Conifer Regeneration Research Articles

Size structure, growth and regeneration of tropical conifers along a soil gradient related to altitude and geological substrates on Mount Kinabalu, Borneo

Conifers often co-occur with angiosperm trees at high altitudes and on infertile soils in tropical rainforests. To explore the mechanism of conifer–angiosperm coexistence, we investigated size structure, growth rate and regeneration of conifers along soil gradient across altitudes and geological substrates. Tree measurements were conducted in ten plots (0.06–1 ha) with varied geology at four altitudes (700, 1700, 2700 and 3100 m) on Mount Kinabalu, Borneo. Conifer juveniles were counted and understory light conditions were analyzed with hemispherical photographs. Size structure of conifers showed inverse-J shape distributions on ultrabasic rocks at ≥1700 m but unimodal or sporadic distributions in other plots. Densities of conifer seedlings and saplings were generally greater on ultrabasic rocks than on non-ultrabasic substrates at comparable altitudes, which concurred with the pattern in understory light conditions. Growth rates over 4 (or 5) years of conifers at 4.8–25 cm diameter were higher than angiosperm trees only under well-lit conditions on non-ultrabasic substrates, but were always similar or higher on ultrabasic rocks even in shaded conditions. Conifers showed continuous regeneration on ultrabasic rocks at ≥1700 m. This suggested that, on infertile soils, competition with angiosperm trees was relaxed and well-lit understory facilitated recruitment of conifers.

A field experiment informs expected patterns of conifer regeneration after disturbance under changing climate conditions

Climate change may inhibit tree regeneration following disturbances such as wildfire, altering post-disturbance vegetation trajectories. We implemented a field experiment to examine the effects of manipulations of temperature and water on ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & C. Lawson) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings planted in a low-elevation, recently disturbed setting of the Colorado Front Range. We implemented four treatments: warmed only (Wm), watered only (Wt), warmed and watered (WmWt), and control (Co). We found that measures of growth and survival varied significantly by treatment type. Average growth and survival was highest in the Wt plots, followed by the Co, WmWt, and Wm plots, respectively. This general trend was observed for both conifer species, although average growth and survival was generally higher in ponderosa pine than in Douglas-fir. Our findings suggest that warming temperatures and associated drought are likely to inhibit post-disturbance regeneration of ponderosa pine and Douglas-fir in low-elevation forests of the Colorado Front Range and that future vegetation composition and structure may differ notably from historic patterns in some areas. Our findings are relevant to other forested ecosystems in which a warming climate may similarly inhibit regeneration by dominant tree species.

Partial harvesting in boreal mixedwoods: A case for planned heterogeneity in industrial silvicultural prescriptions

In large areas of the boreal mixedwoods of eastern Canada, conventional forestry practices dominated by large-scale clearcutting have led to an increase in early-successional trembling aspen (Populus tremuloides Michx.) stands and a decrease in late-successional mixedwood stands. Partial harvesting provides an alternative practice that could promote a return to mixedwood composition with greater potential economic returns. Our objective was to identify the stand attributes that have an effect on trembling aspen regeneration following industrial harvest operations. Ninety plots were surveyed immediately before and five years after partial harvesting, to collect information on harvested trees (stumps), residual cover and pre- and post-harvesting regeneration. Using zero-inflated beta regression models, we found that the transition probabilities (projected relative abundance) of trembling aspen were positively influenced by an increase in removal percentage and by an increase in initial basal area of trembling aspen in the overstory. Abundant balsam fir advance growth had a strong negative influence on trembling aspen transition probabilities. This information could be incorporated into silvicultural prescription decision tools to suggest optimal local basal area removal targets that would limit the regeneration success of trembling aspen. Using these results, we propose a new approach that consists of deliberately introducing heterogeneity within partial cutting prescriptions in order to limit deciduous encroachment and to promote the recruitment of coniferous regeneration in eastern Canadian boreal mixedwoods.

