Shrub Composition Research Articles

Forest vegetation responses to climate and environmental change: A case study from Changbai Mountain, NE China

The distribution of plant species has always been altered by changing climatic conditions. Nonetheless, the potential for species’ range shift responses has recently become severely limited, as exceptionally fast temperature changes coincide with a high degree of anthropogenic habitat fragmentation. This study provides rare insights into the effects current temperature increases have on pristine temperate forest ecosystems, using the forests of Changbai Mountain, NE China, as a case study. On the northern slopes of the mountain at elevations between 750 and 2100 m, the composition of trees, shrubs and herbaceous species was recorded on 60 plots in 1963 and 2006/07. Multiple linear regression (MLR) and canonical correspondence analysis (CCA) were used to establish the response of plant diversity and plant distribution patterns to environmental conditions. Climatic factors proved important in explaining the spatio-temporal trends within the vegetation. The composition of dominant trees remained mostly unchanged over the last 43 years, reflecting a very slow response of the forest canopy to environmental change. The composition of young trees, shrubs and herb species showed varied changes in the different forest types. A homogeneous species composition in the cohort of regenerating trees indicates an increased future uniformity in the mixed broadleaved and coniferous forest. The understory vegetation of high elevation birch forests was invaded by floristic elements of the lower-elevation coniferous forests. Both these trends pose potential threats to forests plant diversity. Future research investigating climate change responses in forest canopy composition needs to be based on even longer timescales, while investigations in the near future need to pay particular attention to the changes in the distribution of rare and threatened herbaceous species.

Land-Use Legacies and Vegetation Recovery 90 Years After Cultivation in Great Basin Sagebrush Ecosystems

Agricultural land use is known to alter ecological processes, and native plant communities can require decades to centuries to recover from the disturbance of cultivation. ‘‘Recovery’’ is typically measured by comparison to undisturbed adjacent sites as a control. Recovery following cultivation in sagebrush ecosystems of the Great Basin remains largely unexamined even though nearly a half million hectares of land were dry-farmed and abandoned in the early 1900s. We tested the hypothesis that the native vegetation has not recovered from this exotic disturbance by evaluating differences in canopy cover of shrubs, grasses, and forbs between paired sets of historically dry-farmed land and adjacent never-cultivated areas. Paired sites were located in three ecological sites in northwestern Utah. We found that vegetation recovery from cultivation is variable by growth form, species, and ecological site. Shrub recovery was different among sagebrush (Artemisia) species. Yellow rabbitbrush (Chrysothamnus viscidiflorus [Hook.] Nutt.) and black greasewood (Sarcobatus vermiculatus [Hook.] Torr.), which often increase following disturbance, maintained higher cover inside old fields. At one of the paired sets, shrub composition was altered from a mix of four species to dominance of mainly Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young). Total forb cover was generally lower in cultivated areas and some species, such as spiny phlox (Phlox hoodii Richardson), had not recovered. The most common grass species encountered across all ecological sites, bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey), had higher cover in cultivated areas. Surprisingly, exotic annual species, such as cheatgrass (Bromus tectorum L.), did not dominate these sites as they have for decades after cultivation in other areas of the Great Basin. This study demonstrates that the land-use legacy of dry farming on vegetation remains nearly a century after cultivation has ceased, and has direct implications for describing ecological site conditions.

Recovery of Plant Species Richness and Composition in an Abandoned Forest Settlement Area in Kenya

Cultivation of annual crops in the initial stage of reforestation has been commonly practiced in the tropics. In recent decades, however, cultivation of such areas has been discontinued, resulting in widespread abandoned settlements. In this article we used a former forest village settlement in Kenya, which had been cleared, cultivated and then abandoned, to study how natural vegetation recovers after such disturbances. Species richness, abundance, and composition of tree seedlings, saplings, adult trees, shrubs, and herbs were recorded in different zones, from a heavily degraded zone in the center of the settlement, through less disturbed transition zones (TZs), and in the surrounding secondary forest (SF). Species richness and abundance of tree seedlings, saplings, and adult trees increased gradually from the heavily degraded zone to the SF, whereas shrub and herb richness were the same for TZs and SF and abundance was lowest in the SF. Total species richness was highest in the SF. Some pioneer tree species were highly associated with the TZs, whereas sub‐canopy tree species were associated with the SF. A group of tree species were not particularly associated with any of the four zones. Thus, these species might have good potential as restoration species. The results of our study contribute to the knowledge of natural regeneration in general, and of individual species characterizing the different stages of recovery of abandoned settlements in particular. Such information is urgently needed in designing ecologically sound management strategies for restoring abandoned forest settlements in tropical areas.

