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At least 37 records · Page 2Linked to original sources
USGS2015

Legacy effects of no-analogue disturbances alter plant community diversity and composition in semi-arid sagebrush steppe

Questions (i) What role does the type of managed disturbance play in structuring sagebrush steppe plant communities? (ii) How does the composition of post-disturbance plant communities change with time since disturbance? (iii) Does plant community diversity change over time following managed disturbance? Location Field study within the sagebrush steppe ecosystem. Rich County, Utah, USA. Methods We developed a chronosequence spanning up to 50 yrs post-treatment to study sagebrush steppe vegetation dynamics. Direct ordination was used to examine plant community composition by managed disturbance type and time since disturbance, and factorial analysis of covariance was used to examine diversity dynamics following disturbance. Indicator species values were calculated in order to identify characteristic species for each disturbance type. Results Plant communities experienced a shift toward distinct community composition for each of the three managed disturbance types, and gave no indication of returning to untreated community composition or diversity. Small post-disturbance increases in the number of non-native grass species were observed in the treatments relative to reference, with native forb species making the largest contribution to altered composition. On fire- and chemically-treated sites the proportional native forb species richness increased over time since disturbance, while the proportional contribution of non-native forbs to total species richness decreased. For all three treatment types, native grasses contributed less on average to total richness than on reference sites, while non-native grasses made up a higher proportion of total richness. Conclusions Common shrubland management techniques have legacy effects on the composition and diversity of sagebrush steppe plant communities, and no-analogue disturbances, such as chemical or mechanical treatments, have more pronounced legacy effects than treatments similar to natural disturbance regimes (fire). This study informs a broader understanding of how management actions affect natural systems by highlighting the importance of long-term management legacies as drivers of plant community structure and function.

Utah↗
USGS2015

Plant-plant interactions in a subtropical mangrove-to-marsh transition zone: effects of environmental drivers

Questions Does the presence of herbaceous vegetation affect the establishment success of mangrove tree species in the transition zone between subtropical coastal mangrove forests and marshes? How do plant–plant interactions in this transition zone respond to variation in two primary coastal environmental drivers? Location Subtropical coastal region of the southern United States. Methods We conducted a greenhouse study to better understand how abiotic factors affect plant species interactions in the mangrove-to-marsh transition zone, or ecotone. We manipulated salinity (fresh, brackish or salt water) and hydrologic conditions (continuously saturated or 20-cm tidal range) to simulate ecotonal environments. Propagules of the mangroves Avicennia germinans and Laguncularia racemosa were introduced to mesocosms containing an established marsh community. Both mangrove species were also introduced to containers lacking other vegetation. We monitored mangrove establishment success and survival over 22 mo. Mangrove growth was measured as stem height and above-ground biomass. Stem height, stem density and above-ground biomass of the dominant marsh species were documented. Results Establishment success of A. germinans was reduced under saturated saltwater conditions, but establishment of L. racemosa was not affected by experimental treatments. There was complete mortality of A. germinans in mesocosms under freshwater conditions, and very low survival of L. racemosa . In contrast, survival of both species in monoculture under freshwater conditions exceeded 62%. The marsh species Distichlis spicata and Eleocharis cellulosa suppressed growth of both mangroves throughout the experiment, whereas the mangroves did not affect herbaceous species growth. The magnitude of growth suppression by marsh species varied with environmental conditions; suppression was often higher in saturated compared to tidal conditions, and higher in fresh and salt water compared to brackish water. Conclusions Our results indicate that herbaceous marsh species can suppress mangrove early seedling growth. Depending on species composition and density, marsh plants can slow mangrove landward migration under predicted climate change scenarios as salinity in freshwater and oligohaline wetlands increases with rising sea levels. Change in the relative coverage of mangrove forests and marshes will depend on both the ability of marsh species to migrate further inland as mangroves advance, and the ability of shoreline mangroves to adjust to rising sea level through accretionary processes.

