Hardwood Regeneration Research Articles

Twenty-year responses of aspen stands to forest tent caterpillar defoliation and overstory dieback in Northeastern Ontario, Canada

Forest tent caterpillar (Malacosoma disstria Hbn.) is a major forest defoliator in North American boreal forests. This pest periodically affects hardwood trees such as trembling aspen (Populus tremuloides Michx.) and balsam poplar (Populus balsamifera L.) across large areas, causing mortality and altering stand attributes and long-term dynamics. In this study, I quantified the responses of aspen stands to forest tent caterpillar defoliation and overstory dieback, including short-term (5 years after dieback) and long-term (20 years later) dynamics. Results indicate that affected stands fully recovered to pre-dieback density but not basal area. Defoliation caused overstory dieback that stimulated understory growth and regeneration but the hardwood regeneration (mostly aspen) did not adequately replace hardwood trees lost to defoliation, resulting in decreased hardwood composition relative to unaffected stands. The high density in affected stands suggested possible further basal area recovery as regeneration and released understory conifers grew into main canopy, following the general trends of boreal mixedwood succession. The results support earlier projections based on residual stand attributes shortly after dieback and reported boreal species growth and mortality rates that indicate forest tent caterpillar defoliation and subsequent overstory dieback would accelerate aspen stand transition to conifer dominance and delay the availability of stands for harvesting by 40–50 years as stands recover.

Harvest block aggregation as a driver of intensive moose browsing pressure on hardwood regeneration in a temperate forest

In many regions of the world, browsing pressure by ungulates has increased over the last century, often reaching unsustainable levels. Overbrowsing by ungulates is threatening biodiversity and causing delays in the establishment of forest regeneration. Moose (Alces alces) is considered as an ecological engineer, as it can cause severe impacts on stand structure, composition, quality, and succession through overbrowsing. In conifer-dominated stands, moose browsing pressure has been shown to vary with the distribution of forage and cover patches across the landscape, but such spatial relationships have not been explored in hardwood-dominated landscapes, where intensive forest management can create clustered patches of good-quality forage and cover, ideal conditions for wintering moose. We investigated the influence of local and landscape variables on browsing by North American moose (Alces alces americana) on commercial and non-commercial woody regeneration in an intensively managed forest landscape of northwestern New Brunswick, Canada. We predicted that browsing pressure at the local scale (vegetation sampling plot) would increase with moose winter counts in the surrounding landscape (1 to 3 km radius). We modeled moose counts as a function of environmental features and road density, using a quasi-Poisson regression. According to an aerial survey (25 km2 sampling plots), moose counts increased with the proportion of forage patches (disturbed stands < 20 years old), whereas they decreased with the proportion of mixed mature stands > 80 years old, which offer both forage and cover. We extrapolated this model to a 2770 km2 study area and used predicted counts as an independent variable to assess its influence on browsing pressure. In 720 plots of 4.15 m2, browsing pressure was quantified using occurrence (i.e. proportion of seedlings/saplings with at least one twig browsed during the previous winter) and intensity (i.e. mean proportion of twigs browsed per stem) on commercial and non-commercial tree seedlings and saplings. We explained variation in occurrence and intensity using zero-inflated models with snow precipitation and local vegetation variables as covariates. Browsing pressure increased with predicted moose counts within a 3 km radius, with snow precipitation and with the proportion of coniferous trees in the canopy, whereas it decreased with sapling density. These results highlight the importance of seedlings and saplings in moose winter diet and confirm the attraction of moose toward recent (<20-year-old) harvest blocks during winter. Therefore, we should avoid aggregating harvest blocks to decrease their attractiveness to moose and browsing pressure on natural hardwood regeneration.

