British Columbia

SORTIE-ND-related research in British Columbia is conducted mostly through the Bulkley Valley Centre for Natural Resources Research and Management and the University of British Columbia.

SORTIE-related research started at Date Creek in the mid-1990s. The model was fully parameterized for the mixed interior cedar-hemlock forests of the area. Ongoing work in this area is described below.

Current SORTIE-ND-related projects

• Interactions between light availability and foliar nitrogen status on juvenile tree growth. Lead researcher is Marty Kranabetter (e-mail: marty.kranabetter@gov.bc.ca).


• Regeneration and stand structure following Mountain Pine Beetle infestation in the sub-boreal spruce zone. Lead researcher is Dave Coates (e-mail: dave.coates@gov.bc.ca).


• Improving juvenile tree growth prediction for complex Mountain Pine Beetle damaged stands. Lead researcher is Dave Coates (e-mail: dave.coates@gov.bc.ca).


• Prediction of white spruce and trembling aspen juvenile growth as a function of size and light availability in western boreal forests. Lead researcher is Rasmus Astrup (e-mail: astrup@interchange.ubc.ca).


• Evaluation of the simulation model SORTIE-ND for prediction of growth and yield in mixed aspen-spruce stands. Lead researcher is Rasmus Astrup (e-mail: astrup@interchange.ubc.ca).


• Modeling individual tree mortality for northern mixed-species stands. Lead researcher is Rasmus Astrup (e-mail: astrup@interchange.ubc.ca).


• Predicting development and productivity of southern interior mixed species stands through calibration and modeling. Lead Researcher is Suzanne Simard (e-mail: suzanne.simard@ubc.ca).


• Improving predictions of juvenile tree growth in complex mixtures for sustainable forest management. Lead Researcher is Suzanne Simard (e-mail: suzanne.simard@ubc.ca).


• Juvenile and adult tree growth of black spruce and balsam fir in boreal forests of Labrador. Lead Researcher is Bryn Wood (e-mail: bwood@labmetis.org).

SORTIE and SORTIE-ND-related publications

Kneeshaw, D. D., R. K. Kobe, K. D. Coates, and C. Messier. 2005. Sapling size influences shade tolerance ranking among southern boreal tree species. In press, J. Ecology.
Abstract: Traditional rankings of shade tolerance of trees make little reference to individual size. Greater respiratory loads with increasing sapling size imply that larger individuals will be less able to tolerate shade than smaller individuals of the same species and that there may be shifts among species in shade tolerance with size. We tested this hypothesis using maximum likelihood estimation to develop individual-tree-based models of the probability of mortality as a function of recent growth rate on seven species: trembling aspen, paper birch, yellow birch, mountain maple, white spruce, balsam fir and eastern white cedar. Shade tolerance of small individuals, as quantified by risk of mortality at low growth, was mostly consistent with traditional shade tolerance rankings such that cedar > balsam fir > white spruce > yellow birch > mountain maple = paper birch > aspen. Differences in growth dependent mortality were greatest between species in the smallest size classes. With increasing size, a reduced tolerance to shade was observed for all species except trembling aspen. At a given level of radial growth larger trees, apart from aspen, had a higher probability of mortality than smaller trees. Successional processes associated with shade tolerance may thus be most important in the seedling stage and decrease with ontogeny.

Greene, D. F., C. D. Canham, K. D. Coates, and P. T. LePage. 2004. An evaluation of alternative dispersal functions for trees. J. Ecology, 92:758-766.
Abstract: We compared three commonly-used empirical seed/seedling dispersal functions for trees (lognormal, 2Dt, and two-parameter Weibull) by analysis of published studies where the location of the source is known, as well as by inverse modeling within an old growth hardwood forest in southern Québec. Almost all the species were wind-dispersed. For the discrete source studies, the lognormal was clearly superior, while for the inverse modeling the performance of the three dispersal functions was somewhat more even. We speculate that collisions with boles spuriously enhanced the likelihood of the 2Dt and the Weibull with inverse modeling, as both these functions assume that the greatest seed/seedling density will occur at the base of the maternal parent bole. We conclude that the lognormal function is to be preferred because, as well as providing a framework for mechanistic interpretation, it tends to provide a closer approximation to observed dispersal curves. We also argue that mean distances traveled by seed crops are far more extensive than indicated by previous studies that used the Weibull function.