Journal of Vegetation Science↗
USGS2015

Topography and climate are more important drivers of long-term, post-fire vegetation assembly than time-since-fire in the Sonoran Desert, US

Questions Do abiotic environmental filters or time-since-fire (TSF) explain more variability in post-fire vegetation assembly? Do these influences vary between vegetation structure and composition, and across spatial scales? Location Sonoran Desert of southwestern Arizona, US. Methods We measured perennial vegetation in a chronosequence of 13 fires (8-33 yr TSF) spanning a broad regional gradient. The relative influence of environmental filters (topography and climate) and TSF were compared as predictors of long-term, post-fire vegetation assembly. Analyses considered different measures of vegetation structure (cover, height and density) and scales of community organization (species composition, structure and landscape). Results Species and growth form composition did not exhibit directional responses with increasing TSF, but sorted along abiotic gradients. Differences in vegetation cover and height between burned and unburned control areas were attributed primarily to gradients of topography and climate. In contrast, vegetation density initially increased in burned areas but declined to pre-burn levels with increasing TSF. The strongest predictors of landscape-scale recovery of vegetation cover, height and density were elevation, post-fire precipitation and average annual precipitation, respectively. Recovery of vegetation height was positively correlated with precipitation in the first year following fire, suggesting that abiotic conditions of the immediate post-fire environment may drive long-term variability in vegetation structure. Conclusions We find substantial evidence that environmental filters, rather than TSF, drive the majority of variability in long-term, post-fire vegetation assembly within the Sonoran Desert. Careful consideration of spatial variability in abiotic conditions may benefit post-fire vegetation modelling, as well as fire management and restoration strategies.

Journal of Vegetation Science↗
USGS2015

Stress-gradient hypothesis explains susceptibility to Bromus tectorum invasion and community stability in North America's semi-arid Artemisia tridentata wyomingensis ecosystems

Questions: (1) What combinations of overlapping water and heat stress and herbivory disturbance gradients are associated with shifts in interactions between Artemisia tridentata subsp. wyomingensis (Artemisia) and herbaceous beneficiary species? (2) Do interactions between Artemisia and beneficiaries shift from competition to facilitation with increasing stress-disturbance where facilitation and competition are most frequent and strongest at the highest and lowest levels, respectively? (3) Do such relationships differ for native and non-native beneficiaries? (4) What are the implications of any observed shifts in interactions between community compositional stability in space and susceptibility to invasion? Location: North American Artemisia communities. Methods: We tested the stress-gradient hypothesis (SGH) in an observational study consisting of 75 sites located along overlapping water and heat stress and disturbance gradients. We used spatial patterns of association among Artemisia and six native and two non-native beneficiary species; including the invasive annual grass Bromus tectorum, representing a diverse array of life history strategies, to infer whether the net outcome of interactions was facilitation or competition. We assessed implications for community stability by examining shifts in community composition in space and resistance to invasion. Results/Conclusions: Cattle herbivory, a novel disturbance and selective force, was a significant component of two overlapping stress gradients most strongly associated with observed shifts in interactions. Facilitation and competition were strongest and most frequent at the highest and lowest stress levels along both gradients, respectively. Contrasting ecological optima among native and non-native beneficiaries led to strikingly different patterns of interactions. The four native bunchgrasses with the strongest competitive response abilities exhibited the strongest facilitation at their upper limits of stress tolerance, while the two non-natives exhibited the strongest competition at the highest stress levels, which coincided with their maximum abundance. Artemisia facilitation enhanced stability at intermediate stress levels by providing a refuge for native bunchgrasses, which in turn reduced the magnitude of B. tectorum invasion. However, facilitation was a destabilizing force at the highest stress levels when native bunchgrasses became obligate beneficiaries dependent on facilitation for their persistence. B. tectorum dominated these communities, and the next fire may convert them to annual grasslands.

Oregon↗
USGS2016

Temperature is better than precipitation as a predictor of plant community assembly across a dryland region