Historical and recent land-use impacts on the vegetation of Bathurst, a municipal commonage in the Eastern Cape, South Africa

We assessed past and present vegetation patterns in relation to land use on a municipal commonage in South Africa. We asked specifically whether the reassignment of the commonage for the use of historically disadvantaged town residents after 1994 has impacted negatively on the vegetation of the commonage. Analysis of land cover change using aerial photography time series revealed that the most significant human impacts on the Bathurst commonage occurred prior to 1942 due to heavy and uncontrolled communal land use. Vegetation change since then has been characterised by a recovery of thicket vegetation and an encroachment of woody species into grassland. Additional field sampling of the species composition and age class distributions of trees and shrubs in thicket and broken thicket vegetation showed these units to be of high veld condition status. Thornveld and old lands have both been encroached upon by woody species, particularly by Acacia karroo, and possessed the lowest veld condition scores. There is little evidence, however, that recent land-use activities have impacted negatively on commonage vegetation. We discuss these results in terms of the vegetation's potential to provide for the diverse needs of commonage users, and the implications for commonage management and policy.

Dry season herbivore utilization of open grasslands in Lower Zambezi National Park, Zambia

Utilisation of open grassland plains by large herbivores (≥100 kg) and harvester ants (Messor capensis) in Lower Zambezi National Park, Zambia was assessed every September from 1997 to 2007. A point intercept method was used to estimate percent cover for grass, shrub, bare, litter, herbivore droppings and presence of harvester ants in the Jeki open grassland vegetation community as indicators of range condition. Results showed a reduction in grass cover from 35% in 1997 to 10% in 2007 while litter remained stable. Incidence of herbivore droppings and harvester ants showed a decline while shrub cover and species composition of shrubs increased significantly. As grass cover and grass species composition declined, herbivore droppings and incidence of harvester ants also decreased. Unpalatable species such as Vernonia spp. were assumed to be signs of poor quality range. Increase in bush encroachment indicated heavy utilization by herbivores in the dry season when quality of range deteriorated as a consequence of over utilization of grass species. Further research is required to determine population estimates and grazing capacity of key herbivores such as buffalo (Syncerus caffer). Key words: Range utilization, overgrazing, flood plains, valley floor, shrub encroachment.

Diversity and composition of trees and shrubs in Kasagala forest: a semiarid savannah woodland in central Uganda

AbstractThe diversity and composition of trees and shrubs of ≥5 cm diameter at breast height (DBH) were investigated in Kasagala woodland in central Uganda using 1 ha permanent sample plots. A total of 2745 trees and shrubs with a mean stem density of 686 ha−1 were recorded. These included 69 tree species belonging to 28 families and 47 genera. There was a larger number of small stems compared with that of larger stems. There was significant variation in stem size class distribution between the plots (F = 3.14, P = 0.027). The variation in stem densities (counts) across different size classes was significant (F = 8.31, P < 0.001). Species diversity was higher in the low lands compared with that in the elevated sites in the woodland. The species encountered were unevenly distributed across the plots. Species abundance was not significantly different across the sample plots (F = 2.63, P = 0.053). We suggest that the structure of the forest is typical of any regenerating forest, but other human influences may have played a part in the dominance of size classes <10 cm DBH. The causes of the present status and composition of the woodland require further investigation.

