Effects of fire on landscape heterogeneity in Yellowstone National Park,Wyoming

Abstract. A map of burn severity resulting from the 1988 fires that occurred in Yellowstone National Park (YNP) was derived from Landsat Thematic Mapper (TM) imagery and used to assess the isolation of burned areas, the heterogeneity that resulted from fires burning under moderate and severe burning conditions, and the relationship between heterogeneity and fire size. The majority of severely burned areas were within close proximity (50 to 200 m) to unburned or lightly burned areas, suggesting that few burned sites are very far from potential sources of propagules for plant reestablishment. Fires that occurred under moderate burning conditions early during the 1988 fire season resulted in a lower proportion of crown fire than fires that occurred under severe burning conditions later in the season. Increased dominance and contagion of burn severity classes and a decrease in the edge: area ratio for later fires indicated a slightly more aggregated burn pattern compared to early fires. The proportion of burned area in different burn severity classes varied as a function of daily fire size. When daily area burned was relatively low, the proportion of burned area in each burn severity class varied widely. When daily burned area exceeded 1250 ha, the burned area contained about 50 % crown fire, 30 % severe surface burn, and 20 % light surface burn. Understanding the effect of fire on landscape heterogeneity is important because the kinds, amounts, and spatial distribution of burned and unburned areas may influence the reestablishment of plant species on burned sites.     

Physico-chemical characteristics of a permanent Spanish hypersaline lake: La Salada de Chiprana (NE Spain)

La Salada de Chiprana Lake, located in the Ebro River basin, northeastern Spain, is the only permanent and deep water hypersaline ecosystem in all of western Europe. With a total surface of 31 ha and a maximum depth of 5.6 m, it has several basins bounded by elongated sandstone-bodies or ribbons which are paleochannels of Miocene age. Its salinity varied from 30 to 73 g 1^–1 during the 1989 hydrological cycle and the most abundant ions were magnesium and sulphate. Depth-time distributions of major physico-chemical variables demonstrated that the lake was stratified in two distinctive layers during most of the year. The chemocline disappeared only in October, with the complete overturn of the water column. In the deep water, three conditions occurred which allowed development of green sulphur bacteria populations: (1) oxygen depletion, (2) presence of hydrogen sulphide and (3) presence of light. Benthic microbial mats covered the sediments of shallow shores of moderate slope.     

On the ecology of Colurellidae (Rotifera)

A material consisting of 45 colurellid rotifers from diverse waters in south and central Sweden was analyzed to reveal their relationships to their substrate. Periphytic substrates were generally preferred. Most species are obviously mobile and more or less euryecious, but a few show a predilection for bog environments. Some colurellids are euryhaline, but when inhabiting fresh water they prefer rivers and other environments with a high oxygen concentration, probably because of problems with osmoregulation.     

Winter feeding ecology of cod (Gadus morhua) in a fjord of southern Norway

We investigated the winter feeding ecology of cod ( Gadus morhua ) in the Risørfjord and Flødevigen areas on the Skagerrak coast, southern Norway. Diets from the ice-covered Risørfjord were compared with diets from the more coastal Flødevigen area. In the Risørfjord area the diet featured numerically both decapods (56.0%) and fish (27.8%), but fish dominated by mass (75.1%). The most numerous dietary items from the Flødevigen area were decapods (48.1%) and isopods (30.6%), although fish still made up the bulk of the diet's mass (52.6%). Diets at Flødevigen shifted from winter to spring, as polychaetes became important numerically (67.8%) and also contributed substantially by weight (53.6%). Since cod feed opportunistically, differences between areas and seasons probably reflected differences in prey diversity and abundance. Prey size variability increased with increasing predator length, but maximum prey size relative to predator length was constant at about 9%. Prey fish increased in both length and numbers with the length of cod, particularly in the Risørfjord area, where fish were more important in the diet than at Flødevigen. However, the majority of fish consumed in both areas were small gobiids. Based on growth patterns observed in otoliths, with opaque zones (indicating faster growth) formed during winter, the quality and quantity of the winter diet may determine annual growth rates of cod on the Skagerrak coast. Fish and decapods constituted important, high energy food sources, and there was little indication that cod were food limited during winter in this area.     

