Boreal Forest Of Ontario Research Articles

Watershed characteristics and chemical properties govern methyl mercury concentrations within headwater streams of boreal forests in Ontario, Canada

Methyl mercury (MeHg) concentrations in boreal headwater streams are influenced by complex natural processes and disturbances such as forestry management. Understanding drivers of MeHg within boreal streams in Ontario, Canada, is of particular interest as there are legacy MeHg concerns. However, models accounting for the complexity of underlying processes have not yet been developed. We assessed how catchment characteristics and stream water chemistry influence MeHg concentrations within 19 watersheds of the Dryden – Wabigoon Forest in Ontario, Canada, using a structural equation modelling (SEM) approach. Despite the study area encompassing a large variation of boreal forest watersheds in the Canadian Shield, our SEM had substantial explanatory power across the region (χ251 = 45.37, p-value = 0.70, R2 = 0.75). Nitrate concentrations (p-value <0.001), water temperature (p-value = 0.002), and the latent watershed characteristic (p-value <0.001) had a positive influence on MeHg concentrations once variable interactions were accounted. Due to the inherent strengths of applying an SEM approach, we describe two plausible pathways driving MeHg concentrations: 1) indirect effect of forest-derived nutrients increases in-situ MeHg production in Dryden – Wabigoon Forest streams, and 2) direct supply of MeHg from inundated soils following consistent precipitation and inundation events (i.e., fill, sit, and spill).

Individual response traits of understory plants vary along linked-press and compounded-pulse disturbance gradients in northern temperate and boreal forests

Community-weighted means (CWM) and functional dispersion (FDis) of response traits of woody and herbaceous understory plants in northern temperate and boreal forest communities were studied to determine how these traits respond to linked-press (i.e., climate, historic fire regimes, and silviculture systems) and compounded-pulse (i.e., harvest, site preparation, and release treatments) disturbances. We used fifth year post-harvesting disturbance data from the NEBIE plot network (NEBIE), a large-plot field experiment in northern temperate and boreal forests in Ontario, Canada. To analyze treatment effects, a randomized complete block design was assumed. Treatments were applied in a semi-operational manner to two-hectare experimental units. Individual response traits were affected by linked-press and compounded-pulse disturbances in unique ways, with logarithmic (stress-gradient hypothesis) or hump-shaped (intermediate disturbance hypothesis) patterns typically observed. Some traits (i.e., lateral spread of clones, seed weight) did not differ between disturbance types. Results suggest that all interactions between linked-press and compounded-pulse disturbances typically exert non-linear effects on CWM and FDis of individual plant response traits for both woody and herbaceous understory plants in boreal and temperate forests. Specific responses varied with trait, understory layer, and type of disturbance.

P207 A rare case of disseminated Blastomycosis in an immunocompetent host: A report from North India

