Large Snags Research Articles

Avian foraging and nesting use of created snags in intensively-managed forests of western Oregon, USA

Snags are critical structural features for managing biological diversity in forests of the Pacific Northwest, USA. However, commercial forests in this region often contain reduced numbers of snags compared to unmanaged forests and managers require effective methods to augment snag numbers in harvest units. Therefore, we created snags by topping live trees with a mechanical harvester and studied foraging and nesting use by cavity-nesting birds of these snags in clearcuts in Douglas-fir (Pseudotsuga mensezii) forests along the west slope of the Cascade Mountain Range and east slope of the Coast Range in Oregon, USA. We used a completely randomized design to assign 6 different treatments (single or scattered distribution by 3 different densities) to 31 different harvest units. We created 1111 snags from February 1997 through April 1999 and monitored them from 2–5 years after harvest (1999–2002). Fraction of created snags with nest cavities in harvest units was generally low across all treatments and years of the study, although some individual stands demonstrated increased nesting use with snag age. While the highest fractions of snags with nest cavities were found in units with low density and scattered snags, the mean fraction of snags used for nesting did not differ among treatments. Treatment type, distribution of snags (i.e., scattered or clumped), and associated interactions did not influence fraction of snags used for foraging. However, fraction of created snags used for foraging in all harvest units increased with snag age. Fraction of snags used for foraging was greatest in the low density treatments. While this technique provides managers with a relatively economical option for creating snags, mechanical harvesters cannot be used to create tall, large snags upon which several cavity-dependent species rely and provides only a partial solution to a critical forest management issue.

Snag frequency, diameter and species distribution and input rate in Newfoundland boreal forests

Summary Dead-tree (snag) density (stems per hectare), diameter, species distribution and input rate were examined in Newfoundland boreal forests dominated by black spruce ( Picea mariana (Mill.) B.S.P.) and balsam fir (Abies balsamea (L.) Mill.). Examinations were based on permanent sample plot data. Total snag densities were higher in fir than spruce and were densest in 40- to 59-year-old stands of both species. Densities of >9 cm diameter at breast height (d.b.h.; 1.3 m, hereafter all dimensions are dbh) snags and live trees and larger live and dead trees (>19 cm stems) were also higher in fir than spruce. Fir also generated more larger snags at a younger age than spruce. Precommercial thinning reduced snag densities, virtually eliminating >9 cm snags from 37- to 48-year-old forests. Disturbance regime had a minor impact on snag densities in >40-year-old forests. The annual rate of >9 cm snag production in >60-year-old forests was 9 cm tree fall down in >60-year-old forests was <0.6 and <0.9 per cent in fir- and spruce-dominated forests, respectively.

A lack of large-diameter logs and snags characterises dead wood patterns in Irish forests

Dead wood is an important component of forest ecosystems and volumes vary depending on forest age, management intensity and productivity. This is the first large-scale study to quantify dead wood in Irish forests and to compare them to forests in other locations. We measured the volume and size distribution of logs, the density and size distribution of snags and the volume of dead wood contained in stumps in Oak ( Quercus spp.) and Ash ( Fraxinus excelsior) forests and in Sitka spruce ( Picea sitchensis) plantations throughout Ireland. We also assigned each log, snag and stump to one of three decay classes (intact, part-rotted and well-rotted). We found no significant difference in log volume between any of the forest types. The majority (>90%) of logs were less than 20 cm in diameter, and large logs (>40 cm diameter) were scarce. We found a relatively high density of snags in all forest types but, as in the case of logs, over 90% of snags were <20 cm DBH and large snags (>40 cm DBH) were rare. The volume of dead wood contained in stumps was significantly higher in plantations than in Oak or Ash forests as a result of thinning and harvesting. Most logs and snags were moderately decayed but, in plantations, most stumps were intact. Log volume and the size of logs and snags were considerably lower than in old-growth forests in other regions. These patterns may reflect historical use of Irish forests for coppice and timber production. Management for biodiversity should aim to accelerate dead wood accumulation to increase the frequency of large-diameter logs and snags. Although management seeking to replicate the dead wood volumes of old-growth forests is ideal, it may be unrealistic in the short term.

