Overstory Removal Research Articles

Rehabilitating Degraded Hardwood Stands on a Bottomland Terrace Site with Overstory Removal and Oak Enrichment Planting: 14-Year Results

Exploitative harvesting can lower stand quality in the short term and diminish forest productivity over the long term. In 2003, a rehabilitation experiment was installed in a southern hardwood stand on a bottomland terrace site, degraded by periodic exploitative cutting, to test the effectiveness of overstory removal and oak enrichment planting for improving stand quality and composition. Overstory removal treatments included clearcutting, stand improvement partial cutting, and an uncut control. Overstory treatment units were either planted with Nuttall oak (Quercus texana) seedlings or not planted. We revisited this study in 2017 to assess the outcome of oak enrichment planting across levels of overstory removal. Results in year 14 indicated poor survival of planted oaks under all overstory removal treatments (14% - 24%) and minimal height growth (0.3 m in 13 years) in areas treated with partial cutting and in uncut areas. Growth performance of planted oaks was significantly enhanced by clearcutting (p < 0.01). However, the overwhelming response of natural oak regeneration initiated by clearcutting trumped the contribution from enrichment planting on this low quality bottomland terrace site. Enrichment planting of Nuttall oak did not increase oak regeneration success in our study. The ineffectiveness of enrichment planting in this study was likely related to the shady understory of partially cut stands and intense competition in clearcuts. Additional treatments, such as pre-planting site preparation and post-planting release may be necessary for enhancing and maintaining competitiveness of planted red oak seedlings on similar sites.

Effects of the Light Environment and Stand History on Beargrass (Xerophyllum tenax) Morphology and Demography

Beargrass (Xerophyllum tenax [Pursh] Nutt.) is an herbaceous, evergreen perennial found in higher elevations of the northern Rocky, Sierra Nevada, Klamath, Siskiyou, Cascade and Olympic Mountains and in coastal areas from Washington to northern California. It is used by Native Americans for basketry and is an important floral green, but the conditions needed for reproduction and commercially valuable characteristics are not well known. We studied how the light environment affects size, morphology, color, and reproduction of a lowland, southeastern Olympic Peninsula beargrass population. We examined beargrass crown size distribution in relation to current and past overstory structure and found that beargrass plants had longer, greener leaves, lower crown density, smaller basal diameter, and fewer vegetative offshoots in shaded areas compared to more open areas. Flowering was less and there were fewer seedlings in shaded areas. Beargrass did not reproduce sexually in areas with < 0.3 of full photosynthetically active radiation (equivalent to at least 50% tree cover in our stand). Beargrass abundance matched the locations of anthropogenically maintained woodland openings that have since become forested preventing beargrass reproduction, suggesting that many plants have survived in the shade for more than 60 years. Overstory removal and prescribed burning in a portion of the stand stimulated sexual and asexual reproduction. We concluded that plants in shaded areas, although of somewhat higher commercial quality, are likely to recover more slowly from foliar harvest, and are less likely to be replaced after mortality. Population sustainability requires periodically or permanently open stand conditions.

Predicting tree-seedling height distributions using subcontinental-scale forest inventory data

The importance of tree seedlings in determining future stand composition and structure is well-documented in forestry literature. When planned or unanticipated overstory removal events occur, subsequent regeneration success is often linked to the number of seedlings and their height distribution. Yet, in most forest inventories, only counts of seedlings are obtained as it is too time-consuming to measure individual seedlings. To better understand the expected height distribution, models were developed to predict Weibull distribution parameters based on seedling abundance information and stand/site characteristics. A number of these characteristics were found to be statistically significant predictors of the distribution parameters; however, a more parsimonious model using stand basal area, stand age, number of seedlings, and latitude provided essentially the same fit statistics. Models were fitted for all species and for selected species subgroups, but there was generally insufficient data at this time to develop species-level analyses.

