Conifer-dominated Forests Research Articles

Fungal and beetle diversity in deciduous fine woody debris in spruce-dominated forests in relation to substrate quantity and quality

AbstractDeciduous fine woody debris (DFWD) is a common deadwood substrate type in boreal conifer-dominated forests, but it is usually present in low volumes, and its importance for deadwood dependent biodiversity is poorly understood. In this study, we investigated how DFWD-associated fungal and beetle diversity depends on local substrate availability and quality, and how species diversity differs between DFWD and coarse deciduous deadwood (birch logs) in boreal mixed spruce-dominated forests in southern Finland. We studied 25 forest plots (each 0.16 ha), measuring and sampling all pieces of DFWD with a diameter of 2–5 cm and minimum length of 50 cm. Wood-inhabiting fungi were surveyed from wood samples by DNA metabarcoding and saproxylic beetles were surveyed by bark sieving. Our results showed a clear positive relationship between DFWD abundance and the diversity of fungi and beetles. Tree species and decay class diversity were not important in explaining fungal and beetle diversity or community composition, possibly due to low degree of variation in DFWD quality among the study plots. DFWD hosted more diverse fungal assemblages than birch logs, including species of conservation concern, while no red-listed beetle species were observed on DFWD. Overall, species assemblages associated with fine and coarse deciduous deadwood were non-nested. Thus, DFWD represents a non-redundant complementary deadwood resource type alongside coarse deciduous deadwood in boreal forests.

A maritime location reduced palynofloral turnover and extirpation across the end Cretaceous boundary interval on the west coast of Canada

A well-preserved suite of ∼163 spore-pollen taxa from a recently discovered K/Pg interval within the maritime Oyster Bay Formation, Vancouver Island, British Columbia, Canada, reveals a pattern of floral turnover across the boundary event with local extirpations of ∼15 % of Cretaceous taxa. Along the margin of the eastern North Pacific, a shift occurred in near-coastal vegetation composition from uppermost Cretaceous diverse fern and bryophyte-dominated communities to Danian conifer-dominated forests with a fern understory. The ‘fern spore spike’ common in other K/Pg records was not detected within the sandstone to mudstone sequence. Spore-pollen assemblages preserved herein align with those of the Continental Margin floristic province. Palm pollen is noteworthy in the studied sections including Arecipites spp. (aff. Arecaceae), Spinizonocolpites spp. (aff. Nypa) and Pandaniidites typicus (aff. Pandanus) suggesting a warm, frost-free, sub-tropical climate prevailed across the K/Pg interval. The presence of numerous endemic spore-pollen taxa is indicative of geographic isolation from the North American Western Interior. Maritime climate buffering along the west coast of North America contributed to microrefugia permitting greater stability in terrestrial plant communities than in continental regions.

Floristic Diversity and Green-Tree Retention in Intensively Managed Temperate Forests: A Case Study in Puebla, Mexico

Clearcutting has tended to simplify forest structure and species composition, with potential negative consequences for biodiversity. Retention forestry emerged as an alternative to minimize this concern in intensively managed forests. In central Mexico, this approach was first implemented a decade ago in temperate forests, but an examination of its effects on floristic diversity and composition is non-existent. We evaluated and compared richness, diversity, and floristic composition among harvested, retention, and conserved areas in a conifer-dominated forest of central Mexico, with various parametric and non-parametric analyses. Species’ ecological and structural importance was also evaluated. We recorded 138 species, 95 genera, and 44 families of plants. Harvested areas listed the most species (99) with herb dominance, tree homogeneity, and the highest number of exotics. Retention and conserved areas’ floristic composition was similar, with the presence of epiphytes and terrestrial orchids, considered indicators of conservation. The retention areas recorded rare and endangered species, tree heterogeneity, and juveniles of structural species of temperate forests. Conserved areas showed a greater number of structural mature elements and exclusive species, though there was a smaller species number (75). We demonstrated that retention forestry is achieving its goal by maintaining the structural elements, habitats, and plant diversity of the temperate forests analyzed.