Question How closely do plant communities track climate? Research suggests that plant species converge toward similar environmental tolerances relative to the environments that they experience. Whether these patterns apply to severe environments or scale up to plant community-level patterns of relative climatic tolerances is poorly understood. Using estimates of species' climatic tolerances acquired from occurrence records, we determined the contributions of individual species' climatic niche breadths and environmental filtering to the relationships between community-average climatic tolerances and the local climates experienced by those communities. Location Southwestern United States drylands. Methods Interspecific variation in niche breadth was assessed as a function of species' climatic optima (median climatic niche value). The relationships between climatic optima and tolerances were used as null expectations for the relationship between abundance-weighted mean climatic tolerances of communities and the local climate of that community. Deviations from this null expectation indicate that species with greater or lesser climatic tolerances are favoured relative to co-occurring species. The intensity of environmental filtering was estimated by comparing the range of climatic tolerances within each community to a null distribution generated from a random assembly algorithm. Results The temperature niches of species were consistently symmetrical and of similar breadths, regardless of their temperature optima. In contrast, precipitation niches were skewed toward wetter conditions, and niche breadth increased with increasing precipitation optima. At the community level, relationships with climate were much stronger for temperature than for precipitation. Furthermore, cold and heat were stronger assembly filters than drought or precipitation, with the intensity of environmental filtering increasing at both ends of climatic gradients. Community-average climatic tolerances did deviate significantly from null expectations, indicating that species with higher or lower relative climatic tolerances were favoured under certain conditions. Conclusions Despite strong water limitation of plant performance in dryland ecosystems, communities tracked variation in temperature much more closely, intimating strong responses to anticipated temperature increases. Furthermore, abundance distributions were biased toward species with higher or lower relative climatic tolerances under different climatic conditions, but predictably so, indicating the need for assembly models that include processes other than simple environmental filtering.

Journal of Vegetation Science↗
USGS2018

Individual species–area relationships in temperate coniferous forests

Questions What drives individual species–area relationships in temperate coniferous forests? Location Two 25.6‐ha forest plots on the Pacific Slope of North America, one in California, and one in Washington State. Methods We mapped all trees ≥1 cm in diameter and examined tree species diversity of their local neighbourhoods by calculating the individual species–area relationship for each species and for each of three diameter classes (saplings, mature trees and large‐diameter trees). Results In the California plot, small trees in four of the five major species occurred in neighbourhoods with higher levels of diversity than would be expected at random. In the Washington plot, small trees for four of five abundant species had neighbourhoods with lower than expected diversity at distances ≤5 m for small trees. However, at distances >5 m, all five species showed higher than expected diversity in their neighbourhoods. Larger trees at both plots tended to occur in neighbourhoods with lower than expected diversity, and no large‐diameter focal species had neighbourhoods with higher than expected diversity. Conclusion Diversity and co‐existence in temperate conifer‐dominated forests do not appear to be the result of random processes. Competitive interactions appear to dominate for the largest trees of most species, resulting in neighbourhoods with lower diversity. For smaller trees, we suggest that a positive response to environmental heterogeneity is the likely driver of neighbourhoods with higher than expected diversity, although we cannot rule out the possibility that facilitation or conspecific negative density dependence (CNDD) also play a role.

Journal of Vegetation Science↗
USGS2019

Regeneration of Metrosideros polymorpha forests in Hawaii after landscape‐level canopy dieback

Questions (a) Have Metrosideros polymorpha trees become re‐established in Hawaiian forests previously impacted by canopy dieback in the 1970s? (b) Has canopy dieback expanded since the 1970s? (c) Can spatial patterns from this dieback be correlated with habitat factors to model future dieback in this area? Study Site An 83,603 ha study area on the eastern slopes of Mauna Loa and Mauna Kea volcanoes on the island of Hawaii, USA. Methods We analyzed very‐high‐resolution imagery to assess status of Metrosideros polymorpha forests across the eastern side of the island of Hawaii. We generated 1,170 virtual vegetation plots with a 100‐m radius; 541 plots in areas mapped in 1977 with trees dead or mostly defoliated (dieback), and 629 plots in adjacent wet forest habitat, previously mapped as non‐dieback condition. In each plot we estimated the frequency of M. polymorpha trees that were dead or mostly defoliated, and the frequency of trees with healthy crowns. These results were combined with habitat data to produce a spatial model depicting probability of canopy dieback within the study area. Results Seventy‐nine percent of plots mapped in 1977 in dieback condition recovered their canopy and were now considered in non‐dieback condition. Ninety‐one percent of plots in previous non‐dieback areas were found to still have a healthy M. polymorpha canopy in 2015. A spatial model allowed us to identify areas within the study area with high, medium, and low probability of experiencing this same type of canopy dieback in the future. Conclusions Most former dieback areas mapped within the study area in 1977 now show recovery of the tree canopy through growth of new cohorts of young M. polymorpha trees. This suggests these forest communities are resilient to this type of canopy loss and tree death so long as other factors do not disrupt the natural regeneration process.

