Understanding the influence of post‐disturbance forest management on tree regeneration is critical for assessing ecosystem recovery and guiding future responses. In particular, the influx of elevated ...coarse woody material (CWM) following wind disturbance, if left in situ, may impede herbivore access, thereby protecting saplings from browsing damage through a natural ‘exclosure effect’.
In 2013, a tornado in northcentral Maine, United States and subsequent salvage logging operations created three clear ‘treatments’ for evaluation of the exclosure effect: blowdown, blowdown plus salvage logging and an undamaged control. Nine years post‐tornado, we inventoried tree regeneration within these treatments to evaluate differences in sapling abundance, species composition, size structure and browsing intensity. We also inventoried CWM, including the height above forest floor.
Results revealed significant differences in sapling composition and browsing intensity among treatments. The salvage treatment had the highest proportion of browsed saplings (56 ± 28%; mean ± standard error), followed by the control (9 ± 10%) and blowdown (5 ± 8%). Blowdown had by far the greatest mean (50 ± 9 cm) and average maximum (169 ± 43 cm) heights for CWM. Binomial generalized linear models revealed that browsing probability was a function of mean CWM height and an interaction between sapling density and proportion of sapling hardwoods. Thus, browsing damage was less likely in plots with greater CWM heights and more likely in plots with greater sapling density and more hardwood saplings.
Synthesis and applications. This study furthers our understanding of ecosystem recovery following blowdown and salvage logging. Results suggest that salvage logging created important differences in coarse woody material (CWM) abundance and height distribution, when compared to un‐salvaged areas, and that these differences in turn altered sapling size structure and browsing intensity. These findings highlight the potential long‐term effects of successive disturbances, as the differences evident in these early stages may persist for decades or longer. Importantly, we provide evidence of the exclosure effect, suggesting that CWM retained in the un‐salvaged area protected saplings from moose browsing. Thus, in post‐disturbance areas where browsing threatens regeneration, we recommend that managers consider retaining CWM to serve as a natural exclosure.
This study furthers our understanding of ecosystem recovery following blowdown and salvage logging. Results suggest that salvage logging created important differences in coarse woody material (CWM) abundance and height distribution, when compared to un‐salvaged areas, and that these differences in turn altered sapling size structure and browsing intensity. These findings highlight the potential long‐term effects of successive disturbances, as the differences evident in these early stages may persist for decades or longer. Importantly, we provide evidence of the exclosure effect, suggesting that CWM retained in the un‐salvaged area protected saplings from moose browsing. Thus, in post‐disturbance areas where browsing threatens regeneration, we recommend that managers consider retaining CWM to serve as a natural exclosure.
•How competition is expressed varies with stand developmental history.•Age decreased tree growth, but did not influence response to competition.•Information on spatial structure improved growth ...models in uneven-aged forests.
Factors influencing tree growth in structurally complex forests remain poorly understood. Here we assessed the influence of competition on Pinus resinosa (n=224) and Pinus strobus (n=90) growth in four old-growth stands in Minnesota, using mixed effects models. A subset of trees, with accurate age estimates, was used to further test the influence of tree age. Our analyses included the weighted Voronoi diagram (WVD) as a novel competition index, representing a detailed description of the spatial structure of a tree’s neighborhood.
Competition was variably expressed depending on stand developmental history and tree species. For P. resinosa in single-cohort stands, and P. strobus in multi-cohort stands, tree size relative to the population mean size best predicted tree growth. In contrast, for P. resinosa in multi-cohort stands, the spatial configuration of competitors became important, as shown by the superior performance of the WVD index. Surprisingly, while tree age had a negative influence on growth, it did not influence the intensity of competition.
Our results highlight the importance of considering stand developmental history and tree age in analyses of tree growth and competition, and the potential for improving assessments of competition in complex stands, using detailed quantification of neighborhood structure.
The conic-paraboloid volume equation is receiving increased use with downed coarse woody material (CWM), but the consequences for taper have not been identified mathematically. Requiring that ...subdivision of a conic-paraboloid yields two smaller conic-paraboloids leads to an exact taper equation intermediate between those of cones and second-order paraboloids. This exact taper equation does not have an explicit inverse, however. An alternative, naive approach does have an explicit inverse, but subdivision does not yield two conic-paraboloids. The exact conic-paraboloid is closely approximated by Fermat’s paraboloid with exponent 7/5. The exact and naive conic-paraboloids match in volume; differences in taper are ≤2.2% of large-end cross-sectional area and ≤5.9% of large-end diameter, while differences in inverse taper are ≤3.7% of total length. Fermat’s paraboloid is always within 1.2% of total volume; differences in taper are ≤0.8% of large-end cross-sectional area and ≤2.0% of large-end diameter, while differences in inverse taper are ≤1.1% of total length. Such differences are negligible given the variety of CWM shapes and practical measurement challenges. Either the exact conic-paraboloid or the corresponding Fermat’s paraboloid provides appropriate equations for estimating the volume and taper of CWM that is intermediate between conical and ordinary paraboloid frusta.
