David T. Price

A comparison of two statistical methods for spatial interpolation of Canadian monthly mean climate data

Two methods for elevation-dependent spatial interpolation of climatic data from sparse weather station networks were compared. Thirty-year monthly mean minimum and maximum temperature and precipitation data from regions in western and eastern Canada were interpolated using thin-plate smoothing splines (ANUSPLIN) and a statistical method termed ‘Gradient plus Inverse-Distance-Squared’ (GIDS). Data were withheld from approximately 50 stations in each region and both methods were then used to predict the monthly mean values for each climatic variable at those locations. The comparison revealed lower root mean square error (RMSE) for ANUSPLIN in 70 out of 72 months (three variables for 12 months for both regions). Higher RMSE for GIDS was caused by more frequent occurrence of extreme errors. This result had important implications for surfaces generated using the two methods. Both interpolators performed best in the eastern (Ontario/Quebec) region where topographic and climatic gradients are smoother, whereas predicting precipitation in the west (British Columbia/Alberta) was most difficult. In the latter case, ANUSPLIN clearly produced better results for most months. GIDS has certain advantages in being easy to implement and understand, hence providing a useful baseline to compare with more sophisticated methods. The significance of the errors for any method should be considered in light of the planned applications (e.g., in extensive, uniform terrain with low relief, differences may not be important). ©2000 Elsevier Science B.V. All rights reserved.

Spatial distribution of carbon sources and sinks in Canada's forests

Annual spatial distributions of carbon sources and sinks in Canada’s forests at 1 km resolution are computed for the period from 1901 to 1998 using ecosystem models that integrate remote sensing images, gridded climate, soils and forest inventory data. GIS-based fire scar maps for most regions of Canada are used to develop a remote sensing algorithm for mapping and dating forest burned areas in the 25 yr prior to 1998. These mapped and dated burned areas are used in combination with inventory data to produce a complete image of forest stand age in 1998. Empirical NPP age relationships were used to simulate the annual variations of forest growth and carbon balance in 1 km pixels, each treated as a homogeneous forest stand. Annual CO2 flux data from four sites were used for model validation. Averaged over the period 1990–1998, the carbon source and sink map for Canada’s forests show the following features: (i) large spatial variations corresponding to the patchiness of recent fire scars and productive forests and (ii) a general south-to-north gradient of decreasing carbon sink strength and increasing source strength. This gradient results mostly from differential effects of temperature increase on growing season length, nutrient mineralization and heterotrophic respiration at different latitudes as well as from uneven nitrogen deposition. The results from the present study are compared with those of two previous studies. The comparison suggests that the overall positive effects of non-disturbance factors (climate, CO2 and nitrogen) outweighed the effects of increased disturbances in the last two decades, making Canada’s forests a carbon sink in the 1980s and 1990s. Comparisons of the modeled results with tower-based eddy covariance measurements of net ecosystem exchange at four forest stands indicate that the sink values from the present study may be underestimated.

Forest ecosystems, forest management and the global carbon cycle

Globally, forest vegetation and soils are both major stores of terrestrial organic carbon, and major contributors to the annual cycling of carbon between the atmosphere and the biosphere. Forests are also renewable resources, vital to the everyday existence of millions of people, since they provide food, shelter fuel, raw materials and many other benefits. The combined effects of an expanding global population and increasing consumption of resources, however, may be seriously endangering both the extent and future sustainability of the worlds forests. This work covers four main themes: the role of forests in the global carbon cycle, effects of the past, present and future changes in forest land use, the role of forest management, products and biomass on carbon cycling, and socio-economic impacts.

Postulated Feedbacks of Deciduous Forest Phenology on Seasonal Climate Patterns in the Western Canadian Interior

Abstract A large portion of the western Canadian interior exhibits a distinctive seasonal pattern in long-term mean surface temperatures characterized by anomalously warmer conditions in spring and autumn than would be expected from a sinusoidal model. The anomaly is greatest over the southern boreal forest of western Canada, where trembling aspen (Populus tremuloides Michx.)—a deciduous, broad-leaved species—is an important component. In this region, mean temperatures are 2°–3°C warmer in April and October but nearly 2°C cooler in June and July, relative to a best-fitting sinusoidal function. Another feature of the climate in this region is that average precipitation is low (15–30 mm month−1) from October to April but increases sharply during the summer growing season (50–100 mm month−1 from June to August). Eddy correlation and sap flow measurements in a boreal aspen forest indicate profound seasonal changes in transpiration and energy partitioning associated with the deciduous nature of the forest cano...

