Old Forests Research Articles

Quantifying Long-Term Bird Population Responses to Simulated Harvest Plans and Cumulative Effects of Disturbance

There is interest in linking outputs from land use simulators to bird species distribution models to project how boreal birds will respond to cumulative effects of caribou (Rangifer tarandus) conservation, harvest, fire, and energy-sector development in Alberta. Our hypotheses were: 1) species associated with older mixed-wood stands would decline more if harvest was shifted away from areas used by caribou to areas with more mixed-wood; and 2) species associated with older forests would be more negatively affected by the combined effects of harvest, fire, and non-forestry footprint than by harvest alone. We used vegetation data from two harvest scenarios produced in Patchworks as inputs for density models of 20 boreal forest songbird and woodpecker species in Alberta. We projected abundance of these species over 50 years under: 1) two scenarios created in Patchworks, without fire but with and without deferral of timber harvest within a caribou conservation zone on lands tenured to Alberta-Pacific Forest Industries Inc.; 2) a scenario with fire but no human footprint; and 3) five scenarios in ALCES Online, in which habitat was affected by Patchworks harvest locations, fire (1-2 × current rate), and energy sector development (present or absent; with or without seismic line reclamation to improve caribou habitat). In the Patchworks scenarios, we found similar projected numbers of each bird species over time, whether harvest deferral occurred or not. Both harvest plans increased habitat and numbers for most species associated with older forests over 50 years, while most species associated with younger forests declined in both harvest plans, because average projected forest age increased over 50 years. Fire and other footprint generally reduced relative amount of habitat for species associated with older forests, which still increased over time, while other species responded positively or less negatively to fire. Seismic restoration created habitat for three-quarters of species that responded negatively to energy sector development over 50 years. As projections depended on whether just harvest, fire or all footprints were analyzed, multiple human impacts over time beyond harvest should be considered in conservation and land use planning based on long-term predictions about wildlife in anthropogenic landscapes.

Estructura de los bosques de Gleditsia triacanthos en función de la edad (valle de La Sala, Tucumán, Argentina)

Gleditsia triacanthos is an exotic invasive species in Argentina, widely distributed in several ecoregions. This species forms monospecific forests whose structure and dynamics remain poorly understood. These aspects are key to assess the behavior of the invader and the capacity of native species to colonize invaded forests. In this study we describe the structure and composition, and infer the temporal dynamics of G. triacanthos forests in La Sala Valley, an area highly invaded by this species in the province of Tucuman. In 2019, in four forest patches of 9, 18, 25-29 and 36-37 years old dominated by G. triacanthos, we established experimental plots and registered density, species richness and height of trees ≥5 cm in diameter, recruits, and other characteristics such as tree health and presence of cattle, gaps or open spaces. The 9-year-old forest had low height, low density and open spaces not yet colonized by G. triacanthos. The 18-year-old forest had higher density than the rest. In older forests (25-29 and 36-37-years-old patches), we detected an increase in the height and diameter of trees, and in the number of fallen and leaning trees. We suppose that Vachellia aroma, a native tree species that colonize early stages of invaded forests, was rapidly outcompeted by G. triacanthos. Lately, other native species colonized forests, but at low densities. G. triacanthos forests were almost monospecific because of its high density and the facilitation effect of the cattle in the valley, which consume and disperse the seeds.

Spatiotemporal changes of carbon storage in forest carbon pools of Western Turkey: 1972-2016.

This study analyzes the impacts of spatiotemporal changes on C dynamics based on the various C pools and forest structure in western Turkey. The forest C dynamics were projected by forest inventory data between 1972 and 2016, and the spatial distribution of C storage was mapped by GIS. Total C storage increased from 1135.22Gg in 1972 to 1816.60Gg in 2016 with a net accumulation of 681.38Gg. While the largest contribution to C pool was from soil organic carbon with 58.6% and 49.3% of the total C storage in 1972 and 1994, it was from living biomass with 54.0% and 57.7% in 2004 and 2016, respectively. The mean annual C sequestration was 1.57Mgha-1year-1, including 1.49Mgha-1year-1 in biomass and 0.08Mgha-1year-1 in soil over four decades. The mixed cover type was the most significant contributor to biomass, soil, and total C storages. However, the hardwood cover type was the most significant contributor to C densities due to the higher growing stock. The mature development stages (35.6Ggyear-1), the fully covered areas (13.2Ggyear-1), and the older forests have played an essential role in C sequestration. The spatial distribution of C dynamics was heterogenic due to forest cover type, forest structure, and species composition. Monitoring spatiotemporal changes in forest ecosystems in terms of forest cover type, development stage, coverages, and age class distribution can provide opportunities in developing effective forest management policies based on the ecological sustainability of C pools and mitigating climate change effects.

