Progress 01/17/01 to 01/16/07
Outputs
The studies reported include fertilization studies in an age sequence of aspen and birch forests, an NPK factorial fertilization study in aspen, a partial NPK factorial fertilization study in birch, a nitrogen rate study in birch, a combination thinning and fertilization study in two white spruce stands, environmental monitoring in black spruce stands and analysis of sugar, sawdust and drought treatments in key successional turning points (LTER sites). The duration of the studies has been 35 years in the upland stands and 14 years in the LTER study. The primary results of the studies included information on tree level dynamics, stand level dynamics, and landscape level dynamics related to tree growth. At the stand level young aspen stands were nutrient limited but this limitation decreased as the stands aged. Birch stands did not show a nutrient limitation. Although in the one single application study coupled with a thinning treatment birch growth did improve 10 years
after treatment. In white spruce stands fertilization increased growth for two years. The combination of thinning and fertilization resulted in growth increases for up to 28 years. Low-level fertilization in the LTER sites started to show significant increases in growth 5 years after the start of the study. The sugar and sawdust treatments resulted in decreased growth in the first two years after application and the drought treatments resulted in significant decreases in growth on floodplain sites as opposed to uplands. The opposite of what was expected. The complexity of ecosystem dynamics across the landscape is related to a differential structure and interaction of process limiting factors. Fertilization may increase tree growth if other major limiting factors (such as moisture) are satisfied. So a direct change in that factor, like irrigation in a dry environment, should increase growth up to the limit set by the next environmental factor. However a change in the potential
amplitude of a limiting factor, like thinning a forest stand to reduce the total water utilization (an indirect change related to the limiting factor availability), may not augment the control of growth with comparable effectiveness that would be observed by irrigation (a direct change in the limiting factor availability). Within a forest stand a number of growth limiting factors could be diminished as a result of thinning. Factors like nutrient availability would increase due to reduced competition, greater site utilization by the remaining trees, and increased nutrient turnover in the soil environment. The results of these studies lead to the following structure of forest growth controlling factors. Temperature is a major control that defines the growing season in white spruce and hardwood ecosystems. Once the growing season starts the major limitation is hypothesized as nutrient limitation that is followed by moisture limitation further into the growing season when the recharge of
soil moisture by spring snowmelt has been utilized. Therefore moisture is the primary growth limiting factor and can easily explain the results of fertilization studies when combined with thinning treatments.
Impacts
Forest growth in interior Alaska is controlled by a number of well defined environmental state factors. There growth limiting factors include (1) soil and air temperature, (2) soil moisture dynamics, and (3) nutrient availability. The structure of these factors is also dependent on the topographic location of the ecosystem. For example on north facing slopes the temperature dynamics, both air and soil, will be the primary limiting controls on ecosystem processes and tree growth. On south facing slopes, temperature dynamics will control the length of the growing season, but soil moisture may then become the primary control once a threshold temperature has been reached. Understanding the functional structure of the ecosystem controls will then allow for a substantial increase in our ability to predict tree growth in the future especially with the continued influence of climate change in the boreal forest.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
Work has continued on the preparation of five research papers that detail the analysis of seven major long-term studies focused on the relationship between forest stand density, nutrient availability and tree growth dynamics in interior Alaska. The studies include fertilization studies in a time sequence of aspen and birch forests, an NPK factorial fertilization study in aspen, a partial NPK factorial fertilization study in birch, a nitrogen rate study in birch, a combination thinning and fertilization study in two white spruce stands, environmental monitoring in black spruce stands and analysis of sugar, sawdust and drought treatments in key successional turning points in upland and floodplain successional sequences (LTER sites). The current duration of the studies has been 37 years in the upland stands and 15 years in the LTER study sites. Results indicate that young aspen stands were nutrient limited but this limitation disappeared as the stands grew older. Birch
stands in most studies did not show a nutrient limitation. Although in the single application study birch growth did improve approximately 10 years after fertilization and a thinning treatment. It is not clear if the change in growth was the direct result of the fertilization treatment. White spruce stands showed increased growth for two years as a result of five years of fertilization. The combination of thinning and fertilization resulted in growth increases for 28 years during the 37-year study period. Low-level fertilization in the LTER sites started to show significant increases in growth 5 years after the start of the study. In these studies the fertilization level was designed to simply double the natural mineralization rate. Sugar and sawdust treatments resulted in growth decreases in the first two years after application and the drought treatments resulted in significant decreases in growth on floodplain sites as opposed to uplands. The opposite of what was expected. The
complexity of ecosystem dynamics across the landscape is related to a differential structure and interaction of the process limiting factors. Fertilization may only increase tree growth if other major limiting factors (such as moisture) are satisfied. So a direct change in that factor, like irrigation in a dry environment, should increase growth up to the limit set by the next environmental factor, say nitrogen. However a change in the potential amplitude of a limiting factor, like thinning a forest stand to reduce the total water utilization on a site (an indirect change related to the limiting factor availability), may not augment the control of growth with comparable effectiveness that would be observed by irrigation (a direct change in the limiting factor availability). In the case of a forest stand a large number of growth limiting factors could be diminished as a result of thinning. Factors like nutrient availability would be increased as a result of reduced competition, greater
site utilization by the remaining individual trees, and possibly increased nutrient turnover in the soil environment. These factors may require several years to produce an increase in growth in the remaining trees.
