High Plant Cover Research Articles

Using multi-scale sampling and spatial cross-correlation to investigate patterns of plant species richness

Land managers need better techniques to assess exotic plant invasions. We used the cross-correlation statistic, IYZ, to test for the presence of spatial cross-correlation between pair- wise combinations of soil characteristics, topographic variables, plant species richness, and cover of vascular plants in a 754 ha study site in Rocky Mountain National Park, Colorado, U.S.A. Us- ing 25 large plots (1000 m 2 ) in five vegetation types, 8 of 12 variables showed significant spatial cross-correlation with at least one other variable, while 6 of 12 variables showed significant spatial auto-correlation. Elevation and slope showed significant spatial cross-correlation with all variables except percent cover of native and exotic species. Percent cover of native species had significant spatial cross-correlations with soil variables, but not with exotic species. This was probably because of the patchy distributions of vegetation types in the study area. At a finer resolution, using data from ten 1 m 2 subplots within each of the 1000 m 2 plots, all variables showed significant spatial auto- and cross-correlation. Large-plot sampling was more affected by topographic factors than species distribution patterns, while with finer resolution sampling, the opposite was true. However, the statistically and biologically significant spatial correlation of native and exotic species could only be detected with finer resolution sampling. We found exotic plant species invading areas with high native plant richness and cover, and in fertile soils high in nitrogen, silt, and clay. Spatial auto- and cross-correlation statistics, along with the integration of remotely sensed data and geographic information systems, are powerful new tools for evaluating the patterns and distribution of native and exotic plant species in relation to landscape structure.

Post-fire regeneration patterns in the eastern Iberian Peninsula

Post-fire regeneration patterns (plant cover and richness) in the Valencia region (eastern Iberian Peninsula) are studied by analysing data from two different samplings after two periods of large fires (1991 and 1994). Emphasis is given to comparing different environmental conditions (thermo-Mediterranean vs. meso-Mediterranean; south facing vs. north facing slopes) and different bedrock types (limestone vs. marls). Results suggest that the highest post-fire cover and species richness is reached in thermo-Mediterranean conditions on limestone, and the main species are the resprouters Quercus coccifera and Brachypodium retusum . North-facing sites have higher plant cover than south-facing ones, and most life forms (trees, shrubs, grasses) have higher cover in these sites. Species richness is higher on north-facing sites than on the south-facing ones at the small scale (1 to 200 m 2 ), but differences were not significant at the highest scale studied (1 000 m 2 ). Plant species richness with increasing sampling area follows the classical log-log relationship; however, when species are segregated by life forms (woody species and herbs), different species-area relationships were found.

Vegetation in an altitudinal gradient along the Rı́o Loa in the Atacama Desert of northern Chile

Six sites between 0 m and 4000 m were sampled for plant and soil chemical characteristics along the Rı́o Loa, Atacama Desert, Chile. Sites located between 0 m and 1500 m showed lower species richness, higher plant cover and higher herbaceous productivity than the upper part of the altitudinal gradient. The number of species varied non-linerly with precipitation along the altitudinal gradient. Plant cover and herbaceous productivity in the lowlands is characterized by thePluchea absinthioides Distichlis spicataassociation of anthropic origin. We propose that vegetation structure along the altitudinal gradient has been affected by past and present human activities, and climatic and edaphic factors.

Survival of nests of the terecay turtle (Podocnemis unifilis) in the Nichare‐Tawadu Rivers, Venezuela

AbstractMortality factors and hatching success of 422 terecay turtle (Podocnemis unifilis) nests on seven beaches in the Nichare and Tawadu Rivers, Venezuela, were studied following the oviposition phase. Beaches (3.4‐28.4 km2), predominantly sandy, and bordered by riparian vegetation, were searched to record nest numbers and their distribution. Elevation and surrounding plant cover were measured for each nest. Most nests were found close to the vegetation's edge (0‐11 m), at a significant distance from the water's edge (21‐80 m), in more open ground, and along the highest points of the beach (1‐2.5 m above the water's edge). Nest density was positively correlated with beach elevation but not with beach dimensions. Most nests were concentrated in less than 10% of beach area, along the upper 20% of the beach. Average clutch size was 20.1±1.7 eggs, but larger clutches were found significantly further away from vegetation. No significant correlation between hatching success and clutch size was found.A large proportion of nests were subject to animal and human predation but environmental factors (especially flooding) affected some. The major cause of egg loss was human predation. Most clutches collected by humans were found away from vegetation, on the upper 10‐20% of beaches, in exposed unvegetated sites. Animals preyed upon those nests along the vegetation's margin (1‐2 m) in the upper 0‐9% of beaches, in sites of high plant cover (75‐100%). Nests reaching the incubation phase were mainly located in the open areas, which are more prone to human predation. About three‐quarters of nests showed high hatching rates (91‐100%). However, hatchability was highest furthest away from the vegetation. Our results indicate that humans are collecting eggs mostly from sites in which nests have the larger clutches and the higher potential hatching success. Because of this relationship between nest viability and location, sustainable yield programmes must consider where harvesting can take place and must avoid the application of standard harvests per nest.

