Unmanaged Forests Research Articles

Long-Term Suppression of Hardwood Regeneration by Chinese Privet (Ligustrum sinense)

Native hardwood regeneration in the southeast United States is hindered by repeat disturbance events and the presence of invasive species. Our study aimed to determine the ability of native species in an unmanaged urban forest fragment to persist following high winds from hurricane Gustav in 2008 and subsequent salvage logging. In 2009, researchers estimated the density and composition of the regeneration and overstory trees as well as percent crown cover of invasive Chinese privet. Percent Chinese privet cover was visibly high, leading them to believe it may be inhibiting native hardwood establishment. Ten years later in 2019, we returned to the plots to take repeat measurements. Forest composition remains the same and privet crown cover remains high. There has been no increase in regenerating individuals, and overstory trees per hectare and basal area remains low. These results confirm that the heavy Chinese privet presence is persistent long term and will require management to promote reproduction of native overstory tree species.

Diversity of click beetles in managed nonnative coniferous and native beech stands: Consequences of changes in the structural and species composition of tree stands in Central Europe

The natural composition of forests has undergone significant changes over recent centuries. A closer-to-natural tree species composition has long been perceived as key to a high biodiversity. We investigated the impact on communities of click beetles (Elateridae) caused by changes in the tree species composition of spruce monocultures compared to reference sites of recently unmanaged natural beech forests. To collect data, passive interception traps were distributed within managed spruce stands of different age classes and natural beech forests of various developmental stages. The beetle species richness was slightly but not significantly higher in the beech forests. The saproxylic species group was significantly more common in the spruce stands, whereas the group of nonsaproxylic species was significantly more abundant in the beech stands. In the commercial stands, the significantly highest species richness was in the clearings (0–10-year-old stands), and at this forest age class, the vast majority of the beetle species occurred in the spruce stands. In the developmental stages of the natural forest, a slightly higher beetle richness was found at the disintegration stage. The study results suggested that different tree species compositions and stand structures affect the communities of click beetles and substantially change their species composition and thus their response to external influences. Therefore, management of stands using diverse silvicultural systems is recommended for creating diverse ecological niches in forests.

Long-Term Changes in Soil Composition in Unmanaged Central European Mountain Spruce Forests after Decreased Acidic Deposition and a Bark Beetle Outbreak

Long-Term Changes in Soil Composition in Unmanaged Central European Mountain Spruce Forests after Decreased Acidic Deposition and a Bark Beetle Outbreak

Long-Term Changes in Soil Composition in Unmanaged Central European Mountain Spruce Forests after Decreased Acidic Deposition and a Bark Beetle Outbreak

Long-Term Changes in Soil Composition in Unmanaged Central European Mountain Spruce Forests after Decreased Acidic Deposition and a Bark Beetle Outbreak

Regeneration Status and Diversity under Irregular Shelterwood System: A Study from Panchkanya Community Forest, Sunsari, Nepal

The present study is the outcome of vegetation sampling conducted in the managed and unmanaged forest patch under the irregular shelterwood system to analyze community structure and plant diversity in a degraded mixed forest in eastern Terai, Nepal. Systematic random sampling was followed by laying out 15 quadrates sized 4m2 with uniform spacing of 50 meters in both managed and unmanaged blocks, respectively. This study revealed that the first and second-year regeneration felling subsisted the Shorea robusta in the managed forest patch. There was observed a remarkable increase in regeneration but a decrease in plant diversity in the managed area in comparison to the unmanaged one. Simpson’s index of diversity was 0.760 and 0.890 and Shannon-Wiener indexes were 1.82 and 2.43 in managed and unmanaged forest blocks, respectively. Independent sample t-test showed a significant difference in the total number of regenerations between managed and unmanaged forest blocks since P-value <0.05 (P=0.0166) i.e., managed blocks with opened canopy had higher regeneration but a lower diversity. This study concludes that the irregular shelterwood system is deemed pivotal for increased regeneration of Shorea robusta particularly in the eastern lowland of Nepal.

