Ecological Factors Influencing Norway Spruce Regeneration on Nurse Logs in a Subalpine Virgin Forest

Abstract

Regeneration of Picea abies in high-elevation mountain forests often depends on the presence of coarse woody debris (CWD), as logs provide sites with more favorable conditions for spruce regeneration compared to the forest floor. However, there is little quantitative knowledge on the factors that are conducive to or hindering spruce establishment on CWD. We examined spruce regeneration on CWD by sampling 303 plots (50 cm × 50 cm each) on 56 downed logs in a virgin forest in the Swiss Alps. Variables describing microsite conditions were measured, and fungi were isolated from wood samples. To investigate the relationship between the ecological factors and establishment success, two models were fitted with seedling and sapling density as response variables, respectively. Besides log diameter, the models identified different ecological factors as significant for seedling and sapling establishment, i.e., regeneration depends on different factors in different development stages. Seedling density depended on the type of rot, log inclination, and decay stage. Sapling density depended mainly on light availability, cover by bark and moss, the time of tree fall, and the distance between the log surface and the forest floor. A total of 22 polypore fungi were isolated from the wood samples, four of them being threatened species. White-and brown-rot fungi were found in all decay stages. The visual assessment of the type of rot in the field corresponded in only 15% of cases to the type of rot caused by the isolated fungi; hence caution is needed when making field assessments of rot types.

Evidence of elevation-specific growth changes of spruce, fir, and beech in European mixed mountain forests during the last three centuries

“…Norway spruce may also have a chance to establish under disturbances that cause abrupt opening of the previously dense canopy and exposure of the soil. In addition, spruce regeneration depends on nurse logs in some stand conditions (Stroheker et al 2018). Where there is not yet impeding competition by already established fir and beech, spruce regeneration may benefit from its ability to quickly establish on open mineral soil and establish successfully, although the further development may be questionable because of the previously mentioned restrictions.…”

Applying molecular and genetic methods to trees and their fungal communities

“…and detritivorous soil meso- and macrofauna with multiple pathways of turnover and accumulations of intermediate microbial and faunal transformation products, which is further influenced in interactions with the vegetation, with soil properties and (bio)chemistry, and also by climate parameters (Prescott and Vesterdal 2021 ; Veldkamp et al 2020 ). What is more, coarse wooden material degradation will prepare fermented porous-structured moisture-retaining nutritious grounds for better germination and rooting of seedlings and anchorage of developing trees (Fukasawa et al 2017 , 2020 ; Stroheker et al 2018 ) and provides also habitat for saproxylic communities (Fukasawa 2021 ). Seed beds of decaying logs or stumps may harbor less fungal seed pathogens and they can provide favoring associations of N 2 -fixing bacteria with specific selections of mycorrhiza-promoting fungi (Huusko et al 2015 ; Izumi et al 2006 ; Tedersoo et al 2008 ; Willis and Walters 2018 ).…”