Poster session 2, September 22, 2022, 12:30 PM - 1:30 PM ObjectivesBlastomycosis is a serious life-threatening systemic infection caused by dimorphic fungi Blastomyces dermatitidis. Infection is acquired via inhalation of airborne conidia or traumatic inoculation. It may produce a spectrum of infections ranging from asymptomatic infections in immunocompetent patients to disseminated disease, including skin, bone, genitourinary tract, and central nervous system (CNS) involvement in immunocompromised patients. This fungal infection is very rare in India. We report a unique case of disseminated blastomycosis in an immunocompetent patient.MethodsA 37-year-old male patient from Kanpur, Uttar Pradesh presented with chief complaints of hematuria associated with passage of blood clots for 3 months. There was no history of dysuria, fever, or pain abdomen. When he was evaluated for gross hematuria, his USG abdomen was suggestive of bilateral renal masses. To rule out bilateral renal cell carcinoma an FDG pet scan was done which was suggestive of FDG avid lesions in the bilateral kidneys. He also had enlarged left supraclavicular and left cervical lymph nodes. Multiple nodular and verrucous lesions were seen all over the face. He complained of pain in the left ankle; with a small wound opening on the medial malleolus of the left ankle.ResultsA skin biopsy was taken from one of the nodular and verrucous lesions over face. A total of 10% wet mount KOH preparation shows no epithelial cells, plenty of pus cells, no RBCs, and plenty of thick-walled round yeasts and some with broad-based budding yeasts (8-12 microns) suggestive of Blastomyces species. Renal abscess pus FNAC, left cervical lymph node, and CT-guided biopsy from the medial malleolus of the left ankle also showed similar round yeasts and some with broad-based budding suggestive of Blastomyces species. Hence, a preliminary diagnosis of disseminated blastomycosis was made.Cultures were put in SDA at 25°C and 37°C and after a week, colonies appeared as fluffy white glabrous with reverse cream-colored non-sporulating colony. On day 25, colony appears as tan glabrous fluffy with brownish reverse with sporulation. LPCB was done from the colony which showed thin septate hyphae with pedunculated and sessile spherical to pyriform and smooth walled microconidia suggestive of Blastomyces dermatitidis.He was started on IV liposomal amphotericin B for 20 days. HCV RNA was detected incidentally and he had transaminitis therefore, he could not be started on itraconazole, he was started on fluconazole. His facial lesions cleared dramatically; his left ankle pain and swelling had resolved. At present, he was symptomatically better and was discharged on 200 mg fluconazole once daily and advised for follow-up after 2 weeks.ConclusionBlastomycosis is a relatively uncommon geographically restricted chronic granulomatous disease that mainly occurs in the endemic regions. This fungus lives primarily in moist soil and decomposing matter, and inhabits the mid-west, south-central, southeastern United States as well as the boreal forests of Ontario and Quebec in Canada. Very little is known about the natural habitat and environmental distribution of Blastomyces species in India. This case is unique because the patient is immunocompetent and has no history of travel outside of India.

Developing a forest inventory approach using airborne single photon lidar data: from ground plot selection to forest attribute prediction

Abstract An increasing number of jurisdictions are integrating airborne laser scanning (ALS) into forest inventory programs to produce spatially explicit and accurate inventories of forest resources. However, wall-to-wall ALS coverage relative to the total area of managed forest remains limited in large forest nations such as Canada, wherein logistics, cost and acquisition capacity can be limiting factors. Technologies such as single photon light detection and ranging (SPL) have emerged commercially, which have the capacity to provide efficient ALS acquisitions over large areas and with a greater point density than conventional linear-mode ALS. However, the large-scale operational application of SPL in a forest inventory still needs to be effectively demonstrated. In this study, we used wall-to-wall SPL data (collected with a Leica SPL100) across a 630 000 ha boreal forest in Ontario, Canada to develop a forest inventory. Specifically, we used a structurally guided sampling approach enabled via a principal component analysis of the SPL100 data to establish a network of 250 ground plots. Random forest models were then used to produce area-based estimates of forest attributes of interest. Results demonstrated that the sampling approach enabled the optimization and enhancement of the existing plot network by extending the range of sampled structural types and reducing the number of plots in oversampled forest types. Moreover, Lorey’s height, basal area, quadratic mean diameter at breast height, stem density, gross and merchantable volume and above-ground biomass were estimated with a relative root mean square error of 8.5, 19.76, 13.97, 30.82, 21.53, 23.79 and 22.87 per cent, respectively, and relative bias &amp;lt;1 per cent. Model accuracies achieved using the SPL100 were comparable with those obtained using linear-mode ALS in a previous forest inventory. This study demonstrates the utility of the SPL100 for the complete development of a forest inventory over large forest areas, from ground plot establishment through to the production of forest attribute estimates.