Resilience of understory vegetation after variable retention felling in boreal Norway spruce forests – A ten-year perspective

We studied the ten-year response of understory vegetation and lichens in mature boreal Norway spruce forests to five felling treatments in southern Finland. The stand level treatments represent a range in intensity of overstory removal: clear felling (CF) with site preparation and planting, retention felling (RF) (7% of stand volume retained) with site preparation and planting, gap felling with site preparation (GFs) (50% retained) and without planting, gap felling (GF) (50% retained) without site preparation or planting, and selection felling (SF) (67% retained) without site preparation or planting. Disc trenching was used for site preparation. Vegetation was sampled before and 1, 2, 3 and 10years after the treatments. Both species cover and number decreased significantly immediately after all treatments. The resistance of understory vegetation, defined as the amount of change in the community structure caused by the treatments, increased in the order CF<RF<GFs<SF<GF. The dynamics of vascular plants depended on the felling intensity. The dynamics of non-vascular species depended both on the felling intensity and site preparation. CF and RF caused almost similar effects on understory vegetation composition. Local extinctions of mosses and liverworts were caused especially by CF and RF. However, even with 67% retention, 18 bryophyte species were lost during the study period. Loss of bryophyte species was higher after SF than after GF treatments, suggesting that aggregated retention is better for maintaining bryophyte species in felling areas. The resilience of understory vegetation increased in the order CF<RF<GFs<GF<SF. The abundance of mosses, liverworts and dwarf shrubs had not recovered ten years after treatments. Herb species were the most resilient compared to other species groups. We conclude that in intensively managed forest landscapes, GF and SF can be recommended as alternatives to CF to better maintain understory diversity on the stand level. However, the aim with GF and SF treatments was to further harvest the stands. Subsequent removal of the residual stands may cause substantial changes in understory vegetation for the whole treatment area. To protect late-successional bryophytes in felling areas in mesic spruce forests, high levels of retention and minimizing soil disturbance would be required.

Understory vegetation dynamics 15 years post-thinning in 50-year-old Douglas-fir and Douglas-fir/western hemlock stands in western Oregon, USA

Recent trends in forest management practices designed to restore or enhance late-successional structure for habitat values typically include provisions for the creation and maintenance of structural and compositional diversity within and among stands. The Pacific Northwest in particular has expanses of young, structurally simple forests that range from high stocking (unthinned and little understory development) to relatively lower stocking having been previously thinned or initially regenerated at low densities. We have remeasured two long-term study sites in Oregon, USA, for 15years to examine structural development and understory persistence at a range of overstory canopy cover, spatial arrangement, and understory treatments (spraying and planting). Understory responses to thinning varied primarily by site and species group, given the range of pre-existing plant communities, and through time. In general, shrub cover increased after thinning, while forb cover increased initially after thinning and then declined. Though spraying effects were still visible 15years after treatment driven by reductions in one dominant understory species, it had little effect on the long-term development of structure at these overstory densities. Indeed, the range of overstory densities and spatial arrangements in this study did not have any large effects because all of the thinning treatments resulted in increased light availability to the understory at least through fifteen years after thinning. Combining more extensive overstory removal and understory treatments likely can be used to stimulate heterogeneous structure and composition development in these forests, including the possible stimulation of persistent early-seral vegetation within older stands.

Midstory removal reduces effectiveness of oak (Quercus) acorn dispersal by small mammals in the Central Hardwood Forest region

Timber harvests that aim to promote oak (Quercus) regeneration may have indirect impacts on seedling recruitment by altering trophic interactions between oak and animals. For example, changes in habitat structure following harvest may alter the conditionally mutualistic relationship between oak and small mammal granivores like the gray squirrel (Sciurus carolinensis), eastern chipmunk (Tamias striatus) and white-footed mouse (Peromyscus leucopus) that act both as acorn predators and as dispersers. Over 4years (2010–2013), we tracked the fate of a total of 8000 tagged acorns placed beneath black (Quercus velutina) and white oaks (Quercus alba) at 5 control (unharvested) sites and 5 sites where the midstory was removed as part of a three-phase shelterwood harvest in an oak-dominated forest in southern Indiana, USA. We found that acorns in harvested sites were more likely to be taken by granivores and were less likely to survive the winter, resulting in an overall 67% reduction in seed dispersal effectiveness (SDE). Harvested sites had more vegetative cover and coarse woody debris in the understory, providing increased cover from aerial predators and potentially facilitating greater acorn removal and a higher probability of cache recovery. Reduced seed dispersal effectiveness following midstory removal has potential to slow accumulation of oak regeneration prior to overstory removal and therefore to reduce the effectiveness of shelterwood treatments in promoting future oak dominance in harvested stands. Augmentation of shelterwoods with prescribed fire or other treatments to reduce understory density may counter this effect.

