Changes In Forest Composition Research Articles

Impact of increased salinity on the plant community of the Sundarbans Mangrove of Bangladesh

The overreaching objective of the study was to assess the changes in eco-regional forest composition and the colonization of invasive plant species in the Sundarbans, the largest single block of tidal halophytic mangrove forest globally. The study also aimed to examine the relationship between different plant types and the salinity level. Additionally, the interconnection between the salinity and the ‘top dying’ disease of the pioneer and dominant species was also measured. Thirty sample plots were established at the mouths of an equal number of canals to collect the plant community’s primary data. In addition, secondary historical data were utilized to understand the natural dynamics of the forest eco-regions in this mangrove. The study revealed that the fresh swamp forests disappeared from their historical range. Over time, the Screw Pine (Pandanus tectorius) became extinct from the study area. Simultaneously, rice grass (Leersia hexandra) and wild rice (Potresia coarctata) stand on the brink of extinction. Sundari (Heritiera fomes), the pioneer and dominant species, suffers from the increased salinity, and its stocks are declining due to intensified “top dying” disease. In contrast, the salt lover species, notably white mangrove (Avicennia marina), enjoy the incremental hegemony. The abundance of the indicator species, Nypa Palm (Nipa fruticans), and Mangrove Date Palm (Phoenix pelludosa) show a declining trend because of increased salinity. A total number of 25 invasive plant species were enumerated in this study. Immediate mitigation actions are required to protect this alteration in the vegetation composition of this mangrove. Hence, the study proposed a conceptual model of a mitigation plan spotlighting the local pressures.

Network analysis can guide resilience-based management in forest landscapes under global change.

Forests are projected to undergo dramatic compositional and structural shifts prompted by global changes, such as climatic changes and intensifying natural disturbance regimes. Future uncertainty makes planning for forest management exceptionally difficult, demanding novel approaches to maintain or improve the ability of forest ecosystems to respond and rapidly reorganize after disturbance events. Adopting a landscape perspective in forest management is particularly important in fragmented forest landscapes where both diversity and connectivity play key roles in determining resilience to global change. In this context, network analysis and functional traits combined with ecological dynamic modeling can help evaluate changes in functional response diversity and connectivity within and among forest stands in fragmented landscapes. Here, we coupled ecological dynamic modeling with functional traits analysis and network theory to analyze forested landscapes as an interconnected network of forest patches. We simulated future forest landscape dynamics in a large landscape in southern Quebec, Canada, under a combination of climate, disturbance, and management scenarios. We depicted the landscape as a functional network, assessed changes in future resilience using indicators at multiple spatial scales, and evaluated if current management practices are suitable for maintaining resilience to simulated changes in regimes. Our results show that climate change would promote forest productivity and favor heat-adapted deciduous species. Changes in natural disturbances will likely have negative impacts on native conifers and will drive changes in forest type composition. Climate change negatively impacted all resilience indicators and triggered losses of functional response diversity and connectivity across the landscape with undesirable consequences on the capacity of these forests to adapt to global change. Also, current management strategies failed to promote resilience at different spatial levels, highlighting the need for a more active and thoughtful approach to forest management under global change. Our study demonstrates the usefulness of combining dynamic landscape-scale simulation modeling with network analyses to evaluate the possible impacts of climate change as well as human and natural disturbances on forest resilience under global change.

Drought Increases Vulnerability of Pinus ponderosa Saplings to Fire-Induced Mortality

