Showing papers on "Vegetation (pathology) published in 1996"

Vegetation characteristics and underlying topography from interferometric radar

Abstract: This paper formulates and demonstrates methods for extracting vegetation characteristics and underlying ground surface topography from interferometric synthetic aperture radar (INSAR) data. The electromagnetic scattering and radar processing, which produce the INSAR observations, are modeled, vegetation and topographic parameters are identified for estimation, the parameter errors are assessed in terms of INSAR instrumental performance, and the parameter estimation is demonstrated on INSAR data and compared to ground truth. The fundamental observations from which vegetation and surface topographic parameters are estimated are (1) the cross-correlation amplitude, (2) the cross-correlation phase, and (3) the synthetic aperture radar (SAR) backscattered power. A calculation based on scattering from vegetation treated as a random medium, including the effects of refractivity and absorption in the vegetation, yields expressions for the complex cross correlation and backscattered power in terms of vegetation characteristics. These expressions lead to the identification of a minimal set of four parameters describing the vegetation and surface topography: (1) the vegetation layer depth, (2) the vegetation extinction coefficient (power loss per unit length), (3) a parameter involving the product of the average backscattering amplitude and scatterer number density, and (4) the height of the underlying ground surface. The accuracy of vegetation and ground surface parameters, as a function of INSAR observation accuracy, is evaluated for aircraft INSAR, which is characterized by a 2.5-m baseline, an altitude of about 8 km, and a wavelength of 5.6 cm. It is found that for ≈0.5% accuracy in the INSAR normalized cross-correlation amplitude and ≈5° accuracy in the interferometric phase, few-meter vegetation layer depths and ground surface heights can be determined from INSAR for many types of vegetation layers. With the same observational accuracies, extinction coefficients can be estimated at the 0.1-dB/m level. Because the number of parameters exceeds the number of observations for current INSAR data sets, external extinction coefficient data are used to demonstrate the estimation of the vegetation layer depth and ground surface height from INSAR data taken at the Bonanza Creek Experimental Forest in Alaska. This demonstration shows approximately 5-m average ground truth agreement for vegetation layer depths and ground-surface heights, with a clear dependence of error on stand height. These errors suggest refinements in INSAR data acquisition and analysis techniques which will potentially yield few-meter accuracies. The information in the INSAR parameters is applicable to a variety of ecological modeling issues including the successional modeling of forested ecosystems.

Nitrogen-or phosphorus-limited growth in herbaceous, wet vegetation : relations with atmospheric input and management regimes

Abstract: Herbaceous vegetation under temperate climatic conditions generally shows nitrogen- or phosphorus-limited plant growth, which creates conditions for a high botanical diversity. Is nitrogen (N) or phosphorus (P) the most important limiting factor, or are both generally in short supply? What are the consequences of Increased N and P inputs that result from anthropogenic disturbances? A new indicator of N or P limitation, that is, the vegetation N:P ratio, allows us to address these questions for a range of mires, dune slacks and moist grasslands.

The making of the Cretan landscape

Abstract: Chronology history, pseudo-history and the use of evidence the environment - making the mountains, weather and water the inhabitants - wild animals, wild trees and plants, domestic animals and plants, people and settlements the landscape - place-names, vegetation, vegetation history, terraces, fields and enclosures, boots, mules and roads, shepherding, buildings, sacred landscapes unusual places - the high mountains, coasts and the sea, islets the future - conservation and the future.

A refined classification of the primary vegetation of madagascar based on the underlying geology: using gis to map its distribution and to assess its conservation status.

Abstract: The map of vegetation domains drawn by HUMBERT (1955) and the more recent vegetation cover map of FARAMALALA (1988, 1995), produced from satellite images, are accepted as reflecting the broad vegetation zones of Madagascar. These maps have been superimposed on maps of the geology and protected areas, and analysed using Geographical Information Systems (GIS) techniques. The species composition of the primary vegetation is very strongly influenced by the type of rock on which it occurs: the geology map @%ESAIRIE, 1964) was therefore reclassified according to broad rock type categories which would markedly affect the composition of the vegetation which they support. A map of the current distribution of the

Cover is safe during the day but dangerous at night: the use of vegetation by European wild rabbits

Abstract: The use of protective cover by prey animals is commonly associated with high predation risk. Rabbits (Oryctolagus cuniculus) in southern Spain use vegetated patches in daylight but open prairie dur...

