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Approaches to forest management have changed markedly in the Pacific Northwest in recent decades, yet legacies of past management persist on the landscape. Following clearcut logging, woody residues were typically burned to reduce future fire hazard, create planting spots, facilitate natural recruitment, and retard growth of competing vegetation. We asked whether legacies of broadcast burning persist in the forest understory during the early stages of stand closure, how they manifest structurally or compositionally, whether they are altered by subsequent management (pre-commercial thinning), and how they vary with gradients in the physical environment or stand structure. We used data from 44 pairs of burned and unburned plots sampled 37–42 years after clearcut logging of mature and old-growth forests in western Oregon and Washington. Burning had persistent, but mostly subtle effects on community structure and composition. Burned plots had greater cover of early-seral species and lower cover of woody forest species. Among the latter, tall shrubs showed consistently negative responses to burning. Smaller-statured woody and herbaceous species were more variable in their responses, reflecting a greater diversity of regenerative traits. For some understory attributes, effects of burning were contingent on thinning history. For example, burning enhanced species richness and reduced species evenness, but only in unthinned sites. Conversely, burning increased the spatial variability of tall shrub cover, but only in thinned sites. In some instances, thinning compounded the effects of burning, resulting in a four-fold increase in cover of early-seral herbs and a 50% reduction in cover of forest tall shrubs relative to plots that received neither treatment. For most understory attributes, regional variation in the magnitude of the burn effect was not easily explained by burn severity, site environment, or stand structure. Collectively, our results highlight the persistent, but highly variable, effects of broadcast burning on the post-harvest development of the forest understory. They suggest that, where it is feasible, controlled burning can be used in regeneration-harvest units to achieve a variety of management objectives, with minimal effect on the forest understory. • We detected persistent, but subtle, effects on the understory 40 years after broadcast burning • Burning led to greater cover of early-seral species, but lower cover of woody forest species • Burning enhanced species richness and reduced species evenness, but only in unthinned sites • Thinning compounded the effects of burning on early-seral herbs and residual tall shrubs • Variation in the magnitude of the burn effect was not easily explained by site characteristics [ABSTRACT FROM AUTHOR]

A large research effort was initiated in the 1990s in western United States and Canada to investigate how the development of old-growth structures can be accelerated in young even-aged stands that regenerated following clearcut harvests, while also providing income and ecosystem services. Large-scale experiments were established to compare effects of thinning arrangements (e.g., spatial variability) and residual densities (including leave islands and gaps of various sizes). Treatment effects were context dependent, varying with initial conditions and spatial and temporal scales of measurement. The general trends were highly predictable, but most responses were spatially variable. Thus, accounting for initial conditions at neighborhood scales appears to be critical for efficient restoration. Different components of stand structure and composition responded uniquely to restoration thinnings. Achieving a wide range of structures and composition therefore requires the full suite of silvicultural treatments, from leave islands to variable density thinnings and creation of large gaps. Trade-offs among ecosystem services occurred as result of these contrasting responses, suggesting that foresters set priorities where and when different vegetation structures are most desirable within a stand or landscape. Finally, the results suggested that foresters should develop restoration approaches that include multiple treatments. [ABSTRACT FROM AUTHOR]