Fire legacies impact conifer regeneration across environmental gradients in the U.S. northern Rockies

An increase in the incidence of large wildfires worldwide has prompted concerns about the resilience of forest ecosystems, particularly in the western U.S., where recent changes are linked with climate warming and 20th-century land management practices. To study forest resilience to recent wildfires, we examined relationships among fire legacies, landscape features, ecological conditions, and patterns of post-fire conifer regeneration. We quantified regeneration across 182 sites in 21 recent large fires in dry mixed-conifer forests of the U.S. northern Rockies. We used logistic and negative binomial regression to predict the probability of establishment and abundance of conifers 5–13 years post-fire. Seedling densities varied widely across all sites (0–127,500 seedlings ha−1) and were best explained by variability in distance to live seed sources (β = −0.014, p = 0.002) and pre-fire tree basal area (β = 0.072, p = 0.008). Beyond 95 m from the nearest live seed source, the probability of seedling establishment was low. Across all the fires we studied, 75 % of the burned area with high tree mortality was within this 95-m threshold, suggesting the presence of live seed trees to facilitate natural regeneration. Combined with the mix of species present within the burn mosaic, dry mixed-conifer forests will be resilient to large fires across our study region, provided that seedlings survive, fire do not become more frequent, high-severity patches do not get significantly larger, and post-fire climate conditions remain suitable for seedling establishment and survival.

POTENTIAL OF UAV BASED CONVERGENT PHOTOGRAMMETRY IN MONITORING REGENERATION STANDARDS

Abstract. Several thousand hectares of forest blocks are regenerating after harvest in Canada. Monitoring their performance over different stages of growth is critical in ensuring future productivity and ecological balance. Tools for rapid evaluation can support timely and reliable planning of interventions. Conventional ground surveys or visual image assessments are either time intensive or inaccurate, while alternate operational remote sensing tools are unavailable. In this study, we test the feasibility and strength of UAV-based photogrammetry with an EO camera on a UAV platform in assessing regeneration performance. Specifically we evaluated stocking, spatial density and height distribution of naturally growing (irregularly spaced stems) or planted (regularly spaced stems) conifer regeneration in different phases of growth. Standard photogrammetric workflow was applied on the 785 acquired images for 3D reconstruction of the study sites. The required parameters were derived based on automated single stem detection algorithm developed in-house. Comparing with field survey data, preliminary results hold promise. Future studies are planned to expand the scope to larger areas and different stand conditions.

The history of forest fires and post-fire successions based on cartographic and archival data (Belomor-Kuloy Plateau)

Based on 1900-1917 archival data and 1947 topographic maps large contours of burnt land in the first half of the 20 th century were identified. The total burnt area was more than 200 000 ha, which is about 10 % of the entire area of the plateau. We specially focused on Zolotitsa region, where forest fires in the 1930s covered about 130 000 ha. It is shown that the process of natural regeneration of conifers (especially spruce) in pre-tundra forests (northern taiga subzone) may take a long time of up to 150-200 years.

Conifer regeneration in managed temperate mixedwood stands: the balance between release and competition

We established a long-term experiment in a temperate mixedwood stand to evaluate the effectiveness of silvicultural treatments in regenerating a mixed-species cohort while maintaining the dominance of conifers. Silvicultural treatments included clearcutting using careful logging around advanced growth (CLAAG), uniform shelterwood (US), group shelterwood with (GS-s) or without scarification (GS), and an uncut control (control). After 10 years, height and ground-line diameter growth responses of advanced balsam fir (Abies balsamea [L.] Mill.) regeneration were substantial in CLAAG and GS compared to the control, and intermediate in US. Growth responses were proportional to increases in canopy light transmittance resulting from harvest. Advanced balsam fir regeneration had low mortality (<10 %) and a high potential for release as measured by the apical dominance ratio. At the stand level, however, a shift in species composition occurred in the regenerating cohort. Over the 10-year period, composition changed from conifer-dominated to hardwood-dominated in CLAAG, GS, and GS-s compared to the control. Scarification increased the magnitude of this shift by favoring shade-intolerant hardwoods. Results highlight the need to find a balance between releasing advance conifer regeneration and limiting competition from less desirable species.

Conifer Recruitment in Trembling Aspen (Populus Tremuloides Michx.) Stands along an East-West Gradient in the Boreal Mixedwoods of Canada

Ongoing climate change is likely to result in shifts in successional dynamics in boreal mixedwood stands. Using data from provincial forest inventory databases, we examined the occurrence and abundance of the regeneration of various coniferous species (white spruce, black spruce and balsam fir) along an east-west Canadian gradient in aspen-dominated stands. The interpretation of the results was based on environmental conditions, including climate, natural fire regime and human impacts. We found that conifer regeneration was present in aspen stands along the entire gradient, despite differences in climatic conditions and fire regimes between the west (warmer and drier, with large recurrent fires) and east (more humid with relatively long fire cycles). However, abundance and distribution varied from one conifer species to the next. The abundance of white spruce decreased towards the eastern end of the longitudinal gradient, while balsam fir and black spruce abundance decreased towards the west. Although abundance decreased, balsam fir and black spruce regeneration was still present in western Canada. This study shows that it is difficult to interpret the effects of climate change on conifer recruitment without accounting for the superimposed effects of human activities.

