Long-term spruce canopy gaps reduce soil nematode functional diversity via taxa loss and trait convergence

Abstract

Forest gaps are widely implemented to enhance aboveground biodiversity within continuous cover forestry, yet their long-term impacts on soil fauna functional dynamics remain unclear. We used a trait-based framework to reveal how old gaps in subalpine spruce plantations affect the nematode functional identity (integrating body weight, trophic level, and lifespan) and functional richness (multidimensional functional space volume). We found that gaps reduced soil moisture, driving nematode communities toward fast-growing strategies characterized by smaller body weight (weighted mean biomass reduced 58%) and shorter lifespan (proportion of long-lived taxa decreased 66%). Moreover, nematode functional richness decreased by 38% in gaps through dual pathways: reduced taxa richness (relative importance 0.51) linked to litter stoichiometry; and moisture-regulated trait convergence (relative importance 0.32, eliminated resource-conserving strategists). Neither nematode functional identity nor functional richness affected soil multifunctionality, highlighting canopy loss may disrupt the nematode-soil functioning relationships. These findings indicate that understory development alone is insufficient to enhance belowground functionality, underscoring the need to align aboveground and belowground restoration goals in forestry practices.

Graphical abstract

Keywords

Forest gap / Planted forest / Soil nematode / Functional trait / Soil multifunctionality

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