Uneven-aged Silvicultural Systems Research Articles

Natural disturbance regimes as a guide for sustainable forest management in Europe.

In Europe, forest management has controlled forest dynamics to sustain commodity production over multiple centuries. Yet over-regulation for growth and yield diminishes resilience to environmental stress as well as threatens biodiversity, leading to increasing forest susceptibility to an array of disturbances. These trends have stimulated interest in alternative management systems, including natural dynamics silviculture (NDS). NDS aims to emulate natural disturbance dynamics at stand and landscape scales through silvicultural manipulations of forest structure and landscape patterns. We adapted a "Comparability Index" (CI) to assess convergence/divergence between natural disturbances and forest management effects. We extended the original CI concept based on disturbance size and frequency by adding the residual structure of canopy trees after a disturbance as a third dimension. We populated the model by compiling data on natural disturbance dynamics and management from 13 countries in Europe, covering four major forest types (i.e., spruce, beech, oak, and pine-dominated forests). We found that natural disturbances are highly variable in size, frequency, and residual structure, but European forest management fails to encompass this complexity. Silviculture in Europe is skewed toward even-aged systems, used predominately (72.9% of management) across the countries assessed. The residual structure proved crucial in the comparison of natural disturbances and silvicultural systems. CI indicated the highest congruence between uneven-aged silvicultural systems and key natural disturbance attributes. Even so, uneven-aged practices emulated only a portion of the complexity associated with natural disturbance effects. The remaining silvicultural systems perform poorly in terms of retention compared to tree survivorship after natural disturbances. We suggest that NDS can enrich Europe's portfolio of management systems, for example where wood production is not the primary objective. NDS is especially relevant to forests managed for habitat quality, risk reduction, and a variety of ecosystem services. We suggest a holistic approach integrating NDS with more conventional practices.

Assessing multi-scale habitat relationships and responses to forest management for cryptic and uncommon herpetofauna in the Missouri Ozarks, USA

Behaviorally cryptic or uncommon herpetofauna are often understudied due to the extensive effort it requires to obtain adequate data for statistical analysis. Additionally, potential impacts from forest management on these already small or difficult to study populations may have a dissimilar effect in comparison to more common species. To address this, we examined species-specific responses of uncommon herpetofauna within the Missouri Ozarks to even-aged and uneven-aged silvicultural systems at multiple scales, as well as their habitat relationships. Using capture histories collected over 23 years (1992–2014) on the Missouri Ozark Forest Ecosystem Project (MOFEP) we examined the cumulative effects of two harvest entries (1996 and 2011) at both the local- (stand-level) and landscape-scale (compartment-level) for eight uncommon herpetofauna, which includes one toad, two salamanders, one skink, and four snakes. We modeled capture probabilities with respect to multiple habitat- and harvest-related covariates. Three species showed compartment-level declines in the post-treatment period, however only two of the declines appeared to be related to forest management; the decline for the third species was observed in both treatment and control compartments suggesting that the cause was environmental related. In contrast to compartment-level responses, we observed stand-level responses in five species, mostly positive. In general, our observed declines were minimal and currently we have no concerns that forest management will lead to the loss of any of the uncommon herpetofauna species considered here. Our models showed habitat relationships for multiple species, which aids our understanding of species’ life history strategies and can also guide future management efforts.

Functional diversity response to hardwood forest management varies across taxa and spatial scales.

