Climatic impacts on the vegetation of eastern North America during the past 2000 years

Pollen diagrams from seven lakes with annually laminated sediments sampled at 40-year intervals are analyzed to isolate the climatic effects from other effects on the long-term dynamics of vegetation during the past 1000–2000 years along a transect from Maine to Minnesota. Principal components analysis is used to reduce the dimensionality of the pollen data. The pollen records from all lakes show long-term trends, medium frequency oscillations, and higher frequency fluctuations. The long-term trend is associated with the neoglacial expansion of the boreal forest. The mechanism causing this replacement is a change in frequency of air masses in the area. The medium-frequency oscillations are also associated with climate changes, the most recent of which is the ‘Little Ice Age’. The climate-related mechanism causing the medium-frequency changes may be changes in disturbance frequency. The higher frequency fluctuations may also be related to disturbance. This analysis of pollen diagrams into time scales of variation has enabled the separation of climate from other factors affecting vegetation dynamics. By comparing the principal components across a transect of sites it proved possible to interpret the climatic effects on vegetation at most sites and not only at range boundaries and ‘sensitive’ sites.     

Geometric morphometric analysis of the freshwater prawn Macrobrachium borellii (Decapoda: Palaemonidae) at a microgeographical scale in a floodplain system

Morphometric studies are useful for delineating the shapes of various populations and species over geographical ranges and as evidence of regional differences in crustaceans. Hydrological fluctuations in a floodplain system modulate the dispersal and presence of decapods among habitats and constitute an important macrofactor that regulate other environmental variables and which could explain the richness, distribution and abundance of organisms that live in these systems. Morphological variations among populations of the freshwater prawn Macrobrachium borellii in a floodplain system at a microgeographical scale were studied using geometric morphometrics. Carapace structure was represented using 16 digitised landmarks. Allometry and sexual dimorphism was tested. Variation in shape was explored via Principal Component Analysis. Canonical Variate Analyses was applied to compare the differences in shape between species’ populations. The correlations and covariations among shapes and hydrometric level, current velocity, geographical location and hydrologic distances were analysed. The average carapace shape was different between sexes in all sites. Populations that were near each other in terms of hydrological distance had similar shapes, but all of the populations differed in shape from the farthest population. The environmental variables were not good predictors of the carapace shape. Instead, the shape was strongly related to the hydrologic distance and geographical location. The swimming characteristics of these prawns and their passive movements, together with the dynamics of a floodplain system, explain the low morphological variation between populations in this study. The dynamic characteristics of the system influence the dispersal of the prawns and allow populations to remain connected.     

The Structure of the Mammalian Predator Guild in the Santa Cruz Formation (Late Early Miocene)

The Santa Cruz Formation (late early Miocene, Santacrucian age) registers 11 species of mammalian predators (Metatheria, Sparassodonta). Together with large carnivorous flightless birds, they comprised the terrestrial predator guild. The Santacrucian sparassodonts were diverse in body size, had different locomotory habits, and were primarily hypercarnivores. The objective of this work is to analyze the guild structure of the sparassodonts of the Santa Cruz Formation, using the variables of body mass, diet, and locomotion as proxies. Furthermore, we analyze the interaction with other predators and potential prey. The univariated test V of Poole and Rathcke and the multivariated test of Clark-Evans were used to construct the models. In the multivariate test, we made a Principal Component Analysis to resume and standardize the variables. With body mass and locomotion we obtained an evenly spaced pattern of segregation for the sparassodont species, being non-significant and significant, respectively. The pattern was aggregated and significant only with diet. The analysis of all variables together resulted in an evenly spaced and significant pattern, which is consistent with character displacements (segregation of species throughout the morphospace) that would help to diminish interspecific competition during the Santacrucian age and would allow selection of prey species of different sizes and substrate specializations. When the body size pattern of predator birds and sparassodonts were plotted together, the pattern is evenly spaced and non-significant. Other factors, including locomotion, would differentiate these species and their ecological niches.     