Harvest volumes and carbon stocks in boreal forests of Ontario, Canada

We used models to project forest carbon stocks for a series of harvesting scenarios for 29 boreal forest management units totalling 23.3 million ha in Ontario, Canada. Scenarios evaluated for 2020 to 2050 ranged from a no harvesting option to annual harvesting of 2% of the total merchantable volume present in 2020. For each scenario, we estimated the following carbon quantities: (a) forest ecosystem carbon stocks, (b) sum of carbon stocks in forest ecosystem and harvested wood products (HWP) minus emissions associated with HWP production and decomposition, and (c) net greenhouse gas (GHG) effects of harvesting estimated as (b) combined with emissions avoided by substituting HWP for non-wood materials. The average of each carbon quantity for 2020 to 2050 was linearly dependent on the annual harvest volume. The developed relationships were used to estimate harvest volumes for which the three carbon quantities would equal equilibrium forest ecosystem carbon stocks for a pre-suppression natural disturbance cycle. These estimates indicate the range of harvest volumes for which resulting carbon stocks would equal or exceed those in an unmanaged forest. Also discussed are possible criteria for determining annual harvest volume.

Predictive Modeling of Black Spruce (Picea mariana (Mill.) B.S.P.) Wood Density Using Stand Structure Variables Derived from Airborne LiDAR Data in Boreal Forests of Ontario

Our objective was to model the average wood density in black spruce trees in representative stands across a boreal forest landscape based on relationships with predictor variables extracted from airborne light detection and ranging (LiDAR) point cloud data. Increment core samples were collected from dominant or co-dominant black spruce trees in a network of 400 m2 plots distributed among forest stands representing the full range of species composition and stand development across a 1,231,707 ha forest management unit in northeastern Ontario, Canada. Wood quality data were generated from optical microscopy, image analysis, X-ray densitometry and diffractometry as employed in SilviScan™. Each increment core was associated with a set of field measurements at the plot level as well as a suite of LiDAR-derived variables calculated on a 20 × 20 m raster from a wall-to-wall coverage at a resolution of ~1 point m−2. We used a multiple linear regression approach to identify important predictor variables and describe relationships between stand structure and wood density for average black spruce trees in the stands we observed. A hierarchical classification model was then fitted using random forests to make spatial predictions of mean wood density for average trees in black spruce stands. The model explained 39 percent of the variance in the response variable, with an estimated root mean square error of 38.8 (kg·m−3). Among the predictor variables, P20 (second decile LiDAR height in m) and quadratic mean diameter were most important. Other predictors describing canopy depth and cover were of secondary importance and differed according to the modeling approach. LiDAR-derived variables appear to capture differences in stand structure that reflect different constraints on growth rates, determining the proportion of thin-walled earlywood cells in black spruce stems, and ultimately influencing the pattern of variation in important wood quality attributes such as wood density. A spatial characterization of variation in a desirable wood quality attribute, such as density, enhances the possibility for value chain optimization, which could allow the forest industry to be more competitive through efficient planning for black spruce management by including an indication of suitability for specific products as a modeled variable derived from standard inventory data.

Relative influence of climate, soils, and disturbance on plant species richness in northern temperate and boreal forests

In this study we sought answers to two questions (i) What is the relative influence of silvicultural disturbances on species richness in northern temperate and boreal forests? and (ii) In a scenario where emulating natural disturbances is applied, do collinearity and hierarchical structure exist among climate, soils, disturbance of the forest canopy and forest floor, exotic species, and species richness? By capitalizing on the NEBIE plot network, a large-plot experimental study designed to evaluate the effects of intensification of silviculture on fiber production and biodiversity. We demonstrate that silvicultural disturbances act with contemporary climate, soils, and historic fire regimes to influence plant species richness in northern temperate and boreal forests in Ontario, Canada. Relationships between various factors and plant species richness (total and for each life form: woody, herbaceous, bryophyte, and lichen) were analyzed using general linear (GLM) and structural equation modelling (SEM). Results of GLM indicate that climate accounted for the overwhelming percentage of variation in species richness of each of the plant life form groupings (>50% and often >70%), while soil properties, canopy structure, silvicultural practices, and degree of natural disturbance each accounted for on the order of 10% or less of variation in species richness. Results of fitted SEM suggested strong collinearity and hierarchy among climate, soils, historic fire regimes, and silviculture systems; however, the effect of silvicultural intensity on plant species richness was independent of climate, soils, and historic fire regimes.

