Single-tree Harvesting Research Articles

Science, policy, and sustainable indigenous forestry in New Zealand

Background: Over 80% of New Zealand’s indigenous forests are in public ownership with logging prohibited, and logging of private indigenous forests is restricted to sustainable harvesting only. Such limitations are highly unusual globally and were imposed only in the last few decades of the 20th century. Previously, the national goal had been indigenous wood production in perpetuity. Here we review the role of forestry science in this outcome, and in particular in relation to the policies and practices adopted by the New Zealand Forest Service. Methods: Literature review Results: As early as 1900, it was recognised that economically viable management of indigenous forests for timber production was marginal at best. Nevertheless, the Forest Service, from its formation in 1919 to its abolition in 1987, advocated sustainable commercial management of indigenous forests. However, it failed to bring any significant areas under such management nor prevented conversion of substantial tracts of old-growth forest to exotic plantations or agriculture. Indigenous forest logging would have continued until commercial exhaustion of tall conifer species if a confluence of factors (urbanization, political upheaval, rise of an assertive conservation movement, and declining economic contribution) had not weakened the influence of provincial logging advocacy. Forestry research played a minor role in this saga as it focused on the technical issues of indigenous silviculture (e.g., coupe vs group vs single-tree harvesting methods) while the main drivers of change were economic, social, and cultural. Conclusions: Commercially valuable indigenous forests were protected only when the political cost of continuing logging was greater than that of halting it. However, it is an open question if the current policy settings will remain. Changes in governance (including increased Māori participation), land use change, planted indigenous forests and formation of exotic-indigenous forest communities will affect public attitudes as regards their use. If indigenous forestry science is to be of more consequence than in the past, New Zealand will need clear forestry goals and policies to deal with these changed circumstances, and the will to implement them.

Opportunity costs of growing space – an essential driver of economical single-tree harvest decisions

Controlling the growing space available to trees is essential for silvicultural management. For an efficient, i.e. economical, allocation of the scarce growing space, a qualitative and quantitative knowledge of all drivers of harvest decisions is required. The fundamental Faustmann-Pressler-Ohlin-Theorem reveals these drivers at the stand level: In the economical optimum, the stand's future value increment is equal to the interest of its value plus the land rent of the following stand. However, with increasing availability of single-tree data and single-tree-oriented management of heterogeneous stands, the need to transfer these fundamental economic relationships to the single-tree level arises. While several studies already focus on this problem, approaches using practice-related growth and harvest simulations that omit assumptions on the optimal thinning type are still somewhat rare. Our study seeks to provide a deeper understanding of basic economic principles underlying single-tree harvests. We thus aim to contribute to the methodological improvement of decision support systems regarding the implementation of silvicultural-economic linkages. We present a simulation-optimization model to analyze the importance of opportunity costs of growing space for economical harvests of even-aged single-trees under varying production goals and individual tree characteristics. Here, we show that controlling the competition-based growing space efficiency should guide harvest decisions at a young age, whereas with age the focus should shift to possible investment alternatives for the financial resources fixed in a tree. Our analyses of economical harvest decisions indicate that the importance of individual tree characteristics rises with increasing heterogeneity. We found some surprising economically optimal harvest sequences in heterogeneous groups of trees, which underlines the high potential of our model to inform practical decision making at the single-tree level. By implementing economic theory in marteloscopes, our approach could enable an improved training of forest managers to face complex silvicultural decisions. In an environment shaped by scarcities, the derived principles can be applied to various ecosystem services.

Impacts of Timber Harvest on Communities of Small Mammals, Ticks, and Tick-Borne Pathogens in a High-Risk Landscape in Northern California.

Timber harvest may impact tick-borne disease by affecting small mammal and tick community structures. We assessed tick and small mammal populations in older second-growth redwood (Sequoia sempervirens (D. Don) Endl) habitat at two harvested sites in Santa Cruz County, California, where local risk of tick-borne disease is high and determined the prevalence of tick-borne pathogens in ticks. After single-tree removal harvest in 2014, there was a modest reduction in canopy, primarily toward the end of the study. Harvested sites showed strong reductions in California mouse (Peromyscus californicus, (Gambel)) captures 2-yr after harvest, resolving such that treatments and controls were comparable by the end of the study. Following harvest, treated sites experienced a transient decreased tick infestation while control plots experienced an increase. Ixodes angustus (Neumann) infestation probability on harvested plots decreased immediately after harvest, increasing with time but remaining lower than control plots, whereas I. pacificus (Cooley and Kohls) prevalence was higher shortly after the harvest on harvested plots, and continued to increase. Mean abundance of ticks on vegetation increased on control plots. We detected Borrelia burgdorferi ((Johnson et al.) Baranton) and Anaplasma phagocytophilum ((Foggie 1949) Dumler) in 3.8 and 3.1% of ticks on rodents, but no differences were associated with harvest. Impacts of forest harvest on tick-borne disease depend on removal practice and intensity, whether or not hosts are habitat specialists, and whether or not ticks are host specialists.