Remnant American Chestnut (Castanea dentata) Near the Historical Western Range Limit in Southwestern Tennessee

The American chestnut (Castanea dentata) was once widespread in eastern North America and an ecologically important hardwood tree of deciduous forest communities prior to its near-eradication by chestnut blight (Cryphonectria parasitica). Remnant populations occur across much of its historical range, especially in older forests of the Appalachians and northeastern U.S. However, broad swaths of the southwestern portion of the species' historical range remain poorly documented, potentially limiting the representation of genetic variation important for local adaptation in restoration efforts. Ongoing discovery and life-history characterization efforts for remnant C. dentata remains a priority to better understand the distribution and ecological status of this once important species, while identifying potential genetic sources of locally adapted or blight resistant trees. Here, we report the discovery of 22 C. dentata at four sites in southwestern Tennessee, adding novel observations that extend the range of known extant occurrences to the extreme western edge of the historical distribution in Fayette County. These observations include potentially reproductive individuals that should be revisited to assess reproductive and blight status, and that should be evaluated for current germplasm collection and restoration efforts.

Bat community response to intensification of biomass production for bioenergy across the southeastern United States.

Human demand for food, fiber, and space is accelerating the rate of change of land cover and land use. Much of the world now consists of a matrix of natural forests, managed forests, agricultural cropland, and urbanized plots. Expansion of domestic energy production efforts in the United States is one driver predicted to influence future land-use and land management practices across large spatial scales. Favorable growing conditions make the southeastern United States an ideal location for producing a large portion of the country's renewable bioenergy. We investigated patterns of bat occurrence in two bioenergy feedstocks commonly grown in this region (corn, Zea mays, and pine, Pinus taeda and P. elliottii). We also evaluated potential impacts of the three major pathways of woody biomass extraction (residue removal following clearcut harvest, short-rotation energy plantations, and mid-rotation forest thinning) to bat occurrence through a priori land-use contrasts. We acoustically sampled bat vocalizations at 84 sites in the Southeastern Plains and Southern Coastal Plains of the southeastern United States across three years. We found that mid-rotation thinning resulted in positive effects on bat occurrence, and potential conversion of unmanaged (reference) forest to managed forest for timber and/or bioenergy harvest resulted in negative effects on bat occurrence when effects were averaged across all species. The effects of short-rotation energy plantations, removal of logging residues from plantation clearcuts, and corn were equivocal for all bat species examined. Our results suggest that accelerated production of biomass for energy production through either corn or intensively managed pine forests is not likely to have an adverse effect on bat communities, so long as existing older unmanaged forests are not converted to managed bioenergy or timber plantations. Beyond bioenergy crop production, mid-rotation thinning of even-aged pine stands intended for timber production, increases to the duration of plantation rotations to promote older forest stands, arranging forest stands and crop fields to maximize edge habitat, and maintaining unmanaged forests could benefit bat communities by augmenting roosting and foraging opportunities.

Restoring tropical forest composition is more difficult, but recovering tree-cover is faster, when neighbouring forests are young

Neighbouring forests constitute biological sources that enable the succession from species-poor systems, such as tree-plantings, to highly diverse forests. However, old forest patches are becoming rare in tropical agricultural landscapes. We were interested in if, and how, spontaneous regeneration under tree-plantings reflects the age and the amount of the neighbouring forest cover. We anticipated that older forests promote a compositionally broader recovery in neighbouring tree-plantings, because older forests likely include disturbance-sensitive species, particularly within least deforested landscapes. We studied twenty-seven restoration sites implemented as tree-plantings in the Brazilian Atlantic Forest. We quantified the effects of age and amount of neighbouring forest cover on structural and compositional characteristics of the regeneration community (dbh < 5 cm). We used two landscape groups (presence, or absence, of forests older than 30 years.) with a similar areal range of forest cover, enabling the disentanglement of forest age from forest amount effects on regeneration community responses. Surprisingly, we found that greater forest cover correlated with denser and more species-rich regeneration communities only when neighbouring forests were young. This pattern was promoted by non-vertebrate dispersed species. Regeneration communities in tree-plantings near to young forests had lower seed-mass and relative abundances of forest-specialists, compared to communities found near old forest patches. Regeneration is likely denser in landscapes of vast young-forest coverage. However, small-seeded and habitat-generalist species, frequently related to disturbance tolerance, tend to be dominant if old-growth forests are far away. This biased seed source appears to preclude the restoration of typical historic tropical forest composition.

