Canadian Journal of Forest Research

The basic assumptions of regression analysis are recalled with special reference to the use of a logarithmic transformation. The limitations imposed on inference-making by failure to comply with these assumptions are discussed and ways to avoid the limitations indicated. A systematic bias of the order of 10 to 20% which is inherent in most, if not all, prior uses of the logarithmic equation to estimate plant biomass is noted as is the correction for the bias.

Some theory and observations are presented on the factors governing the start and spread of crown fire in conifer forests. Crown fires are classified in three ways according to the degree of dependence of the crown phase of the fire on the ground surface phase. The crown fuel is pictured as a layer of uniform bulk density and height above ground. Simple criteria are presented for the initiation of crown combustion and for the minimum rates of spread and heat transfer into the crown combustion zone at which the crown fire will spread. The theory is partially supported by some observations in four kinds of conifer forest.

For many types of forest studies, it is essential to identify the exact years of formation of annual rings in increment cores taken from living trees. To accomplish this, dendrochronologists employ cross dating, which involves both ring counting and ring-width pattern matching, to ensure against counting error, or errors, caused by missing or false rings. To date, published accounts of the cross-dating process generally describe a graphical method for achieving cross dating, known as skeleton plotting. However, when working with cores from living trees, skeleton plotting is seldom necessary. Such cores can commonly be cross-dated more quickly and easily by listing the narrow rings that are present in each core in a laboratory notebook and then comparing core notes for shared narrow rings. The latter approach permits faster recognition of ring-width patterns because calendar-year, rather than relative-year, dates are assigned to rings in cores. It also allows cross-dating records to be stored in a more concise manner.

Bayesian belief networks (BBNs) are useful tools for modeling ecological predictions and aiding resource-management decision-making. We provide practical guidelines for developing, testing, and revising BBNs. Primary steps in this process include creating influence diagrams of the hypothesized "causal web" of key factors affecting a species or ecological outcome of interest; developing a first, alpha-level BBN model from the influence diagram; revising the model after expert review; testing and calibrating the model with case files to create a beta-level model; and updating the model structure and conditional probabilities with new validation data, creating the final-application gamma-level model. We illustrate and discuss these steps with an empirically based BBN model of factors influencing probability of capture of northern flying squirrels (Glaucomys sabrinus (Shaw)). Testing and updating BBNs, especially with peer review and calibration, are essential to ensure their credibility and reduce bias. Our guidelines provide modelers with insights that allow them to avoid potentially spurious or unreliable models.

Climate models project that by 2100, the northeastern US and eastern Canada will warm by approximately 3–5 °C, with increased winter precipitation. These changes will affect trees directly and also indirectly through effects on “nuisance” species, such as insect pests, pathogens, and invasive plants. We review how basic ecological principles can be used to predict nuisance species’ responses to climate change and how this is likely to impact northeastern forests. We then examine in detail the potential responses of two pest species (hemlock woolly adelgid ( Adelges tsugae Annand) and forest tent caterpillar ( Malacosoma disstria Hubner)), two pathogens (armillaria root rot ( Armillaria spp.) and beech bark disease ( Cryptococcus fagisuga Lind. + Neonectria spp.)), and two invasive plant species (glossy buckthorn ( Frangula alnus Mill.) and oriental bittersweet ( Celastrus orbiculatus Thunb.)). Several of these species are likely to have stronger or more widespread effects on forest composition and structure under the projected climate. However, uncertainty pervades our predictions because we lack adequate data on the species and because some species depend on complex, incompletely understood, unstable relationships. While targeted research will increase our confidence in making predictions, some uncertainty will always persist. Therefore, we encourage policies that allow for this uncertainty by considering a wide range of possible scenarios.

Analysis of the frequency of past moderate and high-intensity disturbances has been hindered in forests of complex age structure by methodological problems. A methodology is proposed for developing a disturbance chronology in such stands by identifying the probable date of canopy accession for each sample tree. Canopy accession dates are based on an evaluation of radial growth pattern and early growth rates of existing canopy trees. Canopy disturbance intensity is defined as the percentage of sample trees with canopy accession events in each decade. Rotation periods for disturbances of various intensities are calculated from the chronology. The method was evaluated using 893 increment cores from 70 plots in northern hardwood stands of western Upper Michigan. The estimated average disturbance rate for all plots and decades was 5.7–6.9% of land area per decade, with an implied average canopy tree residence time of 145–175 years. These estimates are similar to those obtained by on-site estimates of canopy tree residence time and studies in the literature on the rate of gap formation. Problems in radial increment analysis and possible solutions are discussed.