Thinning and Prescribed Fire Effects on Snag Abundance and Spatial Pattern in an Eastern Cascade Range Dry Forest, Washington, USA

Abstract Mechanical thinning and prescribed burning practices are commonly used to address tree stocking, spacing, composition, and canopy and surface fuel conditions in western US mixed conifer forests. We examined the effects of these fuel treatments alone and combined on snag abundance and spatial pattern across 12 10-ha treatment units in central Washington State. A snag census was conducted before and immediately after treatments on each unit where all snags were measured and classified as either “new” (&amp;lt;1 year as a snag) or “old” (&amp;gt;1 year as a snag) mortality, and bark beetle species were censused on the bottom 3-m of the bole. Before treatment, snags were found in all units and more than two-thirds of the snags were ponderosa pine. Burning (burn-only and thin + burn combined) treatments led to increases in total snag abundance in all but the largest diameter class. Snag abundance in the large snag class (&amp;gt;60 cm dbh) decreased in most treatment units indicating that units with high abundance before treatment had the potential to lose more snags with treatment or time. Treatments also affected the spatial distribution of snags. The thin-only treatment reduced clumpiness, leading to a more random snag distribution, whereas the burn-only and thin + burn treatments generally retained or enhanced a clumped snag distribution. Bark beetles attacked &amp;gt;75% of snags across all units before and after treatments, and red turpentine beetle (Dendroctonus valens LeConte) occurrence tended to increase after prescribed burning. Managers can use this information to tune silvicultural prescriptions to meet stocking, spacing, and fuel reduction objectives while retaining or recruiting snags, thereby increasing the utility of conditions for certain wildlife species.

Potential future dead wood dynamics in a multi-ownership region: The Coastal Province of Oregon, USA

Dead wood is important to the processes, structural complexity, and biodiversity of forested ecosystems. Forest management may have unforeseen consequences to dead wood via the interaction of proposed activities with the legacy of past management, natural disturbance, and site productivity. We assessed the potential effects of future forest management for a 300-year period across a large (ca. 23,000km2) forested region that contains numerous ownerships and land management strategies. To do this, we used an ecological gap model (ZELIG), a dead wood decomposition dynamics model (CWDM), live and dead wood data from a physiographic province-wide plot database, and ownership- and land-allocation-specific management prescriptions. Dead wood amounts were projected to increase over the simulation period across the region, primarily because conservation-oriented management approaches utilized on federal lands increased the volume of large logs and snags and number of large snags on federal lands. Large snags and logs decreased on forest industry lands as legacy dead wood derived from historical natural disturbance events was not replaced through management. The results of this study provide an estimate of the maximum potential amounts of dead wood in the forests of the Coastal Province of Oregon, USA, under current policies and forest management, given model assumptions. In cases where current amounts of dead wood may be lower than those present historically, conservation-oriented policies designed to maintain or increase dead wood amounts, such as the Northwest Forest Plan, may have a strong positive influence on large dead wood abundance and related biodiversity in parts of a region that are also under intensive management.

Ponderosa pine mortality during a severe bark beetle (Coleoptera: Curculionidae, Scolytinae) outbreak in southern British Columbia and implications for wildlife habitat management

