Juniper Woodlands Research Articles

Implementation of mid-scale fire regime condition class mapping

We used mid-scale Fire Regime Condition Class (FRCC) mapping to provide Hawthorne Army Depot in the Mount Grant area of Nevada, USA, with data layers to plan fuels restoration projects to meet resource management goals. FRCC mapping computes an index of the departure of existing conditions from the natural range of variability, and consists of five primary steps: (1) mapping the Potential Natural Vegetation Types (PNVT) based on interpretation of a soil survey; (2) refining PNVTs based on additional information; (3) modelling the natural range of variability (NRV) per PNVT; (4) using field verification, calculation and mapping of departure of current distribution of structural vegetation classes interpreted by remote sensing (IKONOS 4-m resolution satellite imagery) from the NRV; and (5) mapping structural vegetation classes that differ from reference conditions. Pinyon–juniper and mountain mahogany woodlands were found within the NRV, whereas departure increased from moderate for low and big sagebrush PNVTs and mixed desert shrub to high for riparian mountain meadow. Several PNVTs showed departures that were close to FRCC class limits. The common recommendation to reach the NRV was to decrease the percentage of late-development closed and cheatgrass-dominant classes, thus increasing the percentage of early and mid-development classes.

Effect of Pinyon–Juniper Tree Cover on the Soil Seed Bank

As pinyon–juniper (specifically, Pinus monophylla and Juniperus osteosperma) woodlands in the western United States increase in distribution and density, understory growth declines and the occurrence of crown fires increases, leaving mountainsides open to both soil erosion and invasion by exotic species. We examined if the loss in understory cover that occurred with increasing tree cover was reflected in the density and diversity of the seed bank. Seed banks in stands with low, medium, and high tree cover were measured in late October for 2 yr. Multivariate analyses indicated that cover and diversity of standing vegetation changed as tree cover increased. However, the seed bank did not differ in overall seed density or species diversity because seeds of the 13 species that comprised 86% of the seed bank occurred in similar density across the tree-cover groups. Sixty-three percent of the species that were in the seed bank were absent from the vegetation (mostly annual forbs). In addition, 49% of the species that occurred in the standing vegetation were not in the seed bank (mostly perennial forbs and shrubs). Only Artemisia tridentata, Bromus tectorum, and Collinsia parviflora displayed positive Spearman rank correlations between percent cover in the vegetation and density in the seed bank. Thus, much of the standing vegetation was not represented in the seed bank, and the few species that dominated the seed bank occurred across varying covers of pinyon–juniper. Conforme los bosques de “Pinyon–juniper” (específicamente, Pinus monophylla Torr. & Frém. y Juniperus osteosperma (Torr.) Little) del oeste de Estados Unidos de América se incrementan en distribución y densidad, el crecimiento del estrato herbáceo disminuye y la ocurrencia de incendios aumenta, dejando las laderas de las montañas expuestas a la erosión del suelo y la invasión de especies exóticas. Examinamos si la pérdida de cobertura herbácea, que ocurre al aumentar la cobertura de los árboles, se reflejó en la densidad y diversidad del banco de semillas del suelo. Durante 2 años, a finales de octubre, se midió el banco de semillas en poblaciones con cobertura de árboles baja, media, y alta. Los análisis multivariados indicaron que la cobertura y diversidad de la población vegetal cambió al incrementarse la cobertura de árboles. Sin embargo, el banco de semillas del suelo no difirió en la densidad y diversidad general de especies, porque las semillas de las 13 especies que constituyeron el 86% del banco de semillas, ocurrieron en densidad similar en los tres niveles de cobertura de árboles. El 63% de las especies que formaban el banco de semilla no estaban presentes en la vegetación (principalmente hierbas anuales). Además, 49% de les especies presentes en la vegetación no estaban en el banco de semilla (principalmente hierbas perennes y arbustos). Solo Artemisia tridentata Nutt., Bromus tectorum L. y Collinsia parviflora Lindl. Mostraron correlaciones de rango Spearman positivas entre el porcentaje de cobertura en la vegetación y la densidad en el banco de semilla. Por lo tanto, buena parte de la vegetación no estuvo representada en el banco de semillas, y las pocas especies que dominaron el banco de semillas ocurrieron en los diferentes niveles de cobertura de “Pinyon–juniper”.