QUESIONS: What were the long‐term disturbance rates (including variability) and agents in pristine Norway spruce‐dominated (Picea abies (L.) Karst.) forests? Have soil moisture conditions influenced ...disturbance rates across this boreal spruce‐dominated forest? Were the temporal recruitment patterns of canopy dominants associated with past disturbance periods? LOCATION: Interfluvial region of Northern Dvina and Pinega rivers, Arkhangelsk, northwest Russia. METHODS: We linked dendrochronological data with tree spatial data (n trees = 1659) to reconstruct the temporal and spatial patterns of canopy gaps in a 1.8‐ha area from 1831–2008, and to develop a growth‐release chronology from 1775–2008. RESULTS: No evidence of stand‐replacing disturbances was found within selected forest stands over the studied period. Forest dynamics were driven by small‐ to moderate‐scale canopy disturbances, which maintained a multi‐cohort age structure. Disturbance peaks were observed in the 1820s, 1920s, 1970s and 2000s, with decadal rates reaching 32% of the stand area disturbed. CONCLUSIONS: The overall mean decadal rate was 8.3% canopy area disturbed, which suggests a canopy turnover time of 122 yr, with a 95% confidence envelop of 91–186 yr. Bark beetle outbreaks (possibly exacerbated by droughts) and wind‐storms emerged as the principal disturbance agents. Recruitment of both Norway spruce and downy birch was associated with periods of increased canopy disturbance. Moisture conditions (moist vs mesic stands) were not significantly related to long‐term disturbance rates. The studied spruce‐dominated boreal forests of this region apparently exhibited long‐term forest continuity under this mixed‐severity disturbance regime. These disturbances caused considerable structural alterations to forest canopies, but apparently did not result in a pronounced successional shifts in tree species composition, rather occasional minor enrichments of birch in these heavily spruce‐dominated stands.
Abstract
Stand density management is central to achieving diverse silvicultural objectives. Decision-support tools in this domain range from expert opinion to sophisticated computer models that vary ...by forest type, region, and organization. The graphical frameworks represented by density management diagrams (DMDs) and stocking guides (SGs), collectively called size-density management charts (SDMCs), are well established and balance quantitative rigor with user accessibility. Regional differences in species composition and site quality are known to influence maximum size-density relationships, historically limiting the development of reliable charts. Advances in statistical modeling and data availability are overcoming this issue and should encourage more widespread use. We briefly review the history of SDMCs and propose the adoption of relative density based on stand density index as a logical metric for linking the DMD and SG formats. Examples of SDMC construction and use are illustrated for spruce-fir stands in Maine, USA.
Study Implications: Recognition of the importance of stand density management has increased in recent years owing to its potential to address threats such as susceptibility to catastrophic wildfires and forest health issues exacerbated by environmental stress. Natural resource managers will benefit from adopting a language around density management that is both biologically grounded and consistent. A relative density framework is compatible with the two primary types of size-density management charts and thus meets this objective well. Relative density provides an ideal launching point for articulating levels of stand density, or stocking, to meet diverse management objectives determined under relevant socioecological constraints.
A key component in describing forest carbon (C) dynamics is the change in downed dead wood biomass through time. Specifically, there is a dearth of information regarding the residence time of downed ...woody debris (DWD), which may be reflected in the diversity of wood (for example, species, size, and stage of decay) and site attributes (for example, climate) across the study region of eastern US forests. The empirical assessment of DWD rate of decay and residence time is complicated by the decay process itself, as decomposing logs undergo not only a reduction in wood density over time but also reductions in biomass, shape, and size. Using DWD repeated measurements coupled with models to estimate durations in various stages of decay, estimates of DWD half-life (T HALF), residence time (T RES), and decay rate (k constants) were developed for 36 tree species common to eastern US forests. Results indicate that estimates for T HALF averaged 18 and 10 years for conifers and hardwoods, respectively. Species that exhibited shorter T HALF tended to display a shorter T RES and larger k constants. Averages of T RES ranged from 57 to 124 years for conifers and from 46 to 71 years for hardwoods, depending on the species and methodology for estimating DWD decomposition considered. Decay rate constants (k) increased with increasing temperature of climate zones and ranged from 0.024 to 0.040 for conifers and from 0.043 to 0.064 for hardwoods. These estimates could be incorporated into dynamic global vegetation models to elucidate the role of DWD in forest C dynamics.