Canham, C. D., P. T. LePage, and K. D. Coates. 2004. A neighbourhood analysis of canopy tree competition: effects of shading versus crowding. Can. J. For. Res., 34:778-787.
Abstract: Partial harvesting and all-aged management require consideration of an almost infinite variety of spatial configurations of the level of removal of different species and tree sizes within a stand, and an almost infinite variety of permutations of residual stand conditions. We have developed an extension of traditional distance-dependent, spatial competition models that allows independent estimates of (1) the potential maximum tree growth for a given set of climatic and edaphic conditions, as a function of tree species and size, and (2) the magnitude of the competitive effects of neighboring trees on target tree growth as a function of the species, size, and distance to neighboring trees. The analyses provide empirical estimates of inter- and intraspecific competition coefficients, and explicitly partition the competitive effects of neighbors into the effects of shading versus the residual effects of "crowding". We developed and tested the method using data from forests of northern, interior British Columbia dominated by western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata (Donn ex D. Don in Lamb). We used maximum likelihood estimation to test a suite of alternate models. For both species, the most parsimonious models included terms for (1) the effects of tree size, (2) crowding, (3) shading, and (4) separate competitive effects of 4 different groups of competing species. The models explained 33-59% of the variation in radial growth of the 2 species. Potential radial growth peaked at 34 - 40 cm DBH for the two species. For both species, growth declined more steeply as a function of crowding than shading, particularly in redcedar. There was a striking asymmetry in the strength of interspecific competition between hemlock and redcedar, with crowding by hemlock having a very strong per capita effect on redcedar, while crowding by redcedar had relatively little effect on the radial growth of hemlock.

Coates, K. D., C. D. Canham, M. Beaudet, D. L. Sachs, and C. Messier. 2003. Use of a spatially explicit individual-tree model (SORTIE/BC) to explore the implications of patchiness in structurally complex forests. For. Ecol. Manage. Vol 186, Issue 1-3:297-310.
Abstract: The discipline of silviculture is evolving rapidly, moving from an agricultural model that emphasized simple stand structures toward a natural disturbance- or ecosystem-based model where stands are managed for multiple species and complex structures. Predicting stand dynamics and future yields in mixed-species complex structured stands cannot be easily accomplished with traditional field experiments. We outline the development and structure of SORTIE/BC, a descendent of the SORTIE model. SORTIE/BC is a light-mediated, spatially explicit, mixed-species forest model that makes population dynamic forecasts for juvenile and adult trees. We use the model to simulate partial cutting prescriptions in temperate deciduous, boreal and temperate coniferous mixed-species forests. The species, amount and spatial pattern of canopy tree removal had a major influence on understory light environments. Low and uniform removal of canopy trees were less successful in favouring the growth and survival of regenerating trees of intermediate to shade intolerant species and the growth of retained canopy trees than patch removal. In the boreal mixedwood, strip cutting can maintain mixed stands but careful attention must be paid to buffer and strip management to optimise stand growth. We conclude that SORTIE/BC can be very useful to explore and explain the silvicultural implications of complex silvicultural prescriptions for which there are no existing long-term experiments.

LePage, P. T., C. D. Canham, K. D. Coates, and P. Bartemucci. 2000. Seed abundance versus substrate limitation of seedling recruitment in northern temperate forests of British Columbia. Can. J. For. Res. 30:415-427.
Abstract: We examine the influence of (1) the spatial distribution and abundance of parent trees (as seed sources) and (2) the abundance and favourability of seedbed substrates, on seedling recruitment for the major tree species in northwestern interior cedar-hemlock forests of British Columbia, under 4 levels of canopy openness (full canopy, partial canopy, large gap, and clearcut). Substrate distribution varied with canopy openness, and substrate favourability was a function of both canopy openness and seedling species. Lack of suitable substrates was the predominant factor limiting seedling density under full canopies. Partial canopy and gap sites provided a broad range of favourable substrates in close proximity to parent trees, resulting in the highest observed seedling densities. There was much higher effective dispersion of seedlings away from parent trees in gaps than in the partially cut stands. Seedling dispersion to clearcut sites was poor with seedlings being tightly restricted to a narrow band along the forest edge. Thus, seedling recruitment in these forests was a reflection of the interaction between the abundance of seed and substrate favourability, and the relative importance of these factors varied significantly with canopy structure.

Wright, E. F., C. D. Canham, and K. D. Coates. 2000. Effects of suppression and release on sapling growth for eleven tree species of northern, interior British Columbia, Can. J. For. Res. 30:1571-1580.
Abstract: Saplings of canopy tree species frequently undergo alternating periods of suppression and release before reaching canopy size. In this study, we document the effects of periods of suppression and release on current responses to variation in light by saplings of the 11 major tree species of northwestern, interior British Columbia. We were specifically interested in the degree to which increasing length of suppression had long-term effects on subsequent response to release in gaps or following partial cutting, and the degree to which the effects of suppression were ameliorated with time following release. At least some saplings of all 11 species had undergone alternating periods of suppression and release. The most shade tolerant species generally did not show either a decline in growth over time during suppression, or a gradual increase in growth at a given light level over time during release. The least shade tolerant species exhibited significant declines in growth rate during suppression; however, in all of the species except trembling aspen (Populus tremuloides), the effects of suppression disappeared over time during release. Failure to account for the effects of past suppression and release leads to significant overestimates of the initial responses of shade intolerant species to release. Our results suggest that competitive balances between species shift substantially over time as a result of growth history, and that these shifts have significant effects on successional patterns.