Impacts
Forest growth in interior Alaska is controlled by a number of well defined environmental state factors. These growth limiting factors include (1) soil and air temperature, (2) soil moisture dynamics, and (3) nutrient availability. The structure of these factors is also dependent on the topographic location of the ecosystem. For example on north facing slopes the temperature dynamics, both air and soil, will be the primary limiting controls on ecosystem processes and tree growth. On south facing slopes, temperature dynamics will control the length of the growing season, but soil moisture may then become the primary control once a threshold temperature has been reached. Understanding the functional structure of the ecosystem controls will then allow for a substantial increase in our ability to predict tree growth in the future especially with the continued influence of climate change in the boreal forest.
Publications
- Chapin, III, F. S., A. D. McGuire, R. W. Ruess, M. W. W. Walker, R. Boone, M. Edwards, B. Finney, L. D. Hinzman, J. B. Jones, G. P. Juday, E. S. Kasischke, K. Kielland, A. H. Lloyd, M. W. Oswood, C. Ping, E. Rexstad, V. Romanovsky, J. Schimel, E. Sparrow, B. Sveinbjornsson, D. W. Valentine, K. Van Cleve, D. L. Verbyla, L. A. Viereck, R. A. Werner, T. L. Wurtz, J. Yarie. 2006. Summary and Synthesis: Past and future changes in Alaskas boreal forest. Chapter 21. Alaskas Changing Boreal Forest. F. Stuart Chapin III, Mark W. Oswood, Keith Van Cleve, Leslie A. Viereck and David L. Verbyla (eds.). Oxford University Press. 354 pgs.
- Yarie, J. and W. Parton. 2005. Potential changes in carbon dynamics due to climate change measured in the past two decades. Can. J. For. Res. 35:2258-2267.
- Yarie, J. and J. Garron. 2005. Log decomposition dynamics in interior Alaska - Preliminary results of the 10-year time frame. XXII IUFRO World Congress. Brisbane Australia. Poster won one of nine awards out of 850 posters at the meeting.
- Chapin, III, F. S., J. Yarie, K. Van Cleve, and L. A. Viereck. 2006. The Conceptual basis of LTER studies in the Alaskan boreal forest. Chapter 1. Alaskas Changing Boreal Forest. F. Stuart Chapin III, Mark W. Oswood, Keith Van Cleve, Leslie A. Viereck and David L. Verbyla (eds.). Oxford University Press. 354 pgs.
- Yarie, J. and K. Van Cleve. 2006. Controls over forest production in Interior Alaska. Chapter 11. Alaskas Changing Boreal Forest. F. Stuart Chapin III, Mark W. Oswood, Keith Van Cleve, Leslie A. Viereck and David L. Verbyla (eds.). Oxford University Press. 354 pgs.