We examined the extent and severity of bark beetle ( Dendroctonus sp.) attack in ponderosa pine forests in southern British Columbia using stand monitoring plots and forest insect overview survey data, and relate these results to vertebrate wildlife habitat conditions. Monitoring plots established in ponderosa pine stands in 2007 indicate overall mortality levels of 77.8% for trees >7.5 cm dbh by 2008, with lower mortality rates for small stems in the 7.6–15 cm dbh range (53%) and very high mortality (94.9%) of large stems >30 cm dbh. Data from insect overview surveys indicated the attack was extensive and continues to expand. In the Kamloops district, 52,126 ha, or 36% of the area with ponderosa pine as a component of the stand was attacked in 2007 alone, with many areas likely attacked in more than one year. The current bark beetle attack represents a strong “thinning from above” disturbance that is extensive and will have long-term consequences for canopy closure and overstory structure. These changes will have implications for species dependant on mature overstory trees or large snags for foraging and nesting, with effects greatest in pure stands of ponderosa pine. In mixed stands of ponderosa pine and Douglas-fir, ponderosa pine mortality will likely enhance habitat for species dependent on mature or old forest structure by increasing levels of snags, downed wood and creating natural within-stand gaps and heterogeneity. An extensive natural disturbance like the current bark beetle outbreak, following the extensive harvesting in ponderosa pine forests between 1850 and 1950 may frustrate management attempts to provide future diverse habitat conditions for flora and fauna, and other commodities such as viewscapes, recreation and timber. Silvicultural interventions can facilitate the development of mature conditions in some pure stands of ponderosa pine where mature trees have been killed, and should be considered to reconcile current conditions with desired mid- and long-term habitat requirements.

Long-term snag and downed woody debris dynamics under periodic surface fire, fire suppression, and shelterwood management

There are pronounced differences in the processes that act to determine the type and amount of standing and downed coarse woody debris present under partial harvesting versus other noncatastrophic disturbances. To evaluate long-term differences in snag and downed woody debris (DWD) dynamics, we developed a simulation model to project snag density and DWD volume by size and decay class in white pine ( Pinus strobus L.) and red pine ( Pinus resinosa Ait.) dominated stands under (i) a high-retention shelterwood system, (ii) periodic surface fire, and (iii) fire suppression. Snag densities under a high-retention shelterwood system were consistently lower than those in the fire-suppression and surface-fire scenarios, even if no large snags were felled at the time of harvest. Regular inputs from harvest residues were important in maintaining the total volume of DWD, but this material tended to be concentrated in a narrow range of decay classes at any given time. Preserving existing DWD at harvest was less influential than the level of inputs from harvest residues. Active measures for snag creation and staggering of harvest stages among adjacent stands may help minimize differences in the overall supply and temporal variation of coarse woody debris between managed and both naturally disturbed and old-growth stands.

Monitoring Landscape-Scale Ponderosa Pine Restoration Treatment Implementation and Effectiveness

We evaluated landscape-scale forest restoration treatment implementation and effectiveness in meeting objectives in a ponderosa pine forest at Mt. Trumbull, Arizona, U.S.A. The goal of the project was to alter forest structure by thinning and burning to more closely resemble forest conditions prior to Euro-American settlement in 1870. We measured 117 permanent plots before (1996/1997) and after (2003) treatments. The plots were evenly distributed across the landscape (approximately 1,200 ha), about half of which was an untreated control. We evaluated treatment implementation and effectiveness based on 1870 structure and/or goals outlined by managers. The success of treatment implementation varied: about 94% of the area originally planned for restoration was treated in some manner by 2003, but only 70% received the full planned treatment (thin and burn). Although density of ponderosa pines >2.5 cm was reduced significantly by 66% from approximately 429 pines/ha to approximately 146 pines/ha in the treated area, the targeted residual density was exceeded by 111–256% (all plots) or 10–85% (thinned and burned plots). Thirteen percent of the pre-settlement pines died in the treated area by 2003, but 9% percent also died in the control, indicating that pre-settlement pines in untreated areas were nearly as vulnerable as those exposed to restoration treatments. Large snags increased 45%, and 65% of logs >50 cm were retained, achieving implementation goals. Although restoration treatments were not implemented totally to specifications, they were effective in attaining the overall project goal of restoring more open forest structure while preserving more than 75% of the pre-settlement pines. Canopy fuel loads were substantially reduced, allowing for the reintroduction of surface fires.

