Temporal dynamics and decay of coarse wood in early seral habitats of dry-mixed conifer forests in Oregon’s Eastern Cascades

Early seral forest habitats are increasingly valued for the unique structural resources they provide in many western US forests. Coarse woody detritus (CWD) are a significant feature of this developmental stage and are highly dynamic, suggesting these environments exhibit temporally diverse structural conditions prior to forest canopy closure. In dry-mixed conifer forests, snags are hypothesized to decay slower than logs making long-term dynamics in these forests dependent on snag fall, breakage and the decay rates of both standing and surface CWD. We estimated snag fall and breakage rates for Pinus ponderosa, Abies sp., P. menziesii and P. contorta snags in three diameter classes (<23 cm, 23–41 cm and > 41 cm) from 6057 snags across a 24-year chronosequence of early seral environments. Snag and log decay rates were estimated by felling 60 Abies sp. and 60 P. ponderosa snags, and sampling 40 P. Ponderosa logs. Half-life estimates for snags <23 cm, 23–41 cm, and >41 cm were 7, 12, and 17 years for Pinus sp., 10, 15, and 20 years for Abies sp., and 11, 17, and 23 years for P. menziesii. Breakage rates were lowest for small snags and not significantly different for medium and large snags, but did vary across species. We estimated an Abies sp. snag decomposition loss-rate constant of k = 0.0179 yrÀ1 (SE = 0.00533, p-value = 0.0014) but P. ponderosa snags did not exhibit statistically significant decay (k = 0.0024 yrÀ1, SE = 0.00518, p-value = 0.6414). P. ponderosa logs had an estimated decomposition loss-rate constant of k = 0.0243 yrÀ1 (SE = 0.0073, p-value = 0.0023), confirming reduced decay rates in snags and variation among species. Following high-severity fire, dry-mixed conifer stands experience relatively rapid temporal changes in CWD resources largely dependent on snag species and diameter-at-breast-height (DBH). Variation in fall, breakage and decay rates among species and DBH suggests maintaining a diverse selection of snag species and diameters would meet multiple ecological needs across a broader temporal scale. Additionally, given the rapid temporal changes in CWD, defining early seral habitat as the period immediately following disturbance until canopy closure may not adequately account for the diversity in habitat structures and resources available over time.