First evidence of nitrogen fixation associated with bryophytes from coastal Wabanaki–Acadian forests

Associations between bryophytes and dinitrogen (N2)-fixing bacteria are a significant source of exogenous N in unmanaged boreal and possibly temperate ecosystems. However, the extent to which biological N2-fixation (BNF) applies to the boreal–temperate ecotone remains elusive. The current focus on common species limits our understanding of BNF at the community level. Our objective was to characterize the presence of cyanobacteria and BNF activity associated with bryophytes in the coastal forests of Fundy National Park (New Brunswick, Canada). In 2021, we harvested three liverwort and 11 moss species from two sites (71 samples) and measured environmental covariates (e.g., canopy composition and soil pH). We used stable isotope incubations with 15N2 gas in growth chambers to quantify potential BNF activity and used phycocyanin extractions as a cyanobacteria abundance proxy. Many species presented detectable BNF rates, which were similar to or higher than those of well-studied feather mosses. These included species that have rarely been found to contribute to BNF. While cyanobacteria were present on most samples, we found no positive association between abundance and BNF. Our findings are among the first records for bryophyte-associated BNF in the boreal–temperate ecotone of eastern Canada and offer insights into the potential role of this process in N cycling in coastal conifer-dominated forests.

Multiproxy palaeoenvironmental reconstruction of the Bathonian Castelbouc sauropod tracksite (Causses Basin, southern France): Insight into a Middle Jurassic insular ecosystem

We report lignitic fossil rich-beds from the Bathonian Castelbouc sauropod tracksite (Castelbouc Cave N°4, Causses Basin, southern France). Showing the co-occurrence of amber with plant, vertebrate and invertebrate remains, they are a precious tool to reconstruct Middle Jurassic dinosaur ecosystems. A multiproxy approach combining sedimentology, petrology, mineralogy and palaeontology led to determine that these fossil rich-beds were deposited in a range of insular coastal palaeoenvironments. They include protected backshore areas such as freshwater/brackish ponds and brackish bay/lagoon showing co-occurrence of terrestrial and marine inputs. The backshore environments were particularly rich in ostracods (Darwinula sp., Fabanella bathonica) and gyrogonites of charophytes (Porochara douzensis). The abundance of conifer remains including leafy axes (Brachyphyllum), cones (cf. Classostrobus), wood (Brachyoxylon) and pollen grains (Classopollis) shows that ponds and bay/lagoon were bordered by conifer-dominated forests in which Cheirolepidiaceae were the main component. Such a rich and relatively diverse flora was probably an attractive source of food for megaherbivorous dinosaurs. Vertebrate microremains mostly consist of fish scales (Ginglymodi indet.) and crocodylomorph teeth (Atoposauridae indet.), two groups that are common components of Middle Jurassic paralic faunas. The palaeobotanical assemblage suggests a warm subtropical climate probably tropophilous with marked alternation between a wet and a dry season.

Branching out: species-specific canopy architecture limits live crown fuel consumption in Intermountain West USA conifers

BackgroundAccurate estimates of available live crown fuel loads are critical for understanding potential wildland fire behavior. Existing crown fire behavior models assume that available crown fuels are limited to all tree foliage and half of the fine branches less than 6 mm in diameter (1 h fuel). They also assume that this relationship is independent of the branchwood moisture content. Despite their widespread use, these assumptions have never been tested, and our understanding of the physiochemical properties that govern live crown flammability and consumption remains limited. To test these assumptions, we sampled branches from 11 common Intermountain West USA conifers and determined the corrected available fuel estimates using physiochemical measurements, diameter subsize class distributions, and a bench-scale consumption experiment. Additional branches were air-dried to explore interaction between moisture content and consumption. Corrected available live crown fuel was compared to existing models across species and then used to determine potential differences in crown fire energy release.ResultsAcross the 11 common conifers, distinct patterns of sub 1 h fuel distributions were strong predictors of whether the existing available live crown fuel models overestimated, approximately correctly estimated, or underestimated available live fuel. Fine branchwood distributions generally fell into three archetypes: fine skewed, normally distributed, and coarse skewed. Based on our corrected estimates, existing models overestimated the potential canopy energy by 34% for an average-sized western larch and underestimated it by 18.8% for western hemlock. The critical fine branchwood consumption diameter varied with species and moisture content. Larger proportions of fine branches were consumed as the branchwood dried, and nearly all the 1 h fuel was consumed when the branches were completely dry.ConclusionsThese results suggest that available live canopy fuel load estimates should consider species and moisture content to accurately assess and map fuel loads across landscapes. This work has implications for forest and fire management in conifer-dominated forests throughout western North America, and in other similar forests worldwide.

