State of the Greater Fundy Ecosystem - Permanent Sample Plots

GREATER FUNDY ECOSYSTEM RESEARCH PROJECT

UNB Faculty of Forestry and Environmental Management

State of the Greater Fundy Ecosystem

Use of Permanent Sample Plots in Fundy National Park to Monitor Forest Conditions

Douglas Clay
Fundy National Park
P.O. Box 40, Alma, N.B. E0A 1B0

Monitoring programs within Fundy NP investigate changes in the bio-physical resources of the Park . One of the longest term biological science programs in the Park is a permanent sample plot (PSP) survey of forest tree communities. The national park PSPs, although distinctive, are similar in purpose to the existingnetwork of PSPs in the province of New Brunswick. The Park’s PSP survey began in 1976 with subsequent surveys conducted in 1983, 1989, and 1992. Although PSPs are typically used to assess standing stock and growth/regeneration on managed silvicultural stands, they have recently been used to test whether it is possible to detect changes in forest ecosystems, such as response to a Spruce Budworm outbreak.

In the Acadian Forest Region, the Spruce Budworm is important in maintaining the successional cycles of the Spruce/Fir/Birch forest. The last outbreak of the Spruce Budworm was first noticed in Fundy NP in 1966. Stress from infestation could be seen in the Park's forests in the early 1970's. Significant tree mortality in both Balsam Fir and Red Spruce occurred by 1976. Mortality continued until the mid-1980's, and ended by 1989.

Spruce Budworm (Adult stage)
(Photo: B. Townsend/Fundy NP)

Forest insect monitoring within Fundy NP indicate two major outbreaks of budworm in 1977 and 1982. These observations and others indicate that budworm was beginning one of its cycles immediately prior to the time the PSP monitoring began. With this known budworm outbreak, the PSPs should track the expected Spruce/Fir mortality.

Goals

The objective of this investigation was to determine if monitoring of PSPs since 1976 at approximately 5 year intervals by different lay personnel in every survey, tracked changes known to be occurring in the forest ecosystem due to Spruce Budworm. The obvious problem of how to distinguish true successional changes over time from the observational biases of differing personnel is not easily solved. As no direct data are available upon which to conduct comparative analysis, indirect evidence from the literature must be used to confirm that this monitoring program captured documented trends in the forest. For this purpose, the development of indices of the populations of Balsam Fir and Red Spruce were investigated.

Methods

In 1976, 34 PSPs, each with an area of 0.4 ha., were chosen by Fundy NP staff to represent forest cover types based on uniqueness, representativeness, fragility/stability, ecological importance, and scientific interest (Figure 1). The centre of each circular plot was marked with a metal post to establish a permanent point of reference. In 1992, the ecological land system in which each PSP was located was identified, based on the integrated resource survey of the Park (Hirvonen and Madill, 1978). The fixed site survey was adopted to develop only relative indices of population size.

Figure 1. Permanent Sample Plot (PSP)
locations within Fundy National Park

Sampling occurred once in the year of the survey (1976, 1983, 1989, and 1992). Each of the four surveys was conducted by different individuals, although a single individual or team surveyed all plots in each survey. Personnel had various backgrounds in biology but all relied on the same written instructions (outlined in Clay, 1995). In each plot, data were collected on location (latitude and longitude), tree species, dbh, and mortality state. As well, tree cores were taken for growth ring observations. Other variables collected but not used in this analysis included: site type, drainage, aspect, tree crown density, understory vegetation species, count of seedling trees by size class, and age and height of individual trees.

Trees over 2 m in height were counted separately for live and dead standing individuals (stems) for each species. Dbh was recorded in 2 cm intervals, measured at 1.4 m above ground level using calipers. Biomass estimates were calculated from equations provided by Ker (1980a), Ker and van Raalte (1981) and Stanek and State (1978). Calculated biomass by species for each plot were standardized to numbers or tonnes per hectare. Standardized values for plots within one strata were then averaged and weighted by strata area to provide indices of abundance for each land system sampled in the park. Mean biomass of individual trees was calculated for the entire park using the same method of weighting.

A pre-infestation (1971) baseline estimate of Spruce and Fir populations was developed by noting all standing trees in 1976 (both live and dead). Ostaff and MacLean (1989) observed that blowdowns of dead Fir trees began in year 5 after the outbreak, and after 10 years, 21% of all merchantable Fir (living and dead) had blown down. It was assumed that the mortality recorded in the 1976 survey occurred close enough to 1976 that no wind fall had yet occurred. For the purposes of this analysis, it was assumed that the forest suffered no mortality from the Spruce Budworm before 1971 and 2% of the estimated volume of standing conifer trees in 1976 were dead in 1971.