Hawaii↗
USGS2019

Fire severity and changing composition of forest understory plant communities

Questions Gradients of fire severity in dry conifer forests can be associated with variation in understory floristic composition. Recent work in dry conifer forests in California, USA, has suggested that more severely burned stands contain more thermophilic taxa (those associated with warmer and drier conditions), and that forest disturbance may therefore accelerate floristic shifts already underway due to climate change. However, it remains unknown how rapidly thermophilic taxa shifts occur following disturbance, how long such shifts are likely to persist, and how different thermophilic post‐disturbance communities are from pre‐disturbance communities. Location Colorado Front Range, USA. Methods We investigated these questions using a unique 15‐year vegetation plot dataset that captures pre‐ and post‐fire understory community composition across a gradient of fire severity in dry conifer forests, classifying taxa using the biogeographic affinity concept. Results Thermophilization (defined here as a decrease in the ratio of cool‐mesic taxa to warm‐xeric taxa, based on biogeographic affinity of paleobotanical lineages) was observed as early as one year post‐fire for all fire severity classes, but was stronger at sites that burned at higher severity. The ratio of cool‐mesic to warm‐xeric taxa recovered to pre‐fire levels within 10 years in stands that burned at low severity, but not in stands that burned at moderate or high severity. The process of thermophilization after high‐severity fire appears to be driven primarily by the gain of warm‐xeric taxa that were absent before the fire, but losses of cool‐mesic taxa, which did not return during the duration of the study, also played a role. Conclusions Decreases in canopy cover appear to be a main contributor to understory thermophilization. Fine‐scale heterogeneity in post‐fire forest structure is likely an important driver of floristic diversity, creating the microclimatic variation necessary to maintain floristic refugia for species mal‐adapted to increasingly warm and dry conditions.

Colorado↗
USGS2020

Soil water availability shapes species richness in mid-latitude shrub steppe plant communities

Questions Ecological communities are controlled by multiple, interacting abiotic and biotic factors that influence the distribution, abundance, and diversity of species. These processes jointly determine resource availability, resource competition, and ultimately species richness. For many terrestrial ecosystems in dryland climates, soil water availability is the most frequent limiting resource for plant species. We used field sampling coupled with process‐based soil water balance modeling to explore the relative importance of multiple macroclimatic, ecohydrological, and biotic variables on plant species and functional type richness at the landscape scale in dryland plant communities. Location Dryland plant communities dominated by big sagebrush ( Artemisia tridentata ) that span climatic and elevational gradients in Wyoming, USA. Methods We quantified species richness at 1,000 m 2 and used multiple regression to determine whether mean climatic conditions, multiple metrics of soil moisture from a soil water balance model (SOILWAT2), soil physical and chemical properties, and shrub stand structure (biotic) variables were related to species and functional type richness. Results Species richness varied between 16 and 54 across sites. We found that species and functional type richness were related to both macroclimate and ecohydrology, but ecohydrology explained slightly more variation than climate. Biotic variables were always secondary to macroclimate and ecohydrology in our models. Variance partitioning revealed that large portions of variability in species (~54%), forb (~47%), and grass (~40%) richness were explained by ecohydrological variables. Conclusions Our results highlight the importance of the spatial and temporal distribution of soil water for dryland plant species richness and suggest that documenting the ways in which climate, vegetation, and soil properties interact to determine soil water availability is critical for understanding biodiversity patterns in dryland plant communities. This work has relevance for other mid‐latitude, shrub‐dominated dryland plant communities where soil water availability strongly influences ecosystem structure and function.

Wyoming↗
USGS2020

Disentangling the effects of multiple fires on spatially interspersed sagebrush (Artemisia spp.) communities

