Lumbricid associations on a former open clay pit after recultivation with different tree species

The earthworm fauna was recorded from a former open clay pit five and seven years after the area had been recultivated with various tree species. The highest abundances (200–245 specimens/m²) and biomasses (46.8 to 48.4 g/m²) were found in the following stand types: mixed woodland of balsam poplar (various sorts) and grey alder (Alnus incana (L.)Moench), mixed woodland of balsam poplar (Andoscoggin) and black alder (Alnus glutinosa (L.)Gaertn.), and a pure stand of black alder. Clearly lower values were found in a plot with common oaks (Quercus robur L.) under a dense shelterwood of naturally regenerated willows (Salix spec.), and a plot exclusively stocked with naturally regenerated willows. The rapid resettlement of the backfilled, compacted clay soil is above all explained by the high pH-values found in the surface soil. The differences between the studied plots regarding total abundance and biomass might be explained by the different qualities and amounts of litter. The highest species diversity — expressed by the Shannon-index — and the highest proportion of endogeic species, particularlyAporrectodea caliginosa Savigny 1826, were calculated for the two stands with a mixture of alder and balsam poplar. This result could have been caused by the lack of parent soil bed and the particularly high pH-value of the soils found there.     

Long-term deer exclusion in yew-wood and oakwood habitats in southwest Ireland: Changes in ground flora and species diversity

Changes in ground flora were monitored over a 32-year period in deer exclosures in a yew-wood and a neighbouring oakwood in Killarney National Park, southwest Ireland; both woods are Annex I habitats under the European Habitats Directive. Comparison was made with unfenced plots adjacent to each of the exclosures. During the period of the study, both woods were heavily grazed by introduced sika deer (Cervus nippon). In the yew-wood exclosures, total ground flora cover increased markedly during the period of deer exclusion, the main species to increase in abundance being Rubus fruticosus agg. and Hedera helix. Herbaceous species increased initially in frequency but subsequently declined; herbaceous species had higher total cover in unfenced plots than in fenced plots at the end of the study. In the oakwood, Luzula sylvatica and Vaccinium myrtillus expanded their cover in one exclosure with cover in ferns declining, but in other exclosures where dense holly thickets developed, it was instead R. fruticosus and H. helix that became more abundant within the fences than outside. Overall, long-term fencing has caused a shift from vegetation characterised by woodland specialist to woodland generalist species and there are indications of a long-term decline in diversity. We conclude that chronic heavy grazing in these woodlands has strongly influenced the overall abundance and composition of the ground flora, but that complete exclusion of grazing is also undesirable due to potential declines in diversity of woodland specialists.     

The potential for developing a normal age-structure in managed ancient woodland at a local scale in three English counties

This paper describes a model for assessing the potential forsustained management of ancient woodland at the local landscapescale, based on the premise that a ‘normal’ foreststructure is the best option for integrating nature conservationwith provision of a regular supply of timber. The concept of‘normality’ is applied to clusters of small ancientwoods which are considered together and treated as a whole. Data on ancient woodland distribution are used from West Sussex,Essex and North Yorkshire. At ten sample points within eachcounty the woodland area within a 25-km² block centred on thepoint was considered to see whether a normal forest structurecould be created and maintained by sustained management usinglikely minimum felling rates and average rotation lengths forthe main species for both high forest and coppice systems. Themodel was also tested for situations where small woods or woodswith conservation status were excluded from the system, as wellas for different minimum felling rates. The areas proposed forfelling within ancient semi-natural woods currently listed withinthe Woodland Grant Scheme (WGS) (II) are higher than can bemaintained in the longer term in West Sussex and Essex. The model provides a preliminary method for setting the contextof individual forestry schemes withn the wooded landscape asa whole.     

Recent Changes in the Conservation Value of Woodlands in Rockingham Forest

Surveys of all woodlands within Rockingham Forest, Northants,in 1946 and 1972 show that, whilst the total area of woodlandremains almost unchanged, considerable changes have taken placein woodland distribution, management systems, crop species,and physiognomy. These changes are quantified and their impacton the value of the woodlands for wildlife conservation andfeatures of interest is assessed by reference to criteria relatedto the development of the woods. It is concluded that therehas been a substantial decline in the conservation value ofRockingham Forest woodlands, caused mainly by State forest policyand open-cast mining, and that this decline is likely to continue.     