A Mixed-Effects Heterogeneous Negative Binomial Model for Postfire Conifer Regeneration in Northeastern California, USA

Many western USA fire regimes are typified by mixed-severity fire, which compounds the variability inherent to natural regeneration densities in associated forests. Tree regeneration data are often discrete and nonnegative; accordingly, we fit a series of Poisson and negative binomial variation models to conifer seedling counts across four distinct burn severities and three forest types 10 years after the 23,000-ha Storrie Fire, a large mixed-severity fire in northern California. Despite the accessibility and power of the zero-inflated negative binomial mixture model, a flexible heterogeneous negative binomial model offered a superior fit. Incorporation of a random stand effect further improved model performance. A parametric bootstrap analysis was conducted to examine seedling distributions and stand stocking. Mean simulated seedling densities had an expansive range (272–29,257 ha−1). Stocking analyses suggest a high probability of deficient conifer coverage in the majority of lower-elevation high-severity burn stands. In addition, models were fit to fir and pine seedling counts. Only a minority of postfire stands were likely to be stocked in the pine-only analysis. These models will help land managers prioritize limited resources for artificial reforestation in mixed-severity burned landscapes.

Isolation and characterization of 11 polymorphic microsatellite markers in the highly invasive Western conifer seed bug, Leptoglossus occidentalis (Heteroptera, Coreidae)

Eleven polymorphic microsatellite markers were developed from enriched DNA libraries for the invasive Western conifer seed bug, Leptoglossus occidentalis. The number of alleles ranged from 2 to 11 and observed heterozygosities from 0.038 to 0.933. Additional results of cross-species amplifications are reported for two congeneric species. This set of microsatellite markers, the first one available for L. occidentalis, enables further investigations of population structure of this species which represents a serious threat for European conifer regeneration.

Variation in post-wildfire regeneration of boreal mixedwood forests: underlying factors and implications for natural disturbance-based management

To test the direct regeneration hypothesis and support natural disturbance-based forest management we characterized the structure and composition of boreal mixedwood forests regenerating after large wildfires and examined the influence of pre-fire stand composition and post-fire competing vegetation. In stands which had been deciduous (Populus sp.)-dominated, conifer (white spruce)-dominated, or mixed pre-fire we measured regeneration stocking (presence in 10 m2 plots), density and height 10–20 years post-burn in five wildfires in Alberta, Canada. Most plots regenerated to the deciduous or mixed stocking types; plots in the older fire and in stands that were pure conifer pre-fire had higher amounts of conifer regeneration. Surprisingly, regeneration in pre-fire ‘pure’ white spruce stands was most often to pine, although these had not been recorded in the pre-fire inventory. Pre-fire deciduous stands were the most resilient in that poplar species dominated their post-fire regeneration in terms of stocking, density and height. These stands also had the highest diversity of regenerating tree species and the most unstocked plots. High grass cover negatively affected regeneration density of both deciduous and conifer trees. Our results demonstrate the natural occurrence of regeneration gaps, pre- to post-fire changes in forest composition, and high variation in post-fire regeneration composition. These should be taken into consideration when developing goals for post-harvest regeneration mimicking natural disturbance.

Regeneration and Recruitment Correlate with Stand Density and Composition in Long-Unburned Aspen Stands Undergoing Succession to Conifer in the Sierra Nevada, USA

Succession of aspen stands to conifer in the Sierra Nevada Mountains of California and Nevada, USA, is being interrupted by forest managers thinning conifers to sustain aspen stands in situ. However, patterns of stand density, species composition, and regeneration prior to management intervention have scarcely been described. We established a grid of sample plots throughout nine aspen stands encircling Lake Tahoe in the central Sierra Nevada. The degree of succession to conifer throughout each aspen stand was spatially heterogeneous. Patches of pure aspen were rare. Stand density index (SDI) reached an upper limit of 1700 in pure aspen. As composition shifted in favor of conifer, SDI approached or attained a maximum of 2500 in some plots. Stand density and species composition data were tested as predictors of conifer and aspen regeneration densities in each plot. Conifer seedlings had an average density of 3261 ha-1; they were most abundant in aspen-dominated areas of any density, and in conifer-dominated areas of higher density. Aspen regeneration had an average density of 3211 ha-1 and was one order of magnitude less frequent in areas of pure conifer versus areas of pure aspen, but remained relatively abundant in most areas. Aspen saplings were rare (average density of 42 ha-1 for saplings 10-15 cm DBH), especially at high stand densities or in areas where conifers dominated. Our findings suggest that forest managers interested in sustaining aspen stands in situ will need to control stand density to promote recruitment of younger aspen to the overstory.