Questions Relative to a landscape with a mosaic of two sagebrush community types and increasing fire frequency, we asked: (a) do vegetation characteristics vary significantly with number of times burned for each sagebrush community; (b) how do vegetation responses to different fire frequencies compare between the two sagebrush communities? Location Columbia Plateau Ecoregion, Washington, USA. Methods We sampled vegetation across a landscape that burned three times over a 10‐year period in two sagebrush community types that are interspersed on unique land forms: big sagebrush ( Artemisia tridentata ) communities that occur on small “mounds” and scabland sagebrush ( A. rigida ) communities that occur on surrounding “flats.” Spatially overlapping fires permitted a balanced sampling design to assess unburned and once‐, twice‐, and thrice‐burned locations for each land form/community type. We utilized a suite of statistical analyses to determine differences among plant functional groups and biomass among unburned/burned strata by land form and compared results between land forms. Results Big sagebrush and scabland sagebrush communities responded uniquely to multiple fires, due to different fuel loadings, fire severities, succession and invasion dynamics. Big sagebrush experienced nearly complete shrub loss and conversion from exotic‐invaded shrubland to exotic annual grassland after only one fire. In contrast, scabland sagebrush retained a minor shrub component and higher relative cover of native herbaceous species, even after three fires. Both communities retained cover of native perennial grasses, including shallow‐ and deep‐rooted species, likely reflecting decreasing fire intensity with number of times burned. Conclusions Despite different community‐level responses, increasing fire frequency is transforming the entire landscape to a non‐native/native grassland mix. Quantifying unique ecosystem responses to altered wildfire regimes is critical to understanding the relative resilience of communities to disturbance and their resistance to exotic species invasion (and community type conversion). Management actions may help to maintain spatial heterogeneity of ecosystems and fire‐tolerant native species.

Washington↗
USGS2023

Vegetation change over 140 years in a sagebrush landscape of the Rio Grande del Norte National Monument, New Mexico, USA

Questions Big sagebrush ( Artemisia tridentata ) ecosystems across the western United States have experienced many changes in ecosystem dynamics and vegetation composition over the last century due to livestock grazing, non-native species, and changing climate and fire regimes. We conducted the first systematic investigation of historical vegetation composition and vegetation change in a sagebrush landscape in the southwestern United States, asking whether sagebrush or grass dominated the landscape historically? Location The Rio Grande del Norte National Monument (RGDN), northern New Mexico, USA. Methods We combined General Land Office (GLO) surveys from 1881 with modern vegetation maps, field vegetation surveys, and sagebrush ages from growth ring analysis to test for changes in vegetation in the RGDN over the last 140 years. Results We found that big sagebrush presence across the study area increased significantly, from being present on 16% of section lines in 1881 to 79% in 2019, and only three section lines lost sagebrush presence during that period. Concurrently, the number of section lines with low grass index more than doubled since 1881, while moderate and high grass index declined. Grass declined equally in areas where sagebrush increased and areas with no change in sagebrush, suggesting that changes in both vegetation types were catalyzed by external factors, likely including overgrazing. The growth ring analysis of 93 sagebrush revealed a maximum age of 87 years and establishment in every decade since the 1930s, consistent with the GLO results. Conclusions The significant vegetation changes in the RGDN over the last century, including an increase of sagebrush, provide important context about the shifting mosaic of grasslands and shrublands relevant to current and future management and ecosystem dynamics.

New Mexico↗
USGS2024

Trends in plant cover derived from vegetation plot data using ordinal zero-augmented beta regression

Questions Plant cover values in vegetation plot data are bounded between 0 and 1, and cover is typically recorded in discrete classes with non-equal intervals. Consequently, cover data are skewed and heteroskedastic, which hampers the application of conventional regression methods. Recently developed ordinal beta regression models consider these statistical difficulties. Our primary question is whether we can detect species trends in vegetation plot time series data with this modelling approach. A second question is whether trends in cover have additional value compared to trends in occurrence, which are easier to assess for practitioners. Location The Netherlands, Western Europe. Methods We used vegetation plot data collected from 10,000 fixed plots which were surveyed once every four years during 1999–2022. We used the ordinal zero-augmented beta regression (OZAB) model, a hierarchical model consisting of a logistic regression for presence and an ordinal beta regression for cover. We adapted the OZAB model for longitudinal data and produced estimates of cover and occurrence for each four-year period. Thereafter we assessed trends in cover and in occurrence across all periods. Results We found evidence of a trend in cover in 318 out of the 721 species (44%) with sufficient data. Most species showed similar directional trends in occurrence and percent cover. No trend in occurrence was detected for 64 species that had evidence of a trend in cover. Declining species had stronger relative changes in cover than in occurrence. Conclusions Our model enables researchers to detect trends in cover using longitudinal vegetation plot data. Cover trends often corroborated trends in occurrence, but we also regularly found trends in cover even in the absence of evidence for trends in occurrence. Our approach thus contributes to a more complete picture of (changes in) vegetation composition based on large monitoring data sets.