Post-fire forest management commonly requires accepting some negative ecological impacts from management activities in order to achieve management objectives. Managers need to know, however, whether ecological impacts from post-fire management activities are transient or cause long-term ecosystem degradation. We studied the long-term response of understory vegetation to two post-fire logging treatments – commercial salvage logging with and without additional fuel reduction logging – on a long-term post-fire logging experiment in northeastern Oregon, USA. We sampled understory plant cover and species diversity on 10–11 sampling plots within each of nine experimental treatment units to see if post-fire logging treatments produced any lasting effects on understory plant cover, species diversity, community composition, or exotic species cover. Post-fire logging treatments produced no significant effects on understory vegetation cover, diversity, or community composition 15 years after treatment. We found no significant treatment effects on graminoid, forb, woody plant, or exotic plant cover and species richness, and differences among treatment means were generally small. Differences in treatment means were larger at the individual species level, but were only statistically significant for one native grass, California brome ( Bromus carinatus ), which responded differently to the two logging treatments. Multivariate analysis of understory plant communities across 91 sample plots found two major gradients in understory plant community composition, one correlated with regenerating forest (sapling) density and one correlated with residual overstory tree density, suggesting that initial fire severity (tree mortality) and post-fire regeneration may have greater long-term impacts on post-fire understory vegetation than post-fire logging. This study demonstrates that understory vegetation can be resilient to post-fire logging, particularly when best management practices, like logging over snow, are used to limit damage to soils and understory vegetation. Further research is needed to establish the generality of our results and to identify sources of variability in understory plant community responses to wildfire and post-fire logging. If further research confirms our findings, post-fire logging debates will be able to focus more on how to mitigate short-term disturbance impacts and manage fire-killed trees to meet wildlife habitat, fuel reduction, and economic objectives, and less on concerns over long-term ecosystem degradation. [ABSTRACT FROM AUTHOR]

Abstract: The effects of early vegetation management on the survival and growth of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] were examined 5 and 15years after planting in the Oregon Coast Range. Our first objective was to document the effects of vegetation species competition upon key ecosystem properties. The second objective was to document the effects of vegetation removal during early Douglas-fir stand establishment upon long-term tree growth and on biomass production by vegetation components. Seven levels of manual vegetation removal were maintained for the first 5years after planting: 0%, 25%, 50%, 75%, and 100% shrub removal; and 100% shrub removal combined with 50% or 100% herbaceous vegetation removal. Shrub and herb removal did not affect Douglas-fir survival at year five, but treatments providing less than 75% shrub removal significantly reduced Douglas-fir survival by year 15. Removing shrubs and herbs completely (100S+100H) during the 5years following tree planting allowed successful tree establishment, with a 366% increase in biomass accumulation per hectare for Douglas-fir in that treatment at the end of 14years of growth. At 15years stand age, even with shrub removal alone, a 304% gain in tree biomass per hectare was obtained compared to no vegetation removal (NVR). By stand age 15years, any increase in the degree of understory removal beyond 75% did not contribute significantly to additional tree survival and growth. The understory vegetation on NVR treatment plots and the herbaceous vegetation on 100% shrub removal (100S) treatment plots, contained >90% and >80% of aboveground biomass N at 5years, respectively, indicating possible competition for soil N. Soil moisture was not different among treatments at 5years. Complete vegetation removal (100S+100H) for 5years resulted in a significant increase in soil bulk density (P <0.05), a significant decrease in total soil C (P <0.05) and no change in total soil N in the upper 15cm of the mineral soil. By 14years, however, only the soil bulk density remained greater (P <0.05) on the 100S+100H treatment. We conclude that greater tree survival and growth occurred with at least 75% shrub removal. Our results suggest that managers may have substantial flexibility in maintaining a partial understory component suitable for ecosystem productivity, canopy cover and wildlife habitat, while maintaining forests productive for timber resources. [Copyright &y& Elsevier]

An observational study of early seedling establishment (first 1–2 summers after emergence) was conducted in four ponderosa pine (Pinus ponderosa var. ponderosa Dougl. ex Laws.) stands east of the Cascade Range crest in central Oregon, USA. Newly emerged ponderosa pine seedlings were identified at the start of summer and were monitored through their second summer; a subsequent cohort of seedlings was identified and monitored for one summer. About 3% of the viable seed that was produced resulted in new seedlings. Mortality was substantial immediately following emergence. Most seedlings emerged without shading from understory vegetation, but few survived. Most seedlings alive after one year had emerged beneath live cover; by the end of two summers only shaded seedlings were alive. 63–85% of new seedlings initiated in clusters attributed to rodent caching, and seedlings originating in clusters remained a substantial proportion of the cohort (60%) after two seasons. Results suggest that understory vegetation in these types of stands facilitates the recruitment of ponderosa pine seedlings, most likely by buffering them against environmental stressors during the seedling establishment phase. They also reveal that seed caching rodents are highly active in seed redistribution and can exert a lasting influence on seedling recruitment. [ABSTRACT FROM AUTHOR]