Propensities of Old Growth, Mature and Regrowth Wet Eucalypt Forest, and Eucalyptus nitens Plantation, to Burn During Wildfire and Suffer Fire-Induced Crown Death

There are conflicting conclusions on how the flammability of wet eucalypt forests changes in the time after disturbances such as logging or wildfire. Some conclude that forests are most flammable in the decades following disturbance, while others conclude that disturbance has no effect on flammability. The comparative flammability of Eucalyptus nitens plantations in the same environment as wet eucalypt forest is not known. We determined fire incidence and fire severity in regrowth, mature and old growth wet eucalypt forest, and E. nitens plantation, in the Huon Valley, Tasmania after the January–February 2019 wildfire. To control for topographic variation and fire weather, we randomly selected sites within the fire footprint, then randomly located a paired site for each in different forest types in the same topographic environment within 3 km. Each pair of sites was burned on the same day. Old growth forest and plantations were the least likely to burn. Old growth and mature forest exhibited scorched eucalypt crowns to a much lesser degree than regrowth forests. In a comparison of paired sites, plantation forest was less likely to burn than combined mature and old growth forests, but in all cases of detected ignition the canopy of plantation was scorched. The lower flammability of older forests, and their importance as an increasing store of carbon, suggests that a cessation of logging outside plantations might have considerable benefits.

Depth patterns and connections between gross nitrogen cycling and soil exoenzyme activities in three northern hardwood forests

Despite the enormous size of the organic nitrogen (N) pool contained in mineral subsoils, rates of N cycling and soil exoenzyme activities are rarely measured in soils below 10 or 20 cm depth. Furthermore, assumed relationships between N mineralization rates and the activities of various decomposition exoenzymes are poorly characterized. We measured rates of gross and net N mineralization and nitrification as well as the potential activities of hydrolytic and oxidative enzymes at five soil depths (forest floor to 50 cm) in Spodosols at three hardwood forests of varying age (45 and 100 years post-harvest and old growth) at and near the Hubbard Brook Experimental Forest in New Hampshire, USA. As expected, rates of N cycling and potential enzyme activities per unit soil mass correlated strongly with soil carbon (C) concentration, and these parameters declined exponentially with increasing soil depth. After normalization per unit soil organic matter, N cycling rates and specific enzyme activities generally decreased little with depth within the mineral soil. Gross N mineralization rates correlated with specific activities of those enzymes that hydrolyze cellulose (β-glucosidase, cellobiohydrolase) and N-rich glucosamine polymers (N-acetylglucosaminidase), but not those that degrade protein or more complex C compounds. Hence, gross N cycling appear associated with the N released during microbial N recycling, rather than from decomposition of soil organic matter. Across the three stands, the youngest had a larger ratio of N- to-phosphorus-acquiring enzyme activities, indicating a greater N demand in younger than older forests. For all three stands, mineral soil below 10 cm contributed 30–53% of total gross and net N cycling per unit area to 50 cm depth. Overall, even though microbial N cycling and enzyme activities per unit soil mass decreased with depth, microbial processes in subsoils contributed substantially to ecosystem-scale gross N fluxes because of the sustained microbial activity per unit soil organic matter at depth and the large size of the organic matter pool in the mineral soil. These results support the inclusion of often-ignored mineral subsoils and microbial N recycling in both ecosystem N budgets and in model simulations, due to their contribution to soil N fluxes and the importance of microbial N dynamics in forest stands.

Fire deficit increases wildfire risk for many communities in the Canadian boreal forest

The top priority of fire management agencies in Canada is to protect human life and property. Here we investigate if decades of aggressive fire suppression in the boreal biome of Canada has reduced the proportion of recently burned forests (RBF; <30 years) near human communities, and thereby inadvertently increased the risk of wildfire. We measured the percentage of RBF, which are usually less flammable than older forests, up to a 25-km radius around communities compared to that in the surrounding regional fire regime zone. Our analysis of 160 communities across boreal Canada shows that 54.4% exhibited a deficit or lack of RBF, whereas only 15.0% showed a surplus. Overall, a majority (74.4%) of communities are surrounded by a low (≤10%) proportion of RBF, indicating a higher vulnerability of those communities to wildfire. These findings suggest that suppression policies are increasing flammability in the wildland–urban interface of boreal Canada.