The combination of drought and fire can cause drastic changes in forest composition and structure. Given the predictions of more frequent and severe droughts and forecasted increases in fire size and intensity in the western United States, we assessed the impact of drought and different fire intensities on Pinus ponderosa saplings. In a controlled combustion laboratory, we exposed saplings to surface fires at two different fire intensity levels (quantified via fire radiative energy; units: MJ m−2). The recovery (photosynthesis and bud development) and mortality of saplings were monitored during the first month, and at 200- and 370-days post-fire. All the saplings subjected to high intensity surface fires (1.4 MJ m−2), regardless of the pre-fire water status, died. Seventy percent of pre-fire well-watered saplings recovered after exposure to low intensity surface fire (0.7 MJ m−2). All of the pre-fire drought-stressed saplings died, even at the lower fire intensity. Regardless of the fire intensity and water status, photosynthesis was significantly reduced in all saplings exposed to fire. At 370 days post-fire, burned well-watered saplings that recovered had similar photosynthesis rates as unburned plants. In addition, all plants that recovered or attempted to recover produced new foliage within 35 days following the fire treatments. Our results demonstrate that the pre-fire water status of saplings is an important driver of Pinus ponderosa sapling recovery and mortality after fire.

Indirect biogeomorphic and soil evolutionary effects of spruce bark beetle

Outbreaks of bark beetles, for example Ips typographus L. in Eurasia or Dendroctonus ponderosae Hopkins in North America, have serious impacts on forest resources, biodiversity, and ecological dynamics, with economical and social ramifications. Moreover, many models predict increasing frequency and severity of such biotic disturbances due to ongoing climate change, and land use driven changes in forest structure and composition. Bark beetles are recognized as keystone species due to their strong and complex effects on ecosystem dynamics. However, due to the increasingly widely recognized biogeomorphic impacts of trees, bark beetles may have significant indirect biogeomorphic and pedogenetic impacts through their effects at scales ranging from individual trees to forest landscapes. These include: (1) Reduced uprooting, with associated impacts on topography, mass movements, regolith and soil formation, and slope hydrology; (2) Reductions in bioprotection via trapping of downslope sediment movement; (3) Hydrological impacts, including increased total runoff and increased proportion of subsurface flow; (4) Decreased microtopographic irregularity (and associated hydrological and pedological impacts); and (5) Changes in biochemical and biomechanical effects on soils, regolith, and hillslope morphology. Five separator factors (discriminators between different developmental trajectories) were revealed for the case of the central European region. These factors may determine the occurrence and severity of biogeomorphic impacts: First is whether the site is prone to potential uprooting or whether an spruce bark beetle (SBB) outbreak is initiated by a blowdown/uprooting event. Second is whether the site is dominated by mineral soils or Histosols. A third discriminating factor is whether the forest is managed or unmanaged, which determines the pre-attack tree species composition and coarse woody debris and disturbance regimes; and a fourth is the post-outbreak management. Finally, the fifth separator factor relates to slope thresholds that determine the significance of impacts on mass movements and erosion. These findings support the need, and provide guidelines, for research on geomorphic impacts of bark beetle infestations. Though we mainly restrict our consideration to bark beetles in Europe, both our approach and findings are likely to have broader relevance for biogeomorphic impacts of extensive tree mortality. • Spruce bark beetles (SBB) influence various geomorphic and pedogenetic processes. • SBB influence soils and hillslope dynamics from local scale of tree to landscape scale. • Five separator factors may determine the occurrence and severity of SBB impacts. • Findings have broader relevance for geomorphic impacts of other biotic disturbances.

Do recent NDVI trends demonstrate boreal forest decline in Alaska?

Remote sensing analyses of boreal forest regions have found widespread decreasing or increasing trends in normalized difference vegetation index (NDVI). Initially, these trends were attributed to climate change induced shifts in primary productivity. It is emerging, however, that fire disturbance and subsequent succession also strongly impact the optical properties of boreal forests. Here we use NDVI time series data from Landsat (1999–2018) paired with surveys of 102 forest stands with known recent fire history to investigate the relationship between NDVI and forest structure during succession. We found that NDVI varies systematically with stand age as a result of successional changes in forest structure and composition and that the proportion of deciduous (broad-leaved) trees in the upper canopy is a better predictor of NDVI than leaf area index. Recent fire disturbance led to strong NDVI decreases and early post-fire recovery of herbaceous and deciduous vegetation to strong NDVI increases. The mid-succession transition from deciduous to evergreen (needle-leaved) stands led to weak NDVI decreases, while mid-to-late succession thinning of evergreen canopies led to weak NDVI increases. Thus, both increasing and decreasing NDVI stands occur naturally across the landscape, and do not necessarily reflect a large-scale shift in boreal forest productivity.