Effects of Thinning and Overstory Removal on Western Larch and Western Larch Dwarf Mistletoe

Effects of Thinning and Overstory Removal on Western Larch and Western Larch Dwarf Mistletoe

Predicting the height growth of oak species (Quercus) reproduction over a 23-year period following clearcutting

We resampled plots from a repeated measures study implemented on the Hoosier National Forest (HNF) in southern Indiana in 1988 to investigate the influence of site and seedling physical attributes on height growth and establishment success of oak species (Quercus spp.) reproduction in stands regenerated by the clearcut method. Before harvest, an array of physical attributes were documented for individual stems of advance reproduction. Across all surveys, the same characteristics were remeasured in years 6, 12, and 23 for all reproduction types (advance reproduction, stump sprouts, and new seedlings). In order to characterize topo-edaphic conditions, soil samples were collected and analyzed in 2011, and slope aspect, slope percent, and slope position were measured in the field. Random Forest (RF) analysis was used to determine the best physical and environmental predictors of height growth for oak species and their competitors in developing stands. Overall, advance reproduction of oak species fared poorly following harvests. Sprout-origin oak stems proved stronger competitors in developing stands, although their abundance relative to competing species was quite low. Advance and sprout origin maple (Acer spp.) stems, along with new seedlings of black cherry (Prunus serotina Ehrh.) and yellow-poplar (Liriodendron tulipifera L.), quickly overtopped oak advance reproduction and established dominance in the developing canopy. The height of stems during prior sampling periods was the best overall predictor of stem height in subsequent sampling periods. Species was also an important predictor of stem height. Comparatively, environmental variables were poor predictors of height growth of individual stems throughout the study, although more mesic aspects, greater cation exchange capacity, and greater soil magnesium saturation were associated with greater height of non-sprout origin stems from species groups other than oak or hickory in year 6. Our results suggest that overstory removal has driven stand demographics towards species favored by infrequent large-scale disturbance events such as clearcutting. Without post-harvest treatments to control competitors, oak regeneration on more mesic sites is unlikely to recruit into developing stands.

A multiscale analysis of the effects of alternative silvicultural treatments on windthrow within balsam fir dominated stands

Boreal ecosystem functioning is largely controlled by disturbance dynamics. There have been efforts at adapting forest management approaches to emulate natural disturbance effects, as this is expected to maintain ecosystem resilience. In many instances, this involves resorting to partial cutting strategies that are likely to increase windthrow losses. The objective of this study was to determine the effects of alternative silvicultural practices on windthrow damage and how these effects vary with the scale of treatment. The study was conducted in the Quebec North Shore region (Canada), an area dominated by balsam fir (Abies balsamea (L.) Mill.) and accompanied by black spruce (Picea mariana (Mill) B.S.P.). Four different silvicultural treatments (overstory removal, heavy partial cutting, and two patterns of selection cutting) and control areas were implemented in 2004 and 2005. The experiment used a nested approach where treatment at the plot level was independent and yet nested within the block-level treatment. At the block level, treatments were applied over 10–20 ha units, leaving a small portion of the block for a smaller application of each treatment (plot scale, 2500 m2). Inventory was carried out before harvesting and monitoring was done yearly after harvesting, with the aim to better understand the plot- and block-level factors that drive windthrow damage levels and the effects of alternative silvicultural treatments. Results after 6–7 years show that basal area proportion windthrown differs substantially between treatments, as well as between treated sites and control sites. Windthrow levels were higher under heavy cuts relative to selection cuts and also increased with balsam fir proportion. Windthrow proportions were better correlated to block-level treatment than plot-level treatment, showing that the environment surrounding the treated plot can have an important effect on windthrow losses. Overall, the selection cutting system, particularly SC2, retains the most green-tree basal area and thus best meets the management objective of retaining old-growth attributes. A simple empirical model was calibrated that could aid in hazard rating.