Impact of informal timber harvesting on habitat structure and bird assemblages in a coastal forest of the Eastern Cape, South Africa

SummaryAfrican forests are under increasing pressure to supply local, regional, and international demand for timber. Much of this trade is unregulated, such that there is increasing concern regarding the ecological sustainability of this resource use. However, there is a lack of studies investigating the ecological impact of informal timber harvesting in African forests. While forest species have adapted to natural canopy gap dynamics, harvesting may alter natural disturbance regimes, with adverse effects on biodiversity. Information regarding harvest gaps, and concomitant impacts on habitat and biodiversity is thus essential to inform sustainable management. This study compared the frequency and nature of harvest gaps and natural gaps in a coastal forest in the Eastern Cape, South Africa, where informal selective timber harvesting occurs. Habitat condition and bird species richness and composition were compared across intact forest, natural gaps, and harvest gaps. Harvest-created gaps increased the number of canopy gaps by 30%, but were comparable with natural gaps in size. Habitat conditions in harvest gaps represented an intermediate state between intact forest and natural gaps, thereby increasing forest-scale habitat heterogeneity. While bird species richness was not affected, species composition differed across intact forest, harvest gaps and natural gaps, driven by changes in habitat condition, and mediated by species’ feeding and nesting traits. Specifically, insectivores, cavity- and ground-nesting species, and hawking and arboreal probing species were negatively affected by the habitat gradient from intact sites to canopy gap conditions, while nectarivores, omnivores and ball/cup nesting species were positively affected. Thus, while the single-tree selective harvesting method used by informal harvesters largely emulated natural canopy disturbances, the harvest-mediated increase in the frequency of canopy gaps may reduce the abundance of certain bird species sensitive to canopy gap conditions and reduce forest-scale beta-diversity.

Group-selection silviculture conditionally enhances recruitment of yellow birch in a shade-tolerant hardwood forest

Wide-spread use of single-tree harvest methods has inhibited regeneration of yellow birch in shade-tolerant hardwood forests. Shelterwood harvesting can improve recruitment, but incurs higher costs, longer harvesting cycles, and produces an even-aged structure. Group selection (GS) harvesting provides an alternative method with the benefits of single-tree selection (STS; mixed-ages, shorter cycles), yet produces larger gaps that may favour recruitment of mid/intolerant tree species. Recent GS trial studies have shown promise, but results vary and differences in edaphic conditions and competition dynamics associated with climate, historical management, and season of harvesting may influence responses. We evaluated the yellow birch recruitment efficacy of GS in an Ontario shade-tolerant hardwood forest by comparing change in regeneration as percent ground cover (stems <50 cm) and large stem density (>50 cm) over ten years in STS harvested and unharvested forest relative to two types of GS gaps: “typical” gaps placed in suitable microsites, and indiscriminate “systematic” interval gaps harvested on a grid.Autumn-harvested gaps established 2–4× more yellow birch cover and recruited 7–10× more large stems by year ten than STS and winter harvested gaps; unharvested controls remained unchanged. Typical gaps recruited 3× more stems than systematic gaps in autumn-only. Soil disturbance and seed tree proximity were correlated to establishment of yellow birch cover in year 1, which predicted large stem recruitment by year 10. Winter-harvesting favoured sugar maple cover in year 1, which predicted lower yellow birch recruitment by year 10. These results indicate that autumn-harvested typical gaps optimised germination and growth conditions for yellow birch (light availability, soil disturbance, reduced competition, seed proximity/dispersal). Consequently, GS harvesting in autumn can be considered an effective alternative to shelterwood harvesting for yellow birch recruitment in poorly-represented shade-tolerant hardwood stands.