Forest Compositional Changes after a Decade of Emerald Ash Borer

Emerald ash borer is an invasive pest in North American forests. Ecological impacts of ash mortality from emerald ash borer are wide-ranging, including shifts in insect communities and wildlife behavior. Additionally, loss of ash from forests may have important implications regarding plant succession. Surveys of overstory, midstory, and understory trees within forests in northeastern Indiana, Lower Peninsula of Michigan, and northwestern Ohio were conducted to quantify the change in forest composition over a 10 year period. Interpolation of ash dominance illustrated inversion of live and dead ash values between 2007 and 2017. Even though more than 83% of overstory live ash basal area was lost across the study area, green ash was the most abundant midstory and understory species representing regeneration. Additionally, loss of ash from many of the sites resulted in compositional changes that were greater than merely the subtraction of ash. Due to the relatively large number of forest types with which ash species are associated, loss of ash will have broad ecological consequences, including on community composition.

Species composition modulates seedling competitiveness of temperate tree species under hemiboreal conditions

Mixed stands are advised for reduction of impacts of natural hazards, and species composition can largely affect sustainability and productivity of the stands. Early development of a stands after a stand-replacing disturbance can have considerable legacy effects on growth via alterations in the diversity-productivity relationships. Accordingly compatibility of growth and competitiveness of different species is one of the key issues for susceptibility of mixed stands. A two-year chamber experiment was conducted to assess early growth and intra- and inter-specific competition for light and soil resources among the seedlings of temperate tree species simulating the predicted effect of warming (presuming optimal moisture regime). Five species, which have high economic importance or potential to become so in the eastern Baltic region (Scots pine, Norway spruce, silver birch, red oak, and European beech) were studied. Among the studied species, European beech had the fastest height growth and competitiveness, suggesting ability to concur a stable niche outside its natural range, particularly under increased temperature. Beech also maintained high competitiveness despite the damages suffered during the overwintering, supporting legacy effects of early development and suggesting invasive properties. Among the studied, Norway spruce had the slowest growth and suffered the highest competition, which is in line with predicted changes in forest composition. Scots pine, silver birch, and red oak showed intermediate growth and competitiveness, particularly when growing together, suggesting balanced development and optimal productivity of such mixed stands. Nevertheless, growth and competitiveness of these species was reduced by increased temperature, indicating negative effects of warming.

Divergent Hydraulic Strategies Explain the Interspecific Associations of Co-Occurring Trees in Forest–Steppe Ecotone

Research Highlights: Answering how tree hydraulic strategies explain the interspecific associations of co-occurring trees in forest–steppe ecotone is an approach to link plant physiology to forest dynamics, and is helpful to predict forest composition and function changes with climate change. Background and Objectives: The forest–steppe ecotone—the driest edges of forest distribution—is continuously threatened by climate change. To predict the forest dynamics here, it is crucial to document the interspecific associations among existing trees and their potential physiological drivers. Materials and Methods: Forest–steppe ecotone is composed of forest and grassland patches in a mosaic pattern. We executed two years of complete quadrat surveys in a permanent forest plot in the ecotone in northern China, calculated the interspecific association among five main tree species and analyzed their hydraulic strategies, which are presented by combining leaf-specific hydraulic conductivity (Kl) and important thresholds on the stem-vulnerability curves. Results: No intensive competition was suggested among the co-occurring species, which can be explained by their divergent hydraulic strategies. The negative associations among Populus davidiana Dode and Betula platyphylla Suk., and P. davidiana and Betula dahurica Pall. can be explained as the result of their similar hydraulic strategies. Tilia mongolica Maxim. got a strong population development with its effective and safe hydraulic strategy. Generally, hydraulic-strategy differences can explain about 40% variations in interspecific association of species pairs. Oppositely, species sensitivity to early stages of drought is convergent in the forest. Conclusions: The divergent hydraulic strategies can partly explain the interspecific associations among tree species in forest–steppe ecotone and may be an important key for semiarid forests to keep stable. The convergent sensitivity to early stages of drought and the suckering regeneration strategy are also important for trees to survival. Our work revealing the physiological mechanism of forest compositions is a timely supplement to forest–steppe ecotone vegetation prediction.