Influence of Forest Management on Acorn Production in the Southeastern Missouri Ozarks: Early Results of a Long-Term Ecosystem Experiment

Since acorn production is a foundational process of ecosystems dominated by oaks, understanding the impact of forest management practices on acorn production is critical to the sustainable management of oak forests. This investigation addressed the impact of even-aged management (EAM), uneven-aged management (UAM), and no-harvest management (NHM) on the production of mature, sound acorns over an 18-year period (1993-2010) of a long-term, landscape-scale forest management experiment in the Missouri Ozarks. Forest management impacts were investigated at two operational scales: the multi-stand compartment and the stand. We hypothesized that acorn production at both scales would be lower under active management (EAM and UAM) than NHM on these oak-dominated landscapes. Acorn production (acorns/ha/year) of red oaks (mainly black oak (Quercus velutina) and scarlet oak (Q. coccinea)) at the compartment level was lower under active management than NHM during the post-treatment period (1997-2010), but not for white oaks (mainly white oak (Q. alba) and post oak (Q. stellata)), which was largely a result of greater abundance and preferential harvesting of mature red oaks. At the stand scale, acorn production following either intermediate thinning or single-tree selection was comparable to yields observed in untreated stands suggesting that partial overstory removal can be implemented for harvesting timber and other silvicultural objectives without sacrificing acorn production. In many oak-dominated forests, active management will be necessary to mitigate future losses of acorn production driven by oak decline, succession, and climate change, including approaches for sustaining oak recruitment and acorn production.

Multiscale Controls on Natural Regeneration Dynamics after Partial Overstory Removal in Douglas-Fir Forests in Western Oregon, USA

We examined natural regeneration following operational-scale variable density retention treatments in 40 – 60-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests at seven sites for a decade following treatment. Treatments included residual overstory densities of 300, 200, and 100 trees/ha, with leave islands and gaps of three sizes (0.1, 0.2, and 0.4 ha) and an untreated control (600 trees/ha). Natural regeneration was influenced by factors from multiple spatial scales including broad-scale differences in overstory composition among sites, mesoscale variability in topographic position, and fine-scale variability in overstory and understory competition. High local basal area (BA) decreased the probability of seedling establishment, though some seedlings established even under high BA, particularly shade-tolerant western hemlock. In contrast, recruitment of saplings (> 1.37 m height) required lower residual overstory density (i.e., 100 trees/ha), especially for shade-intolerant Douglas-fir. Understory vegetation had little effect on saplings but was negatively related to seedling densities, particularly when overstory density was low. Variable density prescriptions can take advantage of the importance of fine-scale variability to promote regeneration of desired species mixtures, though other factors such as site overstory species composition and variation in topographic position will also influence regeneration dynamics. Including heavy overstory removal or gap creation could facilitate rapid recruitment of saplings, especially for shade-intolerant Douglas-fir.

