Regeneration and Fuel Loading with Varying Overstory Retention in Redwood Stands 10 Years after Transformation to Multiaged Management
Abstract
Forest managers practicing retention forestry in the west need data on regeneration dynamics and hazardous fuels to design structures that are productive and fire resilient. This analysis of the 10-year re-measure of the redwood multi-aged experiment in the Jackson Demonstration State Forest in Mendocino County, California, explores the regeneration response of several species following different harvesting techniques including group selection (GS), high-density aggregated retention (HA), and high/low density dispersed retention (HD; LD). We measured size and growth of 10-year old redwood and tanoak stump sprout regeneration, the density of all tree species, and surface fuels 10 years after partial harvests.
Redwood regeneration responded strongly and positively to increasing openness (10.1 m2 ha-1 in GS vs 0.9 m2 ha-1 in HD). Tanoak basal area response was comparatively modest and was lowest in the HA treatment (2.2 m2 ha-1 in GS vs 1.3 m2 ha-1 in HA). The difference between redwood and tanoak sprout basal area decreased quickly with increasing canopy cover and tanoak basal area was slightly greater than that of redwood in the HD treatment. Douglas-fir seedling counts were consistent across treatments with an average expectation of 413 seedlings per hectare.
Redwood grew faster and achieved greater heights than tanoak across all treatments and growth periods. But redwood height growth slowed more than tanoak in years 5-10 compared to years 1-5 (0.8 m yr-1 -> 0.67 m yr-1 for redwood, vs. 0.39 m yr-1 -> 0.34 m yr-1 for tanoak). The mean height of redwood sprouts at Year 10 ranged from 10.64 m in the GS treatment to 6.3 m in the HD treatment. For tanoak, predicted mean height ranged from 5.2 m (GS) to 3.08 m (HD).
Fuel loading generally showed few statistically significant differences between treatments. Vegetative fuel loading was highest in the GS treatment and nearly 3 times that of the HA treatment which was lowest. One-hour fuels were highest in the HA treatment and around double that of the GS treatment.
The PCT dramatically reduced live surface fuels and increased fine dead surface fuels including 10- and 100-hour fuels, leading to greater stratification of treatments in terms of dead fuels.
Harvesting techniques designed to promote productivity (like GS, LD) resulted in significantly greater redwood growth and height. However, these same techniques also produced higher levels of live vegetation fuels pre-PCT and, consequently, higher volumes of fine dead fuels (10-hr and 100-hr) immediately following the PCT fuels treatment.
Acknowledgements
I would like to thank my advisor Pascal Berrill for his long standing support and unwavering flexibility in accommodating my not-always-most-direct path and unfailing confidence in my abilities. I’m indebted to his long-time investment in me through the sharing of his knowledge and experience and enriched by his friendship. My other committee members, Jeffrey Kane, and Rosanna Overholser have also offered their long-suffering support, and friendship and have been invaluable resources and trusted sounding blocks as I have navigated this process. Their direction, advice, and encouragement were instrumental in my continued commitment to completing my thesis. This thesis would not have been possible without the administrative support of Nona Mineva, Erin Kelly, and Eric Riggs. My field data would have been measly at best were it not for the dedicated efforts of our field crew: Alan Cooper, JD Wilder, Destiny Rivera, Keith Shuttle, Aidan Jack Murphy, Ian Blundell, Hanna Upton, and Ally Medina.
I acknowledge that this research was conducted on the unceded territory of the Northern Pomo tribes, the original stewards of these lands. I recognize and deeply regret our failure to engage with the tribe during our fieldwork. This omission carries significant implications for the responsible management of these forest ecosystems, particularly regarding the health and development of tanoak, a keystone species and a principal food source sustaining the Pomo people since time immemorial. I understand the importance of incorporating Indigenous knowledge into ecological research and management, and I sincerely hope that future projects on these lands will be conducted in genuine and collaborative partnership with Pomo tribal members. I believe their expertise is essential to ensuring the respectful and sustainable stewardship of their ancestral territory.
I would like to thank my children: Fox and Hazel, and my loving partner Megan for their support and patience in allowing me the time and space to continue working on this thesis even when it went on much longer than I had originally anticipated and meant the sacrifice of some of our precious shared weekend time. I’m deeply grateful for their willingness to prioritize my personal development and their confidence in my eventual success.