Estimating fine-root biomass and production of boreal and cool temperate forests using aboveground measurements : A new approach

Information of fine-root biomass and production is critical for quantifying the productivity and carbon cycle of forest ecosystems, and yet our ability to obtain this information especially at a large spatial scale (e.g., regional to global) is extremely limited. Several studies attempted to relate fine-root biomass and production with various aboveground variables that can be measured more easily so that fine-root biomass and production could be estimated at a large spatial scale, but found the correlations were generally weak or non-existed at the stand level. In this study, we tested a new approach: instead of using the conventional way of analysing fine-root biomass at the stand level, we analysed fine-root data at the tree level. Fine-root biomass of overstory trees in stand was first separated from that of understory and standardized to a common fine-root definition of < 2 mm or < 5 mm diameter. Afterwards, we calculated fine-root biomass per tree for a ‘representative’ tree size of mean basal area for each stand. Statistically significant correlations between the fine-root biomass per tree and the diameter at the ground surface were found for all four boreal and cool temperate spruce, pine, fir and broadleaf forest types, and so allometric equations were developed for each group using a total of n = 212 measurements. The stand-level fine-root biomass of trees estimated using the allometric equations agrees well with the measurements, with r2 values of 0.64 and 0.57 (n = 171), respectively, for fine-roots < 2 mmand < 5 mm diameter. This study further estimated fine-root production as the product of fine-root turnover rate and fine-root biomass, and determined the turnover rate as a function of fine-root biomass, stand age, and mean annual temperature. The estimates of tree fine-root production agree well with reported values, with r2 value of 0.53 for < 2 mm and 0.54 for < 5 mm diameter (n = 162) at the stand level.

Integrated forestry assessments for climate change impacts

Forests and the forest sector are sensitive to climate change at greatly varying scales. The complexity of the interactions among the physical environment, forest growth, the management and utilisation of forest resources, and market responses has stimulated efforts to model the impact of global changes on the forest sector by linking impact models developed from different disciplines. This paper reviews existing experiences in integrated forest sector impact assessments. Different ways of integrating cross-disciplinary impact assessments are classified as linking, coupling and integrated modelling. To date the most common method is a “one-way” linking, where results from one model are used as input to a different model. When different impact models are coupled, feedbacks can be analysed, e.g. between ecological and economic systems. Integrated modelling is described as a third step, where different sub-models are embedded into a common model framework. The concept of balance is introduced as a key to successful integration of different disciplines in integrated assessment (IA) studies. The review of existing experiences emphasises the problem of complexity and the need to simplify disciplinary approaches. It also illustrates how methodologies applied to forest sector IA studies have evolved over the last few years. Several scaling issues that are particularly important for IA modelling in forestry are discussed, including the consequences of heterogeneity in site conditions, the variable influence of extreme events on ecosystems and on the economic sector, and the differences in temporal and spatial scales over which key forest growth and renewal processes operate. Climate impact assessments include uncertainties. Some common sources of uncertainty in forest IA modelling are outlined, and methods that have been used to address this uncertainty are reviewed. We discuss the policy relevance of integrated impact assessments and stress the importance of stakeholder involvement in IA projects. The paper concludes with some recommendations for future developments in this relatively new field of research.

Boreal forest responses to climate-change scenarios along an ecoclimatic transect in central Canada

The FORSKA2 patch model was used to simulate responses of forest biomass and species composition to four GCM projections of climate change at 11 locations along a transect oriented northeast-southwest across the boreal zone of central Canada. In agreement with earlier results, FORSKA2 produced estimates of present-day biomass accumulation and functional types very consistent with local inventory data. Simulated responses to the four GCM scenarios of climate change produced different results. The GFDL scenario consistently reduced total biomass accumulation compared to present-day conditions, whereas the other three GCMs produced overall increases. In the north, where ecosystem productivity is thought to be limited by low temperature, changes in steady-state biomass accumulation and species composition were relatively minor. In the south, where productivity is probably limited by summer water deficits, the GCM scenarios resulted in larger absolute changes, with generally large increases under GISS, and OSU and generally smaller increases under UKMO. Pronounced changes in species composition were not evident in most simulations, with the exception that warmer winter temperatures evidently allowed invasion by species currently excluded through intolerance to winter minima.