Journal of Vegetation Science↗
USGS2006

Sample size and the detection of a hump-shaped relationship between biomass and species richness in Mediterranean wetlands

Questions: What is the observed relationship between biomass and species richness across both spatial and temporal scales in communities of submerged annual macrophytes? Does the number of plots sampled affect detection of hump-shaped pattern? Location: Don??ana National Park, southwestern Spain. Methods: A total of 102 plots were sampled during four hydrological cycles. In each hydrological cycle, the plots were distributed randomly along an environmental flooding gradient in three contrasted microhabitats located in the transition zone just below the upper marsh. In each plot (0.5 m x 0.5 m), plant density and above- and below-ground biomass of submerged vegetation were measured. The hump-shaped model was tested by using a generalized linear model (GLM). A bootstrap procedure was used to test the effect of the number of plots on the ability to detect hump-shaped patterns. Result: The area exhibited low species density with a range of 1 - 9 species and low values of biomass with a range of 0.2 - 87.6 g-DW / 0.25 m2. When data from all years and all microhabitats were combined, the relationships between biomass and species richness showed a hump-shaped pattern. The number of plots was large enough to allow detection of the hump-shaped pattern across microhabitats but it was too small to confirm the hump-shaped pattern within each individual microhabitat. Conclusion: This study provides evidence of hump-shaped patterns across microhabitats when GLM analysis is used. In communities of submerged annual macrophytes in Mediterranean wetlands, the highest species density occurs in intermediate values of biomass. The bootstrap procedure indicates that the number of plots affects the detection of hump-shaped patterns. ?? IAVS; Opulus Press.

Journal of Vegetation Science↗
USGS2007

Species richness and soil properties in Pinus ponderosa forests: A structural equation modeling analysis

Question: How are the effects of mineral soil properties on understory plant species richness propagated through a network of processes involving the forest overstory, soil organic matter, soil nitrogen, and understory plant abundance? Location: North-central Arizona, USA. Methods: We sampled 75 0.05-ha plots across a broad soil gradient in a Pinus ponderosa (ponderosa pine) forest ecosystem. We evaluated multivariate models of plant species richness using structural equation modeling. Results: Richness was highest at intermediate levels of understory plant cover, suggesting that both colonization success and competitive exclusion can limit richness in this system. We did not detect a reciprocal positive effect of richness on plant cover. Richness was strongly related to soil nitrogen in the model, with evidence for both a direct negative effect and an indirect non-linear relationship mediated through understory plant cover. Soil organic matter appeared to have a positive influence on understory richness that was independent of soil nitrogen. Richness was lowest where the forest overstory was densest, which can be explained through indirect effects on soil organic matter, soil nitrogen and understory cover. Finally, model results suggest a variety of direct and indirect processes whereby mineral soil properties can influence richness. Conclusions: Understory plant species richness and plant cover in P. ponderosa forests appear to be significantly influenced by soil organic matter and nitrogen, which are, in turn, related to overstory density and composition and mineral soil properties. Thus, soil properties can impose direct and indirect constraints on local species diversity in ponderosa pine forests. ?? IAVS; Opulus Press.

Journal of Vegetation Science↗
USGS2009

Measuring phenological variability from satellite imagery

Vegetation phenological phenomena are closely related to seasonal dynamics of the lower atmosphere and are therefore important elements in global models and vegetation monitoring. Normalized difference vegetation index (NDVI) data derived from the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer (AVHRR) satellite sensor offer a means of efficiently and objectively evaluating phenological characteristics over large areas. Twelve metrics linked to key phenological events were computed based on time-series NDVI data collected from 1989 to 1992 over the conterminous United States. These measures include the onset of greenness, time of peak NDVI, maximum NDVI, rate of greenup, rate of senescence, and integrated NDVI. Measures of central tendency and variability of the measures were computed and analyzed for various land cover types. Results from the analysis showed strong coincidence between the satellite-derived metrics and predicted phenological characteristics. In particular, the metrics identified interannual variability of spring wheat in North Dakota, characterized the phenology of four types of grasslands, and established the phenological consistency of deciduous and coniferous forests. These results have implications for large-area land cover mapping and monitoring. The utility of remotely sensed data as input to vegetation mapping is demonstrated by showing the distinct phenology of several land cover types. More stable information contained in ancillary data should be incorporated into the mapping process, particularly in areas with high phenological variability. In a regional or global monitoring system, an increase in variability in a region may serve as a signal to perform more detailed land cover analysis with higher resolution imagery.

