Tree mortality and deadwood dynamics in late-successional boreal forests

Abstract

Here I aimed at quantifying the main components of deadwood dynamics, i.e. tree mortality, deadwood pools, and their decomposition, in late-successional boreal forests. I focused on standing dead trees in three stand types dominated by Picea mariana and Abies balsamea in eastern Canada, and on standing and down dead trees in Picea abiesdominated stands in three areas in Northern Europe.Dead and living trees were measured on five sample plots of 1.6-ha size in each study area and stand type. Stem disks from dead trees were sampled to determine wood density and year of death, using dendrochronological methods. The results were applied to reconstruct past tree mortality and to model deadwood decay class dynamics.Site productivity, stand developmental stage, and the occurrence of episodic tree mortality influenced deadwood volume and quality. In all study areas tree mortality was continuous, leading to continuity in deadwood decay stage distribution. Episodic tree mortality due to either autogenic or allogenic causes influenced deadwood volume and quality in all but one study area. However, regardless of productivity and disturbance history deadwood was abundant, accounting for 20-53% of total wood volume in European study areas, and 15-27% of total standing volume in eastern Canada. Deadwood was a persistent structural component, since its expected residence time in early-and midstages of decay was 18 yr even in the area with the most rapid decomposition.The results indicated that in the absence of episodic tree mortality, stands may eventually develop to a steady state, in which deadwood volume fluctuates around an equilibrium state. However, in many forests deadwood is naturally variable, due to recurrent moderateseverity disturbances. This variability, the continuous tree mortality, and variation in rates of wood decomposition determine the dynamics and availability of deadwood as a habitat and carbon storage medium in boreal coniferous forest ecosystems.

Assessment of tree mortality on the Estonian Network of Forest Research Plots/ Puude väljalangevuse hindamine metsa kasvukäigu püsiproovitükkidel

“…Depending on disturbance factors (storms, increase in insect population, etc. ), they may cause the death of trees or the physiological weakening of trees (Aakala, 2010). The process of dying is usually slow in the beginning and the weakening of a tree may take years, but after the tree has been populated by secondary pests, pest groups start varying quickly, thus accelerating the process of dying ).…”

Coarse woody debris in late-successional Picea abies forests in northern Europe: Variability in quantities and models of decay class dynamics

“…Data for the study were collected from three areas in northern Europe that were known to hold unmanaged late-successional P. abies-dominated forests, and also whose past disturbance histories were known (Aakala et al, 2009;Caron et al, 2009;Aakala, 2010) (Fig. 1).…”

“…The study was conducted in three geographically distinct areas in northern Europe that were known to hold unmanaged forests, located in northern Finland, and in the Murmansk and Arkhangelsk provinces of northwestern Russia. The areas differed in their climatic and edaphic conditions and, based on our earlier studies from the same areas (Aakala et al, 2009;Aakala, 2010), differed in their disturbance histories. Here, the specific aims were: (1) to quantify the existing CWD pools, (2) to establish relationships between wood density and an appearance-based decay classification, and (3) to develop decay class transition models for snags and DWD in order to assess their longevities as components of ecosystem structure.…”

Dead standing pine trees in a boreal forest landscape in the Kalevala National Park, northern Fennoscandia: amount, population characteristics and spatial pattern

“…This result is in accordance with that of Rouvinen et al (2002), looking at tree mortality dynamics in the same area but on a larger pine-dominated forest landscape. We did not measure the time since tree death for the kelos, but based on the decay class distribution that is known to be linked to time since tree death (Aakala 2010), it is clear that kelos are continuously formed in the studied landscape. This, together with the results of Rouvinen et al (2002), indicate that the kelo formation process is in action across the larger forest landscape in the Kalevala National Park.…”

“…Each of these trees were classified into one of five decay classes, based on their visual appearance, mainly the presence or absence of needles, and branches of different order (Aakala 2010). In addition, the basal area of the forest surrounding each recorded tree was measured with a relascope separately for pine, spruce and deciduous trees.…”