Snag abundance and species composition in a managed forest landscape in central Japan composed of Larix kaempferi plantations and secondary broadleaf forests

Larix kaempferi is the main plantation species in the low-snow, cool-temperate zone of Japan. I studied L. kaempferi plantations of various stand ages in central Japan to examine and compare the effect of stand age on the abundance, size, and species composition of snags (standing dead trees) compared to those in secondary broadleaf forests. Plantations that were older than the standard rotation age had more and larger snags than young plantations, and the species diversity of snags was positively correlated with stand age. Because the density of living planted L. kaempferi showed little correlation with snag variables, whereas that of naturally regenerated tree species was positively correlated with snag variables, the density dependence of snag occurrence was stronger in naturally regenerated trees than in planted L. kaempferi. Snag species that were positively correlated with stand age were the main species in secondary broadleaf forests in this area. Basal area, density, and number of species of snags in standard-rotation plantations were significantly lower than in long-rotation plantations and secondary broadleaf forests. Long-rotation plantations are useful for retaining snags compared to standard-rotation plantations.

Aboveground large tree mass estimation in a coastal forest in British Columbia using plot-level metrics and individual tree detection from lidar

Plot-level large tree and snag aboveground mass (TSAM) in a second-growth coastal Douglas-fir forest stand in British Columbia was estimated using light detection and ranging (lidar) combining metrics from individually identified trees and snags and plot-level lidar canopy return density. Individual trees were identified using the tree variable window (TreeVaW) algorithm, which identifies tree crowns using a circular moving filter and the relationship between tree height and crown diameter. A multiple linear regression model was then developed to predict plot-level TSAM as determined from ground plots. The predicted heights of individually identified trees were very accurate (r2 = 0.92, SEE = 0.69 m). Plot TSAM was predicted with an r2 = 0.75 and SEE = 29.68 Mg/ha using lidar density and height metrics alone, and a slightly lower r2 = 0.71 and SEE = 31.95 Mg/ha using lidar density metrics with individually identified tree heights. Using individual tree metrics did not improve plot-level TSAM estimation, since a large component of TSAM is contained in complex canopy levels where individual trees are difficult to identify.

Nest-site selection by cavity-nesting birds in relation to postfire salvage logging

Large wildfire events in coniferous forests of the western United States are often followed by postfire timber harvest. The long-term impacts of postfire timber harvest on fire-associated cavity-nesting bird species are not well documented. We studied nest-site selection by cavity-nesting birds over a 10-year period (1994–2003), representing 1–11 years after fire, on two burns created by mixed severity wildfires in western Idaho, USA. One burn was partially salvaged logged (the Foothills burn), the other was primarily unlogged (the Star Gulch burn). We monitored 1367 nests of six species (Lewis’s Woodpecker Melanerpes lewis, Hairy Woodpecker Picoides villosus, Black-backed Woodpecker P. arcticus, Northern Flicker Colaptes auratus, Western Bluebird Sialia mexicana, and Mountain Bluebird S. currucoides). Habitat data at nest and non-nest random locations were characterized at fine (field collected) and coarse (remotely sensed) spatial scales. Nest-site selection for most species was consistently associated with higher snag densities and larger snag diameters, whereas wildfire location (Foothills versus Star Gulch) was secondarily important. All woodpecker species used nest sites with larger diameter snags that were surrounded by higher densities of snags than at non-nest locations. Nests of Hairy Woodpecker and Mountain Bluebird were primarily associated with the unlogged wildfire, whereas nests of Lewis’s Woodpecker and Western Bluebird were associated with the partially logged burn in the early years after fire. Nests of wood-probing species (Hairy and Black-backed Woodpeckers) were also located in larger forest patch areas than patches measured at non-nest locations. Our results confirm previous findings that maintaining clumps of large snags in postfire landscapes is necessary for maintaining breeding habitat of cavity-nesting birds. Additionally, appropriately managed salvage logging can create habitat for some species of cavity-nesting birds that prefer more open environments. Our findings can be used by land mangers to develop design criteria for postfire salvage logging that will reserve breeding habitat for cavity-nesting birds.