Biomass production and carbon balance in two hybrid poplar (Populus euramericana) plantations raised with and without agriculture in southern France

Poplar is useful in different climates for bioenergy production and carbon sequestration when planted as a single species or in agroforestry. Europe has large areas potentially suitable for poplar forestry and a bioenergy policy that would encourage poplar forestry. In this study I estimated biomass production and carbon sequestration in poplar monoculture plantation and poplar-wheat agroforestry, in the Mediterranean region of France. A single-tree harvesting method was used to estimate biomass and an empirical conversion factor was adopted to calculate sequestered carbon. Total biomass was higher in agroforestry trees (1223 kg tree−1) than in monoculture plantation trees (1102 kg tree−1). Aboveground and belowground biomass distributions were similar in both cases (89 and 88% aboveground, and 11 and 12% belowground, respectively in agroforestry and monoculture). The partitioning of total biomass in an agroforestry tree in leaves, branch, and trunk (aboveground), and fine roots, medium roots, coarse roots and underground stem (belowground) was 1, 22, and 77, and 6, 9, 44 and 40%, respectively. Except for branch and trunk, all other compartments were similarly distributed in a monoculture tree. Storage of C was higher in agroforestry trees (612 kg tree−1) than in monoculture trees (512 kg tree−1). In contrast, C storage on a per hectare basis was lower in agroforestry (85 Mg ha−1) than in monoculture (105 Mg ha−1) due to the lower density of trees per hectare in agroforestry (139 trees in agroforestry vs 204 trees in monoculture). On a per hectare basis, soil C stocks pattern were similar to per tree stocking: They were higher in agroforestry at 330 Mg ha−1 than in monoculture 304 Mg ha−1. Higher C accumulation by agroforestry has a direct management implication in the sense that expanding agroforestry into agriculture production areas with short rotation and fast growing trees like poplar would encourage quicker and greater C sequestration. This could simultaneously fulfil the requirement of bioenergy plantation in Europe.

Plentern mit Kiefern – Ergebnisse aus den USA

Plentering with pines – results from the United States Until now, scientifically reliable data on plentering of light-demanding tree species in Europe have been lacking. This gap is filled with long-term trials from the USA, among others with southern yellow pines. In the southern state of Arkansas, two plots of 16 hectares were installed in 1936, in the context of a large-scale trial of mixed loblolly pine (Pinus taeda L.) and shortleaf pine (Pinus echinata Miller) stands, in which plentering has been applied using single-tree harvest of predominantly sawtimber-sized trees (dbh &amp;gt;30 cm) with natural regeneration. The aim of the experiment is to investigate the possibilities and limits of uneven-aged silviculture with shade-intolerant tree species, and whether this can be applied in cutover southern yellow pine stands in order to improve the stand structure, to increase growth, and to make periodic harvests possible. The two plots were in different initial states – one more or less fully stocked, the other with poor initial stocking. Since 1936, 18 complete surveys have been conducted where all trees 10 cm and larger were tallied by diameter. During that same time period, 14 plenter harvests have been carried out using the Volume Control-Guiding Diameter Limit method in both plots. In order to check the variability of stand structure within the 16-hectare stands, each was subdivided into four quarters, and the diameter distributions were compared within each quarter. The uneven- aged structure was checked by a sample of tree-ring counts. Both stands retained continuous canopy cover throughout the observation period. The initial differences in the number of stems, the basal area, the standing volume, the proportion of sawtimber, the average basal area and the mean quadratic diameter dg became alike in the course of time, which shows the flexibility of plentering and the tendency to develop stands where the harvest of growth appears to be sustainable. The dg of the harvest was initially slightly more than 20 cm, but is today more than 50 cm. The average total growth is 6 m3/ha and year. The results show that these stands are uneven-aged stands in an advanced stage of the transformation to plentering. We suspect that in the absence of a major natural disturbance event, the plentering approach in southern yellow pines will continue to be promising in the future.