Perceptions of Local Inhabitants towards Land Management Systems Used in the Rainforest Area of Ecuador: An Evaluation Based on Visual Rating of the Main Land Use Types

Land management policy and practice affects a wide segment of stakeholders, including the general population of a given area. This study evaluates the perceptions of local inhabitants towards the land management systems used in the rainforest area of Ecuador—namely, unmanaged (natural) forest, managed forest, croplands, and pasturelands. Data collected as ratings on 12 pictures were used to check the aggregated perceptions by developing the relative frequencies of ratings, in order to see how the perception rating data were associated with the types of land management systems depicted by the pictures, and to see whether the four types of land management could be mathematically represented by a clustering solution. A distinctive result was that the natural forests were the most positively rated, while the managed forests were the least positively rated among the respondents. It seems, however, that human intervention was not the landscape-related factor affecting this perception, since croplands and pasturelands also received high ratings. The ratings generated a clear clustering solution only in the case of forest management, indicating three groups: natural forests, managed forests, and the rest of the land management systems. Based on the results of this study, a combination of the four land use systems would balance the expectations of different stakeholders from the area, while also being consistent to some extent with the current diversity in land management systems. However, a more developed system of information propagation would be beneficial to educate the local population with regards to the benefits and drawbacks of different types of land management systems and their distribution.

Pine savanna restoration on agricultural landscapes: The path back to native savanna ecosystem services

Restoration of savanna ecosystems within their historic range is expected to increase provision of ecosystem services to resident human populations. However, the benefits of restoration depend on the degree to which ecosystems and their services can be restored, the rate of restoration of particular services, and tradeoffs in services between restored ecosystems and other common land uses. We use a chronosequence approach to infer multi-decadal changes in ecosystem services under management aimed at restoring fire-dependent pine savannas, including the use of frequent prescribed fire, following abandonment of row-crop agriculture in the southeastern U.S. We compare ecosystem services between restored pine savannas of different ages and reference pine savannas as well as other common land uses (row-crop agriculture, improved pasture, pine plantation, unmanaged forest). Our results suggest that restoring pine savannas results in many improvements to ecosystem services, including increases in plant species richness, perennial grass cover, tree biomass, total ecosystem carbon, soil carbon and C:N, reductions in soil bulk density and predicted erosion and sedimentation, shifts from soil fungal pathogens to fungal symbionts, and changes in soil chemistry toward reference pine savanna conditions. However, the rate of improvement varies widely among services from a few years to decades. Compared to row-crop agriculture and improved pasture, restored savannas have lower erosion, soil bulk density, and soil pathogens and a higher percentage of mycorrhizal fungi and ecosystem carbon storage. Compared to pine plantations and unmanaged forests, restored pine savannas have lower fire-prone fuel loads and higher water yield and bee pollinator abundance. Our results indicate that restoration of pine savanna using frequent fire provides a broad suite of ecosystem services that increase the landscape's overall resilience to climate change. These results are likely relevant to other savannas dominated by perennial vegetation and maintained with frequent fire.

Factors influencing the rate of formation of tree‐related microhabitats and implications for biodiversity conservation and forest management

