Old Forests Research Articles

The conservation value of secondary forests in the southern Brazilian Mata Atlântica from a spider perspective

In many tropical areas of the world, pristine forests have become rare. Nevertheless, due to shifts in the human population the area covered by secondary forests is increasing. These forests may harbor a rich flora and fauna and are considered to be main refuges for species of primary forests. However, this issue is far from clear. To assess the conservation value of secondary forests in the Atlantic Forest of Brazil, we compared the diversity of spiders in differently aged secondary forests with old-growth forests. Within a larger project treating several invertebrate taxa, we sampled spiders using a standard protocol in 24 sites of three successional stages (5-8, 15-20, 30-50 years old) and old-growth forests (. 100 years untouched) in two nature reserves. We describe the diversity and structure of the assemblages using morphospecies and genera and analyze richness at the genus level. Generic richness and diversity showed no differences between successional stages; i.e., did not increase from the youngest to older forests, but guild diversity did increase. The youngest stage showed the highest variability in generic composition, and the turnover of genera and species was strong between the younger forests (5-20 years old) and forests older than 30 years. High alpha diversity, high turnover among sites and the lack of differences in richness between stages support the value of secondary forests for species conservation in the region studied.

Forest canopy cover determines invertebrate diversity and ecosystem process rates in depositional zones of headwater streams

Summary Previous studies of the ecological linkages between forest and headwater streams have focussed primarily on patterns and processes in erosional habitats, typically riffles. Depositional zones trap large amounts of sediments and particulate organic matter, suggesting that they may be important for forest–stream linkages. We studied the invertebrate benthos and two key ecological processes, surface sediment reworking and leaf litter breakdown, in the depositional zones of streams bordered by contrasting riparian vegetation. We compared three stream reaches, draining open canopy forest regenerating after recent clearcut harvesting, with reaches on three different streams bordered by older forests with closed canopies. We also assessed whether, and to what extent, forest canopy cover determined abiotic factors at the reach scale (physicochemistry of stream water) and patch scale (sediment properties). Depositional zones in both types of stream harboured a taxonomically and functionally diverse invertebrate community, including efficient sediment reworkers and specialised shredders. Higher diversity was found in open canopy than in closed canopy streams, despite similarities in habitat morphology and sediment properties. Water temperature and sediment reworking rate were higher in open canopy forest than in closed canopy forest. As rates of sediment reworking, adjusted for temperature, did not differ between forest types, temperature was probably a key factor linking the forest canopy to stream depositional zones. The rates of leaf litter breakdown sometimes varied substantially between streams, but no consistent forest effect was detected for this process. Temperature‐adjusted rates of surface sediment reworking and litter breakdown were positively correlated with the density of invertebrates that rework sediments and shredders, respectively. A relationship between these two ecological processes was found across depositional zones in closed canopy forest, but not in open canopy forest. This study on depositional zones provides new evidence of the strong linkage between forest and headwater streams. By moderating stream summer temperature, riparian canopy cover has the potential to affect invertebrate metabolic rates and, indirectly, the intensity of surface sediment reworking. However, other factors, such as the quality and diversity of basal trophic resources, may also account for invertebrate diversity pattern across streams and the positive relationship between litter breakdown and sediment reworking in closed canopy forest.

Relative abundance of small mammals in nest core areas and burned wintering areas of Mexican Spotted Owls in the Sacramento Mountains, New Mexico

Mexican Spotted Owls (Strix occidentalis lucida) are common in older forests within their range but also persist in many areas burned by wildfire and may selectively forage in these areas. One hypothesis explaining this pattern postulates that prey abundance increases in burned areas following wildfire. We observed movement to wintering areas within areas burned by wildfire by four radio-marked Mexican Spotted Owls in the Sacramento Mountains, New Mexico. These movements occurred during the winters of 2004–2005 and 2005–2006, with some owls migrating in both winters and others in only one. Wintering areas of these owls occurred within the perimeters of two wildfires that burned in May 2000 and April 2002, respectively. We estimated relative prey abundance and biomass during December 2006 within paired burned wintering areas and nest core areas used by these owls. Species richness and relative abundance of small mammals were greater in the burned wintering areas than in the associated nest core areas for all four owls, and estimated prey biomass ranged from 2–6 times greater in burned wintering areas relative to the paired nest core areas. Burned wintering areas used by these owls were similar in elevation to their nest core areas, and likely experienced similar weather conditions during winter. These results suggest that wintering owls moved to areas with greater food resources, rather than to areas with milder weather. They further suggest that relative prey abundance was greater in burned wintering areas than in the nest core areas >5 years post-fire, and that these burned wintering areas provided important habitat for Mexican Spotted Owls in our study area during an energetically stressful season.