Distribution patterns of shrubby N‐fixers and non‐N fixers in an arid valley in Southwest China: implications for ecological restoration

AbstractShrubs play different key roles in arid regions. Comparisons of shrubs and their site adaptability are essential for correct selection of candidates in developing restoration theory and practice. A survey of topography, soil properties and shrub composition was conducted in fifty‐seven 5‐m × 5‐m plots in an arid valley of the upper Minjiang River, Southwest China. With cluster analysis and critical examinations based on edaphic properties, soil was classified into three groups: dry cinnamon soils (DCS), calcareous cinnamon soils (CCS) and eluvial‐accumulation cinnamon soils (EACS). EACS had the highest fertility level, DCS the next and CCS the lowest level. For non‐N fixers, soil moisture is the primary limiting factor, and nitrogen the next. However, N‐fixers are weakly constrained by soil moisture and nitrogen, the extent of which is species‐specific. N‐fixers had a significantly higher cumulative relative importance value (44.4%) in CCS than in DCS (34.0%) and EACS (17.3%). The results suggest that it would be reasonable to restore non‐N fixers in DCS and EACS and that N‐fixers are appropriate for CCS. Compared with grass, shrubs significantly enhanced the availability of nitrogen and phosphorus and soil electric conductivity, and significantly decreased the soil C/N ratio. The median fertility level of soil dominated by N‐fixers indicates that N‐fixers are suitable driver candidates from grassland to non‐N‐fixing shrub land. Four native shrubby legumes (Indigofera amblyantha, Sorphora viciifolia, Desmodium podocarpum and Bauhinia faberivar) and one soil‐conserving shrub (Ajania potaninii) are the top‐priority pioneers for ecological restoration.

Assessing long-term hydrological and ecological responses to drainage in a raised bog using paleoecology and a hydrosequence

Question: We studied vegetation succession after drainage in a bog, as an analogue for potential persistent water table drawdown due to climate change. We asked: (1) how does bog vegetation change following a long-term water table lowering and (2) how are effects of drainage on hydrology and vegetation distributed temporally and spatially? Location: Mer Bleue peatland, Ontario, Canada (45.41°N, 75.48°W). Methods: Analyses of changes in vegetation and hydrology associated with drainage were examined spatially along a hydrosequence and temporally using paleoecological reconstructions from peat cores (testate amoebae, pollen) in a drained portion of a peatland untouched for 85 years following drainage. Relationships between modern vegetation and water table were assessed through clustering and ordination analyses of vegetation releves. Results: Post-drainage increases in tree cover, especially Betula and Larix, decreases in Sphagnum cover and shifts in species composition of dominant shrubs were observed. Present-day vegetation patterns along the hydrosequence were primarily related to seasonal variability of water table depth. Paleoecological records reveal that where the present-day vegetation has been impacted by drainage, persistent water table lowering occurred in response to drainage. However, in an area with relatively natural vegetation, a transient drop in water table depth occurred at the time of drainage. Conclusions: Temporal and spatial patterns revealed that the bog response to drainage was spatially and temporally heterogeneous, and probably mediated by feedbacks among vegetation, peat structure and hydrology. Spatial patterns along the hydrosequence were similar to those observed in paleoecological reconstructions, but the use of the two complementary techniques provides additional insights.

Recovery of plant species richness and composition after slash-and-burn agriculture in a tropical rainforest in Madagascar

Slash-and-burn agriculture is an important driver of deforestation and ecosystem degradation, with large effects on biodiversity and carbon sequestration. This study was conducted in a forest in Madagascar, which consists of fragments of slash-and-burn patches, within a matrix of secondary and primary forest. By recording species richness, abundance, and composition of trees, shrubs, and herbs in fallows of various age and slash-and-burn history, and in the secondary and primary forest, we show how slash-and-burn intensity (number of cycles, duration of abandonment), years since last abandonment, and environmental factors (distance to primary forest and topography) affect the natural succession and recovery of the forest ecosystem. We used ordination analyses to examine how the species composition varied between the different successions stages, and to examine tree recruitment. Our results show shrub dominance the first years after abandonment. Thereafter, a subsequent increase in species richness and abundance of tree seedlings and saplings suggests a succession towards the diversity and composition of the secondary and primary forest, although a big gap between the oldest fallows and the secondary forest shows that this will take much more than 30 years. A high number and frequency of slash-and-burn cycles decreased tree seedling and sapling richness and abundance, suggesting that reducing slash-and-burn intensity will increase the speed of tree recruitment and fallow recovery. Trees can be planted into fallows to speed up vegetation and soil recovery, such that fallows can be usable within needed time and thus the extension of cultivated areas reduced. We recommend further testing of six potential species for restoration based on their early colonization of the fallows and their survival through vegetation succession.