Parallel variation among populations in the shell morphology between sympatric native and invasive aquatic snails

A phenotypic response, either plastic or evolved, is often required for successful invasion of novel environments. Populations of the invasive snail Potamopyrgus antipodarum have colonized a wide range of environments in the western U. S. since 1985, but the extent of plastic adjustment and evolved adaptation to local environments is largely unknown. We examined variation in shell morphology among four sites in the Snake River, Idaho, including both still-water and free-flowing river habitats and compared the variation to that of a native snail (Pyrgulopsis robusta) using geometric morphometric techniques. Using Generalized Procrustes analysis, we tested for phenotypic responses by determining (1) whether Po. antipodarum from the four locations differed in shell morphology, and (2) whether these snails exhibited corresponding shell shape variation with sympatric populations of a native snail. Both native and invasive snails exhibited similar variation in shell morphology across three of the four sites. The Canonical Variate assignment test grouped 85 % of both snail species to their rightful sample site. In addition, the Principal Component Analysis displayed similar patterns of shell variation across the four sites, indicating parallel variation in shell shape. For three of the four sites, both the native and invasive snails exhibited differences in shell shape consistent with water flow variation (still-water versus fast free-flowing river). Taken together, these results suggest that the shell shape of the invasive snail has changed either through plasticity or evolution, and that both native and invasive snail populations responded to local environmental conditions in a similar manner.     

Pleistocene Extinctions and the Perceived Morphofunctional Structure of the Neotropical Felid Ensemble

The felid Neotropical ensemble has experienced important changes from the Pleistocene to the present, the extinction of sabertooth cats being the most significant. Assuming that the morphofunctional structure of the Neotropical felid ensemble was maximally expressed when machairodontines were present, we added specimens of Smilodon fatalis and S. populator to a morphological dataset inclusive of all extant species of Neotropical felids to explore the hypothetical effect of extinction of machairodontines on the perceived morphofunctional structure of the ensemble. We studied 321 specimens of 12 extant species of Neotropical felids plus S. populator and S. fatalis by measuring 123 skull and postcranial morphofunctional variables. We used Principal Component Analysis to find morphofunctional patterns of the skull, postcranium, and both combined (with and without correction for size) of both ensembles, past (with Smilodon) and present (with Smilodon lost to extinction). Canonical Phylogenetic Ordination was performed to assess the degree of phylogenetic influence on this morphospace. We also explored the effect of including homotherines in the Pleistocene guild by including specimens of North American Homotherium serum. Size was the principal factor structuring ensembles. Important morphological characters were associated to ecological performance of species. A pattern of bodily proportions was apparent: more stout species with larger skull, longer rostrum, stronger bite force, and longer pectoral crests, versus gracile, jumping species with opposing characters. The felid morphospace shrank after the extinction of Smilodon and Homotherium, but the configuration of the portion of space containing extant felids remained stable. This pattern is associated with deep phylogenetic roots.     

Classification of vegetation sequences in Toohey Forest,Queensland

In this paper we consider one method of mapping larger units identified from the spatial pattern of sequences of vegetation types. The basic data were presence/absence data for 6450 stands arranged in 90 transects. A second set of data was derived by averaging the species occurrences in non-overlapping groups of 5 stands. A divisive numerical classification was used to determine the primary vegetation units. In all, 5 different sets of primary types were derived, using different species suites, different sample sizes and different numerical methods. We briefly discuss the types identified and their spatial patterns in the area.Each of these types was then used to define a string of type-codes for every transect so that each transect represents a sample from the landscape containing information on the frequency and spatial distribution of the primary vegetation types. The transects may be classified using a Levenshtein dissimilarity measure and agglomerative hierarchical classification, giving 5 analyses of transects, one for each of the primary types discussed above. We then examine these transect classifications to investigate the stability of the vegetation landspace patterns under changes in species used for the primary classification, in size of sample unit and in method of primary classifications. There is a considerable degree of stability in the results. However it seems with this vegetation that the tree species and non-tree species have considerable independence. We also indicate some problems with this approach and some possible extensions.     