Fire severity, residuals and soil legacies affect regeneration of Scots pine in the Southern Alps

Regeneration of non fire-adapted conifers following crown fires on the European Alps is often delayed or unsuccessful. Fire may limit establishment by eliminating seed trees, altering soil properties, or modifying microsite and soil conditions via disturbance legacies. However, the effect of soil legacies on post-fire establishment has rarely been discussed. We analyzed the abundance of Scots pine regeneration in a 257ha wildfire in an inner-alpine forest. Our aims were (1) to model fire intensity at the soil surface and topsoil heating along a gradient of increasing fire severities; (2) to assess the differences in soil properties along the fire severity gradient; (3) to model the effect of disturbance and soil legacies on the density of pine seedlings. We reconstructed fire behavior and soil heating with the First Order Fire Effects Model (FOFEM), tested the effect of fire severity on soils by nonparametric distributional tests, and modeled seedling density as a function of site, disturbance and soil legacies by fitting a GLM following a variable selection procedure. Topsoil heating differed markedly between the moderate and high severity fires, reaching temperatures high enough to strongly and permanently alter soil properties only in the latter. High fire severity resulted in decreased soil consistency and wet aggregate stability. Burned soils had lower organic matter and cations than those unburned. Pine seedlings favored low-fertility, eroded, and chemically poor sites. Establishment was facilitated by the presence of coarse woody debris, but hampered by increasing distance from the seed source. These results suggest that in dry, inner-alpine valleys, fire residuals and soil legacies interact in determining the success of Scots pine re-establishment. High severity fire can promote favorable soil conditions, but distance from the seed source and high evaporation rates of bare soils must be mitigated in order to ensure a successful restoration.

Salvage logging and forest renewal affect early aspen stand structure after catastrophic wind

Among the major natural disturbances that occur in the North American boreal forest, the effects of catastrophic wind are the least studied due to its infrequent occurrence, often in inaccessible areas, and lack of rapid research response. Most documented studies have been conducted in conifer or mixedwood forests and generally have not considered follow up forest renewal operations such as salvage logging followed by planting and tending. In 2006 after a severe wind disturbance in trembling aspen (Populus tremuloides Michx.) forest in northeastern Ontario, we established an operational study to investigate the effects of post-wind disturbance treatments on stand structure (residual live trees, snags, and downed wood) and early forest regeneration. The treatments were blowdown (B), blowdown followed by salvage logging (BS), blowdown followed by salvage logging, windrowing and planting (BSP), BSP followed by aerial spray (tending) with glyphosate 1year after planting (BSPT), and clearcut (C).The operational salvage logging removed about 55% of the 60 m3 ha−1 of the snags and 15% of the 390 m3 ha−1 of the coarse downed wood. The relatively low rate of salvage removal increased the abundance (density and stocking) of aspen regeneration and reduced moss cover, but did not affect average height of aspen suckers or the abundance (cover) of other vegetation types. The mechanical operations damaged much of the advanced growth of conifers (mostly black spruce and balsam fir (Abies balsamea (L.) Mill.) released by the wind. However, these stems were not sufficiently abundant to contribute significantly to the regenerating forest. Windrowing before planting slightly reduced the amount of area covered by downed wood, while the tending reduced broadleaf regeneration and the abundance of shrubs and increased conifer regeneration and the abundance of grasses. If the management objective is to renew aspen forests lost to catastrophic wind, salvage logging is a viable option to clear the site for regeneration. Forest renewal treatments, including planting and tending, are required when the management objective is conifer regeneration.