Contemporary forest management offers a trade-off between the potential positive effects of habitat heterogeneity on biodiversity, and the potential harm to mature forest communities caused by habitat loss and perforation of the forest canopy. While the response of taxonomic diversity to forest management has received a great deal of scrutiny, the response of functional diversity is largely unexplored. However, functional diversity may represent a more direct link between biodiversity and ecosystem function. To examine how forest management affects diversity at multiple spatial scales, we analyzed a long-term data set that captured changes in taxonomic and functional diversity of moths (Lepidoptera), longhorned beetles (Coleoptera: Cerambycidae), and breeding birds in response to contemporary silvicultural systems in oak-hickory hardwood forests. We used these data sets to address the following questions: how do even- and uneven-aged silvicultural systems affect taxonomic and functional diversity at the scale of managed landscapes compared to the individual harvested and unharvested forest patches that comprise the landscapes, and how do these silvicultural systems affect the functional similarity of assemblages at the scale of managed landscapes and patches? Due to increased heterogeneity within landscapes, we expected even-aged silviculture to increase and uneven-aged silviculture to decrease functional diversity at the landscape level regardless of impacts at the patch level. Functional diversity responses were taxon-specific with respect to the direction of change and time since harvest. Responses were also consistent across patch and landscape levels within each taxon. Moth assemblage species richness, functional richness, and functional divergence were negatively affected by harvesting, with stronger effects resulting from uneven-aged than even-aged management. Longhorned beetle assemblages exhibited a peak in species richness two years after harvesting, while functional diversity metrics did not differ between harvested and unharvested patches and managed landscapes. The species and functional richness of breeding bird assemblages increased in response to harvesting with more persistent effects in uneven- than in even-aged managed landscapes. For moth and bird assemblages, species turnover was driven by species with more extreme trait combinations. Our study highlights the variability of multi-taxon functional diversity in response to forest management across multiple spatial scales.

Multiple developmental pathways for range-margin Pinus banksiana forests

Empirical knowledge of forest structure and development in early successional and range-margin populations is often lacking, limiting our ability to effectively model and manage these forests. Such is the case for jack pine (Pinus banksiana Lamb.) in central Minnesota, USA, where it reaches its southwestern range limit. Our objective was to quantify this population’s historical range of variability of structural conditions and developmental pathways. We collected structural, spatial, and dendrochronological data on 0.25 ha plots from 10 jack pine dominated sites that initiated and developed outside of active management. Our results revealed a broad range of structural characteristics and developmental pathways, including rapid and protracted recruitment windows (5–50 years), with subsequent even- and uneven-aged structures, and random and clumped stem spatial arrangements. As such, these mature, early successional forests often displayed a degree of complexity more typically associated with old-growth forests. Our findings suggest that this population, like other southern range-margin populations with mostly nonserotinous cones, historically followed a variety of stand development pathways and did not solely follow the rapid establishment, even-aged pathway often attributed to this forest type. We suggest that even- and uneven-aged silvicultural systems should be used to reflect this historical range of developmental pathways and to increase resilience and adaptability.

Architecture of Fagus sylvatica regeneration improves over time in mixed old-growth and managed forests

Basic dimensions and morphological characteristics of European beech (Fagus sylvatica L.) saplings were measured in an old-growth forest and in a selectively managed mixed Dinaric silver fir–beech forest in 2000 and 2005. Over the 5-year period, average relative diffuse radiation above saplings (DIF), sapling length, and root collar diameter significantly increased. Light proved to be an important factor influencing beech sapling crown architecture. There was a strong negative relation between plagiotropic sapling occurrence and DIF, while the relation between DIF and forked and broom-shaped crown forms was positive. Occurrence of all three crown irregularities was negatively related to the regeneration density. Crown plasticity was less expressed after the 5-year period of growth, as the number of plagiotropic, broom-shaped, and forked saplings decreased dramatically. The results of this study indicate that broom-shaped, forked, and plagiotropic trees did not recruit successfully, or that these types of morphological adaptations were no longer an advantage in the late sapling stage of development. The hypothesis that small-scale uneven-aged silvicultural systems, such as the selective system, result in poor beech regeneration architecture to the extent that the future quality of beech logs is affected was not confirmed by the results of this study.

Les sylvicultures des forêts de production résineuses : en perpétuelle évolution ?