Relationships Between Western Juniper (Juniperus occidentalis) and Understory Vegetation

AbstractWestern juniper has been actively invading sagebrush plant communities for about 130 yr. Western juniper canopy cover generally increases as western juniper invades sagebrush steppe communities and succession progresses toward a western juniper woodland. Our goal was to estimate the impact of juniper invasion and canopy increase on understory vegetation structure and productivity on 101 sites in northeastern California. The primary objectives of this study were to: (1) examine the influence of increasing western juniper canopy cover on the composition and productivity of understory vegetation; and (2) assess the effects of western juniper removal on understory vegetation. Sites in early, mid-, and late successional stages and sites on the same soils that had not been invaded were selected. Sites where western juniper had been removed by prescribed fire, mechanical, or chemical methods were compared to adjacent untreated sites. Western juniper canopy cover, understory cover and species composition, productivity, and bare ground were determined at each site during May through July 2005 and 2006. Regression analysis was used to evaluate the relationship between western juniper canopy cover and understory vegetation parameters. Logistic regression was used to detect understory differences between treated (juniper removed) and untreated (juniper not removed) sites. A significant relationship was found between western juniper canopy cover and understory species richness, shrub cover, forb cover, total grass cover, cheatgrass cover, herbaceous productivity, and bare ground. Removal of western juniper increased total grass cover, cheatgrass cover, and productivity, and reduced bare ground. The results of this study support findings by researchers in other states that western juniper influences plant community structure and productivity, and removal of western juniper might reverse these changes in structure, but also might increase opportunities for invasion of cheatgrass.

Characterizing and classifying complex fuels — A new approach

In the United States, fire managers have relied on a small number of stylized fuel models for over 30 years (Anderson 1982)—standard descriptions of homogeneous surface fuel constituents associated with specific types of fire behaviour—as inputs to mathematical calculations of surface fire behaviour. Other systems for describing fuels and calculating fire behaviour have been developed for Canada (Forestry Canada Fire Danger Group 1992) and Australia (Cheney and Sullivan 1997). Scientists and managers are seeking more accurate predictions of fire behaviour and fire effects for operational use, planning, and simulations. While categorical descriptors of fuels have served managers reasonably well in the past, improved predictions might require more comprehensive descriptions of fuelbeds (soil organic matter and all live and dead vegetation) that discriminate among fuel components. Regional resource managers challenged scientists at the US Forest Service Pacific Wildland Fire Sciences Laboratory to develop a comprehensive library of measured fuelbeds that would meet their needs for quantifying fuels over a wide range of vegetative types, such as temperate rainforests, dry ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) forests, juniper (Juniperus spp.) woodlands, and sagebrush (Artemisia spp.). In principle, realistic multistrata fuelbeds could better represent fuels than could stylized models, providing information about the biophysical environment that would be useful to assessment of fire and biological conditions. The Fuel Characteristic Classification System (FCCS) was developed in response to this challenge. A significant component of the FCCS is a large fuelbed library complied from federal agencies and the scientific literature. This data library assembled from ecosystems throughout the United States includes quantitative and qualitative variables for a wide range of structural components. The FCCS could potentially provide input for a variety of applications including fire behaviour, fire effects on ecological components (e.g., standing dead wood and large woody debris), smoke production (e.g., calculation of particulate emissions), and stand dynamics modeling (e.g., stem density and stem sizes). For example, the FCCS fuelbeds are already being used as inputs for calculating fuel consumption and large-scale emissions (Wiedinmyer et al. 2006). The articles in this feature describe and document the key components and applications of the FCCS. Because the FCCS is a substantial departure from traditional fuel inventory and modeling concepts, extensive input has been elicited from scientists and resource managers in North America during development and beta testing. In addition, the FCCS was formally reviewed by a panel of 12 fire scientists in November 2005. Scientists asked important questions about the validity and scientific foundation of the FCCS. For example, could measured fuelbeds better account for differences in fire behaviour and effects than could stylized fuel models? The following articles were revised in response to this extensive review prior to submission for publication and additional peer review.

