Restoration of former agricultural fields in Estonia: comparative growth of planted and naturally regenerated birch

摘要

We examined the growth of birch (Betula pendula Roth. and Betula pubescens Ehrh.) regenerated on 22 former agricultural fields in Estonia. Birch stands on half of the former fields were planted, while the other half were from natural regeneration. After 2 years of data collection, stem and crown variables were correlated with growth indices, revealing differences between individual stem growth in plantations and naturally regenerated stands. Live crown ratios of birch correlated with growth variables in plantations, but not in natural stands. This finding is attributed to differences in competition levels and stand densities between natural and planted stands. The growth model was composed using increments of consecutive years for plantations (R-2 = 0.37). The live crown ratio was selected as an additional variable for multiple regression (R-2 = 0.35). Our results are discussed within the context of ecological, growth and yield, and economic aspects of establishing forests on former agricultural fields.