Seasonal Resource Selection and Use of Hardwood Regeneration by Translocated Wild Turkeys in the Mississippi Alluvial Valley

Reforestation practices have intensified in the Mississippi Alluvial Valley (MAV) of the United States of America with the aid of Farm Bill programs during the past three decades. Increases in reforested land also enhance possibilities to restore once-abundant but currently sparse species, such as eastern wild turkeys (Meleagris gallopavo silvestris) in the MAV. However, it is unknown whether &lt;20-year-old hardwood regeneration provides a suitable habitat for re-establishing wild turkey populations in the MAV. We translocated wild turkeys to two study sites in reforested areas of the MAV. We monitored 74 wild turkeys’ habitat use and resource selection using radio telemetry from February 2009 to June 2010. We developed land use and land cover maps for the resource selection analysis of translocated wild turkeys. We found that turkey habitat use varied by site, sex, season, land cover type, and distance to mature hardwoods. Habitat use by wild turkeys decreased as distance to mature hardwood forest increased. Female wild turkeys used more hardwood regeneration during nesting and post-nesting seasons than during pre-nesting seasons. Although wild turkeys did not use regenerating and mature hardwood forests to the same extent, management of these forests appears critical to restoring wild turkeys in the MAV.

Hardwood regeneration in red pine plantations: Thinning and site quality effects on changes in density and species composition from edges to interiors

Red pine plantations may promote more desirable hardwood regeneration than hardwood stands because of differences in: 1) the composition and quantity of tree seeds available, and 2) abiotic and biotic properties of growth and establishment environments. However, information on how distance from hardwood edges, thinning of overstory pine, and site quality shapes hardwood regeneration properties in red pine plantations is scarce. Such information would aid in understanding and managing red pine plantation effects on hardwood regeneration processes and guide spatial and temporal rotations of such effects across landscapes. To elucidate relationships, we monitored hardwood seedlings and canopy openness across transitions from hardwood edges to red pine plantation interiors at 40 sites spanning a site quality gradient in northwestern-lower Michigan. Hardwood seedling density: 1) declined substantially from edges to interiors at all but low-quality sites before stabilizing 30-m into plantations, 2) was reduced, or not affected, by thinning despite positive effects on seedling light environments, and 3) was greater at intermediate than high- and low- quality sites. From edges to interiors, species composition shifted towards Acer rubrum, Quercus species, and Prunus serotina and away from Acer saccharum, Fagus grandifolia, Fraxinus americana, and Ostrya virginiana. Species increasing in relative abundance and/or density from edges to interiors were generally more drought-tolerant, shade-intolerant, large-seeded, and animal-dispersed than decreasing species. Shifts towards less shade-tolerant species from edges to interiors were consistent with increases in canopy openness and were most pronounced where changes in light were greatest (i.e., thinned plantations on high-quality sites). Changes in hardwood seedling density and composition were likely driven by differences across species in dispersal traits, seed characteristics, and relative adaptation to interior conditions (likely hotter, drier, and nutrient poor). To promote commercially valuable hardwoods, increase mast for wildlife, or improve climatic resiliency, the most suitable targets for conversion to hardwoods may be plantations with significant interiors (i.e., area > 30-m from hardwood edges) on higher quality sites adjacent to desirable seed sources (e.g., Quercus rubra, Prunus serotina, Acer saccharum). More desirable hardwood regeneration may result from reevaluating thinning timings and intensities originally designed to maximize red pine production. Our results also indicate that intentional management of surrounding hardwood forest composition (i.e., seed sources), within plantation retention of hardwood islands (e.g., mature oak stems), and greater control of Acer rubrum competition may further increase the desirability of hardwood regeneration in red pine plantations.

