Aggregated Retention Research Articles

Effects of dispersed and aggregated retention on epiphytic microarthropod assemblages: A northern hardwood forest case study

Epiphytic lichens and bryophytes provide important habitat for microarthropods, yet little work has documented epiphytic microarthropod assemblages. Further, the response of epiphytes and their associated microarthropod communities to varying levels of forest disturbance and cutting intensity are not well known. We conducted a case study to provide an initial community description of epiphyte-dwelling microarthropods in Adirondack northern hardwoods, and to assess potential for impacts of aggregated and dispersed patterns of reserve tree retention to these communities. In total, 79 families of microarthropods were identified in the 0.14 m2 of samples. Late summer average daily maximum temperatures were 3.2 °C higher in the shelterwood, and three years following treatments the per-unit area dry weight of the bole-associated bryophyte Neckera pennata was 34 % lower in the shelterwood. Microarthropod richness and density were distinctly greater in epiphyte substrates at the base of trees, and were reduced in the shelterwood. Several indicator taxa were identified within the basal bryophytes in the reserve treatment, and in both bryophytes the microarthropod assemblages were more homogenous in the shelterwood. A few mobile and heavily sclerotized taxa persisted in shelterwood substrates, especially in the lichens which lacked 3-dimensional structure. This case study revealed a diverse community of microarthropods in northern hardwood forests that were structured by epiphyte type, height on tree and, potentially, by canopy removal, and suggests conservation value of aggregated tree retention when applying even-age regeneration methods with respect to epiphytic bryophytes, lichens, and their associated invertebrates.

Variable retention harvesting and climate variations influence over natural regeneration dynamics in Nothofagus pumilio forests of Southern Patagonia

Natural regeneration is a key process to sustain structure, function, and composition in harvested forests over time. Variable retention harvesting system is a strategy that maintains a high level of heterogeneity in managed stands for multiple ecosystem services, which provides different micro-environmental conditions for natural regeneration that respond differently according to climate variations. The objective was to determine the influence of remnant over story on the dynamics of Nothofagus pumilio natural regeneration in forests managed under variable retention in the medium term (0 to 16 years-after-harvesting, YAH) and its interaction with climate variables. Recruitment period, survival, seedling bank of pre- and post-harvesting periods, regeneration age and heights were determined at permanent plots under three different harvested forest conditions (1: AR = aggregated retention, 2: DRI = dispersed retention under the influence of AR, 3: DR = dispersed retention without influence of AR) and one primary forests (PF) as a control (4 treatments × 6 replicates × 3 areas × 16 YAH). Height growth rates were associated to combined occurrence of hemispheric modes (ENSO and SAM) that influence over climate variations. Results showed different regeneration dynamics according to remnant forest over story: (i) a recruitment stage occurred during the first 4 YAH; (ii) 67,000 and 33,000 individuals ha−1 for DRI and DR established respectively, with 15,000 individuals ha−1 higher than 130 cm height at 16 YAH; (iii) equal density proportion of pre- and post-harvesting saplings between treatments (DRI and DR); (iv) significant differences in regeneration heights among treatments from 3 to 16 YAH, which were higher at DRI and DR, reaching to 130 cm height at 16 ± 1 years of age. Saplings height growth reacted favourably to higher mean temperatures associated with positive SAM and ENSO. These results reflect a successful and resilient natural regeneration process for N. pumilio where variable retention system to obtain timber products is below the thresholds of no-return, reacting differently according to climatic drivers by the presence of different structures of remnant over story. This provides useful information for forest management practices in the medium term, where the maintenance of stand heterogeneity (e.g., different types of over story retention) ensures successful and resilient regeneration to recover the stand original structure within a context of climate change.