Long-term recovery of forest structure and composition after harvesting in the coastal temperate rainforests of northern British Columbia

We examined young harvested (41–100) and naturally disturbed mature (101–250), and old (>250) temperate rainforests on the central and north coast of British Columbia to quantify the recovery rates of tree size, density, and species composition of young harvested stands towards old-growth condition. Significant variations in recovery rates were noted due to differences in site productivity. Nonmetric multidimensional scaling (NMS) ordinations, Multi-response Permutation Procedure (MRPP) summary statistics, and Sorensen’s similarity coefficients (SC) all indicate moderate levels of similarity between young and old stands. Rich sites show greater similarity between young and old forests (SC=55%) than do medium sites (SC=41%), indicating more rapid recovery. Differences in tree species composition, especially for western redcedar, were apparent among young and older forests on all sites. We believe that proactive management is required to ensure that western redcedar, an ecologically, culturally, and economically valuable tree species, is maintained as a significant component in the managed second-growth forests of central and north coast British Columbia. Our results indicate that second-growth forests, while not as structurally developed as old-growth, are developing some ecologically important structural characteristics at relatively young ages (80–100years) and as such, contribute towards ecological integrity and biodiversity of the coastal temperate rainforest landscape.

A comparison of avian habitat in forest management plans produced under three different certification systems in Ontario, Canada

ABSTRACTConsiderable discussion and theoretical reviews of forest certification systems have been published that outline the potential impact of forest certification on biodiversity and wildlife habitat. Three common approaches to forest certification used in Canada include the Forest Stewardship Council, the Canadian Standards Association, and the Sustainable Forestry Initiative. In this study, I reviewed forest management plans in Ontario, Canada, and compared the plans' potential impact on habitat for 6 species of birds that use mature and older forests: pileated woodpecker (Dryocopus pileatus), ruby‐crowned kinglet (Regulus calendula), boreal chickadee (Poecile hudsonicus), black‐backed woodpecker (Picoides arcticus), great gray owl (Strix nebulosa), and red‐breasted nuthatch (Sitta canadensis). The purpose was to determine whether the different certification systems in use resulted in different impacts on avian habitat, and to compare certified forest management plans with plans prepared for un‐certified forest units. Based on 27 Forest Management Plans in Ontario, there seems to be little reason to believe that certified forests are more likely to protect and conserve habitat for these 6 bird species that use older forests than are forests that are not certified. © 2014 The Wildlife Society.

Parasites and forest chronosequence: Long-term recovery of nematomorph parasites after clear-cut logging

Temporal scales at which anthropogenic disturbances affect ecosystem linkages are often unclear. The nematomorph parasites tightly link forests to stream ecosystems via manipulation of their terrestrial hosts. We examined the abundance and species/genetic diversities of nematomorphs with their terrestrial hosts along a forest-recovery gradient after clear-cut logging, using a chronosequence. Only one nematomorph species was found from eight watersheds with different forest ages (3–48years). The nematomorphs suffered local extinction immediately after logging and then increased linearly with forest age. Their relative abundances were highest in September in older forests, but in October in younger forests, suggesting clear-cut logging can cause not only long-term (>50years) disruption of the magnitude but also timing of the forest–stream linkage mediated by the nematomorphs. Camel crickets (Diestrammena tsushimensis and D. elegantissima), dominant definitive hosts of the nematomorphs, recovered with a peak at around 30-year-old forests, which was insufficient to explain the long-term recovery of the nematomorphs. This study provided an empirical example of the time-scale (>50years) at which forests and streams should be managed as integrated systems.