Assessing the Effectiveness of China's Panda Protection System.

Protected areas form the backbone of biodiversity conservation, yet their effectiveness is often not known nor even evaluated [1-3]. China-best known for its record of ecological degradation in the face of rapidly increasing gross domestic product and resource consumption [4]-has in recent years enacted a series of policies and programs to conserve its natural resources. Chief among them is an ambitious protected area system covering 17% of its terrestrial land mass [4, 5]. An important early impetus for the establishment of this reserve system was the protection of the giant panda (Ailuropoda melanoleuca) [5-8]. Using data from two previous large-scale surveys [9, 10] separated by a decade, and including over 50,000 habitat plots, we examined the panda population and habitat trends inside and outside reserves. Despite ambitious ecocompensation programs in panda habitat outside reserves [11-13], the protection provided by reserves reduced most classes of human disturbance compared to outside reserves, and most disturbances decreased through time more strongly inside than outside reserves. Reserves also contained more and increasing suitable panda than found outside reserves [14, 15]. Comparing reserve performance, reserves with increasing older forests and bamboo correlated with increasing panda populations. Together these findings indicate that China's panda reserves have been effective and that they are functioning better over time, conserving more and better habitats and containing more pandas. While China's protected area system still has much room for improvement [4, 5], including to support pandas [16], these findings underscore the progress made in China's nascent environmental movement.

Lianas reduce biomass accumulation in early successional tropical forests.

Early successional tropical forests could mitigate climate change via rapid accumulation of atmospheric carbon. However, liana (woody vine) abundance and biomass has been increasing in many tropical forests over the past decades, which may slow the speed at which secondary forests accumulate biomass. Lianas decrease biomass accumulation in tropical forests, and may have a particularly strong effect on young forests by stalling tree growth. As forests mature, trees may outgrow or shed lianas, thus escaping some of the negative effects of lianas. Alternatively, lianas may have the strongest effect in older successional forests if the effect of lianas is commensurate with their density, which increases dramatically in the first decades of forest succession. We tested these two hypotheses using a landscape liana-removal experiment in 30 forest stands that ranged from 10 to 35yr old in Central Panama. We measured tree growth and biomass accumulation in the stands every year from 2014 to 2017. We found that the effect of liana removal on large trees (≥20-cm diameter) decreased with forest age, supporting the hypothesis that lianas have the strongest negative effects on trees, and thus biomass uptake and carbon storage, in very young successional forests. Large trees accumulated more biomass in the absence of lianas in younger forests than in older forests (compared to controls) even after accounting for the effect of canopy completeness and crown illumination, implying that the detrimental effects of lianas go well beyond resource availability and crown health. There was no significant effect of lianas on small trees (1-20-cm diameter), likely because lianas seek light and thus do not deploy their leaves on small trees that are trapped in the forest understory. Our results show that high liana density early in forest succession reduces forest biomass accumulation by negatively impacting large trees, thus decreasing the capacity of young secondary forests to mitigate climate change. Although the negative effects of lianas on forest biomass diminish as forests age, they do not disappear, and thus lianas are an important component of tropical forest carbon budgets throughout succession.

Succession of a broad-leaved Korean pine mixed forest: Functional plant trait composition

Abstracts A longstanding goal of ecology and conservation biology is to understand the climatic and biological controls of forest succession. However, the patterns and mechanisms that guide forest succession, especially within broad-leaved forests, remain unclear. We collected leaf traits and abiotic data across a 200-year chronosequence within a broad-leaved Korean pine forest in northeastern China. We focused on five key leaf traits related to resource acquisition and competition by quantifying the community-weighted trait distributions for specific leaf area (SLA), leaf dry matter concentration (LDMC), leaf nitrogen content (Nmass (g/kg)), leaf phosphorus content (Pmass (g/kg)) and the ratio of nitrogen content to phosphorus content (Nmass/Pmass). We also studied how these traits respond to changing environmental variables (climatic, soil and topographical) during succession. Redundancy analysis was used to examine the importance of the environmental variables in shaping the successional variation in plant traits. Our results revealed the following. Older forests differed significantly from younger forests in species composition and trait distribution. For example, SLA, leaf N and P content and the N/P ratio tended to increase and then decrease throughout the community during forest succession (p