Northern hardwood regeneration dynamics 10 years after irregular shelterwood and mechanical control of understory American beech

In northern hardwood stands of the northeastern USA and southeastern Canada, the abundance and occurrence of American beech (Fagus grandifolia Ehrh) regeneration have increased substantially over the past decades, to the detriment of other deciduous species such as sugar maple (Acer saccharum Marshall) and yellow birch (Betula alleghaniensis Britton). To promote the regeneration of these declining species, we established an experimental study near Québec City (Quebec, Canada) to compare the effects of various partial cutting treatments and mechanical control of understory American beech. The design comprises 4 randomized complete blocks, each containing an uncut control, a hybrid single-tree and group selection cutting (SC), two intensities of continuous cover irregular shelterwood (CCIS) and an extended irregular shelterwood (EIS). American beech regeneration, which dominated the sapling layer before cutting, was removed with brush saws in gaps created in the SC and CCIS treatments as well as in the entire understory of the EIS treatment. In addition, gaps and the EIS understory were scarified to favor yellow birch regeneration, and 12 exclosures were built to prevent cervid browsing in CCIS gaps and in entire understory of the EIS treatment. Ten years after cutting, yellow birch regeneration was more abundant in gaps and in the EIS treatment than in the uncut control. These results confirm that increasing the understory light level, eliminating American beech saplings and scarifying the soil can successfully favor yellow birch establishment. However, preferential browsing of yellow birch outside exclosures maintained the overall dominance of American beech in the long term. Thus, under these conditions, damage from repetitive browsing outweighed the positive effects of actions aimed at promoting the regeneration of yellow birch. In the end, despite abundant seed availability, sugar maple remained only a minor component of the regeneration.

Long-Term Suppression of Hardwood Regeneration by Chinese Privet (Ligustrum sinense)

Native hardwood regeneration in the southeast United States is hindered by repeat disturbance events and the presence of invasive species. Our study aimed to determine the ability of native species in an unmanaged urban forest fragment to persist following high winds from hurricane Gustav in 2008 and subsequent salvage logging. In 2009, researchers estimated the density and composition of the regeneration and overstory trees as well as percent crown cover of invasive Chinese privet. Percent Chinese privet cover was visibly high, leading them to believe it may be inhibiting native hardwood establishment. Ten years later in 2019, we returned to the plots to take repeat measurements. Forest composition remains the same and privet crown cover remains high. There has been no increase in regenerating individuals, and overstory trees per hectare and basal area remains low. These results confirm that the heavy Chinese privet presence is persistent long term and will require management to promote reproduction of native overstory tree species.

Hardwood Regeneration in Red Pine Plantations: Thinning and Site Quality Effects on Changes in Density and Species Composition from Edges to Interiors

Hardwood Regeneration in Red Pine Plantations: Thinning and Site Quality Effects on Changes in Density and Species Composition from Edges to Interiors

AVID: A rapid method for assessing deer browsing of hardwood regeneration

Extensive deer browsing threatens the ability of many forests in the northeastern United States to regenerate and sustain their biodiversity. To reliably assess whether deer are reducing the regeneration of key tree species valued for timber and wildlife, we developed a rapid field protocol for Assessing Vegetation Impacts from Deer (AVID, http://AVIDdeer.com). AVID is a method for foresters, landowners, volunteers, and others to measure the effect of deer browsing on seedling growth. Our objectives were to: 1. Determine if the AVID method could detect differences in growth rates for protected (fenced) and unprotected seedlings, 2. Evaluate AVID’s usefulness as a regeneration monitoring tool for citizen-science engagement, and 3. Compare and contrast the relative strengths and weaknesses of common methods for measuring deer impacts to vegetation. We compared fenced and unfenced plots at 10 research sites in New York State to validate the sensitivity of AVID for detecting deer impacts to seedling growth. Tagged seedlings were measured annually for height growth in replicated plots. Deer reduced average seedling height growth of palatable species several fold at these sites often in combination with the effects of site and year. From 2016 through 2020, we conducted 59 AVID training events with 1,399 participants including landowners, students, educators, naturalists, resource management professionals, and land trust staff. Volunteers established plots at 83 sites in 24 New York counties demonstrating that AVID provides a valued citizen-science approach for both teaching people and assessing deer impacts to forest regeneration. Once volunteers consistently monitor a statistically valid number of plots for several years, the New York’s Department of Environmental Conservation intends to use AVID data to inform deer management decisions.