North Dakota↗
USGS2009

Distribution and conservation status of coastal sage scrub in southwestern California

A landscape-based characterization of vegetation has been developed for southwestern California using satellite imagery, air photos, existing vegetation maps, and field data. Distribution maps of nine dominant coastal scrub species and 13 species assemblages that were identified by divisive information analysis have been analyzed to quantify spatial patterns of species co-occurrence. Three general distribution patterns are identified that suggest the Diegan, Ventaran and Riversidian Associations identified by other workers. Vegetation data have also been related to land ownership and management to assess the conservation status of upland plant communities. A large proportion of the mapped distribution of species and vegetation types is on private land, and several taxa show less than 4 % of mapped distribution in nature reserves. The analysis highlights the need to extend current conservation planning efforts into the northern part of the region to encompass areas where Salvia leucophylla is a frequent community dominant.

Journal of Vegetation Science↗
USGS2009

Demographic structure of California chaparral in the long-term absence of fire

Demographic structure of 12 chaparral sites unburned for 56 to 120 years was investigated. All sites were dominated by vigorous shrub populations and, although there was colonization by seedlings of woodland tree species in several stands, successional replacement of chaparral was not imminent. Although successional changes in community composition were evident, there was no indication of a decline in species diversity. Non-sprouting species of Ceanothus suffered the greatest mortality at most, but not all, sites. Sprouting shrubs, such as Quercus and Heteromeles had very little mortality, even in stands more than a century old. All postfire resprouting species had multiple stems of different ages indicating these shrubs were capable of continuously regenerating their canopy from basal sprouts. Ceanothus populations were highly clumped and there was a significant correlation across all sites between variance/mean ratio and percentage mortality. As Ceanothus populations thinned, they became less clumped. In mixed chaparral stands, Quercus and Heteromeles were significantly taller than associated Ceanothus shrubs and overtopped the Ceanothus ; at two sites, the density of live Quercus per plot was correlated with the density of dead Ceanothus. Thus, mortality of Ceanothus stems is likely related to both intra and interspecific interations. Seedling recruitment was observed for most shrub species that regenerate after fire by resprouting; seedling and sapling densities ranging from 1000–36 500 ha -1 were recorded for Quercus dumosa, Rhamnus crocea, Prunus ilicifolia, Heteromeles arbutifolia and Cercocarpus betuloides. For all but the last species, seedlings and saplings were most abundant beneath the canopy cover and not in gaps. Across all sites, recruitment was significantly correlated with depth and bio-mass of the litter layer. Cercocarpus betuloides was present in several stands, but seedling establishment was found only in one very open, disturbed stand. Regardless of stand age, taxa such as Adenostoma, Arctostaphylos and Ceanothus, which recruit seedlings after fire, had no significant seedling production.

Journal of Vegetation Science↗
USGS2009

Past and current trends of change in a dune prairie/oak savanna reconstructed through a multiple-scale history

The history of a rapidly changing mosaic of prairie and oak savanna in northern Indiana was reconstructed using several methods emphasizing different time scales ranging from annual to millennial. Vegetation change was monitored for 8 yr using plots and for 30 yr using aerial photographs. A 20th century fire history was reconstructed from the stand structure of multiple-stemmed trees and fire scars. General Land Office Survey data were used to reconstruct the forest of A.D. 1834. Fossil pollen and charcoal records were used to reconstruct the last 4000 yr of vegetation and fire history. Since its deposition along the shore of Lake Michigan about 4000 yr ago, the area has followed a classical primary dune successional sequence, gradually changing from pine forest to prairie/oak savanna between A.D. 264 and 1007. This successional trend, predicted in the models of Henry Cowles, occurred even though the climate cooled and prairies elsewhere in the region retreated. Severe fires in the 19th century reduced most tree species but led to a temporary increase in Populus tremuloides . During the last few decades, the prairie has been invaded by oaks and other woody species, primarily because of fire suppression since A.D. 1972. The rapid and complex changes now occurring are a response to the compounded effects of plant succession, intense burning and logging in the 19th century, recent fire suppression, and possibly increased airborne deposition of nitrates. The compilation of several historical research techniques emphasizing different time scales allows this study of the interactions between multiple disturbance variables.

Journal of Vegetation Science↗