Succession of Ephemeral Secondary Forests and Their Limited Role for the Conservation of Floristic Diversity in a Human-Modified Tropical Landscape

Both local- and landscape-scale processes drive succession of secondary forests in human-modified tropical landscapes. Nonetheless, until recently successional changes in composition and diversity have been predominantly studied at the patch level. Here, we used a unique dataset with 45 randomly selected sites across a mixed-use tropical landscape in central Panama to study forest succession simultaneously on local and landscape scales and across both life stages (seedling, sapling, juvenile and adult trees) and life forms (shrubs, trees, lianas, and palms). To understand the potential of these secondary forests to conserve tree species diversity, we also evaluated the diversity of species that can persist as viable metapopulations in a dynamic patchwork of short-lived successional forests, using different assumptions about the average relative size at reproductive maturity. We found a deterministic shift in the diversity and composition of the local plant communities as well as the metacommunity, driven by variation in the rate at which species recruited into and disappeared from the secondary forests across the landscape. Our results indicate that dispersal limitation and the successional niche operate simultaneously and shape successional dynamics of the metacommunity of these early secondary forests. A high diversity of plant species across the metacommunity of early secondary forests shows a potential for restoration of diverse forests through natural succession, when trees and fragments of older forests are maintained in the agricultural matrix and land is abandoned or set aside for a long period of time. On the other hand, during the first 32 years the number of species with mature-sized individuals was a relatively small and strongly biased sub-sample of the total species pool. This implies that ephemeral secondary forests have a limited role in the long-term conservation of tree species diversity in human-modified tropical landscapes.

Wild boar rooting in a northern coniferous forest – minor silviculture impact

European wild boar (Sus scrofa) is expanding northwards beyond its preferred habitat of broadleaved forests. We studied wild boar habitat use in a northern coniferous forest, and noted whether their rooting damaged roots, thereby influencing timber quality and forest regeneration (n = 562 rootings). Overall, the animals selected older spruce (Picea abies L.) forest of higher soil fertility with sparse field vegetation for rooting. During winter, they rooted more in pine (Pinus sylvestris L.) forest on lower soil fertility, possibly because the lichen cover can easily be removed even on frozen ground. Average size and depth of rootings were 6 ± 0.6 m2 and 10 ± 0.2 cm, respectively. Rooting occurred on <1% of the area and caused negligible damage to roots of trees with commercial value. Because the wild boar mainly rooted in older forest, rootings will do little to improve germination of seeds by scarification of the top soil layer.

Late-successional and old-growth forest carbon temporal dynamics in the Northern Forest (Northeastern USA)

Comprehensive data on the capacity and rates of change for carbon pools in managed and unmanaged forests is essential for evaluating climate change mitigation options being considered by policy makers at regional and national levels. We currently lack real and long-term data on forest carbon dynamics covering a wide range of forest management practices and conditions. Because of this, selecting the best policies for conserving forest carbon must rely on forest growth and yield models such as US Forest Service (USFS) Forest Vegetation Simulator (FVS) to predict the future forest carbon impacts of management actions. FVS may underestimate the capacity of older stands to accumulate carbon because the model relies on USFS Forest Inventory and Analysis data that lack data from late-successional and old-growth (LSOG) stands. Improving these models will increase the likelihood of selecting policies that successfully use forests to reduce atmospheric carbon. From 1995 to 2002, Manomet Center for Conservation Sciences conducted research on 65 10m by 50m permanent plots to evaluate forest structure (standing live and dead trees, and down coarse woody material) in LSOG stands across northern Maine. We re-measured these plots in 2011 to assess long-term carbon sequestration trends in LSOG stands of common forest types in the Northern Forest region for above ground alive, standing dead, and coarse woody material carbon pools. Late-successional (LS) and Old-growth (OG) aboveground live carbon (C) stocks were very high relative to regional mean C stocks (2.0–2.5 times the mean), LS plots were accumulating aboveground live C at a positive rate (0.61Mgha−1 year−1), while C stocks on OG plots are declining (−0.54Mgha−1 year−1). This change is driven by the presence of beech bark fungus (Nectria sp.) that is leading to mortality in larger diameter American beech (Fagus grandifolia) trees. We also found that the Northeast Variant of the Forest Vegetation Simulator is not a reliable predictor of aboveground live carbon accumulation rates in Northeastern LS and OG stands. This work provides important baselines for understanding the role of older forests and forest management within climate change mitigation strategies in the northeastern US. Late-successional and old-growth forests can play an important role in mitigating climate change, but understanding and quantifying natural disturbance risk to forest carbon stocks is critical for successful implementation of mitigation strategies. Further, regional forest carbon models will need calibration to accurately predict carbon accumulation rates in older forests.