Mire vegetation in the Apuanian Alps (Italy)

Mire vegetation in the Apuanian Alps (N Italy) is analyzed from the phytosociological and the synecological points of view. Three vegetation types are delimited by numerical methods and compared with mire communities of the Alps and the Apennines. Furthermore, a chorological evaluation of this vegetation is attempted on a floristical basis.     

The persistence of calcareous grassland species in the soil seed bank under developing and established scrub

The relationships between the composition of the soil seed bank, the field layer vegetation, and the scrub canopy were investigated along a 69 m transect, grading from incipient woodland, through scrub, into intensively rabbit-grazed calcareous grassland. The results are used to assess the persistence of species associated with open calcareous grassland in the seed bank under developing scrub. Scrub age, composition and density, changed along the transect from the woodland to open grassland. A total of 35 forb and grass species were found in the field layer. The pattern evident in the scrub layer was also reflected in the herbaceous vegetation. The field layer in the most closed portion of the transect, where the scrub was oldest, was dominated by shade-tolerant species normally associated with woodland habitats. The abundance of these species decreased along the transect as the scrub age declined, and the field layer became increasingly dominated by species typical of open grassland. A total of 47 species germinated from the seed bank. Few species were recorded in the seed bank along the entire length of the transect. Overall, the seed bank was dominated by Hypericum perforatum and Centaurium erythraea, which accounted for 38.2% and 28.6% of emerging seedlings respectively. As with a number of similar studies, the composition of the seed bank had a low correspondence with the composition of the field layer vegetation. The results also emphasise that the composition of the seed bank can be viewed as an ecological palimpsest, with germinable seed of species from each stage of the old-field succession occurring in the soil. The seed bank is an important component in the re-vegetation of an area after disturbance such as scrub removal. This study supports the findings of previous research in showing that relatively few characteristic calcareous grassland species form persistent seed banks. The soil seed bank would therefore appear to be of limited value in the restoration of such grassland following scrub removal.     

Plant communities of the Accra Plains,Ghana

A new classification, using the Zürich-Montpellier procedures, is presented for the grassland, thicket and forest vegetation of the Accra Plains, Ghana. Newly described syntaxa comprise 1 class (Vetiverietea), 4 orders, 9 alliances, 16 associations and 16 subassociations. Altogether 350 species of vascular plants were recorded in 140 relevés. Correlations are made between syntaxa and climatic, edaphic and anthropogenic factors. The floristic distinctness of the area is assessed: 4 endemic species and about 40 widely disjunct species occur. Although the majority of species are of Guinean affinity, the plant communities of the Accra Plains are unique in the context of African tropical vegetation.     

Mowing for biodiversity: grass trimmer and knife mower perform equally well

Mowing of semi-natural grasslands is an important management method to maintain the conservation value and species-richness of this habitat. Mowing using cutting instruments, e.g. sickle bar mowers, is thought to be superior by practitioners compared with other mechanical instruments that tears off the plant material, e.g. grass trimmers. However, almost no studies exist that supports this assumption. We analysed a 12-year field trial in a semi-natural grassland in south-eastern Sweden, with the aim of determining which mowing technique best maintains the conservation value of semi-natural grasslands. Two mowing techniques were compared: mowing using a hand-pushed sickle bar mower (a type of knife mower), or mowing using a grass trimmer at a 5-cm or 0-cm cutting height. The odds that a recorded species belongs to a group of indicator species were calculated for sample plots, and odds ratios were calculated contrasting treatments. Three types of indicator species classification systems were used: (i) indicators of management for species richness, (ii) indicators of excess nitrogen and (iii) indicators of lack of management. The odds ratios were calculated for years 1–5, 7 and 12 of the trial. In addition, Principal Response Curve analysis was performed to analyse the change in vegetation composition over time and ANOVA for plant species richness in plots. The results showed that over time there were no differences in the odds of finding indicators of any of the three types, for any of the mowing techniques. Furthermore, there were no apparent change in vegetation composition and only a small effect on richness. These results suggest that mowing using a sickle bar mower or a grass trimmer had the same effect on the floristic composition of grasslands, and both techniques can be recommended for use in semi-natural grasslands.     

