Forest Investment Account (FIA) - Forest Science Program
FIA Project Y071160

    Implications of management practices for mitigating Mountain Pine Beetle on ecosystem production and soil-based indicators of SFM
 
Project lead: Day, Steve
Contributing Authors: Day, Steven; Welham, Clive; Seely, Brad A.; Straker, Justin; Blanco, Juan A.
Imprint: Belcarra, BC : FORRx Consulting Inc., 2007
Subject: Forest Investment Account (FIA), Dendroctonus Ponderosae, British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
Maintaining ecosystem productivity is fundamental to the principles of sustainable forest management (SFM) and yet effective methods for measuring and monitoring the impacts of management activities on ecosystem production are not well developed. The latter task is particularly challenging for many interior BC forest companies because activities designed to mitigate the future risk of damage to stands by Mountain Pine Beetle (MPB) could potentially compromise SFM goals and objectives. In this proposal, the impact of a variety of management options on projected stand susceptibility to MPB is evaluated within the context of one of Canfor’s soil-based indicators of SFM using a combination of field measurements and model simulations. Soil health is critical to SFM Soil is a vital element of healthy forest ecosystems and soil protection and enhancement is essential if forest management is to be sustainable. The recovery of an ecosystem following disturbance depends heavily on the degree to which soil-based processes are disrupted. As yet, there is no generally accepted method for quantifying the impacts of management activities on soil function and, hence, ecosystem recovery. One approach, the Canadian Council of Forest Ministers Criteria and Indicator system, uses a set of soil quality indicators to assess functional ability, and measure changes in function over time (CCFM 2003). Unfortunately, quantitative relationships between most conventional soil indicators and long-term forest productivity (a basic tenet of Sustainable Forest Management) are lacking (Nambiar 1996, Staddon et al. 1999). This issue will not be resolved any time soon due to the long time frames required before field results can be considered as definitive. This proposal provides a solution by linking empirical measures of a given soil-based indicator with an ecosystem model to project targets for that indicator and compare them against thresholds of long-term productivity. This protocol was developed with funding from a previous FIA project (2004), and an FSP-funded study (project Y06-1143). The thresholds represent an early warning that forest management practices are compromising a given SFM indicator such that, when measures violate threshold boundaries, this should trigger remedial actions. Criterion 2 of the SFM Framework developed by Canfor (see Robinson 2002) is concerned with maintaining the productive capacity of forest ecosystems within the Timber Harvesting Landbase (THLB). One of its principal indicators is 2-1: Biological components of forest soils are sustained. Two useful measures for this indicator are forest floor mass and soil organic matter (SOM)(see Seely 2005). Mitigating risk of MPB outbreak could compromise soil-based indicators of SFM The Quesnel timber supply area is dominated by stands of lodgepole pine (Pl). Extensive mortality of pine-dominated stands by MPB has occurred and there is a concentrated effort to harvest the recently-killed and any remaining susceptible stands. Of principle concern to forest managers now is how to regenerate these stands. This issue is particularly pressing because regional harvest projections indicate a significant timber volume shortfall over the next 25 – 60 years. Lodgepole pine is fast-growing and well adapted to the region and so one option is to restore the original pine-dominated forests. This tactic could simply re-create the forest conditions that triggered the original outbreak problem. According to Shore and Safranyik (1992), stand susceptibility to MPB attack can be predicted as a function of susceptible basal area, age, density, and location; the first three variables can be influenced by management practices. One way to mitigate susceptibility then is by planting pine at very low densities (300-500 sph; Whitehead and Russo 2005, see Shore and Safranyik 1992). As a general rule this approach is unsatisfactory since mature stands will likely not develop sufficient merchantable volume to harvest economically and individual stems are likely to be very 'branchy’ (i.e., their wood quality is poor). These stands could possess a high biodiversity value, however. Another possible solution is to establish pure Pl stands that are fully stocked and then harvest them on short rotation (< 60 years) before they become susceptible to MPB (see Shore and Safranyik 1992). This approach will help mitigate the mid-term timber supply problem but at the expense of substantial volume gains foregone by the early rotation harvest. This tradeoff could be at least partially offset if fertilizers were used to enhance early growth (Welham and Kimmins 2005). The difficulty from the perspective of SFM principles, however, is that repeated, short-rotation harvests can cause a significant loss of SOM and forest floor material, potentially compromising ecosystem productivity over the long-term (Seely et al. 2002, Seely 2005, Welham et al. 2005). A third option is to introduce mixtures of species either at the stand-level, or