This article deals with changes in silvicultural practices, in particular for pine and spruce. Silvicultural practices for production are the main topic of the article but other functions are dealt with as the multi-functional approach is predominant in France. For instance, uneven-aged silvicultural systems have gained considerable ground, particularly using deciduous species, in response to a demand from society (stability, landscapes), but which in the case of softwoods may be in contradiction with optimal, highly mechanised silvicultural practices. Another remarkable change is the wood industry’s demand for increasingly small diameters, which is also offers a means for adapting forests to climate change. But this trend is controversial. The revisiting of silvicultural methods that began in 1990 remains topical, with a view to establishing stands that are less capital-intensive and more mixed. However, the implementation of these methods has changed. Diversification of silvicultural practices might be further broadened by production models for medium-diameter trees with very little tapering.

Survival and Growth of Suppressed Baldcypress Reproduction in Response to Canopy Gap Creation in a North Carolina, USA Swamp

Little is known of the ability of baldcypress (Taxodium distichum (L.) L.C. Rich.) in a suppressed sub-canopy position to respond to increases in light. We measured 3 years of diameter growth response of long-suppressed baldcypress saplings to canopy gap creation in a hydrologically altered, water tupelo-dominated backswamp of the lower Roanoke River floodplain in eastern North Carolina. Baldcypress saplings responded strongly to gap creation. Saplings showed a significant positive growth trend, with mean basal area growth in gaps expanding from 2.5 cm2 in year one, 4 times that of control saplings, to 8.5 cm2 in year three, 20 times that of control saplings. Within canopy gaps, a positive trend between growth and initial sapling diameter was evident, while such a trend among controls was non-existent. Mortality was similar between gap and control saplings after 1 year, but by year three gap sapling mortality had declined to 2 %, while control mortality increased to 16 %. It is clear that long-suppressed baldcypress, sometimes at the brink of death, are able to respond vigorously to an increase in light from canopy gaps with decreased mortality and increased growth. This has important implications for wetlands requiring restoration or baldcypress management within the framework of two-age or uneven-aged silvicultural systems.

Application of the CBM-CFS3 model to estimate Italy's forest carbon budget, 1995–2020

The estimation of past and future forest carbon (C) dynamics in European countries is a challenging task due to complex and varying silvicultural systems, including uneven-aged forest management, and incomplete inventory data time series. In this study, we tested the use of the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) in Italy, a country exemplifying most of these challenges. Our objective was to develop estimates of forest carbon budgets of the Forest Management area (including all forests existing in 1990) for the period 1995–2009, and to simulate alternative scenarios of natural disturbance (fire) and harvest rates to 2020. A number of methodological challenges required modifications to the default model implementation. Based on National Forest Inventory (NFI) data, we (i) developed a historic library of yield curves derived from standing volume and age data, reflecting the effect of past silvicultural activities and natural disturbances, and a current library of yield curves derived from the current net annual increment; (ii) reconstructed the age structure for a period antecedent to the reference NFI year (2005), to compare the model results with data from other sources; and (iii) developed a novel approach for the simulation of uneven-aged forests. For the period 2000–2009, the model estimated an average annual sink of −23.7Mt CO2yr−1 excluding fires in Italy's managed forests. Adding fires to the simulation reduced the sink to −20.5Mt CO2yr−1. The projected sink (excluding all fires) for the year 2020 was −23.4Mt CO2yr−1 assuming average (2000–2009) harvest rates. A 36% increase in harvest rates by 2020 reduced the sink to −17.3Mt CO2yr−1. By comparing the model results with NFI data and other independent studies, we demonstrate the utility of the CBM-CFS3 both for estimating the current forest sink in even-aged and more complex uneven-aged silvicultural systems in Italy, and for exploring the impact of different harvest and natural disturbances scenarios in managed forests. This study demonstrates the utility of the CBM-CFS3 to national-scale estimation of past and future greenhouse gas emissions and provides the foundation for the model's future implementation to other European countries.