Early forest dynamics in stand-replacing fire patches in the northern Sierra Nevada, California, USA

There is considerable concern over the occurrence of stand-replacing fire in forest types historically associated with low- to moderate-severity fire. The concern is largely over whether contemporary levels of stand-replacing fire are outside the historical range of variability, and what natural forest recovery is in these forest types following stand-replacing fire. In this study we quantified shrub characteristics and tree regeneration patterns in stand-replacing patches for five fires in the northern Sierra Nevada. These fires occurred between 1999 and 2008, and our field measurements were conducted in 2010. We analyzed tree regeneration patterns at two scales: patch level, in which field observations and spatial data were aggregated for a given stand-replacing patch, and plot level. Although tree regeneration densities varied considerably across sampled fires, over 50 % of the patches and approximately 80 % all plots had no tree regeneration. The percentage of patches, and to a greater extent plots, without pine regeneration was even higher, 72 and 87 %, respectively. Hardwood regeneration was present on a higher proportion of plots than either the pine or non-pine conifer groups. Shrub cover was generally high, with approximately 60 % of both patches and individual plots exceeding 60 % cover. Patch characteristics (size, perimeter-to-area ratio, distance-to-edge) appeared to have little effect on observed tree regeneration patterns. Conifer regeneration was higher in areas with post-fire management activities (salvage harvesting, planting). Our results indicate that the natural return of pine/mixed-conifer forests is uncertain in many areas affected by stand-replacing fire.

Performance of planted spruce and natural regeneration after pre- and post-harvest spraying with glyphosate and partial cutting on an Ontario (Canada) boreal mixedwood site

In the boreal mixedwood region of Canada, management for conifer regeneration after clearcutting generally involves mechanical site preparation, planting and aerial spraying with glyphosate to minimize post-planting competition from natural broadleaf regeneration. However, the resulting conifer plantations have economic and ecological disadvantages compared with mixedwood stands with healthy and productive broadleaf components. This study examined 10-year growth of planted spruce and natural regeneration after pre- and post-harvest spraying and partial cutting treatments on a boreal mixedwood site in northeastern Ontario, Canada. The treatments were as follows: (1) pre-harvest broadcast spraying with glyphosate to suppress trembling aspen (Populus tremuloides Michx.) regeneration, (2) clearcut (unsprayed) for broadleaf regeneration, (3) partial cut to suppress shade-intolerant vegetation, and (4) post-harvest broadcast spraying to promote conventional conifer plantations. Planted spruce trees were tallest in the pre-harvest spray treatment but had the largest basal diameter in the post-harvest spray treatment; neither of the differences was significant at 0.05. Total broadleaf regeneration density in the pre-harvest spray treatment was similar to that in the partial cut, but higher than that in the post-harvest spray treatment. Additional shade from greater amounts of shrubs and residual overstory trees in the partial cut treatment resulted in higher quality spruce trees than in the spray treatments; based on branch size, branch-free stem length and stem taper, wood quality was generally lowest in the post-harvest spray treatment. Pre-harvest spraying provided a better balance between growth and quality of planted spruce than either post-harvest spraying or partial cutting.

Forest resilience, climate change, and opportunities for adaptation: A specific case of a general problem

Ecosystems and ecosystem services are subjected to both typical disturbances (e.g., fire) and shifting climatic baselines resulting from anthropogenic drivers. Recovery from these perturbations is of prime interest to researchers and land managers. We explore how differing regeneration of the coniferous forest to specific disturbances and a shifting climate are mediated through managerial responses, in terms of both species composition and an important ecosystem service, carbon sequestration in the southern Rocky Mountains, Colorado, USA. 112 sites across a variety of disturbance histories were surveyed for post-fire regeneration; carbon stock growth was then simulated in the US Forest Service Forest Vegetation Simulator under a variety of climate change scenarios for 100years. Simultaneously, we simulated three managerial responses to the disturbance: no action, planting of local species (resilience-oriented management), and planting of the most climatically suitable species (adaptation-oriented management). These managerial responses simulate varying levels of intervention which attempt to maintain forest properties and associated carbon stocks. Carbon stocks, initially, were more resilient than the coniferous forest system; areas with little coniferous regeneration recovered carbon at a similar pace due to an influx of deciduous seedlings. However, future climate exerts a strong influence on carbon stocks. Both the no-action scenario and the resilience-oriented management scenario transitioned to non-forest by the end of the simulation period, due to climatic changes. Active, adaptation-oriented management, which included establishment of non-local species, maintained forest structure and carbon stocks under most future climate projections, albeit at lower densities. So while this preserves the presence of a forest, it does not preserve the presence of a specific forest. However, for ecosystem services associated with the mere existence of forest cover (e.g., carbon stocks and general forest habitat), this may be sufficient. In a sense, disturbances are opportunities for more climatically-adapted species/communities to establish, although the complexities of assisted migration and novel ecosystems remain.