Long-term responses of disturbance-associated birds after different timber harvests

Timber harvest provides favorable habitat for many species of shrub-dependent birds. Because of historical dominance, effect of clearcutting on early successional birds has been widely studied, but less information is available on alternatives such as shelterwood and group selection, which have become a more dominant means of regenerating pines (Pinus spp.) on federal lands of the southeastern US. We compared detection of 12 species of early successional forest birds prior to harvest and at various intervals for 16years after harvest in stands subjected to clearcutting, shelterwood, single-tree selection, and group-selection harvests. We also compared detection rates of these species between harvested and unharvested control stands. Detection rate for all early successional species combined peaked 5years after harvest and was greatest in clearcuts 5–12years after harvest. Clearcuts retained some species for longer periods than other treatments. Hooded warbler (Setophaga citrine) and Kentucky warbler (Oporornis formosus) benefitted more from partial harvesting than clearcutting; partially harvested areas had increased understory shrub abundance but retained overstory trees. Detections of many species were lower in group selection stands than other harvested treatments, likely because openings were too small for area-sensitive species. Due to the level of overstory removal, shelterwoods likely provided the closest alternative to clearcutting and retained all the species found in clearcuts; shelterwoods also provided habitat to species rare in clearcuts, including hooded and Kentucky warbler. In terms of presence and absence, regeneration methods other than clearcutting provided habitat for most early successional species, but densities of birds are likely lower. Thus, greater expanses of harvesting may be needed to sustain populations of some early successional birds at levels similar to those under even-aged systems that use clearcutting as the primary regeneration method.

Effects of precommercial thinning on the forest value chain in northwestern New Brunswick: Part 2 – Efficiency gains in cut-to-length harvesting

The Green River precommercial thinning trials were established between 1959 and 1961 in naturally regenerating balsam fir (Abies balsamea [L.] Mill.)-dominated stands an average of eight years after overstory removal. Three nominal spacings of 4 ft (1.2 m), 6 ft (1.8 m) and 8 ft (2.4 m) were compared to an unthinned control in six replicate blocks. In the fall of 2008, following completion of the ninth sequential evaluation of the study’s 48 permanent sample plots, three of the six replicates were clearcut harvested using a cut-to-length system; data were collected on harvesting, forwarding and loading efficiency. Largely due to increased average tree size, precommercially thinned stands were associated with improvements in both harvesting and forwarding productivity, proportional to thinning intensity. For example, the nominal 6-ft spacing yielded 30% to 35% gains in harvesting productivity, and 16% to 39% gains in forwarding productivity (p ≤ 0.04), these ranges spanning the different levels of operator expertise and block conditions observed. In total, estimated harvesting costs were $12.58/m3 in the unthinned stands, compared to $9.10/m3 in the 6-ft spaced stands (p = 0.02). Such a difference represents a $3.48/m3 savings, which translates into just over $1000 per ha, based on the gross merchantable volume produced in the 6-ft spaced stands.

Effects of precommercial thinning on the forest value chain in northwestern New Brunswick: Part 3 – Incidence of root and butt decay

The Green River precommercial thinning (PCT) trials were established between 1959 and 1961 in naturally regenerating balsam fir (Abies balsamea [L.] Mill.)-dominated stands an average of eight years after overstory removal. Three nominal spacings of 4 ft (1.2 m), 6 ft (1.8 m) and 8 ft (2.4 m) were compared to an unthinned control in six replicate blocks. In the fall of 2008, following completion of the ninth sequential evaluation of the study’s 48 permanent sample plots, three of the six replicates were clearcut harvested; butt rot data were collected immediately afterwards. To date, forest management research and goals have focused on the benefits of PCT, such as increased tree size and merchantable volume, shorter rotation ages, and better stem form and uniformity. Comparatively little attention has been placed on negative aspects of PCT, such as the incidence and development of root and butt rots, and their impact on fibre yields and wood product values. Results from the Green River study provide evidence that PCT may increase the incidence of butt rot in balsam fir, with incidence proportional to thinning intensity (p &lt; 0.01). We also observed incidence and volume of butt rot to increase with stem diameter (p ≤ 0.05). The experiment suggests that factors such as stand age at time of thinning, and age at the time of harvest are important considerations when it comes to mitigating the impacts of butt rot through forest management.

