Contrasting interactions of remnant spruce trees with indigenous broadleaves in a partially converted stand from a former plantation

Abstract

Although important for both restoration and conservation provisions, little is known of the multispecific tree interactions involved in secondary spruce-broadleaf stands undergoing natural conversion from conifer monospecific plantations. We aimed to identify signals of such interactions in a partially converted, 60-year-old stand located in the Eastern Carpathians (northern Romania) and composed of sycamore, ash, maple, and wych elm (hereinafter, SAE), beech and remnant spruce trees.The position and size of all standing tree species individuals at least 1.50 m tall were measured within a 1.5 ha plot. Bivariate spatial pattern analysis, hierarchical Strauss models, and generalised linear squares regression were used for estimating tree neighbourhood interaction and interference.At fine scales, the beech sapling distribution was closely described through opposite models of attraction or inhibition with respect to spruce and SAE trees, respectively. The repulsion detected within the 3 m neighbourhood between SAE and spruce trees translated also in a significant inhibition process. This was in accordance with the negative effect of the nearest spruce on SAE tree growth. The significant segregation and spatial dissociation between beech and SAE trees was very likely related to the negative effect of neighbouring beech veterans on SAE tree diameter. Negative effects on spruce tree growth were only detected through interference with the nearest beech tree.In the given context of site conditions and stand development stage, the observed spatial interdependence and interference patterns were probably determined, to a large extent, by the intense interspecific competition for below-ground resources and light. The remnant spruce trees can act as both growth promoter and inhibitor in relation to the neighbouring beech and SAE trees, respectively. The spruce trees slow down the natural conversion to a mixed SAE stand by contributing to beech dominance, but that will eventually lead through negative feedback to the gradual exclusion of spruce.