Juvenile and Adult Tree Growth Studies

We have undertaken several studies to better understand and quantify the processes controlling growth of seedling, saplings and adult trees. For seedlings and saplings, or juvenile trees, our early studies concentrated on the light-growth relationship on mesic site types. Our most recent study has expanded the light-growth relationship to include different site types and gradients of soil moisture and nutrients. Currently, in SORTIE-ND, seedlings and saplings grow as a function of understory light availability to a size of 3-5 cm diameter (DBH) depending on species and then shift to adult tree growth functions based on neighbourhood competition. Our most detailed study of adult tree growth has been recently published (Coates et al. 2009, see below) for interior cedar hemlock forests.

Over the past 5 years we have been studying adult tree growth in sub-boreal spruce forests; first we established 16 stem-mapped sites on mesic sites and results from this study were incorporated into our Research Parameter File 1.0. We then undertook a new study to stem-map multiple sites across a gradient of successional stages and productivity (broader gradient of soil moisture and nutrients). This larger dataset combined with our earlier dataset for mesic sites has been analyized and a paper is in preparation.  

None of the juvenile or adult tree growth functions across productivity gradients have been incorporated into the SORTIE-ND model. This work has been delayed due to funding cuts to the Forest Science Program. 

Above- versus below-ground competitive effects and responses of a guild of temperate tree species
Coates, K. David, Charles D. Canham and Philip T. LePage. 2009.

This paper builds on our earlier study by Canham et al. (2004), see below, in the interior cedar hemlock forests (ICH) of northwestern British Columbia. This paper provides a comprehensive description of our approach to studying and modeling adult tree growth. The neutral theory debate has highlighted the scarcity of robust empirical estimates of the magnitude of competitive effects and responses within guilds of co-occurring tree species. Our analysis quantifies the relative magnitude of all possible pairwise competitive interactions within a guild of nine co-occurring tree species in temperate forests of northern, interior British Columbia, and explicitly partitions the competitive effects of neighbours into the effects of shading versus the residual effects of "crowding", assumed to reflect belowground competition. Model selection techniques effectively separated above- and belowground competition these complex interior cedar hemlock forests, and allowed us to assess differences among species in competitive effects and responses. While belowground effects were strong, they were due to proximity of neighbours from a very specific (and small) subset of strong competitors within the guild. Response to crowding varied with tree size but the nature of the relationship varied widely among the species.

Evaluation of stand dynamics in old mountain pine beetle attacked stands
Coates, K.D., Astrup, A., Amoroso, A.M., Burleigh, J. 2008.

This Forest Science Program funded study (M085196) of regeneration and growth dynamics after mountain pine beetle (MPB) attack was undertaken in 2007 in the Flathead area which was impacted by the MPB between 1978 and 1982. A paper is in preparation. The regeneration component of the study was designed to complement the Astrup et al. 2008 study of recruitment dynamics, see below, where we were able to examine regeneration success up to 10 years after attack in the current epidemic hitting northern BC. The growth component of the study was to gain a better understanding of the growth potential of secondary structure (see Coates et al. 2006) that survives a MPB disturbance.  

The extent of MPB mortality, regeneration delay, release of advance regeneration and other surviving residual trees (secondary structure) and post-beetle stand growth was determined. Five plots were established in each of 22 stands representing a range of MPB attack intensity. Pre-attack basal area varied between 29 and 58 m2 ha-1. The percent of basal area killed by beetles varied from 42 to 100% with most stands between 60 and 80%. Six stands exceeded 80% basal area mortality and 3 stands were below 60% mortality. In 2007, twenty-five to 30 years after attack basal area varied between 4 and 51 m2 ha-1. Five stands, ranging in mortality at time of attack from 51 to 79%, had fully recovered their pre-attack stand basal area. Four stands, ranging in mortality at time of attack from 68 to 100%, had poor basal area recovery. Growth release on surviving trees exhibited species and size variability. Release of surviving lodgepole pine trees was often dramatic. Recruitment of new regeneration post-beetle attack was often, but not always, delayed by 5-10 years. Densities of post-beetle regeneration were often high in 2007. Based on age of understory trees in 2007, there was little advance regeneration in these forests at the time of the beetle attack.   

Growth patterns of juvenile aspen and spruce in the western boreal forests of Canada
Astrup, Rasums. 2007.

This study is part of Rasmus Astrup's Ph.D studies at UBC. A paper is in preparation. The study presents diameter and height growth models as a function of growing season light availability, tree size and geographic region for juvenile trembling aspen and spruce for different regions across western boreal and sub-boreal Canada. There was strong support for region-specific models for both tree species. The models developed in this study build on and improve on the models presented in Wright et al. 1998.

For the sub-boreal spruce forests impacted by the mountain pine beetle epidemic we combined data from this study and the study by Wright et al. 1998 and tested the new diameter and height growth models. The best models were incorporated into Research Parameter File 1.0 for sub-boreal spruce forests. 

Evaluation of competition and light estimation indices for predicting diameter growth in mature boreal mixed forests
Stadt, Kenneth J., Carolyn Huston, K. David Coates, Zhili Feng, Mark R.T.Dale, Victor J. Lieffers. 2007.

This paper presents results from boreal forests in Alberta. Part of the analysis uses models developed by Canham et al (2004) - see below. Any of the models presented in this paper could be added as growth behaviours in SORTIE-ND. 

Using the large dataset of natural-origin, spatially-mapped trees in the permanent sample plot (PSP) program maintained by the Alberta Land and Forest Division we compared competition indices for modeling the growth of individual trees. Specifically we wanted to test: (1) the effectiveness of conventional distance-independent and distance-dependent competition indices as well as distance dependent light resource indices as predictors of future tree diameter growth, (2) examine differences in competitive ability among the common boreal forest species, (3) compare functions for determining the effect of tree size on diameter increment, and (4) determine if competitive ability and coefficients for competition indices are different across ecosites.

