Pinyon-juniper Type Research Articles

Fire and Climate Suitability for Woody Vegetation Communities in the South Central United States

Climate and fire are primary drivers of plant species distributions. Long-term management of south central United States woody vegetation communities can benefit from information on potential changes in climate and fire frequencies, and how these changes might affect plant communities. We used historical (1900 to 1929) and future (2040 to 2069 and 2070 to 2099) projected climate data for the conterminous US to estimate reference and future fire probabilities using a physical chemistry fire frequency model. We then used the fire probability data with additional climate parameters to construct maximum entropy environmental suitability models for three south central US vegetation communities. The modeled communities included an oak type (dominated by post oak, Quercus stellata Wangenh., and blackjack oak, Q. marilandica Münchh.), a mesquite type (dominated by honey mesquite, Prosopis glandulosa Torr., and velvet mesquite, P. velutina Wooton), and a pinyon-juniper type (dominated by pinyon pine, Pinus edulis Engelm., and Utah juniper, Juniperus osteosperma [Torr.] Little). We mapped baseline and future mean fire-climate suitability using data from three global climate models for 2040 to 2069 and 2070 to 2099; we also mapped future locations of threshold conditions for which all three models agreed on suitability for each community. Future projections included northward, southward, and eastward shifts in suitable conditions for the oaks along a broad path of fire-climate stability; an overall reduction in suitable area for historic mesquite communities coupled with potential expansion to new areas; and constriction and isolation of suitable conditions for pinyon-juniper communities. The inclusion of fire probability adds an important driver of vegetation distribution to climate envelope modeling. The simple models showed good fit, but future projections failed to account for future management activities or land use changes. Results provided information on potential future de-coupling and spatial re-arrangement of environmental conditions under which these communities have historically persisted and been managed. In particular, consensus threshold maps can inform long-term planning for maintenance or restoration of these communities, and they can be used as a potential tool for other communities in fire-prone environments within the study area and beyond its borders.

Impact of Burning and Grazing on Soil Water Patterns in the Pinyon-Juniper Type

Impact of Burning and Grazing on Soil Water Patterns in the Pinyon-Juniper Type

Diets of Domestic Sheep and Other Large Herbivores in Southcentral Colorado

Diets of Domestic Sheep and Other Large Herbivores in Southcentral Colorado

Herbage Production following Tree and Shrub Removal in the Pinyon-Juniper Type of Arizona

Herbage production was evaluated after overstory removal from different sites within the pinyon-juniper type. Average annual production varied from 43 to 643 kg/ha before treatment and 715 to 3,703 kg/ha after treatment. Production variation among sites was related to annual precipitation, pretreatment tree canopy, pretreatment nitrate-nitrogen, and presence or absence of limestone soils. Grasses increased in the composition from 46 to 73% on the average, while forbs decreased from 21 to 19%, and half-shrubs and shrubs decreased from 33 to 8%. The pinyon-juniper vegetation type covers a substantial portion of western and southwestern United States. Recent estimates range from 17.3 million (Forest-Range Task Force 1972) to 32.5 million ha (West et al. 1975), with 3.4 million (Forest-Range Task Force 1972) to 5.7 million ha (Ffolliott and Thorud 1975) in Arizona. The extent of this vegetation type makes it important even though the per-hectare productivity is relatively low. The diversity of products available from pinyon-juniper woodlands, which gives it some of its appeal, has also resulted in conflicts of use (Gifford and Busby 1975; Aldon and Loring 1977). Many have suggested that the best use is as range for grazing animals (Springfield 1976). As a result, substantial areas of pinyon and juniper trees have been removed to reduce forage plant competition. Better productivity information is needed so research and management attention can be focused to obtain the best yield of all products and amenities from this vegetation type. The objective of this study was to determine the herbage production after overstory removal from various sites within the pinyon-juniper type of Arizona. Sites with soils developed from different parent rocks were evaluated for their ability to produce native herbaceous vegetation. Description Climate The climate throughout the pinyon-juniper type is rather severe for tree growth, characterized by low precipitation, low relative humidity, hot summers, and much clear weather and intense sunshine. Average annual rainfall in the Arizona pinyon-juniper type varies from 30 to 50 cm while typical January and July mean temperatures are 2’ and 22’ C, respectively. In Arizona, a prominent and unique climatic feature is the presence of two distinct precipitation periods. This biomodal pattern is most distinct in the Flagstaff/ Prescott area (Jameson 1969). Precipitation generally comes from the Pacific Ocean during the winter and from the Gulf of Mexico during the summer. Topo

Impact of Incremental Surface Soil Depths on Plant Production, Transpiration Ratios, and Nitrogen Mineralization Rates

From October 1974 to August 1976, a study was conducted to measure how incremental surface soil depths from the pinyonjuniper type affected plant production, plant transpiration rates,

Vegetation Changes following Fire in the Pinyon-Juniper Type of West-Central Utah

Highlight: The stages of succession following fire began with weedy annuals that reached a peak within 3 to 4 years. Juniper woodlands were well developed 8.5 to 90 years following fire. Intermediate stages of succession varied, but followed a general pattern of perennial grasses, perennial grasses-shrubs, and perennial grasses-shrubs-trees. The percentage of dead sagebrush was positively correlated with density of junipers. Thirtythree years was the average minimum age at which Utah juniper produced seed. Juniper and pinyon trees in the Intermountain region have expanded their range greatly since settlement, primarily in the last 100 years. Existing speculation suggests that a major cause of this expansion, either directly or indirectly, was the reduction in fires following settlement. Some authors consider the juniper-pinyon expansion to be several times that of the original cover (Cottam and Stewart, 1940; Woodbury, 1947). In 195 1 it was estimated that this type covered about 30% of the State of Utah (Reuss and Blanch, 1951). The expansion has been primarily into the sagebrush-grass community on the lower edges of original pinyon-juniper. If unchecked, trees become dominant and eventually crowd out most herbaceous and shrub species that provide forage for livestock and big game. The purpose of this study was to examine the vegetation on burns of various ages and determine the successional patterns following fire. The study was conducted primarily on the lower slopes and foothills of the Sheeprock Mountains in Utah and surrounding areas in the vicinity of the Benmore Experimental Range; however, one area was located in the Valley Mountains west of Fayette, Utah. Fire scars of various ages are generally evident in these areas. Tree species in the areas studied were Utah juniper (Juniperus osteosperma) and singleleaf pinyon (Pinus monophylla).

Heat and Desiccation Resistance of Tissue of Important Trees and Grasses of the Pinyon-Juniper Type

1. Relative heat and desiccation resistances of tree twigs and grass culm bases were determined by raising the tissues to various temperatures. The treatments were followed by testing for tissue viability with 2,3,5-triphenyltetrazolium chloride. 2. Grass culm bases, including those of Hilaria jamesii, Bouteloua gracilis, B. eriopoda, and B. curtipendula, were the most sensitive tissues studied. Juniperus deppeana and Pinus edulis twigs were the least sensitive. Twigs of J. monosperma and J. osteosperma were intermediate. 3. Variations in heat resistance were negatively correlated with depression of the wet-bulb thermometer on the day of sampling. During hot, dry weather air temperatures at the soil surface were very near the lethal temperatures determined for grass culm bases. It is probable that fires at this time would be more damaging to grass plants than fires would be during cooler weather when lethal temperatures determined for culm bases are higher.