Light-mediated influence of three understorey species (Calluna vulgaris, Pteridium aquilinum, Molinia caerulea) on the growth of Pinus sylvestris seedlings

Abstract

Pinus sylvestris is a pioneer species and as such is relatively light-demanding. Therefore, its natural regeneration may be inhibited by some forest understorey species that develop with light and can then reduce light as well as soil resources (i.e. nutrients and water) availability for the pine seedlings. To better quantify these effects, we designed two experiments in a nursery. The first one aimed at studying the influence of density of three common understorey species in temperate forests (Calluna vulgaris, Pteridium aquilinum and Molinia caerulea) on pine seedlings survival and growth. The purpose of the second experiment was to quantify the development of these three species relatively to light that varied in our experiment from 6 to 100% of relative light. An increase in weed density, i.e. a concomitant decrease of light availability and soil moisture content, resulted in reduced pine seedlings growth (diameter and biomass) and higher stem height/diameter ratio but had no significant effect on seedlings survival. Height and cover of the three weedy species followed a non linear relationship relative to light availability. Results are discussed according to the quantity of available light as well as its quality assessed through the red/far red ratio, both for the pine seedlings development and weed species height and cover, and their interactions.