Geochemical processes in the formation of ‘forest rings’: examples of reduced chimney formation in the absence of mineral deposits

Forest rings are large circular features common in boreal forests in Ontario, Canada, characterized by ring-shaped topographic depressions in carbonate-rich soil. This paper documents the compositional variation of soil and of the peat that commonly fills the depression, along transects across two representative rings: one centred on an accumulation of CH 4 in glacial sediments and the other on H 2 S in both glacial sediments and bedrock. Clayey mineral soil at the ring edge (annulus) shows low pH, oxidation-reduction potential (ORP), Ca and carbonate, and high Al, Fe and Mn by both aqua regia digestion and a 0.25M hydroxylamine hydrochloride leach (0.25M NH 2 OH.HCl at 60 ° C). Antithetic responses occur in the overlying peat, including elevated carbonate and pH over the areas with low pH, ORP and carbonate in the mineral soil. The observed relationships suggest vertical migration of carbonate species from mineral soil into peat at the annulus, and lateral migration from the annulus to adjacent areas in the mineral soil. The geochemical data support the hypothesis that forest rings are the surface expression of reduced chimneys, similar to those observed over metallic mineral deposits, despite both these sites being known to be barren. Strongly negative ORP values in shallow soils in the annulus suggest autotrophic microbiological activity contributes to the sharp change in redox conditions at the ring boundaries. The similar geochemical responses at forest rings and soils over mineral deposits show that these features can be used to understand the variation in redox, pH, metals and soil hydrocarbons over mineral deposits and to help differentiate ore-related from secondary geochemical features due to the presence of a reduced chimney.

Congruence of community structure between taxonomic identification and T-RFLP analyses in free-living soil nematodes

Abstract Molecular-based methods of community analysis are becoming a popular alternative to the traditional, highly specialized, and time-consuming taxonomic identifications especially for morphologically challenging groups like free-living soil nematodes. In particular, terminal restriction fragment length polymorphism (T-RFLP) analysis has become popular as a quick and efficient tool to provide researchers with broad-scale assessments of community structure. The majority of studies comparing T-RFLP with morphological-based assessments have used cultured or previously characterized communities. Here we compare morphological identification to T-RFLP analyses in a previously unexplored system for nematode diversity, the boreal forest of Ontario, Canada. Samples were collected from five silvicultural treatments over two sampling seasons with nematodes extracted using the Baermann funnel technique. We found significantly greater richness from T-RFLP analyses than morphological identifications at both sampling times, but in both cases silvicultural treatment had no effect. Despite differences in taxonomic richness, community compositional similarities were highly correlated between morphological and molecular methods for both sampling times. We suggest that both methods are reliable in studies of previously undescribed communities where the goal is community assessment under treatment.

Factors influencing the seasonal diet selection by woodland caribou (Rangifer tarandus tarandus) in boreal forests in Ontario

We used remote video cameras to assess seasonal diet composition of woodland caribou (Rangifer tarandus tarandus (L., 1758)) at three areas across the boreal forest of Ontario. Caribou consume lichens in winter, but we expected they would significantly reduce lichen consumption in favour of higher protein levels in green plants in summer. We sampled videos from 23 caribou, from 2 years, to derive seasonal diet composition. Diet differed among seasons and study areas, except in winter when lichens dominated. Diet breadth doubled from winter to summer, but overlap between seasons was still &gt;60%. Green plants were less commonly eaten than we expected, only three genera were preferred, and few species constituted more than 2% of the diet. Preferred foods varied by land-cover types. Diet differed between managed and unmanaged landscapes but did not result from use of plant species found in successional habitats. Caribou selected a nonoptimal diet in the snow-free seasons, especially with respect to protein, suggesting factors other than nutrition influenced diet choice, and indicating the possibility of bottom-up limitation on production.