Abstract The retention of trees bearing tree‐related microhabitats (TreMs) has become an important means of conserving biodiversity in production forests. However, we lack estimates of TreM formation rates and evidence on factors driving TreM formation. Based on the observation of 80,099 living trees from 19 species groups in Europe and Iran, we estimated the probability of TreM occurrence on trees and the associated rate of first TreM formation as a function of tree DBH, management, tree species group and random site effects. We built a separate model for each of 11 TreM groups. The hazard rate of first TreM formation (defined as the probability of formation of a first TreM forming on a tree that is known to have none, during an infinitesimal DBH increment) increased with DBH for some TreM groups like breeding‐woodpecker‐hole, rot‐hole or root‐concavity, indicating an acceleration in TreM formation during tree growth. However, it decreased with DBH for TreM groups like bark‐loss or dendrotelm, indicating slower formation on very large trees. Most TreM groups had reduced formation rates in managed forests (last logging less than 100 years ago) compared to unmanaged forests (no logging for at least 100 years), with the exception of dendrotelms. No general difference appeared between broadleaves and conifers, but early‐successional species tended to have different TreMs than mid‐ and late‐successional species. Abies, Alnus, Betula, Fagus, Prunus, Quercus, Sorbus, Tilia and Ulmus displayed high formation rates for six TreM groups or more. Variability among sites was considerable. Synthesis and applications. The rate of formation of tree‐related microhabitats (TreMs) varies greatly among TreM groups, tree species, locations, tree diameters at breast height and forest management. The high rate of formation of some TeM groups on small trees implies that tree retention for biodiversity should concern trees of all sizes and start as soon as thinning operations have occurred. Biodiversity conservation should value not only forest stands and trees that already have many TreMs but also those where the likelihood of future TreM formation is high due to species, maturity or local environmental conditions. The addition of quantitative models of TreM formation to forest stand dynamics simulators is necessary to better take into account biodiversity conservation in forest management.

Understanding the Long-Term Impact of Bamboos on Secondary Forests: A Case for Bamboo Management in Southern Brazil

As secondary forests become more common around the world, it is essential to understand successional pathways to ensure their proper forest management. Despite optimism about secondary forests in terms of landscape restoration, the influence of invasive species on their development has been poorly explored. Here, forest plots in the Araucaria Forest, Southern Brazil, are used to compare forest dynamics over a 14-year period between unmanaged bamboo forest development (control) and the removal of bamboo. Six control plots (15 × 15 m) were monitored for all adult trees since 2007 alongside six adjacent removal plots; after the initial measurement of the control in 2007, all plots were measured bi-annually from 2010 to 2020. Comparisons were based on tree species diversity, composition, and structure parameters. Removal plots show a trend towards developing a forest composition with more secondary and late successional species while the control plots demonstrate succession restricted to the pioneer trees that regenerated immediately after bamboo die-off (2005–2006). Without the presence of bamboos, removal plots are mirroring the well-known successional pathway typical of the Araucaria Forest. Conversely, bamboos are effectively arresting successional development in the control, resulting in lower levels of diversity and less complex forest structure. For the first time, this study presents a direct analysis of the influence of bamboos on forest succession, providing evidence on which practices to manage bamboo forests can be developed so these secondary forests can fulfill their ecological and economic potential.

Forest management and conservation of faunal diversity in Italy: a review

We re-examined the knowledge on the relationships between fauna and forest management in Italy. We focused our attention on Vertebrates, including small mammals (Rodents and Soricomorphs), bats, birds, reptiles and amphibians, and on carabid and saproxylic beetles. We found that nearly all groups respond in accordance with Angelstam’s scheme of the traditional forestry cycle, with open habitat specialists followed by generalists and forest specialists when pristine conditions have been attained, though with some differences for some taxa. In all groups, some forest “superspecialists” or old growth indicators could be found, in (sub)Mediterranean forests some carabid beetles could be defined as “dendrophilous,” i.e. associated with the presence of old trees. Poplar plantations are poor substitutes for native forests, as well as exotic conifers. We propose a model for an ideal forest structure that may efficiently preserve the faunal components, at the microscale level this coincides with the structure of an unmanaged old growth forest stand, marked also by a deep and humus-rich soil layer. Some caveats at the landscape scale have dealt with in relation to the size of the designed area, in order to avoid fragmentation effects. A sustainable harvesting scheme has indicated in the “systemic silviculture” proposed by Ciancio and other scientists.