Restoration of oak forest: Effects of former arable land use on soil chemistry and herb layer vegetation

Abstract

Stands of pedunculate oak (Quercus robur) planted 50–80 years ago on two types of land (previously forested land and former arable fields) were compared regarding vegetation and soil. Former arable soils were characterized by a higher pH, higher nitrate concentration and higher soil density, but had lower organic matter content and lower ammonium concentration in the topsoil (0–5 cm). These differences, however, decreased with soil depth. Phosphorus concentration was consistently higher in former fields throughout the soil profile (0–45 cm). Nitrogen mineralization, determined by in situ incubation, showed a strong seasonal pattern with peak values in spring. Non-metric multidimensional scaling ordination revealed marked compositional differences in the vegetation between the two land-use categories, and also compositional turnover along gradients in soil pH and nitrogen availability. Differences in soil pH between land-use categories occurred in a range critical for the establishment of many typical forest herb layer species. Plant indicator species were identified for the two land-use categories. The results showed that acid-sensitive forest herbs may benefit from the higher pH soils in new woodlands, in contrast to ancient forest soils with little buffer capacity towards natural and anthropogenic acidification. In conclusion, former arable use has long-lasting effects on soil properties and vegetation composition in broadleaved forests. New woodlands on former fields can thus offer relatively persistent new habitats for acid-sensitive species that have suffered from reduction in habitat area during historic periods of deforestation and cultivation.     

Influence of forest growth on former heathland on nutrient input and its consequences for nutrition and management of heath and forest

The low nutrient supply of heathland soils is often insufficient for the nutrient demand of growing forests and woodlands, and additional atmospheric input of nutrients is beneficial for the tree growth. On old heathland soils tree species influencing nutrient input with regard to higher amounts have competitive benefits on the early stages of succession and/or as first planted trees with consequences for both the successional development and the nutrition and management of heathland and forests. In three stages of heathland forest succession on highly acidified and nutrient poor soil, the influence of the canopies of a Calluna heathland, a pioneering birch-pine woodland, and a terminal oak-beech forest on nutrient input was investigated. Of all investigated species Scots pine has the highest interception of water and nutrients (N, K, Ca, Mg). As a consequence, the nutrient input into the pioneering birch-pine forest is the highest of the three types of ecosystems. This ability to meliorate the nutrient supply by increasing the nutrient input favours pine in the early stages of the succession. The enhanced nutrient input and accumulation within the young successional forest ecosystems involves two different succession and/or management considerations depending upon the further ecosystem development.

• 1.The increasing nutrient availability mitigates the negative influence of the highly acidified nutrient poor soil on the growth of oak and beech and facilitates the conversion of pine dominated woodlands and forests into forests dominated by broadleaved species.
• 2.For regeneration of heathland from naturally established pine woodlands and forests, deforestation have to be combined with techniques of nutrient impoverishment of the soil.

     

Carbon sequestration and biodiversity of re-growing miombo woodlands in Mozambique

Land management in tropical woodlands is being used to sequester carbon (C), alleviate poverty and protect biodiversity, among other benefits. Our objective was to determine how slash-and-burn agriculture affected vegetation and soil C stocks and biodiversity on an area of miombo woodland in Mozambique, and how C stocks and biodiversity responded once agriculture was abandoned. We sampled twenty-eight 0.125 ha plots that had previously been cleared for subsistence agriculture and had been left to re-grow for 2 to ∼25 years, and fourteen 0.25 ha plots of protected woodlands, recording stem diameter distributions and species, collecting wood for density determination, and soil from 0 to 0.3 m for determination of %C and bulk density. Clearance for agriculture reduced stem wood C stocks by 19.0 t C ha⁻¹. There were significant relationships between period of re-growth and basal area, stem numbers and stem biomass. During re-growth, wood C stocks accumulated at 0.7 t C ha⁻¹ year⁻¹. There was no significant difference in stem C stocks on woodlands and on abandoned farmland 20–30 years old. Soil C stocks in the top 0.3 m on abandoned land had a narrower range (21–74 t C ha⁻¹) than stocks in woodland soils (18–140 t C ha⁻¹). There was no discernible increase in soil C stocks with period of re-growth, suggesting that the rate of accumulation of organic matter in these soils was very slow. The re-growing plots did not contain the defining miombo species, and total stem numbers were significantly greater than in woodland plots, but species richness and diversity were similar in older abandonments and miombo woodlands. Wood C stocks on abandoned farmland were capable of recovery within 2–3 decades, but soil C stocks did not change on this time-scale. Woodland soils were capable of storing >100 t C ha⁻¹, whereas no soil on a re-growing area exceeded 74 t C ha⁻¹, so there is a potential for C sequestration in soils on abandoned farmland. Management should focus on identifying C-rich soils, conserving remaining woodlands to protect soil C and preserve defining miombo species, and on investigating whether fire control on recovering woodland can stimulate accumulation of soil C and greater tree biomass, and restore defining miombo species.     