Preservation of old‐growth forests: a case study of Big Timber Park, Whistler, BC

This paper explores the concepts of old‐growth forests, preservation and natural disturbance and demonstrates how contemporary biogeographic theory contributes to successful preservation of old‐growth forests. The case study analyzes the composition, structure, age and growth histories of trees in Big Timber Park, Whistler, British Columbia. Composition. The structure of the forest was diverse and tree ages ranged from 122 to 305 years. The densities of large old Douglas‐fir, shade‐tolerant trees and all snags are indicative of old‐growth forests; however, maximum tree diameters and densities of large snags and logs do not meet quantitative criteria for old‐growth forests. The abundance of tree regeneration and understory vegetation are relatively low. We conclude that some aspects of Big Timber Park are transitional between the mature and old‐growth stages of forest development. In the future, fine‐scale canopy gaps caused by tree senescence and interactions among insects, pathogens and wind are expected to dominate stand dynamics. Forest structure will become increasingly complex, exemplifying the dynamic nature of old‐growth forests. To successfully preserve Big Timber Park and La préservation des forêts other old‐growth forests in Canada requires understanding of natural disturbances. Preservation and the criteria and indicators used to measure successful preservation must explicitly include elements of natural change.

Abundance, habitat preference and distribution of small mammals in Dinder National Park, Sudan

Abundance, habitat preference and distribution of small mammals in Dinder National Park, Sudan

Vegetation responses to stand structure and prescribed fire in an interior ponderosa pine ecosystemThis article is one of a selection of papers from the Special Forum on Ecological Studies in Interior Ponderosa Pine — First Findings from Blacks Mountain Interdisciplinary Research.

A large-scale interior ponderosa pine ( Pinus ponderosa Dougl. ex P. &amp; C. Laws.) study was conducted at the Blacks Mountain Experimental Forest in northeastern California. The primary purpose of the study was to determine the influence of structural diversity on the dynamics of interior pine forests at the landscape scale. High structural diversity (HiD) and low structural diversity (LoD) treatments were created with mechanical thinning on 12 main plots. Each plot was then split in half with one-half treated with prescribed fire. During the 5 year period after the treatments, the LoD treatments showed slightly higher periodic annual increments for basal area (BA) and significantly higher diameter increments than did the HiD treatments, although HiD carried twice as much BA as LoD did immediately after the treatments. Prescribed fire did not affect growth, but killed and (or) weakened some trees. No interaction between treatments was found for any variable. Stand density was reduced from the stands before treatments, but species composition did not change. Old dominant trees still grew and large snags were stable during the 5 year period. Treatments had minor impacts on shrub cover and numbers. These results suggest that ponderosa pine forest can be silviculturally treated to improve stand growth and health without sacrificing understory shrub diversity.

Preburn Characteristics and Woodpecker Use of Burned Coniferous Forests

ABSTRACT Large wildfires are common in many western coniferous forests, and these fires can affect woodpecker reproduction and habitat use. Our objectives were to examine nesting densities, reproductive parameters, and species‐specific habitat selection of woodpeckers in a recently burned region of the Black Hills in South Dakota, USA, between 2001 and 2004. Postfire nesting densities were greatest in areas dominated by high prefire canopy cover, and reproductive success averaged &gt;70%. For some species of woodpeckers, factors such as diameter at breast height, burn severity, and distance to unburned patches were important for nest‐site selection. Our data indicated that nesting densities of many woodpeckers in the Black Hills were lower than what has been recorded elsewhere following recent, large wildfires in ponderosa pine (Pinus ponderosa) forests. Management activities that simulate mixed‐severity fire effects and retain higher numbers of large snags are likely to benefit cavity nesters in this region.