LONG-TERM VEGETATION DYNAMICS IN A CUT WESTERN JUNIPER WOODLAND

Abstract Western juniper (Juniperus occidentalis spp. occidentalis Hook.) expansion in the northern Great Basin has reduced shrubsteppe productivity and diversity. Chainsaw cutting of western juniper woodlands is commonly applied to remove tree interference and restore sagebrush plant communities. Studies assessing understory response following cutting have been limited to early successional stages and have not evaluated the effects of western juniper debris on plant succession. Cutting western juniper produces a large amount of debris which is commonly left on site, occupying a significant portion of treated areas. This study evaluated successional dynamics spanning 13 years after western juniper cutting. Four 0.45-ha blocks were selected on Steens Mountain in southeastern Oregon. Western juniper cover averaged 26% and mature tree density averaged 250 trees · ha−1. Blocks were cut in late summer 1991. Understory standing crop, cover, and density were compared among 3 locations: old canopy litter mats (ca...

Slow recolonization of burned oak–juniper woodlands by Ashe juniper ( Juniperus ashei): Ten years of succession after crown fire

Fire is an important control on the distribution of plant communities on the Edwards Plateau in central Texas. Although the effects of fire in grasslands have been well studied, little is known about the recovery of mature oak–Ashe juniper ( Quercus spp.– Juniperus ashei) woodlands after crown fire. These woodlands are the only nesting habitat of the endangered golden-cheeked warbler ( Dendroica chrysoparia). In February 1996, crown fires burned more than 4000 ha of woodland on Fort Hood Military Reservation. Permanent transects were installed in moderately to severely burned areas on three soils types in 1996 and data were collected annually from 1996 to 2002 and again in 2005. We also sampled 36 transects in unburned areas on the same soil types in 2001 and 2005. Overall stem density (all species combined) in the burned areas recovered rapidly, at least in the smaller size classes (<1.8 m tall), and, by 2005, sapling stem density (>1.8 m tall, <5 cm dbh) was higher in burned areas than in unburned areas for all soil types (ANOVA, p < 0.02). Tree density (>5 cm dbh) in burned areas remained low until 2005 (2001: 20 ± 36 stems/ha; 2005: 326 ± 260 stems/ha). The dominant oak species recovered rapidly due to vigorous resprouting. Ashe juniper, a fire-sensitive species, recovered much more slowly. Only six Ashe juniper saplings (and no trees) were found in burned transects in 2005, compared to 646–871 trees/ha in unburned areas. Although Ashe juniper was largely absent from the burned areas, post-fire species composition was otherwise similar to unburned communities and became more similar with time (Sorenson similarity index in 1996: 0.70–0.83; 2005: 0.86–0.88). NMS ordination separated burned communities on different soils more than unburned communities, because all unburned areas were dominated by Ashe juniper. Due to the slow recovery of Ashe juniper, it will likely be decades before the burned areas are again suitable as breeding habitat for golden-cheeked warblers.

Juniper removal may not increase overall Klamath River Basin water yields

Based on published research and watershed assessment techniques, we evaluated the feasibility of augmenting water yields in the Klamath River and its major tributaries by removing western juniper, which has expanded dramatically within the Klamath River Basin over the past 130 years. The results suggest that the conversion of western juniper woodlands to shrublands or grasslands would not substantially increase water yields for the Basin as a whole. However, researchers should further examine the potential for juniper management to increase both summer flow rates in small tributaries and spring flows that support small wetlands across the upper Basin; other possible benefits could include restoring wildlife in sagebrush-rangeland habitat, reducing wildfire risks and increasing the land available for livestock grazing.

Seiridium cardinale on Juniperus species in Greece

Summary Seiridium cardinale, the cause of cypress canker disease, was found on Juniperus foetidissima, J. excelsa, J. oxycedrus and J. phoenicea, in a number of natural juniper woodlands in Greece. The presence of infections was sporadic in most cases, with a limited number of plants affected by the pathogen. At one locality in the Prespes Lakes region of northern Greece, however, the incidence of infection was very high, especially on J. foetidissima and J. excelsa. The identity of S. cardinale was confirmed using morphological characters and comparisons of DNA sequences for the β‐tubulin gene region. The pathogenicity of S. cardinale isolates from Juniperus and Cupressus was verified in cross‐inoculation trials on both potted and field grown plants.