1. Disturbance histories derived from old-growth forest remnants in Europe and eastern North America have shaped many of our current theories of forest dynamics and succession. Yet the small size ...typical of these remnants suggests they might not capture the full range of variability that may emerge at larger scales. 2. We investigated the frequency and severity of natural disturbance in a 2000-ha old-growth landscape (Big Reed Forest Reserve) in northern Maine, USA. Given its size, the Reserve provides an ideal opportunity to study, at multiple scales, natural forest processes in a region that has otherwise been dramatically altered by human activities. Using dendrochronological methods, we reconstructed disturbance histories for 37 randomly located plots stratified by five forest types (hardwood forests, mixed woods forests, red spruce forests, northern white-cedar seepage forests and northern white-cedar swamps). 3. We found no evidence of stand replacing disturbance on any plot during the last 120-280 years (depending on plot). The overall mean disturbance rate was 9.6% canopy loss per decade (median 6.5%, maximum 55%, plots pooled), yet the distribution was strongly skewed toward the lower rates. 4. We found little differences in disturbance rates between forest types, save a slightly lower rate in the northern white-cedar swamps. However, if we ignore forest-type classifications, we see that disturbance rates are clearly influenced by gradients in the relative abundance of component tree species, owing to species' relative susceptibilities to particular disturbance agents. 5. Synthesis. Relatively low rates of canopy disturbance allow the accrual of shade-tolerant saplings. The abundance of this advance regeneration, coupled with the absence of stand-replacing disturbance, has maintained canopy dominance by shade-tolerant species in all plots, all forest types and throughout the entire landscape. Disturbance histories from individual plots coalesce to form a picture of a landscape in which pulses of moderate-severity disturbance are interposed upon a background of scattered small-scale canopy gaps. The landscape-level mosaic resulting from this disturbance regime consists of patches in various stages of structural development, not various stages of compositional succession.
Wildfires, insect outbreaks, and windstorms are increasingly common forest disturbances. Post-disturbance management often involves salvage logging, i.e., the felling and removal of the affected ...trees; however, this practice may represent an additional disturbance with effects on ecosystem processes and services. We developed a systematic map to provide an overview of the primary studies on this topic and created a database with information on the characteristics of the retrieved publications, including information on stands, disturbance, intervention, measured outcomes, and study design. Of 4341 retrieved publications, 90 were retained in the systematic map. These publications represented 49 studies, predominantly from North America and Europe. Salvage logging after wildfire was addressed more frequently than after insect outbreaks or windstorms. Most studies addressed logging after a single disturbance event, and replication of salvaged stands rarely exceeded 10. The most frequent response variables were tree regeneration, ground cover, and deadwood characteristics. This document aims to help managers find the most relevant primary studies on the ecological effects of salvage logging. It also aims to identify and discuss clusters and gaps in the body of evidence, relevant for scientists who aim to synthesize previous work or identify questions for future studies.
Black ash (Fraxinus nigra Marsh.) forests of north-central North America are currently threatened by the non- native emerald ash borer (Agrilus planipennis, EAB). Despite the wide distribution of F. ...nigra ecosystems, and the concern over EAB impact, little is known about their structure and natural stand dynamics. We sampled six old-growth F. nigra stands to assess structure, composition, tree recruitment, and past disturbance. Dendrochronological results revealed that disturbance rates fluctuated markedly over the past 200 years or more, but remained relatively low, suggesting small- to moderate-scale disturbances. Recruitment age structures revealed that (i) F. nigra is able to maintain long-term dominance through extended longevity as a canopy tree, and (ii) these systems have fairly continuous recruitment over time, with most sites showing F. nigra recruitment in every decade in the chronology. We speculate that recruitment is coupled with water table fluctuations, in addition to canopy disturbance, as these stands are subject to both frequent flooding and effective soil drought (given the shallow root systems). The low rates of past canopy disturbance and associated gap-phase replacement by F. nigra highlight the potential for dramatic shifts in these systems following emerald ash borer invasion and subsequent canopy tree mortality.
•Reserves showed a comparably low annualized mortality rate among long-term studies.•Hemlock had the lowest cumulative mortality.•White cedar had the highest cumulative mortality.•Low mortality ...likely due to non-traditional silvicultural prescription.
Land managers are increasingly called upon to maintain ecosystem function and restore late-successional forest structures by retaining trees (“reserves”) in harvest prescriptions. Such retention practices often result in mortality of reserve trees owing to increased exposure to wind and ‘gap shock’, thereby compromising management objectives. This study investigated the mortality of reserve trees (n=787) retained over 20years in the Acadian Forest Ecosystem Research Project (AFERP), a long-term ecological forestry experiment in central Maine, USA. Cumulative mortality across 18 species was very low (8.4%±3.3%, mean±SD) relative to similar studies throughout the world. Annualized mortality of reserve trees of the two silvicultural systems was 1.1% for the large-gap treatment and 0.4% for the small-gap treatment. Cumulative mortality of Tsuga canadensis was lowest (2%) among species with >50 individuals, while the cumulative mortality of Thuja occidentalis was highest at 19%. Over 59% of cumulative mortality was wind-related. Annualized wind-related mortality of the reserve trees was 0.6% in the large-gap treatment and 0.2% in the small-gap treatment. More vigorous trees showed lower mortality rates. Cumulative mortality and wind-related deaths were somewhat higher in large gaps, and were influenced by spatial position within gaps. The non-traditional, expanding-gap, multi-aged silvicultural systems in this study may explain the lower incidence of windthrow and gap shock experienced by reserve trees relative to the annualized mortality rates from studies of similar, though predominantly single-cohort, silvicultural systems.
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