Structure and dynamics of old-growth Pinus nigra stands in Southeast Europe

Abstract

Pinus nigra has a scattered but widespread distribution across Mediterranean mountain regions, where it has often been planted to restore degraded sites, yet few studies have examined the dynamics of natural P. nigra stands. Old-growth P. nigra stands often occur on precipitous, rugged locations in the Southeastern Alps and Dinaric Mountain range, providing unique opportunities to study their natural dynamics and disturbance history. We quantified the structure and composition and used dendroecological methods to reconstruct disturbance history, including samples of fire-scarred trees, in two old-growth stands located in Slovenia and Bosnia-Herzegovina. The study stands were dominated by P. nigra, but also included a number of other thermophilic tree species, as well as shade-tolerant species common in the surrounding mountain forests. Both sites had an irregular uneven-age structure with several pulses of recruitment, perhaps indicating the influence of past fire events, and P. nigra regeneration was relatively abundant (> 3000 stems ha−1). The most recent fires at each site burned in 1947 and 1969, and there was evidence of post-fire recruitment at the study sites. However, although tree cores sampled from fire-scarred trees suggest there were scattered, but infrequent fires over the past few centuries, we did not find evidence suggesting a regime of frequent recurring surface fires. The results suggest that rare surface fires may play a role in preventing successional replacement of P. nigra on productive sites, whereas steep, rocky sites likely support persistent populations in the absence of fire.