Pinyon-Juniper/Shrublands Long-Term Successional Trends: Implications For Woodland Health and Management

Transcription

1 Pinyon-Juniper/Shrublands Long-Term Successional Trends: Implications For Woodland Health and Management Robin J. Tausch 1 Richard Miller 2 and Durant McArthur 3 1. Rocky Mountain Research Station, Reno, Nevada 2. Oregon State University, Corvallis, Oregon 3. Rocky Mountain Research Station, Provo, Utah, Retired

2 Although we now have a good idea of how woodlands have been changing across the Great Basin as a whole, these woodlands have never had the inventories necessary to adequately understand the types and distribution of the changes involved or their variability. Although they can give the appearance of simplicity, these woodlands are highly complex. They are first highly variable in the associated perennial species present in the understory communities. Depending on location there are: Different species and subspecies of sagebrush present Different species of deep rooted perennial grasses present Different species of perennial forbs present The different combinations of these perennial plant species indicate significant differences in how a site may be changing and should be managed.

3 Woodland sites differ widely in climate, elevation, topography, aspect, slope, geology, and soils, all of which affect productivity. Most importantly, woodland sites also have major differences in the land use impacts they have received over the last 14 years. These differences affect the needs, and options available, for effective management to minimize negative impacts, and determines the procedures available for use for this management. Central to an understanding the underlying variability, and its affects on management is an understanding of how the woodlands have changed over the last 1 to 15 years, and how they may continue to change over the next 5 to 1 years. These ongoing changes have direct affects on the possibilities for management, and on the outcomes from treatment.

4 Great Basin Study Sites for the Changing Fire Regimes Study Funded by the Joint Fire Sciences Program Nevada: Robin Tausch, Rocky Mountain Research Station, Reno, NV Oregon and Idaho: Rick Miller, Oregon State University Utah: Durant McArthur, Rocky Mountain Research Station, Provo, UT, Retired Shoshone (Robin Tausch) High Desert Lahontan Humboldt High Central North & South Steens (Rick Miller) South Mt Juniper Mt High Calcareous Bonneville East Tintic S. Nevada Megan Bradely, Geography Dept.,UNR Mt. Irish # # Clover Mountains = Cross-Mountain Transect of Plots # = Mountain Top Grid of Plots

5 Comparisons of Community Types Sampled, and Comparison of Relative Abundance of Pre- Settlement (age oldest tree > 14 yrs.) and Post-Settlement (age of oldest tree < 14 yrs.) plots for two cross-mountain transects sampled in Nevada and Utah for the Changing Fire Regimes Study. A Joint Fire Sciences Program Funded Project Percent of Total Shoshone Mountains East Tintic Mountains 68% 32% 13% 87% Percent of Total Plots Shoshone Mountains East Tintic Mountains 22% 21% 78% 79% Sagebrush Woodland Tree Dominance Level >14Yrs <14Yrs Age of the Oldest Tree in the PLot An average of ¾ of the area sampled was woodland and for nearly 8% of those sites the trees established after 186.

6 Rates of Tree Establishment By Decade for Three cross-mountain Study Transects. Establishment began in the late 18 s, peaked in the 2 th century, and has declined since. 12 Post-settlement Tintic Utah 5 4 Post-settlement Shoshone, Nevada Juniper Mountain, Idaho Post-settlement Pre-settlement 5 4 Pre-settlement 2 Pre-settlement Trees / Ha Total 5 4 Total 25 2 Total Decade A Joint Fire Sciences Program Funded Study

7 Southern Nevada Mountain Top Grid Pinyon-Juniper Woodland Sites have the same establishment pattern as the rest of the region. Megan Bradley 29, M.S. Thesis, University of Nevada, Reno

8 Average tree Age plus 95% C.L. by Crown Diameter Class for data from Four Great Basin Transects. Tree age by region is most closely related to crown diameter (meters). In Nevada and Utah Classes 1-3 established after 195 and classes 4-6 between 19 and 195. Combined, classes 4-6 dominate the woodland biomass. Sampled (m)

9 Underdown Canyon Transect, Shoshone Mountains, Nevada. The mid-2 th century peak, followed by a decline, occurs regardless of the level of tree dominance

10 Pattern of Understory Decline Over Time With the Increase in Pinyon/Juniper Dominance Tree Dominance = Low Mid High Phase Identification Phase 1 Phase 2 Phase Total Understory Leaf Bio. (kg) Total Under Picture 1 Picture 2 Total Tree Total Tree Leaf Bio. (kg) Leaf Bio. W eighted Avg. Age of Pinyon Pictures 1 and 2 are on the two slides that follow.