Prey of reintroduced fishers and their habitat relationships in the Cascades Range, Washington

Conservation and recovery of forest carnivores requires an understanding of their habitat requirements, as well as requirements of their prey. In much of the western United States, trapping and habitat loss led to extirpations of fishers (Pekania pennanti) by the mid-20th century, and reintroductions are ongoing to restore fishers to portions of their former range. Fisher recovery in Washington State has been limited by isolation from other populations, but other potentially important factors, such as diet of fishers in this region and prey availability, have not been thoroughly investigated. We collected hair samples from potential prey and fishers for stable isotope analysis to identify important prey items for fishers within a reintroduction area in southern Washington. We then estimated the abundance of prey species at 21 sites across a gradient of forest structural classes within the fisher reintroduction area, and assessed the effects of forest age and vegetation on the prey community using permutational multivariate analysis of variance and non-metric multidimensional scaling. Stable isotopes revealed that larger prey items, including snowshoe hares (Lepus americanus) and/or mountain beavers (Aplodontia rufa), were the most important prey item(s) for fishers in the southern Cascades. We found distinct but equally diverse prey communities in old-growth (unmanaged) and young (heavily managed) forest stands, with snowshoe hares and mountain beavers most common in young forests, while chipmunks (Neotamius spp.) and small mammals were more common in older forests. Our results suggest a discrepancy between the habitats where important fisher prey are most abundant and habitat requirements of fishers. Snowshoe hares and mountain beavers were most abundant in young forests, whereas fishers are associated with landscapes dominated by older forest stands or those that provide large woody structures, which fishers use for denning and resting. Our results add to growing evidence that forest landscape mosaics provide valuable habitat for fishers in the Pacific Northwest, suggesting that both mature and younger forest stands are important for fishers and fisher recovery.

Early detection of rapid Barred Owl population growth within the range of the California Spotted Owl advises the Precautionary Principle

Abstract Biological invasions are most practical to manage when invasive species population densities are low. Despite a potentially narrow window of opportunity for efficient management, managers tend to delay intervention because the cost of prompt action is often high and resources are limited. The Barred Owl (Strix varia) invaded and colonized the entire range of the Northern Spotted Owl (S. occidentalis caurina), but insufficient population data contributed to delays in action until the Barred Owl posed an existential threat to the Spotted Owl. The leading edge of the Barred Owl expansion has since reached the Sierra Nevada, the core range of the California Spotted Owl (S. o. occidentalis). We conducted passive acoustic surveys within 400-ha grid cells across ~6,200 km2 in the northern Sierra Nevada and detected a 2.6-fold increase in Barred Owl site occupancy between 2017 and 2018, from 0.082 (85% confidence interval: 0.045–0.12) to 0.21 (0.14–0.28). The probability of Barred Owl site colonization increased with the amount of older forest, suggesting that Barred Owls are first occupying the preferred habitat of Spotted Owls. GPS-tagged Barred Owls (n = 10) generally displayed seasonal and interannual site fidelity over territories averaging 411 ha (range: 150–513 ha), suggesting that our occupancy estimates were not substantially upwardly biased by “double counting” individuals whose territories spanned multiple grid cells. Given the Barred Owl’s demonstrated threat to the Northern Spotted Owl, we believe our findings advise the Precautionary Principle, which posits that management actions such as invasive species removal should be taken despite uncertainties about, for example, true rates of population growth if the cost of inaction is high. In this case, initiating Barred Owl removals in the Sierra Nevada before the population grows further will likely make such action more cost-effective and more humane than if it is delayed. It could also prevent the extirpation of the California Spotted Owl from its core range.