Using Unmanned Aerial Vehicles (UAV) to Quantify Spatial Gap Patterns in Forests

Gap distributions in forests reflect the spatial impact of man-made tree harvesting or naturally-induced patterns of tree death being caused by windthrow, inter-tree competition, disease or senescence. Gap sizes can vary from large (&gt;100 m2) to small (&lt;10 m2), and they may have contrasting spatial patterns, such as being aggregated or regularly distributed. However, very small gaps cannot easily be recorded with conventional aerial or satellite images, which calls for new and cost-effective methodologies of forest monitoring. Here, we used an unmanned aerial vehicle (UAV) and very high-resolution images to record the gaps in 10 temperate managed and unmanaged forests in two regions of Germany. All gaps were extracted for 1-ha study plots and subsequently analyzed with spatially-explicit statistics, such as the conventional pair correlation function (PCF), the polygon-based PCF and the mark correlation function. Gap-size frequency was dominated by small gaps of an area &lt;5 m2, which were particularly frequent in unmanaged forests. We found that gap distances showed a variety of patterns. However, the polygon-based PCF was a better descriptor of patterns than the conventional PCF, because it showed randomness or aggregation for cases when the conventional PCF showed small-scale regularity; albeit, the latter was only a mathematical artifact. The mark correlation function revealed that gap areas were in half of the cases negatively correlated and in the other half independent. Negative size correlations may likely be the result of single-tree harvesting or of repeated gap formation, which both lead to nearby small gaps. Here, we emphasize the usefulness of UAV to record forest gaps of a very small size. These small gaps may originate from repeated gap-creating disturbances, and their spatial patterns should be monitored with spatially-explicit statistics at recurring intervals in order to further insights into forest dynamics.

Physiology and growth of advance Picea rubens and Abies balsamea regeneration following different canopy openings

We examined the ecophysiology and growth of 0.3-1.3 m tall advance red spruce (Picea rubens Sarg.) and balsam fir (Abies balsamea [L.] Mill.) regeneration during a 5-year period following the application of different harvest types producing three sizes of canopy openings: (i) small gaps (<100 m(2) in area; SMA) created by partial uniform single-tree harvest; (ii) irregular gaps of intermediate size (100-300 m(2); INT) created by group-selection harvest (removal of groups of trees, mainly balsam fir, with uniform partial removal between groups); and (iii) large circular gaps (700 m(2); LAR) created by patch-selection harvest (removal of trees in 30-m diameter circular areas with uniform partial removal between gaps). An unharvested control (CON) was monitored for comparison. At the ecophysiological level, we mainly found differences in light-saturated photosynthesis of red spruce and specific leaf area of balsam fir among treatments. Consequently, we observed good height growth of both species in CON and INT, but fir surpassed spruce in SMA and LAR. Results suggest that intermediate 100-300 m(2) irregular openings create microenvironmental conditions that may promote short-term ecophysiology and growth of red spruce, allowing the species to compete with balsam fir advance regeneration. Finally, results observed for spruce in large 700-m(2) openings confirm its inability to grow as rapidly as fir in comparable open conditions.

Influence of wood harvest on tree-ring time-series of Picea abies in a temperate forest

Tree-ring width data are the prime source of high-resolution climate reconstructions covering recent millennia. Their variations, from year-to-year, are calibrated against regional instrumental data to evaluate the strength of associations with temperature and precipitation records, though the level of variance explained by climatic variables is frequently less than 50%. Among the remaining factors affecting tree growth, the influence of forest management for tree-ring width time-series used to resolve annual climate reconstructions remains relatively unexplored. We here evaluate the impact of conventional single-tree harvesting on tree-ring data using a compilation of circumstantially mapped Picea abies sites in western Germany. Climate signals are explored by calibration against regional temperature and precipitation data, and the influences of forest management analyzed using long-term logging data spanning the past 40–80years and mapped stumps (and neighboring trees) spanning the past 20years. Our results indicate a weak but statistically significant control of total May–July precipitation of P. abies growth. This association is only marginally, if at all, affected by forest management, i.e. wider tree-rings due to improved access to light and nutrients in years after logging events are either not found or in line with increased precipitation sums following single-tree harvest. These findings suggest only minor influences of selective harvesting on Picea tree-ring growth in western Germany, and overall limited biases of annually resolved climate reconstructions from lower elevation central European sites due to historical logging events.