Ground-dwelling arthropods of pinyon-juniper woodlands: Arthropod community patterns are driven by climate and overall plant productivity, not host tree species.

Pinyon-juniper (PJ) woodlands have drastically changed over the last century with juniper encroaching into adjacent habitats and pinyon experiencing large-scale mortality events from drought. Changes in climate and forest composition may pose challenges for animal communities found in PJ woodlands, especially if animals specialize on tree species sensitive to drought. Here we test habitat specialization of ground-dwelling arthropod (GDA) communities underneath pinyon and juniper trees. We also investigate the role of climate and productivity gradients in structuring GDAs within PJ woodlands using two elevational gradients. We sampled 12,365 individuals comprising 115 taxa over two years. We found no evidence that GDAs differ under pinyon or juniper trees, save for a single species of beetle which preferred junipers. Climate and productivity, however, were strongly associated with GDA communities and appeared to drive differences between sites. Precipitation was strongly associated with arthropod richness, while differences in GDA composition were associated with environmental variables (precipitation, temperature, vapor pressure, and normalized difference vegetation index). These relationships varied among different arthropod taxa (e.g. ants and beetles) and community metrics (e.g. richness, abundance, and composition), with individual taxa also responding differently. Overall, our results suggest that GDAs are not dependent on tree type, but are strongly linked to primary productivity and climate, especially precipitation in PJ woodlands. This implies GDAs in PJ woodlands are more susceptible to changes in climate, especially at lower elevations where it is hot and dry, than changes in dominant vegetation. We discuss management implications and compare our findings to GDA relationships with vegetation in other systems.

Long-lasting effects of unplanned logging on the seed rain of mixed conifer-hardwood forests in southern South America

Understanding the effects of disturbance on seed rain is critical to predict changes in forest species composition and diversity. Logging effects on seed rain in a mixed conifer-hardwood forest complex in southern Brazil were evaluated. One year of seed rain data were collected from a large-scale observational experiment in logged and protected forests and quantity and average seed size weighted by species abundance (CWM) were compared between old-growth and logged stands 55 years after logging activities. Using these data, variations in frequency of functional groups of species in the seed rain were examined to see if they could be attributed to logging. Results show that the number of seeds per trap was highly right-skewed, ranging from 13 to 12,788 seeds per trap in one year. Seed rain was affected by logging history, with seed traps in old-growth plots receiving significantly less seeds than traps in logged plots. All species included mean seed size weighted by species abundance were significantly smaller in logged than in old-growth forests. This difference persisted after the exclusion of Araucaria angustifolia, a large-seeded pioneer which was intensively logged, although the difference of seed size between the two forest classes was greatly reduced. Species abundance in the seed rain differed significantly from the established tree community, between logged and old-growth stands. The composition of the seed rain was much more variable than the composition of the established tree community and its points more scattered over the ordination space than the points corresponding to the protected forests. The number of collected seeds across different functional groups of species significantly differed between logged and old-growth plots. The seed rain of logged forests reflects their arrested succession as indicated by reduced abundance of functional groups such as pioneers, large seeded pioneers and Araucaria, as well as reduced functional diversity. Seed rain differences between logged and old- growth stands reflect the intensive logging of A. angustifolia.

