State of the Greater Fundy Ecosystem

GREATER FUNDY ECOSYSTEM RESEARCH PROJECT

UNB Faculty of Forestry and Environmental Management

State of the Greater Fundy Ecosystem

Changes in the Quantities of Woody Biomass Associated with the Conversion of Natural, Mixed-species Forests to Conifer Plantations in the Greater Fundy Ecosystem

Tracey Fleming and Bill Freedman
Dept. of Biology, Dalhousie University
Halifax, N.S. B3H 4J1

Various studies are indicating that increases in atmospheric concentrations of CO2 and other radiatively active gases will cause an intensification of Earth's greenhouse effect, resulting in global climatic warming (IPCC, 1995). Changes in the quantities of organic carbon stored in forests have important implications for net CO2 emissions to the atmosphere, and are therefore highly relevant to the debate about human influences on global climate change.

Landscapes covered in natural, mixed-species forests in southern New Brunswick face two major types of disturbance: (1) a natural disturbance regime associated with such agents as Spruce Budworm infestations, wildfire, and windstorms, and (2) anthropogenic disturbances associated with forestry, especially clear-cutting and plantation establishment. Both kinds of disturbance regime create landscape mosaics consisting of stands of mature forest interspersed with regenerating forests, most of which are conifer-dominated. However, there are substantial differences in the amounts and distributions of woody biomass between naturally-disturbed forests and those that develop as the result of a silvicultural system (Birdsey, 1990; Harmon et al., 1990; Freedman and Keith, 1995). These differences are an ecologically important implication of the conversion of natural forests into intensively managed plantations, in part because of the effects on carbon storage in the ecosystem.

An aerial view of typical clearcut areas adjacent to the northern boundary of Fundy National Park. In the background are the Park's Bennett, Tracey and Bruin Lakes (Photo: G. Daigle)

GOALS

Achieving a better understanding of how Canadian forestry activities are affecting global atmospheric CO2 requires quantification of the amounts of carbon currently stored in Canadian forests, as well as the implications of changes in management practices (Apps and Kurz, 1991). The primary objective of this study is to compare the above-ground carbon storage of natural, mixed-species forests with that of conifer plantations of various ages in the Greater Fundy Ecosystem (GFE). We also compared the species and structural diversities of these forest systems.

METHODS

All 20 study sites are in the vicinity of Fundy National Park (Fundy NP). The surrounding area of the park is largely managed for commercial forestry. Together, these areas are known as the GFE. The study area occurs within the Acadian Forest Region, more specifically the Southern Uplands (Rowe, 1972). Two distinct climax forest types have been identified by Loucks (1962): the spruce - fir coast zone, and the sugar maple - yellow birch - fir zone. The latter occurs on top of the Fundy plateau, and is the forest type in which the present study sites are located.

Outside of the Park, a patchwork of conifer plantations of various ages is interspersed with remnants of the original, un-managed forest. The most commonly planted conifer species is Black Spruce, which is less vulnerable to budworm attack than other native species of Spruce and Fir. Some plantations have been stocked with other species, particularly Jack Pine, Eastern Larch, and Norway Spruce.

A total of 20 stands were selected for study. Seven were reference stands of natural, mixed-species forest - all but one of which were in Fundy NP - and 13 were plantations, aged 3 to 21 years since establishment. To extend the chronosequence of plantations beyond 21 years of growth, merchantable volume data were obtained from J.D. Irving Limited for anticipated growth of crop trees (Black Spruce/Red Spruce and Jack Pine) to age 70. The stands of reference forest were situated as close as possible to the plantations that were studied.

Living and dead tree-sized plants were sampled in twelve plots of 20 m x 20 m in reference forests, and in sixteen plots of 10 m x 10 m in plantations (where vegetation was more homogenous). Shrub-sized plants were measured in two 5m x 5m quadrats nested in opposite corners of each tree plot. The diameter and length of all coarse woody debris (CWD) with diameter > 5 cm was also recorded in the 20m x 20m quadrats.