Palynological data from the hauterivian Avilé Member, Pampa Tril section, Agrio Formation, Neuquén Basin, Argentina

The present contribution provides data to the palynological characterization of the non-marine deposits of the Avilé Member, Agrio Formation (Pampa Tril and San Eduardo sections), Neuquén Basin, Argentina. The Avilé Member, which represent a low-order regressive event, is one of the most important hydrocarbon reservoirs in the subsurface of the eastern part of the basin. A continental palynological association mainly represented by gymnosperms with Classopollis as a dominant taxon was recorded. The findings of Shambeipollenites proxireticulatus in the unit, extend the biostratigraphical range of the species to the Hauterivian and suggest the Neuquén Basin as an important dispersal place for the species within Gondwana landmass during the Early Cretaceous. A conifer-dominated forest was indicated by the pollen assemblage. The high percentages of Classopollis, the presence of pollen with Gnetidae affinity (Weltwischia/Ephedra) added to the evidence of fluvial-aeolian interaction given by the lithology, may be indicative of a deposition in a dryland setting. The recovered palynoflora was compared to published palynological data from different units underlying and overlying the Avilé Member, in order to evaluate the response of the vegetation in the central part of the basin, during the onset of non-marine accumulation relative to a sea level fall and the subsequent flooding again of the basin. An important variation in abundance between two groups of conifers (Cheirolepidiaceae versus Araucariaceae) is observed throughout the Agrio Formation members. Going up in the stratigraphic column there is an evident increase in abundance of Araucariaceae and a decrease in Classopollis and ferns spores.

Increasing spruce budworm defoliation increases catchment discharge in conifer forests

Forest insect outbreaks cause significant reductions in the forest canopy through defoliation and tree mortality that modify the storage and flow of water, potentially altering catchment runoff and stream discharge patterns. Despite a growing understanding of the impacts of insect outbreaks on the hydrology of broadleaf forests, little is known about these impacts to catchment hydrology in northern conifer-dominated forests. We measured the effects of cumulative defoliation by spruce budworm (Choristoneura fumiferana) on stream discharge and runoff in 12 experimental catchments (6.33–9.85 km2) across the central Gaspé Peninsula in eastern Québec, Canada over a three-year period (2019–2021). Six catchments were aerially treated with BtK (Bacillus thuringiensis kurstaki) insecticide to suppress the outbreak and six catchments were left untreated, leading to a defoliation gradient across the study sites. Stage-discharge relationships were established between June and October from 2019 to 2021. Stream volumetric discharge (r = 0.71, p < 0.01, t(34) = 5.85), runoff (r = 0.55, p < 0.01, t(34) = 3.81) and runoff ratios (r = 0.67, p < 0.01, t(33) = 5.19) were all strongly positively correlated with cumulative defoliation intensity, likely by reducing available water storage in the catchment and therefore enhancing runoff generation. Seasonally, volumetric discharge, runoff, and runoff ratios were more strongly correlated with defoliation in the summer than autumn months, likely because available catchment storage was more limited following the freshet. Overall, we found that insect defoliation impacts forested catchment hydrology similar to other landscape disturbances, and such consequences should be considered in forest management and the control of forest insect outbreaks.

Nesting-tree preferences of the black woodpecker—the biggest cavity excavator in a conifer-dominated forests in Poland

The black woodpecker Dryocopus martius is an ecologically disproportionately important forest species owing to its abundance. Its large cavities provide breeding sites and shelter for many species—large birds, mammals, and social insects. I evaluated the nest tree preferences of black woodpeckers in the Augustów Forest, northeast Poland. Approximately 400 black woodpecker cavities were observed. The Scots pine, Pinus sylvestris, was the most commonly selected tree species, accounting for 90%. The cavity trees were 55–225 years old. All trees younger than 90 years were broadleaved tree species. The trees used to excavate the cavities had a larger diameter at the breast height (DBH) than the average of the stand. The trees selected by black woodpeckers were significantly shorter than the average height of the stands. Over 60% of the cavities were excavated 10–16 m above ground level. I found that the DBH and the first branch height were critical factors affecting the cavity entrance height. In pine-dominated forests, black woodpeckers preferred dead trees. Approximately 44% of new cavities were excavated from dead trees. Leaving dead or dying large trees in commercial forests benefits black woodpeckers and large secondary cavity nesters that depend on it and promotes biodiversity conservation. Birds excavate new cavities at a high rate yearly, in contrast with beech-dominated forests.