“Blue-ice”: framing climate change and reframing climate change adaptation from the indigenous peoples' perspective in the northern boreal forest of Ontario, Canada

The northern boreal forest in Ontario, Canada, in the sub-Arctic above the 51st parallel, is the territorial homeland of the Cree, Ojibwe, and Ojicree Nations. These Nations are represented by the political organization Nishnawbe Aski Nation (NAN). January 6–March 31, 2011 the researchers and NAN collaborated in a study to record observations of changes in the forest environment attributed to climate change and share and exchange information and perspectives about climate change. Data were collected from 10 First Nation communities across a geographic area of ∼110,800 km2 (43,000 mi2). We explore climate change impacts through the lens of “blue-ice”, a term embedded in their languages across the fieldwork area and reframe adaptation in the First Nations' perspective and worldview. Changes in blue-ice on the landscape are affecting transportation in traditional activities such as hunting and fishing, as well as the delivery of essential community supplies. The word “adaptation” linked to climate change does not exist in their languages and the term is associated with European colonization. We propose the term “continuity” to reflect the First Nation worldview. Our recommendation is giving First Nations' perspectives and knowledge of their territorial landscape a foundational role in the development of climate change policy for Ontario's northern boreal forest.

Is forest certification delivering on First Nation issues? The effectiveness of the FSC standard in advancing First Nations' rights in the boreal forests of Ontario and Quebec, Canada

Forest certification has become a key driver in efforts towards sustainable forest management. Certification processes include commitments to respect the rights of Aboriginal peoples. However, there has been little investigation into the relationship between certification and Aboriginal rights. This paper examines the effectiveness of certification in addressing a range of First Nation concerns, taking the example of FSC's National Boreal Standard, applied in the provinces of Quebec and Ontario, Canada. This is done through documentary analysis of audit reports for all public land certificates in this region, with particular attention paid to ‘conditions’ (required changes) issued as part of the audit process. Results indicate that 86% of FSC certifications led to at least one condition relating to First Nations' rights, but that most were deemed minor. The two most common issues flagged by conditions were: agreement for the management plan and the evaluation and protection of First Nations' resources and sites. Analysis of subsequent reports revealed that all conditions were resolved within the allotted time period. A qualitative analysis of conditions revealed a tendency for auditors to accept partial conformance when evaluating compliance. We conclude that FSC certification is pushing forest managers to make progress on a wide variety of fronts, but through a lens of ‘continual improvement’ rather than strict conformance with the standard.

Where Have All the Caribou Gone?

As a mid-June sun slid behind a firtipped ridge in the boreal forest of Ontario, Canada, biologists John Fryxell of the University of Guelph and Jim Baker of the Ontario Ministry of Natural Resources were on a mission. They passed the blue waters of Lake Nipigon and skirted cliffs that could be the sheer rock faces of Yosemite before stopping at the railroad hamlet of Nakina. Nakina may be derived from a Cree word meaning “land covered with moss,” a clue to the scientists’ quarry. The “gray ghost,” or caribou, passes almost without a trace through the black spruce and jack pines of the Boreal, as the northern spruce–fir forest is colloquially known. Scientists have dedicated their professional lives to the animal, yet many have never glimpsed it on the ground. Where have all the caribou gone? To find out, Fryxell; Baker; and a team of researchers at Canada’s University of Guelph and Trent University, the Canadian Forest Service, and the Ontario Ministry of Natural Resources are conducting a four-year study of woodland caribou (Rangifer tarandus caribou) in Ontario. Using what is known as a population viability analysis (PVA), the group hopes to determine what has happened to caribou and to learn how to better conserve the animals and their habitat.

The use of dynamic landscape metapopulation models for forest management: a case study of the red-backed salamander

Spatial models of population dynamics have been proposed as a useful method for predicting the impacts of environmental change on biodiversity. Here, we demonstrate advances in dynamic landscape metapopulation modelling and its use as a decision support tool for evaluating the impacts of forest management scenarios. This novel modelling framework incorporates both landscape and metapopulation model stochasticity and allows their relative contributions to model output variance to be characterized. It includes a detailed sensitivity analysis, allowing defensible uncertainty bounds and the prioritization of future data gathering to reduce model uncertainties. We demonstrate this framework by modelling the landscape-level impacts of eight forest management scenarios on the red-backed salamander ( Plethodon cinereus (Green, 1818)) in the boreal forest of Ontario, Canada, using the RAMAS Landscape package. The 100 year forest management scenarios ranged in intensity of timber harvesting and fire suppression. All scenarios including harvesting predicted decreases in salamander population size and the current style of forest management is predicted to produce a 9%–17% decrease in expected minimum population size compared with scenarios without harvesting. This method is amenable to incorporating many forms of environmental change and allows a meaningful treatment of uncertainty.