Seed morphology in New WorldAntirrhineae (Scrophulariaceae): Systematic and phylogenetic implications

Seeds of 39 species representing all native genera and sections of New WorldAntirrhineae were examined with the Scanning Electron Microscope and Light Microscope. Based on seed shape and surface ornamentation, seven morphological categories are recognized: cristate, tetracostate, foveolate, tumid tuberculate/cristate, circumalate, medusiform, and a miscellaneous category. Most sections and/or generic categories can be characterized by a single morphological type, althoughMaurandya s.l. has several distinctive seed types included within present generic boundaries. The cristate seed type is believed to be the “primitive type” from which the medusiform and tumid tuberculate/cristate types have developed. The tumid tuberculate/cristate type presumably gave rise to the circumalate, tetracostate, and foveolate patterns. The miscellaneous category (represented byLinaria andKickxia) may be phyletically remote from the other New World types. Seeds of the New WorldAntirrhineae mostly seem to be adapted for water dispersal although some adaptations for wind dispersal (e.g. wings, light weight) are evident. Free-hand sections and seed coat clearings indicate that circumalate seeds are of two different anatomical patterns; such structural diversity may be found in the other seed types.     

The forest-cerrado transition zone in southern Amazonia: Results of the 1985 Projeto Flora Amazônica expedition to Mato Grosso

An account of the history of collecting in the Mato Grosso is followed by a discussion of the current views on the nature of the vegetation along the transition from Amazonian forest to cerrado. The purpose of the 1985 Projeto Flora Amazônica expedition was to sample the vegetation in the transition region in northern Mato Grosso. In order to characterize the vegetation at the various localities, the identified collections were assigned to one of five broad distributional categories: Planaltine, Transitional, Amazonian, Wide-spread, or Other. In most cases, as expected, the collecting sites in the north and the west were characterized by Amazonian forest species while those in the south and east comprised mainly cerrado elements. Our collections show that the transition zone is a complex mosaic of Amazonian forest and cerrado formations.     

Aspect-vegetation complex effects on biochemical characteristics and decomposability of soil organic carbon on the eastern Qinghai-Tibetan Plateau

Background

Meadows and shrublands are two major vegetation types on the Qinghai-Tibetan Plateau, but little is known about biochemical characteristics and its relation to decomposability of soil organic carbon (OC) under these two vegetation types. The present study was designed to evaluate effects of aspect-vegetation complex on biochemical characteristics and decomposability of soil OC.

Methods

Two hills were randomly selected; both with vegetation being naturally divided into southward meadows and northward shrublands by a ridge, and soils were sampled at depths of 0–15 and 15–30 cm, along contours traversing the meadow and shrubland sites. Particulate (particle size 2–0.05 mm) OC and nitrogen (N), microbial biomass C and N, non-cellulosic sugars, and CuO lignin were analyzed, and OC mineralization was measured for 49 days at 18 and 25 °C under laboratory incubation, respectively.