Canham, C. D., K. D. Coates, P. Bartemucci, and S. Quaglia. 1999. Measurement and modeling of spatially-explicit variation in light transmission through interior cedar-hemlock forests of British Columbia. Can. J. For. Res. 29:1775-1783.
Abstract: We have characterized canopy geometry and light transmission by the nine dominant conifer and hardwood tree species of the interior cedar-hemlock (ICH) forests of northern British Columbia. Our field data were used to parameterize a spatially-explicit model of light transmission through mixed-species forests. That model, a component of the forest dynamics simulator SORTIE, was developed for eastern deciduous forests, and this paper presents a test of that model in a very different ecosystem. Our results show that individual crowns of the ICH forests generally intercepted much more light than species of eastern deciduous forests, but that the canopy as a whole allowed much greater light penetration, largely because of openings between the relatively narrow, conical crowns of the western conifers. Light transmission by individual crowns was correlated with shade tolerance among the conifers (as in eastern deciduous species), but crown depth was not (in contrast to eastern species). Despite the fundamental differences in the nature of light transmission in the two ecosystems, the SORTIE light model developed for eastern deciduous forests was very effective at predicting spatial variation in understory light levels in these western coniferous forests. The goodness of fit of such a simple model suggests that the most important factors regulating spatial variation in understory light levels in forests are simply the sizes and distribution of nearby trees, and the local sky brightness distribution. Discrete canopy gaps represent a special case in which a region of the canopy is not occupied by crowns.

Coates, K. D., and P. J. Burton. 1999. Growth of planted tree seedlings in response to ambient light levels in northwestern interior cedar - hemlock forests of British Columbia. Can. J. For. Res. 29:1374-1382.
Abstract: Insights into field-planted conifer seedling growth were gained by fitting height and diameter growth to relative irradiance over the growing season using Michaelis-Menton functions. There was little difference among tree species (Abies lasiocarpa, Picea glauca x sitchensis, Pinus contorta, Thuja plicata, Tsuga heterophylla) in response to ambient light. No meaningful variation in whole-plant compensation points was observed among species but the ranking of species' compensation points was consistent with their shade tolerance ranking. Five years after planting, total size and recent growth rates varied little among species from low to high light, implying an absence of trade-offs in low- and high-light growth strategies. Thuja plicata had the greatest response to increased light under deep shade (<20% relative irradiance). All species increased growth above 40% relative irradiance, with no clear whole-plant light saturation point evident under field conditions. Growth rates at high light were broadly overlapping and varied considerably within species. As expected, Pinus contorta growth exceeded that of other species above 70% relative irradiance, but it also exhibited high growth rates at low light. Greatest variability among species was at intermediate light levels (30-70% relative irradiance) where careful matching of tree species to light environment can maximize growth rates.

Wright, E. F., K. D. Coates, and P. Bartemucci. 1998. Regeneration from seed of 6 tree species in the interior cedar-hemlock forests of British Columbia as affected by substrate and canopy gap position. Can. J. For. Res. 28:1352-1364.
Abstract: Canopy gap size can play a major role in determining composition of tree regeneration after disturbance. The effect of different positions within gaps and within the intact forest has received less study. We seeded 6 tree species onto 2 substrates (organic and undisturbed moss) in 3 positions along a north-south gradient within 8 replicate 600 m² canopy gaps and in the intact forest off the south end of each gap (the gap positions), in 1995 and 1996. Germination of all species was strongly affected by gap position, seedbed substrate and year, but there was little evidence of partitioning by gap position among the species. Average germination was higher in north-facing positions of gaps and within the intact forest, and significantly higher on organic than undisturbed moss substrates (with the exception of Abies lasiocarpa (Hook.) Nutt which showed no preference for seedbed). Seedling survival was greatest for all species in the south end of the gap (north facing position) where soil moisture remained highest and light levels around 20% full sun were adequate for survival. Survival rapidly decreased with time in the intact forest, especially for the more shade-intolerant species, suggesting a possible species trade-off in the understory. In order to predict regeneration success in these forests, for either silvicultural purposes or to permit a better understanding of community dynamics and succession, it is important to consider the influence of position inside and outside of gaps and the nature of the seedbed substrate.

