Distribution Of Woody Vegetation Research Articles

Woody vegetation dynamics in the tropical and subtropical Andes from 2001 to 2014: Satellite image interpretation and expert validation.

The interactions between climate and land‐use change are dictating the distribution of flora and fauna and reshuffling biotic community composition around the world. Tropical mountains are particularly sensitive because they often have a high human population density, a long history of agriculture, range‐restricted species, and high‐beta diversity due to a steep elevation gradient. Here we evaluated the change in distribution of woody vegetation in the tropical Andes of South America for the period 2001–2014. For the analyses we created annual land‐cover/land‐use maps using MODIS satellite data at 250 m pixel resolution, calculated the cover of woody vegetation (trees and shrubs) in 9,274 hexagons of 115.47 km2, and then determined if there was a statistically significant (p < 0.05) 14 year linear trend (positive—forest gain, negative—forest loss) within each hexagon. Of the 1,308 hexagons with significant trends, 36.6% (n = 479) lost forests and 63.4% (n = 829) gained forests. We estimated an overall net gain of ~500,000 ha in woody vegetation. Forest loss dominated the 1,000–1,499 m elevation zone and forest gain dominated above 1,500 m. The most important transitions were forest loss at lower elevations for pastures and croplands, forest gain in abandoned pastures and cropland in mid‐elevation areas, and shrub encroachment into highland grasslands. Expert validation confirmed the observed trends, but some areas of apparent forest gain were associated with new shade coffee, pine, or eucalypt plantations. In addition, after controlling for elevation and country, forest gain was associated with a decline in the rural population. Although we document an overall gain in forest cover, the recent reversal of forest gains in Colombia demonstrates that these coupled natural‐human systems are highly dynamic and there is an urgent need of a regional real‐time land‐use, biodiversity, and ecosystem services monitoring network.

Community Classification and Character of Distribution of Woody Vegetation in Mt. Gyebangsan

Community Classification and Character of Distribution of Woody Vegetation in Mt. Gyebangsan

Composition, structure, and regeneration patterns in a gallery forest along the Tana River near Bura, Kenya

This study used classification and ordination techniques to characterize the composition and distribution of woody vegetation along the Tana River floodplain near Bura in eastern Kenya. Results obtained from cluster analysis of tree and shrub vegetation corroborated the results from non-metric multidimensional scaling (NMS), separating the forests into seven fairly well-defined assemblages of species. The primary vegetation gradient summarized by the ordination was significantly correlated (0.257–0.394, p < 0.01) with soil texture and soil carbon at depths of 50–120 cm. The secondary vegetation gradient was significantly correlated (0.480–0.483, p < 0.01) with indicators of river flood regime. Measured environmental variables, however, only partially explained observed vegetation patterns. Many overstory species were well represented in the regeneration layer of low-lying point-bar and oxbow forests, but were poorly represented in the higher elevation levee forests. There were significant correlations (0.278–0.320, p < 0.01) between the first ordination axis for the regeneration layer and flood regime of the river, and between the second ordination axis and soil texture (0.321–0.346, p < 0.01) in the top 20 cm where seedling roots are likely to be settled. Spirostachys venenifera and Acacia elatior had the widest environmental tolerance, occurring in 78% and 60% of all sample plots, respectively. Populus ilicifolia had the narrowest environmental tolerance, occurring in less than 1% of plots, all located on point-bars.

Correspondence analysis of functional groups in a riparian landscape

We used multivariate analysis and ordinations to characterize thecomposition and distribution of woody vegetation within the Ozark NationalScenic Riverways (ONSR), Missouri, USA. The objectives of the study were to: 1)evaluate patterns of woody species distributions along existing environmentalgradients; 2) determine if different classes of woody plants (i.e., dominantoverstory trees, all trees, understory trees, and shrubs) responded similarlytothe same suite of environmental variables; and 3) determine if discreteecotonaland/or ecoclinal vegetation patterns were present across the landscape. Woodyvegetation was sampled from 94 plots along 35 transects positioned at rightangles to the river channel. Sample plots were analyzed with DetrendedCorrespondence Analysis (DCA), Canonical Correspondence Analysis (CCA), andTWINSPAN. Overall, woody vegetation was correlated with several environmentalgradients, including elevation of the plot above the river, soil pH, soilmoisture, and soil particle size. Responses to secondary gradients differedamong the four classes of plants analyzed, however. CCA biplots of understorytrees indicated that patterns of those species were strongly correlated withslope through the plot and sand content of soil. CCA biplots of shrubs showedthat CCA axes were most strongly correlated with soil organic matter content,soil moisture, and silt content. Further, there was limited evidence fordiscrete assemblages of woody species, with the exception of streamsidevegetation. Instead, mixing of woody species was observed across a broadtransition zone. Because there is little correspondence between vegetationlayers, our results demonstrate including plant classes other than a subset ofcanopy dominant trees can provide additional resolution in characterizingvegetation responses along complex environmental gradients.