The effects of shade on the plant communities of rides in plantation woodland and implications for butterfly conservation

During 1985-6 the vegetation in the rides (forest tracks) of eight English lowland woods, planted on ancient woodland sites was surveyed. Shade was measured in each transect by hemispherical photography. Dicotyledonous species richness and the majority of dicot plant species declined as shade increased. The results for individual species compare favourably with Ellenberg's (L) value in most cases, and a method is suggested for modifying Ellenberg's data in the light of new information. The woodlands contained species of both open and shaded habitats and communities were influenced by soil acidity. Because shade in woodland rides increases as the trees mature, theory states that there will almost certainly be a reduction in plant species diversity. Butterfly populations would also be adversely affected, partly because of the reduction in direct sunlight, and partly because their larval foodplants decline in both quantity and quality since they are generally associated with low to moderate shade.     

Development of alder carr after the abandonment of wet grasslands during the last 70 years

? The secondary succession of wet grasslands to communities of alder carr dominated by Alnus glutinosa was recorded in different parts of Europe during the 20th century. However, knowledge of such development of alder carr remains insufficient.

? The development of alder carr was reconstructed at five sites in the Czech Republic, using historical aerial photographs and methods of dendrochronology. The aims were to investigate the succession from wet grasslands to alder carr at sites previously intensively managed for agriculture and to find out the role of fluctuations in the groundwater table, caused by artificial drainage channels, in the observed stand dynamics and tree growth.

? The spread of forest (i.e., an increase in forest cover) predominated until the 1970s at all sites. This trend was disrupted by a large-scale dieback of forest stands in four of the five sites after the 1970s, followed by an increase in patch heterogeneity, as indicated by landscape metrics. The radial growth increment in Alnus glutinosa has been affected predominately by local environmental factors, probably including the changing degree of waterlogging. Forest dieback was presumably connected with a lesser extent of drainage channels.

? Our results indicate that observed successional pathways at sites of alder carr were probably caused by local changes in the groundwater table.

     

Floristic and ecological differences between recent and ancient forests growing on non-acidic soils

The aim of this work was to investigate differences in soil chemistry and understory composition between recent forests (sites afforested in the last 170 years) and ancient forests growing on non-acidic soils. The study was carried out on hardwood forests at moderate elevation (400–600 m asl) in the Jura Mountains (N.E. France) on four main pedological substrates with different characteristics. The floristic composition of 127 stands from recent forests (n = 65) or ancient forests (n = 62) was surveyed. Some functional traits and the Ellenberg indicator values of the surveyed species were recorded. In addition, the topsoil from 30 stands was analysed. The composition of the flora was analysed by Detrended Correspondence Analysis and the species which were typical of one class of forest age were identified using a chi-square (χ²) test. The difference between forest classes for plant traits, their indicator values, or soil chemistry was tested using the generalized linear model and Bonferroni t-tests (or Kruskall–Wallis tests). The floristic composition of the ancient forests was significantly different from that of the recent forests and was characterized by a high occurrence of shrub species in recent forests. These differences were associated with higher specific leaf area, low-range seeds dispersal, and some life forms like geophytes. There was no clear difference in soil chemistry between the two classes of forests, except for δ¹⁵N values. The weakness of the difference in the soil between ancient and recent forests suggested that changes in soil chemistry caused by a former agricultural land use were not responsible for the differences in understory composition recorded. The differences in functional traits between the two forest classes supported this conclusion. We finally concluded that (i) past land use modifies the vegetation composition of current forests, even on neutral soils and that (ii) in our context, biological filters were probably responsible for these changes.     

