Restoration potential of native forests after removal of Picea abies plantations

Abstract

Coniferous plantations may reduce biodiversity and homogenise environmental conditions but there is a lack of knowledge on the restoration potential of such sites. We assess whether first generation plantation impacts on soil and biodiversity are reversible. The study was carried out in western Norway and we compared species composition, alpha and beta diversity of vascular plants and bryophytes, and soil conditions on five sites of 4-year old wind-felled clearings and adjacent, remnant Norway spruce (Picea abies) plantations. Local native birch (Betula pubescens) forests provided a reference point for assessing the restoration potential of the Norway spruce plantations. We found that species composition in the wind-felled clearings quickly developed similarities to the local birch forests. A rise in humus pH, calcium concentrations and available nitrogen (total N in percentage of loss on ignition), indicates that one rotation of Norway spruce plantations has not imposed long-term impairment of soil conditions. After removal of the plantation tree layer, mean species number per plot (alpha diversity) increased for vascular plants but remained unchanged for bryophytes. Heterogeneity, in terms of beta diversity, and the variance of some soil elements (calcium and magnesium) increased, and beta diversity trends were similar for both vascular plants and bryophytes. During the course of succession, we predict that species composition and vascular plant alpha and beta diversity in wind-felled clearings of Norway spruce plantations may stabilise at levels similar to native birch forests.