Potential Yields and Economic Returns of Natural Disturbance-Based Silviculture: A Case Study from the Acadian Forest Ecosystem Research Program

Intrastand variability is promoted by many silvicultural systems designed to emulate natural disturbance regimes (natural disturbance-based silviculture [NDBS] systems) in the eastern United States and Canada but this variability is difficult to model in many growth-and-yield models, limiting application by the region's forest managers. We used a resampling approach to integrate intrastand variability into Forest Vegetation Simulator (FVS) growth-and-yield projections. We subsequently compared potential yield and financial returns over a 100-year period for two NDBS systems monitored in the Acadian Forest Ecosystem Research Program with two conventional systems: a two-stage uniform shelterwood and a single-tree selection system. NDBS systems produced the widest diameter distribution at the end of the harvest rotation and were more effective in recruiting large trees (>24 in.) and more diverse species relative to conventional silviculture systems. Projected merchantable yield and financial return were highest for the single-tree selection, followed by the two NDBS systems and finally the shelterwood; however, if standing merchantable value at the end of simulation was included, the NDBS systems ranked first and third overall financially. Our analysis suggests that NDBS systems are capable of sustaining a greater diversity in forest structure and composition while producing volume yields and financial returns that are competitive with conventional even- and uneven-aged silvicultural systems.

Recruitment of tree species in mixed selection and irregular shelterwood forest stands

Context Recruitment is an important process in forest stand dynamics, especially in uneven-aged stands. Continuous recruitment is a prerequisite for diverse, uneven-aged silvicultural systems, but patterns may vary significantly.

Relationships between growth, quality, and stocking within managed old-growth northern hardwoods

An understanding of long-term growth dynamics is central to the development of sustainable uneven-aged silvicultural systems for northern hardwood forests in eastern North America. Of particular importance are quantitative assessments of the relationships between stocking control and long-term growth and quality development. This study examined these relationships in a long-term silviculture experiment established in northern hardwood stands in the Upper Peninsula of Michigan, USA. Stands were old growth at the onset of the experiment and were maintained at three residual stocking levels (11.5, 16.1, and 20.7 m2·ha–1) over a 57-year period. Several aspects of long-term stocking control were evaluated, including the effects of residual stocking on tree quality development and the relationships between stand stocking and individual tree growth and stand-level production. Results suggest that residual stocking had little impact on quality development, likely due to the initial old-growth condition of the stands examined. In contrast, our results indicate that a range of stand densities will maintain acceptable rates of stand-level production in selection systems and that growth can be shifted between diameter classes depending on desired future stand conditions.

Linking stand attributes to cartographic information for ecosystem management purposes in the boreal forest of eastern Québec

In the North American boreal forest, the adoption of forest ecosystem management strategies usually increases the number of forest stands to be treated with irregular or uneven-aged silvicultural systems. However, it is difficult to properly target the stands most appropriate for partial cut treatments in remote areas where road access is limited, because current inventory data do not include an assessment of key stand characteristics for silvicultural prescriptions, such as the abundance of small stems in the understory. In this study, we present a forest classification performed using classification and ordination methods, based on ground-measured structural and compositional stand characteristics, in a region of eastern Québec, Canada. This classification resulted in six forest types, which range in composition and structure from relatively regular post-fire stands dominated by black spruce (Picea mariana) to relatively irregular stands co-dominated by balsam fir (Abies balsamea) and black spruce. This classification was linked with cartographic information currently available to forest managers. Information from a fine-scale forest map predicted slightly better the presence of forest types with irregular stand structures compared with a coarse-scale forest map complemented with a fire map. Thus, areas most suitable for the implementation of uneven-aged silvicultural systems can be roughly delineated from existing cartographic information, which will facilitate their integration into large-scale and long-term forest management plans.Key words: boreal forest, forest classification, forest dynamics, stand structure, silviculture

Impact of four silvicultural systems on birds in the Belgian Ardenne: implications for biodiversity in plantation forests

Uneven-aged management of conifer plantations is proposed as a way to increase the value of these forests for the conservation of bird diversity. To test this assumption, we compared the impact of four common silvicultural systems on bird communities, defined by cutblock size (large in even-aged silvicultural systems/smaller in uneven-aged silvicultural systems) and tree species composition (spruce/beech) in the Belgian Ardenne where beech forests have been replaced by spruce plantations. The abundances of bird species were surveyed in young, medium-aged and mature stands in 3–5 forests per silvicultural system (66 plots in all). The effect of silvicultural systems on bird species richness, abundance and composition were analysed both at the plot and at the silvicultural system levels. In plots of a given age, beech stands were richer in species. The composition of bird species at the plot level was explained by stand age and tree composition, but weakly so by stand evenness. For the silvicultural systems, bird species richness was significantly higher in even-aged and in beech forests, and bird species composition depended on the silvicultural system. This study emphasises the importance of maintaining native beech stands for birds and suggests that uneven-aged management of conifer plantations does not provide a valuable improvement of bird diversity comparatively with even-aged systems.