Changes in ponderosa pine site productivity following removal of understory vegetation

Abstract: Competition from understory vegetation for water and nutrients can limit productivity of young forest stands. Less is known of the effect of understory vegetation on long-term stand growth or soil organic properties. The effect of understory vegetation on periodic annual increments (PAIs) of basal area, height, and volume for ponderosa pine (Pinus ponderosa Doug].) in central Oregon at 4 or 5-yr intervals was examined for a 35-yr period. Soil C, N, and microbial biomass C (MBC) were also quantified after 32 and 35 yr with and without understory vegetation on a sandy loam pumice soil (Xeric Vitricryand). Five tree spacings, ranging from 2.0 to 8.0 m (1542469 trees ha -1 ), in combination with two understory treatments (understory vegetation present or continuously absent) were installed in 1959. Total understory vegetation cover averaged 3570 between 1959 and 1994 for treatments with understory vegetation present, and was dominated by three shrub species: antelope bitterbrush [Purshia tridentata (Pursh) DC.], greenleaf manzanita (Arctostaphylos patula Green), and snowbrush (Ceanothus velutinus Dougl. ex Hook.). Covariance analyses of PAIs for each successive interval were performed using appropriate stand parameters at the start of each interval as covariates. Tree growth was reduced by competing understory vegetation during the first 12 to 20 yr only; understory vegetation did not reduce the adjusted PAIs during the last 15 yr. Soil C and N were measured incrementally to a depth of 24 cm. Presence of understory vegetation resulted in greater C and N in the O horizon and upper 4 to 12 cm of mineral soil. Seasonal MBC, measured at 14-d intervals from May to November, was greater when understory vegetation was present. The results suggest that understory vegetation plays an important role in maintaining soil quality.

A numerical model for assessing the additional resistance to flow introduced by flexible vegetation

Abstract: The accelerating movement to restore wetlands, and especially to return flood plains to more natural conditions, leads to the widespread introduction and propagation of reeds and other forms of more-or-less flexible vegetation. These reeds and other types of vegetation then influence flows across wetlands, and the need to control flooding sequences and intensities using numerical models and other hydroinformatics tools necessitates a better understanding of this influence of flexible vegetation on flows. A numerical model is introduced that serves as a means for investigating the influence of the several factors that contribute to flow resistance induced by flexible vegetation. The model has been partially calibrated from data obtained in experiments with inflexible vegetation.

Dynamics of understory vegetation in an old-growth boreal coniferous forest, 1988 -1993

Abstract: . Understorey vegetation changes in a South Norwegian old-growth coniferous forest were studied between 1988 and 1993 in 200 1-m2 vegetation plots. Our aims were to quantify the amount of between-year compositional change, and to elaborate the environmental basis for long-term vegetation change, including the previously identified gradient structure with a major gradient related to topography (and soil nutrient status and soil depth) and a minor gradient reflecting paludification and canopy coverage. Species richness (yearly mean and cumulative species number) and change in species richness differed between vascular plants and cryptogams, and between forest types. The number of vascular plant species decreased in pine forest in dry years; bryophyte species number increased in spruce forest. Statistically significant vegetation change, as tested by constrained ordination (CCA) with time as the constraining variable, is demonstrated for most one-year periods and for the five-year period in most forest types. Vegetation change along identified gradients, measured as plot displacement along DCA ordination axes, also occurred. The magnitude of year-to-year vegetation change was related neither to forest type nor to one-year period; different responses to climatic and environmental change were observed in each forest type. The largest average displacement observed, from medium-rich spruce forest towards poor spruce forest, was interpreted as a long-term trend. Humus-layer pH decreased by ca. 0.25 units from 1988 to 1993, most strongly in medium-rich spruce forest where exchangeable Ca decreased and Al and Mn increased strongly. Our study supports the hypothesis that vascular plants show a long-term and broad-scale response to soil acidification. Change in bryophyte composition is linked to some very long growing-seasons. Detailed analysis of short-term vegetation dynamics enhances the interpretation of long-term changes and stresses the complementarity of univariate and multivariate methods in the analysis of vegetation change.