Short-term effects of retention forestry on the diversity of root-associated ectomycorrhizal fungi in Sakhalin fir plantations, Hokkaido, Japan

We have examined the effects of dispersed and aggregated retention on the diversity of root-associated ectomycorrhizal fungi (EcMf) in Sakhalin fir (Abies sachalinensis) plantations, 4 years after logging. Roots of Sakhalin fir seedlings and the adjacent broadleaved or Sakhalin fir trees were sampled in broadleaved dispersed retention sites (10, 50, or 100 trees/ha), conifer aggregated retention sites (a single 60 × 60 m square patch of Sakhalin fir trees per site), clear-cut sites, unharvested Sakhalin fir plantations, and natural broadleaved forest stands. The EcMf on the roots were grouped into operational taxonomic units based on the similarity of the internal transcribed spacer sequences within the nuclear ribosomal DNA. Clear-cutting significantly reduced the species richness and diversity of the EcMf and altered the species composition when compared with the unharvested Sakhalin fir plantations and natural broadleaved forests. In contrast, both the aggregated and dispersed retention sites maintained higher levels of EcMf diversity, as well as different EcMf communities when compared with the clear-cut sites. Aggregated retention was effective at conserving EcMf diversity at the unharvested Sakhalin fir plantations, but the effects were limited within retained patches. Broadleaved dispersed retention did not retain the EcMf communities that were present prior to logging even at high retention levels, but they could retain unique EcMf communities, which differed between the Sakhalin fir plantations, natural broadleaved forests, and clear-cut sites. The species richness and diversity values for some of the dispersed retention sites were comparable to the values for the unharvested Sakhalin fir plantations and tended to be greater than the values for the aggregated retention sites. The results indicate that dispersed retention could be an effective strategy by which to preserve a larger number of EcMf species and unique EcMf communities in logged conifer plantations, although the positive effects were likely limited spatially within the rooting zones of the retained broadleaved trees. Finally, naturally regenerating Sakhalin fir seedlings were found to share a large amount of their EcMf with adjacent broadleaved retention trees, indicating that multi-host EcMf of retained trees largely contribute to ectomycorrhizal colonization of the surrounding regenerated seedlings in the logged areas. Our findings demonstrated that both dispersed and aggregated retention methods could be used to mitigate the impacts of logging on EcMf diversity in Sakhalin fir plantations, in Japan, and that there were large differences in the effects among the different retention methods.

Do forest edges reduce timber productivity – Implications for retention forestry techniques

Retention forestry techniques such as aggregated retention rely on proximity to an adjacent standing forest to increase the speed and success of biological community regeneration post-disturbance. However, increased competition near a standing forest may result in a decrease in the growth of targeted timber species which in turn may impact on timber yields. This study examined the impact that standing forest adjacent to regenerating forest has on the height of Eucalyptus spp. regeneration in the wet temperate forests of Tasmania, Australia. We used LiDAR data to test whether the height of the regenerating forest varied with proximity to the adjacent forest following harvesting and regeneration treatments. The distance response was examined across two silvicultural systems, aggregated retention (ARN) and clearfell, burn and sow (CBS), and across two broad age classes (1–7 years and 11–24 years). Height growth was reduced within 23 m of a retained edge, with a maximum reduction of 12% occurring closest to the edge. The edge effect was similar across ages and between silvicultural systems, although ARN silviculture will suffer greater losses compared to CBS due to the greater percentage of area adjacent to a standing forest. Understanding productivity losses associated with increasing edges in harvesting systems, provides important information for forest managers balancing economic and biodiversity conservation requirements.

Green-tree retention and relative habitat use by mule deer (Odocoileus hemionus) 20 years after harvest of Douglas-fir (Pseudotsuga menziesii) – Lodgepole pine (Pinus contorta) forest

Mule deer (Odocoileus hemionus) are a major mammal species in many interior Douglas-fir (Pseudotsuga menziesii) forest ecosystems in western North America. During winter in areas of relatively high snowpacks, mule deer seem to require older trees with large crowns for snow interception, but these forests are often targeted for harvest. Green-tree retention (GTR) may offer a solution to this conundrum. We tested three hypotheses (H) that, at 20–22 years after harvest, (H1) abundance (e.g., basal area and density of residual trees and understory stand structure) of conifers, (H2) abundance, species richness, and diversity of understory vegetation, and (H3) relative habitat use by mule deer, will decline with lower levels of tree retention. Fecal pellet-groups of deer were counted in summer and winter periods for three years in replicated stands of dispersed retention, aggregated retention, patch-cut, group selection, and uncut forest in mixed Douglas-fir - lodgepole pine (Pinus contorta) forest in southern British Columbia, Canada.Mean basal area, density, and canopy closure of overstory Douglas-fir trees were generally greater in the patch-cut, group selection, and uncut forest sites than dispersed and aggregated retention sites, and hence supported the overstory part of H1. Mean density of understory conifers did not support H1 as the majority of these trees were in the dispersed and aggregated retention stands. There was no difference in mean abundance nor species richness of understory vegetation among treatment sites. Mean species diversity tended to be 1.4–1.8 times higher in the patch-cut and group selection than the other sites, and hence provided weak support for H2. Patch-cut and group selection sites were dominated by Douglas-fir trees in both the overstory and understory, along with potential forage shrub species, and were used by deer more than the dispersed and aggregated retention stands in both summer and winter. Relative habitat use by deer in uncut forest was greater than the retention stands and generally similar to the patch-cut and group selection sites in both seasons. These results suggest that partial harvesting of these mixed Douglas-fir – lodgepole pine stands across a range of opening sizes (e.g., 0.1 to 2–5 ha) should provide suitable habitat for mule deer over time.