Modeling tolerant hardwood sapling density and occurrence probability in the Acadian forests of New Brunswick, Canada: Results 14 years after harvesting

Natural forest regeneration after natural or anthropogenic disturbance is difficult to predict given its high variability. The process is poorly documented for commercial northern hardwood species in the Acadian forest of eastern Canada. Our objective was to identify the silvicultural, environmental, and ecological factors that best explain the variability in sapling density and occurrence of two commercial tolerant hardwood species in New Brunswick: American beech (Fagus grandifolia Ehrh.) and sugar maple (Acer saccharum Marsh.). Forty-three permanent sample plots were established in 2002 and measured before harvesting in 2004. Sapling density and occurrence were measured 14 years after harvesting. The results showed that the interactions between the species and the residual merchantable basal area and between the species and the percent of hardwoods in the original stand best explained the sapling density and occurrence variation of tolerant hardwoods. The sapling density of sugar maple increased with increasing merchantable residual basal area. However, the effect of this variable was not significant for the density of American beech saplings. The density and occurrence of tolerant hardwood saplings both increased along with the percent of hardwoods in the original stand. These results provide an improved understanding about tolerant hardwood regeneration dynamics in New Brunswick forests.

Development of Redwood Regeneration after Conifer Partial Harvest and Hardwood Management

Abstract Harvesting of commercial conifer species from conifer-hardwood mixtures can leave residual stands dominated by hardwoods. Removing unwanted hardwoods by cutting or herbicide makes growing space available to residual trees and regeneration and can restore conifer dominance. Forest managers of north coastal California need guidance on how such treatments affect subsequent growth of planted redwoods (Sequoia sempervirens [D. Don.] Endl.) or natural regeneration, as well as proliferation of undesirable species. Our observational study reconstructed growth of 108 regenerating redwoods in 26 treated stands. Residual stand density was the main driver of height and diameter growth in the new cohort of redwoods, irrespective of whether hardwoods were cut or received herbicide frill treatment (prevents resprouting). At lower residual stand densities, there were higher densities of natural regeneration (ingrowth) of conifers and hardwoods, which affected diameter at breast height (dbh) growth of regenerating redwoods. After heavier cutting of hardwoods, this ingrowth comprised a greater proportion of unwanted hardwood regeneration. Therefore, frill treatment is recommended when the objective of management is to reduce hardwood stocking and regeneration. Combining partial harvesting of conifers with cutting or frill treatment of hardwood is another option that reduces stand density to promote height and dbh growth of regenerating redwoods.

Prescribed burn frequency, vegetation cover, and management legacies influence soil fertility: Implications for restoration of imperiled pine barrens habitat

In fire-dependent ecosystems, the absence of fire can contribute to a positive feedback in which increased vegetation cover leads to increased accumulation of soil organic matter and nutrient stocks. These changes in turn can influence competitive shifts among plant communities, resulting in increased woody plant establishment, canopy closure, and ultimately leading toward mesophication. Poor soil conditions may be especially important for maintaining the open structure characteristic of pine barrens ecosystems, which are imperiled due to loss of key ecosystem processes such as fire and land conversion to cropland or pine plantations. Our objectives were to determine how soil characteristics are related to recent prescribed fire management, and how soils vary along gradients of current and historic vegetation cover in a barrens-forest mosaic in northern Wisconsin, USA. We sought to understand whether management with prescribed fire shifts soils toward barrens-type soil conditions, and whether soil conditions typify barrens habitat relative to shrub and forest habitat We analyzed organic (i.e. forest floor) and mineral soil horizons collected along gradients of recent prescribed burn history and current (barrens, pine woodlands, brush, and closed-canopy forest) and historic vegetation cover types (barrens, pine plantations, deciduous forests) to investigate the influence of each on specific components of soil fertility. Using a model selection approach, we found forest floor soil properties were most frequently associated with differences in current vegetation cover; for instance, pine woodland sites had greater organic matter stocks than barrens sites, and cation stocks were generally greater at brush sites than barrens and pine woodland sites. Some soil properties, including pH, however, appeared to be driven by prescribed burn frequency. Using ordination techniques to characterize multidimensional characterizations of soils, we identified a soil legacy effect related to historic vegetation cover and land management; native barrens sites had soil characteristics intermediate to restored barrens of pine woodland and deciduous forest origin. Our findings suggest restoration of pine plantations to barrens could benefit from fire activities that enhance consumption of the forest floor, while restoration of deciduous forest and brush habitats will likely be more related to the effective control of hardwood regeneration, after which soil conditions may return to a more archetypical barrens state.