Woody plant regeneration after blowdown, salvage logging, and prescribed fire in a northern Minnesota forest

Salvage logging after natural disturbance has received increased scrutiny in recent years because of concerns over detrimental effects on tree regeneration and increased fine fuel levels. Most research on tree regeneration after salvage logging comes from fire-prone systems and is short-term in scope. Limited information is available on longer term responses to salvage logging after windstorms or from forests outside of fire-prone regions. We examined tree and shrub regeneration after a stand-replacing windstorm, with and without salvage logging and prescribed fire. Our study takes place in northern Minnesota, USA, a region where salvage logging impacts have received little attention. We asked the following questions: (i) does composition and abundance of woody species differ among post-disturbance treatments, including no salvage, salvage alone, and salvage with prescribed burning, 12 years after the windstorm?; (ii) is regeneration of Populus, the dominant pre-blowdown species, inhibited in unsalvaged treatments?; and (iii) how do early successional trajectories differ among post-blowdown treatments? Twelve years after the wind disturbance, the unsalvaged forest had distinctly different composition and abundance of trees and woody shrubs compared to the two salvage treatments, despite experiencing similar wind disturbance severities and having similar composition immediately after the blowdown. Unsalvaged forest had greater abundance of shade tolerant hardwoods and lower abundance of Populus, woody shrubs, and Betula papyrifera, compared to salvage treatments. There was some evidence that adding prescribed fire after the blowdown and salvage logging further increased disturbance severity, since the highest abundances of shrubs and early successional tree species occurred in the burning treatment. These results suggest that salvage treatments (or a lack thereof) can be used to direct compositional development of a post-blowdown forest along different trajectories, specifically, towards initial dominance by early successional Populus and B. papyrifera with salvage logging or towards early dominance by shade tolerant hardwoods, with some Populus, if left unsalvaged.

Conversion of Rare Grassy Openings to Forest: Have These Areas Lost Their Conservation Value?

ABSTRACT: Grassy openings have a high conservation value because they provide habitat for a number of rare and endemic species and contribute to landscape level biodiversity. However, these communities are at risk because tree encroachment causes the conversion of grassy openings into closed-canopy forest. Many land managers have taken an active position in maintaining these openings by introducing disturbances such as fire, grazing, or mowing to slow or halt the invasion of tree species. The objective of this study was to trace the closure of grassy openings, in the absence of active management, and identify whether the forest that developed was unique in tree and shrub composition and structure or whether it mirrored the surrounding forest matrix. Our study site was an area with historical grassy openings visible on a 1937 aerial photograph. We sampled the vegetation in these former openings, now closed-canopy forest, and compared them with paired plots on similar aspects and elevations but forested in ...

Boundaries and scales in shrublands of the Doñana Biological Reserve, southwest Spain

To verify that the stabilized sand dunes of Donana, southwest Spain, are hierarchically nested, vegetation was sampled along topographic gradients at three spatial scales and Split Moving Window Boundary Analysis was applied to identify vegetation boundaries and ecotones. At small scale, only one window width was used, while for boundaries detection at upper scales the information from five windows was pooled. Environmental factors controlling plant composition were studied along topographic gradients, and diversity was estimated within the boundaries. According to several theoretical frameworks, I discuss the types of boundaries produced at different scales. Lower level boundaries are characterized by transitory gradients linked to local exchanges; intermediate boundaries are symmetric and very stable over the time; the large scale boundary is asymmetric with strong inherent abiotic constraints reinforced by strong biotic feedbacks. In spite of a similar plant composition, a plant community, the mixed shrub, works as an ecocline or an ecotone depending on the spatial scale considered. A certain parallelism exists between shrub composition along dune slopes and dune generations; however, processes at upper scale constraint plant composition at lower scale resulting in different mature formations.