Timber Harvesting Does Not Increase Fire Risk and Severity in Wet Eucalypt Forests of Southern Australia

AbstractLindenmayeret al. proposed that logging makes “some kinds of forests more prone to increased probability of ignition and increased fire severity.” The proposition was developed most strongly in relation to the wet eucalypt forests of south‐eastern Australia. A key argument was that logging in wet forests results in drier forests that tend to be more fire‐prone, and this argument has gained prominence both in the literature and in policy debate. We find no support for that argument from considerations of eucalypt stand development, and from reanalysis of the only Australian study cited by Lindenmayeret al. In addition, there is no evidence from recent megafires in Victoria that younger regrowth (&lt;10 years) burnt with greater severity than older forest (&gt;70 years); furthermore, forests in reserves (with no logging) did not burn with less severity than multiple‐use forests (with some logging). The flammability of stands of different ages can be explained in terms of stand structure and fuel accumulation, rather than as a dichotomy of regrowth stands being highly flammable but mature and old‐growth stands not highly flammable. Lack of management of fire‐adapted ecosystems carries long‐term social, economic, and environmental consequences.

Use of multi‐state models to explore relationships between changes in body condition, habitat and survival of grizzly bears Ursus arctos horribilis

One of the principal goals of wildlife research and management is to understand and predict relationships between habitat quality, health of individuals and their ability to survive. Infrequent sampling, non‐random loss of individuals due to mortality and variation in capture susceptibility create potential biases with conventional analysis methods. To account for such sampling biases, we used a multi‐state analytical approach to assess relationships between habitat, health and survival of grizzly bears Ursus arctos horribilis over a 10‐year period along the east slopes of the Canadian Rockies in Alberta, Canada. We defined bear health states by body condition estimated from the relationship between weight and body length. We used a sequential model building process to first account for potential sampling biases, and then explored changes in body condition relative to habitat use and survival. Bears that used regenerating forest habitats (mostly due to forest harvesting) containing a diversity of age classes were more likely to see gains in their body condition, whereas bears that used older forests were more likely to see reductions in body condition. Survival rate was reduced most by road densities which in turn were positively correlated with regenerating forest habitat. Human activities which promote young regenerating forests, such as forest harvesting, therefore promotes improved health (increased body condition) in bears, but are offset by reductions in survival rates. Multi‐state analyses represents a robust analytical tool when dealing with complex relationships and sampling biases that arise from dynamic environments.

Resting site selection by large herbivores – The case of European bison (Bison bonasus) in Białowieża Primeval Forest

Resting site selection by European bison (Bison bonasus, L., 1758), the largest terrestrial mammal of Europe, was studied in the free-ranging population in Białowieża Primeval Forest (Poland) in 2009–2010. In total, 104 sites of 21 bison (both collared and uncollared) were analysed to determine the most important microhabitat characteristics selected by resting bison during summer and winter and to study the influence of supplementary feeding on resting behaviour of this herbivore. Resting sites were identified on the basis of GPS locations and activity records collected by GPS collars, as well as direct observations of bison, and were compared with control sites. Microhabitat selection by bison did not differ significantly between the sexes. During summer and winter, bison resting sites displayed a high tree density, low visibility and high complexity (structures providing cover). Summer resting sites were also characterised by a significantly lower abundance of blood-sucking insects and denser canopy than control sites. Winter resting sites showed a lower complexity and higher visibility than summer sites, and were less often located in mixed forest habitats. During winter, bison rested more frequently in forest below 50 years of age than in older forest. Resting sites of non-fed bison were more often located in young coniferous forests, were lower in visibility and situated closer to open areas than sites of bison using supplementary winter feeding, suggesting a trade-off between food and cover. The results indicate that European bison select their resting sites in areas of mosaic habitat structure providing cover from disturbances with access to profitable natural forage grounds.