The dawn of the Late Villafranchian: Paleoenvironment and age of the Pantalla paleontological site (Italy; Early Pleistocene)

Biochronology is the most widely used method for organizing the successions of continental vertebrate faunas in geological time and for allowing the correlation of continental deposits. However, due to the fragmentary nature of the paleontological record and the diachronicity of first and last occurrences of vertebrate taxa in different areas (i.e., bioevents), it is difficult to precisely define the temporal boundaries between biochronological units. That is why it is crucial to calibrate biochronological data with independent proxies wherever possible. Here, thanks to an interdisciplinary approach that combines sedimentology and stratigraphy, vertebrate paleontology, micropaleontology (ostracods), palynology, and geochronology, we provide a chronological framework and a paleoenvironmental reconstruction of the paleontological site of Pantalla (Central Italy). The combination between biochronological/biostratigraphic and geochronological (U-series/ESR dating and paleomagnetism) data allows us to refer the site to c. 2.2 Ma, i.e., in the transition phase between the Middle and Late Villafranchian in the European biochronological scheme. We reconstruct the environment as a fluvial area with a frequently flooded wet floodplain and marked (probably seasonal) variations of the water level of the channel river. The depositional system was surrounded by a conifer-dominated forest, which is suggestive of a glacial phase.

Vegetation type change in California’s Northern Bay Area: A comparison of contemporary and historical aerial imagery

The North Bay area of California is a populous and ecologically diverse area that has experienced significant changes in the past century, as well as a series of recent wildfires, after over a century of fire suppression practices. While much research has been conducted quantifying drivers and patterns of vegetation change in conifer-dominated ecosystems, and how such changes have influenced current trends in fire behavior, studies of similar focus and scale are rarer in non-conifer ecosystems, including mixed-hardwood forests or shrub-dominated ecosystems in central and coastal Northern California. This is despite the fact that ecosystems other than conifer forests make up the majority of area burned in California wildfires. As such, expanding research focused on patterns of large-scale vegetation change as a possible driver of this trend in this area is a priority. In this study, we sought to map the overall extent and patch sizes of broad vegetation classes across a 52,000 ha study area based on historical (1948) and contemporary (2014) aerial imagery and to investigate shifts in vegetation patterns, as well as potential pathways and drivers of detected changes. We classified vegetation types through segmenting our imagery into homogenous polygons, and assigning broad vegetation categories using a random forest algorithm. We then analyzed patterns of change using spatial statistics and conditional inference tree analyses. We detected a large increase (12%) in the relative landscape proportion and average patch size of the forest class, characterized by dense tree canopy cover. Woodlands and shrub patches were most susceptible to type change, with the majority (57% and 65%, respectively) of converted areas subsequently identified as denser forest stands. By contrast, herbaceous and forest patches were most persistent. We additionally found that disturbance history, specifically whether an area burned or not, and topographic variables, including elevation and aspect, were important influences on the likelihood of vegetation persistence, while slope and water availability were not. Historical aerial imagery, which provides fine resolution and accurate data over a large spatial scale, is a useful tool for detecting landscape-scale vegetation shifts in ecosystems where widespread vegetation monitoring was not common historically. The marked increase in dense forest we detected, specifically due to the conversion of large areas of shrub and woodland vegetation may correspond to higher surface and ladder fuel load and continuity, and potentially higher wildfire risk. Fuel reduction treatments typically implemented in conifer-dominated forests may also be warranted in these mixed hardwood forests. However, more research is needed to understand drivers of change in non-conifer-dominated ecosystems in California and how such change influences wildfire behavior.

Shaded fuel breaks create wildfire-resilient forest stands: lessons from a long-term study in the Sierra Nevada

BackgroundIn California’s mixed-conifer forests, fuel reduction treatments can successfully reduce fire severity, bolster forest resilience, and make lasting changes in forest structure. However, current understanding of the duration of treatment effectiveness is lacking robust empirical evidence. We leveraged data collected from 20-year-old forest monitoring plots within fuel treatments that captured a range of wildfire occurrence (i.e., not burned, burned once, or burned twice) following initial plot establishment and overstory thinning and prescribed fire treatments.ResultsInitial treatments reduced live basal area and retained larger-diameter trees; these effects persisted throughout the 20-year study period. Wildfires maintained low surface and ground fuel loads established by treatments. Treatments also reduced the probability of torching immediately post-treatment and 20 years post initial thinning treatments.ConclusionsFuel treatments in conifer-dominated forests can conserve forest structure in the face of wildfire. Additionally, findings support that the effective lifespans of treatments can be extended by wildfire occurrence. Our results suggest that continued application of shaded fuel breaks is not only a sound strategy to ensure forest persistence through wildfire but may also be compatible with restoration objectives aimed at allowing for the use of more ecologically beneficial fire across landscapes.

