Managed forest stands will become increasingly complex in structure and species composition in the future because of the positive trends toward sustainable forest management. Foresters and land managers will need to understand the implications and trade-offs between timber production and other ecosystem values under new silvicultural strategies that will include continuous retention of canopy trees and management of multiple tree species with different life history characteristics. To design silvicultural strategies that optimise timber production and sustain other values, foresters and managers will require an understanding of how juvenile trees (seedlings and saplings) grow and survive across the full range of potential canopy retention levels and site qualities. Tree species preferences, expected growth rates and survival probabilities will likely shift among tree species across gradients of canopy retention, site quality and local neighborhood crowding by other juvenile trees. Using data collected in the Montane Spruce zone in linked FSP project, Y072028 (Improving predictions of juvenile tree growth in complex mixtures for sustainable forest management), we will model growth responses of juvenile subalpine fir to variation in residual lodgepole pine canopy cover, site quality, and crowding under a range of silviculture systems scenarios using the SORTIE model.
The SORTIE model was originally developed as a small scale disturbance model in the early 1990?s (Pacala et al 1993; Pacala et al 1996). Recently, the model was re-parameterized with data from northern interior mixed species stands and the latest version of the model is now referred to as SORTIE-ND (Kobe and Coates 1997; Wright et al. 1998, 2000; Canham et al. 1999; LePage et al. 2000). SORTIE-ND is a resource-mediated, spatially explicit, mixed-species forest model that makes population dynamic forecasts for juvenile and adult trees and can test to a wide range of silvicultural systems. Initial attempts at calibrating the SORTIE-ND model for Northern Interior mixtures suggest that an improved understanding of the factors affecting juvenile tree growth would greatly enhance the model?s ability to make accurate growth predictions. Earlier work in northwestern BC has concentrated on the light-growth relationship for juvenile trees (Wright et al. 1998, 2000), since light has been shown to be a good proxy for predicting juvenile tree growth (Klinka et al. 1992, Pacala et al. 1994, Wang et al. 1994, Kayahara et al. 1996, Chen 1997, 1998, Coates and Burton 1999, Claveau et al. 2002), and is the resource most easily manipulated by silvicultural interventions. The light-growth relationship, however, has been shown to vary with site quality, especially at higher light levels (Drever and Lertzman 2001). Growth response to increasing light availability may be reduced, for example, on sites where soil and nutrient availability are limiting. Conversely, low soil resource availability may be compensated to a certain degree by high light availability. Competition for soil resources has also been shown to increase in importance relative to light with increased crowding (Simard and Sachs 2004). This research assesses how the light-growth relationship varies across a range of site qualities.
In this proposal, we will use a modeling approach that builds on SORTIE-ND, allowing quantification and prediction of juvenile tree responses to different management strategies in complex structured, mixed species stands. The new SORTIE-ND submodel will be capable of making growth predictions for seedlings/saplings growing across a light gradient over a wide range of tree densities and site qualities, where site quality is represented by soil moisture regime. We will develop the submodel using the C++ programming language. C++ is a versatile programming language that will allow us to easily integrate the submodel into SORTIE-ND and possibly other existing growth models. SORTIE-ND is a res ...
Simard, Suzanne W.. 2009. Modelling Light, Site Quality and Crowding Effects on Growth of Understory Subalpine Fir in Lodgepole Pine Forests. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2009MR428
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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