Fine root-arbuscular mycorrhizal fungi interaction in Tropical Montane Forests: Effects of cover modifications and season

Tropical Montane Forests are unique climate-influenced ecosystems with a vital role for some ecosystem services, of which one of the most important is soil carbon storage. Changes in forest cover affect forest structure, composition and functioning, but little is known about how such changes influence the belowground carbon content. In this study, we addressed this issue by evaluating whether fine-root production differed between forest-cover types and contrasting seasons after controlling arbuscular mycorrhizal fungi (AMF) traits, and what the minimum time required to detect such differences is. We also determined whether AMF-related traits were affected by distinct forest cover and seasons after controlling fine-root production. The objects of study were four forests with distinct degradation histories in the Atlantic Forest: Old-growth, Post-selective logging, Post-clear-cut and Post-pasture forests. Data were collected in four 2500-m2 plots installed in each area and analyzed through multivariate statistics. Fine-root production differed significantly between forest covers, and marginally between seasons, as it was greater in the post-pasture area and in the rainy season. Some AMF traits also differed between forest covers and seasons, especially the abundance of viable spores in the dry season. We found that the shortest period necessary to identify differences in the production of fine roots was over three months. This study shows that forests with different degradation histories and annual climatic variations significantly affect fine-root production and AMF dynamics in Tropical Montane Forests. In particular, ecosystems that have been more perturbed tend to invest more in fine-root production (post-pasture). Our results help to better understand belowground interactions and biomass investment under different managed ecosystems.

Qualitative synthesis of temperate bat responses to silvicultural treatments—where do we go from here?

AbstractMost bat species depend on forests for roosting, foraging, and drinking during part or all of their life cycles. Many of the world’s forests are managed using a variety of silvicultural treatments and, over the past 40 years, researchers have studied the responses of bats to these treatments. I carried out a qualitative synthesis of the literature on roosting and foraging responses of temperate insectivorous bats to silvicultural treatments at the stand level to determine what treatments may be most compatible with conservation and to guide future research. Eighty-eight studies from Canada, the United States, Europe, Australia, and New Zealand, met review criteria. Based on my results, foraging and commuting habitat use was less affected by changes in forest structure and composition than roost habitat use. Mid-rotation treatments that reduce clutter while retaining overstory structure (e.g., thinning and fire) had more neutral and positive effects than treatments that removed all or most of the overstory. Based on an examination of the methods and assumptions of the 88 studies included in this review, I conclude that future studies should: 1) strive to account for treatment effects on detection probability of bats when using acoustic detectors; 2) examine responses of bats to silvicultural treatments outside the maternity season; 3) examine demographic and physiological responses to silvicultural treatments in addition to habitat use to fully understand the effects of these treatments on bat populations; and 4) use stand-level data to model forest management effects across large landscapes and over long time periods.

Ancient forest statistics provide centennial perspective over the status and dynamics of forest area in France

Centenary forest statistics informing major attributes of French forests were digitized, checked for consistency, and used to infer forest dynamics. Comparison to forest inventory data highlights increases in forest area and tree diversity, and substantial maturation of forests. Dataset access at https://doi.org/10.5281/zenodo.3739458 The history of European forest dynamic remains fragmental. In France, the Daubree statistics (1908) and agricultural statistics (1892, 1929) formed fundamental material to fill this gap. Release, test, and summarize the digitalized dataset. Analyze long-term forest changes in forest area, composition, and structure. Primary data on forest area across NUTS-3 geographic units, split by forest management and ownership categories and dominating tree species (Daubree), were digitized and cross-compared. Centennial changes in forest attributes were assessed from modern forest inventory data. Cross-comparison revealed: (1) strong temporal consistency in forest changes over time, (2) systematic and interpretable biases in ownership/management categories between Daubree and agricultural statistics. Strong shift from coppices to high forests, increased prevalence of private ownership, and constant proportion of broadleaf- and conifer-dominated forests were highlighted, with increased tree species diversity at country scale. Ancient statistics are shown to play a major role in retrospective land-use and forest policy analysis.