Variable retention forestry conserves habitat of bird species in Patagonian Nothofagus pumilio forests

Variable retention is an alternative harvesting system that could be implemented instead the more traditional ones (e.g. shelterwood cut for N. pumilio forests in southern Patagonia), because it was designed not only for timber purpose, but also for conservation. However, the impact of different retention types on diversity is not clear, e.g. stenotopic and eurytopic bird species. The objective of this work was to analyse the habitats (inside, edge or outside of aggregated retention) and the use of strata (canopy, stem, debris and floor) for different bird species under two different variable retention harvesting types (aggregated + dispersed retentions, or ggregated retention + clear-cuts). We analysed four years of bird observation data in variable retention harvested and unharvested forest permanent plots located in Tierra del Fuego province (Argentina) belonging to PEBANPA (Parcelas de Ecologia y Biodiversidad de Ambientes Naturales en Patagonia Austral) network, also with understory and crown cover data. Statistical analysis included uni- and multivariate tests, and comparisons with unharvested forests. We inventoried nine bird species, six of which showed significantly different habitat preference in variable retention types (Carduelis barbata, Phrygilus patagonicus and Tachycineta leucopyga in aggregated + dispersed retentions, and Enicognathus ferrugineus, P. patagonicus, T. leucopyga, Troglodytes aedon and Zonotrichia capensis in aggregated retention + clearcuts). Likewise, all evaluated species presented differential use of strata, and some species changed comparing harvested and unharvested forests. DCA (Detrended Corresponded Analysis) highlighted association between species and habitats (e.g. P. patagonicus is more related to outside aggregated retentions) as well as differences between variable retention types, showing that bird species move toward edges when clear-cuts were carried out, among aggregated retention, instead of dispersed retention. These results support the effectiveness of the variable retention to conserve habitat of bird species inside managed forests, which satisfy both stenotopic and eurytopic species requirements.

Microclimatic edge effects in a recently harvested forest: Do remnant forest patches create the same impact as large forest areas?

Microclimatic forest influence (edge effects into open or regenerating areas) occurs within harvested forest, but the depth and magnitude may change depending on the design of the harvested area. This is an important consideration for managers, because gradients in microclimate can significant affect the ability of species to recolonise following disturbance. One harvesting method that can increase the amount of forest influence is aggregated retention. This technique involves leaving groups of trees (aggregates) within the harvested area, thus increasing the amount of regenerating forest that is near to an edge and therefore under forest influence. However, differences in the scale of forest influence generated from aggregates compared to unlogged forests surrounding harvested areas have not been tested. Understanding the ability of retained aggregates to generate forest influence is important in designing and implementing aggregated retention harvesting practices.This study tested whether retained aggregates generated similar levels of forest influence as mature forest surrounding harvested areas. Microclimatic forest influence was examined by monitoring spatial changes in air temperature and relative humidity along transects running from within standing mature forest into harvested forest. Intact forest and aggregate transects were located in the direction of maximum expected forest influence (south-facing edges). Results showed that forest influence was mostly similar in both depth and magnitude regardless of the type of forest from which it was generated. Temporal examination of forest influence showed that it changed throughout the day and across the year, with peaks in magnitude occurring during the middle of the day, and in months close to the equinoxes. Shade derived from standing trees was a potential driver of temporal patterns in microclimatic forest influence.At its peak magnitude, the microclimatic forest influence observed will likely have significant impacts on habitat suitability and thus, presumably, species recolonisation after disturbance. Results indicated that aggregated retention is an effective method for generating forest influence within harvested areas. Therefore, aggregated retention has the potential to be a valuable harvesting technique to alter microclimate and have beneficial impacts on the recovery of harvested forests.

