Dimensional relationships of naturally established European beech trees beneath Scots pine and Silver birch canopy

Abstract

Huge areas of the mid-elevation mountains of the French Massif central were abandoned by agriculture after grazing abandonment. They were colonized by pioneer trees, like Scots pine and Silver birch, that have formed monospecific stands in the space of a few years. In such stands beech ( Fagus sylvatica L.), a late-sucessional species, has been established naturally. In order to study beech growth and development, beech trees of various ages were sampled under birch and Scots pine canopy. Dimensions, age, radial and height growth of the subject beech tree and dimensions of branches at the top of the canopy were measured. Local competition around each beech was assessed with competition indices and below-ground competition was quantified by root biomass measurements. Despite slightly greater light availability under birch than under Scots pine, beech saplings exhibited superior growth and dimensions at a given age under Scots pine than under birch. However, this trend tended to decrease while beech was aging and started penetrating into the upper tree layer. Although, competition index values were significantly different between birch and Scots pine stands, growth or size were reduced by competition in the same proportions when comparing the two types of cover. Beech fine root biomass was comparable for young and intermediate trees, whereas fine root biomass of both competitor trees and ground vegetation was clearly more abundant under birch. Lastly, branching pattern only exhibited significant differences for young trees, branches were more vertically distributed and of lower dimensions beneath birch canopy than beneath pine canopy. We concluded that beech growth was, in the first stage, more limited under birch than under pine due to a higher below-ground competition.