Restoration of Shortleaf Pine (Pinus echinata)-Hardwood Mixtures in Low Quality Mixed Upland Hardwood Stands Using Cluster Planting and Natural Regeneration

Cluster planting of shortleaf pine, along with various site preparation and release treatments, were tested to restore mixed shortleaf pine (Pinus echinata Mill.)–hardwood stands in areas where the shortleaf pine has diminished in recent years. Shortleaf pine–hardwood mixtures were once a common forest type throughout the Cumberland Mountains and Plateau physiographic regions of the southeastern United States. Knowledge of how to restore shortleaf pine–hardwood mixtures is limited throughout shortleaf pine’s large native range. The objectives of this study were to compare planted shortleaf pine and natural hardwood regeneration survival, growth, and composition following various site preparation and early release treatments. Cluster planting and partial timber harvesting were used to reintroduce shortleaf pine and create two-aged stands in the Cumberland Mountains of Tennessee, USA. Results indicated that shortleaf pine survival, basal diameter, and height growth did not differ following four growing seasons among treatments. Natural regeneration stem densities and heights within shortleaf pine clusters did not differ significantly by treatment. Natural regeneration stem densities differed by species group and height class across the site, while the treatment × species interaction term was also significant. At this early stage of stand development, the brown-and-burn treatment appears poised for greater shortleaf pine growth rates than the other treatments. The herbicide treatment had the fewest regenerating hardwoods per hectare and the most desirable hardwood species composition.

Effects of burn season on large seedlings of oak and other hardwood regeneration three years after shelterwood harvest

Abstract The effects of fall and spring prescribed fires on large seedlings (0.3 to 1.3 m height) of oak and other hardwood species three years after a shelterwood harvest were examined in Richland Furnace and Zaleski State Forests in southern Ohio. Fall and spring burns appeared to be more deleterious to red oaks (Quercus rubra L., Q. velutina Lam., Q. coccinea Muenchh.) than white oaks (Q. alba L., Q. prinus L.). Red oak experienced reductions in numbers and canopy volume after spring burns, and canopy reductions after fall burns. White oak experienced small increases in numbers of stems after both fall and spring burns, and an increase in the canopy volume after fall burns, but a slight decrease after spring burns. Yellow-poplar (Liriodendron tulipifera L.), a major oak competitor prior to fire, experienced dramatic reductions in the number of regenerating stems and canopy volume after both fall and spring burns. On the other hand, red maple (Acer rubrum L.) experienced large increases in the number of regenerating stems and canopy volume after both fall and spring burns. Based on importance value, the oak species remained relatively unchanged after both fall and spring burns. Yellow-poplar became the least dominant species after spring burns and the second to last dominant species after fall burns.

Stand dynamics and competition in a mixed forest at the northern distribution limit of evergreen hardwood species.

