Differences In Vegetation Composition Research Articles

Spatial vegetation patterns based on palynological records in the loess area between the Dnieper and Odra Rivers during the last interglacial–glacial cycle

Pollen analysis was done on loess–palaeosol sequences situated to the north of the Carpathians and Sudetes, in the belt characterized by stronger influence of oceanic climate in the West and continental climate in the East. This fact conditioned the occurrence of loess as isolated patches in the West and thick continuous covers in the East, as well as the diversity of natural vegetation cover from deciduous forests and mixed coniferous forests, through forest-steppe to steppe zone. Three loess sites were examined in Poland (Biały Kościół, Tarnawce, Polanów Samborzecki), and three in Ukraine (Yezupil, Velyka Andrusivka, Stari Kodaky). Local pollen zones, distinguished in each site, were correlated in order to define the phases of vegetation development from the end of the penultimate glacial, through the Eemian Interglacial to the end of the Vistulian. The obtained picture of vegetation changes supplements the analysis results of organogenic deposits with the description of flora in cold periods when aeolian deposition occurred. In the area under study, the common features of vegetation development were conditioned by a general trend of climatic changes during the last interglacial–glacial cycle. They overlapped with the vegetation changes, expressed by the eastward rising proportion of open landscape elements, which resulted from the increasing continentality of climate. The proportion of trees and shrubs in plant communities during interstadials was also influenced by the proximity of refuges occurring in the Carpathians and Sudetes, and the situation of the examined profiles in river valleys, which were also natural refuges. Other differences in vegetation composition between individual sites resulted from their different meso- and micro-palaeomorphologic situation.

Differences in vegetation composition and plant species identity lead to only minor changes in soil-borne microbial communities in a former arable field

To examine the relationship between plant species composition and microbial community diversity and structure, we carried out a molecular analysis of microbial community structure and diversity in two field experiments. In the first experiment, we examined bacterial community structure in bulk and rhizosphere soils in fields exposed to different plant diversity treatments, via a 16S rRNA gene clone library approach. Clear differences were observed between bacterial communities of the bulk soil and the rhizosphere, with the latter containing lower bacterial diversity. The second experiment focused on the influence of 12 different native grassland plant species on bacterial community size and structure in the rhizosphere, as well as the structure of Acidobacteria and Verrucomicrobia community structures. In general, bacterial and phylum-specific quantitative PCR and PCR-denaturing gradient gel electrophoresis revealed only weak influences of plant species on rhizosphere communities. Thus, although plants did exert an influence on microbial species composition and diversity, these interactions were not specific and selective enough to lead to major impacts of vegetation composition and plant species on below-ground microbial communities.

Differences in regeneration between hurricane damaged and clear-cut mangrove stands 25 years after clearing

The effect of human disturbance on mangrove forest may be substantially different from the effects of natural disturbances. This paper describes differences in vegetation composition and structure of five vegetation types in two mangrove areas near Darwin, Australia, 25 years after disturbance. The vegetation in clear-felled forest showed more adult Avicennia marina than in the hurricane-affected forest, and a virtual absence of A. marina juveniles and saplings. This indicates that A. marina will be replaced by other species in the canopy, showing a multi-phase vegetation development in mangrove forest after human disturbance. The mechanism of disturbance and the conditions after clearing therefore affects the vegetation composition for at least 25 years after this disturbance took place.

Detecting differences in vegetation among paired sites using pollen records

The ‘Qualitative Assessment of Difference’ method (QAD) is proposed to objectively detect differences in the relative abundance of vegetation between paired sites using pollen percentages. This method corrects for intertaxonomic differences in pollen productivity and neutralizes influences of background pollen on pollen representation of vegetation, using an inverse form of the Extended R-value model. We test the method using modern pollen-vegetation data from small hollows in northern Michigan (6 taxa; 45 sites) and from northwestern Wisconsin (7 taxa; 43 sites) in the USA. Compared with pollen percentages, the one-tailed Fisher Exact test shows that the QAD method significantly improves the accuracy of the results for all taxa. The rank order of sites based on QAD is significantly correlated to the rank order of sites based on a survey of vegetation composition surrounding the hollow for each taxon (Spearman's rank-order correlation coefficients; p<0.001). We apply QAD to 9000-yr pollen records from two forest hollows c. 6 km apart in northern Michigan. Among seven taxa compared, Pinus, a taxon with well-dispersed pollen and a high pollen producer, often displays discrepancies in the direction of difference between QAD and the percentage-based method, demonstrating that pollen percentages alone do not always reflect differences in vegetation composition accurately. When several similarly sized sites are available in the same vegetation zone, QAD can objectively rank-order sites for individual taxa in relation to, for example, differences in soils, topography, patterns of species invasion, natural and anthropogenic disturbances, and other factors.