Comparing Classification Systems for Ponderosa Pine Snags in Northern Arizona

Abstract The degree to which snag classification systems predict actual snag “age” (time since tree death) is rarely known. We used dendrochronology to determine the death dates of 79 large (more than 40 cm dbh, more than 3 m in height) ponderosa pine snags in northern Arizona and compared the snag ages to those predicted by a commonly used simulation model and to five classification systems. The methods are limited to trees for which intact tree-ring samples could be extracted, but the data provided evidence of some snags standing for long periods (to 141 years) and correlation of snag traits with age. The simulation model underestimated snag age in the first three categories. Mean ages of snags in the last category were estimated accurately but with low precision. Comparison of snag ages to their classification in five systems showed that bole breakage was unrelated to snag age, that limb loss occurs at divergent rates between individual trees, and that wood decay does not necessarily proceed sequentially. A system based on the attrition of bark from snag boles proved useful for distinguishing snags by physical traits, but different classification systems may be needed to meet specific needs for assessing past forest structure and wildlife habitat.

An index to identify late-successional forest in temperate and boreal zones

Old forests of the temperate and boreal zones are globally critical for forest biodiversity conservation yet are rapidly declining where commercial forestry dominates. Forest certification programs are the only global policy instruments that require private landowners to conserve old forest, but certified landowners lack the necessary practical tools to do so. We developed statistically based, practical late-successional indices that can be used in the field to quickly identify high-conservation value old forest. We measured late-successional forest attributes in economically mature and older stands to be able to distinguish economically mature stands from late-successional stands for two forest types: northern hardwood forest and upland spruce-fir forest. Based on step-wise discriminant function analysis, the best single variable for both forest types was large (≥40 cm dbh) alive and dead tree density. For upland spruce-fir forest, the best linear discriminant function was created by adding one variable: large (≥35 cm dbh) log count. The thresholds levels between economically mature and late-successional stands were: 9 large live and dead trees/0.02 ha plot for northern hardwoods, 8 large live and dead trees/0.02 ha plot for upland spruce-fir forest, and a linear discriminant function score of 2.147 for upland spruce-fir forest. Indices were developed using old-growth data to provide reference levels with scores ranging from 0 to 10. The indices misclassified approximately 15% of economically mature and late-successional stands from an independent dataset. The indices increased across a range of seral classes with the greatest increases occurring between late seral stages. The indices were correlated with other late-successional attributes including: large snags, large logs, abundance of seven LS epiphyte taxa, tree size distribution, and dead wood variables. Our indices have been used to: conserve old forest by certified landowners; train foresters about ecological forestry; verify the implementation of late-successional management goals; and assess trends of late-successional forest in the region. Our approach could be used to develop LS indices for other regions to help conserve old forest.

Effect of thinning and prescribed fire restoration treatments on woody debris and snag dynamics in a Sierran old-growth, mixed-conifer forest

Forest managers have little information of the effects of common restoration treatments, thinning and burning, on dead woody material (DWM) dynamics in fire-suppressed forests. Fine woody debris (FWD; 0.6–29.9 cm), coarse woody debris (CWD; ≥30.0 cm), and snags (≥5 cm) were inventoried and mapped in eighteen 4 ha plots before and after applying thinning (overstory, understory, and no thinning) and burning (burn and no burn) treatments. The combination of burning and thinning reduced FWD and CWD quantity and mean piece size, removed highly decayed logs, and increased small (5.0–24.9 cm) snag recruitment. In contrast, thin-only treatments produced similar results but increased FWD and did not remove many small snags. There were no differences in DWM response between the two thinning treatments. Log and snag spatial patterns prior to and following treatment were similar. These results indicate that burning in combination with thinning is more effective at reducing surface FWD and CWD, and removing small trees than are burn-only and thin-only treatments. Although large snags and logs were consumed in the burn, long-term recruitment of these habitat structures relies on managers retaining large-diameter trees. Repeated burns need to be conducted after initial restoration treatments to understand natural patterns of DWM.