Dispersal of woody plants in forest edges and hedgerows in a Southern Swedish agricultural area: the role of site and landscape structure

The distribution of woody vegetation was studied in forest edges and hedgerows in a 28 km2 southern Swedish agricultural area, characterised by species-rich edge zones. The occurrence of 21 selected woody species (taxa) was related to differences in both edge structure and landscape structure. All the species studied were represented in both edge types, but a higher frequency of animal-dispersed species was found in hedgerows. Animal dispersed species were more affected by edge width and density than wind dispersed species. A higher number of wind-dispersed species were more frequent in forest edges, in hedgerows near to forest, or with a high proportion of forest within 500 m. A clear relationship was found between the number of physically connected elements in hedgerow networks and increasing frequency of occurrence for Corylus avellana, Crataegus spp., Euonymus europaeus, and Quercus robur; which indicate the ecological significance of connectedness for certain animal dispersed species. The study supports the general principle that woody species distribution and landscape structure are linked in a positive feedback loop. The results match findings from studies in other countries and are interpreted in the context of landscape processes and the ecological characteristics of woody plant species. We emphasise the importance of understanding dispersal mechanisms of woody species for the design and improvement of edge habitats in agricultural landscapes.

Composition, structure, and distribution of woody vegetation on the Cache River Floodplain, Arkansas

This study characterizes the species composition, structure, and distribution of woody plants on the floodplain of the Cache River in northeastern Arkansas. Trees, saplings, and shrubs were sampled in 249 plots along with 28 environmental variables. Classification of the plots resulted in four forest dominance types being identified. The basal area, density, species richness, and diversity of these four types were within the range of values established for similar floodplain forests throughout the Coastal Plain of the southeastern United States. Canonical correspondence analysis revealed the distribution of species to be significantly correlated with flood depth and flood duration as well as geomorphic position and soil texture.

Landscape and Climatic Control of Woody Vegetation in a Dry Tropical Ecosystem: Turkana District, Kenya

The spatial organization of a dry woodland/ savanna/shrub-steppe ecosystem in a 9000 km2 region of arid Northern Kenya was explored by analysing the abundance and distribution of woody vegetation in relation to landscape gradients and gradients in rainfall. Woody species assemblages were clustered into four major groups. Three of these (and most of the sites) were dominated by species of Acacia. Acacia tortilis was the community dominant in riparian and riverine zones, A. senegal on hilly and rocky sites, and A. reficiens on non-riparian sites with fine soils. The fourth group, found at highest elevations, was distinguished by a very low abundance of Acacia. These soil/landform associations were systematically distributed along land system gradients (mountains, pediment, valley, bajada), thus relating woody species groups to large-scale landscape characteristics. Tree woody canopy cover ranged from < 1.0% to 100% over the region as a whole. Cover was directly related to precipitation when the effects of water concentration in riparian zones were removed. However, canopy cover was not greatly influenced by either species composition or landscape characteristics. Fire reduced woody canopy cover, however, fires appeared to affect a relatively small portion of the ecosystem. Recent anthropogenic disturbances such as wood-cutting and livestock corralling were encountered in patches, but the cumulative long-term effects of patch scale disturbances could not be discerned in vegetation patterns at the regional scale. Vegetation physiognomy (woodland, bush, bushed grassland, etc.) was controlled by both water availability and landscape pattern. Woodland and forest occurred almost exclusively in riparian and riverine situations while the driest parts of the region supported dwarf shrub grassland with few trees. Over the region as a whole, climate and landscape gradients converged in diverse ways, giving rise to structurally variable associations of woody plant species. Vegetation structure in tropical savannas and dry woodlands is often interpreted in terms of competition between woody and herbaceous life forms for soil moisture. The outcome of this competitive interaction is thought to be influenced by disturbances that shift the system from one stable state to another. However, our findings suggest that dry tropical ecosystem structure is hierarchically constrained by physical factors: by climate at regional to continental scales; by topographic effects on rainfall and landscape water redistribution, and geomorphic effects on soil and plant available water at the landscape to regional scales; and finally by water redistribution and disturbance at local and patch scales.

Land use history of Jebel Marra, Sudan, as related to the present distribution of woody vegetation

This study attempts to relate vegetation distribution to land use history in Jebel Marra, the Democratic Republic of the Sudan. There are evidences that most,if not all, of the woody vegetation communities in Jebel Marra have been derived from some more complex types by continuous disturbance ssince antiquity. Here past and contemporary land use types are described and associated to woody plants distribution. Empirical stratified sampling methods of plant geographers and ecologists are applied to both natural and artificial systems. Frequencies, densities and diversities for all woody plant communities are estimated by standard ecological indices. It was found that throughout known history woody plant communities were subjected to different degrees of suppression. Thus, the present distribution of the woody plant communities reflects the different stages as well as modes of suppression. Drastic population movements and the resulting changes in land use types since antiquity, seem to be the chief explanation behind the variations in modes of suppression.