Tree species of three growth forms (evergreen conifers, deciduous hardwoods, and evergreen hardwoods) codominate at the northern distribution limit of evergreen hardwoods in central Japan. This study examined the stand dynamics and competition during 13 years at a single plot to reveal how three growth forms codominate at the ecotone. Species were characterized as large DBH and low tree density for evergreen conifers, and conversely for evergreen hardwoods. Total basal area increased during the examined period, accompanied with the reduction in tree density (i.e., mortality exceeded the recruitment rate). Mortality increased with time especially for small trees of deciduous hardwoods. The effect of competition among the three growth forms on tree growth was not detected. Species were classified into two axes. Ingrowth and recruitment rates of large evergreen conifers were lower than those of small evergreen hardwoods. The population growth rate was lower in species with greater mortality within each growth form. Deciduous hardwoods showed the highest mortality and lowest population growth rates among the three growth forms. Although the tree‐ring analysis revealed that disturbances occurred to some extent, the current disturbance regime would not trigger the regeneration of deciduous hardwoods. This study suggests that negative relations of maximum DBH with ingrowth and recruitment rates contribute to codominance of evergreen conifers and evergreen hardwoods, and more frequent or larger disturbances than at present are necessary for regeneration of deciduous hardwoods.

Delayed tree mortality, bark beetle activity, and regeneration dynamics five years following the Wallow Fire, Arizona, USA: Assessing trajectories towards resiliency

Warm/dry mixed conifer forests have undergone changes in disturbance regimes, forest structure, species composition, and surface fuel accumulation which have led to increased susceptibility to large, uncharacteristically severe wildfires and pathogenic outbreaks. Ecosystems resilient to fire events return to a similar set of structures (e.g., forest and understory composition and density) or processes (e.g., fire, decomposition rates); however, when exposed to disturbances outside the evolutionary envelope, may transition to a different state (e.g., type conversion). We sampled warm/dry mixed conifer forest stands treated prior to the 2011 Wallow Fire and paired untreated sites five years following the fire. Our objective was to evaluate mid-term ecosystem resiliency in terms of forest structure, bark beetle activity, and tree regeneration. We hypothesized that treated units would have higher mid-term post-fire resiliency compared to untreated units. In 2016, average total tree density remained significantly lower in treated compared to paired untreated units; conifer density and BA decreased in both treated and untreated units. Diameter distributions in 2016 treated units remained similar to those observed in 2012 with the exception of increased density in the smallest diameter class. In untreated units, the majority of tree density reductions occurred in the 10–30 cm dbh classes. Post-fire tree mortality was stable across treated and untreated units, with no significant differences; however, abundant ingrowth of small hardwoods occurred throughout the study area. Large-tree density decreased by about 20% in both treated and untreated units between 2012 and 2016. Evidence of post-fire bark beetles was generally low and patchy throughout the study site; however, beetle activity was more widespread in untreated units. Twice as many trees were attacked by bark beetles in untreated versus treated units suggesting treatments may have reduced post-fire beetle activity. Following wildfire, observed conifer regeneration was lower and hardwood regeneration was higher with increasing burn severity; conifer regeneration was nearly three times higher in treated units. This study suggests that pre-fire fuel reduction treatments contribute less to mid-term resiliency than to short-term resiliency of forested ecosystems. We observed trends of higher resilience to insect outbreaks and potential implications for type change from conifer to deciduous forest. Furthermore, our study underscores the importance of understanding mid-term post-fire recovery, and while it provides insights regarding recovery of these ecosystems, additional monitoring and research is needed to fully understand the implications toward long-term resiliency.