TRANSVERSE AND LONGITUDINAL VARIATION IN WOODY RIPARIAN VEGETATION ALONG A MONTANE RIVER

This study explores how the relationship between flow and riparian vegetation varies along a montane river. We mapped occurrence of woody riparian plant communities along 58 km of the San Miguel River in southwestern Colorado. We determined the recurrence interval of inundation for each plant community by combining step-backwater hydraulic modeling at 4 representative reaches with Log-Pearson analysis of 4 stream gaging stations. Finally, we mapped bottomland surficial geology and used a Geographic Information System to overlay the coverages of geology and vegetation. Plant communities were distinctly arrayed along the hydrologic gradient. The Salix exigua Nuttall (sand-bar willow) community occurred mostly on surfaces with a recurrence interval of inundation shorter than 2.2 years; the Betula occidentalis Hooker (river birch) community peaked on sites with recurrence intervals of inundation between 2.2 and 4.6 years. The hydrologic position occupied by communities dominated by Populus angustifolia James (narrowleaf cottonwood) was strongly related to age of trees and species composition of understory shrubs. The fraction of riparian vegetation on surfaces historically inundated by the river decreased in the upstream direction from almost 100% near Uravan to <50% along the South Fork of the San Miguel River. In upstream reaches much of the physical disturbance necessary to maintain riparian vegetation is provided by valley-side processes including debris flows, floods from minor tributaries, landslides, and beaver activity. Where valley-side processes are important, prediction of riparian vegetation change based on alterations of river flow will be incomplete.

Establishing Artemisia tridentata ssp. wyomingensis on Mined Lands: Science and Economics

In 1977, the USA Surface Mine Control and Reclamation Act mandated that reclaimed plant communities must be as productive or more productive than the premined plant community and must possess diversity representative of the premine community and serve the same land uses. In much of the Northern Great Plains this meant that reclaimed mined lands must support postmined land uses for livestock grazing and wildlife habitat. In 1996, the Wyoming Department of Environmental Quality enacted regulations governing the reestablishment of woody shrubs on mined lands. The regulation required that an average density of one shrub m−2 be reestablished on at least 20% of the disturbed land area and that the shrub composition must include dominant premine species. In Wyoming, and much of the Northern Great Plains, that meant that Artemisia tridentata Nutt. ssp. wyomingensis (Beetle and Young) (Wyoming big sagebrush) had to be reestablished on mined lands. Artemisia tridentata Nutt. ssp. wyomingensis had proven difficult to reestablish on mined lands because of poor quality seed, seed dormancy and a poor understanding of the seedbed ecology of this species. Research in the last two decades has produced significant knowledge in the area of direct-seed establishment of Artemisia tridentata Nutt. ssp. wyomingensis on mined lands. Our research has shown that reducing grass seeding rates will reduce competition and result in larger sagebrush plants that are more likely to survive and provide greater structural diversity to the plant community. Economic analyses demonstrated that big sagebrush can be established at a cost of $0.01–0.05 per seedling using direct seeding methods compared to transplanting nursery grown seedlings, estimated to cost $0.72–$1.65 per seedling (depending on size) to grow and from $1.30–$2.40 to plant (flat land to 2:1 slopes). An adequate level of precipitation will be necessary to ensure successful establishment of this species no matter what method of propagation is selected and direct seeding gives greater opportunity for success because of the demonstrated longevity of the seed to germinate 3–5 years after the initial seeding.