Nesting Ecology and Survival of Scaled Quail in the Southern High Plains of Texas

Scaled quail (Callipepla squamata) populations have been declining since the early 1960s, and there is no clear understanding of what is causing this decline. It has been suggested that reproductive failure is a probable cause of this decline. We used radiotelemetry to evaluate nesting ecology and survival of scaled quail in the Southern High Plains of Texas in 1999 and 2000. We radio-marked 138 hens (66 in 1999 and 72 in 2000) and reported nesting activity on 106 nests. In 1999, 50 nests were detected with a nesting success of 44%. In 2000, 56 nests were detected with a nesting success of 64%. Chick survival was recorded at 21 days posthatch and was analyzed as present or absent, as exact numbers were difficult to determine. Two hens had chicks present at 21 days in 1999, but 16 hens had chicks present at 21 days in 2000. Chick presence with the hen at 21 days was negatively associated with cool and wet weather. Logistic regression revealed predictive relationships for models describing vegetation characteristics at and around nest sites as predictors of nesting success and nest sites. Variables in the models included percentage of bare ground, forb diversity, and amount of visual obstruction at different heights. Hen survival, nesting success, and chick survival were higher in 2000 than in 1999. Differences in vegetation composition and structure were likely responses to differences in precipitation between years. Drought and overgrazing by livestock increase the percentage of bare ground and reduce visual obstruction; these are likely contributors to the reduced scaled quail populations in the Southern High Plains.

Signature extension through space for northern landcover classification: A comparison of radiometric correction methods

Northern landcover mapping for climate change and carbon modeling requires greater detail than what is available from coarse resolution data. Mapping landcover with medium resolution data from Landsat presents challenges due to differences in time and space between scene acquisitions required for full coverage. These differences cause landcover signatures to vary due to haze, solar geometry and phenology, among other factors. One way to circumvent this problem is to have an image interpreter classify each scene independently, however, this is not an optimal solution in the north due to a lack of spatially extensive reference data and resources required to label scenes individually. Another possible approach is to stabilize signatures in space and time so that they may be extracted from one scene and extended to others, thereby reducing the amount of reference data and user input required for mapping large areas. A radiometric normalization approach was developed that exploits the high temporal frequency with which coarse resolution data are acquired and the high spatial frequency of medium resolution data. The current paper compares this radiometric correction methodology with an established absolute calibration methodology for signature extension for landcover classification and explores factors that affect extension performance to recommend how and when signature extension can be applied. Overall, the new normalization method produced better extension and classification results than absolute calibration. Results also showed that extension performance was affected more by geographical distance than by differences in anniversary dates between acquisitions for the range of data examined. Geographical distance in the north–south direction leads to poorer extension performance than distance in the east–west direction due in part to differences in vegetation composition assigned the same class label in the latitudinal direction. While extension performance was somewhat variable and in some cases did not produce a best classification result by itself, it provided an initial best guess of landcover that can subsequently be refined by an expert image interpreter.