Temperate tree expansion into adjacent boreal forest patches facilitated by warmer temperatures

Temperate and boreal forests are forecast to change in composition and shift spatially in response to climate change. Local‐scale expansions and contractions are most likely observable near species range limits, and as trees are long‐lived, initial shifts are likely to be detected in the understory regeneration layers. We examined understory relative abundance patterns of naturally regenerated temperate and boreal tree species in two size classes, seedlings and saplings, and across two spatial scales, local stand‐scale ecotones (tens of meters) and the regional temperate–boreal transition zone (˜250 km) in central North America, to explore indications of climate‐mediated shifts in regeneration performance. We also tested for the presence of strong environmental gradients across local ecotones that might inhibit species expansion. Results showed that tree regeneration patterns across ecotones varied by species and size class, and varied across the regional summer temperature gradient. Temperate tree species regeneration has established across local ecotones into boreal forest patches and this process was facilitated by warmer temperatures. Conversely, boreal conifer regeneration exhibited negative responses to the regional temperature gradient and only displayed high abundance at the boreal end of local ecotones at cool northern sites. The filtering effects of temperature also increased with individual size for both boreal and temperate understory stems. Observed regeneration patterns and the minor environmental gradients measured across local ecotones failed to support the idea that there were strong barriers to potential temperate tree expansion into boreal forest patches. Detectable responses, consistently in the directions predicted for both temperate and boreal species, indicate that summer temperature is likely an important driver of natural tree regeneration in forests across the temperate–boreal transition zone. Regeneration patterns point toward temperate expansion and reduced but continued boreal presence in the near‐future, resulting in local and regional expansions of mixed temperate‐boreal forests.

Conifer regeneration following stand-replacing wildfire varies along an elevation gradient in a ponderosa pine forest, Oregon, USA

Climate change is expected to increase disturbances such as stand-replacing wildfire in many ecosystems, which have the potential to drive rapid turnover in ecological communities. Ecosystem recovery, and therefore maintenance of critical structures and functions (resilience), is likely to vary across environmental gradients such as moisture availability, but has received little study. We examined conifer regeneration a decade following complete stand-replacing wildfire in dry coniferous forests spanning a 700m elevation gradient where low elevation sites had relatively high moisture stress due to the combination of high temperature and low precipitation. Conifer regeneration varied strongly across the elevation gradient, with little tree regeneration at warm and dry low elevation sites. Logistic regression models predicted rapid increases in regeneration across the elevation gradient for both seedlings of all conifer species and ponderosa pine seedlings individually. This pattern was especially pronounced for well-established seedlings (⩾38cm in height). Graminoids dominated lower elevation sites following wildfire, which may have added to moisture stress for seedlings due to competition for water. These results suggest moisture stress can be a critical factor limiting conifer regeneration following stand-replacing wildfire in dry coniferous forests, with predicted increases in temperature and drought in the coming century likely to increase the importance of moisture stress. Strongly moisture limited forested sites may fail to regenerate for extended periods after stand-replacing disturbance, suggesting these sites are high priorities for management intervention where maintaining forests is a priority.

Twelve-year responses of planted and naturally regenerating conifers to variable-retention harvest in the Pacific Northwest, USA

We studied patterns of conifer regeneration over 12 years as part of a regional-scale experiment in variable-retention harvest in the Pacific Northwest, the DEMO Study. We compared survival and height growth of planted conifers and density and seral composition of natural regeneration among treatments with differing retention levels (15% versus 40%) and patterns (dispersed versus aggregated) replicated across a range of latitudes and forest zones. We also assessed plot-scale relationships of natural regeneration with overstory density and basal area, competing vegetation, and slash accumulations. Early (1- to 2-year) survival of planted seedlings was greater in dispersed treatments (Pinus monticola Douglas ex D. Don, Abies spp.) or unaffected by retention level or pattern (Pseudotsuga menziesii (Mirb.) Franco). Later (5- to 12-year) survival did not differ (all species), but growth was distinctly reduced in dispersed treatments and (or) at higher levels of retention. Density of natural regeneration was 1.5–2.5 times greater in dispersed treatments than in the cleared areas of aggregated treatments. Low-level dispersed retention promoted Pseudotsuga, the early-seral dominant, presumably by enhancing seed rain within a relatively high-light environment. Dispersed retention favored late-seral conifers. The ability to manipulate retention pattern and level to influence regeneration density and composition provides managers with flexibility in developing structurally complex and compositionally diverse forests.