Carbon Offset Potentials of Four Alternative Forest Management Strategies in Canada: A Simulation Study

Using an Integrated TerrestrialEcosystem C-budget model (InTEC), we simulated thecarbon (C) offset potentials of four alternativeforest management strategies in Canada: afforestation,reforestation, nitrogen (N) fertilization, andsubstitution of fossil fuel with wood, under differentclimatic and disturbance scenarios. C offset potentialis defined as additional C uptake by forest ecosystemsor reduced fossil C emissions when a strategy isimplemented to the theoretical maximum possibleextent. The simulations provided the followingestimated gains from management: (1) Afforesting allthe estimated ∼ 7.2 Mha of marginal agricultural landand urban areas in 1999 would create an average Coffset potential of ∼ 8 Tg C y-1 during 1999–2100,at a cost of 3.4 Tg fossil C emission in 1999. (2)Prompt reforestation of all forest lands disturbed inthe previous year during 1999–2100 would produce anaverage C offset potential of ∼ 57 Tg C y-1 forthis period, at a cost of 1.33 Tg C y-1. (3)Application of N fertilization (at the low rate of 5kg N ha-1 y-1) to the ∼ 125 Mha ofsemi-mature forest during 1999–2100 would create anaverage C offset of ∼58 Tg C y-1 for this period,at a cost of ∼0.24 Tg C y-1. (4) Increasingforest harvesting by 20% above current average ratesduring 1999–2100, and using the extra wood products tosubstitute for fossil energy would reduce averageemissions by ∼11 Tg C y-1, at a cost of 0.54 TgC y-1. If implemented to the maximum extent, thecombined C offset potential of all four strategieswould be 2–7 times the GHG emission reductionsprojected for the National Action Plan for ClimateChange (NAPCC) initiatives during 2000–2020, and anorder of magnitude larger than the projected increasein C uptake by Canadas agricultural soils due toimproved agricultural practices during 2000–2010.

If forest dynamics in Canada's west are driven mainly by competition, why did they change? Half-century evidence says: Climate change.

In a recent paper (1), Zhang et al. present analyses of “forest dynamics” inferred from measurements collected during 1958–2009 at permanent sample plots (PSP) distributed across Canada’s western forests. Their results are almost unanimous in showing widespread increases in mortality, and declines in relative growth and recruitment (figure 2 in ref. 1). Zhang et al. conclude these trends are explained primarily by changes in stand-scale competition, and that recent changes in climate are of secondary importance. Surprisingly, Zhang et al. do not explain the temporal changes in competition they detected. We accept that stand dynamics depend upon competition for light, nutrients, and water, but argue that climate affects the supply of these resources. We find some major problems with the report by Zhang et al., including misinterpretation of results and a critical lack of clarity on key model assumptions, which cast serious doubt on their conclusions.

Climate change impacts on forest landscapes along the Canadian southern boreal forest transition zone

ContextForest landscapes at the southern boreal forest transition zone are likely to undergo great alterations due to projected changes in regional climate.ObjectivesWe projected changes in forest landscapes resulting from four climate scenarios (baseline, RCP 2.6, RCP 4.5 and RCP 8.5), by simulating changes in tree growth and disturbances at the southern edge of Canada’s boreal zone.MethodsProjections were performed for four regions located on an east–west gradient using a forest landscape model (LANDIS-II) parameterized using a forest patch model (PICUS).ResultsClimate-induced changes in the competitiveness of dominant tree species due to changes in potential growth, and substantial intensification of the fire regime, appear likely to combine in driving major changes in boreal forest landscapes. Resulting cumulative impacts on forest ecosystems would be manifold but key changes would include (i) a strong decrease in the biomass of the dominant boreal species, especially mid- to late-successional conifers; (ii) increases in abundance of some temperate species able to colonize disturbed areas in a warmer climate; (iii) increases in the proportions of pioneer and fire-adapted species in these landscapes and (iv) an overall decrease in productivity and total biomass. The greatest changes would occur under the RCP 8.5 radiative forcing scenario, but some impacts can be expected even with RCP 2.6.ConclusionsWestern boreal forests, i.e., those bordering the prairies, are the most vulnerable because of a lack of species adapted to warmer climates and major increases in areas burned. Conservation and forest management planning within the southern boreal transition zone should consider both disturbance- and climate-induced changes in forest communities.