Classification and ordination of plant communities along an altitudinal gradient on the Presidential Range,New Hampshire,USA

An analysis of vegetation along an altitudinal gradient on the Presidential Range, New Hampshire, USA, using the Braun–Blanquet approach followed by multivariate data analysis is presented. Twelve main plant communities have been distinguished. Floristic information is presented in twelve tables and one appendix. The relationships of the communities to complex environmental gradients are analyzed using Correspondence Analysis. Floristic composition and community structure are controlled primarily by the altitudinal gradient (temperature, precipitation), and by mesotopographic conditions (snow accumulation, exposure and cryoturbation, slope position, and soil moisture).     

Nutrient conservation strategies in native Andean‐Patagonian forests

Abstract. Nutrient conservation in vegetation affects rates of litter decomposition and soil nutrient availability. Although resorption has been traditionally considered one of the most important plant strategies to conserve nutrients in temperate forests, long leaf life‐span and low nutrient requirements have been postulated as better indicators. We aimed at identifying nutrient conservation strategies within characteristic functional groups of NW Patagonian forests on Andisols. We analysed C‐, N‐, P‐, K‐ and lignin‐concentrations in mature and senescent leaves of ten native woody species within the functional groups: broad‐leaved deciduous species, broad‐leaved evergreens and conifers. We also examined mycorrhizal associations in all species. Nutrient concentration in mature leaves and N‐ resorption were higher in broad‐leaved deciduous species than in the other two functional groups. Conifers had low mature leaf nutrient concentrations, low N‐resorption and high lignin/N ratios in senescent leaves. P‐ and K‐resorptions did not differ among functional groups. Broad‐leaved evergreens exhibited a species‐dependent response. Nitrogen in mature leaves was positively correlated with both N resorption and soil N‐fertility. Despite the high P‐retention capacity of Andisols, N appeared to be the more limiting nutrient, with most species being proficient in resorbing N but not P. The presence of endomycorrhizae in all conifers and the broad‐leaved evergreen Maytenus boaria, ectomycorrhizae in all Nothofagus species (four deciduous, one evergreen), and cluster roots in the broad‐leaved evergreen Lomatia hirsuta, would be possibly explaining why P is less limiting than N in these forests.     

Sedimentation in fluvial and lacustrine environments

Sedimentation in rivers is dominated by a complex set of physical processes, associated with the unidirectional flow of water. Variations in these processes give rise to different fluvial channel types, whose character can commonly be recognised in the ancient record. Chemical and biological processes are comparatively unimportant in fluvial sedimentation. In contrast, physical, chemical or biological processes can each dominate sedimentation in lakes. Physical (clastic) deposition dominates in high-latitude and mountain lakes (in which chemical and biological activity are low), and in lakes with high relief of the drainage basin and lake floor. Its variety reflects a range of processes influenced by river inflow, wave and current action, thermal and density effects. Economic benefits from the study of lake and river sedimentation include both resource and environmental aspects. An example is given of a mercury pollution study in a fluvial ecosystem. It shows that return to background levels can take place within a relatively short interval after cessation of pollutant input.     

Large-scale,millennial-length temperature reconstructions from tree-rings

Over the past two decades, the dendroclimate community has produced various annually resolved, warm season temperature reconstructions for the extratropical Northern Hemisphere. Here we compare these tree-ring based reconstructions back to 831 CE and present a set of basic metrics to provide guidance for non-specialists on their interpretation and use. We specifically draw attention to (i) the imbalance between (numerous) short and (few) long site chronologies incorporated into the hemispheric means, (ii) the beneficial effects of including maximum latewood density chronologies in the recently published reconstructions, (iii) a decrease in reconstruction covariance prior to 1400 CE, and (iv) the varying amplitudes and trends of reconstructed temperatures over the past 1100 years. Whereas the reconstructions agree on several important features, such as warmth during medieval times and cooler temperatures in the 17th and 19th centuries, they still exhibit substantial differences during 13th and 14th centuries. We caution users who might consider combining the reconstructions through simple averaging that all reconstructions share some of the same underlying tree-ring data, and provide four recommendations to guide future efforts to better understand past millennium temperature variability.     

Daphniopsis australis nov.sp. (Crustacea: Cladocera), a further daphniid in Australian salt lakes

Daphniopsis australis, a new species of cladoceran in Australian salt lakes, is described, and some brief comments on its distribution are given.     