Quantifying Regional Surface Energy Responses to Forest Structural Change in Nordic Fennoscandia

AbstractIn a climate model, surface energy and water fluxes of the vegetated ecosystem largely depend on important structural attributes like leaf area index and canopy height. For forests, management can greatly alter these attributes with resulting consequences for the surface albedo, surface roughness, and evapotranspiration. The sensitivity of surface energy and water budgets to alterations in forest structure is relatively unknown in boreal regions, particularly in Nordic Fennoscandia (Norway, Sweden, and Finland), where the forest management footprint is large. Here we perform offline simulations to quantify the sensitivity of surface heat and moisture fluxes to changes in forest composition and structure across daily, seasonal, and annual time scales. For the region on average, it is found that broadleaved deciduous forests cool the surface by 0.16 K annually and 0.3 K in the growing season owed to higher year‐round albedo and lower Bowen ratio, yet in some locations the local cooling can be as much as 2.4 K and 3.0 K, respectively. Moreover, fully developed forests cool the surface by 0.04 K annually in our domain owed to higher evapotranspiration, reaching up to 0.4 K locally in some locations, whereas undeveloped forests warm annually by 0.14 K owed to much lower evapotranspiration reaching up to 0.8 K for some locations. If regional forests are ever to be managed for the local climate regulation services that they provide, our results are an important first step illuminating the potential adverse impacts or benefits across space and time.

Integration of dendrochronological and palaeoecological disturbance reconstructions in temperate mountain forests

Disentangling the long-term changes in forest disturbance dynamics provides a basis for predicting the forest responses to changing environmental conditions. The combination of multidisciplinary records can offer more robust reconstructions of past forest disturbance dynamics. Here we link disturbance histories of the central European mountain spruce forest obtained from dendrochronological and palaeoecological records (fossil pollen, sedimentary charcoal, bark beetle remains and geochemistry) using a small glacial lake and the surrounding forest in the Šumava National Park (Czech Republic). Dendrochronological reconstructions of disturbance were created for 300-year-long records from 6 study plots with a minimum of 35 trees analyzed for the abrupt growth increases (releases) and rapid early growth rates, both indicative of disturbance events. High-resolution analysis of lake sediments were used to reconstruct 800-year long changes in forest composition and landscape openness (fossil pollen), past fire events (micro- and macroscopic charcoal), bark beetle occurrence (fossil bark beetle remains), and erosion episodes (geochemical signals in the sediment) potentially resulting from disturbance events.Tree-ring data indicate that disturbances occurred regularly through the last three centuries and identify a most intensive period of disturbances between 1780 and 1830 CE. Geochemical erosion markers (e.g. K, Zr, % inorganic) show greater flux of catchment sediment and soils in the periods 1250–1400 and 1450–1500 CE, before a substantial shift to a more erosive regime 1600–1850 and 1900 CE onwards. Pollen records demonstrate relatively small changes in forest composition during the last 800 years until the beginning of the 20th century, when there was decrease in Picea. Fossil bark beetle remains indicate continuous presence of bark beetles from 1620s to 1800s, and charcoal records suggest that more frequent fires occurred during the 18th century. Each of the dendrochronological, palaeoecological and sedimentological records provide a unique perspective on forest disturbance dynamics, and combined offer a more robust and complete record of disturbance history. We demonstrate that sedimentary proxies originating from the lake catchment mirror the forest disturbance dynamics recorded in the tree-rings. The multidisciplinary records likely record forest disturbances at different spatial and temporal scales revealing different disturbance characteristics. Integrating these multidisciplinary datasets demonstrates a promising way to obtain more complete understanding of long-term disturbance dynamics. However, integrating datasets with variable spatial and temporal influence remains challenging. Our results indicated that multiple disturbance factors, such as windstorms, bark beetle outbeaks and fires, may occur simultaneously creating a complex disturbance regime in mountain forests, which should be considered in forest management and conservation strategies.

Paleoecological and paleolandscape modeling support for pre-Columbian burning by Native Americans in the Golden Trout Wilderness Area, California, USA