Multi-cohort stand structure as a coarse filter of variation in mixedwood boreal bird communities

In targeting mature and over-mature forests for harvesting, management in the boreal forest has resulted in a net loss of older forests that often exhibit complex structural variation and multiple cohorts of trees. Multi-cohort forest management has been proposed as a management approach for these older forests that maintains structural wildlife habitat attributes. At the stand level, the approach relies on various partial harvest techniques to emulate the range of structural variation found in natural boreal landscapes. Here, we examine the extent to which boreal bird communities respond to multi-cohort-related structural variation in boreal mixedwood forests. In particular, we test the utility of parameters of Weibull distributions fitted to stand stem diameter distributions, which have figured prominently in methods to characterize multi-cohort structure, to explain variation in the entire bird community and in various species groupings defined by feeding guilds and forest-type associations. We also compare the explanatory power of the two Weibull parameters against 21 forest structure variables and stand age. In general, Weibull parameters outperformed stand age as a correlate of bird community variation and they were significant explanatory variables for the matrix of all species and for four species groupings, whereas age was significant for only one species grouping. When one or the other Weibull parameter was significant, it also tended to be significant even when variation due to the other was partialled out, supporting the importance not only of forest stature, but also of forest heterogeneity in understanding bird community composition. Thus, we found that multi-cohort-associated structural variation was important in explaining variation among boreal bird communities, supporting the idea of silvicultural approaches that aim at diversifying stand structural characteristics.

Phylogenetic structure of ectomycorrhizal fungal communities of western hemlock changes with forest age and stand type

On Vancouver Island, British Columbia, fertilization with nitrogen (N) and phosphorus (P) following clearcutting increases growth of western hemlock. To explore whether fertilization also resulted in ectomycorrhizal fungal communities that were more or less similar to neighboring unlogged stands, we sampled roots from western hemlock from three replicate plots from each of five different, well-characterized, forest stand types that differed in site type, and in logging and fertilization history. We harvested four samples of 100 ectomycorrhizal root tips from each plot, a total of 60 samples per stand type. From each sample, we analyzed fungal ribosomal internal transcribed spacers and 28S DNA, sequencing 15-29 clones per sample and 60-116 clones per plot. We detected 147 fungal operational taxonomic units among a total of 1435 sequences. Craterellus tubaeformis was frequently present and resulted in a pattern of phylogenetic overdispersion in the fungal communities. Fungal species composition was strongly correlated with foliar nitrogen concentration. However, other site quality factors were also important because the fertilized regenerating hemlock and mature hemlock-amabilis fir forests had similar foliar nitrogen content but little overlap in fungal species. Compared with unfertilized regenerating forests, fungal communities in N + P-fertilized regenerating forests had significantly more species overlap with old growth forests. However, the fungal communities of all regenerating forest were similar to one another and all differed significantly from older forests. By correlating fungal clades with habitats, this research improves understanding of how forest management can contribute to maintaining diverse ectomycorrhizal fungal communities across a landscape.

The combined controls of land use legacy and earthworm activity on soil organic matter chemistry and particle association during afforestation