Markov models of land cover dynamics in a southern Great Plains grassland region

Grassland regions of the southern Great Plains are fragmented by agricultural activity and many habitat remnants have experienced encroachment by juniper (Juniperus virginiana L.). Recently, many cropland areas have been converted to monoculture grassland (pastures) and enrolled into the Conservation Reserve Program (CRP). Our objectives were to develop spatial and temporal Markov models to characterize land cover dynamics relative to juniper expansion and CRP using aerial photography from 1965, 1981, and 1995. We used landscapes surrounding three Breeding Bird Survey routes with varying levels of juniper encroachment in Oklahoma as study areas. As expected, land cover changes from 1965 to 1995 included increases in juniper woodland, mixed juniper-deciduous woodland, and pastures from CRP activity. Markov models revealed that juniper had a low likelihood of self-replacement in early stages of encroachment. In all areas, relatively little native grassland was lost to juniper encroachment, but other native habitat types such as deciduous woodland were heavily impacted. Transition probabilities for land cover dynamics varied significantly both spatially and temporally. Projections of these raw transition matrices produced widely varying models of future land cover conditions. By modifying the matrices to account for recent and potential socio-political and ecological changes occurring in this region, a number of more plausible land cover scenarios were produced than those resulting from simple projections of raw transition matrices.

On the phylogenetics and population differentiation of the Great Tit and Blue Tit in Jordan

IntroductionThe Great Tit, Parus major, is a widespread and commonpasserine species throughout the western parts of the NearEast and can be found in both mountainous and lowlandMediterranean climate areas. It is a common resident of themountains and rift margins of northwest Jordan (Andrews1995) in a variety of woodland habitats. In addition, anapparently distinct population isolated by the Moab plateauoccurs in the southwestern highlands of Jordan, in the relicoak–juniper woodlands of Dana (Khoury 1998), which aresurrounded by open desert and steppe. The southern limitof the Great Tit is the Sinai and southwest Jordan. Thesubspecies of the Near Eastern Great Tit is generallydocumented as P. m. terraesanctae (Harrap and Quinn1996) and is similar to the birds of continental Europe, butwith duller grey-green, less bright dark-green coloration onthe upperparts than the nominate major from Asia Minorand underparts that are distinctly a paler yellow, less sat-urated, and dark (Shiriahi 1996).The Blue Tit, Parus caeruleus, is currently restrictedwithin the Near East to the mountains of northwestern(NW) Jordan (Andrews 1995), and although it possiblybreeds in NW Syria (David Murdoch, personal communi-cation; Snow and Perrins 1998), there are no recent recordsof breeding south of Turkey, except in Jordan. The isolatedpopulation of NW Jordan is confined to relatively humidMediterranean climate zones, in rather dense evergreen oakwoodland and pine–oak forests, the remnants of whichcover an area of less than 100 km

Ecological restoration needs derived from reference conditions for a semi-arid landscape in Western Colorado, USA

Semi-arid ecosystems cover tens of millions of hectares in the Intermountain West of the United States, and most have altered plant communities due to land use, especially livestock grazing. Thus, relatively unaltered “reference” plant community information is needed to guide restoration. Plant communities were sampled over a large (∼600 000 ha) semi-arid landscape in western Colorado, within piñon–juniper woodlands, sagebrush shrublands, and grasslands, and over conditions ranging from relict areas without livestock grazing to heavily utilized areas. Ordination was used to group samples into ranked categories of ecological condition within 18 communities, and means–tests and other techniques were used to identify ecological differences among ranks across vegetation types. With few exceptions, grass and forb cover, biological soil crust cover, and species diversity declined concomitant with ranks representing increasingly degraded conditions, while non-native species cover was variable among ranks. Landscape-level species abundance patterns also differed significantly among ranks, with herbaceous species generally exhibiting less constancy and cover within degraded samples compared to samples of reference quality. These semi-arid ecosystems will require both active (e.g., reseeding) and passive (grazing management) restoration approaches, at local- and landscape-levels, respectively, if the goal is to restore native plant composition and abundance.