The vegetation of linear desert dunes in the north-western Negev, Israel

Summary In 1992 the flora and vegetation of an area of linear sand dunes at Nizzana, western Negev desert, Israel, was investigated. Seven different plant communities were found and a vegetation map of the research area was produced. The plant communities were distinguished by only the dominating perennial species. Nevertheless, the results of the study indicate, that also annual species may be suitable as a tool to distinguish between desert plant communities The results suggest, that the most important environmental factor determining patterns of plant distribution in the Nizzana research site is the structure and dynamics of the soil-surface. Vegetation cover was lowest in highly stable areas with hard surface crust or a high amount of fines in the soil (playas) and on the mobile dune tops. Highest plant cover was found at the dune bases and in areas which had been used for cultivation in former times. Mean species richness per unit area was lowest on the dune tops and highest in the interdune areas with more or less stable surface crust. Absolute number of species found was highest for the playas and lowest on the dune-tops. As most of the plant communities described for the research site are restricted to areas which are characterized by a certain surface stability it is discussed to regard some of the vegetation units as succession stages in a process of continuing stabilization of the dunes.

Assessing the performance indices and design parameters of treatment wetlands for H +, Fe, and Mn retention

Using correlations analysis on water quality and wetland design parameters from a set of 35 natural wetlands receiving mine water, treatment efficiency was found to be a better index of Fe and Mn treatment than area-adjusted mass removal. However, area-adjusted mass removal was found to be a better index of performance for pH treatment. Weaknesses of using an area-adjusted measure to evaluate wetland performance for Fe retention included a significant load dependency aspect, strong positive correlations to inlet and outlet Fe concentrations, null correlations with vegetation parameters, and a tendency to rate highly small wetlands receiving high flow rates. H + retention was a better indication of pH treatment than treatment efficiency because of its relationships with inlet H + concentration, Fe treatment efficiency, and H + load. Design parameters enhancing Fe treatment efficiency included broad shapes, non-channelized flow patterns, high plant diversity, a southern exposure, and low Fe loads. Design parameters enhancing Mn treatment efficiency included large areas, non-channelized flow patterns, high vascular plant and bryophyte cover, high plant diversity, and low inlet Fe concentrations. Design parameters favoring pH mitigation included broad shapes, low flow rates, low surface water depths, non-channelized flow patterns, high plant diversity and cover, and low inlet Fe concentrations.

Refuge strategies and habitat segregation in two sympatric rodents Otomys unisulcatus and Parotomys brantsii

The possibility of different refuge strategies resulting in habitat segregation in two sympatric rodents, the bush Karoo rat, O. unisulcatus and the whistling rat, P. brantsii was investigated. The rodents' habitats were characterized by using the multivariate analysis procedures: ordination diagrams and hierarchical classification. The most important environmental variables were identified. Otomys unisulcatus was restricted to areas with high percentage plant cover (60.6%) and dense foliage compared to P. brantsii habitat (plant cover=34.8%). The high percentage plant cover is necessary for nest construction. Parotomys brantsii habitat was characterized by deep Soil (76.9+15cm) with larger soil particles (0.31+0.2mm) compared to 47.5+30.3 cm soil depth and 0.15+0.1 mm soil particles in O. unisulcatus habitat. A suitable substratum therefore determines distribution of P. brantsii.The different refuge strategies result in habitat segregation and may be an important means of partitioning resources between these two sympatric rodents which have comparable body sizes, adtivitym dietary and thermoregulatory patterns.

STRUCTURAL PATTERN IN ALPINE TUNDRA VEGETATION

Several aspects of the spatial pattern of plants were investigated in six very different stands in the alpine tundra of the Colorado Front Range. Pattern was related to the internal structure of the stands, to interactions among the species, and to microhabitats within the stands.Evidence from species‐species associations and species ordinations clearly divided the stands into two groups. The first was characterized by thin, coarse, unstable soils, low plant cover, and nurse‐plant establishment. The second group was characterized by deeper, more mature, and more stable soils, higher plant cover, and more competition between species.Pattern evidence allowed some species to be categorized as competitors, ruderals, or stress‐tolerators in the context of the alpine vegetation. The two groups of stands also differed in the relative importance of species with these “strategies.”

Susceptibility to Environmental Impact in the Queen Elizabeth Islands

Exploration for oil and gas is proceeding on a rapidly increasing scale in the Queen Elizabeth Islands, and the region needs therefore to be assessed comprehensively in terms of susceptibility of habitat to physical disturbance. ... The evaluation is however necessarily provisional, since only a small part of the total land area has so far been the subject of detailed biological description. Areas likely to be ecologically critical are delimited with the object of assisting governmental and industrial planning. ... Land areas were subdivided into four broad categories based largely on observations made by the present authors. ... The categories are as follows: 1) Polar Desert (31% of land area): susceptibility low .... 2) Polar Semi-desert (25% of land area): susceptibility moderate .... 3) Diverse terrain (22% of land area): susceptibility high in many sites. ... 4) Large meadows (<2% of land area): susceptibility high .... While biological diversity and plant cover are far less in the High Arctic than in the warmer mainland Arctic, there are numerous areas where the land is susceptible to disturbance. The most common forms of degradation are sheet and gully erosion in areas of sparse plant cover, and the softening in summer of slightly disturbed surfaces on moist, fine-grained substrates. This situation contrasts with that in the Low Arctic where removal of vegetation and potential thermokarst are of great concern. In relatively small areas of high plant cover, surfaces have a susceptibility similar to the extensive tundra areas farther south. The biological consequences of disturbance can be much greater, however, not because of deleterious effects on the landscape alone, but because these isolated rich sites comprise the bulk of the energy base for the remainder of the terrestrial food web.