Disturbances and biodiversity in forest ecosystems: A temperate zone perspective

In the temperate zone windstorms and bark beetle attacks represent the main natural forest disturbances; in steep mountain areas snow avalanches also may “destroy” forest stands completely. In the densely populated and intensively used temperate zone of Europe affected forest stands will be cleared and reforested immediately after such “catastrophes”. Therefore we have only little knowledge about the influence of such natural disturbances on both the stand development and the biodiversity of native forest ecosystems. And we do not have quantitative data on to which degree forest management changes the biodiversity compared to the natural disturbances. Since about two decades several permanent plot studies have been running in European forests affected by such natural disturbances, mainly with focus on plant species. Here we first outline the importance of disturbances for biodiversity in forest ecosystems and then discuss whether it is possible to combine both biodiversity protection and forest management. For that we use four recent case studies carried out in the two oldest national parks in Germany, three of them being long-term observations on permanent plots for up to two decades. Disturbances like wind throw, bark beetle outbreak and snow avalanche strongly influences the tree layer structure, creating micro-habitats for many plant, animal and fungi species, which naturally belong to the forest ecosystem. Such disturbances in future should be included into management schemes in forestry to improve biodiversity. We found evidence that it is really possible to combine timber utilization with biodiversity protection. As long as the management impact is reduced (e.g. single tree harvesting, using natural regeneration), species diversity of several taxonomic groups (in our study: vascular plants, soil living Carabidae, and soil living fungi) may not be different significantly from a pristine forest. Interconnecting resource use with biodiversity protection will be a main task for both foresters and conservationist in the decades to come – and it seems to be a possible option for a sustainable land use in many parts of the world.doi: http://dx.doi.org/10.3126/botor.v8i0.5552 Botanica Orientalis – Journal of Plant Science (2011) 8: 1-9

Energy wood harvesting productivity of three harvesting methods in first thinning of scots pine (Pinus sylvestris L.)

Abstract Energy wood harvesting in young forests presents an economical challenge and has been dependent on subsidies in Finland. Whole-tree harvesting systems have proved to be most productive when carrying out energy wood harvesting in cleanings and early thinnings in young forests. The application of integrated energy wood and pulpwood harvesting is less common. It was hypothesized that multi-tree harvesting (MTH) with the OM-Waratah 745 single grip harvester head could change harvesting logistics and improve productivity for integrated energy wood and pulpwood thinnings. Two variations of MTH were compared with single-tree harvesting (STH). The logging methods studied were: (1) conventional single-tree harvesting with pulpwood and energy wood processed at the strip road; (2) multi-tree harvesting with pulpwood and energy wood processing along the strip road (MTH1); and (3) multi-tree harvesting at the stump where the aim was to leave the logging residues distributed evenly over the harvesting area and not on the strip roads (MTH2). MTH methods were 28–35% more productive than the single-tree harvesting. The biggest differences in work stages were found in the felling and delimbing stages. In single-tree harvesting felling was 9–26% and delimbing 14–27% slower than in multi-tree harvesting. MTH2 distributed 13% of residues further than 7 m from the strip road center. With STH and MTH1 only a good 1.2–1.7% was placed this far, and 74.4 and 62.0% respectively within 3 m.

Regeneration and structure of mixed conifer forests under single-tree harvest management in the western Bhutan Himalayas

We examined the regeneration and structure of mixed conifer forests under single-tree harvest management in western Bhutan. Sixteen 900 m 2 (30 m × 30 m) plots were sampled at four Forest Management Units (FMUs; Chamgang, Gidakom, Paro-Zonglela, and Haa-East) representing the forest type, including half the plots in single-tree harvest stands and half in unlogged stands. In addition, we solicited information on traditional forest management practices from informants using survey questionnaires and collected tree species data from felling records from respective local forest offices. Rural timber demand is concentrated on the removal of straight and well-formed bluepine trees for beams, planks, and scaffolding. Single-tree harvest, however, has not significantly altered stand structures from unlogged stands. Similarly, tree regeneration is not different when comparing single-tree harvest and unlogged stands, except at Chamgang FMU, where seedling densities were generally higher in harvested stands than in unlogged stands. These results indicate that single-tree harvest is not detrimental to regeneration and utilization of mixed conifer forests in western Bhutan.

