Forest Investment Account (FIA) - Forest Science Program
FIA Project Y083028

    Improving predictions of juvenile tree growth in complex mixtures for sustainable forest management [2007/2008 project description only]
Project lead: Simard, Suzanne (University of British Columbia)
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Here, we propose an experimental approach that will allow quantification and prediction of juvenile tree responses to different management strategies in complex structured, mixed species stands. This proposal will examine the growth responses of subalpine fir to variation in residual canopy cover, site quality and crowding. The study will be conducted in the Montane Spruce zone in the Southern Interior Forest Region. We will sample subalpine fir seedlings/saplings growing across a light gradient over a wide range of tree densities and site qualities. Sample trees will be destructively sampled to measure growth increment, which will be used to relate seedling growth to its micro-environment. For each tree, we will also measure light availability, foliar nitrogen, soil water availability, and water use efficiency in order to understand the mechanisms by which subalpine fir competes for resources. Our improved mechanistic understanding of juvenile pine growth will be linked to SORTIE-BC. SORTIE-BC is a resource-mediated, spatially explicit, mixed-species forest model that makes population dynamic forecasts for juvenile and adult trees. It has a flexible user-interface that allows the user to incorporate a wide range of silvicultural strategies (e.g., clearcutting, understory protection, understory planting, diameter limit harvesting, shelterwood, single or group selection, and variable retention). With the model, we can examine how complex stands respond to a wide range of silvicultural strategies, at different spatial scales and over different time periods, which is an impossible task for traditional field-based research. Our research approach can assist foresters and managers in testing, developing and choosing silvicultural strategies to achieve sustainable management objectives. 2.2 Relevance 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, forester 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 neighbourhood crowding by other juvenile trees. Here, we propose an experimental approach that will allow quantification and prediction of juvenile tree responses to different management strategies in complex structured mixed-species stands. This proposal will examine the growth responses of subalpline fir to variation in residual canopy cover, site quality and crowding. We have designed the study so that we can examine the relative strength of different factors on juvenile tree growth (light, water, nutrient availability and neighbourhood crowding), and our mechanistic understanding of juvenile subalpline fir growth will be linked to the SORTIE-BC stand dynamics model. The SORTIE model was originally developed as a small scale disturbance model in the early 1990ís (Pacala et al 1993; Pacala et al 1996). More recently the model has been modified, now referred to as SORTIE-BC, and re-calibrated to make population dynamic forecasts for northern interior mixed species stands (Kobe and Coates 1997; Wright et al. 1998, 2000; Canham et al. 1999; LePage et al. 2000). Initial development of the model focused on the light-growth relationship for juvenile trees (<10cm DBH), 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. Once juvenile tree light-growth functions were developed, efforts were redirected to determine if there was a relationship between juvenile tree growth and mortality. Kobe and Coates (1997) sampled eight tree species and determined the minimum annual growth increment (for the last 4 yrs) each species required to stay alive. The quantitative growth-mortality functions they developed were consistent with previous categorizations of species into shade tolerance classes. More recent efforts to calibrate the SORTIE-BC model have focused on predicting the growth of adult trees (>10cm dbh) as a function of their competitive environment. This information, in addition to the juvenile tree growth information, was then incorporated into the model (Canham et al.2004). The model was then tested against existing permanent sample plot data. During the validation process, it was discovered that the model was unable to accurately predict juvenile tree growth at low light levels and in dense neighbourhoods of seedlings and saplings. As a result, we think we must account for either soil resources or neighbourhood crowding in order for the model to make accurate juvenile tree growth predictions. Our proposed research will improve our understanding of the factors affecting juvenile tree growth and enhance the models ability to make accurate growth and yield predictions for complex mixed species stands. This is a difficult task for traditional growth and yield models, which tend be better suited for making predictions post-harvest in managed and uniformly regenerated stands. Objectives: 1) To determine the role of different resources (light, water, nutrients) in predicting juvenile tree growth across gradients of overstory canopy retention and site quality. 2) To determine how local neighbourhood density around a target juvenile tree affects the resource-growth relationship. 3) To incorporate the derived empirical relationships into SORTIE-BC. 4) To test model predictions of juvenile tree growth and mortality based on the growth relationships derived in objectives 1 and 2 using long-term permanent sample plot data.
Related projects:  FSP_Y061028FSP_Y072028
Contact: Simard, Suzanne, (604) 822-1955,

Updated August 16, 2010 

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