Vegetation changes after single fire-events in the Okavango Delta wetland, Botswana

A comparative study on burned and unburned areas has been conducted for the south-eastern floodplains of the Okavango Delta wetland, Botswana to assess differences in vegetation composition and structure after single fire-events. Main findings on plant traits and species occurrences supported the theory of only slight vegetation changes after fire in fire-prone environments. No specific plant trait was found to be favoured by the fire-event and only Urochloa mosambicensis showed a highly significant correlation to burning. Main changes were observed in vegetation structure, e.g. height and cover of the herb layer or biomass production. Interestingly, no main trends regarding how vegetation structure is generally affected by fire-events were derivable. Detailed analyses of five derived habitat types clearly showed different and contradictory responses to burning. This variability of vegetation response to fire-events, dependent on the habitat, was explained along a productivity gradient from active floodplains to dry Mopane woodlands. While floodplains showed an obvious decrease of standing biomass after the fire-event, an increase of biomass was observed for the Mopane woodlands. The nutrient pulses often described after fire-events, therefore seem to improve nutrient conditions best in poorer habitats, while for more productive sites, the enhanced nutrient availability after burning seem to be minor. Nomenclature: Arnold and De Wet (1993).

Functional equivalency of natural and excavated coastal plain ponds

A major obstacle to assessing functional equivalency of restored or created wetlands is the time needed to develop the functions of natural wetlands. We compared hydrologic, water-quality, and vegetation-composition functions of nine natural coastal plain ponds in the New Jersey Pinelands with those of four small, well-established excavated basins that are at least 50 years old. Our study revealed that well-established (> 50 yr old) excavated ponds achieved a moderate degree of functional equivalency with Pinelands wetlands, representing a range of coastal plain pond characteristics. Based on water-depth-fluctuation patterns and the similarity of most hydrologic indices, including high-water pond area, mean water depth, area of exposed substrate (drawdown), and the presence of a clay lens, the excavated ponds seemed to achieve hydrologic equivalency with the natural reference wetlands. However, steeper bank slopes found at most of the excavated ponds affected nearshore water depths and resulted in the absence of plant zonation that characterizes coastal plain ponds. The water-quality function, represented by pH, specific conductance, and total organic carbon, differed between pond types. The pH and specific conductance of the excavated ponds were higher and total organic carbon concentrations were lower compared with the natural ponds. We attributed these differences to landscape setting, reflected by adjacent vegetation and contrasting plant zonation. Elevated specific conductance values in the natural ponds were likely due to the higher hydrogen ion concentrations. Reduced light transmission due to higher organic carbon concentrations in the natural ponds may have greater ecological importance. However, differences in water-quality functions between the pond types may make excavated ponds more prone to changes in pH if constructed within landscapes with extensive developed or agricultural lands. The excavated ponds met or exceeded most vegetation-composition reference criteria associated with the natural wetlands. Total and herbaceous species richness were greater in the excavated ponds. Most importantly, the excavated ponds supported a native Pinelands species composition, thus preserving regional biodiversity. Because all ponds were acidic and displayed pH values within the range associated with native Pinelands plants, differences in pH may not have been the cause of the greater species richness. Although overall species composition differed between the two pond types, the flora of the created wetlands was similar to that of coastal plain ponds found in other regions and other areas of the Pinelands. The major difference in vegetation composition between ponds was both the lack of distinct vegetation zonation due to steeper slopes and lower patch-type diversity in the excavated ponds. These structural differences can be overcome by constructing ponds with slopes that are comparable to natural ponds. Because the transitional-upland location of the excavated ponds is a more likely location for a mitigation wetland, the effect of landscape setting on water quality may not be as easily remedied as the lack of nearshore slopes.

Vegetation Composition, Dynamics, and Management of a Bracken?Grassland and Northern?Dry Forest Ecosystem

We investigated differences in vegetation composition and dynamics for two globally rare ecosystems, bracken-grasslands and northern-dry forests of northern Wisconsin. These ecosystems commonly have been viewed as degraded pine barrens. Bracken-grasslands contained a high dominance of exotic species, low native richness, and no obvious prairie species, suggesting logging-era anthropogenic origins. Differences in cover for common plants among ecosystems were examined using Mann-Whitney U tests of equivalence. Cover of all 8 graminoid species, 4 of 5 Ericaceae and Myricaceae species, and 10 of 17 species of forbs were significantly different between ecosystems. Vegetation changes over a 4-year period were examined through detrended correspondence analysis (DCA) and analysis of variance (ANOVA) repeated measures. DCA analyses of community composition failed to detect significant temporal trends within individual management units, although differences were apparent between ecosystems, regardless of sample year. In addition, no apparent patterns could be detected between years when comparing dominant individual species to management history (prescribed fire). This is contrary to what would be expected for a degraded pine barrens and questions the efficacy of using repeated prescribed fire as a management tool in bracken-grasslands. Methods for conservation and restoration of xeric ecosystems of northern Wisconsin have historically relied heavily on single species (e.g., sharp-tailed grouse) wildlife models, without full consideration of other factors. We suggest that stakeholders involved in these restoration projects examine historic processes and reference conditions prior to formulating management goals. Greater attention to the differentiation and individual management needs of pine barrens, northern-dry forests, and bracken-grasslands is needed.

