Mark Cole, Becky Sorensen, and Tyler Winder
The objective of our project was to measure the growth of vegetation in Yellowstone National Park since the forest fires of 1988. Our research will demonstrate that the fires were beneficial in providing the soil with new nutrients and greater plant growth. Although the canopy of the forest is still charred, the ground cover, which provides the wildlife with habitat and forage, is now revitalized with greener and healthier vegetation. Four areas of the park were chosen and then studied. Three were areas surrounding Yellowstone Lake that were burned by the fires. The last area, which was also in close proximinty to Yellowstone Lake, was untouched by the fires. For this project we used the imagine program to construct polygons that contained the four specified areas. The unburned area was used as a control to correlate with the other three areas. The conclusions derived from this project show that the burned areas now closely resemble, and in some cases have exceeded the areas that were untouched by fire.
During 1988, Yellowstone National Park was ravaged by forest fires which lasted from the beginning of summer in late June until the snows fell in early October. There were many negative opinions of park officials and the Department of Interior concerning the efforts to extinguish the fires. Although the fires left visible scars on the overhead canopy, the positive aspects were overlooked. History illustrates that Native Americans used controlled burns to enhance vegetation growth and keep the herds of elk and bison in the Yellowstone area. The key idea here was the use of controlled burns, something that the park had somewhat overlooked for serveral years. Fires are needed to replenish the earths soil with nutrients for greater plant growth. In many instances, fire is needed to facilitate tree species such as lodgepole pine. Many trees will not seed and reproduce unless fire produces temperatures hot enough to open the cones and let the seeds escape.
The former park policy instituted a no-burn policy which lasted for many years. Current government officials now believe that fires are necessary and productive. DeSpain illustrates the number of fires in Yellowstone National Park since the year 1972 (DeSpain, 1990).
Year <2.5a 2.5-12a 12-123a >123a Total fires Total acres ______________________________________________________________________ 1972 2 0 0 0 2 <1 1973 2 0 0 0 2 <1 1974 2 0 2 2 6 824 1975 6 0 0 0 6 <1 1976 9 0 1 1 11 1.550 1977 1 1 0 0 2 10 1978 1 0 0 0 1 <1 1979 6 0 0 2 8 4,942 1980 1 0 0 0 1 <1 1981 6 0 2 5 13 2,095 1982 2 0 0 0 2 <1 1983 1 0 0 0 1 <1 1984 7 0 0 0 7 <1 1985 26 0 0 0 26 <1 1986 14 0 0 0 14 <1 1987 8 0 0 0 8 <1 1988 8 0 1 6 15 127,213 Total 101 1 5 10 116 136,634 _____________________________________________________________________*This figure illustrates that due to the no-burn policy, which was in effect until 1988, there was abundant supplies of dry fuel on the forest floor.
Our group first obtained information on the Yellowstone area for the years of 1990, 1991, and 1992. A Julian dating system was used. A figure such as 004017-91I refers to January 4 - January 17 of 1991. This dating system uses a 364 day calendar. Our data sets are composed of nine 2-week intervals that were created from many periods. The composites are from the periods of May 1 until August 31 from the years 1990 - 1992.
The next step was to designate three areas in the park that were burned and one area that was unburned.The 2-week composite periods for 1990 were: ____________________________________________________________ Period Date of Coverage Julian Day ____________________________________________________________ 1 04/27 - 05/10/1990 117 - 130 2 05/11 - 05/24/1990 131 - 144 3 05/25 - 06/07/1990 145 - 158 4 06/08 - 06/21/1990 159 - 172 5 06/22 - 07/05/1990 173 - 186 6 07/06 - 07/19/1990 187 - 200 7 07/20 - 08/02/1990 201 - 214 8 08/03 - 08/16/1990 215 - 228 9 08/17 - 08/30/1990 229 - 242 ___________________________________________________________
Our methods for picking the fire areas was to overlay our Yellowstone image with fire grids that produced polygons of the fires. These fire grids were under the vector file in our imagine directories. We were then able to choose the three largest polygons and obtain the statistics for each. The areas we chose are located around Yellowstone Lake where many fires occurred. We examined the vegetation growth in the areas only during the summer months from May 1 - August 31 due to snow coverage in the remaining months. This project covered the years 1990 to 1992 using the normalized difference vegetation index (NDVI).
Our next procedure was to set up the polygons and obtain statistics for each area. First, we lumped all nine composites together to create a layer stack from the AOI; we then named that AOI and identified the selected areas by diagonal lines. Second, we brought up the classifier window and signature editor to examine the statistics for each of our three fire polygons. After collecting data on those three fire areas, our research demanded a need to examine an area that was not disturbed by the fire. We purposely designated an area that was close to our fire polygons so as to limit the bias results. This was done due to climate variations and soil types that differ across the park. In order to accomplish this we used the signature editor, AOI tools, and Seed Properties dialog boxes to help in identifying an area in our image. We used the "queens rule" icon and increased the Spectral Euclidean Distance to a value of 15. By doing this we were able to obtain an area that was sufficiently large enough to gain statistics. After selecting an area we then added it to our signature editor by clicking on the "Create New Signature from AOI Button". To determine if vegetation growth has steadily increased since the fires we did the same procedure as outlined above for all three years on each of our burn and no burn areas.
Figures pictured above are multi-temporal color composites of 1990, 1991, and 1992. Variations in these composites are, for the most part, attributed to year-to-year variations within the precipitation levels. The Figure below shows an overall map of Yellowstone National Park and the polygons or areas that were chosen and outlined. Area 1 is northwest of the lake, area 2 is northeast of the lake, and area 3 is just south of the lake. Area 4, or the no-burn area is just north of the lake between areas 1 and 2. Area 4 was used as a control area to compare areas 1, 2, and 3 to.
*These are the mean statistics obtained from the four areas for each of the three years:
Graphs 1-4 illustrate the areas growth rates from 1990 to 1992. Graphs 1, 3, and 4 show a sharp decline near mid-summer. This is thought to be an area that was hit by fires in 1992. The graphs and data show that there has been a steady increase in vegeatation growth since 1990. There are instances where the graphs actually show a decline, but overall the growth has been fairly steady and rising. Graphs 5, 6, and 7 illustrate a yearly growth of all four areas. These graphs show that by 1992 the burned areas (1, 2, and 3) have caught up to the area that was not burned (4) and in some instances have surpassed it in growth during the mid-summer months.
As our group began this investigation of the park we really were not sure what we would find. The park's overall growth rates do increase over time, however during the 1992 season the sharp decline provided the vegetation with a higher ablility to recover. This recovering exceeded the previous and later years moderately. The park's annual increase in vegetation provides information and insight that fire in a controled environment is beneficial. The data from 1992 supports the hypothesis significantly.
Yellowstone National Park is a very delicate ecosystem. This everchanging environment is difficult to manage and sometimes impossible. This was demonstrated by the fires that roared through uncontrollable in 1988. As our group gatherd and collected data we learned that fire plays an intricate role in the health of forest ecosystems. Controlled and manged fire is the key to a healthy ecosystem's success. When man supresses fire, it is only for his advantage. This logic that man incorporates into the ecoststems is not always in the envionments best interest or what Mother Natrure had ever intened.
Dispain, Doug. Yellowstone Vegetation Growth and Type
Ramsey, Doug. GER 575/576 Remote Sensing 1 Lab Exercise 6 How TO Create an AOI.
Smith, Chris. Pyden, Nancy. Cole, Pam. ERDAS Field Guide, The Third Edition. February, 1994.