Legacies of forest harvesting on plant diversity and plant community composition in temperate deciduous forest

AbstractAimsTo conserve forest natural heritage, sustainable forest harvesting requires the recovery of plant diversity and ecosystem functions following management. There is a need to clarify the temporal dynamics of plant diversity following harvesting, for both even‐aged and uneven‐aged silvicultural systems. To achieve this goal, the temporal dynamics of plant diversity in the herb layer were measured in unmanaged forests (control) and along a chronosequence (<5 years, 15 years and 30 years after harvesting) for even‐aged and uneven‐aged managed forests.LocationHardwood forest of southern Quebec, Canada.MethodsPlant diversity, plant community composition and ecosystem functioning were investigated using metrics exploring richness, evenness and disparity diversity components, and included two scales of diversity partitioning (alpha and beta). Shrub–canopy layer, forest tree species composition and structure, and total forest basal area were also measured.ResultsIn both uneven‐aged and even‐aged managed forest stands, we found: (a) a substantial decrease in mean plant phylogenetic diversity compared with unmanaged forest, even 30 years after harvesting (i.e., decrease of 16% and 22%, respectively); and (b) lowest plant alpha‐diversity in the herb layer 15 years after harvesting. Modification of community composition based upon dissimilarity (beta‐diversity) metrics demonstrated more numerous effects of even‐aged management than uneven‐aged management. For forest composition and structure, plant community and plant traits, dissimilarity relative to the unmanaged control was highest 5 years after even‐aged management. Trait‐based communities were more similar to unmanaged forest at the intermediate levels of forest density (i.e., ~20 m2/ha) that were found 5 years after uneven‐aged management.ConclusionsForest management clearly affected diversity, community composition and ecosystem functions along the chronosequence, highlighting the strongest effects of more intensive management (i.e., even‐aged) and the need to improve the sustainability of forest management.

Fungal diversity, woody debris, and wood decomposition in managed and unmanaged Patagonian Nothofagus pumilio forests

Fungal diversity, woody debris, and wood decomposition in managed and unmanaged Patagonian Nothofagus pumilio forests

Land-use change alters associations between personality and microhabitat selection.

Ecologists commonly assess ecological patterns at the population level, focusing on the average response of all individuals within a population, but to predict how populations will respond to land-use change we must understand how changes to habitat differentially affect individuals within a population. For example, forest management is a widespread type of land-use that impacts wildlife through the loss of key habitat features, but individuals within a population may vary in their responses to this loss due to differences in habitat selection among individuals. Specifically, intraspecific variation in habitat selection has been linked to animal personalities (i.e., consistent behavioral differences among conspecifics), but previous research has not examined whether the relationship between personality and habitat selection is influenced by land-use change. To address this knowledge gap, we tested the hypothesis that land-use change alters the association between personality and microhabitat selection in small mammals. Specifically, we investigated two main questions: (1) To what extent are personality type and microhabitat selection correlated among conspecifics? (2) Does land-use change alter individual patterns of microhabitat selection? To answer these questions, we conducted a large-scale field experiment over 4 years, contrasting unmanaged forest (control) with managed forest (two silvicultural treatments) in Maine, USA. We examined the relationships between habitat selection and personality traits in deer mice (Peromyscus maniculatus) and southern red-backed voles (Myodes gapperi). We found that personality traits were correlated with microhabitat selection at multiple spatial scales. Furthermore, land-use change altered these patterns of selection; resulting in either the loss of personality-associated selection or in novel patterns of selection in managed forests. These findings suggest that promoting structural complexity at multiple spatial scales, such as by interspersing stands of mature forest with managed stands, may maintain a variety of intraspecific habitat selection patterns and the associated ecological outcomes.