HABITAT USE BY THE BICKNELL'S THRUSH IN THE ESTRIE REGION, QUEBEC

Concern has been raised that the viability of Bicknell's Thrush (Catharus bicknelli) populations is precarious due, in part, to threats to its breeding habitat. Qualitative descriptions of habitat use have suggested that the species breeds primarily in dense, high elevation forests of northeastern North America. However, there is little quantitative information on habitat use patterns, which impedes formulation of effective conservation plans. To address this knowledge gap, we characterized the habitat of 42 sites occupied by Bicknell's Thrushes and 19 unoccupied sites on two mountains in the Estrie region, Quebec. Occupied sites were dominated by balsam fir (Abies balsamea) growing at high density, whereas unoccupied sites had a larger component of hardwoods at lower density. We found significant differences in vegetation composition and habitat structure between occupied and unoccupied sites for each mountain separately, and the two combined, though the particular variables distinguishing the two site types varied between the two mountains likely because of differences in management history. Our results show that the structure of occupied habitats may differ among sites even within a single region. However, it was evident that dense balsam fir-dominated habitats were used selectively by Bicknell's Thrushes at both study sites, and that the maintenance of such habitats should be a conservation priority in the Estrie region.

Rural reforms and changes in land management and attitudes: a case study from inner Mongolia, China.

The international science community stresses the importance of the local perspective in the context of dryland degradation. This paper explores changes in management and attitudes in a mixed farming system in northern China, since the introduction of the economic reforms in the early 1980s, and the following changes in land-use rights. The area encompasses a dune landscape scattered with crop-land, as well as the Daqinggou Nature Reserve, an area of natural vegetation. According to farmers new varieties of maize in combination with increased use of fertilizers have improved yields, though high yield variability persists due to erratic rainfall. Farmers acknowledge the importance of the 30-year contract on cultivated land in 1997 for their investment in long-term management, but emphasize the importance of chemical fertilizers for short-term economic survival. The farmers stressed the negative impact of grazing and cultivation on soil erosion and stated that differences in vegetation composition and cover in the nature reserve are due to anthropogenic factors.

Characteristics of Nest Sites of Northern Bobwhites in Western Oklahoma

Previous authors have described nesting habitat of the northern bobwhite (Colinus virginianus) throughout its range, but few have compared structural or compositional differences of vegetation between nest sites and random non-use sites, and successful and non-successful nests. From 1996-1998, we compared cover and structure of 85 plant species from 80 nest sites of northern bobwhite in western Oklahoma. Nest sites were consistently associated with greater structural complexity than what was available at random. Bobwhites selected nest sites with a greater coverage of grass (ca. 50%) and woody (ca. 20-30%) vegetation with a relatively low percentage of bare ground, presumably because these attributes maximize their chance for successful reproduction by providing protection against weather and predators. Successful nests were more concealed during 1996 and 1997 (12.37 and 10.74% visibility, respectively) than non-successful nest sites (21.6 and 27.65% visibility), but levels of concealment did not differ during 1998. We found no significant differences in vegetation composition or structure between successful and non-successful nest sites. DOI:10.2458/azu_jrm_v54i3_townsend

Characteristics of nest sites of northern bobwhites in western Oklahoma

Previous authors have described nesting habitat of the northern bobwhite (Colinus virginianus) throughout its range, but few have compared structural or compositional differences of vegetation between nest sites and random non-use sites, and successful and non-successful nests. From 1996-1998, we compared cover and structure of 85 plant species from 80 nest sites of northern bobwhite in western Oklahoma. Nest sites were consistently associated with greater structural complexity than what was available at random. Bobwhites selected nest sites with a greater coverage of grass (ca. 50%) and woody (ca. 20-30%) vegetation with a relatively low percentage of bare ground, presumably because these attributes maximize their chance for successful reproduction by providing protection against weather and predators. Successful nests were more concealed during 1996 and 1997 (12.37 and 10.74% visibility, respectively) than non-successful nest sites (21.6 and 27.65% visibility), but levels of concealment did not differ during 1998. We found no significant differences in vegetation composition or structure between successful and non-successful nest sites.