Biomass in the following compartments was quantified: live woody vegetation (tree- and shrub-sized), snags (standing dead wood), coarse woody debris (CWD); and forest floor (Table 1). Above-ground tree biomass was estimated from diameter at breast height (DBH) using standing crop equations (MacLean and Wein, 1976; Ker, 1980a, 1980b, 1984; Freedman, 1984; Crowell, 1989). Shrub biomass was estimated from basal diameter using equations of Crowell (1989). The choice of regression for species of snags was the same as that used for live trees, except that equations corresponding to stem-only (including bark) biomass was used. Shrub-sized snags were estimated as the difference between live biomass and foliage biomass, as reported in Crowell (1989). Dry weight of biomass (tonnes/ha) was converted to organic carbon using a factor of 0.50 (Brown and Lugo, 1982; Freedman et al., 1992; Schroeder, 1992).

Ten representative 5-cm discs of CWD were sampled within 5-cm diameter classes, using a chain saw. The wood discs were oven-dried at 90o C, weighed, and were used to determine a volumetric ratio of dry weight : CWD volume. This ratio was used to calculate biomass of CWD (in tonnes/ha) from stand-level volume data.

Samples of forest floor were collected from a sub-sample of eleven sites. A total of twenty 30 cm2 samples was collected per site, including all organic material down to, but not including, the Ae horizon. These samples encompassed the litter, duff, humus, and Ah horizon of the upper mineral soil. Each sample of forest floor was homogenized, dried, and weighed. All of the samples from each site were aggregated, and were then reduced in bulk several times using the heap-and-quarter method (Allen, 1989). The concentrations of organic matter in 1-g sub-samples were determined using loss-on-ignition (LOI) (Allen, 1989). The percentage LOI was used to calculate organic biomass from forest floor dry weights, and this was converted to carbon (in tonnes/ha) using a factor of 0.5.

Several other biomass compartments were beyond the scope of sampling for this study, notably herbaceous plants, tree stumps, and living and dead roots in the forest floor.

RESULTS

On average, reference forests dominated by conifer tree species had a greater proportion of the total above-ground biomass as dead woody biomass per hectare than natural mixed-wood or angiosperm-dominated stands. This would reflect the natural disturbance regime, especially Spruce Budworm dynamics, to which conifer stands are subjected. Comparable-aged reference and mature plantation forests (the latter from projections) were also similar in total above-ground living woody biomass. However, both snag and CWD compartments were severely reduced in the plantations, as evidenced by the almost complete absence of these dead-biomass elements in a 21-yr-old plantation.

No significant reduction in forest floor biomass was observed over the plantation chronosequence, or between the plantation system and the reference stands. However, the composite nature of the forest floor changed between the two forest systems. Plantations appeared to have more litter in their forest floors, such as small sticks from logging slash, than those of un-managed stands within the Park.

IMPLICATIONS FOR MANAGEMENT

These results have implications for forest structure and function, both in terms of reductions in the biomass and carbon storage in rotation-aged plantations, as well as simplification of the habitat of plantation forests. Plantations have few snags or coarse woody debris, which are required by numerous species of wildlife as critical habitat features (Freedman et al., 1996; Woodley and Freedman, this volume). Large quantities and greater varieties of carbon storage media are important to the integrity and biodiversity of forest ecosystems (McCarthy and Bailey, 1994; Freedman et al., 1996).

At the landscape level, a system of intensively managed plantations will store considerably less organic-carbon in both living trees and dead woody compartments. Plantation trees will be harvested at a rotation period of 40 to 60 years in southern New Brunswick, which will not allow these anthropogenic forests to attain a living biomass comparable to that of natural forests in the region. Moreover, successive rotations of plantations will preclude the development of snags and coarse woody debris, unless specific management is undertaken for these features. Carbon storage on the silvicultural landscape is further decreased by the lack of these important detrital components. Management objectives in the GFE should include allowances for the development and maintenance of snags and large-dimension woody debris.

- Table of Contents

- View other case studies

- Bibliography