Evaluating the relationship between trapper harvest of American martens (Martes americana) and the quantity and spatial configuration of habitat in the boreal forests of Ontario, Canada

We investigated the relationship between trapper harvest of martens (Martes americana) and the quantity and spatial configuration of marten habitat on traplines in the eastern and western boreal forests of Ontario. We used region-specific habitat models to estimate the total amount of suitable marten habitat on each trapline, and the proportion of each trapline identified as suitable habitat in various patch size classes. To control for variability in trapper success not associated with habitat, we included an index of trapper effort, as well as variables related to access, temperature, and precipitation as covariates in our regression analyses. Region-specific habitat models identified a positive relationship between the proportion of suitable marten habitat on traplines (irrespective of patch size) and trapper success. Although there did not appear to be an effect of patch size on trapper success in the eastern study region, we observed an effect in the western region. Results from the western study region suggest that traplines with suitable habitat in patches ≥500 ha will have higher trapper success than traplines with similar proportions of suitable habitat but distributed in smaller patches. Our study was conducted in a forested landscape (80% of trapline area was forested). Therefore, our findings should not be applied to areas where suitable marten habitat lies in a matrix comprised of a significant amount of non-forested area.

Stand age, fire and clearcutting affect soil organic carbon and aggregation of mineral soils in boreal forests

Soil organic carbon (SOC) in mineral soil accounts for a large portion of total ecosystem carbon (C) in boreal forests. We evaluated the effects of stand age and disturbance origin on SOC, soil aggregate stability, and aggregate-associated SOC in the boreal forests of Ontario, Canada. Mineral soils at 0–15 cm depth were sampled in 27 stands of six post-fire age classes (2- to 203-year-old) and three post-clearcut age classes (2- to 29-year-old), each with three replications. In post-fire stands, the SOC pool increased from 2- and 10-year-old to 29-, 85- and 140-year-old, and then decreased in 203-year-old stands. Aggregate-associated SOC showed a similar trend. Abundance of water stable aggregates (>0.25 mm in diameter) was the highest in 2-year-old stands. Compared with the same-aged post-fire stands, the SOC pool and aggregate-associated SOC were higher, and aggregate stability was lower in 2- and 10-year-old post-clearcut stands. But the differences in SOC pool, aggregate-associated SOC, and aggregate stability between the two stand origins diminished or became less dramatic in 29-year-old stands. Our results indicate that aggregate stability is more dependent on thermal modification of SOC by fire than on aggregate-associated SOC. Our results also show higher SOC pool and aggregate-associated SOC but lower aggregate stability in post-clearcut than post-fire stands shortly after disturbance; however, differences between the two stand origins diminish when stands become older.

Mixed-effects basal area increment models for tree species in the boreal forest of Ontario, Canada using an ecological land classification approach to incorporate site effects

Summary Individual-tree basal area increment (BAI) models were developed for major tree species in the boreal forest of Ontario, Canada. A composite distance-independent individual-tree BAI model was structured based on the log-linearized gamma base function using a dataset derived from a network of ~1800 permanent growth plots. A suite of fixed effects covariates that included basal area of trees larger than the subject tree, diameter at breast height, stand basal area and latitude, along with ecological land classification ecosites used as a random effect parameter, were found to be significant covariates in the model. A model fitted with the intercept designated as a mixed-effects parameter had a smaller Akaike’s information criterion compared with other competing models. The mixed-effects modelling approach allowed us to select the best suite of covariates by correctly specifying the covariance structure according to the hierarchy of the fitting data. Furthermore, inclusion of ecosite as a random effect parameter increased ecological resolution in the BAI model by localizing its prediction and improves compatibility between growth and yield modelling and other important management tools such as the forest resources inventory.