Impacts of black stain root disease in recently formed mortality centers in the piñon-juniper woodlands of southwestern Colorado

Thirty discrete black stain root disease (BSRD) mortality centers, caused by Leptographium wageneri (Kendr.) Wingf. var. wageneri, were examined in 1999 to determine the effects of BSRD on the composition and structure of piñon–juniper woodlands at the tree, shrub, and herbaceous plant levels and on tree-seedling regeneration. In these recently formed mortality centers, the majority (68%) of all piñon (Pinus edulis Engelm.) was dead, 76% of piñon were affected by BSRD, and 70% had evidence of piñon ips bark beetle (Ips confusus Leconte) attack. BSRD mortality centers had a mean area of 0.28 ha (range 0.07 to 0.63 ha). There were no statistically significant (p &gt; 0.05) differences in shrub composition, cover, or diversity between mortality centers and the unaffected surrounding woodlands. Herbaceous plant cover was significantly greater (p &lt; 0.001) within mortality centers and frequency responses were species specific. There were no significant (p = 0.629) differences in the density of piñon regeneration inside mortality centers compared with outside mortality centers. The pathogen was regularly isolated from piñon roots dead for 5–8 years and once from a root dead for 16 years. The rate of radial expansion of mortality centers averaged 1.1 m/year (0.07 SE). The rate of mortality center expansion was not significantly (p &gt; 0.05) related to available water-holding capacity, percent organic matter, pH of soils, piñon density, or any other site data recorded.

Multiscale control of vegetation patterns: the case of Doñana (SW Spain)

The early studies about the plant ecology of Donana carried out at a small scale showed that the main process controlling vegetation composition of the stabilized dunes was soil water availability. However, the extrapolation of this model to larger spatial scales failed to explain observed vegetation patterns. In this work, the vegetation patterns and the processes causing them are studied at a larger scale. Data of topography, soil pH, electrical conductivity, and available iron allowed to distinguish three large geomorphologic zones on the stabilized dunes of the Donana Biological Reserve which correspond to different dune building episodes. Different dune episodes showed differences in both water table depth and dynamics, which are due to groundwater flow systems of different scale. It is further manifested by differences in shrub composition. The results show that geomorphology controls the vegetation pattern at different scales mediated through water availability. Differences in water availability are due to the connection to groundwater flow systems of contrasted scale. On a small scale (10−102 m), along dune slopes, there is a gradient from dune ridges to slacks, from xerophyte to hygrophyte vegetation types. On a mesoscale (102−103 m), there are several dune episodes with variable topographic altitude, dominated by different types of xerophytes. On a regional scale (>103 m), the discharges of the regional aquifer produce strong environmental and biotic stresses resulting in a mixed community.

Lichens — the biodiversity value of western woodlands

Summary The Atlantic broad-leaved woodlands of Britain are of international renown for their lichen floras. They are inhabited by 517 lichens, representing 28.3% of the total lichen flora and 73.2% of all British woodland lichens, and they are the main habitat for 165 species. Of these, 31 have a marked southern distribution and do not reach Scotland, whereas 26 species are found in Scotland, but not England or Wales. Their British Red-listed species are outnumbered by the 86 species for which Britain has International Responsibility. Within the Atlantic broad-leaved woodlands, only 30 lichens show a preponderance for oak. With the exception of some ancient oakwoods in southern England, a high lichen biodiversity is rarely dependent on a dominance of oak in the woodland canopy, more usually it is the result of a long ecological continuity, often a varied tree and shrub composition, a varied canopy density, and good air quality. Consequently, the oak stands within former ‘industrial’ woodlands have a much lower lichen biodiversity compared with woodlands that have a history as ‘pasture woodland’ or, as with some ravine woodlands, have otherwise escaped intensive management. The life-history of an oak tree is considered in relation to the niches it provides for lichen colonisation with time. Some management scenarios are provided with the enhancement of the lichen interest of former ‘industrial’ oakwoods as an objective.

Response of vegetation and vertebrate fauna to 23 years of fire exclusion in a tropical Eucalyptus open forest, Northern Territory, Australia