at the landscape-level with stands of pure but different species, in order to mitigate the risk of catastrophic outbreak (Martin et al. 2005). The difficulty here is that, as an early seral species, pine has a higher growth rate than most of the other conifers with which it is associated. A mid-rotation harvest will therefore result in relatively low volumes because of the lower overall proportion of pine (assuming the other species are too small to harvest). Clearly, no single approach represents the idea solution. Most forest companies are therefore likely to favor a mix of options but which sites are best suited to a given option? This proposal will address this issue by linking field estimates of forest floor and SOM with simulated outcomes of the different options using an ecosystem model. Outcomes will be evaluated within the context of the two soil-based measures associated with indicator 2-1 of Canfor’s SFM Framework. Baseline measures of carbon and nitrogen in forest floor and SOM pools will be obtained from beetle-killed Pl stands in the timber harvesting landbase of Canfor’s Quesnel Division that are slated for salvage logging. Sampling will be restricted to sites with roughly a mesic moisture regime but include enough site series that collectively, the nutrient regime varies from very poor to rich. These carbon and nitrogen estimates will be used as (a) baseline measures for a long-term SFM monitoring program (which is independent of this proposal) to determine any changes in SOM and nutrient pools as a result of management activities, and (b) input values for the ecosystem management model (further details below). Ecosystem models can help identify appropriate beetle management strategies In the second component of the study, projections of long-term productivity will be made with a model (FORECAST) that can represent SOM and nutrient pools and the effect of changes in these pools as a consequence of management activities. FORECAST uses a hybrid simulation approach in which the rates of key ecosystem processes are derived from empirical data on forest growth and yield (Kimmins et al. 1999). These process rate estimates are then used in conjunction with a management interface to simulate forest ecosystem productivity. The model incorporates both light competition and nutrient cycling as key drivers of productivity. FORECAST can simulate productivity and competition in both overstory and understory tree populations, as well as other minor vegetation. Details of model structure and calibration are described in Kimmins et al. (1999) and Seely et al. (1999). FORECAST is well established as a management tool and has been applied throughout western Canada (see, for example, Seely et al. 2002, 2004, Welham et al. 2002), including interior BC (Wei, et al. 2000, 2003, Seely 2005). It has been used to simulate soil organic matter dynamics as a criterion of forest sustainability (Morris et al. 1997, Seely 2005), applications similar to that proposed here. The main objective is to simulate a set of stand-level strategies designed to mitigate MPB susceptibility and determine their effect upon SOM, forest floor mass, and the associated nitrogen content, measures that Canfor is monitoring as part of its SFM program (Robinson 2002). To do this, FORECAST output will be linked to the Shore and Safranyik (1992) MPB susceptibility rating (SR) model and the latter used to calculate the change in stand susceptibility over time. The utility of this protocol was described and demonstrated at a FORREX-sponsored ecosystem productivity workshop held in October 2005 (Welham and Kimmins 2005). FORECAST will simulate the development of salvage-logged stands using their SOM content from the field study as a starting condition, in conjunction with the various management options detailed above. In this regard, the simulated stands will be planted to varying proportions of Pl and hybrid spruce (Sxw), at different planting densities, with and without fertilizer. An understory shrub and grass community will be included in all simulations. The starting site index for the simulations will be derived from the field estimates. Thereafter, site index will be permitted to vary so as to determine how management activities affect the inherent productivity of the site. The linked FORECAST-SR model will be used to calculate potential rotation lengths for all of the species-planting density-fertilizer combinations, according to each of three criteria: 1) Minimal acceptable MPB susceptibility (the rotation length where the susceptibility index equals 20%), 2) Culmination of mean annual increment (MAI), and 3) Maximum expected net benefit (calculated from the susceptibility index times merchantable volume, at each year in the rotation). Each rotation length will then be used with each species-planting density-fertilizer combination as the basis for five consecutive rotations of whole-tree harvesting. The forest floor, SOM and N pools will be calculated for each rotation. This protocol will thus determine which management strategies for MPB can produce the highest net benefit (in terms of mid-rotation and long-term volume) without unduly compromising the soil-based indicators of SFM.

    Deliverables:

Executive Summary (18Kb)
Extension Note (30Kb)
Final Report (0.8Mb)
Managing for timber volume and Mountain Pine Beetle susceptibility (0.5Mb)

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Updated August 16, 2010 

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