ABOVEGROUND AND BELOWGROUND EFFECTS OF SINGLE‐TREE REMOVALS IN NEW ZEALAND RAIN FOREST

There has been considerable recent interest in how human-induced species loss affects community and ecosystem properties. These effects are particularly apparent when a commercially valuable species is harvested from an ecosystem, such as occurs through single-tree harvesting or selective logging of desired timber species in natural forests. In New Zealand mixed-species rain forests, single-tree harvesting of the emergent gymnosperm Dacrydium cupressinum, or rimu, has been widespread. This harvesting has been contentious in part because of possible ecological impacts of Dacrydium removal on the remainder of the forest, but many of these effects remain unexplored. We identified an area where an unintended 40-year "removal experiment" had been set up that involved selective extraction of individual Dacrydium trees. We measured aboveground and belowground variables at set distances from both individual live trees and stumps of trees harvested 40 years ago. Live trees had effects both above and below ground by affecting diversity and cover of several components of the vegetation (usually negatively), promoting soil C sequestration, enhancing ratios of soil C:P and N:P, and affecting community structure of soil microflora. These effects extended to 8 m from the tree base and were likely caused by poor-quality litter and humus produced by the trees. Measurements for the stumps revealed strong legacy effects of prior presence of trees on some properties (e.g., cover by understory herbs and ferns, soil C sequestration, soil C:P and N:P ratios), but not others (e.g., soil fungal biomass, soil N concentration). These results suggest that the legacy of prior presence of Dacrydium may remain for several decades or centuries, and certainly well over 40 years. They also demonstrate that, while large Dacrydium individuals (and their removal) may have important effects in their immediate proximity, within a forest, these effects should only be important in localized patches containing high densities of large trees. Finally, this study emphasizes that deliberate extraction of a particular tree species from a forest can exert influences both above and below ground if the removed species has a different functional role than that of the other plant species present.

Do the size and landscape context of forest openings influence the abundance and breeding success of shrubland songbirds in southern New England?

Early successional birds have declined in the northeastern United States due to the regeneration of forest on abandoned farm fields and the suppression of natural disturbances that once provided appropriate habitat. These species have become increasingly dependent on early successional habitats generated by such activities as timber harvesting. Recent approaches of timber harvesting, which range from single-tree harvesting to clearcutting, create forest openings of different sizes and configurations embedded in landscapes with different land use patterns. To assess the importance of forest openings created by timber harvesting for shrubland birds, we surveyed birds on 50 m radius plots in 34 harvest sites (0.5–21 ha). We collected data on multi-scaled habitat variables ranging from plot-level vegetation characteristics to land use patterns within 1 km of each study site. We also monitored mating and nesting success of Blue-winged Warblers ( Vermivora pinus) in 10 forest openings. The abundance of most shrubland species was influenced by plot-level habitat variables, such as tree density and vegetation height, rather than shrubland area or the composition of land uses in the surrounding landscape. Only Eastern Towhees ( Pipilo erythrophthalmus) were more frequent in survey plots in larger forest openings. In contrast, neither abundance nor reproductive activity of Blue-winged Warblers was correlated with the size of the forest opening. Their abundance was negatively related to vegetation height, however. Only 54% of the territorial male Blue-winged Warblers in forest openings were mated. We documented relatively low nest success rates of 21.1% during the egg laying and incubation nest stages, but increased success rates during the later stages of nesting. Our results indicate that even small forest openings with low vegetation provide habitat for Blue-winged Warblers and other shrubland birds. The overall reproductive rate of territorial male Blue-winged Warblers in forests openings was low during the 2 years of the study, however. Further studies are needed to assess the long-term value of this type of habitat for sustaining shrubland bird populations.

Effects of Silvicultural Practices on Soil Carbon and Nitrogen in a Nitrogen Saturated Central Appalachian (USA) Hardwood Forest Ecosystem

Silvicultural treatments represent disturbances to forest ecosystems often resulting in transient increases in net nitrification and leaching of nitrate and base cations from the soil. Response of soil carbon (C) is more complex, decreasing from enhanced soil respiration and increasing from enhanced postharvest inputs of detritus. Because nitrogen (N) saturation can have similar effects on cation mobility, timber harvesting in N-saturated forests may contribute to a decline in both soil C and base cation fertility, decreasing tree growth. Although studies have addressed effects of either forest harvesting or N saturation separately, few data exist on their combined effects. Our study examined the responses of soil C and N to several commercially used silvicultural treatments within the Fernow Experimental Forest, West Virginia, USA, a site with N-saturated soils. Soil analyses included soil organic matter (SOM), C, N, C/N ratios, pH, and net nitrification. We hypothesized the following gradient of disturbance intensity among silvicultural practices (from most to least intense): even-age with intensive harvesting (EA-I), even-age with extensive harvesting, even-age with commercial harvesting, diameter limit, and single-tree harvesting (ST). We anticipated that effects on soil C and N would be greatest for EA-I and least with ST. Tree species exhibited a response to the gradient of disturbance intensity, with early successional species more predominant in high-intensity treatments and late successional species more predominant in low-intensity treatments. Results for soil variables, however, generally did not support our predictions, with few significant differences among treatments and between treatments and their paired controls for any of the measured soil variables. Multiple regression indicated that the best predictors for net nitrification among samples were SOM (positive relationship) and pH (negative relationship). This finding confirms the challenge of sustainable management of N-saturated forests.