• Temperate forest plants exhibited a common diversity motif. • Initially low diversity peaked rapidly, mildly declined thereafter. • The motif recurred across sixteen disparate climate zones. • Motif consistent for taxonomic, functional, and phylogenetic diversity. Complex early-seral forests support biological legacies and unique understory vegetation (grasses, forbs, shrubs, juvenile trees) important to wildlife and ecosystem functioning. Intensive management in early-seral forest and other stages could reduce understory plant diversity and homogenize community compositions. Furthermore, the relative effects of management regime may vary at different stages of forest development. To what extent do taxonomic, functional and phylogenetic diversity vary by seral stage and/or ownership (a proxy for management regime) after accounting for climatic variation? For 2224 plant species sampled systematically at 16,330 sites in sixteen Plant Association Zones (PAZs) of Washington, Oregon and California, we estimated taxonomic, functional and phylogenetic diversity (both alpha = richness and beta = heterogeneity measures). Seral stage was inferred using forest structural metrics. Permutational multivariate analyses tested the relative effects of seral stage and ownership type. Across PAZs, a common motif emerged: low diversity in sparse, untreed stages indicated an accumulation period after stand-replacing disturbances, followed immediately by peak diversity in early sapling stages, after which gradually declining diversity coincided with the loss of shade-intolerant species during stand development and canopy closure. Departures from this motif tended to be in climatically less-permissive locations. More of the variation in diversity was explained by seral stage than ownership type (and their interactions were seldom significant). Discriminating the nuanced effects of different management regimes will require context-dependent proxies other than ownership. Identifying generalities in vegetation dynamics—and departures from those generalities—can help balance ecological and social objectives in rapidly changing forest landscapes. [ABSTRACT FROM AUTHOR]

Fire exclusion has dramatically altered historically fire adapted forests across western North America. In response, forest managers reduce forest fuels with mechanical thinning and/or prescribed burning to alter fire behavior, with additional objectives of restoring forest composition, structure, and ecosystem processes. There has been extensive research on the effects of fuel reduction and restoration treatments on trees, fuels, regeneration, and fire behavior; but less is known about how these treatments influence understory vegetation, which contains the majority of vascular plant diversity in many dry conifer forests. Of particular interest is how understory vegetation may respond to the season and interval of prescribed burning. The season and interval of prescribed burning is often determined by operational constraints rather than historical fire regimes, potentially resulting in fire conditions and burn intervals to which native plants are poorly adapted. In this study, we examined how understory vegetation has responded to season and interval of prescribed burning in ponderosa pine (Pinus ponderosa) forests in the Blue Mountains of northeastern Oregon, USA. Using over a decade (2002–2015) of understory vegetation data collected in stands with different intervals (5 versus 15 year) and seasons (spring versus fall) of prescribed burning, we quantified how season and interval of prescribed burning has influenced understory vegetation compositional trajectories and indicator species over time. Season of prescribed burning resulted in different understory communities and distinct trajectories of understory composition over time, but interval of burning did not. Indicator species analysis suggests fall burning is facilitating early seral species, with native annual forbs displaying ephemeral responses to frequent burning, while invasive cheatgrass (Bromus tectorum) increased in abundance and frequency across all treatments over time. These findings indicate that understory vegetation in these ecosystems are sensitive to seasonality of burning, but the responses are subtle. Our findings suggest season and interval of prescribed burning used in this study do not result in large changes in understory vegetation community composition, a key consideration as land managers increase the pace and scale of prescribed fire in these forests. [ABSTRACT FROM AUTHOR]