11 Picture 1 Mountain side mostly Phase I, limited Phase II Upper Underdown Canyon, Shoshone Mountains, Nevada, June 1973

12 Picture 2 Mountain side mostly Phase II, Phase III common, and some Phase I Upper Underdown Canyon, Shoshone Mountains, Nevada, June 27

13 37 Years of Changes on the North Kern East Chaining, NE Nevada Hillside has mostly Phase I and some Phase II 1971 Chained in 1969 Hillside mostly Phase III with some Phase II years of re-growth of trees surviving chaining Now nearing the end of Phase II

14 37 Years of Changes on the Blythe Springs Chaining, SE Nevada 1971 Hillside has mostly Phases I and II, with some Phase III (Chained in 1958) 28 5 years of re-growth of trees surviving chaining. Now in Phase III. Hillside has mostly Phase III with some Phase II (Re-chained mid 198 s)

15 Underdown 1973 Underdown 25 Total Understory Leaf Biomass (kg/.1 ha plot) Low Tree High Tree Slope Difference P <.1 Slope break marks Phase II / Phase III boundary Tree Needle Biomass (kg/.1 ha plot) Underdown Canyon, Shoshone Mountains, NV Pre-Treatment Data (4 plots of.1 ha)

16 Pattern of Increase in One-Hour Live Fuels With Increasing Relative Tree Dominance in the Underdown Canyon Demonstraton Area, Shoshone Mountains, NV Underdown Canyon Demonstration Area Fuels 3 Phase 1 Phase 2 Phase 3 Total One-Hour Live Fuels (kg/ha) Low Elevation Plots 5 Mid Elevation Plots High Elevation Plots Relative Tree Percent Cover

17 Distribution of the Study Plots Between Low, Mid, and High Tree Dominance for the Changing Fire Regimes Study (sampled 21) Sweetwater Mtns., CA Upper Underdown Canyon, NV 1973 Upper Underdown Canyon, NV 25 6 Phase II Percent of Total 4 2 Phase I 41% 4% 49% 47% Shoshone Mountains E. Tintic Mountains Phase III 1% 13% Low Mid High Tree Dominance Level

18 From the growth rate in Phase II shown in slide 1 most of the Phase II in the previous slide will be Phase III by the middle of this century. By mid-century about 2/3 of the woodlands in Nevada and Utah will have eight to ten times the fuel loads of the previous sagebrush dominated community. These high fuel loads, plus their increasing continuity, is resulting in an increase in both intense crown fires, and insect attacks (i.e. bark beetle, sawfly, scale insect) covering larger and larger areas of the landscape. The Slides that follow cover a sequence of four years following intense wildfires in Phase III expansion woodlands.

19 This fire burned 2, acres of Phase III expansion woodlands in five hours. Cathedral Burn, White Pine Range, Nevada, Mid-June, 28 (Burned Mid-July 27)

20 Two years after the fire the site is dominated by native annuals Cathedral Burn, White Pine Range, Nevada, Late July, 29 (Burned Mid-July 27)

21 6, acres burned in seven hours. Three years later cheatgrass and tumble mustard increasing in dominance. Jackass Burn, Sweetwater Mountains, Nevada-California, Late August, 29 (Burned 26)

22 Cheatgrass and Tumble Mustard Dominate a Phase III Expansion Woodland Site Four Years After Wildfire Burn Site is located on the East Side of Mount Como, Pine Nut Mountains, Nevada

23 Over the woodlands of Nevada and western Utah there are currently about 1, acres of expansion woodlands a year moving into Phase III. As this continues the potential for both wildfire and insect attack are rapidly increasing across larger and larger areas of the landscape. Management to maintain or improve these sites involves limiting the potential for both wildfire and insect attack, while simultaneously trying to limit the expansion and dominance of exotic annual or perennial plant invaders.