Analysis of energy partitioning between defensive investments and growth in woody plants indicates that increasing a tree's life-span should require increased energy investment in protective measures such as thick bark and defensive chemicals. Increased investment in such defenses, however, logically must slow down the growth rate, thereby raising the mortality rate for juveniles in competition for height growth. Early reproduction should also reduce the growth rate. It is hypothesized that rapid growth can substitute for these defenses, but the consequence is rapid decline upon reaching maturity. These predictions are tested with data compiled from the literature for 159 species of North American trees. Data analysis supports predictions. Longevity of angiosperms, but not of gymnosperms was correlated with increased investment in defenses as measured by volumetric heat content of the wood. Wood density was not as good a measure. Longevity of gymnosperms was predicted by resistance to wood decay. For both taxa there was a negative correlation between growth rate and longevity, supporting the hypothesis of growth trade-offs. Age of sexual maturity was closely predicted by longevity in angiosperms. There was no such relationship for conifers as a whole, though there was for pines. The lack of relationship for all conifers might be explained by (i) variation in reproductive opportunities for young trees of different species, or (ii) variation in growth rates of young trees in certain adverse habitats occupied by conifers.

Wet deposition of nitrogen compounds was measured and dry and cloud water deposition were estimated at 11 forested sites in North America and one site in Europe. Dry deposition was a significant pathway of N input to all the forests, averaging 46% of the total deposition. At most of these sites, NH₄⁺ was the dominant form of fixed N in the air, but HNO₃ vapor dominated the dry deposition of N. Coarse-particle deposition was often important, but fine-particle deposition usually contributed only a small amount of the dry-deposited N. The deposition rates of inorganic N, which ranged between 4.8 and 27 kg N•ha⁻¹•year⁻¹, were generally much higher than has been reported by other studies measuring only wet or bulk deposition. The highest deposition rates were at the high-elevation sites in the southeastern and northeastern United States and much of the deposition at these sites was attributed to cloud water. Throughfall and stemflow (TF + SF) flux was also measured at all sites, and the net canopy exchange (NCE = (TF + SF)–total deposition) was found to be negative (indicating consumption of N in the canopy) for NH₄⁺ and NO₃⁻, and positive (indicating canopy release) for organic N. Past reports of canopy release of NO₃⁻ can probably be attributed to washoff of dry-deposited NO₃⁻ species. Consumption of inorganic N in the canopy ranged from 1 to 12 kg N•ha⁻¹•year⁻¹, and was highest in the spruce and spruce–fir stands. When organic N was included in the canopy N balance, the net canopy uptake of N was generally < 15% of the total system N requirement. Total N deposition was a linear function of wet deposition for low-elevation sites, and dry deposition was a linear function of the net throughfall flux for NO₃⁻.

The history of spruce budworm (Choristoneurafumiferana (Clem.)) outbreaks for the past 200 to 300 years, for nine regions in eastern Canada, indicates that outbreaks have occurred more frequently in the 20th century than previously. Regionally, 21 outbreaks took place in the past 80 years compared with 9 in the preceding 100 years. Earlier infestations were restricted to specific regions, but in the 20th century they have coalesced and increased in size, the outbreaks of 1910, 1940, and 1970 having covered 10, 25, and 55 million ha respectively. Reasons for the increase in frequency, extent, and severity of outbreaks appear mostly attributable to changes caused by man, in the forest ecosystem. Clear-cutting of pulpwood stands, fire protection, and use of pesticides against budworm favor fir–spruce stands, rendering the forest more prone to budworm attack. The manner and degree to which each of these practices has altered forest composition is discussed. In the future, most of these practices are expected to continue and their effects could intensify, especially in regions of recent application. Other practices, including large-scale planting of white spruce, could further increase the susceptibility of forest stands. Forest management, aimed at reducing the occurrence of extensive fir–spruce stands, has been advocated as a long-term solution to the budworm problem. The implementation of this measure at a time when man's actions result in the proliferation of fir presents a most serious challenge to forest managers.