Estimating the response of Himalayan old-growth mountain forests to decreased monsoon precipitation

Forests in the Himalayas are a major carbon store, but are under threat due to changes in precipitation regime. To simulate a precipitation decline, throughfall-exclusion (TFE) shelters were applied during three consecutive monsoon seasons in an oak forest (2.650 m a.s.l.) and a conifer-dominated forest (3.260 m a.s.l.) in central Bhutan. Leaf water potentials, tree mortality, stem increment, soil CO2 efflux, litterfall and fine root dynamics were assessed. TFE significantly and consistently decreased topsoil (0–30 cm) moisture and leaf water potentials of Quercus lanata and Quercus griffithii (lower elevation), and to a lesser extend those of Tsuga dumosa and Quercus semecarpifolia, (higher elevation). TFE did not impose tree mortality. Stem increment remained unaffected until the second TFE year, but showed reductions during the third year with Tsuga dumosa being most severely affected (-60%). Standing fine root biomass stocks were hardly affected by TFE. Increased root necromass and faster fine root growth in the lower elevation forest suggest that the oak trees increased C allocation below ground. Soil CO2 efflux sharply declined during all three TFE years in both forests. Above ground litter input was unaffected by TFE until the second treatment year. Overall, both forest ecosystems appeared highly resistant to the imposed soil drying, with no signs of tree mortality and stable living root biomass stocks.

Habitat heterogeneity is a good predictor of boreal forest biodiversity

Reliable assessment measures are crucial for tracking changes in biodiversity and for evaluating the state of biodiversity. Two of the main drivers of biodiversity are habitat heterogeneity and resource amount. These drivers are used as proxies of biodiversity but assessing both is costly, limiting their practical use. To test which of the drivers best predicts the number and abundance of sessile species of conservation concern (including macrofungi, lichens, bryophytes, and vascular plants), we assessed forest stand heterogeneity using a method developed in Sweden (‘Habitat Heterogeneity Score HHS’), and quantified the resource amount and quality of ecologically important structural variables (deadwood volume, basal area of living trees, proportion of broadleaved trees, and the age of the oldest tree in the stand). We conducted the assessments in 77 boreal conifer-dominated forest stands in two regions of Sweden. Despite some group-specific organism differences, HHS was the best predictor of both number and abundance of all species of conservation concern, regardless of the region. Further, HHS was the best predictor of red-listed species number and abundance in the southern region, while a model including the volume of deadwood and the age of the oldest tree performed best in the northern region. Deadwood (CWD) volume was the single best resource amount predictor of the number and abundance of species of conservation concern, emphasizing the critical role that dead trees have for biodiversity. In addition, we calculated threshold values for deadwood volume and HHS depicting the level above which the number of red-listed species is significantly higher, and found this value to be higher in the southern region (22.4 m3 ha−1 deadwood and a HSS value of 17) than in the north (20.0 m3 ha−1 and 16). These values can be used as guidance when identifying coniferous forests with high enough qualities to support red-listed species. To conclude, the method of assessing habitat heterogeneity presented in this study is a practical and reliable way to identify forests of high biological diversity, and can therefore be part of the toolbox for sustainable forestry in boreal forests.

Low-elevation conifers in California's Sierra Nevada are out of equilibrium with climate.

Since the 1930s, California's Sierra Nevada has warmed by an average of 1.2 C. Warming directly primes forests for easier wildfire ignition, but the change in climate also affects vegetation species composition. Different types of vegetation support unique fire regimes with distinct probabilities of catastrophic wildfire, and anticipating vegetation transitions is an important but undervalued component of long-term wildfire management and adaptation. Vegetation transitions are more likely where the climate has become unsuitable but the species composition remains static. This vegetation climate mismatch (VCM) can result in vegetation conversions, particularly after a disturbance like wildfire. Here we produce estimates of VCM within conifer-dominated forests in the Sierra Nevada. Observations from the 1930s Wieslander Survey provide a foundation for characterizing the historical relationship between Sierra Nevada vegetation and climate before the onset of recent, rapid climate change. Based on comparing the historical climatic niche to the modern distribution of conifers and climate, ∼19.5% of modern Sierra Nevada coniferous forests are experiencing VCM, 95% of which is below an elevation of 2356 m. We found that these VCM estimates carry empirical consequences: likelihood of type-conversion increased by 9.2% for every 10% decrease in habitat suitability. Maps of Sierra Nevada VCM can help guide long-term land management decisions by distinguishing areas likely to transition from those expected to remain stable in the near future. This can help direct limited resources to their most effective uses-whether it be protecting land or managing vegetation transitions-in the effort to maintain biodiversity, ecosystem services, and public health in the Sierra Nevada.