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Progress 01/01/04 to 12/31/04
Outputs
Analysis of seven major long-term studies on tree growth dynamics performed in interior Alaska over a 35-year time frame has been completed. The studies include fertilization studies in a time sequence of aspen and birch forests, an NPK factorial fertilization study in aspen, a partial NPK factorial fertilization study in birch, a nitrogen rate study in birch, a combination thinning and fertilization study in two white spruce stands, environmental monitoring in black spruce stands and analysis of sugar, sawdust and drought treatments in key successional turning points in upland and floodplain successional sequences (LTER sites). The current duration of the studies has been 34 years in the upland stands and 13 years in the LTER study sites. The primary results of the studies included information on stand level dynamics, species level dynamics and landscape level dynamics. At the stand level young aspen stands were nutrient limited but this limitation decreased as the
stands grew older. The birch stands in most studies did not show a nutrient limitation. In the white spruce stands fertilization only increased growth for two years. The combination of thinning and fertilization resulted in growth increases for up to 28 years in the study period. Low-level fertilization in the LTER sites started to show significant increases in growth 5 years after the start of the study. The sugar and sawdust treatments resulted in growth decrease in the first two years after application and the drought treatments resulted in significant decreases in growth on floodplain sites as opposed to uplands. The complexity of ecosystem dynamics across the landscape is related to a differential structure and interaction of the process limiting factors. Fertilization may only increase tree growth if other major limiting factors (such as moisture) are satisfied. So a direct change in that factor, like irrigation in a dry environment, should increase growth up to the limit set by
the next environmental factor, say nitrogen. However a change in the potential amplitude of a limiting factor, like thinning a forest stand to reduce the total water utilization on a site (an indirect change related to the limiting factor availability), may not augment the control of growth with comparable effectiveness that would be observed by irrigation (a direct change in the limiting factor availability). In the case of a forest stand a large number of growth limiting factors could be diminished as a result of thinning. Factors like nutrient availability would be increased as a result of reduced competition, greater site utilization by the remaining individual trees, and possibly increased nutrient turnover in the soil environment.
Impacts
The climatic and nutritional controls of forest growth in interior Alaska are starting to become clear. These studies will help us to understand the state factor structure of the major controls for forest growth and ecosystem function. An understanding of the structure of the major controls of forest growth will give us an enhanced ability to predict the consequences of forest management activities prior to harvest on the growth of trees within the stand. These studies will also allow for better predictions of the effects of climate change on the functioning of forest ecosystems in interior Alaska.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
Three items received continuing work in the past year that will start to produce new knowledge in the coming years. First a first draft of a paper that describes the results of the 35-year continuing study of ecosystem dynamics in the major vegetation types in interior Alaska was completed. Because of the amount of information contained in the paper and its length it is expected that the review process will take the next year to complete with hopeful publication in 2005. Second an additional set of black spruce sites were added to the log decomposition study. These represent the final set of sites needed to cover the major vegetation types on the floodplain of interior Alaska. Third progress was being made on the rewriting of the SAFED model in Visual Basic within the ARC Objects programming environment. The information developed in the 35-year study represents the analysis of seven major long-term studies on tree growth dynamics performed in interior Alaska. The
studies include fertilization studies in a time sequence of aspen and birch forests, an NPK factorial fertilization study in aspen, a partial NPK factorial fertilization study in birch, a nitrogen rate study in birch, a combination thinning and fertilization study in two white spruce stands, environmental monitoring in black spruce stands and analysis of sugar, sawdust and drought treatments in key successional turning points in upland and floodplain successional sequences (LTER sites). The current duration of the studies has been 34 years in the upland stands and 13 years in the LTER study sites. The primary results of the studies included information on stand level dynamics, species level dynamics and landscape level dynamics. At the stand level young aspen stands were nutrient limited but this limitation decreased as the stands grew older. The birch stands in most studies did not show a nutrient limitation. Although in the one single application study birch growth did improve
approximately 10 years after fertilization and a thinning treatment. In the white spruce stands fertilization only increased growth for two years. The combination of thinning and fertilization resulted in growth increases for up to 28 years in the study period. Low-level fertilization in the LTER sites started to show significant increases in growth 5 years after the start of the study. The sugar and sawdust treatments resulted in growth decrease in the first two years after application and the drought treatments resulted in significant decreases in growth on floodplain sites as opposed to uplands. The opposite of what was expected. During the current year (2004) the ten-year sampling of the logs in the decomposition will start. This sampling sequence will require three years to complete after which publication of the 10-year results will commence.
