No abstract

We examined the dynamics of down coarse woody debris (CWD) under an expanding-gap harvesting system in the Acadian forest of Maine. Gap harvesting treatments included 20% basal area removal, 10% basal area removal, and a control. We compared volume, biomass, diameter-class, and decay-class distributions of CWD in permanent plots before and 3 years after harvest. We also determined wood density and moisture content by species and decay class. Mean pre-harvest CWD volume was 108.9 m3/ha, and biomass was 23.22 Mg/ha. Both harvesting treatments increased the volume and biomass of non-decayed, small-diameter CWD (i.e., logging slash), with the 20% treatment showing a greater increase than the 10% treatment and both treatments showing greater increases than the control. Post-harvest reduction of advanced-decay CWD due to mechanical crushing was not evident. A mean of 18.48 m3 water/ha (1.85 L/m2) demonstrates substantial water storage in CWD, even during an exceptionally dry sampling period. The U-shaped temporal trend in CWD volume or biomass seen in even-aged stands may not apply to these uneven-aged stands; here, the trend is likely more complex because of the superimposition of small-scale natural disturbances and repeated silvicultural entries.

The emergence of forest ecosystem management presents new information challenges for forest managers. Shifting views of the forest from primarily one as a production system for wood fibre to an ecosystem with spatially and temporally complex interrelationships is changing the demand for information about the forest. These new information needs are characterized by greater complexity, limited availability of mechanistic hypotheses, and a paucity of data. Empirical and process modelling approaches have evolved in forest management to solve different problems, and debate about the two approaches has existed for some time. Which approach to forest modelling will best be able to meet the challenges of ecosystem management? Empirical models seek principally to describe the statistical relationships among data with limited regard to an object's internal structure, rules, or behaviour. In contrast, process models seek primarily to describe data using key mechanisms or processes that determine an object's internal structure, rules, and behaviour. In addition, mechanisms included in process models are general enough that they can maintain some degree of relevance for new objects or conditions (mechanism constancy), while empirical models tend not to be tied to any specific mechanism, so that derived model parameters must remain constant (parameter constancy) for new objects or conditions. Based on these differences, we argue that process models offer significant advantages over empirical models for increasing our understanding of and predicting forest (a tree, a stand, a landscape) behaviour. Process models are, therefore, more likely to meet the information challenges presented by ecosystem management.

Herbicide technology has evolved with forest management in North America over the past 60 years and has become an integral part of modern forestry practice. Forest managers have prescribed herbicides to increase reforestation success and long‐term timber yields. Wildlife managers and others interested in conserving biodiversity, however, have often viewed herbicide use as conflicting with their objectives. Do herbicides increase forest productivity, and are they compatible with the objectives of wildlife management and biodiversity conservation? Results from the longest‐term studies (10–30 years) in North America suggest that the range of wood volume yield gains from effectively managing forest vegetation (primarily using herbicides) is 30–450% in Pacific Northwest forests, 10–150% in the southeastern forests, and 50–450% in northern forests. Most of the 23 studies examined indicated 30–300% increases in wood volume yield for major commercial tree species and that gains were relatively consistent for a wide range of site conditions. Meeting future demands for wildlife habitat and biodiversity conservation will require that society's growing demand for wood be satisfied on a shrinking forestland base. Increased fiber yields from intensively managed plantations, which include the use of herbicides, will be a crucial part of the solution. If herbicides are properly used, current research indicates that the negative effects on wildlife usually are short‐term and that herbicides can be used to meet wildlife habitat objectives.

Summary 0[ This study was designed to test the hypotheses that "i# abundance and related demographic parameters of small mammal populations would decline after clear! cutting of northern spruce!_r forest\ and "ii# prescribed burning\ following clear! cutting\ an approach to emulating natural disturbance\ would enhance the species richness and diversity of the small mammal community relative to unharvested and clearcut forests[ 1[ Intensive live!trapping of small mammal populations was conducted in replicated forest "uncut#\ clearcut and clearcut!burned sites from 0877 to 0881 in west!central British Columbia\ Canada[ 2[ Mean abundance of southern red!backed voles Clethrionomys gapperi was sig! ni_cantly higher on forest sites "00=63 ha Ð0 # than on clearcut "9=59 ha Ð0 # or clearcut! burned "9=91 ha Ð0 # sites[ Mean numbers of deer mice Peromyscus maniculatus were signi_cantly higher on the clearcut!burned sites "05=77 ha Ð0 # than on forest sites "8=93 ha Ð0 #[ Demographic parameters of reproduction\ survival and body weight of deer mice were similar across all sites[ 3[ The long!tailed vole Microtus longicaudus had a strong annual~uctuation in abun! dance\ particularly on clearcut sites "03=93 ha Ð0 #\ where there were signi_cantly more animals than on either forest "0=42 ha Ð0 # or clearcut!burned "1=56 ha Ð0 # sites[ Meadow voles M[ pennsylvanicus were relatively uncommon but occurred more often on clear! cut and clearcut!burned sites than on forest sites[ 4[ The north!western chipmunk Tamias amoenus occurred at signi_cantly higher numbers on clearcut "3=05 ha Ð0 # and clearcut!burned "2=77 ha Ð0 # sites than on forest sites\ where it was rarely captured[ Shrews Sorex spp[ were at similar numbers across forest\ clearcut and clearcut!burned sites[ Weasels Mustela spp[ were captured more often on clearcut and clearcut!burned sites than on forest sites[ A rare species\ the western jumping mouse Zapus princeps\ was captured on clearcut and clearcut!burned sites only[ 5[ Mean species richness of small mammals was signi_cantly higher on clearcut sites "2=40# than on forest "1=62# or clearcut!burned "1=61# sites[ Species diversity was similar over all sites[ Although species composition was altered by clearcutting\ abundance of all species\ except C[ gapperi\ was the same or higher than that in uncut forest[