Early Jurassic dinosaur-dominated track assemblages, floristic and environmental changes in the Holy Cross Mountains region, Poland

The Early Jurassic succession of the Holy Cross Mountains region in Poland offers a rare opportunity to study ecosystem complexity during the evolution and diversification of early dinosaurs, especially herbivorous ones. The section consists of continental and coastal deposits containing fossil assemblages spanning nearly 25 My of changes in terrestrial plants and some groups of invertebrates and tetrapods. Based on macrofossils and pollen and spores, the broader characteristics of the flora in this succession are presented. The floral assemblages show typical Early Jurassic characteristics and contain lycopsids, sphenopsids, ferns, cycadaleans, bennettitaleans, gnetaleans and ginkgoaleans, as well as conifers, and are similar to other Hettangian–Toarcian floral successions in Europe, showing the presence of a vast coniferous forest dominated by Hirmeriella in the early Hettangian, replaced by ginkgophyte-dominated floras in younger stages and araucarian conifer-dominated forests in the late Pliensbachian. Dinosaurs are documented mainly from their trace fossils (tracks and coprolites). Six distinct track assemblages (stratigraphically separated ichnoassemblages) of different ages can be identified. Current evidence indicates that while Anomoepus tracks are abundant throughout the long Hettangian–late Pliensbachian interval, medium-sized to large ornithischian tracks do not occur below the lower–middle Hettangian transition zone, associated with the first major marine transgression in the region. Hettangian strata with different theropod tracks ( Grallator, Anchisauripus, Eubrontes, Kayentapus , cf. Megalosauripus ), small Anomoepus tracks, numerous medium-sized Anomoepus -like tracks, Moyenisauropus tracks, tetradactyl tracks of sauropodomorphs (cf. Pseudotetrasauropus ) and oval-shaped tracks of sauropods ( Parabrontopodus ) significantly contrast with the higher part of the Lower Jurassic succession (upper Pliensbachian Drzewica Formation and middle–upper Toarcian Borucice Formation) containing new types of medium-sized to large theropod tracks ( Therangospodus ), small and medium-sized bird-like tridactyl tracks (cf. Trisauropodiscus , cf. Anomoepus ), exceptionally large, oval-shaped sauropod tracks ( Sauropoda indet.), and new types of medium-sized and large ornithischian tracks (cf. Deltapodus , cf. Anomoepus ). This points to a noticeable difference between the Hettangian and late Pliensbachian–Toarcian dinosaur ichnofaunas and may facilitate the study of regional and global changes and correlations. Both the palaeofloras and dinosaur trace fossils document ecosystem diversity and ecosystem changes, presented here in review form. The nature of these changes requires more detailed study, but preliminary results suggest the occurrence of rather complex and pronounced transformations in the dinosaur communities of the Holy Cross Mountains region. Based on our observations, the most significant event in Early Jurassic ecosystems took place within the Hettangian (change in floristic composition, the emergence of new groups of dinosaurs), but we also found what we believe to be a record of a major faunal turnover across the late Pliensbachian–middle–late Toarcian interval.

There is still time to reconcile forest management with climate-driven declines in habitat suitability for boreal caribou