Forest fuels and potential fire behaviour 12 years after variable-retention harvest in lodgepole pine

Variable-retention harvesting in lodgepole pine offers an alternative to conventional, even-aged management. This harvesting technique promotes structural complexity and age-class diversity in residual stands and promotes resilience to disturbance. We examined fuel loads and potential fire behaviour 12 years after two modes of variable-retention harvesting (dispersed and aggregated retention patterns) crossed by post-harvest prescribed fire (burned or unburned) in central Montana. Results characterise 12-year post-treatment fuel loads. We found greater fuel load reduction in treated than untreated stands, namely in the 10- and 100-h classes (P = 0.002 and 0.049 respectively). Reductions in 1-h (P < 0.001), 10-h (P = 0.008) and 1000-h (P = 0.014) classes were greater in magnitude for unburned than burned treatments. Fire behaviour modelling incorporated the regenerating seedling cohort into the surface fuel complex. Our analysis indicates greater surface fireline intensity in treated than untreated stands (P < 0.001), and in unburned over burned stands (P = 0.001) in dry, windy weather. Although potential fire behaviour in treated stands is predicted to be more erratic, within-stand structural variability reduces probability of crown fire spread. Overall, results illustrate trade-offs between potential fire attributes that should be acknowledged with variable-retention harvesting.

Variable-retention harvesting in Tasmania: regeneration success?

SummarySociety’s changing expectations for forest management and an improved understanding of wet-forest ecology have led to the adoption of variable-retention silviculture in Tasmania’s old-growth wet eucalypt forests. Aggregated retention (ARN) retains patches of forest after harvesting to help maintain biodiversity and ecosystem function at the site level, but these ecological goals must be balanced against silvicultural considerations such as achieving successful regeneration. We sampled 38 ARN coupes that were harvested and regenerated from 2007 to 2010 and 31 paired clear-fell, burn and sow (CBS) coupes. Despite more complex boundary shapes and thus much higher levels of forest edge influence, the development of successful ‘slow burning’ methods combined with the adoption of aerial sowing in all ARN coupes has resulted in early regeneration densities and growth rates that are very comparable with those in clear-felled coupes. The longer-term effects of ARN harvesting on eucalypt productivity require further research, but these early results indicate that the initial silvicultural goals for eucalypt regeneration can be met after ARN harvesting in wet eucalypt forests.

Single large versus several small: The SLOSS debate in the context of bird responses to a variable retention logging experiment

The Variable Retention Harvest System (VRHS) is a silvicultural system designed to reduce logging impacts and enhance biodiversity conservation. VRHS has been widely applied worldwide but several important questions remain about its effectiveness for biodiversity conservation. A key issue is whether dispersed or aggregated retention is more effective for conservation, and hence what size of retained patches of forest should be maintained within logged areas. Many studies have indicated that increasing the amount of the original stand retained during harvesting increases the amount of biodiversity conserved. But in a form of the SLOSS (single large or several small areas for conservation) debate, a critical question is: does one large retained island better conserve forest biota than several small islands of the same aggregated area? We addressed this question in an experiment in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria, south-eastern Australia. The experiment comprised seven blocks, each with four treatments – an unlogged control, a conventional 15–40ha clearfelled area, a 15–40ha harvest unit with a single 1.5ha retained “island”, and a 15–40ha harvest unit with three 0.5ha islands. A subset of the treatment plots and harvest units in our experiment were burned in a major wildfire in 2009. Given this, a subsequent further question we posed was: are there additional effects on birds resulting from logging operations that were followed by wildfires.We identified a significant gradient in species richness across treatments with lowest values in conventional clearfelled areas and highest values in unlogged controls. Unexpectedly, we identified no significant island size effects on bird species richness. We found no individual species that were significantly more likely to occur in a single large island than several small islands. Nonmetric multidimensional scaling revealed significant differences in the composition of the bird community between treatments, consistent with our findings for some of the more common species of birds. Several species were significantly less likely to be recorded in clearfelled areas, although the Flame Robin was more likely to be recorded in them. When we removed clearfelled areas from our analyses, some species were significantly less likely to occur in retained islands than unlogged controls. The application of VRHS did not appear to mediate bird responses to wildfire relative to effects for birds observed in clearfelled harvest units that were subsequently burned in 2009.Our results suggest that VRHS has positive effects on bird biota in Mountain Ash forests. However, this study found no advantage of setting aside a single large island versus several small islands within a given harvest unit for bird species richness nor the occurrence of individual bird species.