Forest management effects on the ectomycorrhizal macromycete community in tropical montane forests in Mexico

While forest management impacts the ectomycorrhizal fungi (EMF) community, most of the evidence regarding such effects has been obtained from temperate forests of the Northern Hemisphere and little is known of their prevalence in highly diverse tropical habitats. This study analyzes the responses of the EMF community in managed tropical montane forests in the southern Mexican state of Chiapas. EMF community composition and diversity were evaluated over a 2-year period along a gradient of structural and microclimatic conditions of the forest associated with the stages of a cycle of silvicultural practices (R = release cutting, T = thinning, and F = final regeneration cutting), as well as in a mid-successional unmanaged forest (UF) as a reference system. The silvicultural practices involve varying intensities of tree harvesting (≈ 20% in T to ≈ 80% in F). It is hypothesized that: (1) diversity and composition of EMF communities are influenced by changes in forest conditions, principally as a result of canopy cover alteration due to forest management, and (2) late forest successional conditions are associated to more diverse EMF communities, while more intensive silvicultural practices reduce their diversity. A total of 75 EMF species were recorded. Diversity analysis using Hill numbers showed a close relationship between diversity and forest conditions: total species richness, 0D = 5.7 ± 0.6 in F up to 11.7 ± 1.3 in UF; richness of abundant species, 1D = 4.1 ± 0.4 in F up to 7.5 ± 0.4 in UF; richness of very abundant species 2D = 3.3 ± 0.3 in R up to 5.5 ± 0.3 in UF. Canopy cover (9.8 ± 4% in F and 80.6 ± 5% in UF) was the main factor affecting EMF diversity, mainly due to its influence on herbaceous cover, tree species richness (path analysis, R2 = 0.32; p < 0.05), and microclimatic variables. Turnover of the most abundant EMF species from the most intensive management practice towards the later successional forest conditions was observed. Late successional conditions allow for maintenance of more diverse EMF communities, while more intensive practices reduce their diversity (p < 0.05, in both cases). Rare fungal species appear to be more vulnerable to highly intensive management, and account for most of the EMF diversity in UF. The results indicate the importance of preserving relatively undisturbed species-rich forest stands near intensively managed stands in order to maintain biological integrity of the EMF community and ecosystem functioning in tropical montane forests.

Among stand heterogeneity is key for biodiversity in managed beech forests but does not question the value of unmanaged forests: Response to Bruun and Heilmann‐Clausen (2021)

Abstract Schall et al. (2020) assessed how a combination of different forest management systems in managed forest landscapes dominated by European beech may affect the biodiversity (alpha, beta and gamma) of 14 taxonomic groups. Current forest policy and nature conservation often demand for combining uneven‐aged managed and unmanaged, set‐aside for nature conservation, beech forests in order to promote biodiversity. In contrast to this, Schall et al. (2020) found even‐aged shelterwood forests, represented by different developmental phases, to support highest regional (gamma) diversity. By pointing out that unmanaged forests included in our study are not old‐growth forests, Bruun and Heilmann‐Clausen (2021) challenge our conclusion as not providing sound scientific advice to societies. It is true that the studied unmanaged forests are not representing old‐growth forests as defined in the literature. However, we demonstrate the representativeness of our unmanaged forests for current beech forest landscapes of Central Europe, where managed forests were more or less recently set‐aside in order to develop old‐growth structures. We also show that the managed and recently unmanaged forests in our study already differ distinctively in their forest structures. We use this response to stress the role of forest reserves for promoting certain species groups, and to emphasise their importance as valuable research sites today and in the future. Synthesis and applications. We see two main conclusions from our study. First, unmanaged forests still matter. We agree with Bruun and Heilmann‐Clausen (2021) on the general importance of unmanaged, old‐growth or long‐untouched forests, and we do not question the importance of set‐aside forests for biodiversity conservation. However, a complete complementarity to managed systems may only reveal after many decades of natural development. Second, safeguarding biodiversity in largely managed forest landscapes should focus on providing a landscape matrix of different developmental phases with varying environmental conditions rather than on maximising the vertical structure within stands. Such landscapes can partly compensate for structures that are still missing in vital, dense and closed forests recently set‐aside or for unsuitable phases that may occur due to a cyclic synchronisation of forest structures in unmanaged forests.