Long-term nutrient cycling patterns in Douglas-fir and red alder stands: a simulation study

Long-term patterns in nutrient cycling in regrowing Douglas-fir (Pseudosuga menziesii Mirb. Franco) and red alder (Alnus rubra Bong.) on native soils plus soils previously occupied by other species were simulated using the nutrient cycling model. Simulations of regrowing stands were also compared with observations of nutrient cycling in mature Douglas-fir and red alder. We hypothesized that (1) prolonged presence of red alder will cause a depletion in soil base cations due to increased nitrification and NO₃⁻ leaching; (2) lower base cation availability under red alder will ultimately cause biomass production to decline; (3) high N availability in red alder soils will favor regrowth of Douglas-fir; (4) higher base cation and P status of the Douglas-fir soils will favor growth of red alder both in the short- and long-term, since N is not limiting to red alder; and (5) in regrowing red alder, NO₃⁻ leaching will increase with time as a result of increased N fixation. All hypotheses were confirmed, but the effect of soil type on biomass production was minimal both for red alder and Douglas-fir. The higher soil organic matter content in the mature red alder stand most likely reflected previous occupation by old-growth Douglas-fir and also a large litter input from the understory vegetation. In general, the nutrient cycling model simulated differences in nutrient cycling patterns at least qualitatively between Douglas-fir and red alder and was helpful in identifying potential gaps in the understanding of biogeochemical cycling as well as uncertainties in the data. The nutrient cycling model did not fully elucidate differences in P cycling between Douglas-fir and red alder and overestimated weathering rates under Douglas-fir. Uncertainties in the data included: (1) temporal patterns in N fixation in the regrowing stands; (2) understory litterfall; and (3) site history and, consequently, presence of pre-existing differences in site conditions.     

The decreased competition in expanding versus mature juniper woodlands is counteracted by adverse climatic effects on growth

World-wide deforestation is being reversed in Mediterranean continental areas, where abandonment of traditional practises favours the expansion of valuable habitats, like Juniperus thurifera woodlands. We hypothesised that pre-existing trees facilitate establishment in expanding woodlands, whereas in mature woodlands, competition leads to patch disaggregation. We compared the imprint of these processes on growth, demographic and spatial structure of expanding and mature J. thurifera woodlands. We selected plots where we geopositioned, aged and quantified the morphological characteristics of all trees. In the mature woodland, trees arranged in clumps and randomly in the expanding woodland. Competition negatively affected growth, was greater in the mature woodland and led to disaggregation of juvenile clumps. Differences in growth between the mature and the expanding woodland disappeared in climatically unfavourable years, suggesting that adverse climate constrains growth more in expanding than in mature woodlands. We suggest that change in the dispersal agents and a decrease of facilitation underlay differences in spatial patters between the expanding and the mature woodland. Observed effective recruitment in less than 30?years into the expanding woodland evidenced that propagule arrival and sapling survival do not constrain woodland expansion. Furthermore, growth of juveniles established in these new areas is favoured by reduced intra-specific competition. However, we expect growth in expanding woodlands to be negatively impacted by climate change. We conclude that under current global change scenario, conservation of J. thurifera woodlands is favoured by changes in land use, but greater frequency and severity of drier than usual episodes could hamper natural reforestation.     

Effects of experimental acidification,nitrogen addition and liming on ground vegetation in a mature stand of Norway spruce (Picea abies (L.) Karst.) in SE Sweden

During the period 1976–1991, a combined experiment of acidification, liming and nitrogen addition in a mature spruce stand was conducted at Farabol in south-east Sweden. The aim of this study was to investigate the effects of these treatments on the ground vegetation 0, 1, 5 and 15 years after experimental establishment. The treatment regimes were nitrogen (200 kg N ha⁻¹, repeated three times at 4–5-year intervals, totally 600 kg N ha⁻¹), sulphur powder (50 and 100 kg S ha⁻¹ a⁻¹, totally 600 and 1200 kg ha⁻¹), sulphur plus nitrogen (600+600 kg ha⁻¹) and limestone (500 kg ha⁻¹ a⁻¹, i.e. totally 6000 kg ha⁻¹). The results showed that nitrogen addition and liming promoted the abundance of the grass Deschampsia flexuosa, while acidification had a negative effect on D. flexuosa and herbs in the field layer. There was a negative reaction giving immediate damage to the bryophytes in connection with additions of nitrogen, sulphur powder and lime. The magnitude of damage and the capacity to recover varied among species as well as among treatments. The recovery from immediate damage after liming was much faster than after the treatments with sulphur powder and/or nitrogen. A negative interaction between sulphur powder and nitrogen was found for herbs and mosses where the combined effects were stronger than the effects of a single treatment alone. Acidification also had a negative effect on the total number of species. The results of this study showed that acidification and nitrogen deposition could negatively influence forest vegetation by changing the nutrient availability in the soils. Liming led to an improved growth of the forest ground vegetation and the flora changed towards a more nitrophilic species composition.     

