Physiology and Growth of Douglas-Fir and Redwood Seedlings Planted After Partial Harvesting

Abstract

Reforestation following timber harvests and natural disturbances is an essential component of sustainable forest management. As disturbances such as droughtinduced mortality and wildland fires spread across many forests of the western United States, a better understanding of the influences of stand structure on seedling physiology can foster more effective reforestation efforts. Moreover, as climate throughout the West is projected to become hotter and drier, it is important to investigate regeneration under xeric conditions, particularly for species restricted to mesic habitats. To study the influences of stand structure and climate on regeneration success, we monitored physiology [water potential ( ) and stomatal conductance (g s )], growth (change in basal diameter and biomass accumulation), and mortality rate of planted Douglas-fir (Pseudotsuga menziesii) and coast redwood (Sequoia sempervirens) seedlings for two growing seasons after partial harvesting in inland northern California. Compared to seedlings in the no-cut and moderate-retention treatments, seedlings in the gap (100% cut) treatment had the highest and g s , greatest growth, and lowest mortality. We also found that compared to Douglas-fir, redwood had higher and g s , greater growth, and lower mortality. Overall, our study indicates that low-retention silvicultural treatments can minimize water stress and maximize gas exchange, growth, and survival in regenerating seedlings. Our results also demonstrate that redwood, a species generally restricted to mesic coastal habitats, can successfully establish in xeric inland sites when planted after partial harvesting, even during drought conditions.

Restoring bigcone Douglas-fir post-fire in drought-stricken Southern California: Assessing the effects of site choice and outplanting strategies

“…A number of these mechanisms relate to plant hydraulics and rely on the assumption that bigcone Douglas-fir is an isohydric species, meaning it closes its stomata to conserve water as soil moisture decreases. Studies of P. menziesii, a close relative that is less drought tolerant, has confirmed this physiological approach (Kerhoulas et al, 2020). In our study, watering occurred after the end of the growing season, as soil moisture was likely dropping too low to allow for plant productivity.…”

Bark Thickness in Coast Redwood (Sequoia sempervirens (D.Don) Endl.) Varies According to Tree- and Crown Size, Stand Structure, Latitude and Genotype

“…Redwood planting stock with thinner bark tendencies could be deployed in areas where wildfire risk is low (e.g., closer to the Pacific coast) with the objective of sequestering and storing more carbon into long lived wood products and producing less bark residues [43]. Alternatively, redwood planting stock with high BT could be deployed to more xeric and fire-prone inland areas [44], and for use in redwood range expansion projects where redwood is being planted outside its natural range in more stressful environments and may benefit from added protection from the elements [45,46].…”

Measurement and prediction of water consumption by Douglas‐fir, Northern California, USA

“…Trees monitored at the Schatz site were part of a larger experiment examining the impact of thinning on tree growth and seedling water balance (Berrill et al, 2018; Kerhoulas et al, 2020). The site received thinning treatments in the fall of 2014.…”