Topoedaphic and morphological complexity of foliar damage and mortality within western juniper (Juniperus occidentalis var. occidentalis) woodlands following an extreme meteorological event

AbstractAim An extreme early season freeze event in October 2002 resulted in significant foliar damage and/or mortality within western juniper woodlands. We identify the geographical patterns of tree damage based on morphological, topographical and edaphic parameters, and discuss the ecological implications of this event.Location Oregon, USA (44.0–44.2° N, 120.3–120.9° W).Methods We sampled trees on four matched pairs of disturbed and minimally disturbed study sites within the core area of tree damage. We collected information about age, morphology (height, basal area, level of foliar damage), and topographic position (elevation, slope, aspect) for each tree sampled using dendroecological and GPS/GIS procedures. We collected plot‐level data on tree density and degree of cover for shrubs and grasses. We used a series of Mann–Whitney, Kruskal–Wallis and Wilcoxon tests and graphical analyses to determine if significant differences exist in our collected variables both between matched pairs and within our disturbed sites.Results Topographically, we found that aspect was a critical element regulating damage, with trees in colder microenvironments (north‐westerly slopes) experiencing less damage because they were further along in the annual process of cold‐hardening. The majority of damaged trees were found in areas of higher density and more even age structure that are typical of recent juniper afforestation. Morphologically, we show that trees with greater basal areas and/or less stature were less likely to have foliar damage, consistent with winter cavitation.Main conclusions Our results show that the spatial pattern of damage was closely related to topography and tree morphology, parameters that, in turn, correspond closely to differences between the historical locales of western juniper and juniper woodlands that have emerged in a 100+ year period of rapid afforestation. This freeze event fits the criteria for a large, infrequent disturbance in that it was spatially complex and may act as an endogenous factor that can contribute to stand maintenance.

Prescribed fire in a Great Basin sagebrush ecosystem: Dynamics of soil extractable nitrogen and phosphorus

Pinyon and juniper have been expanding into sagebrush ( Artemisia tridentata) ecosystems since settlement of the Great Basin around 1860. Herbaceous understory vegetation is eliminated as stand densities increase and the potential for catastrophic fires increases. Prescribed fire is increasingly used to remove trees and promote recovery of sagebrush ecosystems. We quantified the effects of prescribed fire, vegetation type, and time following fire on soil KCl extractable nitrogen and NaHCO 3 extractable phosphorus in a pinyon–juniper woodland and its associated sagebrush ecosystem immediately before and for 4 years after a spring prescribed burn. Potassium chloride extractable NH 4 + and total inorganic-N increased immediately following prescribed fire, and extractable NO 3 − decreased immediately after the burn. In the surface layer (top 8 cm), extractable NH 4 + remained elevated compared to the control through year 2 after the burn. By the first fall post-burn extractable NO 3 − and total extractable inorganic-N increased and remained elevated over the control through year 3 after the burn in the surface layer. For the entire soil profile (52 cm), the burn had no effect on NH 4 +, and the effects on total extractable inorganic-N were no longer significant after year 1. However, NO 3 − remained elevated over the control through year 2 post-fire for the soil profile. Near surface NaHCO 3 extractable ortho-P increased immediately following fire, and remained elevated through year 2 post-fire. No fire effects were observed for extractable ortho-P in deeper horizons. Our data show that plant available nitrogen can remain elevated for extended periods following prescribed fire. This can influence regrowth and seedling establishment of native plant species, invasion of exotic plant species and, ultimately, site recovery potential.

Seasonal variations in moisture use in a piñon–juniper woodland

In water-limited environments of the intermountain region of North America, summer precipitation may play a role in the structure and function of aridland communities and ecosystems. This study examined the potential reliance on summer precipitation of two widespread, coexisting woody species in the southwestern United States, Pinus edulis Englmn. (Colorado piñon) and Juniperus osteosperma (Torr) Little (Utah juniper). The current distributions of P. edulis and J. osteosperma are highly suggestive of different dependencies on summer rainfall. We hypothesized that P. edulis was dependent on summer precipitation, utilizing summer precipitation even during extremely dry summers, whereas J. osteosperma was not dependent, using summer precipitation only when amounts were above some minimum threshold. Using sap flux and stable isotopic methods to assess seasonal water sources and water use efficiency, we examined the response of these two species to seasonal variations in moisture at a site located near the northern limits of the North American monsoon. Both sap flux and isotopic results indicated that P. edulis was responsive to summer rain, while J. osteosperma was not. Following summer rain events, sap flux density increased in P. edulis for several days, but not in J. osteosperma. Isotopic evidence indicated that P. edulis took up summer-derived moisture to a greater extent than J. osteosperma. Values of the natural abundance stable isotope ratio of carbon of leaf soluble carbohydrates increased over the summer for P. edulis, indicative of assimilation at higher water use efficiency, but were invariant for J. osteosperma. Our results supported the hypothesis that P. edulis and J. osteosperma are differentially sensitive to summer precipitation and are discussed in the light of potential changes in the seasonality of precipitation associated with climate change.