The chemistry and physical association of soil organic matter in the patchwork of successional forest stands in the eastern US is strongly controlled by past land use. Invasive earthworm activity in these same systems, however, may impart a chemical and physical disturbance exceeding that of land use legacy. We established eight plots within forests of the Smithsonian Environmental Research Center (SERC) (Edgewater, MD), to compare sites with no record of significant agricultural disturbance or earthworm activity and successional mixed hardwood forests recovering from past agriculture (60–132yr) that contained both native and non-native earthworms. Soils (0–15cm) were separated into physical fractions by size (microaggregates) and density (light and heavy particulate organic matter) and investigated for organic carbon (C) and nitrogen (N) partitioning. In addition, molecular composition was analyzed using FTIR spectroscopy and lignin phenol and substituted fatty acid (SFA) extraction.Even after 132yr of recovery, the successional forests were nearly devoid of Oa+e horizons; a condition we attribute to high activity of invasive earthworms. Additionally, soil organic carbon (SOC) concentration profiles, and 14C derived mean residence times indicated mixing of the surface soils and fresh input of carbon to 10cm, distinct from the undisturbed, mature sites. The proportion of microaggregated particulate organic matter (iPOM) and silt+clay (iSC) was significantly higher in successional than undisturbed forests, which we attribute to the combined influence of past agricultural land use and high earthworm activity. Among the successional sites, older forests exhibited a significant decrease in the proportion of C and N in iSC but an increase in their proportion in iPOM, suggesting selective incorporation of iPOM with earthworm activity over great periods of time. In addition, continual consumption and mixing activities of the earthworm population could also be a primary control of the higher concentration and less oxidized lignin phenols as well as a higher proportion of lignin phenols to SFA in all soil fractions in the successional sites. Using partial least squares (PLS) regression of FTIR spectra, we also demonstrated a strong correlation between soil C physical distribution (microaggregated vs. non-microaggregated) and chemical aspects of specific FTIR regions which confirmed our findings from the lignin and SFA and showed distinct chemical dominance among the different sites. Our results indicated that while past agricultural practice may have been the primary initial influence on C and N stock and soil physical distribution in the successional sites, the prolonged legacy and trajectory of recovery from the past land disturbance can be controlled by the nature of the invasive and native earthworm activity during afforestation.

Effects of Reforestation Practices on Staphylinid Beetles (Coleoptera: Staphylinidae) in Southwestern China Forests

In 2004, Staphylinid beetle (Coleoptera) assemblages were studied via pitfall trapping to examine the effects of reforestation in southwestern China forests. Sites included two 100-yr-old mature forest types (hemlock-spruce forest and birch forest), and three 40-yr-old forest types established after harvesting (spruce plantation, larch plantation, and natural broad-leaved forest). Staphylinid species richness was greater in natural broad-leaved forests than those in hemlock-spruce forests and spruce plantations, but no significant difference was found in abundance among the five forest types. Beetle assemblages from young forest stands were significantly different from those in older forest stands, and some environmental characteristics, i.e., elevation, proportion of broad-leaved trees, and coarse woody debris, significantly affected species abundances. Moreover, some staphylinid species predominantly found only in older forest stands indicate that mature forest specialists might be threatened by loss of habitat. So it is necessary to retain adequate patches of older successional stages for conserving these beetle assemblages.

Large‐scale forest composition influences northern goshawk nesting in Wisconsin

AbstractThe northern goshawk (Accipiter gentilis atricapillus) is a woodland raptor that uses a variety of forest types for nesting across its breeding range, but strongly depends on older forests with large trees and open understories. Goshawks may select nesting locations by maximizing the convergence of nesting and foraging habitats. Insights into goshawk responses to heterogeneous landscapes can be gained by examining the location of active nest sites through time and at multiple spatial scales. We examined the landscape‐scale forest conditions that influenced the probability of active goshawk nests in the United States Forest Service, Chequamegon‐Nicolet National Forest (CNNF) in northern Wisconsin. We used goshawk nest survey and monitoring data from 1997 to 2006 to determine the probability of an active nest site over time in relation to forest composition and road density at 3 scales (200‐m, 500‐m, and 1,000‐m radii). Goshawk nests were located primarily in upland hardwood (64%), conifer (23%), and older aspen–birch (≥26 yrs old; 11%) habitat cover types. We used Bayesian temporal autoregressive models of nest locations across multiple spatial scales to analyze these data. The probability of active goshawk nest occurrence increased with increasing conifer cover (1,000 m) and decreased with increasing cover of older aspen–birch and density of primary roads (500 m). In addition, lesser proportions of older aspen–birch at intermediate scales around goshawk nests had a stronger effect on the probability of a nest being active than conifer and primary roads. Thus, the ratio of conifer cover (within 1,000 m) to older aspen–birch cover (within 500 m) in landscapes surrounding nest sites was the key driver in predicting the probability of an active nest site. This finding can be used by forest managers to help sustain the active status of a goshawk nesting area through time (i.e., annually), and foster goshawk nesting activity in areas where active nesting is not currently occurring. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

