Land-use legacies affect Norway spruce Picea abies colonization on abandoned marginal agricultural land in Eastern Baltics

Understanding forest regeneration in relation to land-use legacies is an important goal of research on global environmental changes and future ecosystem patterns. Recent findings on spruce regeneration on abandoned agricultural land showed it to be linked to land-use legacies involving increased soil fertility by fertilization. We argue that indirect drivers like land-use changes from arable land to grassland, which affect soil fertility and vegetation density, could also be involved. We selected a study area where changes in land-use involved gradual abandonment of agricultural intervention and created substantial heterogeneity in forest stand age and species composition. Over a 60-year period, the tree colonization pattern changed from deciduous tree species in 1950–1970 to Norway spruce in the later period. Generalized linear logistic regression models were generated to explain the presence of deciduous tree and spruce colonization in relation to soil and land-use factors. The importance of plant community composition on establishment of tree species was studied by Cluster analysis and unconstrained ordination. Deciduous forest development was negatively related to past agricultural use as arable land and positively related to extensively used grasslands (meadows and pastures) and no soil factors entered the explanatory model. Ecological amplitude of deciduous tree species and differing patterns of agricultural land management at landscape and farm scales are discussed as possible explanations. Spruce regeneration was significantly explained by soil moisture and agricultural use as arable land followed by conversion to grassland. We conclude that spruce regeneration is a phenomenon characteristic not only for previously fertilized agricultural land but also for marginal agricultural land if the management ensures development of dense herbaceous layer.