Effect of heating on mineral components of the soil organic horizon from a Spanish juniper ( Juniperus thurifera L.) woodland

Spanish juniper ( Juniperus thurifera L.) grows optimally on high (1000–1100 m) Iberian moorland (Central Spain), in the French Alps, and in the High Atlas mountains of Morocco, where it must withstand adverse climatic conditions. These plants are characterized by their great resistance to the droughts and cold winter spells of the Mediterranean basin. Nowadays, the species is in clear decline due to intensive grazing and its slow growth rate; juniper plants are also susceptible to fire damage due to the resin in their leaves. To avoid soil degradation, however, the conservation of this species is essential. This paper reports the effect of temperature on the mineralogical composition and the dynamics of the soluble cations and anions in the organic horizon of a soil under this type of plant cover. The mineral components of this horizon and of the leaves of J. thurifera were determined, and their transformations recorded when subjected to different temperatures in the laboratory. Whewellite, a mineral that turns into calcite at around 400 °C was detected by X-ray diffraction in both the organic horizon and the leaves. Boehmite, goethite, CT opal, manganese oxide (birnessite), potassium sulphate and mixed sulphates of potassium and ammonium were also found in both types of sample at 300 °C. Maximum mineralogical transformation occurred between 200 and 300 °C. The dynamics of the soluble cations and anions largely explains the presence of calcite, birnessite and sulphates. The tendency of soluble phosphate anions to disappear with increasing temperature would lead to the reduced leaching of P. Nitrates accumulated with increasing temperature, meaning their losses through leaching might increase.

Human Plague in the Southwestern United States, 1957–2004: Spatial Models of Elevated Risk of Human Exposure to &lt;I&gt;Yersinia pestis&lt;/I&gt;

Plague is a rare but highly virulent flea-borne zoonotic disease caused by the Gram-negative bacterium Yersinia pestis Yersin. Identifying areas at high risk of human exposure to the etiological agent of plague could provide a useful tool for targeting limited public health resources and reduce the likelihood of misdiagnosis by raising awareness of the disease. We created logistic regression models to identify landscape features associated with areas where humans have acquired plague from 1957 to 2004 in the four-corners region of the United States (Arizona, Colorado, New Mexico, and Utah), and we extrapolated those models within a geographical information system to predict where plague cases are likely to occur within the southwestern United States disease focus. The probability of an area being classified as high-risk plague habitat increased with elevation up to approximately 2300 m and declined as elevation increased thereafter, and declined with distance from key habitat types (e.g., southern Rocky Mountain piñon--juniper [Pinus edulis Engelm. and Juniperus spp.], Colorado plateau piñon--juniper woodland, Rocky Mountain ponderosa pine (Pinus ponderosa P.& C. Lawson var. scopulorum), and southern Rocky Mountain juniper woodland and savanna). The overall accuracy of the model was >82%. Our most conservative model predicted that 14.4% of the four-corners region represented a high risk of peridomestic exposure to Y. pestis.

