonomic and functional diversity to support ecosystem resilience and functioning. This study assessed how insect functional biodiversity (focusing on beetles [Coleoptera] and ants [Formicidae]) responds to invasive pine (Pinus spp.) removal, in a Mediterranean-type ecosystem (the Cape Floristic Region). Objectives: In Table Mountain National Park, we assessed morphological traits of beetles and ants across four biotopes: active pine plantations, areas cleared 10 years ago (“new recovery”), cleared 30 years ago (“old recovery”), and areas never planted with pine (“pristine fynbos”) to evaluate how functional trait composition responds to passive restoration over time. Methods: Insects were sampled using a combination of pan traps, pitfall traps, and a vacuum sampler, with sampling conducted over three seasons. Results: Our results show striking differences in recovery trajectories. Functional diversity of both taxa was lowest in pine plantations. Beetle assemblages showed relatively rapid functional recovery, with diversity in recovery stages comparable to pristine fynbos within a decade. Herbivorous beetles recovered faster than predatory species, suggesting feeding guilds as useful recovery indicators. Among ants, ground-nesting species showed faster functional recovery during early restoration stages, whereas opportunistic nesters recovered more slowly, reflecting differing ecological requirements. Overall, ant functional diversity remained greatest in pristine fynbos and showed limited recovery even after 30 years. Conclusions: These findings highlight that although beetle functional diversity can recover within one decade, ant assemblages may require considerably longer.