Western redcedar population dynamics in old-growth forests: Contrasting ecological paradigms using tree rings

In coastal British Columbia, late-successional forests dominated by western redcedar (Thuja plicata Donn ex D. Don) are structurally complex, with deep multi-layered canopies, large trees that are &gt; 250 years old, and abundant coarse woody debris (CWD). These forests are presumed to be "old-growth" forests in which fine-scale gaps are the dominant disturbance regime, accounting for their structural diversity. In this study, I have used tree-ring analyses to investigate western redcedar regeneration dynamics in these old-growth forests. Western redcedar dominates canopies of many stands, but is rare in the understorey although it tolerates shade. The traditional interpretation is that western redcedar depends on catastrophic disturbance to regenerate and that it is replaced through succession by western hemlock (Tsuga heterophylla (Raf.) Sarg.) and Pacific silver fir (Abies amabilis (Dougl. ex Loud.) Dougl. ex J. Forbes), which are abundant in the understorey. Dominant trees are perceived to represent an even-aged, post-disturbance cohort and the lack of regeneration indicates a population decline in the absence of catastrophic disturbances. In this paper, I investigate four assumptions underlying this interpretation: (1) Tree size indicates age. (2) Populations establish as even-aged, post-disturbance cohorts. (3) Abundant CWD represents recent mortality. (4) Regeneration is insufficient to maintain canopy dominance. Using tree-ring evidence, I show that population dynamics of western redcedar are a combination of gap-phase establishment and a continuous mode of recruitment from the sub-canopy to the canopy. Specifically, size is a poor surrogate for tree age. Age distributions from 15 sites revealed uneven-aged populations, rather than single post-disturbance cohorts. Both logs and snags of western redcedar may persist more than 270 years; they do not represent recent mortality that is disproportionate to the number of live western redcedar in canopy. The regeneration niches of western redcedar and western hemlock overlap. For both species, gap-phase disturbances result in substrate suitable for successful seedling establishment. Preliminary results from dendroecological analysis of radial growth rates of trees in the subcanopy and canopy strata suggest that western hemlock and Pacific silver fir depend on gaps to recruit to the upper canopy, but recruitment of western redcedar may be independent of canopy gaps. I propose that differences in mode of recruitment to the canopy may explain the differences in population structures between western redcedar, western hemlock, and Pacific silver fir in the old-growth forest. These results provide an ecological precedent for use of a range of silvicultural systems, including clearcuts through single-tree harvesting and protection forests, when managing western redcedar in coastal British Columbia. Key words: Coastal British Columbia, disturbance regimes, regeneration dynamics, Thuja plicata, variable retention silviculture

Stand structure and tree growth in uneven-aged spotted gum (Corymbia maculata) forests: some implications for management

Summary The current trend towards more naturalness and increased protection of biodiversity at the level of forest stands requires the management of structurally diverse forests. In this study we investigated the consequences of single-tree harvesting in mixed-species eucalypt forests on stand structure and tree growth. Data from continuous inventory plots indicated that single-tree selection without additional tending over a period of 40 years leads to the accumulation of high basal areas. Although the diameter distribution indicated a balanced stand, a high proportion of the trees, particularly in small dimensions, was slow growing, and the current structure could not ensure the replacement of trees in sawlog dimensions within acceptable periods. We recommend that some investment is required to reduce basal area of non-merchantable trees in these forests in order to provide the necessary growing space, in particular for smaller trees.

Influence of variable retention harvests on forest ecosystems. II. Diversity and population dynamics of small mammals