Influence of browsing damage and overstory cover on regeneration of American beech and sugar maple nine years following understory herbicide release in central Maine

Northern hardwood stands, notably those with American beech (Fagus grandifolia Ehrh), sugar maple (Acer saccharum Marsh.), and yellow birch (Betula alleghaniensis Britton), are abundant across the forested landscapes of northeastern USA and southeastern Canada. Recent studies have reported an increasing dominance of American beech in the understory and midstory of these forests. Beech is a commercially less desirable tree species due to its association with beech-bark disease, and because it commonly interferes with the regeneration of other more desirable tree species. We examined hardwood regeneration characteristics nine years after application of a 3 × 4 factorial combination of glyphosate herbicide (0.56, 1.12, and 1.68 kg ha−1) and surfactant concentrations (0.0, 0.25, 0.5, and 1.0% v v−1) to release sugar maple regeneration from beech-dominated understories using three stands that received shelterwood seed cutting in central Maine. Measurements nine years after treatment showed that glyphosate rate increased both absolute (AD) and relative density (RD) of sugar maple regeneration, but not its height (HT). In contrast, beech AD, RD, and HT were all significantly reduced with increasing glyphosate rate. Post-release browsing by ungulates and a high residual overstory basal area resulted in reduced sugar maple HT. Our results indicated that glyphosate herbicide applied in stands that have been recently shelterwood seed cut can significantly increase the abundance of sugar maple regeneration. However, subsequent browsing damage combined with the negative influence of the residual overstory cover can limit the longer-term benefit of understory herbicide treatments. Subsequent removal of the overstory and browsing-control measures may be needed to promote sugar maple regeneration over beech in similar northern hardwood stands.

Repeated burning alters the structure and composition of hardwood regeneration in oak-dominated forests of eastern Kentucky, USA

The exclusion of anthropogenic fire is a primary factor responsible for the ‘mesophication’ of eastern oak (Quercus) forests and resultant oak regeneration problems. Consequently, the reintroduction of fire is increasingly used to promote the establishment and growth of oak and hickory (Carya) and control competition from shade-tolerant species (e.g., red maple (Acer rubrum)) in the forest understory. In this study, we examined the effects of fire frequency on the abundance of prominent species in the woody regeneration layer in oak-dominated forests of eastern Kentucky. Treatments included: (1) fire-excluded (FE); (2) frequent fire (FF) – five burns over nine years, and (3) less-frequent fire (LFF) – two burns over seven years. Prior to burning (2002) and again five and seven growing seasons following the cessation of burning in the FF and LFF treatments (2015), respectively, we inventoried tree species in the woody regeneration layer into three size classes: (1) small seedlings (stems<0.6m), (2) large seedlings (≥0.6m and <1.2m) and (3) small saplings (≥1.2m and <3.8cm diameter at breast height). Pre- and postburn, the regeneration layer was dominated by non-Oak-Hickory species, and although Oak-Hickory regeneration was abundant the majority of stems were <0.6m. For Oak-Hickory, significant treatment effects were limited to the large seedling and small sapling size classes. For large Oak-Hickory seedlings, density was significantly greater in the LFF than FE treatment. For small Oak-Hickory saplings, density in the LFF treatment was ∼17 and ∼4 times greater than in the FE and FF treatments, respectively. This study provides support for the notion that fire-free periods may be more of a factor controlling the abundance and composition of the woody regeneration layer than simply the number of burns. However, despite greater stem density, the fate of the Oak-Hickory regeneration layer that developed in response to the LFF treatment is uncertain, as the density of non-oak competitors remains high. Additional treatments (e.g., targeted herbicide application, additional burning) may be necessary to reduce the abundance of non-oak species and increase the likelihood of continued recruitment Oak-Hickory should natural or silvicultural release events occur.

Effects of variable retention harvesting on natural tree regeneration in Pinus resinosa (red pine) forests

Concerns over loss of ecosystem function and biodiversity in managed forests have led to the development of silvicultural approaches that meet ecological goals as well as sustain timber production. Variable Retention Harvest (VRH) practices, which maintain mature overstory trees across harvested areas, have been suggested as an approach to balance these objectives; however, long-term evaluations of outcomes of VRH strategies do not exist for most forest types. The objective of this study was to determine the 11-year effects of overstory tree retention pattern and shrub removal on regeneration in P. resinosa forests in Minnesota, USA using a large-scale manipulative study in which four overstory (control, small gap-aggregated, large gap-aggregated, and dispersed) and two shrub (ambient and reduced shrubs) treatments were applied. Hardwood regeneration greatly outnumbered conifer regeneration and several mechanisms (disease, browse, and seedbed conditions) likely interacted to limit P. resinosa regeneration across treatments. The presence of recalcitrant shrub layers filtered response to retention with regeneration of P. strobus L. being greater under an intact Corylus layer irrespective of overstory conditions. This work reinforced the importance of accounting for shrub competition when designing VRH to secure natural regeneration.