Results

More than half of soil OC was present as particulate fraction across all samples, indicating the coarse nature of soil organic matter in the region. Averaging over depths, shrublands contained 87.7???114.1 g OC and 7.7???9.3 g N per kg soil, which were 63???78 and 26???31 % higher than those in meadows, respectively. Meanwhile the C/N ratio of soil organic matter was 11.4???12.3 under shrublands, being 29???40 % higher than that under meadows. Soil OC under meadows was richer in noncellulosic carbohydrates and microbial biomass in the 0–15 and 15–30 cm depths but contained less lignin in the 15–30 cm depth. Ratios of microbially- to plant-derived monosaccharides and between acid and aldehyde of the vanillyl units were greater in soils under shrublands, showing more abundant microbially-derived sugars and microbially-transformed ligneous substances in OC as compared to meadow soils. By the end of 49 days’ incubation, total CO₂–C evolution from soils under meadows was 15.0–16.2 mg g^?1 OC averaging over incubation temperatures and soil depths, being 27–55 % greater than that under shrublands. Across all soil samples over two sites, total CO₂ ? C evolved per g OC at either 18 or 25 °C was closely correlated to enrichments of noncellulosic carbohydrates and microbial biomass. This indicates that the greater soil OC decomposability under meadows was associated with its larger abundances of readily mineralizable fractions compared with shrublands. However, temperature increase effect on soil OC decomposability did not differ between the two types of vegetation.

Conclusions

Our findings suggest that the aspect-vegetation complex significantly affected pool size, biochemical characteristics, and decomposability of soil OC on the northeastern edge of Qinghai-Tibetan Plateau. However, the response of soil OC decomposability to temperature was similar between southward meadows and northward shrublands.     

Vegetation discontinuities and altitudinal indicator species in mountains of West Greenland: finding the best positions and traits to observe the impact of climate warming in the Arctic

Aims

To delineate boundaries of vegetation belts, characterize these belts by indicator species, plant functional types and plant distribution types, and explore options for climate change monitoring.

Location

Three research sites in the continental inland of West Greenland.

Methods

Based on spatially constrained clustering of 147 vegetation relevés and 145 transect plots of plant communities, boundaries of altitudinal vegetation belts were assessed. Indicators for altitudinal sections were identified from 664 vegetation relevés among vascular plants, bryophytes, lichens and plant functional types using indicator species analysis. The performance of different plant groups along the altitudinal gradient was visualized with response curves.

Results

Boundaries of altitudinal vegetation belts were detected at 400, 800 and 1175 m a.s.l. on north‐facing slopes and at 450, 900 and 1250 m a.s.l. on south‐facing slopes. The resulting four vegetation belts were well defined by 99 indicator species and nine indicator plant functional types. Species, plant functional types and vascular plant distribution types showed clear sequences along the altitudinal gradient, which partly resemble their distribution along the latitudinal gradient.

Conclusions

As an easily observable expansion of shrubs and a decline of mosses and lichens is expected, the boundary at 400/450 m a.s.l. is particularly promising for climate change monitoring. The anticipated replacement of numerous cryophilous by thermophilous indicator species, as well as an obvious shift of plant functional types suggest several monitoring options at 800/900 m a.s.l. The summit areas above 1175/1250 m a.s.l., having a discontinuous plant cover, are considered to be especially vulnerable to fast invasion by species of lower altitudes such as woody plants and sedges. Due to steep gradients and short migration distances in mountains, it can be assumed that these anticipated changes in the study area will be stronger and faster than the already observed changes along the latitudinal gradient in lowland areas of the Arctic.

     

Limitations of a random screen: Search for new anticancer drugs in higher plants

The inherent limitations of a random search of higher plants for novel cancer chemotherapeutic agents are reviewed—the National Cancer Institute’s (NCI) Anticancer Screening Program. A graphic summary of plant exploration for the NCI is depicted on a world map showing 58 floristic regions. It is estimated that less than one-half of the world flora is economically feasible for collection. Random screening of approximately 35,000 species has led to guidelines that precluded further screening of all species in 333 genera and another 2,905 species in 1,773 genera. These taxa are reported to represent one-half to two-thirds of the species that characterize vegetation in geographic areas most frequently explored for the NCI. It is estimated that 40,000 untested species of flowering plants are readily available and meet the NCI guidelines for antitumor screening. However, because of apparent diminishing returns from random screening of chemicals in plant genera, it is suggested that a good representation of the diversity in the world flora could be obtained in 10,000 collections, if random sampling follows the phytogeographic outline that is recommended. Modifications to the screening methodology might be geared to an expected point of diminishing returns for discovering novel chemotypes. Additionally, the NCI should continue random screening to increase the development of new anticancer drugs; past screening has generated a tremendous wealth of data. Finally, in this paper, the author proposes to utilize lists representing taxa commonly collected for the NCI to create a manual of worldwide common plants.     