A Restoration Framework for Federal Forests in the Pacific Northwest

We outline elements of a forest restoration strategy designed to produce ecological and economic benefits on federal forests in Oregon and Washington, along with some of their policy and management implications. Implementation of this restoration strategy has begun on 11 projects (at scales from hundreds to thousands of acres) on federal lands. On Moist Forest sites (MF), the strategy calls for reserving older forest stands, thinning plantations to accelerate development of structural complexity, and implementing variable retention harvests in younger forests to help provide diverse early seral ecosystems. On Dry Forest (DF) sites, the strategy calls for silvicultural treatments that retain and release older trees, reduce stand densities, shift composition toward fireand drought-tolerant tree species, and incorporate spatial heterogeneity at multiple spatial scales. Immediate goals of this restoration framework include increased ecological integrity and resilience in DFs, increased diversity and complexity of successional stages in MFs, and provision of wood products to local communities. Over the long run, we believe this program can provide an acceptable pathway to sustained yield on federal forestlands in the Pacific Northwest.

Level and pattern of overstory retention interact to shape long‐term responses of understories to timber harvest

In many regions of the world, variable retention has replaced clear-cutlogging as the principal method of regeneration harvest. Partial retention of the overstory is thought to ensure greater continuity of the species and ecological processes that characterize older forests. Level (amount) and spatial pattern of overstory retention are two basic elements of forest structure that can be manipulated to achieve specific ecological or silvicultural objectives. However, experiments that elucidate the relative importance of retention level and pattern (or their interaction) are rare. Here we assess long-term (> 10 yr) responses of forest understories to experimental harvests of mature coniferous forests replicated at five sites in the Pacific Northwest (PNW). Treatments contrast both the level of retention (40% vs. 15% of original basal area) and its spatial distribution (dispersed vs. aggregated in 1-ha patches). For most vascular plant groups (early seral, forest generalist, and late seral), postharvest changes in cover and richness were reduced at higher levels of retention and in dispersed relative to aggregated treatments. Although retained forest patches were stable, changes in adjacent harvested (cleared) areas were significantly greater than in dispersed treatments. Late-seral herbs were highly sensitive to level and pattern of retention, with extirpations most frequent in the cleared areas of aggregated treatments and at low levels of dispersed retention. In contrast, early-seral species were most abundant in these environments. Forest-floor bryophytes exhibited large and persistent declines regardless of treatment, suggesting that threshold levels of disturbance or stress were exceeded. Our results indicate that 15% retention (the minimum standard on federal forestlands in the PNW) is insufficient to retain the abundance or diversity of species characteristic of late-seral forests. Although 1-ha aggregates provide refugia, they are susceptible to edge effects or stochastic processes; thus, smaller aggregates are unlikely to serve this function. The ability to achieve multiple ecological or silvicultural objectives with variable retention will require the spatial partitioning of habitats to include dispersed retention and larger undisturbed aggregates along with cleared areas.

Increasing soil methane sink along a 120‐year afforestation chronosequence is driven by soil moisture

AbstractUpland soils are important sinks for atmospheric methane (CH4), a process essentially driven by methanotrophic bacteria. Soil CH4 uptake often depends on land use, with afforestation generally increasing the soil CH4 sink. However, the mechanisms driving these changes are not well understood to date. We measured soil CH4 and N2O fluxes along an afforestation chronosequence with Norway spruce (Picea abies L.) established on an extensively grazed subalpine pasture. Our experimental design included forest stands with ages ranging from 25 to &gt;120 years and included a factorial cattle urine addition treatment to test for the sensitivity of soil CH4 uptake to N application. Mean CH4 uptake significantly increased with stand age on all sampling dates. In contrast, CH4 oxidation by sieved soils incubated in the laboratory did not show a similar age dependency. Soil CH4 uptake was unrelated to soil N status (but cattle urine additions stimulated N2O emission). Our data indicated that soil CH4 uptake in older forest stands was driven by reduced soil water content, which resulted in a facilitated diffusion of atmospheric CH4 into soils. The lower soil moisture likely resulted from increased interception and/or evapotranspiration in the older forest stands. This mechanism contrasts alternative explanations focusing on nitrogen dynamics or the composition of methanotrophic communities, although these factors also might be at play. Our findings further imply that the current dramatic increase in forested area increases CH4 uptake in alpine regions.