A neighbourhood analysis of canopy tree competition: effects of shading versus crowding
Canham, C.D., P.T. LePage, K.D. Coates. 2004.

This Date Creek study is our first attempt to develop, for use in SORTIE-ND, an extension of traditional distance dependent, spatial competition analyses 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 neighbouring trees on target tree growth as a function of the species, size, and distance to neighbouring trees. The analyses provide empirical estimates of competition coefficients that quantify the relative magnitude of the competitive effect of species i on species j and explicitly partition the competitive effects of neighbours into the effects of shading versus the residual effects of “crowding”, which is assumed to reflect both belowground competition and physical, aboveground inhibition of crown development. Our major objective was to develop methods of quantifying canopy tree competition that could be parameterized using data readily available from permanent plots in mapped forest stands and that could then be incorporated in spatially explicit models of forest dynamics. This study used data from the Date Creek experiment in mature and old forest types. Based on results from this study, we further expanded our sampling to a wider range of successional stages and competitive communities to obtain more robust estimates of tree growth - see Coates et al. (2009) above.   

Conifer seedling response to northern temperate forest gaps
Coates K.D. 2000.

This paper presents results from the planted tree esperiments at the Date Creek Experiment. Growth and survival of five commonly planted tree species were contrasted in canopy gaps (single-tree to 5000 m2), in the forest understory and in the open conditions of a clear-cut. There were strong and consistent trends in growth response among the tree species as gap size increased. At five years, growth of all species increased rapidly from small single-tree gaps to about 1000 m2 gaps, but thereafter showed little change up to 5000 m2. Tree size and current growth rates for all species were highest in full open conditions. Performance of lodgepole pine, the most light-demanding species, exceeded that of all other species in large gaps (1001-5000 m2) and clearcuts. Total size and growth rates of all species were nearly identical in small gaps (10-300 m2) and again in the forest understory. Differences in mortality among the tree species were evident, with the most light demanding species having the greatest early mortality in shaded areas of medium gaps, in small gaps and in the forest understory. Careful matching of tree species to gap size and gap position can minimize early mortality and maximize growth rates. At this early stage of development, opening sizes need not be very large (0.1-0.2 ha or larger) in order for most tree species to achieve growth rates similar to those found in the open conditions of clearcuts.

Effects of suppression and release on sapling growth for 11 tree species of northern, interior British Columbia
Wright, Elaine F.,C.D. Canham, K.D. Coates. 2000.

This study builds on our original light-growth study of juvenile trees (Wright et al. 1998, see below).  Here we explore how to incorporate growth functions for young trees that account for past periods of suppression and release. The effects of the lengths of previous periods of suppression or periods of release on current growth responses of the 11 major conifer and broadleaved trees of northwestern British Columbia were examined. These species ranged from very shade tolerant to shade intolerant. We were specifically interested in the degree to which increasing length of suppression had long-term effects on subsequent response to release. The ability of trees to release following partial cutting or natural disturbances like the currrrent mountain pine beetle epidemic are of considerable interest to forest managers and there has also been a long-term debate in forestry over the management of advance regeneration. All northern BC tree species frequently experienced multiple episodes of both suppression and release prior to reaching even sub-canopy size. We found a clear relationship between shade tolerance and the magnitude of the effects of past periods of suppression and release on sapling growth. In general, there was no effect of previous suppression on the current response of shade tolerant species to light. For the more light demanding species, the effects of suppression disappeared over time during release for all species except trembling aspen.

Growth of planted tree seedlings in response to ambient light levels in northwestern interior cedar???????hemlock forests of British Columbia
Coates, K.D. and P.J. Burton. 1999.

This Date Creek study was designed to characterize variation in height and radial growth in response to ambient light levels for the five most commonly planted tree species in northwestern B.C.: lodgepole pine, hybrid spruce, western hemlock, western redcedar, and subalpine fir. 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. Growth of all tree species increased gradually with increasing light and continued to increase even at very high light levels, albeit slowly for the most shade-tolerant species. Growth rates at high light were broadly overlapping and varied considerably within species. Greatest variability among species was at intermediate light levels (30-70%) where careful matching of tree species to light environment can maximize growth rates. 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. An interesting result from this study was our finding that whole-plant aboveground growth rates in the field are not consistent with expectations from leaf-level physiological studies suggesting physiological studies should be viewed with caution as a basis for predicting community dynamics, succession and growth rates in the field.

Species variability in growth response to light across climatic regions in northwestern British Columbia
Wright, Elaine F., K.D. Coates, C.D. Canham, and P.Bartemucci. 1998.

This is the original juvenile tree light-growth study undertaken in the forests of northern British Columbia as part of our overall SORTIE-related studies. This study builds on the work of Pacala et al (1994) but expanded the approach to a much broader range of sites types by sampling across multiple ecological zones in BC (boreal, sub-boreal, subalpine, and temperate forests). The results from this study for the interior cedar hemlock forests were incorporated into SORTIE/BC (Coates et al. 2003).  Light is arguably the most important factor influencing tree growth in temperate and boreal forest biomes and is certainly the factor most directly manipulated by forest management actions. We characterized variation in radial and height growth of saplings of 11 tree species across a range of light levels. 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. When combining the results of this study with the results from Kobe and Coates (1997), we concluded that successional dynamics in northern temperate forests appears to be more strongly governed by interspecific variation in sapling survival than growth.