Effects of precommercial thinning on the forest value chain in northwestern New Brunswick: Part 1 – Roundwood production and stumpage value

The Green River precommercial thinning trials were established between 1959 and 1961 in naturally regenerating balsam fir (Abies balsamea [L.] Mill.)-dominated stands, an average of eight years after overstory removal. Three nominal spacings of 4 ft (1.2 m), 6 ft (1.8 m) and 8 ft (2.4 m) were compared to an unthinned control in six replicate blocks. In the fall of 2008, following completion of the ninth sequential evaluation of the study’s 48 permanent sample plots, three of the six replicates were clearcut harvested and data were collected on roundwood product recovery and value. These data were used to construct treatment-invariant (p ≥ 0.18) functions predicting product volume from tree diameter, allowing the volume of studwood, sawlogs and pulpwood to be predicted for the full Green River data set (all 6 replicates) through time. Mean annual increment of gross merchantable volume culminated in all treatments around stand age 45. Thinning to a nominal spacing of 6 ft, resulting in 1600 merchantable stems per ha by stand age 30, offered the best balance of individual tree and stand growth, producing 20% more gross merchantable volume and 26% more sawlog volume than unthinned stands, potentially increasing landowner stumpage revenues by 22% (p &lt; 0.01). The sawlog volume produced in unthinned stands could be realized up to 15 years sooner in thinned stands, suggesting that PCT may offer substantive flexibility in balancing forest-level wood supply objectives.

Effects of precommercial thinning on the forest value chain in northwestern New Brunswick: Part 6 – Estimating the economic benefits

The Green River precommercial thinning (PCT) trials were established between 1959 and 1961 in naturally regenerating balsam fir (Abies balsamea [L.] Mill.)-dominated stands an average of eight years after overstory removal. Following clearcut harvest of three of the study's six replicates in the fall of 2008, the rotation-length effects of PCT and vegetation management (VM; deciduous tree and brush suppression) on the forest value chain were integrated into a spreadsheet-based model that estimates the net present value (NPV) of these silvicultural treatments. Assuming costs and prices near recent values, both PCT and VM were observed to support positive landowner NPVs through discount rates in excess of 6%. At a discount rate of 4% and an age where sawlog production was maximized, PCT and VM offered similar NPV (&gt;$550/ha). Landowners that can attract buyers willing to pay a premium for wood from thinned stands (equal to the sum of reduced operational overhead charges, harvesting and sawmilling costs and increased pulping costs) could see the value of their stands double. Sensitivity analyses revealed that these results are dependent on site productivity, silvicultural costs and a strong premium on sawlog stumpage rates. Depending on economic circumstances, PCT and VM could be attractive investments on high quality sites that are situated in close proximity to wood processing infrastructure.

Effects of precommercial thinning on the forest value chain in northwestern New Brunswick: A fifty-year legacy of forest research continues

Reduction of the stem density of young, naturally regenerating stands through precommercial thinning (PCT) is widely accepted as beneficial for controlling tree species composition, selecting crop trees and improving their growth, and preparing stand structure for subsequent commercial thinning. Less understood and accepted are the forest-level benefits associated with wood fibre yield and value as they relate to the financial returns of PCT. The Green River PCT trials were established between 1959 and 1961 in naturally regenerating balsam fir (Abies balsamea [L.] Mill.)-dominated stands an average of eight years after overstory removal. Three nominal spacings of 4 ft (1.2 m), 6 ft (1.8 m) and 8 ft (2.4 m) were compared to an unthinned control in six replicate blocks. In the fall of 2008, following completion of the ninth sequential evaluation of the study’s 48 permanent sample plots, three of the six replicates were clearcut harvested and data were collected to quantify the effects of PCT on the forest value chain. This paper is the introduction to a series of six papers that quantify the rotation-length effects of PCT on: 1) stand dynamics and the yield of roundwood products; 2) harvesting and wood handling costs; 3) root and butt rot incidence, severity, and effects on volume recovery; 4) lumber and fibre-based panel recovery and value; 5) pulp and paper recovery and value; and 6) the overall integration of these costs and benefits.