Coarse root biomass allometric equations for Abies balsamea, Picea mariana, Pinus banksiana, and Populus tremuloides in the boreal forest of Ontario, Canada

Abstract Although coarse root (diameter > 1 cm) biomass can account for approximately 30% of total biomass in forest ecosystems, coarse root biomass models are rarely available, especially for larger trees. In this study, we used a back-hoe excavator and pressurized water to excavate the coarse root systems of large size trees of Abies balsamea L., Picea mariana (Mill.) BSP, Pinus banksiana Lamb., and Populus tremuloides Michx. in the boreal mixedwood forest of central Canada in order to develop allometric equations that link stem diameter at breast-height (DBH) and height to coarse root biomass. All regressions for coarse root biomass using DBH or height alone, or both DBH and height as predictors were significant (R2 ≥ 0.796, P

Recent Widespread Tree Growth Decline Despite Increasing Atmospheric CO2

BackgroundThe synergetic effects of recent rising atmospheric CO2 and temperature are expected to favor tree growth in boreal and temperate forests. However, recent dendrochronological studies have shown site-specific unprecedented growth enhancements or declines. The question of whether either of these trends is caused by changes in the atmosphere remains unanswered because dendrochronology alone has not been able to clarify the physiological basis of such trends.Methodology/Principal FindingsHere we combined standard dendrochronological methods with carbon isotopic analysis to investigate whether atmospheric changes enhanced water use efficiency (WUE) and growth of two deciduous and two coniferous tree species along a 9° latitudinal gradient across temperate and boreal forests in Ontario, Canada. Our results show that although trees have had around 53% increases in WUE over the past century, growth decline (measured as a decrease in basal area increment – BAI) has been the prevalent response in recent decades irrespective of species identity and latitude. Since the 1950s, tree BAI was predominantly negatively correlated with warmer climates and/or positively correlated with precipitation, suggesting warming induced water stress. However, where growth declines were not explained by climate, WUE and BAI were linearly and positively correlated, showing that declines are not always attributable to warming induced stress and additional stressors may exist.ConclusionsOur results show an unexpected widespread tree growth decline in temperate and boreal forests due to warming induced stress but are also suggestive of additional stressors. Rising atmospheric CO2 levels during the past century resulted in consistent increases in water use efficiency, but this did not prevent growth decline. These findings challenge current predictions of increasing terrestrial carbon stocks under climate change scenarios.

Validation of empirical yield curves for natural-origin stands in boreal Ontario

In Ontario, yield tables for forest management planning have remained relatively unchanged since initial work in the 1950s that was based on a limited number of temporary sample plots. In 2000, the Forestry Research Partnership accelerated work on the Benchmark Yield Curve Project (initiated several years earlier by the Ontario Ministry of Natural Resources, OMNR) to update these tables. The resulting yield curves incorporated data from more than 3000 permanent sample plots (PSPs) maintained in Ontario as well as PSPs from neighbouring and ecologically similar jurisdictions. Two stratifications were considered: OMNR’s Northeast Region standard forest units and leading species. The 10 forest units considered cover the major commercial species in the boreal forest in Ontario. Equations were fit to the data to predict the growth and yield by stratum. The equations were validated against independently collected data and compared to predictions from the current wood supply yield curves in Ontario: Plonski’s yield tables, modified Plonski, and northeast regional curves. Results of the validation showed that, with the exception of the MW2 and SF1 forest units, the new yield curves generally had less bias for gross total volume than Plonski and modified Plonski. Results for net merchantable volume were consistent with those for gross merchantable volume. The MW2 and SF1 forest units are more mixed in terms of species type, species light tolerance, and age. A leading species approach resulted in better predictions and is recommended for these forest units. Key words: wood supply, benchmark yield curves, mixedwood yield, yield model, Forestry Research Partnership