Biomass growth response to spatial pattern of variable‐retention harvesting in a northern Minnesota pine ecosystem.

Variable-retention harvesting (VRH) is an approach for sustaining complex structure in managed forests. A criticism of VRH is that ecological benefits may come at a cost of reduced growth of regeneration, due to competition with residual trees. However, the spatial pattern of retention, i.e., dispersed or aggregated, in VRH systems can be manipulated to minimize suppression of regeneration, and resource limitation to regeneration might be mitigated by reduction of woody shrubs. Continued growth of the residual cohort will compensate for growth reduction of regeneration, although this may differ with retention pattern. We examined aboveground whole-stand biomass growth of trees in a VRH experiment in Pinus resinosa forest in Minnesota, USA. Treatments included dispersed retention, aggregated retention, and an uncut control, as well as a shrub treatment (reduced density or ambient). We addressed the following hypotheses: (1) biomass growth of a cohort of planted pine seedlings will be highest with aggregated rather than dispersed retention, (2) biomass growth of the planted seedlings will increase with shrub reduction, and (3) biomass growth of the residual overstory will be higher with dispersed rather than aggregated retention. Aboveground biomass growth of the planted pines ranged from 0.4 kg·ha−1·yr−1 in the overstory-control–ambient-shrub treatment to 23 kg·ha−1·yr−1 in the aggregated-retention–shrub-reduction treatment. The difference between the control and the retention treatments was significant (P < 0.0001), but not between dispersed and aggregated retention (P = 0.97). Thus, our first hypothesis was not supported. In all treatments, biomass growth was significantly higher (>100% increase) with shrub reduction (P = 0.001), supporting our second hypothesis. Biomass growth of residual trees ranged from 2404 kg·ha−1·yr−1 in the uncut-control–ambient-shrub treatment to 1043 kg·ha−1·yr−1 in the aggregated-retention–shrub-reduction treatment. Differences were significant between the control and retention treatments (P = 0.003), and marginally higher with dispersed vs. aggregated retention (P = 0.09), lending support to our third hypothesis. Our results suggest that managers have flexibility in application of VRH and can expect similar stand-level biomass growth of planted regeneration regardless of retention pattern, but somewhat higher stand-level biomass growth of retained trees with dispersed retention.

Early regeneration results following aggregated retention harvesting of wet eucalypt forests in Tasmania, Australia

Aggregated retention (ARN) harvesting has been adopted as an alternative to clearfelling in most of Tasmania’s wet eucalypt forests, although the effects of this silvicultural system on regeneration establishment and growth were still uncertain when this decision was made. To address this knowledge gap, eucalypt regeneration was assessed in 31 operational ARN coupes and 31 paired clearfell, burn and sow (CBS) coupes established from 2007 to 2010. There was no difference in eucalypt seedling stocking, density or height between ARN and CBS coupes at 1year of age. At 3years of age, seedling density and height did not vary with silvicultural system, and stocking was only 5% lower in ARN coupes when two outliers were removed. This early regeneration success in the ARN coupes is attributed to the high availability of receptive seedbed achieved in the broadcast burns on these coupes, the adoption of aerial sowing as a standard operating procedure, and to the absence of any increase in browsing pressure or edge-related growth suppression. Although the proportion of the harvested area within one tree height of standing forest (i.e., under ‘forest influence’) was 34% higher in ARN coupes compared to CBS coupes, there was no evidence of suppression of regeneration by the standing forest edge at 3years of age. Seedling height and density were strongly related to the state of the seedbed, and increased with increasing burn intensity. Seedling density increased by an average of 1700sph in both ARN and CBS coupes between the ages of 1 and 3years, but despite this ongoing recruitment, 24% of coupes had low seedling densities at age 3years and a review of sowing rates is recommended. This study confirms that the creation of burnt seedbed is essential for good early regeneration in wet eucalypt forests, and indicates that regeneration can be just as successful after aggregated retention harvesting as after clearfelling, so long as stands are managed appropriately.

