Forest Investment Account (FIA) - Forest Science Program
FIA Project Y092033

    Ecosystem recovey after disturbance: thresholds for biodiversity and resiliency indicators
Project lead: Hamilton, Evelyn (Ministry of Forests and Range)
Contributing Authors: Chandler, Julia R.; Hamilton, Evelyn H.; Haeussler, Sybille
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
The purpose of this work is to assist forest managers in determining whether proposed forest management prescriptions (e.g. logging, salvage harvesting, site preparation) are likely to negatively impact upon the functioning of ecosystems. The study will address First Nations concerns about the sustainability of forest management practices, for example, the effects of harvesting on the abundance on species with important indigenous values such as berries. It will also enhance development of stand decision tools such as PROBE & PROGNOSIS.

The specific objective of this project is to use vegetation indicators of biodiversity to define response curves for measuring ecological resilience in SBS, ESSF & ICH forest ecosystems in central B.C. The initial vegetation indicators to be evaluated are: 1) the rate of regrowth (ie. recovery of vegetation biomass); 2) the rate of recovery of species richness; 3) the rate of recovery of original species composition. Hamilton and Haeussler (in revision) conducted a pilot study with 10 years of post-fire vegetation succession on 12 clearcut and slashburned sites. This work showed that rate of recovery for each of these three indicators varied significantly by ecosystem. Site productivity (which we measured as the spruce site index (SI) at year 50) and the degree of past exposure to wildfire (which we measured as the fire return interval) were important in determining the vegetation recovery rates after burns of varying severity. We propose to improve upon and validate our preliminary findings by analyzing similar vegetation response data from a larger dataset.

Data to be analysed will include:
1. studies of vegetation development after logging and burning in the ESSF, SBS & ICH in the Prince George and Clearwater area started by Hamilton 20 years ago, for which 10 year data has been collected and analysed in the pilot study (Hamilton and Haeussler, 2006 in revision). These sites include Walker, West Twin, Mackenzie, Goat, Genevieve, Frances, Haggen, Indianpoint and Brink sites and 10 year results were reported on in various MoFR Technical Reports. New 20 year data for these sites will be collected.
2. studies of vegetation development after burning in the ESSF, SBS & ICH near Smithers started by Macadam and Trowbridge over 20 years ago and resampled recently by Allen Banner, BC MoFR forest ecologist (e.g ICH - Kinskuch; SBS - Helene, Walcott; ESSF -McKendrick, Herron and Echo sites);
3. studies of vegetation development after slashburning in the ESSF, SBS and ICH the area around Prince George started by Craig DeLong, BC MOFR forest ecologist and others over 10 years ago (e.g. Northern Wet Belt sites, Lucille Mt, Pinkerton Mt, Walker, Vama Vama);
4. studies of vegetation development after logging in the ESSF in the area near Williams Lake started by Michaela Waterhouse, a project partner and others (e.g Quesnel Mts, Mt Tom);
5. studies of vegetation development in the ESSF near Kamloops started by Walt Klenner, a project partner and others (e.g. Sicamous).

We define ecological resilience as the amount of disturbance or stress that an ecosystem can absorb and still recover to the same stability domain (B.C.MOFR Future Forest Ecosystems Initiative 2006). In this study, we use burn severity (measured as the depth of burn of LFH layers; or the % of woody debris consumed) as an index of the amount of disturbance absorbed. Because the long generation times within forest ecosystems makes it difficult or impossible to directly measure stability domains, we will use a variety of proxy indices to assess whether or not a plant community indicator lies within its original stability domain. For example, if plant community composition at 20 years is diverging from, rather than converging towards, the original undisturbed forest condition, we consider this as evidence of a possible shift to an alternative stability domain. Alternatively, our pilot study and the literature suggest that most forest ecosystems follow a predictable flush in herbaceous growth that peaks 5-8 years after fire with woody species becoming dominant, thereafter. Biomass regrowth curves that depart significantly from the normal pattern were predicted at higher burn severities in our pilot study, and also suggest that a shift to alternative domain may have occurred. Species diversity was not found to be a particularly useful predictor after 10 years, but further investigation with the larger dataset is warranted. A significant increase in invasive, non-native after prescribed fire may be a useful indicator that resilience thresholds have been exceeded.

We hypothesize that ecological resilience increases with site productivity (spruce SI50) and decreases with the length of intervals between wildfires (FRI). In the first phase of the study we will test this hypothesis by fitting linear and non-linear mixed models to the three original vegetation indicators using standard model selection techniques. We will evaluate these three vegetation indicators of ecosystem recovery and reassess the data.

In the second phase of the study we will develop a Structural Equation Model (SEM; McCune & Grace 2002) to help explain why differences in ecological resilience exist across the environmental gradients of the SBS, ESSF and ICH study sites. The model will be tested first using plant community composition by species and then by plant community composition according to plant functional types. The plant functional types will be defined a priori using a hierarchical clustering technique that identifies co-occurring vital attributes or life history traits (e.g., Chapin et al. 1996; Kleyer 1999).

Chapin, F.S.II, M.S. Bret-Harte, S.E. Hobbie, H.Zhong. 1996. Plant functional types as predictors of transient responses of arctic vegetation to global change. J. Veg.Sci 7:347-358.

Hamilton, E. and S. Haeussler. 2006. Modeling resilience to slashburning across a sub-boreal to subalpine forest gradient in British Columbia. manuscript in revision.

Kleyer, M. 1999. Distribution of plant functional types along gradients of disturbance intensity and resource supply in an agricultural landscape. J. Veg. Sci. 10:697-708.

McCune, B. and J.B. Grace. 2002. Analysis of Ecological Communities. MJM Software Design. Gleneden Beach, OR.
Related projects:  FSP_Y081033FSP_Y103033


Executive summary (0.2Mb)
Modeling stability & resilience (0.7Mb)

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Updated August 16, 2010 

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