Flowering, Fruiting, Seed Fall and Seed Viability of Acer pseudosieboldianum in Mt. Jungwang, Gangwondo

To examine the natural regeneration in the natural mixed-broadleaved forest, flowering, fruiting, seed-fall, and seed viabilities of Acer pseudosieboldianum (Ap) were investigated in Mt. Jungwang, Gangwon-do, from 2009 to 2015. The flower of Ap consisted many male and bisexual flowers on the corymb. Flowering dates are differed between sex morph in the same inflorescence. Stamens are stop growing and disappeared after pollinated pistil begin to grow in bisexual flowers, and male flowers have vestial pistil. The flowers of Ap might be pollinated by Apis mellifera, Andrenidae spp. and Syrphinae spp. Ap had some mechanism to prevent from self pollination with heterodichogamy. Mean annual seedfall of Ap was 70,780 ea/ha (ranged 310~234,840 ea/ha). Annual seedfall of Ap varied severely, and the maximum was about 760 times the minimum. Annual seed production of Ap might be to a normal distribution. Rates of damaged or decayed seeds are highest 59.3%, and those of sound seeds are 23.9%, Those of undeveloped and empty seeds are 9.2% and 7.6%, respectively. The most important factors influencing sound seed production might be the density and activities of insect pollinators and sucking pest in the flowerwing period, middle-late May. Successful regeneration of Ap might be in masting year and on the gap sites with proper conditions to germinate and grow. To understand the natural regeneration of deciduous hardwoods, further study on the characteristics of flowering and fruiting, preand post-dispersal seed predation, and annual variation on these factor should be needed.

The joint effects of fire and herbivory on hardwood regeneration in central Texas woodlands

Oaks (Quercus spp.) are not regenerating in forests and woodlands in central Texas and elsewhere. This has been attributed to fire suppression. However, overabundant white-tailed deer (Odocoileus virginianus) can also limit oak regeneration. We hypothesized that both fire re-introduction and protection from deer would increase the number and growth of hardwood seedlings, saplings, and sprouts in a central Texas woodland co-dominated by Texas red oak (Quercus buckleyi) and Ashe juniper (Juniperus ashei). We measured the separate and joint effects of prescribed fire and deer herbivory on the number, size, and growth of Ashe juniper and hardwoods, tree mortality, and canopy cover. We collected data one year before and three years after deer-fence construction and a prescribed fire. Fire stimulated re-sprouting in oak and other hardwoods, but had no detectable effect on their seedlings or saplings, even three years later. Deer exclusion increased the number of seedlings transitioning to the sapling size class. Both fire and deer exclusion together were required to increase average sprout height above the browseline. The apparent adaptations of native hardwoods to fire are the strongest evidence we have for an important role for fire pre-settlement. Our results also indicate that fire suppression in central Texas and other parts of the south-central US is causing a shift, not to more mesic-adapted species as observed in the eastern US, but to juniper (Juniperus spp.), which is at least as xeric-adapted as oak. Therefore, thinking about the “oak regeneration problem” needs to be expanded beyond “mesophication” to incorporate the shift to juniper in drier regions. It is likely that deer control is necessary to allow fire to have positive effects on the regeneration of oaks and other hardwoods in this region and wherever deer are over-abundant. Moreover, the negative effects of deer herbivory on oak growth may partially account for reported failures of single fires alone to promote hardwood regeneration elsewhere.