Spatial Patterns of Pinyon–Juniper Woodland Expansion in Central Nevada

The expansion of the pinyon–juniper (Pinus monophylla Torr. & Frem.–Juniperus osteosperma Torr.) woodland type in the Great Basin has been widely documented, but little is known concerning how topographic heterogeneity influences the temporal development of such vegetation changes. The goals of this study were to quantify the overall rates of pinyon–juniper expansion over the past 3 decades, and determine the landscape factors influencing patterns of expansion in central Nevada. Aerial panchromatic photos (1966–1995) were used to quantify changing distribution of pinyon–juniper woodland, over multiple spatial scales (0.002-, 0.02-, and 0.4-ha median patch sizes), and for discrete categories of elevation, slope aspect, slope steepness, hillslope position, and prior canopy cover class. An object-oriented multiscale segmentation and classification scheme, based on attributes of brightness, shape, homogeneity, and texture, was applied to classify vegetation. Over the 30-year period, the area of woodland has increased by 11% over coarse, ecotonal scales (0.4-ha scale) but by 33% over single-tree scales (20-m2 scale). Woodland expansion has been dominated by infilling processes where small tree patches have established in openings between larger, denser patches. Infilling rates have been greatest at lower elevations, whereas migration of the woodland belt over coarser scales has proceeded in both upslope and downslope directions. Increases in woodland area were several times greater where terrain variables indicated more mesic conditions. Management treatments involving removal of trees should be viewed in a long-term context, because tree invasion is likely to proceed rapidly on productive sites.

Litter decomposition in cut and uncut western juniper woodlands

The expansion of western juniper ( Juniperus occidentalis ssp. occidentalis Hook.) in the northern Great Basin has resulted in management efforts to reduce juniper by prescribed fire or tree cutting to restore shrub-grassland plant communities. Herbaceous succession following juniper cutting or prescribed fire has been well documented, however, impacts of these disturbances to litter and nutrient cycling is limited in these invasive semi-arid woodlands. This study evaluated the effects of cutting juniper trees on leaf litter decomposition and nitrogen (N) dynamics over a 2-year period in eastern Oregon, USA. Litter bags were used to measure juniper leaf litter decomposition and track litter carbon (C) and N fluxes in cut and uncut juniper woodland treatments. Litter mass loss was 37% greater in the cut treatment compared to the uncut treatment after 2 years. Greater litter inputs, higher litter fall quality, and micro-environmental differences were suggested to have been the main causes for the higher litter decomposition rate in the cut treatment. In both treatments, litter N was released by the second year of decomposition, though N release was greater in the uncut treatment. Retention of juniper debris on site permits storage and release of nutrients through decomposition processes which is likely important in maintaining site productivity.

POTENTIAL CONTRIBUTION OF RESPIRATION BY ANABRUS SIMPLEX (MORMON CRICKETS) TO NET CO2EXCHANGE IN THREE GREAT BASIN ECOSYSTEMS

Disturbance events can significantly influence net CO2 exchange (NCE) in ecosystems. High densities of Anabrus simplex (Mormon crickets) periodically afflict large areas of the western USA; their sheer numbers could make them a significant source of CO2. We modeled cricket respiration at the ecosystem level using air and body tem- peratures and insect gas exchange measurements. Cricket CO2 efflux values were compared to ecosystem CO2 flux from eddy covariance measurements in 3 Great Basin ecosystems: a juniper woodland, a sagebrush shrubland, and a crested wheatgrass pasture. Mean respiration from Mormon crickets was 0.96 g CO2 ⋅ m-2d-1. Since Mormon crickets are pre- sent when NCE is otherwise near 0, they can potentially alter NCE between 20% ( juniper woodland) and 60% (crested wheatgrass pasture). Transient pests such as Mormon crickets can be an important component of NCE.

Possible effects of nest predation on the breeding success of Ferruginous Ducks Aythya nyroca

To investigate whether nest predation can influence the breeding success of Ferruginous Ducks Aythya nyroca, artificial nests were used in Nagyberek, the strictly protected swamp pond of the Juniper Woodland Nature Conservation Area (Somogy county, south Hungary). Experimentation lasted for 4 weeks, a similar length of time to the incubation period of Ferruginous Ducks. After 1 week, 80% of nests were intact, after 2 weeks only 46%, and after 3 and 4 weeks only 2% remained undamaged. Nest survival rates were not affected by the width of the sedge stands, but as water levels surrounding nests decreased, nests became more accessible to Wild Boar Sus scrofa and other land mammal predators, which increased the rate of predation. Artificially maintaining water levels would not only decrease the predation rate of nests, but would also maintain feeding areas for ducks. Wild Boar were the main cause of clutch loss in this area, and therefore by management measures, such as a reduction in their abundance or attracting them away from potential nesting sites by providing food elsewhere, the breeding success of the Ferruginous Ducks may be further improved.