Forest canopies and their influence on understory vegetation in early-seral stands on west Vancouver Island

Abstract: Klinka et al "Forest canopies and their influence on understory vegetation in early-seral stands on west Vancouver Island." Northwest Science. 1996; 70(3): 193-200

Succession following the catastrophic eruption of Ksudach volcano (Kamchatka, 1907)

Abstract: Ksudach Volcano, southern Kamchatka Peninsula, erupted in 1907 and impacted over 2000 km2 of forests with air-fall pumice deposits We identified three impact zones In Zone I, deposits deeper than 100 cm destroyed all vegetation Two early successional stages occur, a lichen-dominated desert and isolated patches of a pioneer herb stage Zone II is defined by pumice deposits 30 to 100 cm deep Deposits of 70 to 100 cm destroyed all vegetation, but left scattered snags Here primary succession dominates recovery, but its rate varies Isolated trees survived in deposits of 30 to 70 cm and primary and secondary successional stages form a complex mosaic termed an intermediate succession In Zone II, the primary stages found in Zone I are joined by a dwarf shrub-herb stage and a secondary birch forest stage Zone III occurs where thinner deposits permitted some vegetation to survive in all locations Secondary succession dominates in deposits of 10 to 30 cm Trees suffered damage, but survived deposits of 20 to 30 cm, while other vegetation layers were eliminated Deposits of 10 to 20 cm eliminated mosses and lichens and but only reduced the number of dwarf shrubs and herbs Deposits of less than 10 cm damaged herb, moss and lichen layers but did not eliminate any species All sampled vegetation remains in a pre-climax state, having yet to recover fully from earlier eruptions Reconstructed vegetation maps for before 1907 and for ca 1925 are compared to the map of vegetation in 1994 Based on degree of soil formation, vegetation recovery and colonization rates at different pumice depths, and the current vegetation, we estimate that full recovery of the soil-vegetation system will take more than 2000 years

Vegetation change in semiarid communities

Abstract: In arid regions, the effects of grazing or sparing management on natural communities of long-lived plants generally take decades to become evident. Event-driven dynamic behavior, unpredictable and low rainfall and complicated interactions between species make it difficult to assess probabilities and time scales of vegetation change.

The Effects of Surrounding Vegetation and Transplant Age on the Detection of Local Adaptation in the Perennial Grass Aristida Stricta

Abstract: 1 A reciprocal-transplant experiment tested the hypothesis that two populations of a perennial grass were locally adapted. Because population differentiation might be due to differential adaptation to the presence of surrounding vegetation, plants were transplanted into undisturbed areas and areas from which surrounding vegetation had been removed. As an indirect investigation of the effects of temporal environmental heterogeneity on the detection of local adaptation, three age-classes of plants were included in the experiment. 2 Seeds collected from the two populations were sown into soil from both sites in the greenhouse. Seedlings of three age-classes were transplanted reciprocally between the two field sites into both undisturbed quadrats and quadrats from which vegetation had been removed. Seedling survival was recorded for six months, and dry weight was determined for all seedlings that survived to the end of this period. 3 Comparisons of seedling survival and biomass revealed evidence for local adaptation, and the expression of local adaptation was affected very little by the presence of surrounding vegetation. Results for vegetation-removal quadrats closely paralleled those for unmanipulated quadrats. This result does not support the hypothesis that the two populations are differentiated with respect to performance in the presence of vegetation. 4 The detection of local adaptation depended strongly on the age of transplants. Home-site survival and final biomass advantages were greater for older age-classes. The effect of transplant age on the detection of population differentiation suggests that evidence of population differentiation may not always be apparent because of temporal variation in environmental conditions.

Predicting Stage-Discharge Curves in Channels with Bank Vegetation

Abstract: Many flood-control channels are subjected to expensive and environmentally damaging maintenance practices to control vegetation growth in attempts to preserve flood capacity. However, such maintenance regimes are often based on vague and qualitative guidelines. There is a clear need for physically based methods of predicting the impacts of vegetation growth on flow resistance and flood capacity. In the present note, a numerical hydraulic model is coupled with physically based flow-resistance equations for gravel-bed materials and vegetation roughness elements. The resulting model is capable of simulating stage-discharge curves in channels with arbitrary cross-section geometry, gravel-bed materials and bank, and/or flood-plain vegetation, including overbank flows. The new model is demonstrated to be capable of closely replicating the stage-discharge curve at a study site on a natural river channel. Finally, the model is demonstrated using examples in which the effects on flood capacity of seasonal vegetation growth are simulated at the study site.