The effects of mechanical disturbance and burn intensity on the floristic composition of two-year old aggregated retention coupes in Tasmanian wet eucalypt forests

Due to concerns about the ecological impacts of clearfelling in Tasmanian wet eucalypt forests, aggregated retention (ARN) was developed as an alternative harvesting method. It is predicted that, compared to clearfelling, ARN will have ecological benefits such as preservation of old-growth structures and improved regeneration of late successional species in harvested areas. However, early studies have indicated that ARN requires lower intensity regeneration burns and results in greater levels of mechanical soil disturbance than clearfelling. This study therefore aimed to assess the impacts of both soil disturbance and burn intensity on floristic composition, species dominance and species richness following harvesting in ARN coupes. Floristic surveys were conducted on six seedbed classes that reflected the combined effects of both burn intensity and soil disturbance in six two-year-old ARN coupes in southern Tasmania. The results showed that both factors had a significant influence on floristic composition. Higher burn intensities generally favoured colonising species such as eucalypts and Senecio minimus and resulted in lower species richness, while lower fire intensities favoured species regenerating from the seedbank and resulted in higher species richness. In contrast, mechanically disturbed seedbed generally had a high cover of the sedge Gahnia grandis but a low overall species richness due to reduced regeneration of eucalypts and understorey species. The prevalence of the six seedbed classes, and corresponding plant species composition, varied among four general harvesting-related disturbance categories; firebreaks, snigtracks, windrows of piled logging debris and the general harvested area. Maintaining a variety of burn intensities is likely to maximise plant biodiversity within ARN coupes, and soil disturbance should be minimised, with an emphasis on reducing the total area of firebreaks.

Responses of ground-dwelling spiders (Araneae) to variable retention harvesting practices in the boreal forest

Green tree retention has been embraced as an alternative to large scale conventional clear-cutting aimed at managing the boreal forest in a more sustainable way. Ground-dwelling spider assemblages were studied 6 years after the application of variable retention harvesting practices (dispersed to 2%, 10% and 75% retention vs. aggregated retention) in deciduous and coniferous dominated stands as part of the Ecosystem Management Emulating Natural Disturbances (EMEND) project in the mixedwood boreal forest of northwestern Canada. Overall, spider composition was dominated by open-habitat species, especially by the wolf spider Pardosa moesta Banks, in all harvest treatments. However, an important shift in species composition was observed in unharvested controls. Distinctive ground-dwelling spider assemblages were observed in each forest cover-type and these were highly affected by the various harvest treatments, especially in coniferous forests. From the 164 species collected, 37 were indicators for various combinations of forest type, harvesting treatment and retention level. Species richness was affected as harvesting intensity increased; however, greater impact was observed in dispersed retention than in aggregated retention, and in coniferous stands compared to the same treatment in deciduous stands. Dispersed retention, even at 10%, seemed to mitigate adverse effects of harvesting on spider assemblages, but only in deciduous forests; however, important effects on biodiversity were observed in coniferous forests even after 75% retention. Retention of aggregated patches was useful in maintaining forest specialist species after harvesting, but was more effective when applied together with dispersed retention. Responses of spider assemblages to harvesting seemed to be highly correlated with environmental changes. Green tree retention preserves some of the heterogeneity, structural features and environmental conditions required by forest specialist species and thus becomes an effective management practice to maintain forest biodiversity, especially when both aggregated and dispersed retention practices are applied together. However, the effectiveness of these practices varies depending on the forest cover-type prior to harvesting and the amount of post-harvest residual. This suggests that a single prescription is insufficient for maintaining landscape heterogeneity, and that a combination of prescriptions is supported for a more sustainable management of the mixedwood boreal forest.

