Temporal development of decaying log habitats in wet spruce–fir stands in east-central British Columbia

Abstract

Time since death and time since fall were estimated for hybrid spruce (Picea glauca (Moench) Voss × Picea engelmannii Parry ex Engelm.) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) logs to quantify temporal changes in log decay and habitat quality in east-central British Columbia. We sampled 136 logs (72 spruce and 64 fir) for species, size, and morphological attributes and used dendroecological techniques to estimate year of death (n = 97) and fall (n = 122). Time since death and time since fall of spruce and fir were similar in decay classes 1 and 2; fir was older than spruce in more advanced stages of decay. Discriminant analysis based on time since fall correctly classified logs into four decay classes for 67% and 80% of spruce and fir, respectively. Function as wildlife habitat changed significantly as logs decayed. Logs served as elevated runways for approximately 15 years and then increased in value as habitat for invertebrates and insectivores as wood softened and vegetation established. Concealed spaces increased as the wood decomposed but decreased when logs collapsed. We conclude that decay classes represent biologically and statistically significant stages of log decomposition that are relevant to wildlife habitat and therefore provide a useful construct for model development and field interpretation.Résumé : Le temps qui s'est écoulé depuis la mort et la chute des arbres a été estimé pour des billes d'épinette hybride (Picea glauca (Moench) Voss × engelmannii Parry ex. Engelm.) et de sapin subalpin (Abies lasiocarpa (Hook.) Nutt.) afin de quantifier les changements temporels dans la décomposition des billes et la qualité des habitats dans le centre est de la Colombie-Britannique. Les auteurs ont échantillonné 136 billes (72 épinettes et 64 sapins) pour en dé-terminer l'espèce, la dimension et les attributs morphologiques, et ils ont utilisé les techniques dendrochronologiques pour estimer l'année de la mort (n = 97) et de la chute (n = 122) des arbres. La période de temps écoulée depuis la mort et la chute des arbres était similaire pour l'épinette et le sapin dans les classes de décomposition 1 et 2; le sapin était plus vieux que l'épinette dans les stades de décomposition plus avancée. L'analyse discriminante basée sur le temps s'est écoulé depuis la chute des arbres a correctement classé les billes dans les quatre classes de décomposition pour respectivement 67 et 80 % des épinettes et des sapins. Le rôle d'habitat pour la faune a changé de façon significative à mesure que les billes se sont décomposées. Les billes ont servi de voies surélevées pendant environ 15 ans. Par la suite, elles sont devenues plus intéressantes comme habitat pour les invertébrés et les insectivores à mesure que le bois s'est ramolli et que la végétation s'est installée. Les espaces abritées ont augmenté à mesure que le bois s'est décomposé mais elles ont diminué lorsque les billes se sont désintégrées. Ils arrivent à la conclusion que les classes de décomposition correspondent à des stades biologiquement et statisti...

Abundance and attributes of wildlife trees and coarse woody debris at three silvicultural systems study areas in the Interior Cedar-Hemlock Zone, British Columbia

“…Our results were similar to those of DeLong et al (2005), who used the same functional classification system in their study of decaying log habitats in wet subzones of the sub-boreal spruce zone (Meidinger and Pojar, 1991). In our study, small concealed spaces at ground level (CWD2) and long concealed spaces for runways (CWD4) tended to peak in decay class 3, the class in which logs are no longer elevated, but are still solid enough to provide overhead cover.…”

Wood-decaying fungi in the forest: conservation needs and management options

“…Deadwoodologists have thus investigated the species-richness of wooddecaying fungi at diVerent stages of decomposition (e.g. Lumley et al 2001; papers reviewed in Heilmann-Clausen and Christensen 2003), but the eVect of species-richness on decomposition rates has seldom been addressed (Boddy et al 1989;Boddy 2000;Heilmann-Clausen and Boddy 2005;DeLong et al 2005). An exception is a 13-year study of the decomposition of logs of Cyrilla racemiXora in forests of Puerto Rico, which provides evidence that high rates of wood decay are correlated with a high diversity of species and of functional groups of wood-inhabiting organisms (Torres and González 2005).…”

Modelling deadwood supply for biodiversity conservation: Considerations, challenges and recommendations

“…This is a key parameter to model. In addition, snags often decay at different rates than logs on the ground, so a snag that has stood for 30 years may be in the same decay condition as a log that has been on the ground for five years (DeLong et al 2005). Snags frequently break as they age, contributing some downed wood before the entire snag falls, and broken snags provide important habitat for some vertebrate species (Huggard and Kremsater 2007).…”