Fate of leaf litter in restored Kandelia obovata (S. L.) mangrove forests with different ages in Jiulong River Estuary, China

Ecological processing of leaf litter plays important roles in carbon dynamics of mangrove forests. Fate of leaf litter, that is, removal by crabs, microbial decomposition, and tidal export was quantified in two restored Kandelia obovata forests with ages of 24 years and 48 years, respectively, from December 2009 to November 2010. Crab abundance was also investigated to test the role of crabs in leaf litter processing. Daily leaf litter production was 1.064 ± 0.108 g C m−2 day−1 at the 24‐year forest and was 0.689 ± 0.040 g C m−2 day−1 at the 48‐year forest. Annual mean removal of leaf litter by crabs was lower at the 24‐year forest than at the 48‐year forest (0.177 ± 0.046 g C m−2 day−1 vs. 0.220 ± 0.050 g C m−2 day−1), due to a higher crab abundance at the older forest. Microbial decomposition and change in standing stock of leaf litter on the forest floor made a negligible contribution to the annual leaf litter production. Tidal exports of leaf litter were estimated as 0.875 ± 0.090 g C m−2 day−1 and 0.458 ± 0.086 g C m−2 day−1 at the 24‐year and 48‐year forests, respectively, accounting for 82.2% and 66.5% of their daily leaf litter production. Turnover rate of leaf litter was higher at the younger forest (1.7 ± 0.4 day−1) than the older forest (1.2 ± 0.3 day−1). Removal of leaf litter by crabs was higher in warm months while tidal export of leaf litter showed a much less apparent seasonal pattern. Spatial variations of crab removal and tidal export of leaf litter with forest zones were observed within each forest, while microbial decomposition of leaf litter was comparable among the different zones. These indicated that the ecosystem functions of restored mangrove forest could not reach a level equivalent to those of a mature forest even 24 years after restoration.

Waldentwicklung und flachgründige Rutschungen: eine grossflächige GIS-Analyse

Forest dynamics and shallow landslides: a large-scale GIS-analysis Through continuous and abrupt changes in the forest and particularly in its root area, the disposition for shallow landslides also changes. The aim of this article is to learn more about the relationships between long-term forest dynamics and the risk of landslides with the help of large spatial data sets. A total of 6670 shallow landslides were selected from the natural event register StorMe, the event register of the Canton of Obwalden and the WSL database for shallow landslides and slope debris flows and overlaid with GIS data on the current and former forest situation (Siegfried maps of approx. 1880) and with windthrow areas (Vivian and Lothar). Shallow landslides occurred less frequently in the forest than outside of it at inclinations of less than 35 degrees. Higher landslide densities occurred in coniferous and mixed forests (compared to deciduous forests) and in relatively young forests (ingrown after 1880). Landslides in younger forests occurred on slopes less steep than in older forests. More shallow landslides occurred on former windthrow areas during the first 3 to 17 years after the event, however these landslides occurred on comparatively steep slopes. The analyses show that the disposition towards shallow landslides defined by slope inclination and subsoil can change strongly due to reforestation processes and natural disturbances. Silvicultural interventions may contribute to an improvement of the protective effect in the long term if they are carried out carefully and if they contribute to an increased adaptability to natural disturbances.

Determination of Soil Properties and Fungal Interrelations Influenced by Forest Restoration on a Contaminated Zinc Mining Area

Forest restoration in a contaminated zinc mining area must take into account the environmental soil properties. This study aimed to analyze the soil properties from the three different stages of restored forests, at 3, 7 and 17, focusing on the impact on soil microorganisms and availability of fungal species. Three study sites were selected, all located in a zinc mining area in Mae Sot District, Tak Province, Thailand. The results showed that observed soil properties especially soil texture, moisture and nutrients differed between stand initiation and regrowth forests and affected the distribution of fungal species. Soils in older forest stands up to 17 years old showed higher sand content and reduced soil moisture, SOM, and certain nutrients. Forest restoration was found to favour development of a range of soil properties, some of which were suitable for fruiting in nine fungal species from the following families: Agaricaceae, Psathyrellaceae, Cantharellaceae, Phallacae, Coprinaceae, Sclerodermataceae, Lycoperdaceae, Marasmiaceae, and Clavariaceae.

