Western Juniper Woodlands of the Pacific Northwest
Total Page:16
File Type:pdf, Size:1020Kb
Western Juniper Woodlands (of the Pacific Northwest) Science Assessment October 6, 1994 Lee E. Eddleman Professor, Rangeland Resources Oregon State University Corvallis, Oregon Patricia M. Miller Assistant Professor Courtesy Rangeland Resources Oregon State University Corvallis, Oregon Richard F. Miller Professor, Rangeland Resources Eastern Oregon Agricultural Research Center Burns, Oregon Patricia L. Dysart Graduate Research Assistant Rangeland Resources Oregon State University Corvallis, Oregon TABLE OF CONTENTS Page EXECUTIVE SUMMARY ........................................... i WESTERN JUNIPER (Juniperus occidentalis Hook. ssp. occidentalis) WOODLANDS. ................................................. 1 Introduction ................................................ 1 Current Status.............................................. 2 Distribution of Western Juniper............................ 2 Holocene Changes in Western Juniper Woodlands ................. 4 Introduction ........................................... 4 Prehistoric Expansion of Juniper .......................... 4 Historic Expansion of Juniper ............................. 6 Conclusions .......................................... 9 Biology of Western Juniper.................................... 11 Physiological Ecology of Western Juniper and Associated Species ...................................... 17 Introduction ........................................... 17 Western Juniper — Patterns in Biomass Allocation............ 17 Western Juniper — Allocation Patterns of Carbon and Minerals . 18 Western Juniper — Biomass and Leaf Area Estimators ......... 20 Western Juniper — Leaf Morphology of Adult Foliage .......... 26 Western Juniper — Seasonal Ring Growth .................. 26 Western Juniper — Physiological Ecology .................. 27 Western Juniper — Measured and simulated leaf conductance and transpiration .................................... 33 Western Juniper — Modeling Leaf Conductance and Transpiration........................................ 34 Gray Rabbitbrush ...................................... 35 Green Rabbitbrush ..................................... 38 Sandberg Bluegrass .................................... 38 Idaho Fescue ......................................... 40 Ecology of Western Juniper Woodlands .......................... 41 Geology and Soils ...................................... 41 Climate .............................................. 47 Woodland Maturity ..................................... 47 Plant Associations and Communities ....................... 48 TABLE OF CONTENTS (Cont'd.) Page Range Sites ........................................... 51 Plant Species ......................................... 52 Woodland Dynamics .................................... 55 Interactions and Succession ......................... 55 Fire Influences .................................... 57 Grazing Influences ................................. 60 Microbiotic Soil Crusts .................................. 62 Introduction ....................................... 62 Effects of Disturbance on Microbiotic Crusts ............. 63 Crust Influence on Soil Properties and Seedling Establishment ........................... 67 Spatial Heterogeneity Within Microbiotic Crusts .......... 70 Hydrologic Cycle ............................................ 73 Interception........................................... 73 Infiltration ............................................ 75 Runoff, Erosion, and Sedimentation ........................ 78 Wildlife in Western Juniper Woodlands .......................... 83 Large Herbivores ...................................... 83 Birds ................................................ 88 Small Mammals........................................ 89 Amphibians and Reptiles ................................ 90 Conclusions .......................................... 90 Conversion of Western Juniper Woodlands ....................... 91 Grazing Management of Western Juniper Woodlands ............... 98 Grazing Young Woodlands ............................... 99 Grazing Management of Young Closed Western Juniper Woodlands on Shallow Soils ............. 100 Rationale ........................................ 100 Grazing Young Western Juniper Woodlands on Deep Soils ..... 103 Grazing Management Following Western Juniper Control ....... 105 Grazing Management on Sites Susceptible to Western Juniper Encroachment and Dominance ................... 107 BIBLIOGRAPHY .................................................. 108 LIST OF TABLES Table Page 1 Relationships between tree components (y) and tree age (x) .......... 19 2 Dimensions of live junipers on Horse Ridge: n' = measured and n = the 10 destructively analyzed ............................ 