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Defining boreal mixedwoods and exploring their response to management and natural disturbance (fire, MPB) through spatially-explicit ecosystem management modeling Welham, Clive
2009
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Abstract: 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. Occams 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 managem ...
 
Welham, Clive, Blanco, Juan A.; Kimmins, J.P. (Hamish); Scoullar, Kim. 2009. Defining boreal mixedwoods and exploring their response to management and natural disturbance (fire, MPB) through spatially-explicit ecosystem management modeling. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report
 
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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