Climate and groundwater effects on the establishment, growth and death of Prosopis caldenia trees in the Pampas (Argentina)

Semiarid woodlands dominated by Prosopis caldenia thrive at the dry edge of the Argentinean Pampas. Deforestation and increased precipitation have driven sustained water table level rise in the region that are likely to affect the dynamics of remnant woody vegetation patches. Here we analyze the effect of climate and groundwater level on the establishment, growth and death of P. caldenia located on lowland (current water table <0.5 m deep) and upland (current water table 8 m deep) positions within rolling sandy landscape. Standard dendrochronological techniques were applied on 98 cross sections and cores of P. caldenia trees. Results allowed us to estimated that trees in the lowland established a few years earlier than in the upland (1929 vs. 1936) and died between 1991 and 2002, while trees in higher positions are still alive. As a result of a faster growth in the lowland, maximum mean basal area increment took place earlier (1950s vs. 1990s) and achieved a higher mean value than in the upland (41.63 vs. 37.41 mm²). While mean annual chronologies were not associated across stands, an opposite highly significant association was found for the mean growth trends suggesting long-term effects of water table depths on growth. We found a different association between mean annual growth and climate, with lowland trees showing a negative response to precipitation before and during the growing season, and upland trees displaying a positive response to summer rainfall inputs. Temperature at the end of the growing season had a positive effect in the lowland whereas temperature during the growing season had a positive effect in the upland. These results show how groundwater can induce diverging sensitivity of forest growth and survival to climate variability, enhancing growth at optimum depths (2-8 m in our study) but depressing it or even killing trees when it approaches the surface (<2 m in our study). Groundwater dynamic should be considered in forest management and conservation strategies in semiarid woodlands in Central Argentina.     

Farmers’ objectives toward their woodlands in the upper Midwest of the United States: implications for woodland volumes and diversity

This paper reports the results of a study that explores the relationship between farm woodland owners’ stated intentions for owning woodland, and the structure and composition of these woodlands in the states of Illinois, Indiana and Iowa in the upper Midwest of the United States. Data from two sample-based inventories conducted by the USDA Forest Service, Forest Inventory and Analysis (FIA) program were combined for this analysis—the FIA forest resources inventory and the National Woodland Owner Survey (NWOS). We looked for relationships between product value and investment in woodlands, as reflected in volumes and tree quality. We also examined whether measures of diversity reflected specific management focus. Our results partially supported our hypotheses. Woodland-focused ownership reasons were found to have larger volumes and individual tree sizes. We found that a passive woodland ownership reason—that woods were “part of the farm”—generally had lower volumes per hectare. Although we were not able to differentiate between different forest product classes and measures of volume, we did find that those landowners who harvested veneer had more volume than those who harvested for firewood. Woodland owners who salvage-harvested their woodlands—a harvesting reason that is more reactive than proactive—exhibited lower volumes per hectare than those who harvested for more proactive, product-focused reasons. Biodiversity was also found to be related to the ownership focus and harvest intent. Generally, there was lower diversity in overstory species when the woodland was viewed merely as “part of the farm,” when the product harvested was fence posts and when timber was harvested for salvage or land clearing. The small sample size limits our analysis, but we can conclude that focusing the woodland owners on management of their woodlands—regardless of what the specific management goals might be—should increase productivity and biodiversity of those woodlands.

Fire history and understorey vegetation: Water and nutrient relations of Eucalyptus gomphocephala and E. delegatensis overstorey trees

