When does dead wood turn into a substrate for spruce replacement?

Question: How many years must elapse for freshly fallen Picea abies stems to be transformed into a substrate for P. abies recruitment? Location: Natural sub‐alpine spruce forest, 1200–1300 m a.s.l., western Carpathians, Poland. Methods: Coarse woody debris (CWD) was measured on nine plots with a total area of 4.3 ha. All individuals of P. abies regeneration growing on dead wood were counted and their age was estimated. Decay rate of logs was determined using dendrochronological cross‐dating of samples from logs in different decay stages. Results: Although CWD covered only 4% of the forest floor, 43% of the saplings were growing on decaying logs and stumps. The highest abundance of P. abies recruitment occurs on logs 30–60 years after tree death, when wood is in decay stages no. 4–7 (on an 8 degree decay scale). However, much earlier colonization is possible. The first seedlings may germinate on a log during the second decade after tree death and survive for decades. Their slow growth is possibly due to the gradual progressive decomposition of wood. Conclusions: This study confirms the importance of decaying wood for P. abies recruitment. The decaying logs exhibit continuous and favourable conditions for the germination of P. abies seeds throughout their decay process. Logs, irrespective of their decay stage and age, are colonized by young seedlings. This recruitment bank is constantly renewed.