1 Variable retention harvests in temperate coniferous forests provide various intensities and sizes of disturbance across a gradient, from clear-cutting to single-tree harvesting. These ‘green-tree retention systems’ leave large live trees after harvest (i.e. residual trees) to increase structural diversity of the regenerating stand. It is unclear what effect these harvesting patterns will have on wildlife in general, and small mammals in particular. 2 This study was designed to test the hypotheses that: (i) the abundance and diversity of forest-floor small mammals will decline with lower levels of tree retention; (ii) the abundance, reproduction and survival of Microtus spp. and southern red-backed vole Clethrionomys gapperi populations will decline and increase, respectively, with the basal area and density of residual trees after harvest; and (iii) habitat heterogeneity generated by variable retention harvesting will limit population size of Microtus, thereby reducing feeding damage to tree seedlings planted on harvested areas. 3 Small mammals were intensively live-trapped from 1996 to 1999 in replicated clear-cut, single seed-tree, group seed-tree, patch-cut and uncut forest sites in mixed natural forests of Douglas fir Pseudotsuga menziesii–lodgepole pine Pinus contorta in southern British Columbia, Canada. The seed-tree harvesting system leaves a few wind-firm seed trees standing singly, or in groups, to provide seed to regenerate an area naturally. The patch-cut system harvests timber from small (< 1-ha) units dispersed over a given area of forest. 4 Contrary to hypothesis (i), the mean total abundance of small mammals was similar among sites, and mean species richness and diversity of small mammals was lowest in the uncut forest but similar across the other four treatments. 5 The overall mean abundance (ha−1) of Microtus spp. was higher on clear-cut (11·3) sites than single seed-tree (6·0), group seed-tree (3·9), patch-cut (1·8) or uncut forest (0·1) sites. Overall mean abundance (ha−1) of C. gapperi was similar in uncut forest (16·2) and group seed-tree (10·0) sites, which were both higher than patch-cut (6·4), clear-cut (4·2) or single seed-tree (2·7) sites. 6 The recruitment of new Microtus spp. differed significantly among sites, declining from clear-cut to uncut forest. The recruitment of C. gapperi exhibited the opposite trend. The mean number of successful pregnancies was similar among treatments for Microtus spp. but for C. gapperi was highest in uncut forest, group seed-tree and patch-cut sites. The survival of each vole species was similar across treatment sites. 7 Hypothesis (ii) was supported. The mean abundance of Microtus spp. was inversely, and that of C. gapperi positively, related to mean basal area and density of residual trees after harvest. The mean abundance of Microtus spp. was also inversely related to percentage cover and crown volume index of residual trees, and positively related to number of lodgepole pine cones (seeds) in logging debris. 8 In terms of hypothesis (iii), vole feeding damage to planted lodgepole pine seedlings appeared highest in the patch-cut sites during the 1997–98 and 1998–99 overwinter periods, and appeared to have been caused mainly by C. gapperi rather than Microtus spp. 9 The group seed-tree and patch-cut systems achieved both aims of C. gapperi persistence and prevention of Microtus outbreaks. These harvesting methods are as good for overall small mammal abundance, species richness and diversity as any other.

Management of transformation in central Europe

The historical background, the management practice, growth and yield aspects of transformation of artificial coniferous stands in central Europe are outlined. Past management has reduced the proportion of natural broad-leaved forests from 66 to 33% of the forest area. The pure stands of planted Norway spruce ( Picea abies) and Scots pine ( Pinus sylvestris) show increased instability and susceptibility to damage by snow and wind. Proposals for transformation go back to the nineteenth century, but the diversity of sites, stand structures and different goals of owners make transformation a variable task. This paper outlines three case studies of transformation and some results of growth research into transforming coniferous stands, based on the situation in south-western Germany which is comparable to other parts of central Europe. The first case study deals with two experimental stands in the southern Black Forest which have been developed from an even- to an uneven-aged structure. Diameter distribution, residual volumes, harvesting results and periodic increments and yields are characterised. The second case study outlines the transformation of pure Norway spruce stands. On stable sites, an uneven-aged mosaic structure with 20–40% beech can be reached by crop-tree oriented thinning from above, target-diameter harvesting, natural regeneration and underplanting of beech if needed. On unstable sites, transformation will be realised either by clearfelling and seeding, conversion to oak by planting or by underplanting of silver fir and single-tree harvesting. The third case study deals with pure Scots pine stands: natural regeneration of Scots pine allows transformation options either rather fast in combination with clearfelling and/or seeding, or delayed with lasting regeneration procedures, or as nearly continuous cover system with low density of overstorey. Some growth and yield problems in transforming coniferous stands are shown using the example of the “Langenbrand-experiment”, started in 1927 in the northern Black Forest. There are effects of differing regeneration periods on growth rates caused by the interaction between the old and the young stands. These have an influence on the growth reactions of the residual trees, their mortality and the pattern of height/diameter ( h/ d) ratios in the natural regeneration. The h/ d relationships of the young stands depend on the length of the regeneration period with longer periods promoting more favourable ratios which should positively influence the stability of future stands.