Disturbance dynamics influence Carex pensylvanica abundance in a northern hardwood forest1

Abstract We examined relationships involving the abundance of Carex pensylvanica Lam., a native sedge that can form dense mats in northern hardwood understories, and three types of disturbances: forest management, deer herbivory, and exotic earthworm activity. Stands managed using even-aged silvicultural systems in areas with high deer densities (> 20 deer km−2) had greater C. pensylvanica cover than stands managed using even-aged silvicultural systems in areas with lower deer densities (10–20 deer km−2), or unharvested second-growth communities. Stands managed using uneven-aged silvicultural systems were not significantly different from any other treatment group, regardless of deer density. There was a significant management × deer × earthworm interaction, and earthworm density had a positive relationship with C. pensylvanica cover in most management history × deer density combinations. High levels of disturbance associated with at least two of the three factors considered in this study were associated w...

Effects of structural complexity enhancement on eastern red-backed salamander ( Plethodon cinereus) populations in northern hardwood forests

Managing for stand structural complexity in northern hardwood forests has been proposed as a method for promoting microhabitat characteristics important to eastern red-backed salamanders ( Plethodon cinereus). We evaluated the effects of alternate, structure-based silvicultural systems on red-backed salamander populations at two research sites in northwestern Vermont. Treatments included two uneven-aged approaches (single-tree selection and group-selection) and one unconventional approach, termed “structural complexity enhancement” (SCE), that promotes development of late-successional structure, including elevated levels of coarse woody debris (CWD). Treatments were applied to 2 ha units and were replicated two to four times depending on treatment. We surveyed red-backed salamanders with a natural cover search method of transects nested within vegetation plots 1 year after logging. Abundance estimates corrected for detection probability were calculated from survey data with a binomial mixture model. Abundance estimates differed between study areas and were influenced by forest structural characteristics. Model selection was conducted using Akaike Information Criteria, corrected for over-dispersed data and small sample size (QAIC c). We found no difference in abundance as a response to treatment as a whole, suggesting that all of the uneven-aged silvicultural systems evaluated can maintain salamander populations after harvest. However, abundance was tied to specific structural habitat attributes associated with study plots within treatments. The most parsimonious model of habitat covariates included site, relative density of overstory trees, and density of more-decayed and less-decayed downed CWD. Abundance responded positively to the density of downed, well-decayed CWD and negatively to the density of poorly decayed CWD and to overstory relative density. CWD volume was not a strong predictor of salamander abundance. We conclude that structural complexity enhancement and the two uneven-aged approaches maintained important microhabitat characteristics for red-backed salamander populations in the short term. Over the long-term, given decay processes as a determinant of biological availability, forestry practices such as SCE that enhance CWD availability and recruitment may result in associated population responses.

Long-Term Economic Simulation: Even-Aged and Uneven-Aged Examples from the Missouri Ozark Forest Ecosystem Project (MOFEP)

Abstract Much of the software and many of the algorithms commonly used to simulate forest growth and harvesting activities have been optimized for short-term projections based primarily on larger-sized trees and are focused on even-aged silvicultural systems. Using data on trees 1.5 in. dbh and larger from the Missouri Ozark Forest Ecosystem Project (MOFEP), we have adapted the widely available Landscape Management System (LMS) and Forest Vegetation Simulator (FVS) software to make long-term simulations using even and uneven-aged silvicultural management systems. MOFEP is designed to test the long-term effects of even-aged, uneven-aged, and no harvest treatments on a variety of ecosystem attributes. To simulate the economic outcomes of these three treatments, we have written new LMS algorithms that simulate the effects of uneven-aged harvesting. Our results show that in the Missouri Ozarks even-aged and uneven-aged management silvicultural systems yield long-term (100 years) economic outcomes that are not statistically different. This result reinforces the need for land managers or landowners to consider esthetics, nontraditional forest products, and other nonmarket values in their decision matrix. North. J. Appl. For. 22(1):42– 47.