Vegetation trends following fire in the Roggeveld, Mountain Renosterveld, South Africa

The Mountain Renosterveld vegetation of the Roggeveld is an escarpment type renosterveld showing strong karroid affinities. Fire plays an important role as a landscape scale disturbance that shapes plant communities in this vegetation type, however, post-fire succession has never before been documented for renosterveld vegetation. A study was therefore conducted in the northern Roggeveld to improve our understanding of the recovery of the vegetation following fire. The natural vegetation recovery was analysed using line transect data accumulated at five different sites over a ten year period. This paper reports on the post-fire vegetation trends with respect to changes in species composition, species richness, life form composition and life form richness. Vegetation cover began to re-establish within the first nine months following the fire, and remained at a high level from years 3 to 10. At the first survey the species richness varied from 13 to 17 species, with the highest species richness (14 to 31 species) generally encountered at each transect after three years. The highest Shannon index values were generally found within the first three years and the lowest Shannon index values were found in years 9 and 10. In all cases the Principal Co-ordinate Analysis ordinations of the species composition data indicated a clear separation in the species composition between the first two years (years 1 and 2) following the fire and the remaining years (year 3 to 10). This study also supports the ‘initial floristic composition’ model of Egler (1954) in that all or the majority of species encountered during the succession were already present at the beginning of the recovery phase and there was a rapid re-establishment of the initial plant community.     

An altitudinal transect study of the vegetation on Mount Kinabalu,Borneo

A quantitative transect analysis of altitudinal sequences of forest canopy species from 600 to 3400 m asl on Mt. Kinabalu (4101 m), Borneo, resulted in four discrete altitudinal vegetation zones. These were made up of mutually exclusive species groups for lowland (<1200 m asl), lower montane (1200 to 2000–2350 m asl), upper montane (2000–2350 to 2800 m asl), and subalpine (2800 to the forest line, 3400 m asl) zones. Zonal soil types were correlated with the vegetation zones. In upslope sequence, these were: lowland Oxisols, montane Histosol/Spodosol complex, and subalpine Inceptisols. The highest contents of organic carbon, extractable phosphorus, and exchangeable magnesium and potassium were recorded in the lower and upper montane zones. The upper boundaries of the lowland, upper montane and subalpine zones coincided with thermal thresholds of latitudinal bioclimatic zones: 18°C TMIN (Köppen's tropical), WI 85 (Kira's warm temperate), and WI 45 (Kira's cool temperate), respectively. The upper limit of the lower montane zone was correlated with an abrupt increase of water surplus estimated from the annual rainfall minus annual potential evaporation. These climatic characteristics appear to define ecological altitudinal turnover points, so called critical altitudes, where groups of associated species are displaced by other groups.Abbreviations asl = above sea level - DBH = diameter at breast height - PHQ = Park headquarters - TMAX = Mean daily maximum air temperature - TMIN = Mean daily minimum air temperature - TWINSPAN = Two-way indicator species analysis - WI = Warmth index     

Seasonal variation and distribution of microfungi in forest soils of Delhi

Seasonal occurrence and abundance of microfungi at three different depths in tropical forest soils of Delhi were studied using the soil dilution and soil plate techniques. Surface layer in all the soil types exhibited the highest population and species number which gradually declined with depth increase. In total, 58 genera comprising 118 species were isolated of which theDeuteromycetes was represented by 38 genera and 90 species, thePhycomycetes by 10 genera and 18 species, theAscomycetes by 6 genera and 8 species, and theBasidiomycetes andMyxomycetes by single genus and species. Besides the surface vegetation, the edaphic and environmental factors had a profound influence on the occurrence and distribution of microfungi at various depths of soils.