Alternative silvicultural practices with variable retention to improve understory plant diversity conservation in southern Patagonian forests

Understory plants could can act as indicators of temperate forest sustainability, health and conservation status due to their importance in ecosystem function. Harvesting impacts on understory plant diversity depends on their intensity. Variable retention has been proposed to mitigate the harmful effects of timber harvesting, but its effectiveness remains unknown in southern Patagonian Nothofagus pumilio forests. The objectives of this study were to: (i) define a baseline of understory plant diversity in old-growth forests along a site quality gradient and under canopy gaps; (ii) evaluate stands with three different variable retention treatments compared to old-growth forests; and (iii) assess temporal changes during 4 years after harvesting (YAH). A 61 ha N. pumilio forest was selected. Understory plant (Dicotyledonae, Monocotyledonae and Pteridophyta) richness, cover (including woody debris and bare forest floor) and aboveground dry biomass were characterized in summer for 5 years. Before harvesting, baseline samples were conducted along a site quality gradient and outside/inside canopy gaps. Analyzed treatments include a control of old-growth forest (OGF) and three different harvesting treatments with variable retention: (i) dispersed retention (DR) of 30 m 2 ha −1 (20–30% retention); (ii) aggregated retention (AR) with one aggregate per hectare and clear-cuts (28% retention); and (iii) combined dispersed and aggregated retention (DAR) with one aggregate per hectare and dispersed retention of 10–15 m 2 ha −1 (40–50% retention). Data analyses included parametric and permutational ANOVAs, multivariate classification and ordinations. Before harvesting, 31 plant species were found, where richness, cover and biomass were directly related to site quality. The presence of canopy gaps did not have a significant impact on the measured variables. After harvesting, 20 new species appeared from adjacent associated environments (two from N. antarctica forests and 18 from grasslands and peatlands). At the stand level, understory values were higher in AR > DR > DAR > OGF. Most (81–95%) plant richness at baseline conditions was conserved in all treatments, where inside the aggregates understory remained similar to OGF. Combination of aggregated and dispersed retention (DAR) better limited exotic species introduction and protected sensitive species, improving conservation in harvested stands. Changes in understory variables were observed after the first YAH in all treatments; greater changes were observed in the harvested areas than in aggregates. Changes stabilized at the fourth YAH. As a conclusion, the location of retention aggregates should be selected to preserve species understory diversity of more speciose and diverse habitats or particularly uncommon stands. Implementation of different kinds (patterns and levels) of retention for improvement of biodiversity conservation in harvested forests should be included in timber and forest management planning.

Effects of Information on the Social Acceptability of Alternatives to Clearfelling in Australian Wet Eucalypt Forests

The effects of viewing different types of information were investigated in people judging the social acceptability of alternative forest harvest systems. Approximately 500 Tasmanians were shown still-simulated images of four harvest systems (a clearfell system, two aggregated retention systems, and a selective system) and were asked to judge their acceptability. Individual interviews were conducted with 12 of the participants. It was anticipated that people holding different beliefs about the consequences of harvesting would have different responses to information. Cluster analysis was used to group participants according to these beliefs. Responses to still images were compared with responses to two other types of information: information about consequences of the harvest systems in the form of indicator symbols, and information about regeneration over time, presented as visual animations. The effects of information differed across both harvest system and belief cluster groups of participants. The largest effects of information occurred in people who held a mix of beliefs about consequences. Within this group, participants who viewed the indicators rated a 30% aggregated retention system higher and selective harvesting lower, than those who did not view the indicators. Viewing animated sequences led to slightly higher ratings of the more intensive harvest systems and significantly lower ratings of the selective harvest system than those based on the still images. The interview data provided examples of interviewees viewing information critically against their own values and beliefs. Only some interviewees appeared to use it in judging social acceptability.

Changes in soil fauna 10 years after forest harvestings: Comparison between clear felling and green-tree retention methods