What is unmanaged forest and how does it sustain biodiversity in landscapes with a long history of intensive forestry?

Abstract A recent paper by Schall et al. (2020) concluded that beech forests managed in even‐aged (EA) rotation systems were more efficient than unmanaged (UNM) forest and forest managed in uneven‐aged (UEA) selective cutting systems in supporting landscape‐scale biodiversity in Germany. The authors based their conclusion on a comprehensive multitaxon survey and a promising resampling model for assessing gamma diversity at landscape scale. Here, we challenge their conclusions and evaluate the importance of UNM forests for conservation of forest biodiversity. The average amount of dead wood reported from EA stands (27.8 m3/ha) was almost 30% higher than reported from UNM stands (21.6 m3/ha) in the study. Averages from long UNM temperate forests in Europe are typically six to seven times higher (131–157 m3/ha). We therefore conclude the UNM studied stands to reflect legacies of former management, and to be poorly representative of UNM forests. Data from our own studies, including long UNM beech stands in Denmark, demonstrate how this shortcoming seriously undermines the general validity of the presented results to conservation of forest biodiversity. Synthesis and applications. Preservation and restoration of intact forest ecosystems remains essential to biodiversity conservation. We show that the findings of Schall et al. (2020) do not contradict this important notion. Schall and colleagues identified UEA management systems as potentially inferior to more traditional EA management systems for conserving forest biodiversity at the landscape scale. The paper also provides insight into the limited short‐term conservation value of simply abandoning forest management in intensively managed landscapes. Based on this, we call for discarding the current orthodox view of non‐intervention when new forest reserves are created in temperate Europe. Active reinforcement of natural disturbance regimes and active habitat creation may lead to faster recovery of natural stand structure and forest biodiversity.

Statistical Evidence for Managing Forest Density in Consideration of Natural Volatile Organic Compounds

Rapid deforestation, coupled with the growing population seeking forest therapy, urges the necessity for research on how to maximize forests’ therapeutic functions when cultivating damaged or unmanaged forests. This study was formulated to provide a basis for forest stand density management to maximize the therapeutic effects of forests with a focus on natural volatile organic compounds (NVOCs), a representative component of forest therapy through analysis of variance and regression analyses. The results of this study revealed all studied stand densities yield the highest total NVOC (TNVOC) emissions in summer, especially in the study site which has a forest density of 700/ha. In addition, treeless areas (0/ha) were found to have the most significant difference in average NVOC emissions when cultivated at a density of 700/ha. When managing forests with a density of 900/ha to 1000/ha, it has been shown that it is most desirable, in terms of therapeutic function efficiency, to control a density of 500/ha to 700/ha. Finally, regression equations for the five experimental sites with significant explanatory power were derived. Based on the results of the conducted analyses, 700/ha of forest density is recommended to maximize the therapeutic effects of forests, compared to other ranges of forest density.

Current Status and Recent Stand Structure Dynamics in Mixed Silver Fir—European Beech Forests in Croatian Dinarides: Are There Differences between Managed and Unmanaged Forests?

