Colonization and extinction patterns of wood-decaying fungi in a boreal old-growth Picea abies forest

1. Wood-decaying fungi are ubiquitous and functionally important organisms within forest ecosystems world-wide, but remarkably little is known of their population dynamics in relation to the dynamics of their host substrates. Living in transient environments, where local extinctions are caused by gradual substrate (patch) destruction or deterioration due to wood decomposition, the long-term persistence of these species requires successful colonization of new patches. 2. During a 6-year period, we examined the colonization-extinction dynamics of wood-decaying fungi (Aphyllophorales: Polyporaceae and Corticiaceae) in relation to the spatiotemporal distribution of host logs within a boreal old-growth Norway spruce (Picea abies) forest. 3. The dynamics of the species studied were strongly influenced by both local log characteristics (within patch) and connectivity (between patch). Several species (e.g. Asterodon ferruginosus, Phellinus ferrugineofuscus, P. viticola, Phlebia centrifuga) showed a positive effect of connectivity, mainly colonizing logs in the vicinity of previously occupied logs. This implies that some wood-decaying fungi may be dispersal limited in terms of successful colonizations. The relative importance of patch conditions and connectivity was however, highly species specific. 4. Our results further illustrate the importance of life-strategies adopted by species that are present during different stages of wood decomposition. Early colonizers were primarily affected by the stage of decomposition; secondary colonizers were affected by a variety of within patch and/or between patch variables, maintaining high species coexistence within intermediate stages of decay. Phellinus nigrolimitatus was the dominant polyporous decayer at the final stages of decomposition, clearly gaining a competitive advantage from specializing on highly decomposed wood and having very low mean annual mortality rates. 5. Local extinction rates were higher on small diameter logs than large diameter logs, and generally increased as decay proceeded, illustrating the importance of deterministic patch destruction due to wood decomposition. 6. Synthesis. The fungi-log study system was highly dynamic, illustrating that both characteristics and spatiotemporal availability of logs are important in explaining the distribution patterns and population dynamics of wood-decaying fungal communities. The result implies that the dynamics of some wood-decaying fungi can be characterized a