Vertical nutrient transport and its effects on epilimnetic phosphorus in four calcareous lakes

The influence of vertical nutrient transport on epilimnetic phosphorus was studied comparatively in four calcareous Wisconsin lakes during 1972. In the two lakes with steep metalimnetic nutrient gradients (Mendota, Delavan), upward fluxes by entrainment and eddy diffusion exceeded all other influxes combined; here epilimnetic total-P concentrations increased during period of high windpower and thermocline migration, and decreased during comparatively stagnant intervals. In the two lakes lacking upper metalimnetic P gradients (Green, Fish), higher windpower had little or no effect on epilimnetic phosphorus.In each of the four lakes epilimnetic P declined in early summer until a quasi steady-state was achieved between P influxes and P sedimentation. In Mendota and Delavan steady-state featured higher concentrations of total-P, and much higher epilimnetic concentrations of particulate-P and chlorophyll, than in Green and Fish Lakes — mainly on account of the high fluxes of molybdate-reactive, biologically-available P through the seasonal thermocline. The flux analysis illustrates why mean lake TP concentration after ice-out is an inconsistent measure (not sufficient statistic) for estimating nutrient potential and chlorophyll standing crops during the following summer in stratified lakes.     

Effects of recent acidification on Cladocera in small clear-water lakes studied by means of sedimentary remains

Cladoceran populations, as revealed by sedimentary remains, were studied in six lakes which by diatom evidence have become strongly acidified during the past 30 years. The accumulation rates of cladoceran remains and in two of the most strongly acidified lakes both relative and absolute numbers ofBosmina greatly increased during this period. Species numbers were not reduced, but there were shifts in relative abundances of cladoceran species.Bosmina longispina dominated all the lakes. Low pH (4.7) seemed not to be straight-forwardly harmful toDaphnia longispina, but the relative abundances of this taxon were reduced because ofBosmina.     

ASSESSING NORTHERN ELEPHANT SEAL FEEDING HABITS BY STOMACH LAVAGE

Stomach lavaging was used to study the feeding habits of northern elephant seals ( Mirounga angustirostris ) found on San Miguel Island, California, during the spring of 1984. Fifty-nine elephant seals were chemically immobilized with an intramuscular injection of ketamine hydrochloride. Once immobilized, an animal's stomach was intubated, filled with 3–4 liters of water to create a slurry of the undigested food items, and evacuated into a collection device. The stomachs of 57 (96.6%) of the animals lavaged contained identifiable parts of prey. Twenty-nine different food items were identified, 12 of which have not been previously reported as prey of the northern elephant seal: two teleost fish, Coryphaenoides acrolepis (Pacific rattail) and another unidentified macrourid; two crustaceans, Pasiphaea pacifica (glass shrimp) and Euphausia sp.; six squid, Abraliopsis felis, Gonatus berryi, Histioteuthis dofleini, Cranchia scabra, Taonius pavo, and Galiteuthis sp. and two octopi, Octopus dofleini and Octopus rubescens.     

Patterns of energy storage in Pseudoboeckella poppei (Crustacea,copepoda) from two contrasting lakes on Signy Island,Antarctica

The copepod Pseudoboeckella poppei (Daday) (Calanoida, Centropagidae) was sampled from Sombre and Heywood Lakes on Signy Island, Antarctica (60° S, 45° W) between January 1984 and March 1985. Sombre Lake is clear and oligotrophic with little phytoplankton and a bottom sediment low in organic content. By contrast Heywood Lake is turbid and mesotrophic; a substantial phytoplankton develops in summer and the bottom sediments are comparatively rich in organics. Both lakes freeze over for much of the year, forcing the copepods to adopt a benthic feeding strategy over winter. Adult Pseudoboeckella feed on phytoplankton when this is available, but also on detritus, diatoms and short algal filaments stirred up from the sediment. In Heywood Lake, male copepods show a smooth seasonal trend in lipid content with lipid being synthesised in early summer and utilised in late summer and winter. The summer increase in lipid content is associated with an increase in dry weight. Female lipid contents show evidence of two peaks of egg production. In Sombre Lake both male and female copepods increase in size during summer and show a wider range of lipid contents than in Heywood Lake; it is likely that this is due to the poorer winter feeding conditions which necessitate the synthesis of a much larger store of reserves during the summer. In contrast to marine calanoid copepods, lipid stores are exclusively triacylglycerol with no trace of wax ester.