The population structure of the lichen Lobaria pulmonaria in the middle boreal forests depends on the time-since-disturbance

The population structure of the lichen Lobaria pulmonaria (L.) Hoffm. was analyzed in the Vodlozersky National Park (Karelia, Russia), for middle boreal forest stands having a time-since-disturbance spanning 80 to 450 years. To estimate the age of the last disturbance, a method of evaluation for the tree population structure was applied. The forest stand communities belonged to a successional series: middle-aged aspen – mixed aspen-spruce – pre-climax spruce – climax (old-growth) spruce forest. All thalli (1055) of L. pulmonaria from all substrate units (165, separately standing or lying trees and shrubs) were described within 7 sample plots of 1 ha. For each thallus, the area (cm2) and the functional-age group were determined. The number of Lobaria thalli per ha, number of substrate units, number of substrate types (living, standing dead and lying dead trees of different species) colonized by L. pulmonaria, as well as number of substrate types on which the lichen had completed its life cycle increased with time-since-disturbance.

What Might a Sustainable Population of Trees in Wood-Pasture Sites Look Like?

Wood-pastures are important for their open-ground biodiversity and for the old trees they contain. However, younger trees to replace the current generation of old trees are often scarce, a potential threat to the future of the habitat mosaic and of species dependent on the trees. A simple model was used to illustrate how many younger trees might be expected under different assumptions of desired final density of old trees and rates of loss as trees age for an oak-dominated wood-pasture. From these the overall canopy cover of the landscape was estimated under an active pollarding regime and where the trees grow to full crown size. Canopy cover was often five times as great under full crown as under a pollarding regime; much of the canopy cover was in the younger (often missing) cohorts. The openness of current wood-pastures is in part a consequence of the absence of a sustainable tree population structure. Some protected sites may be too small to allow space for the missing generation of trees and at the same time retain current levels of openness. Analogies between current wood-pasture structures and ‘natural wood-pastures’ of the pre-Neolithic era must take account of the missing generations of trees.