Tree Regeneration and Growth in Gaps


In order to predict regeneration success in these ICH 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. These experiments were established to determine the effect of gap size, position within gap and seedbed (substrate) on the abundance and diversity of natural regeneration in clearcuts, undisturbed forests and partially cut forests. The effect of these variables on the survival and growth of planted seedlings was also examined. Planted seedlings in gap
Planted seedlings in logging-created gap
Advance regen in natural gap Germinants on moss
Advance regeneration in a natural forest gap Redcedar and hemlock germinants on moss

Available Literature:

Wright, E.F., Coates, K.D. and Bartemucci, P. 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). Prepared organic seedbed
Prepared organic seedbed in gap
 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.

Coates, K.D and Burton, P.J. 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-Menten functions. There was little difference among tree species (Abies lasiocarpa (Hook.) Nutt., Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carr., Pinus contorta Dougl. ex Loud., Thuja plicata Donn ex D. Don, Tsuga heterophylla (Raf.) Sarg.) in response to ambient light. No significant differences in whole-plant compensation points were 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.

Coates, K.D.  2000. Conifer seedling response to northern temperate forest gaps. Forest Ecology and Management. Vol. 127 pp. 249-269.
Abstract:  Studies of gap dynamics have contributed significantly to our understanding of the role of small-scale disturbance in forest ecosystems, but have been little used by foresters for predicting tree responses to partial cutting. Fifth year 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. Growth of all the 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 (Pinus contorta), the most light-demanding species, exceeded that of all other species in large gaps (1001--5000 m2) and clearcuts. In large and medium gaps (301--1000 m2), the largest trees of all species were found in the middle gap position and there was little difference between the sunny north and shady south positions, except for lodgepole pine which clearly grew poorly in the south position. Total size and growth rates of all species were nearly identical in small gaps (20--300 m2) and again in the forest understory. The light advantage expected off the north end of high latitude gaps was not a benefit for tree growth, suggesting that below-ground effects of canopy edge trees have an important influence on seedling growth in these forests. 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. 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.

Coates, K.D.  2002. Tree recruitment in gaps of various size, clearcuts and undisturbed mixed forest of interior British Columbia, Canada.  Forest Ecology and Management Vol. 155 pp. 387-398.
Abstract:
 
Studies of gap dynamics have contributed signi®cantly to our understanding of the role of small-scale disturbance in forest ecosystems, but have been little used by foresters for predicting tree responses to partial cutting. Fifth year growth and survival of ®ve 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. Growth of all the 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 (Pinus contorta), the most light-demanding species, exceeded that of all other species in large gaps (1001±5000 m2) and clearcuts. In large and medium gaps (301±1000 m2), the largest trees of all species were found in the middle gap position and there was little difference between the sunny north and shady south positions, except for lodgepole pine which clearly grew poorly in the south position. Total size and growth rates of all species were nearly identical in small gaps (20±300 m2) and again in the forest understory. The light advantage expected off the north end of high latitude gaps was not a bene®t for tree growth, suggesting that below-ground effects of canopy edge trees have an important in¯uence on seedling growth in these forests. 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. 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. 

Kranabetter, J.M., and Coates, K.D. 2004. Ten-year postharvest effects of silviculture systems on soil-resource availability and conifer nutrition in a northern temperate forest.  Can. J. For. Res. 34: 800-809.

Abstract:  Silviculture systems (clearcut, partial-cut and unharvested forest) were compared 9 - 10 years after harvesting to determine the effects on soil resource availability, especially nitrogen, and conifer nutrition.  These results were used to discuss the effects of silviculture systems on tree growth in relation to the more commonly described effects of light.  Differences in soil properties across the silviculture treatments were most apparent in the forest floor.  Depth and C:N ratio of the forest floor had decreased slightly in clearcuts, and forest floor moisture was highest under partial-cuts.  Despite these differences in soil chemistry and soil moisture, no differences were detected in mineralizable nitrogen (anaerobic incubation) nor in situ net nitrogen mineralization between treatments.  Height growth and foliar mass were reduced under the low light conditions of the partial-cut, but there were no differences in foliar nitrogen concentrations of hybrid white spruce, western redcedar and western hemlock saplings.  Mature western hemlock trees in the partial-cut also had concentrations of foliar nitrogen equal to mature trees in the unharvested forest.  Overall, we detected only minor effects of silviculture systems on soils after 10 years, and conclude that light availability is likely more responsible for the current differences in tree growth.

 

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