Abstract This opportunistic study compares the vegetation, fuel loads and vertebrate fauna of part of a 120‐ha block of tropical open forest protected from fire for 23 years, and an adjacent block burnt annually over this period. Total fuel loads did not differ significantly between the unburnt and annually burnt sites, but their composition was markedly different, with far less grassy fuel, but far more litter fuel, in the unburnt block. There were major differences between treatments in the composition of trees and shrubs, manifest particularly in the number of stems. There was no overall difference in plant species richness between the two treatments, but richness of woody species was far higher in the unburnt treatment, and of annual and perennial grasses, and perennial herbs in the annually burnt treatment. Change in plant species composition from annually burnt to unburnt treatment was directional, in that there was a far higher representation of rainforest‐associated species (with the percentage of woody stems attributable to ‘rainforest’ species increasing from 24% of all species in the annually burnt treatment to 43% in the unburnt treatment, that of basal area from 9% to 30%, that of species richness from 8% to 17%, and that of cover from 12 to 47%). The vertebrate species composition varied significantly between treatments, but there was relatively little difference in species richness (other than for a slightly richer reptile fauna in the unburnt treatment). Again, there was a tendency for species that were more common in the unburnt treatment to be rainforest‐associated species. The results from this study suggest that there is a sizeable and distinct set of species that are associated with relatively long‐unburnt environments, and hence that are strongly disadvantaged under contemporary fire regimes. We suggest that such species need to be better accommodated by fire management through strategic reductions in the frequency of burning.

Potential impacts of fire and grazing in an endangered ecological community: plant composition and shrub and eucalypt regeneration in Cumberland Plain Woodland

Exclosure plots were used to determine the effect of fire and grazing on the structure of a grassy-woodland community. Eighteen months after fire and fence treatments were applied, the species richness, cover and composition of shrubs, trees, herbs and grasses were assessed and compared to pre-treatment censuses. Unburned plots had fewer shrub species and a lower abundance of shrubs, indicating the importance of fire in promoting regeneration of shrub species. Eucalypt species were more abundant and richer following the wildfire burn in summer, suggesting timing of fires is an important aspect in the establishment of the canopy species. Interactions between fire and grazing were found for the abundance of eucalypts (although weak) and resprouting eucalypts, suggesting a subtle interaction between fire and grazing shortly after fire. There was no effect of grazing and no interaction effect between fire and grazing on shrub species richness and abundance or tree species richness and seedling abundance.All plots showed a change in species composition despite treatment, and 46 species (32% of total richness) were recorded only in the final survey. The high rainfall during the 18-month study is likely to be an important factor in facilitating the establishment of species following all disturbances. This may have ameliorated the impact of grazing as abundant food was available throughout the woodland. The interaction between fire and grazing may be more important in structuring these grassy communities during periods of lower rainfall.

Changes in Vegetation Structure after Long-term Grazing in Pinyon-Juniper Ecosystems: Integrating Imaging Spectroscopy and Field Studies

We used field studies and imaging spectroscopy to investigate the effect of grazing on vegetation cover in historically grazed and ungrazed high-mesa rangelands of the Grand Staircase‐Escalante National Monument, Utah, USA. Airborne hyperspectral remote sensing data coupled with spectral mixture analysis uncovered subtle variations in the key biogeophysical properties of these rangelands: the fractional surface cover of photosynthetic vegetation (PV), nonphotosynthetic vegetation (NPV), and bare soil. The results show that a high-mesa area with long-term grazing management had significantly higher PV (26.3%), lower NPV (54.5%), and lower bare soil (17.2%) cover fractions in comparison to historically ungrazed high-mesa pinyonjuniper rangelands. Geostatistical analyses of remotely sensed PV, NPV, and bare soil were used to analyze differences in ecosystem structure between grazed and ungrazed regions. They showed that PV was spatially autocorrelated over longer distances on grazed areas, whereas NPV and bare soil were spatially autocorrelated over longer distances on ungrazed areas. Field data on the fractional cover of PV, NPV, and bare soil confirmed these remote sensing results locally. Field studies also showed a significantly higher percentage composition of shrubs (27.3%) and forbs (30.2%) and a significantly lower composition of grasses (34.4%) and cacti (1.1%) in grazed areas. No significant difference between grazed and ungrazed mesas was found in percentage composition of trees or in the number of canopies per hectare. Our combined remote sensing and field-based results suggest that grazing has contributed to woody thickening in these pinyon‐juniper ecosystems through an increase in shrubs in the understory and intercanopy spaces. These results improve our understanding of broad-scale changes in pinyon‐juniper ecosystem structural composition and variability due to longterm grazing.