Forest Investment Account (FIA) - Forest Science Program
FIA Project Y071286

    Defining boreal mixedwoods and exploring their response to management and natural disturbance (fire, MPB) through spatially-explicit, stand level, ecosystem management modeling
Project lead: Kimmins, Hamish
Author: Welham, Clive
Imprint: Vancouver, BC : University of British Columbia, 2007
Subject: Forest Investment Account (FIA), Trees, British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Mixedwoods constitute a major forest type across Canada. In this province, they are an important multi-value resource in boreal and sub-boreal northeastern and central BC, and to a lesser degree in the southern interior and on the coast. Defining boreal and sub-boreal mixedwoods from an ecological perspective is problematic because there is a continuum from pure conifers to pure hardwoods, and over this continuum there is a wide range of spatial graininess, from intimate tree-by-tree mixtures to aspen clones or pure birch patches of various sizes intermixed with similar or different sized patches of conifers. The spatial pattern of different mixtures and different graininess of mixtures is variable across the landscape. There are also temporal mixedwoods – seral sequences following disturbance. This spatial and temporal complexity leads to the following research questions: 1) What type of mixedwoods should management attempt to achieve: a dynamic and changing landscape patchwork of all possible combinations of spatial and temporal mixedwoods, or some particular target mixture(s) and pattern(s)? 2) What are the environmental values and management benefits/costs of successional sequences from pure post-disturbance hardwoods through various mixedwood types to pure conifers, and back again following disturbance, and how do these compare with managing for a relatively fixed stand-level mixedwood condition and landscape pattern? Exploring the many types of mixedwoods and their change over time is complicated by their diversity, their complex temporal dynamics, and the large spatial scale and long time frames involved. These factors reduce the value of purely empirical approaches in addressing the above research questions, especially in the face of predicted climate change at boreal latitudes. The only alternative to empirical approaches (such as chronosequence, retrospective and long-term studies) is to represent our experience and understanding in ecosystem management models. Empirically derived population (e.g. TASS) or tree community (e.g. SORTIE, MGM) models have value for short-term, timber-focused tactical applications and silvicultural systems analysis. In contrast, questions of multiple value tradeoffs, defining sustainability and stewardship, analyzing interactions between natural disturbance, management and climate change, and any analyses on sites where soil moisture and fertility or competition from minor vegetation have a significant effect on production ecology and carbon allocation, require the complementary use of ecosystem management models. These should represent explicitly the key determinants of production ecology and carbon allocation, succession, and ecosystem-level response to disturbance and management. Mixedwoods have different biological and ecological characteristics as compared to monocultures that have implications for wildlife habitat, regeneration, biodiversity and its measures, operability, and timber quality, supply and economics. Generally, they have better disease and insect resistance and greater tree productivity compared to monocultures (Man and Lieffers, 1999; Simard et al. 2004), probably because of the differential utilization of resources (light, nutrients and water) and the positive impacts of broadleaf species on nutrient cycling rates and mycorrhizal networks. However, enhanced tree productivity may be at the expense of understory vegetation and related wildlife habitat values. These tradeoffs mean that models which consider only a limited number of individual values are of reduced relevance for strategic SFM decision making and exploring the potential consequences of alternative mixedwood policies and practices. Occam’s Razor suggests that theories (models) should be as simple as possible but as complex as necessary; as Albert Einstein said, theories should be as simple as possible, but no simpler. The exceptionally dynamic nature of mixedwood forests presents a number of management challenges, not the least of which is how best to project the growth, development and timber yields of different types of mixedwoods. Models of the diversity and sustainability of mixedwoods need to be appropriately complex. This calls for ecosystem-level models (see Kimmins et al. 2005). Mixedwood modeling at the ecosystem level is being explored in FSP Project Y061033 – Evaluation of an ecosystem-based approach to mixedwood modeling. This involves a study of the merits of FORECAST, an aspatial ecosystem management model, for simulating growth and yield and other values of boreal mixedwoods. However, despite its merits, FORECAST is unable to address issues of the spatial scale – the graininess - of mixtures, and the key question remains: at what spatial scale of mixing are the various biological, ecological, economic and management costs and benefits of mixedwoods achieved? This project addresses this question. It will capitalize on the growing body of relatively short-term empirical data on the performance of boreal and sub-boreal mixedwood stands under alternative stand management strategies – data that can be used for either model calibration or partial validation. The time when individual forest values could be considered in isolation is over, and making wrong choices about management can be very costly – environmentally, socially and economically. Certification and gaining a social license to manage public forests requires value tradeoff analyses and consideration of possible future trends (scenario analyses) for multiple ecosystem values and environmental services (Vanclay 2003). Forecasting such trends requires knowledge based on both experience and research, but much of the latter is disciplinary in nature and not at the spatial, temporal and complexity scales of the issues of sustainability and stewardship (Kimmins et al. 2005). Long term field trials are valuable, but by the time they are completed the climate, social values and biotic conditions may have changed. For practical reasons, few alternatives can be examined in such trials, and once established the trials generally cannot be changed to suit changing circumstances. There is an urgent need, therefore, to combine our experience, interim results from long-term studies and science-based understanding into forecasting systems, especially when dealing with new and essentially untested (over a full rotation) systems like mixedwood management.
Related projects:  FSP_Y082286FSP_Y093286
Contact: Welham, Clive, (604) 822-8958,


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Updated August 16, 2010 

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