Wright, E. F., K. D. Coates, C. D. Canham, and P. Bartemucci. 1998. Species variability in growth response to light across a climatic gradient in northwestern British Columbia. Can. J. For. Res. 28:871-886.
Abstract: We characterize variation in radial and height growth of saplings of 11 tree species across a range of light levels in boreal, sub-boreal, subalpine and temperate forests of northwestern British Columbia. Shade tolerant species had the greatest response to an increase in light at low light levels, but had low asymptotic growth at high light. Shade intolerant species had weaker responses to increases at low light, but had the highest growth rates at high light. The effects of climate on intraspecific variation in sapling response to light were also related to shade tolerance: across different climatic regions, the most shade tolerant species varied in their response to low light but not high light, while shade intolerant species varied only in their high-light growth. Species with intermediate shade tolerance varied both the amplitude of growth at high light and the slope of the growth response at low light. Despite the interspecific trade-offs between high and low-light growth, there was a striking degree of overlap in the light response curves for the component species in virtually all of the climatic regions. Successional dynamics in these forests appear to be more strongly governed by interspecific variation in sapling survival than growth.

Kobe, R. K., and K. D. Coates. 1997. Models of sapling mortality as a function of growth to characterize interspecific variation in shade tolerance of eight tree species of northwestern British Columbia. Can. J. For. Res. 27:227-236.
Abstract: We have developed models of sapling mortality for the eight dominant tree species of northwestern British Columbia in order to better understand forest community dynamics and succession in this important forest region. The species-specific models characterize an individual's probability of mortality as a function of recent growth (a surrogate for whole-plant carbon balance). Interspecific comparisons of survival under low growth rates (i.e. suppression) provide a quantitative measure of the effective shade tolerance of these tree species. In particular, more shade tolerant species exhibited more rapid decays in mortality probability with increased radial growth. The broad and continuous range in shade tolerance ranking was: [Thuja plicata (Dougl. ex D. Don)] > [Tsuga heterophylla (Raf.) Sarg.] = [Abies lasiocarpa (Hook.) Nutt.)] > [Picea glauca (Moench) Voss x sitchensis (Bong.) Carr.] > [Pinus contorta var. latifolia Engelm.] > [Populus tremuloides Michx.] > [Populus balsamifera ssp. trichocarpa Torr. and Gray] = [Betula papyrifera Marsh]. At low growth rates, mortality varied between T. plicata and B. papyrifera by more than an order of magnitude. For some species, the three replicate sites exhibited significant variation, suggesting that shade tolerance may vary with site conditions (presumably soil moisture in our study sites). The mortality models are consistent with previous qualitative categorizations into shade tolerance classes and parallel the dominance of different species in post-disturbance succession. Our results suggest that species differences in non-catastrophic mortality are critical to understanding and predicting forest dynamics.

Manuscripts in Preparation

Coates, K. D., C. D. Canham, and E. Hall. In prep. Windthrow risk in mixed-species complex structured stands.
Manuscript based on on a maximum likelihood analysis of 24 partially cut stands in interior-cedar hemlock forests of northwestern BC and on 12 years of windthrow data from the Date Creek study.

Coates, K. D., and C. D. Canham. In prep. Competitive dynamics among canopy trees in northern temperate forests.
This is a continuation of the studies reported in Canham et al. 2004. We have established a further 16 stem mapped stands across a wide range of successional and and competitive communities. This paper will discuss all 9 trees species found in the study area. We are also working on a similar study in sub-boreal forests.

Coates, K. D., E. Hall, and C. D. Canham. In prep. Adult tree growth as a function of neighbourhood dynamics in sub-boreal forests: implications for management of Mountain Pine Beetle damaged stands.
Various silvicultural strategies can be applied in Mountain Pine Beetle damaged stands. Full salvage and planting is being employed widely. Other strategies include salvage with protection of advance regeneration and surviving residual canopy trees (with or without supplemental fill planting). Many areas will not be salvaged logged, but future yield predictions for such stands are required. Using the SORTIE-ND model, we assess different management options in complex structured stands.

Poulin, J. K., K. D. Coates, C. Messier, and P. Bartemucci. In prep. Effects of snags in intercepting light in boreal forests: empirical and modeling studies.
This study will quantify variation of light transmission through live trees and snags for the dominant boreal tree species of Québec (Populus tremuloides, Pinus banksiana, Betula papyrifera and Abies balsamea) and for snags in sub-boreal British Colombia forests species (Picea glauca x engelmanni, Abies lasiocarpa and Pinus contorta). Results show that snags in forests can intercept a high percent of light, especially those forests which are affected by some major epidemics that killed many or most of the overstory trees. Our data will be incorporated into SORTIE-ND, a stand dynamics model, to examine how light would vary following the extensive Mountain pine Beetle epidemic in northern British Columbia.