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Herbaceous Vegetation (herbaceous + vegetation)
Selected AbstractsWhy does the unimodal species richness,productivity relationship not apply to woody species: a lack of clonality or a legacy of tropical evolutionary history?GLOBAL ECOLOGY, Issue 3 2008Lauri Laanisto ABSTRACT Aim, To study how differences in species richness patterns of woody and herbaceous plants may be influenced by ecological and evolutionary factors. Unimodal species richness,productivity relationships (SRPRs) have been of interest to ecologists since they were first described three decades ago for British herbaceous vegetation by J. P. Grime. The decrease in richness at high productivity may be due to competitive exclusion of subordinate species, or diverse factors related to evolution and dispersal. Unimodal SRPRs are most often reported for plants, but there are exceptions. For example, unimodal SRPRs are common in the temperate zone but not in the tropics. Similarly, woody species and forest communities in the Northern Hemisphere do not tend to show unimodal SRPRs. Location, Global. Methods, We used data from the literature to test whether a unimodal SRPR applies to woody species and forest communities on a global scale. We explored whether the shape of SRPRs may be related to the lack of clonality in woody species (which may prevent their being competitively superior), or the legacy of evolutionary history (most temperate woody species originate from tropical lineages, and due to niche conservatism they may still demonstrate ,tropical patterns'). We used case studies that reported the names of the dominant or most abundant species for productive sites. Results, Woody species were indeed less clonal than herbaceous species. Both clonality and the temperate evolutionary background of dominating species were associated with unimodality in SRPRs, with woodiness modifying the clonality effect. Main conclusions, The unimodal SRPR has been common in the ecological literature because most such studies originate from temperate herbaceous communities with many clonal species. Consequently, both evolutionary and ecological factors may influence species richness patterns. [source] Hardened foliated fault gouge from the Nojima Fault zone at Hirabayashi: Evidence for earthquake lightning accompanying the 1995 Kobe earthquake?ISLAND ARC, Issue 3-4 2001Yuji Enomoto Abstract Two anomalous features were found in the Nojima Fault zone at Hirabayashi in Awaji Island, south-west Japan: (i) hard foliated gouge between weathered granitic fault breccia and weakly consolidated mudstone of the Osaka Group; and (ii) mudstone near the gouge showing anomalous magnetization behavior. Roots of herbaceous vegetation near the foliated gouge were extraordinarily charred. In order to understand the nature of the gouge, shallow drillings were made to a depth of 3,14 m across the fault zone. Various physicochemical measurements of the gouge at depths and charred roots of herbaceous vegetation were conducted. The main results were: (i) Using electron spin resonance (ESR) analysis, the carbon radical peak (g = 2.006) of the charred roots was found to be 25 times larger than that of the non-charred roots of the same vegetation taken near the fault, indicating that the charred roots were subjected to baking; (ii) the hard foliated gouge clearly showed a lamellar structure consisting alternately of gray and black layers; (iii) the black layers in most of the foliated gouge showed flow structures almost parallel to the fault, but the gray layers rarely showed flow patterns; (iv) natural remanent magnetization (NRM) of the foliated gouge was 430 times greater than that of the granitic fault breccia and approximately 70 times greater than that of the mudstone; (v) the NRM intensity of the mudstone near the fault was highest near the ground level and decreased as the depth increased, although the magnetic susceptibility of the mudstone was almost constant and independent of depth; (vi) the high-coe civity magnetization component vectors of both the mudstone and the foliated gouge in a Schmidt equal-area projection was quite different from that of the present direction of the Earth's field; and (vii) using a magnetic force microscope, intense magnetic force lines were found in the black parts of the foliated gouge. It is suggested that these anomalies were possibly caused by earthquake lightning that accompanied the 1995 Kobe earthquake. In a spark plasma sintering test, which was conducted to simulate the possibility of earthquake lightning-induced sintering of the gouge, weakly altered gouge was successfully sintered within 10 s. The hardness of sintered sample was comparable to that of the hard foliated gouge. [source] Effects of climate and local aridity on the latitudinal and habitat distribution of Arvicanthis niloticus and Arvicanthis ansorgei (Rodentia, Murinae) in MaliJOURNAL OF BIOGEOGRAPHY, Issue 1 2004B. Sicard Abstract Introduction, The genus Arvicanthis (Lesson 1842) (Rodentia: Murinae), usually referred to as the unstriped grass rat, is mainly distributed in savanna and grassland habitats of Sub-Saharan Africa. Among the four chromosomal forms of Arvicanthis