Continuous measurement of microbial heat production in laboratory fermentors

The possibility of continuously measuring the heat produced by microorganisms in an ordinary laboratory fermentor was studies. An inventory of the heat flows influencing the temperature of the culture was made. The magnitude and standard deviation in these heat flows were studied from theoretical and practical viewpoints. Calibration procedures were tested, and a model describing the heat flows in steady state and during dynamic conditions was made. Microbial heat production could be calculated accurately with the help of this model, appropriate temperature measurements, and equipment properties measured during the calibration procedures. It was found that the measurement of heat production could be done with an accuracy similar to that in the O(2) uptake measurement. (c) 1993 John Wiley & Sons, Inc.     

Morphology,distribution, and preservation potential of microbial mats in the hydromagnesite-magnesite playas of the Cariboo Plateau,British Columbia,Canada

Benthic microbial mats are common in the alkaline hydromagnesite-magnesite playa lakes of Interior British Columbia. Four main zones are recognized based on mat morphology that can be related to the type and duration of wetting. From the basin margin toward the playa centre they are: (i) vegetated hummocky ground; (ii) polygonal hummocky ground; (iii) low-domal and stratiform mats, and (iv) laterally continuous and pustular mats. Mats in peripheral mudflats are commonly mineralized by hydromagnesite, mostly precipitated by capillary evaporation of shallow groundwaters. Mats forming in the ephemeral lake tend to have lower carbonate content.Although widespread, the mats are poorly preserved in the Holocene sedimentary record. Underlying sediments are commonly weakly bedded, disturbed or massive. Desiccation, dehydration, wetting-drying cycles, and grazing by invertebrates cause fragmentation of mats at the surface, facilitating erosion. Cryogranulation, interstitial mineral precipitation, vesiculation, bioturbation, compaction, and volume changes associated with diagenesis, disrupt and destroy lamination in the upper few centimetres. Most surviving organic matter is lost by early microbial degradation.     

On choice of substrate and habitat in bdelzoid rotifers

Information on the distributions of 77 bdelloid rotifers from diverse waters in south and central Sweden was analyzed to reveal their relationships to substrate and habitat. Only two species were reported from plankton, both in low frequency. An artificial substrate, white cotton, was utilized only by few bdelloids, mainly by species with eyes. Only one species occurred at higher frequency on the saprobic substrate Sphaerotilus. Most bdelloids prefer environments rich in oxygen, but some species may be found in soft-bottom sediments. Several species dwell preferentially in diverse habitats of bogs. Some bdelloids have an exceptionally broad ecological range, but even for these is it possible to distinguish a pattern of preference and avoidance.     

Diatom ecology in the phyllosphere of the common duckweed (Lemna minor L.)

Epiphyton associated with thick, floating mats of the common duckweed (Lemna minor L.) was studied at four sites in western Canada between 1985 and 1988. Maximum epiphyton abundance generally occurred in spring as biomass of the duckweed mat was increasing. Epiphytic biomass was low during summer and increased at some sites in autumn with mat decomposition. The community was composed mostly of diatoms and, during summer, photosynthetic bacteria. Species richness of the diatom flora was low, suggesting that duckweed mats are environments to which few species are adapted. Photosynthesis - irradiance curves indicated that duckweed epiphyton was not adapted to low light levels that occurred in the mat (< 1 % of ambient), suggesting they may survive via other means of nutrition. The mat phyllosphere was also characterized by wide spatial and temporal variation in temperature, and sharp vertical profiles of dissolved oxygen and nutrients.     

Quaternary and recent Lamprothamnium groves (Charophyta) from Argentina

Only recently have extant Lamprothamnium species been reported from the American continent. L. succinctum (A. Br. in Asch.) R. D. W. was found in Lago Titicaca, Bolivia and L. haesseliae Dont. en Laguna Luro and Laguna La Salada, Argentina.Fossil gyrogonites of L. succinctum and L. haesseliae, however, are here reported to be widely distributed in Quaternary sediments of Argentina, associated with other charophytes, ostracods and foraminiferans. Localities include Laguna del Siasgo, Laguna Salada Grande, Laguna Mar Chiquita, Laguna La Amarga and Salina del Bebedero. Lamprothamnium is a genus that prefers shallow, alkaline, hyposaline to mesosaline environments. Analysis of the characteristics of Laguna La Salada contributes information on the factors that influence the distribution of the genus.The morphology characteristics of the gyrogonites and oospores of L. haesseliae and the gyrogonites of L. succinctum are described. The use of Lamprothamnium as a biomarker and its application in the reconstruction of Quaternary saline environments are also discussed.