Abstract
Abstract Forest regrowth following farmland (agriculture and pasture) abandonment has been positively associated with a number of processes including the regulation of hydrological cycling, the enhancement of soil functioning and an increase in forest productivity and carbon (C) sequestration. Although these changes in ecosystem functioning post‐farmland abandonment have been observed in multiple locations and studies, the ecophysiological basis underpinning these patterns remains unclear. Here, we examine whether increased forest expansion following pastureland abandonment is associated with greater water‐use efficiency (WUE) and legacies from previous land use in terms of nitrogen (N) availability. We thus explored differences in leaf traits and N availability between recently established (post‐1950) beech Fagus sylvatica (L.) forests on former pastureland and long‐established beech forests (pre‐1950). The investigated leaf traits were SLA, leaf N concentration (%N) and intrinsic WUE (iWUE, i.e. the ratio between photosynthesis and stomatal conductance); as well, leaf and soil stable N isotope composition (δ15N) and total %N were used to assess changes in N availability. Finally, we compared the correlation strength between the above‐mentioned parameters and those associated with tree productivity (wood density and basal area increment, BAI) and the richness of ectomycorrhizal fungi (ECM) in these two forest types. Recent forests had greater iWUE than long‐established forests, which was associated more with lower SLA than leaf %N. Leaf and soil δ15N were more robust proxies than %N for detecting differences in N availability. Less negative leaf and soil δ15N values in recent versus long‐established forests suggest, on the one hand, greater N availability, probably due to higher historical N input originating from animal excreta on these former pasturelands, and, on the other hand, an increase in N loss pathways. Our results point to greater correlations between leaf δ15N, tree iWUE and productivity in recent forests than in long‐established forests, thereby suggesting a close link between C and N cycles. Our findings also highlight different N dynamics between the two forest types, with recent forests showing ‘leaky’ N cycling wherever lower N retention by trees and associated ECM fungi occurs as a legacy of previous land use. A free Plain Language Summary can be found within the Supporting Information of this article.
Highlights
Natural forest regeneration associated with climate and land-use changes such as the abandonment of farmland—the focus of this study—is having profound effects on the landscape and is leading globally to a shift towards increased forest cover (FAO, 2020)
Results from linear mixed effects models (LMMs) indicated that forest type had only a significant effect for δ15Ns, as estimates in recent compared to long- established forests were less negative (Table 4)
Established forests showed a negative correlation between intrinsic water-use efficiency (iWUE) and SLA, and positive correlations for SLA with %Nl and Δ13Cl, as well as positive correlations for δ15Nl with %Nl and LA with δ15Nl and %Nl
Summary
Natural forest regeneration associated with climate and land-use changes such as the abandonment of farmland—the focus of this study—is having profound effects on the landscape and is leading globally to a shift towards increased forest cover (FAO, 2020). Greater nutrient availability as a legacy of past land use enhances tree growth and productivity, with 25%–35% more plant biomass reported in forests established after land abandonment 50– 100 years ago than in long-established pre-existing forests (Freschet et al, 2014; Vilà-Cabrera et al, 2017). To assess some of these uncertainties, our study investigated differences along an altitudinal gradient in ecophysiological strategies and N dynamics between beech Fagus sylvatica (L.) forests that have recently become established (post-1950) on former pastureland and long-established beech forests (pre- 1950) We compared these two forest types in terms of the leaf traits associated with plant physiology (i.e. SLA, leaf area, LA, stable C isotope composition, δ13C) and N availability (i.e. leaf N concentration, %N, stable N isotope composition, δ15N). We hypothesized that (3) along the elevation gradient, a reduction in iWUE with increasing altitude would be observed in both recent and long-established forests, due to improvement in moisture conditions
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have