22 3 Regression equations for estimating component biomass, volume, surface area, and biomass treatment for western juniper with basal circumference (cm) as the independent variable. The first 2 12 follow the form ln(Y) = A + B*ln(X) with variances (Sy,x ) in logarithmic units. The last four are linear, untransformed equations with variances in arithmetic units ....................... 23 4 Average dimensions of western juniper estimated by double sampling ............................................. 24 5 Regression equations, standard error of estimate (Sy,x) and correlation coefficients for estimating leaf biomass and leaf area ....... 25 6 Daily total CO2 assimilated in grams per tree and daily water transpired in liters per tree, during a full sun day, for the average sized large-adult western juniper, 4.5 m tall with a basal circumference of 66 + 4 cm (Miller et al. 1992) ................ 29 7 Comparison of Juvenile and large adults classes of Chrysothamnus nauseosus for the Tintic, Utah, population, June 1989, presented as mean ± SD: pre-dawn xylem pressure 5 5 potential ( pd), midday xylem pressure potential ( md), photosynthesis (Amax ), stomatal conductance to water vapour (gmax ), instantaneous ratio of internal to ambient CO2 concentration (cia /c ), transpiration (E), instantaneous A/E, carbon isotope discrimination ( ), integrated cia /c estimated from , integrated A/E estimated from and the leaf-to-air vapour pressure deficit, leaf nitrogen, potential photosynthetic nitrogen use efficiency (PPNUE), and plant height. All differences between juvenile and large adult classes were significantly different (P<0.05) based on a two-tailed Student's t-test comparison of juveniles and adults, with the exception of the instantaneous cia /c which was based on a one-tailed Student's t-test since the direction of the difference was predicted. Sample sizes ranged from 18 to 20 for the juvenile class, and from 19 to 20 for the large adult class ....................................... 37 LIST OF TABLES (Cont'd.) Table Page 8 Some physical and chemical characteristics of western juniper woodland soils .............................................. 43 9 Relationship of grazed and ungrazed conditions to cover of crusts, grasses, and bare soil ........................... 66 10 Permeability, infiltration and sediment production associated with microbiotic crusts on the Colorado Plateau ........... 68 11 Watershed and hillslope-scale hydrologic studies in pinyon-juniper environments................................... 80 12 List of wildlife species observed in western juniper communities (from Puchy and Marshal 1993) ................................. 84 13 Aboveground biomass production response to western juniper removal in central Oregon in 1984 (Vaitkus 1986). Values are for the second year and only for trees with >5 m crown diameter .......... 93 14 Aboveground biomass production response to western juniper removal in central Oregon in 1983 and 1984. Values are weight for percent of area in each zone (sub-canopy and interspace) and include all size classes of trees ............................. 93 15 Estimated biomass and mineral content of a western juniper tree 11 meters (36 ft) tall with a basal diameter of 44 cm (17.3 in) (from Larsen 1993, Kramer 1990, and Miller et al. 1990) ...... 95 i SCIENCE ASSESSMENT EXECUTIVE SUMMARY WESTERN JUNIPER (Juniperus occidentalis Hook. ssp. occidentalis) WOODLANDS Distribution of Western Juniper (Juniperus occidentalis ssp. occidentalis) woodlands is across a broad variety of vegetation types, soils, landscapes and moisture regimes. Area occupied by western juniper woodlands in the Pacific Northwest is nearly 4 million acres (about 1.6 million ha). Over 2.3 million acres of woodland are in Oregon with approximately 10% of the area in old woodlands. Nearly 90% of the area in Oregon is composed of young woodlands with trees less than 150 years old. Data and observation indicate the species continues to expand its range into new areas. Prehistoric Expansion and retraction of western juniper took place over long time periods. Data indicate that where it did occur, its density was less than that at present. Historic Expansion of western juniper woodlands has originated from open, sparse and savannah-like stands of old juniper trees many of which are today 400 to 600 years of age or even older. Many of these stands were growing on topographic situations where fire would have been restricted. Factors which may have influenced the rapid expansion were a combination of mild winters with greater precipitation, reduced fire frequency and livestock grazing that contributed to increases in big sagebrush reduced production of grasses. Development of present day woodlands occurred under a different combination