Robert A. Slesak

The western portion of the Pacific Northwest (PNW) has some of the most productive and iconic forests of the United States. Management of these forests has changed dramatically over the past three decades, driven by the primary objectives and constraints associated with major forest landowner groups. Key changes include 1) increased focus on the establishment phase and a reduction in intermediate treatments for ownerships practicing intensive management (e.g., forest industry), 2) an increase in the use of variable retention harvesting on state, Bureau of Land Management, and tribal managed lands, and 3) and a shift to almost exclusive use of thinning on National Forest System lands. Most silvicultural activity is focused on Douglas-fir on privately owned timberlands despite federal ownerships comprising more than half of all timberland in the region. Regeneration is primarily accomplished via planting using both genetically improved and wild-collected seed depending on species and ownership. Increased fire occurrence and severity have given rise to a broad class of treatments related to fuels reduction and thinning to increase resiliency, which is likely to continue to expand. Future changes in practice will be driven by evolving objectives of major forest landowner groups, but we anticipate increased focus on the establishment phase across all groups. Reduced investment in silviculture research and a trend towards standardized silvicultural prescriptions are key challenges to future innovation in the region at a time when the need for innovation to maintain forests and the benefits they provide has never been greater.

Peatland forest ecosystems play a critical ecological, economic, and cultural role by sequestering carbon, supporting biodiversity, the provisioning of conventional and non-conventional wood products, and providing habitat for specialists. Historically, forest management in these systems has used clearcut harvests to maximize pulp production, often resulting in structurally simplified stands vulnerable to climate change. As climate change reshapes boreal systems through warming, altered hydrology, and increased disturbance, identifying structural features that promote resilience is increasingly important. Ecological forestry, which aims to emulate natural disturbance and subsequent forest development, is an alternative approach to support a broader suite of ecosystem processes. To inform this approach, we examined how forest structure, quantified through lidar-derived metrics, varies across peatland forest types and stand ages, and how these structural attributes influence avian communities, with emphasis on peatland associate species. We used field measurements, bird point count surveys, and lidar data across productive black spruce, stagnant black spruce, and tamarack stands in lowland conifer peatlands of northern Minnesota. Results showed that canopy height, canopy cover, heterogeneity, vertical canopy complexity, and overall complexity did not differ among cover types but increased significantly with stand age, reflecting the gradual development of structural complexity over time. Total bird species richness and diversity showed limited associations with forest type, stand age, or structural metrics, likely reflecting the broad distribution of generalist species across stands. In contrast, peatland-associated species exhibited clear positive responses: their richness and diversity increased significantly with stand age and were positively correlated with lidar-derived measures of canopy cover and the overall complexity index. These results underscore the ecological value of older, structurally complex peatland stands in sustaining specialist bird assemblages and highlight the importance of incorporating fine-scale structural metrics into biodiversity assessments and climate-adaptive management planning aimed at sustaining habitat function under increasing climatic variability. Further, our results have application to the development of silvicultural approaches that better reflect the natural, complex structural dynamics of these ecosystems. Silvicultural approaches that emulate natural structural development, such as irregular shelterwood with reserves or variable density thinning, may enhance canopy complexity while maintaining forest productivity and habitat for peatland specialist birds.

Most measurements and models of forest carbon cycling neglect the carbon flux associated with the turnover of branch biomass, a physiological process quantified for other organs (fine roots, leaves, and stems). Synthesizing data from boreal, temperate, and tropical forests (184,815 trees), we found that including branch turnover increased empirical estimates of aboveground wood production by 16% (equivalent to 1.9 Pg Cy ⁻¹ globally), of similar magnitude to the observed global forest carbon sinks. In addition, reallocating carbon to branch turnover in model simulations reduced stem wood biomass, a long-lasting carbon storage, by 7 to 17%. This prevailing neglect of branch turnover suggests widespread biases in carbon flux estimates across global datasets and model simulations. Branch litterfall, sometimes used as a proxy for branch turnover, ignores carbon lost from attached dead branches, underestimating branch C turnover by 38% in a pine forest. Modifications to field measurement protocols and existing models are needed to allow a more realistic partitioning of wood production and forest carbon storage.

Forested wetlands are common ecosystems within the Great Lakes region (Michigan, Minnesota, and Wisconsin), USA. Projected increases in extreme flooding events and shifting disturbance regimes create challenges for tree regeneration. Forest managers are considering the use of enrichment planting to increase tree species diversity, but limited information is available that quantifies the interactions between the flooding and shade tolerances of candidate tree species. We used a microcosm experiment to manipulate shade and flooding conditions to determine the effects on early survival, growth, and leaf gas exchange of 23 different tree species that vary in shade and flood tolerance. Seedlings were planted in pots and placed in 227 L tanks that were randomly assigned to light reduction (full sun, 40% and 70% reduced sunlight) and flood treatments (water levels of 0, 14, or 27 cm below the soil surface). In general, flooding treatments had a greater influence on seedling growth and leaf gas exchange rates than light reduction treatments. Of the species studied, bald cypress (Taxodium distichum (L.) Rich.) was the most flood-tolerant, but American sycamore (Platanus occidentalis L.) and river birch (Betula nigra L.) were also highly tolerant of flooding conditions throughout the entire growing season. The flood tolerances of the remaining species varied, but none were tolerant of water table depths within 14 cm of the soil surface for the entire growing season. Most species did not respond to the shade treatments in terms of early growth, survival, and leaf gas exchange. When considering species for planting in forested wetlands, matching the flood tolerance of candidate species to local site hydrology is an important step.

Fire suppression has increased competitive tree encroachment of Oregon white oak (Quercus garryanna Douglas ex Hook) ecosystems, threatening maintenance of this important species. Restoration of oak ecosystems is ideal to address this threat but not always possible, giving rise to a need for novel treatments that will allow oak to persist on an altered landscape. We tested the effect of three release treatments centered around individual Oregon oak trees within four forested sites that had developed following encroachment and overtopping by Douglas‐fir (Pseudotsuga menziesii [Mirb.] Franco var. menziesii). The release treatments entailed removal of competitive tree species (>10 cm dimaeter at breast heigh [DBH]) within zero (as control), half, or full distance of the associated Oregon oak trees' height. There was no effect of release treatment on height, but diameter was significantly increased in the full release treatment relative to both the control and half release treatments. The effect on diameter increased up to year 10 and then decreased to year 20. Growth response to canopy damage from an ice storm in year 12 of the study varied significantly with treatment; growth was negatively related to the percent crown damage in both release treatments but not the control treatment. Full release treatments around individual Oregon oak trees can have long‐term positive effects on growth, providing managers with an option to maintain oak within altered ecosystems.