Impacts
The results of the 35-year study will yield a long-term perspective on the climatic and nutrient controls of forest growth in interior Alaska. The duration of this study and its distribution in various vegetation types across the landscape will start to yield a potential understanding of the effects of climate change on the forest ecosystems found in interior Alaska.
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
Environmental and forest growth variables measured include: aboveground and soil climate variables within an age sequence of birch, aspen, white spruce and black spruce forest types; tree growth measurements within the experimental sites; and litterfall estimates within each site. Work dealing with the log decomposition study resulted in the addition of burned sites on the Tanana River floodplain in white spruce and black spruce ecosystems and partial establishment of control, floodplain black spruce sites. Conclusions that have been developed from analysis of data collected in this 35-year study are directly related to the environmental state factors - climate, biotic components, topography, parent material, and the age of the system. As a result it is proposed that the primary control on forest productivity is related to the nitrogen content of the tree foliage. Additional reductions in tree growth then resulted from limitations caused by the additional state
factors. We can now suggest roles for each of the state factors on the control of forest production. Soil parent material and topography represent two relatively stable controls on ecosystem production. The parent materials represent three major groups that are correlated to three major physiographic positions on the landscape. Topography (slope and aspect) has an effect on radiation received at sites. In addition the soil depth to ground water which is controlled by the site elevation above the major river levels and the location of the site in relationship to the major mountain ranges in the state influence forest production. The key components of climate related to productivity are the cold environmental temperatures, both air and soil, and the relatively dry summer growing season. Based on moisture limitation experiments it now appears that current summer rainfall is insufficient for maximum growth of trees. The soil physical and chemical environments display controls on forest
productivity. Soil organic matter turnover rates are limited by soil temperature, which would limit both the uptake potential of nitrogen by the trees and the decomposition dynamics of the organic matter. A number of thinning and fertilization experiments have indicated that both nitrogen availability and tree density have control on the individual tree growth rates. Short-term high-level fertilization studies combined with thinning have indicated that the thinning treatment results in a long-term increased growth rate. The high-level fertilizer addition does result in increasing growth but only for a relatively short time period. A low-level fertilization treatment that has continued for a number of years is starting to show continued increases in growth rates in unthinned forest stands. This would indicate that the availability of the fertilizer nutrient supply would diminish quickly. Finally, there are a number of additional factors that produce short-term events that can have
long-term affects on the subsequent ecosystem structure and function. These events include fire, insect outbreaks, flooding, and permafrost dynamics.
Impacts
The complexity of forest growth limiting factors is beginning to be understood for interior Alaska. It can be suggested that forest growth is controlled by a hierarchical structure of environmental factors. The most important environmental factor appears to be nitrogen availability but its importance is augmented by landscape position and additional environmental characteristics.
Publications
- Yarie, J. and S. Billings. 2002. Carbon balance of the Taiga forest within Alaska. Can. J. For. Res. 32:757-767.
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Progress 01/01/01 to 12/31/01
Outputs
The primary objectives that were addressed in the past year were the continuation of the long-term environmental monitoring of selected forest stands in interior Alaska for the following terms: (a) climate monitoring of air and soil variables, and (b) completion of the five year sample of the log decomposition study. In addition, due to a fire that occurred on the floodplain adjacent to the Bonanza Creek Experimental Forest, two additional sites for log decomposition were established. One site was in a floodplain white spruce stand and other site was in a black spruce/white spruce stand. Within the black spruce/white spruce stand a comparative study was started between black spruce and white spruce logs that were placed on the forest floor and standing black spruce log decomposition dynamics. The utilization of these stands at this time represents a study that was actually started immediately after a major disturbance has occurred in forest stands adjacent to a river.
Currently it is planned to add additional replications for these sites in the summer of 2002.
Impacts
Greater knowledge and understanding of forest growth dynamics, especially after major disturbance, over a long term perspective.
Publications
- No publications reported this period
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