Though people have used fire to alter landscapes across North America for millennia, there remains a debate whether Native Americans altered California’s mountainous forests to create an anthropogenic landscape. We use paleoecological reconstructions and paleolandscape modeling to test whether climate or Native Americans were the driving force of pre-historic forest composition change. Understanding pre-historic forests and land-use legacies becomes more critical in a warming climate as wildfires become deadlier and more extensive. We performed a sub-centennial pollen and charcoal reconstruction for the last 1200 years using standard techniques. We then used a forest succession model to quantitatively test drivers of change: climatic fires only, or the addition of Native American-set surface fires. Hypothesized periods of anthropogenic burning were inferred from the pollen record (more open canopy taxa than climatically expected). Modeled outputs were compared against the paleorecord to determine which drivers best explained changes in the empirical record. Periods of occupation from the archaeological record were compared to hypothesized periods of burning. Pollen and charcoal reconstructions showed intermittent periods inconsistent with climatic expectations. Modeled scenarios including surface fires set by Native Californians during these periods had the greatest correlation with the observed paleoecological record. Inferred periods of burning corresponded temporally with site used based on the archaeological record. California’s pre-historic forests were altered by the traditional use of fire as a tool by Native Americans. Modeled outputs hint that incorporating indigenous resources management practices could improve forest health and decrease the likelihood of catastrophic wildfires.

Impacts of mountain pine beetle outbreaks on lodgepole pine forests in the Intermountain West, U.S., 2004–2019

Mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), is the most important forest insect in western North America. We determined causes and rates of tree mortality and changes in forest structure and composition associated with D. ponderosae outbreaks in the Intermountain West, U.S. during 2004–2019 based on a network of 125 0.081-ha circular plots installed in Colorado, Idaho, Montana, Utah and Wyoming. Incipient populations of D. ponderosae began in 2004; peaked in 2007; and returned to endemic levels in 2011 in Idaho, Montana, Utah and Wyoming. In Colorado, incipient populations began in 2004; peaked in 2009; and returned to endemic levels in 2012. A total of 5107 trees died, 98.6% were lodgepole pine, Pinus contorta Dougl. ex Loud. Fifteen contributing factors were identified, including (in order of importance, highest to lowest) D. ponderosae, unknown causes, pine engraver, Ips pini (Say), wind, breakage and/or adjacent tree fall, Pityogenes knechteli Swaine/Pityopthorus confertus Swaine, suppression, spruce beetle, Dendroctonus rufipennis (Kirby), root disease, western balsam bark beetle, Dryocoetes confusus (Swain), lodgepole pine dwarf mistletoe, Arceuthobium americanum Nutt. ex. Engelm., stem diseases, woodborers, North American porcupine, Erethizon dorsatum (L.), mule deer, Odocoileus hemionus (Rafinesque), and lodgepole pine beetle, Dendroctonus murrayanae Hopkins. Most tree mortality (68.8%) was attributed solely to D. ponderosae, although D. ponderosae also occurred in association with other contributing factors. Overall, significant reductions in mean dbh (by 5.3%), mean quadratic mean diameter (by 8.6%), mean tree height (by 15.9%), mean number of trees (by 40.8%), mean basal area (by 52.9%), and mean stand density index (SDI) (by 51.8%) were observed. Significant reductions in tree density were observed in all diameter classes, except the smallest (midpoint = 10 cm, 5-cm classes). Significant increases in the mean number of snags (by 1324.7%) were observed, and most snags remain standing (71.3%). Pinus contorta remains the dominant tree species, and while significant increases in the number of subalpine fir, Abies lasiocarpa (Hooker) Nuttall, seedlings and saplings were observed, a long-term shift in tree composition is unlikely. Tree mortality (number of trees killed) was positively correlated with the initial number of live trees, basal area of live trees, SDI, and aspect, but not slope or elevation. The implications of these and other results to recovery and management of P. contorta forests in the Intermountain West are discussed.

Demographic shifts in eastern US forests increase the impact of late‐season drought on forest growth