The environmental, social and economic potential of Dinaric uneven-aged forests along with the complex stand dynamics influenced by different long-term management approaches and environmental factors require comprehensive forest monitoring. This study aimed to explore differences in the current status and recent past dynamics of stand structures between unmanaged and managed mixed fir-beech forests in the Croatian part of the Dinaric Alps using large-scale data from an established monitoring system. From the 74 permanent sample plots distributed within the forest type measured in 2008 and re-measured in 2019, we stratified four strata (types of management regimes): (1) forests out of regular management and tree harvest for at least 30 years, (2) managed state forests on carbonate bedrock, (3) managed state forests on non-carbonate bedrock and (4) managed private forests. In each sample plot, 34 structural attributes were computed to assess indicators of their current status and recent past dynamics of stands in the studied forests. An increasing Q shape diameter distribution with a high number of large and very large trees characterize unmanaged forests and managed forests on non-carbonate bedrock. In managed state forests and private forests, variable (rotated sigmoid) and constant (negative exponential) results were obtained, respectively. Principal component analysis (PCA) distinguished managed and unmanaged forests with decreasing harvest volume and recruitment, increasing basal area, number of very large trees, average diameter at breast height (DBH), crown defoliation of firs and basal area of died beech trees. The current structure, recent and expected stand dynamics in the unmanaged forests (accumulation of standing volume, increase of large diameter trees and large snags, large share of beech, large mean DBH) can be recognized as old-growth attributes. The differences between the studied forest types, potential of both unmanaged and state managed fir-beech forests and approaches to sustain multifunctional forest management in the Dinaric region were discussed.

Differential spatial responses of rodents to masting on forest sites with differing disturbance history.

Mast seeding, the synchronized interannual variation in seed production of trees, is a well‐known bottom‐up driver for population densities of granivorous forest rodents. Such demographic effects also affect habitat preferences of the animals: After large seed production events, reduced habitat selectivity can lead to spillover from forest patches into adjacent alpine meadows or clear‐cuts, as has been reported for human‐impacted forests. In unmanaged, primeval forests, however, gaps created by natural disturbances are typical elements, yet it is unclear whether the same spillover dynamics occur under natural conditions. To determine whether annual variation in seed production drives spillover effects in naturally formed gaps, we used 14 years of small mammal trapping data combined with seed trap data to estimate population densities of Apodemus spp. mice and bank voles (Myodes glareolus) on 5 forest sites with differing disturbance history. The study sites, located in a forest dominated by European beech (Fagus sylvatica), Norway spruce (Picea abies), and silver fir (Abies alba), consisted of two primeval forest sites with small canopy gaps, two sites with larger gaps (after an avalanche event and a windthrow event), and a managed forest stand with closed canopy as a control. Hierarchical Bayesian N‐mixture models revealed a strong influence of seed rain on small rodent abundance, which were site‐specific for M. glareolus but not for Apodemus spp. Following years of moderate or low seed crop, M. glareolus avoided open habitat patches but colonized those habitats in large numbers after full mast events, suggesting that spillover events also occur in unmanaged forests, but not in all small rodents. The species‐ and site‐specific characteristics of local density responding to food availability have potentially long‐lasting effects on forest gap regeneration dynamics and should be addressed in future studies.

Multi‐Decadal Carbon Cycle Measurements Indicate Resistance to External Drivers of Change at the Howland Forest AmeriFlux Site

AbstractA long‐standing goal of ecology has been to understand the cycling of carbon in forests. This has taken on new urgency with the need to address a rapidly changing climate. Forests serve as long‐term stores for atmospheric CO2, but their continued ability to take up new carbon is dependent on future changes in climate and other factors such as age. We have been measuring many aspects of carbon cycling at an unmanaged evergreen forest in central Maine, USA, for over 25 years. Here we use these data to address questions about the magnitude and control of carbon fluxes and quantify flows and uncertainties between the different pools. A key issue was to assess whether recent climate change and an aging tree population were reducing annual C storage. Total ecosystem C stocks determined from inventory and quantitative soil pits were about 23,300 g C m−2 with 46% in live trees, and 48% in the soil. Annual biomass increment in trees at Howland Forest averaged 161 ± 23 g C m−2 yr−1, not significantly different from annual net ecosystem production (NEP = −NEE) of 211 ± 40 g C m−2 y−1 measured by eddy covariance. Unexpectedly, there was a small but significant trend of increasing C uptake through time in the eddy flux data. This was despite the period of record including some of the most climate‐extreme years in the last 125. We find a surprising lack of influence of climate variability on annual carbon storage in this mature forest.