Foraging Ecology of Pileated Woodpeckers in Coastal Forests of Washington

In the Pacific Northwest, providing adequate habitat for pileated woodpeckers (Dryocopus pileatus) has been a key component of federal forest management strategies for over 20 years. Although their nesting and roosting ecology has been well studied, information on their foraging ecology is limited. From 1990 to 1995, we studied food habits of pileated woodpeckers in coastal forests (with scat analysis); estimated the relative abundance of their primary prey, carpenter ants (Camponotus spp.), associated with logs and cut stumps; and investigated selection of forest structures and site characteristics used by pileated woodpeckers for foraging. Pileated woodpeckers primarily consumed carpenter ants (54% of diet), but round-headed beetle larvae (Coleoptera, Cerambycidae) and dampwood termites (Isoptera, Termopsidae) were important food items during the breeding season (Mar–Jun). Selection of foraging structures was related to wood characteristics and microsite conditions that influence the presence and abundance of arthropod prey. Pileated woodpeckers foraged almost exclusively (95%) on standing structures, selecting tall, large-diameter snags in early to moderate stages of decay. Contrary to previous studies, pileated woodpeckers rarely (2%) foraged on logs. Carpenter ants were scarce at logs in closed-canopy habitats, which suggested that in coastal forests logs are too cool and wet to support abundant populations of carpenter ants. Selection of foraging sites by pileated woodpeckers was influenced by the abundance of potential foraging structures; 0.4-ha plots with recent foraging activity had greater densities of large snags (>51 cm dbh and ≥7.5 m tall) than plots without recent foraging. The efficacy of management strategies designed to provide habitat for pileated woodpeckers would be enhanced if they included specific provisions for foraging habitat and accounted for regional differences in the types of structures that provide suitable conditions for wood-dwelling arthropods.

Managing for late-successional/old-growth characteristics in northern hardwood-conifer forests

In the northern hardwood region of North America managing for late-successional forest habitats and functions is an important element of ecosystem management. This study tests the hypothesis that uneven-aged practices can be modified to accelerate rates of late-successional forest development. An approach, termed “structural complexity enhancement” (SCE), is compared against conventional uneven-aged systems modified to increase post-harvest structural retention. Experimental treatments, including controls, were applied to 2 ha units and replicated at two multi-aged northern hardwood forests in Vermont, USA. Structural objectives include vertically differentiated canopies, elevated large snag and downed log densities, variable horizontal density (including small gaps), and re-allocation of basal area to larger diameter classes. The latter objective is achieved, in part, by cutting to a rotated sigmoid diameter distribution. This is generated from a basal area (34 m 2 ha −1) and tree size (90 cm dbh) indicative of old-growth structure. Forest structure data have been collected over 2 years pre-treatment and 3 years post-treatment. Fifty-year simulations of stand development were run in NE-TWIGS and FVS comparing treatment and no treatment scenarios. Simulations also tested the sensitivity of large tree development to prescription parameters. Leaf area index retention was spatially variable but significantly ( P < 0.001) greater under SCE (91%) compared to conventional treatments (75%). Post-harvest aboveground biomass ( P = 0.041), total basal area ( P = 0.010), and stem density ( P = 0.025) were significantly different among treatments, with SCE generally retaining more structure than conventional treatments. SCE increased coarse woody debris volumes by 140%; there was a 30% increase under conventional treatments. SCE successfully achieved the rotated sigmoid diameter distributions, and sustained these 50 years into the future, resulting in reallocated basal area. Cumulative basal area increments are projected to increase by 3.7 and 5.0 m 2 ha −1 compared to no treatment scenarios for SCE and conventional treatments, respectively. Basal areas will be significantly ( P = 0.025) greater after 50 years in SCE units due to higher residual basal areas. Conventional treatments are projected to produce 10 fewer large trees per hectare (>50 cm dbh) than would have developed without treatment, whereas SCE is likely to recruit five more large trees per hectare than the no treatment scenario. Large tree recruitment rates were related primarily to the form of residual diameter distributions ( P = 0.006) and, possibly, to maximum diameter limits. Late-successional characteristics in northern-hardwood systems can be promoted through a variety of modified uneven-aged silvicultural approaches based on the results.