The influence of overhead shade on the shade mortality of Abies xborisii-regis Mattf. seedlings and saplings in the central Rhodope mountains of north-eastern Greece

Abstract

In order to examine how overhead shade affects the shade mortality of Abies xborisii-regis Mattf. seedlings and saplings in the central Rhodope mountains of Greece, two plots of 0.1 ha were established in two stands. In each plot, diameter in cm and height in m of all living trees was recorded. Over 50 increment cores and cross sections were used to determine the stand age structure. Moreover, in an area of 0.15–0.2 ha in each stand, all dead A. xborisii-regis trees were cut, and categorized according to their position in the vertical stand structure. In 91 of them, the ring width was measured, to the nearest 0.01 mm, in the stem base radius. The dead A. xborisii-regis trees showed high persistence in deep shade and very low growth rates. The various overhead shade regimes, as a result from the stand's vertical profiles, strongly affected the shade mortality of A. xborisii-regis seedlings and saplings. The major influence refers to the vertical arrangement of dead A. xborisii-regis trees in relation to the stand storeys. Consequently, it was the different overhead shade regimes that most strongly determined the growth pattern of the dead trees in the last years of their life. In particular, most of the dead A. xborisii-regis trees were close to living A. xborisii-regis trees, and died through lasting suppression. The top and branches of the dead trees were just below the foliage of taller living trees belonging to the same stratum. On the contrary, in the case of dead A. xborisii-regis trees whose branches and top were far below a stratum created by the foliage of living trees, only 32% died through lasting suppression, the rest experienced at least one growth increase, in terms of ring width, or the synergistic effect of a growth increase and a growth reduction, in the last 5 years of their life.