We studied the responses of soil decomposer animals to clear felling and alternative, green-tree retention harvesting methods (GRT) in Norway spruce forests in Finland. The study plots which were sampled for immediate treatment effects (up to three years) were resampled after 10 years. We hypothesized that responses of decomposers still depends on the level of GTR. The treatments, in addition to untreated controls (100% retained), were: (1) selection felling (70% dispersed tree retention), (2) and (3) gap felling with and without site preparation, respectively (three small gaps were felled in a 1-ha area and 50% of the stand volume was retained), (4) retention felling (10% of the stand volume was retained in three small tree groups) and (5) traditional clear felling (0% retention). Ten years after the treatments the strong increase of enchytraeids immediately after the harvestings was leveled out and the numbers on all treated plots were at the control level. Total numbers or community structure of soil dwelling collembolans were not affected either. The abundance of macroarthropods on the harvested plots, except selection felling, was ca. 50% lower compared to the control forest. Their community structure was also changed due to the harvestings. The most sensitive animal groups were herbivores, microbivores and some detritivores. After 10 years, predators (mainly spiders and certain coleopterans) were decreased only under retention tree groups, while microbidetritivores (dipteran and coleopteran larvae) were unaffected. Our study showed that dispersed tree retention, at least when only 30% of the stand volume was harvested, induced no significant changes in soil decomposer animal community in boreal coniferous forest. On the other hand, decomposer community in clear-felled areas (either large or small) and in small aggregated retention tree groups is still different from that in unfelled forest 10 years after the harvestings. Mesofauna living in the soil organic layer (humus) seem to be better buffered against environmental changes induced by the harvesting compared to animals dwelling close to or on the soil surface. These animals are affected long after harvestings.

Alternative silvicultural practices with variable retention improve bird conservation in managed South Patagonian forests

Alternative silvicultural approaches to timber management, such as regeneration treatments with different degrees of stand retention, may mitigate negative effects of clear-cutting or shelterwood cuts in forested ecosystems, including changes in old-growth forest bird communities. The aims of this work were: (a) to compare bird species richness and densities among different silvicultural designs with variable retention (dispersed and/or aggregated) and unmanaged primary forests, and (b) to assess temporal changes at community and species levels before and after treatments. A baseline avian survey was conducted prior to harvesting to evaluate canopy gap presence and forest stand site quality influences. Subsequent to harvesting, data on bird species richness and density were collected by point-count sampling during the summer season for 5 consecutive years (4 treatments × 5 years × 6 sampling points × 5 counts). Bird species richness and density (15 species and 9.2 individuals ha −1) did not change significantly with forest site quality of the stands and canopy gap presence in unmanaged forests. However, both variables were significantly modified in managed forests, increasing over time to 18 species and reaching to 39 individuals ha −1. Inside the aggregated retention, bird communities were more similar to unmanaged primary forests than those observed within the dispersed retention or in clear-cuts. Opting for a regeneration method with dispersed and aggregated retention has great potential for managing birds in Nothofagus pumilio forests. This method retained enough vegetation structure in a stand to permit the establishment of early successional birds (at least in dispersed retention), and to maintain the bird species of old-growth forests which could persisted in the retention aggregates.

Aggregate retention in two Tierra del Fuego Nothofagus forests: Short-term effects on bird abundance

Green-tree retention may mitigate detrimental effects of clear-cutting on forest birds. These beneficial effects would depend mainly on the way that retention changes habitat and landscape structure. In this study we examined the effect of aggregated retention on the abundance and richness of birds inhabiting two structurally different Nothofagus forests on Tierra del Fuego Island, Patagonian Chile. In the first year stands were undisturbed and in the second year parts of these stands were partial cut. After cutting abundance of 5 of 10 species was smaller in disturbed stands and only 2 species had increased abundance with aggregate retention. Retention effect was similar in both forest types for all species, but one. Nevertheless, we did not detect a significant aggregate retention effect when we compared pre- and post-harvesting scenarios, although eight species decreased in abundance during the second year in control stands in both forest types. The reduction in abundance of one species was greater in aggregated retention than in control stands and for three other species this reduction was greater in the structurally more simple forest. In retention stands a greater number of bird species were significantly affected by habitat and landscape variables than in control stands. Habitat structures that are changed drastically by retention, including canopy cover, tree density and ground branch cover, affected abundance of birds in addition to landscape structure of treated stands. Thus, the retention effect on bird abundance depends mainly on forest and landscape characteristics.

Generalized working sets for segment reference strings

The working-set concept is extended for programs that reference segments of different sizes. The generalized working-set policy (GWS) keeps as its resident set those segments whose retention costs do not exceed their retrieval costs. The GWS is a model for the entire class of demand-fetching memory policies that satisfy a resident-set inclusion property. A generalized optimal policy (GOPT) is also defined; at its operating points it minimizes aggregated retention and swapping costs. Special cases of the cost structure allow GWS and GOPT to simulate any known stack algorithm, the working set, and VMIN. Efficient procedures for computing demand curves showing swapping load as a function of memory usage are developed for GWS and GOPT policies. Empirical data from an actual system are included.