Testing for effects of stump fumigation with chloropicrin on vegetation in an early seral Douglas-fir stand

The biocide chloropicrin has been suggested for the control of laminated root rot (caused by Phellinus weirii (Murr.) Gilb.), a widespread and economically important disease of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests. This study investigated the effects of chloropicrin use on vegetation. A 65-year-old stand in northwestern Washington dominated by Douglas-fir was harvested by clear-cutting in 1988. At time of harvest, the stand was severely affected by laminated root rot. After harvest, plots were either left unfumigated or fumigated with 3.0-18.2 kg of chloropicrin per 0.04 ha. We used multivariate analyses to investigate the effect of chloropicrin on the abundance of vegetation, accounting for pretreatment plot differences. Five years after harvest and fumigation, no significant differences in vegetation composition or cover were found. Chloropicrin fumigation significantly increased diversity (Hill's measure) but not richness. Of the 10 most abundant species, only two showed significant effects: higher levels of chloropicrin application led to lower Veronica serpyllifolia L. var. serpyllifolia cover and to more Linnaea borealis L. cover. The power of statistical tests to detect effects of chloropicrin on vegetation was high (0.75-0.99) for large effect sizes, lending confidence to the conclusion that chloropicrin use caused few prominent adverse effects.

Characterization of vegetation in an Australian open forest community affected by cinnamon fungus (shape Phytophthora cinnamomi): implications for faunal habitat quality

Phytophthora cinnamomi (cinnamon fungus) is a pathogenic soil fungus which infects plant communities such as open forests, woodlands and heathlands in the south-eastern and south-western corners of Australia, leading to devastating effects upon both structural and floristic features of these plant communities. This study undertaken in open forest in the Brisbane Ranges, south-eastern Australia, sought to characterize two study areas using visual classification and several ordination techniques. Additionally, sites were examined for differences in vegetation composition relating to P. cinnamomi infection, and how these may relate to site habitat quality for resident fauna. This characterization had a high degree of conformity (90% to 96%) between the original visual classification and several ordination methods used. Differences in the cover of understorey vegetation including both low and tall shrubs, and the grass-tree Xanthorrhoea australis were recorded between uninfected and post-infected sites, however the cover of litter or bare ground did not infer infection status. There were no consistent significant differences in projective crown cover of Eucalyptus spp. between uninfected and infected sites, nor in the number of hollows suitable for den or nest sites for arboreal mammals and birds. Hence, the impact of P. cinnamomi upon faunal habitat quality at the sites was considered more likely to relate to changes in ground level vegetation structure than to effects of the pathogen on the dominant Eucalyptus species. Based on the small proportion of sites with detectable isolates of the pathogen (25%), and the slow rate of movement of the disease front during this study (1 to 5 m/3 yr), the current state of disease progression appeared relatively quiescent compared to infestations previously documented in the same area a decade or two earlier.

Microclimate and vegetation edge effects in a fragmented podocarp-broadleaf forest in New Zealand

Microclimate (photosynthetically active radiation; air temperature; vapour pressure deficit) and vegetation edge effects were investigated in five podocarp-broadleaf forest fragments in the North Island of New Zealand. Distinct forest edge microclimate regimes were found to exist for part of the year and these were associated with differences in vegetation composition and structure between the forest edge and interior. Some species-specific edge/interior differences could be related to timing of critical life history stages (e.g. germination and early establishment) relative to the temporal stability of edge microclimate regimes. Penetration of gross microclimatic edge effects was approximately 50 m regardless of fragment size. These results suggest that regularly shaped forest fragments <9·10 ha are dominated by edge patterns and processes and that below 1·0 ha fragments do not support forest interior conditions or vegetation associations.