Reductions in downed deadwood from biomass harvesting alter composition of spiders and ground beetle assemblages in jack-pine forests of Western Quebec

Renewed interest in biomass harvesting has underscored the need for ecologically relevant thresholds and empirical validation of species responses for deadwood retention if biodiversity is to be preserved in managed landscapes. We experimentally reduced volumes of downed deadwood in clear cut jack-pine stands in Western Quebec, Canada and then monitored changes in spider and ground beetle assemblages 1 and 2-years following biomass removal as well as in uncut stands. We reduced volume of downed deadwood by (1) removing residual deadwood placed on machine corridors during the initial harvest of the stand to minimize soil compaction and (2) removing all residual deadwood material throughout the experimental plots. Ground beetle and spider assemblages from deadwood depleted plots were then compared with those in clearcut plots where no additional biomass had been removed and with uncut stands to assess the incremental effect of overstory removal and subsequent biomass removal using multivariate regression trees. We identified 13,822 individual arthropods representing 177 species. We observed differences in species assemblages attributable to the effects of overstory removal (35% of the explained variance) as well as biomass removal, particularly between plots with intensive removal of biomass and those with no additional or moderate removal of biomass (11% of the explained variance). As expected we observed a range of individual species response patterns. Of particular concern were species that experienced incrementally negative effects of overstory and biomass removal and those that were strongly promoted by biomass removal. These species showed responses atypical of those observed following clear cutting and may fall outside both the range of natural variability observed in this region as well as the range of current forest management intensity practiced in North America.

Invasive mangrove removal and recovery: Food web effects across a chronosequence

Red mangrove (Rhizophora mangle) was introduced to Hawai'i in 1902 and has since overgrown many coastal areas in Hawai'i, transforming nearshore sandy habitat into heavily vegetated areas with low water velocity, high sedimentation rates, and anoxic sediments. Introduced mangrove forests provide habitat for exotic species, including burrowing predators, which can exert top-down effects on benthic communities. Removal of mangrove overstory is a popular management technique, and, here, we study community change over a chronosequence of mangrove removals from 2007 to 2011, investigating infaunal community structure, crab abundance, and response to predator exclusion in the presence of mangrove overstory and along the chronosequence of removals. Overstory removal results in gradual changes in community composition concurrent with slow decomposition of sedimentary mangrove biomass (k=0.36±0.06×10−3d−1). Changes over time after removal include an increase in total infaunal abundance, a decrease in sub-surface deposit feeders, and an increase in suspension-feeding worms. Burrowing crab densities are uniform across mangrove and removal sites, and, unlike in native mangroves, their effects on infaunal communities are similarly negligible in both mangrove and removal areas. These results show that recovery from invasion and removal occurs gradually and is not governed by top-down effects.

Influence of partial harvesting and site factors on the abundance and composition of natural regeneration in the Acadian Forest of Maine, USA

Understanding the factors regulating the composition and abundance of natural regeneration in forest ecosystems is critical to sustainable management worldwide. Using a long-term silvicultural experiment in Maine, we partitioned the variation in natural regeneration and examined the contribution of overstory and understory vegetation (biotic factors), substrate and soil attributes (abiotic factors), and silvicultural treatment. We hypothesized that silvicultural treatment (single-tree selection with 5, 10, and 20-year cutting cycles and diameter-limit cutting) would be less influential than abiotic and biotic factors in structuring regeneration pattern. Overall, treatment and site (biotic and abiotic) factors accounted for 26% of the variation in regeneration species composition, highlighting stochasticity of the regeneration process. In support of our hypothesis, regeneration pattern that could be explained was primarily associated with local site factors; overstory and understory vegetation uniquely accounted for 16% of the variation in species composition. Substrate and soil attributes along with silvicultural treatment accounted for 4% of variation, and uniquely accounted for 2% and 4%, respectively. In support of earlier reports, shifts toward hardwood dominance were apparent at early stages of cohort development and were associated with high harvest intensities. Our findings suggested that overstory and understory vegetation exhibit greater control over regeneration patterns than substrate and soil attributes, or silvicultural treatment, in partially harvested Acadian Forest mixedwood stands, and also indicated the potential for composition control through selective overstory removal.