The effects of variable retention forestry on coarse woody debris dynamics and concomitant impacts on American marten habitat after 27 years

Coarse woody debris (CWD) in the form of logs, downed wood, stumps and large tree limbs is an important structural habitat feature for many small mammal species, including the American marten (Martes americana). At a long-term experimental trial in northern temperate hemlock-cedar forests of British Columbia, Canada, we analysed the impact of varying amounts of overstory basal area retention: 0% (clearcut), 40%, 70%, and 100% (unharvested) on CWD volume, decay class, and inputs from windthrow over 27 years. We used CWD attributes (diameter, length, decay class, and height above the ground) known to be favourable for martens to create an index for assessing the impact of harvesting intensity on CWD habitat features. Stands with 70% retention had CWD attributes that resulted in CWD habitat features similar to unharvested stands. Clearcuts contained pieces that were smaller, more decayed, and closer to the ground, which contributed to a habitat that was less valuable, compared with stands that had higher retention. Over the 27-year period, windthrown trees were the majority of CWD inputs, and volume change was positively related to percent retention. Our results highlight that forest management influences CWD size and input dynamics over multiple decades, and the need for consideration of these impacts when undertaking long-term multiple-use forestry planning.

Quantifying loss and degradation of former American marten habitat due to the impacts of forestry operations and associated road networks in northern Idaho, USA

American marten are associated with extensive and unfragmented late seral forest habitats, and are often considered to be particularly vulnerable to habitat loss and fragmentation. This chapter evaluates the impact of road building and timber harvest on habitat suitability for marten in northern Idaho, USA, using an empirically derived, multi-scale habitat suitability model, reconstructing key predictor variables (elevation, forest type, road density, canopy cover, landscape fragmentation and the extensiveness of late seral forest in the landscape) as they appear to have existed prior to harvest, and applying the model to both current and pre-harvest conditions. Calculating changes in the extent and pattern of habitat in the landscape indicate that timber harvest and road construction together reduced marten habitat quality considerably across the study area, which is likely responsible for current patterns of reduced detection rates and lower genetic diversity in areas that have experienced the largest amounts of habitat loss.