Time since death and decay rate constants of Norway spruce and European larch deadwood in subalpine forests determined using dendrochronology and radiocarbon dating

Abstract

Abstract. Due to the large size (e.g. sections of tree trunks) and highly heterogeneous spatial distribution of deadwood, the timescales involved in the coarse woody debris (CWD) decay of Picea abies (L.) Karst. and Larix decidua Mill. in Alpine forests are largely unknown. We investigated the CWD decay dynamics in an Alpine valley in Italy using the chronosequence approach and the five-decay class system that is based on a macromorphological assessment. For the decay classes 1-3, most of the dendrochronological samples were cross-dated to assess the time that had elapsed since tree death, but for decay classes 4 and 5 (poorly preserved tree rings) radiocarbon dating was used. In addition, density, cellulose, and lignin data were measured for the dated CWD. The decay rate constants for spruce and larch were estimated on the basis of the density loss using a single negative exponential model, a regression approach, and the stagebased matrix model. In the decay classes 1-3, the ages of the CWD were similar and varied between 1 and 54 years for spruce and 3 and 40 years for larch, with no significant differences between the classes; classes 1-3 are therefore not indicative of deadwood age. This seems to be due to a time lag between the death of a standing tree and its contact with the soil. We found distinct tree-species-specific differences in decay classes 4 and 5, with larch CWD reaching an average age of 210 years in class 5 and spruce only 77 years. The mean CWD rate constants were estimated to be in the range 0.018 to 0.022 y −1 for spruce and to about 0.012 y −1 for larch. Snapshot sampling (chronosequences) may overestimate the age and mean residence time of CWD. No sampling bias was, however, detectable using the stage-based matrix model. Cellulose and lignin time trends could be derived on the basis of the ages of the CWD. The half-lives for cellulose were 21 years for spruce and 50 years for larch. The half-life of lignin is considerably higher and may be more than 100 years in larch CWD. Consequently, the decay of Picea abies and Larix decidua is very low. Several uncertainties, however, remain: 14 C dating of CWD from decay classes 4 and 5 and having a pre-bomb age is often difficult (large age range due to methodological constraints) and fall rates of both European larch and Norway spruce are missing.

Variation in Downed Deadwood Density, Biomass, and Moisture during Decomposition in a Natural Temperate Forest

“…Herrmann et al [8] deduced from 5 sites on Luvisols, Cambisols, and Podsolic Cambisols that the decomposition rate was 88 years. Petrillo et al [57] calculated residence times of P. abies deadwood to 45, 56, and 84 years based on different methods on Cambisols, Umbrisols, and Podzols. Using the different approaches in our study, we found decomposition rates based on biomass loss for P. abies of 72 and 109 years.…”

Altitude is a better predictor of the habitat requirements of epixylic bryophytes and lichens than the presence of coarse woody debris in mountain forests: a study in Poland

“…The latter includes the type of surrounding vegetation, altitude etc. (Müller et al 2015;Vrška et al 2015;Petrillo et al 2016;Chmura et al 2016;Staniaszek-Kik et al 2019). The colonization processes of plants and lichens on deadwood have been described in many studies since Hackiewicz-Dubowska (1936) and McCullough (1948) who were the first to identify the decomposition classes of logs and snags.…”

Biological Legacies and Rockfall: The Protective Effect of a Windthrown Forest

“…This improvement of the protective role could last for a few years, before lying logs start to rot and the height of the logs from the ground starts to decrease, as observed in Wohlgemuth [12]. Moreover, with a reduction of deadwood height above the ground and with a higher portion of logs in direct contact with the soil, the wood decaying processes may accelerate [38], leading to lower protective efficiency of biological legacies.…”