Many boreal populations of woodland caribou in Canada are declining, mainly due to the prevalence of anthropogenic disturbances which alter predator-prey dynamics. Climate change is expected to exert an additional negative influence on caribou populations in coming decades, but it is unclear whether or how human activities and climate change will interact to influence habitat suitability for caribou, and how important these agents of change will be relative to each other. In this study, we used the LANDIS-II forest landscape model to forecast boreal caribou habitat suitability across its distribution within the harvestable boreal forest in Québec for the period 2020–2100, under three increasing anthropogenic radiative forcing scenarios (baseline, Representative Concentration Pathways [RCP] 4.5 and 8.5), and two contrasting harvest scenarios (with and without harvest). Our simulations revealed that harvesting was the dominant agent explaining future variations in caribou habitat suitability, although climate change also decreased habitat suitability, especially under RCP 8.5. Climate-induced decreases in habitat suitability mostly originated from increases in wildfires that burned mature conifer-dominated forests, i.e., high-quality habitat for caribou. Habitat suitability by 2100 was also predicted to vary spatially, with the northeastern and northwestern parts of the study area supporting better caribou habitat conditions regardless of scenarios. We show that reducing harvest activities in areas where habitat suitability is currently high could help maintain high-quality caribou habitat even under the most intense climate change scenario. Our results also suggest that highly-disturbed regions which currently provide low-quality habitat may not improve in the future unless active habitat restoration is performed. Our study helps disentangle the potential future effects of forest management and climate change as threats to caribou habitat, emphasizing the urgency of reconciling forest management with the conservation of this species at risk in Canada.

Long-Term Impacts of Forest Management Practices under Climate Change on Structure, Composition, and Fragmentation of the Canadian Boreal Landscape

Forest harvesting and fire are major disturbances in boreal forests. Forest harvesting has modified stand successional pathways, which has led to compositional changes from the original conifer-dominated forests to predominantly mixed and hardwood forests. Boreal fire regimes are expected to change with future climate change. Using the LANDIS-II spatially explicit landscape model, we evaluated the effects of forest management scenarios and projected fire regimes under climate change in northeastern Canadian boreal forests, and we determined the subsequent alteration in stand- and landscape-level composition, succession, and spatial configuration of boreal forests. We observed that, in contrast to successional pathways that followed fire, successional pathways that followed forest harvesting favored mixed forests with a prevalence of shade-intolerant hardwoods for up to 300 y after harvesting. This trend was exacerbated under climate change scenarios where forests became dominated by hardwood species, particularly in ecoregions where these species were found currently in low abundance. Our results highlight the failure of existing forest management regimes to emulate the effects of natural disturbance regimes on boreal forest composition and configuration. This illustrates the risks to maintaining ecosystem goods and services over the long term and the exacerbation of this trend in the context of future climate change.

Combustion of Aboveground Wood from Live Trees in Megafires, CA, USA

Biomass combustion is a major biogeochemical process, but uncertain in magnitude. We examined multiple levels of organization (twigs, branches, trees, stands, and landscapes) in large, severe forest fires to see how combustion rates for live aboveground woody parts varied with tree species, size, and fire severity in Ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and mixed conifer-dominated forests of the Sierra Nevada, California, USA. In high severity fire patches, most combustion loss was from branches &lt; 2 cm diameter; in low to moderate severity patches, most was from bole charring. Combustion rates decreased as fire severity declined and with increasing tree size. Pinus species had little branch combustion, leading them to have ≈50% the combustion rate of other taxa. Combustion rates could be 100% for small branch segments and up to 57% for small tree aboveground woody biomass in high severity fire patches. However, combustion rates are very low overall at the stand (0.1%–3.2%) and landscape level (0.6%–1.8%), because large trees with low combustion rates comprise the majority of biomass, and high severity fire patches are less than half of the area burned. Our findings of low live wood combustion rates have important implications for policies related to wildfire emissions and forest management.

Precision thinning – a comparison of optimal stand-level and pixel-level thinning

ABSTRACT Precision forestry allows decision-making on tree level or pixel level, as compared to stand-level data. However, little is known about the importance of precision in thinning decisions and its long-term effects on within-stand variation, stand economy and growth. In this study, silviculture was optimized for Net Present Value (NPV) in 20 conifer-dominated forest stands in hemi-boreal southern Sweden. The precision-thinning approach, Precision Thinning (PT), is compared with a stand-level approach, Stand Level Thinning (SLT) that is optimized for the same criteria but based on stand-level data. The results suggest no substantial long-term benefit or drawback in implementing thinning decisions based on pixel-level data as compared to stand-level data when optimizing stand economy. The result variables NPV and Mean annual increment of living stem volume (MAInet) were not higher for PT than for SLT. The within-stand variation in basal area (m2/ha−1) was lower at the end of the rotation compared to the start of the simulation for both SLT and PT. At the end of the rotation, SLT had higher variation in basal area compared to PT. However, pixel-level information enables adapting the silviculture to the within-stand variation which may favour other forest management goals than strictly financial goals.