Fire regimes in temperate forests and woodlands have changed significantly in Australia since European settlement. We hypothesised that an absence of fire leads to the increased development of woody understorey/midstorey and that this may be correlated with decreased water and/or nutrient availability in overstorey temperate eucalypts currently declining in health. Sites with a history of being long unburnt or recently (and frequently in the case of Eucalyptus gomphocephala woodland) burnt (relative to median fire intervals for the vegetation type) were established in E. gomphocephala woodland in Western Australia and in Eucalyptus delegatensis forest in Tasmania. In long unburnt sites in both E. gomphocephala woodland and E. delegatensis forest, there was greater percent cover of understorey/midstorey and eucalypts had higher water use efficiency, indicative of greater soil water limitation, as estimated by foliar carbon isotope ratios. In E. gomphocephala woodland foliar Cu and Zn were significantly lower in eucalypts of long unburnt, relative to frequently burnt, sites. In E. gomphocephala woodland, understorey/midstorey (shrub) cover was positively correlated, and foliar copper and zinc levels were negatively correlated to health of overstorey trees. In E. delegatensis forest foliar phosphorus (P) was significantly lower in eucalypts of long unburnt, relative to recently burnt, sites. In E. delegatensis forest moss cover was positively correlated and foliar P was negatively correlated to health of overstorey trees. The understorey/midstorey that develops in the long absence of fire may alter ecological processes that lead to less favourable water- and nutrient-relations in E. gomphocephala woodland and E. delegatensis forest that are associated with decline in crown health. However this study does not definitively show a link between understorey/midstorey vegetation and overstorey tree water- and nutrient-relations. This link will be investigated in future research.     

Soil respiration and nitrogen leaching decreased in grey alder (Alnus incana (L.) Moench) coppice after clear-cut

ABSTRACT

Grey alder (Alnus incana) is a highly productive indigenous tree species, potential for short-rotation forestry in the Baltic and Nordic countries. The aim of the study was to investigate the development of a new forest generation, as well as the nitrogen (N) and carbon (C) storages and fluxes in a grey alder regenerating coppice (COP) after clear-cut and in an adjacent unharvested 21-year-old stand (MAT), which had reached its bulk maturity. The regeneration of COP was rapid and 5 years after clear-cut, stem mass was 6.4?t?ha^?1. The nitrogen demand of the aboveground part of the 5-year-old COP trees was estimated to be roughly half of the corresponding value for MAT, depending mostly on leaf production. The annual N leaching flux in MAT was in the range of 16–29?kg?ha^?1, the corresponding values for COP were roughly half of that. Net nitrogen mineralization did not differ significantly between MAT (117?kg?ha^?1) and COP (129?kg?ha^?1). For the soil respiration study, a 32-year-old grey alder stand growing at a similar site was included; soil respiration was significantly higher in MAT compared to COP in all study years in both studied stands.     

Structure and floristic diversity in permanent monitoring plots in forest ecosystems of Tuscany

The sampling method is described which is used for the sampling of plant species richness and cover in a monitoring project on forest ecosystems in Tuscany (named MONITO). Species richness is sampled through a nested plot design, with plot size ranging from 1 to 2500 m², whereas species abundance is estimated in 100 m² plots. This sampling design is simple to install and to manage through time. Species diversity can be monitored not just at one single spatial scale but at many scales, and species–area relations can also be calculated. The analyses of the data that were collected produced the first available data on species richness in relation to plot size for Tuscan forest ecosystems, indeed for any Italian forests. The Arrhenius Power function and the General Root models showed the best fit. Turkey oak (Quercus cerris) woods located on slightly acidic soil were found to be the forest ecosystems with the highest species richness, confirming and quantifying well-established floristic-phytosociological knowledge. Habitat heterogeneity, measured by plot floristic resemblance, showed how the Turkey oak woods were the most heterogeneous at the smaller spatial scales, but not at larger ones.     

土地利用方式对土壤有机碳和碳库管理指数的影响

土壤碳库管理指数反映土壤管理的科学性.对比研究了干热河谷新银合欢林、苏门答腊金合欢林、大叶相思林、印楝林、荒地和旱耕地土壤有机碳(SOC)、易氧化有机碳(ROC)含量和土壤碳库管理指数.结果表明:6种土地利用方式下SOC和ROC含量范围分别为4.22～5.92 g·kg-1和1.34～2.33 g·kg-1.各利用方式...     

Density-dependent tree mortality in pinyon-juniper woodlands

Pathogens and bark beetles are integral disturbance agents in many forest and woodland ecosystems. Over the past decade, pinyon Ips (Ips confusus) has interacted with regional drought to cause widespread mortality in singleleaf pinyon (Pinus monophylla) and Colorado pinyon (Pinus edulis) woodlands of western North America. We used mixed-effects and logistic regression modeling approaches to explore biotic and abiotic influences on the spatial heterogeneity of tree mortality. Stand structure, cumulative canopy and stem mortality, and occurrence of specific mortality agents were measured for 217, 0.1-ha plots, established in 2005 across 11 mountain ranges in central Nevada.