Assessing the influence of the minimum measured diameter on forest spatial patterns and nearest neighborhood relationships

Forest structure analysis is important for understanding the properties and development of a forest community, and its outcomes can be influenced by how trees are measured in sampled plots. Although there is a general consensus on the height at which tree diameter should be measured [1.3 m: diameter at breast height (DBH)], the minimum measured diameter (MMD) often varies in different studies. In this study, we assumed that the outcomes of forest structure analysis can be influenced by MMD and, to this end, we applied g(r) function and stand spatial structural parameters (SSSPs) to investigate how different MMDs affect forest spatial structure analysis in two pine-oak mixed forests (30 and 57 years old) in southwest China and one old-growth oak forest (>120 years old) from northwest China. Our results showed that 1) MMD was closely related to the distribution patterns of forest trees. Tree distribution patterns at each observational scale (r = 0–20 m) tended to become random as the MMD increased. The older the community, the earlier this random distribution pattern appeared. 2) As the MMD increased, neighboring trees became more regularly distributed around a reference tree. In most cases, however, nearest neighbors of a reference tree were randomly distributed. 3) Tree species mingling decreased with increasing diameter, but it decreased slowly in older forests. 4) No correlations can be found between individual tree size differentiation and MMD. We recommend that comparisons of spatial structures between communities would be more effective if using a unified MMD criterion.

Anticoagulant rodenticides in Strix owls indicate widespread exposure in west coast forests

Exposure of nontarget wildlife to anticoagulant rodenticides (AR) is a global conservation concern typically centered around urban or agricultural areas. Recently, however, the illegal use of ARs in remote forests of California, USA, has exposed sensitive predators, including the federally threatened northern spotted owl (Strix occidentalis caurina). We used congeneric barred owls (S. varia) as a sentinel species to investigate whether ARs pose a threat to spotted owls and other old-forest wildlife in northern regions of the Pacific Northwest. We analyzed the liver tissue from 40 barred owls collected in Oregon and Washington and confirmed exposure to ≥1 AR compounds in 48% of the owls examined. Brodifacoum, an extremely toxic second-generation AR, was the most common compound detected (89% of positive cases), followed by bromadiolone (11%), difethialone (11%), and warfarin (5%). Brodifacoum was also detected in one barred owl and one spotted owl opportunistically found dead (liver concentrations were 0.091 and 0.049 μg/g, respectively). We found no evidence that exposure varied with proximity to developed and agricultural areas, or among different study areas, age-classes, and sexes. Rather, exposure was ubiquitous, and the rates we observed in our study (38–64%) were similar to or greater than that reported previously for barred owls in California (40%). Together these studies indicate widespread contamination in forested landscapes used by spotted owls and other wildlife of conservation concern. Owls collected in older forests may have been exposed via illegal use of ARs, highlighting a mounting challenge for land managers and policy makers.

Carbon use efficiency of mycorrhizal fungal mycelium increases during the growing season but decreases with forest age across a Pinus sylvestris chronosequence

Abstract In boreal forest soils, mycelium of mycorrhizal fungi is pivotal for regulating soil carbon (C) cycling and storage. The carbon use efficiency (CUE), a key parameter in C cycling models, can inform on the partitioning of C between microbial biomass, and potential soil storage, and respiration. Here, we test the dependency of mycorrhizal mycelial CUE on stand age and seasonality in managed boreal forest stands. Based on mycelial production and respiration estimates, derived from sequentially incubated ingrowth mesh bags, we estimated CUE on an ecosystem scale during a seasonal cycle and across a chronosequence of eight, 12‐ to 158‐year‐old, managed Pinus sylvestris forest stands characterized by decreasing pH and nitrogen (N) availability with increasing age. Mycelial respiration was related to total soil respiration, and by using eddy covariance flux measurements, primary production (GPP) was estimated in the 12‐ and 100‐year‐old forests, and related to mycelial respiration and CUE. As hypothesized, mycelial CUE decreased significantly with increasing forest age by c. 65%, supposedly related to a shift in mycorrhizal community composition and a metabolic adjustment reducing their own biomass N demand with declining soil N availability. Furthermore, mycelial CUE increased by a factor of five over the growing season; from 0.03 in May to 0.15 in November, and we propose that the seasonal change in CUE is regulated by a decrease in photosynthate production and temperature. The respiratory contribution of mycorrhizal mycelium ranged from 14% to 26% of total soil respiration, and was on average 17% across all sites and occasions. Synthesis. Carbon is retained more efficiently in mycorrhizal mycelium late in the growing season, when fungi have access to a more balanced C and nutrient supplies. Earlier in the growing season, at maximum host plant photosynthesis, when below‐ground C availability is high in relation to N, the fungi respire excess C resulting in lower mycelial carbon use efficiency (CUE). Additionally, C is retained less efficiently in mycorrhizal fungal biomass in older forest stands characterized by more nutrient depleted soils than younger forest stands.