Results

The calculated change in Balsam Fir population between the pre-infestation estimate (1971) and the 1983 survey was 79.8% by biomass and 86.7% by numbers. All land systems experienced a decline in Balsam Fir abundance and biomass. The increase in abundance of Balsam Fir observed in 1992 was due to new recruitment. The minimal increase in biomass was due to the small size of the new trees (2 to 4 cm dbh). The mean mass of a Balsam Fir tree in the Park increased from approx. 85 kg to 118 kg as the smaller trees died, then rapidly declined to approx. 20 kg and finally 6 kg as the larger trees died and the new seedlings were sampled.

The calculated change in Red Spruce population between the pre-infestation estimate and the 1983 survey was 23.7% by biomass and 25.7% by numbers. The variability detected in Balsam Fir mortality among land systems was not seen with Red Spruce. The mean mass of Red Spruce tree in the Park remained between 173 and 185 kg until the new recruitment of small trees lowered the average to 145 kg. These data indicate that Red Spruce in the Park did not appear as susceptible as Balsam Fir to the budworm infestation found during this period, although reduced growth was found in our sampled Red Spruce trees. The stress period for these trees occurred between 1973 and 1984 and may have started as early as 1970.

The high mortality of Balsam Fir and Spruce caused by the budworm infestation increased the number of snags, an important component in the habitat available for cavity nesting birds and mammals.

Spruce Budworm can also affect non-host species by indirect means. Between 1983 and 1992, after the peak of Balsam Fir mortality had passed, the abundance of White Birch increased rapidly and the biomass declined. The abundance of Yellow Birch also increased. However, in contrast to White Birch, the live biomass of Yellow Birch continued to increase.

Estimates of total biomass of the forest tree community have declined by about 20% from the early 1970's and have been relatively stable for the past decade. The largest decline which occurred in Balsam Fir has been partially offset by an increase in hardwoods. Estimates of abundance (numbers) of the forest tree community have increased by nearly 50% from the early 1970's and nearly three-fold over the past decade.

The monitoring indicates that nearly all mortality was recorded prior to the 1983 survey and over 50% before the 1976 survey. Budworm populations grew in four years to numbers that cause noticeable defoliation (Miller, 1975). Mortality should have peaked in Fundy NP between 1972 and 1974.

The mortality observed in numbers in this investigation was 87% of Balsam Fir. Mortality was more protracted and less severe in Red Spruce than in Balsam Fir. This investigation found only 26% mortality by numbers in Red Spruce. Similar ratios were found by other research studies in nearby areas outside of the Park (MacLean, 1980; Dunfield, 1981).

Most of the increase in forest tree abundance was due to seedling Balsam Fir and, to a lesser extent, the birches. Declining White Birch biomass is likely due to natural mortality. Yellow Birch, which is a longer lived species, does not exhibit a decline in biomass over this time.

The changes in estimates of abundance for Spruce and Balsam Fir appear to be consistent with those reported from the literature under similar conditions of budworm infestation. A basic premise of this study is that random (personnel) errors would be unlikely to mimic what has been observed in other studies of Spruce Budworm outbreaks. It appears that any sampling error due to changes in personnel was small in comparison to changes due to major ecological events.

Implications for Management

Long-term monitoring of responses to natural disturbances of forest tree communities requires secure research areas, free from the threat of human disturbances. Protected areas such as national parks meet these requirements.

To monitor the effects of long-term events, programs such as forest monitoring must be institutionalized and designed in a way which will outlast any one individual. Changes in field personnel did not appear to adversely affect the results of this long-term forest monitoring using PSPs.

Collecting data on a variety of forest attributes provides potential research directions related to successional patterns, habitat availability for cavity nesting birds and mammals, fire fuel availability, and effects of climate of growth in natural forests. However, additional data collection will be required to document specific cause and effect relationships in forest ecosystem processes.

Several key factors are shown in Table 1 which will assist in providing continuity for such future work.

Acknowledgments

Regional Forester Arnold Brown of the Canadian Parks Service set up the original region-wide monitoring program and the present work is based mainly on his early efforts. Larry Brown, Atlantic Service Centre, Parks Canada, Halifax, reviewed the manuscript and provided helpful comments. The field work efforts of the following persons are greatly appreciated: Norm Wentzell (1976), Christine Langton (1983), Mark Chappell and Bruce Harper (1989) and Dwayne Simkins (1992). Two anonymous reviewers have helped shape and provide direction to this review.

Further Reading:

Clay, D. (ed.). 1995. Permanent sample plots: protocols for forest ecosystem monitoring (1975 to 1993). Unpublished manuscript of Parks Canada. Research Notes of Fundy National Park No. FUN/95-01. 50 pp.

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