Comparative economic investigations of even-aged and uneven-aged silvicultural systems: a critical analysis of different methods

This study is based on a literature review of comparative economic analyses of even‐aged and uneven‐aged forests, mainly in the European context. An initial hypothesis is formulated that silver fir/Norway spruce ‘Plenterwald’‐type of uneven‐aged forests yield higher financial outputs (net revenues) than similar even‐aged forests under similar site conditions. A model study is described which avoids the weaknesses in the investigations reviewed in the literature. The results of the model study show that the initial hypothesis cannot be upheld. Assuming the same timber quality, the most favourable variants of the even‐aged and uneven‐aged systems yielded almost the same net revenues. The calculation of capital charges on the growing stock alters these results. The most important influence on the results in the even‐aged model is the level of risk. The main difficulties in comparing the economics of even‐aged and uneven‐aged forests are discussed.

Modelling the Growth and Management of Mixed Uneven-aged Maritime Pine - Broadleaved Species Forests in Galicia, North-western Spain

The state of mixed forests of maritime pine ( Pinus pinaster Ait.) and broadleaved species in the coastal region of Galicia (north-western Spain) was described using data from 213 circular sample plots selected among the available 4700 plots of the Spanish National Inventory. A matrix model was developed for this forest type to obtain information about the productivity and potential for sustainable management. The broadleaved species had a diameter distribution close to the inverted J-shape typical of the uneven-aged forests but for maritime pine there were many medium-sized trees and a lack of trees in the first diameter class of 15 cm. The matrix growth model was used to predict the development of mixed forests for three different management options: no harvesting in a well-stocked stand, a regime with a 5 yr harvest cycle and a residual basal area of 15 m 2 ha -1 in a well-stocked stand, and a rehabilitation management applied to an understocked stand. The results showed the possibility of applying uneven-aged silvicultural systems to these forests, leading to the production of high-value timber and to the maintenance of continuous cover and a biodiverse forest.

Structural differences between forests regenerating following spruce budworm defoliation and clear-cut harvesting: implications for marten

American marten (Martes americana Turton) avoid recent clearcuts when establishing territories but do not avoid similarly aged stands with a history of extensive tree mortality caused by the eastern spruce budworm (Choristoneura fumiferana Clem.). We quantified differences in overstory vegetation, understory vegetation, and coarse woody debris between stands that were clear-cut or defoliated by spruce budworms 10-20 years prior to our study. Our objectives were to identify habitat features with functional significance for marten that were lacking in managed stands and to propose goals for silvicultural practices that more closely resemble a natural disturbance (insect defoliation), thus improving habitat quality for marten. In contrast to regenerating clearcuts, defoliated stands had greater volumes of snags, downed logs, and root masses and included taller trees. Although live-tree basal area was similar between stand types, our results suggest that vertical structure provided by large snags can offset limited availability of live trees for marten, particularly where coarse woody debris and understory vegetation are plentiful. In stands under even-aged management, habitat quality for marten may be enhanced by retention of >18 m2/ha cull trees and snags. Uneven-aged silvicultural systems, which more closely mimic natural disturbance by defoliating insects, may have particular promise for maintaining marten habitat.

The Dauerwald: Its Role in the Restoration of Natural Forests

Abstract Following an almost 80-year discussion, several European countries recently mandated natural forest management based on uneven-aged silvicultural systems. This shift from traditional forestry is envisioned to eventually restore forests to a near natural condition, while promoting large volumes of high-quality wood. We review the evolution of the Dauerwald concept, which greatly influenced this significant shift, and briefly assess its relevance for American conditions.