While forest communities are changing as a result of global environmental change, the impacts of tree species shifts on ecosystem services such as carbon storage are poorly quantified. In many parts of the eastern United States (US), more xeric‐adapted oak‐hickory dominated stands are being replaced with mesic beech‐maple assemblages. To examine the possible impacts of this ongoing change in forest composition, we investigated how two wide‐ranging and co‐occurring eastern US species – Acer saccharum (sugar maple) and Quercus alba (white oak) – respond to interannual climate variability. Using 781 tree cores from 418 individual trees at 18 locations, we found late‐growing season drought reduced A. saccharum growth more than that of Q. alba. A gradient in the growth reduction across latitude was also found in A. saccharum, where southern populations of A. saccharum experienced greater reductions in growth during drought. Drought had a legacy effect on growth for both species, with drought occurring later in the growing season having a larger legacy effect. Consequently, as forests shift from oak to maple dominance, drought in the later part of the growing season is likely to become an increasingly important control on forest productivity. Thus, our findings suggest that co‐occurring species are responding to environmental conditions during different times in the growing season and, therefore, the timing of drought conditions will play an important role in forest productivity and carbon sequestration as forest species composition changes. These findings are particularly important because the projected increases in potential evapotranspiration, combined with possible changes in the seasonality of precipitation could have a substantial impact on how tree growth responds to future climatic change.

Responses of soil quality indicators to innovative and traditional thinning in a beech (Fagus sylvatica L.) forest

Soil has a pivotal role in keeping high the productivity of forest ecosystem but its physical and chemical properties are highly influenced by changes in forest species composition and forest management practices. Thinning is the most effective silvicultural practice used in Europe to increase the ecological and economic value of forest stands. The aim of this study was to identify the most appropriate forestry practice to preserve soil fertility and biodiversity in a beech (Fagus sylvatica L.) forest in Calabria, southern Italy. The effects of innovative (T3) and traditional (T2) thinning on soil properties with respect to unmanaged forest (T1) were assessed by using biological indicators. Results showed that T2 had the highest dissolved organic carbon (DOC) and the lowest water content (WC), organic carbon (OC) and nitrogen (N) amount. The humification index was the highest in T2 as well as fungi, ergosterol, fluorescein diacetate hydrolase (FDA) and catalase (CAT). The highest values of NO3−, SO4−, Na+, Mg2+ and Ca2+ were found in the T2. QBS-ar was significantly higher in T2 and T3 than in the T1. In short, our results evidenced that organic matter, total nitrogen, C/N ratio and water content cannot be considered alone or in combination indices of quality to evaluate the effect of thinning on soils. Rather, is the data crossing of microbiota and ions with organic matter pools (stable and labile) that can give important and accurate information on how thinning can affects soil biological properties that are strictly correlated to soil fertility and quality.

Initial response of understorey vegetation and tree regeneration to a mixed‐severity fire in old‐growth Araucaria–Nothofagus forests

AbstractQuestionsFire is a key factor influencing Araucaria araucana forests, but the impact of fire severity on the understorey vegetation is not well understood. In this study we seek to answer the following questions: (a) how do initial plant diversity, composition and spatial distribution of the understorey vegetation change in response to different levels of fire severity; and (b) does the abundance of dominant tree species exhibit different patterns across a fire severity gradient shortly after fire?LocationOld‐growth Araucaria araucana–Nothofagus pumilio forests in the Andes of south‐central Chile (38° S, 71° W) burned in 2015.MethodsWe evaluated the post‐fire plant regeneration across a fire severity gradient ranging from unburned forests to areas of high fire severity. One year after fire (in February 2016), we measured woody and herbaceous species richness, abundance, height, origin (native vs exotic species), life forms and the spatial pattern of plant recovery.ResultsPlant species richness and abundance were significantly higher within the unburned forest and low fire severity areas one year after fire, compared to areas of high and moderate fire severity. Overall, nearly 50% of the species present in the unburned forest were not found in areas of high severity, including the tree Nothofagus pumilio. Rapid vegetative resprouting of pioneer species such as Chusquea culeou resulted in an aggregated spatial distribution of plants after fire.ConclusionsPlant diversity and the abundance of Araucaria araucana and Nothofagus pumilio were reduced in areas of high fire severity one year after fire. Exotic species were more abundant within areas of low severity, being likely mediated by cattle browsing. Our research makes clear the potential changes in forest composition and structure if dominant tree species are not capable of recovering after fire. We recommend the exclusion of cattle within fire‐affected areas and planting Nothofagus pumilio in areas of high fire severity.