recently differentiated in Western and Central Africa, the one with a diploid chromosomal number (2n) of 62 and an autosomal fundamental number (NFa) of 62 or 64 is ascribed to Arvicanthis niloticus (Demarest 1822), while the one with 2n = 62 and a NFa between 74 and 76 is referred to A. ansorgei (Thomas 1910). Despite the broad area of sympatry recently uncovered along the inner delta of the Niger river in Mali [details in Volobouev et al. (2002) Cytogenetics and Genome Research, 96, 250,260], the distribution of the two species is largely parapatric and follows the latitudinal patterns of the West-African biogeographical domains, which are related to the latitudinal patterns of annual rainfall in this region. Here, we analyse the suggestion that the two species show specific adaptations to differences in climate aridity. Methods, Karyologically screened animals were sampled in 19 localities in seasonally flooded regions located along the ,Niger' river in Mali and extending from 1100 to 200 mm of mean annual rainfall. The analysis of trapping success (TS) data allowed us to investigate the respective effects of climate (i.e. annual rainfall) and local (i.e. duration of the green herbaceous vegetation) aridity on the latitudinal and habitat distribution of the two species. Conclusions, The broad zone of sympatry was found to correspond to a northward expansion of the recognized distribution area of A. ansorgei. TS values indicated that the two species responded very differently to climatic and local conditions of aridity. Arvicanthis ansorgei decreased in TS as regional conditions became more arid; a similar trend was also observed within regions where habitat occupancy decreased with local aridity. The higher TS observed in the most humid habitat relative to the others persisted throughout the latitudinal rainfall gradient. In contrast, TS of A. niloticus increased with latitudinal aridity. This species was present in more arid habitats than A. ansorgei from 1000 mm down to 400 mm of mean annual rainfall where a shift to the most humid habitat occurred. These opposite trends in TS distribution between species suggest that A. ansorgei is less adapted than A. niloticus to arid environments at both a regional and habitat level; thus, A. ansorgei would be able to invade dry regions only along the extensive floodplains bordering the inner delta of the ,Niger' river. Several biological traits that may be involved in limiting the southward distribution of A. niloticus are discussed. [source] Conundrums in mixed woody,herbaceous plant systemsJOURNAL OF BIOGEOGRAPHY, Issue 11 2003Joanna I. House Abstract Aims To identify approaches to improve our understanding of, and predictive capability for, mixed tree,grass systems. Elucidation of the interactions, dynamics and determinants, and identification of robust generalizations that can be broadly applied to tree,grass systems would benefit ecological theory, modelling and land management. Methods A series of workshops brought together scientific expertise to review theory, data availability, modelling approaches and key questions. Location Ecosystems characterized by mixtures of herbaceous and woody plant life-forms, often termed ,savannas', range from open grasslands with few woody plants, to woodlands or forests with a grass layer. These ecosystems represent a substantial portion of the terrestrial biosphere, an important wildlife habitat, and a major resource for provision of livestock, fuel wood and other products. Results Although many concepts and principles developed for grassland and forest systems are relevant to these dual life-form communities, the novel, complex, nonlinear behaviour of mixed tree,grass systems cannot be accounted for by simply studying or modelling woody and herbaceous components independently. A more robust understanding requires addressing three fundamental conundrums: (1) The ,treeness' conundrum. What controls the relative abundance of woody and herbaceous plants for a given set of conditions at given site? (2) The coexistence conundrum. How do the life-forms interact with each other? Is a given woody,herbaceous ratio dynamically stable and persistent under a particular set of conditions? (3) The net primary productivity (NPP) conundrum. How does NPP of the woody vegetation, the herbaceous vegetation, and the total ecosystem (woody + herbaceous) change with changes in the tree,grass ratio? Tests of the theory and conceptual models of determinants of mixed woody,herbaceous systems have been largely site- or region-specific and have seldom been broadly or quantitatively evaluated. Cross-site syntheses based on data and modelling are required to address the conundrums and identify emerging patterns, yet, there are very few data sets for which either biomass or NPP have been quantified for both the woody and the herbaceous components of tree,grass systems. Furthermore, there are few cross-site comparisons spanning the diverse array of woody,herbaceous mixtures. Hence, initial synthesis studies should focus on compiling and standardizing a global data base which could be (1) explored to ascertain if robust generalizations and consistent patterns exist; and (2) used to evaluate the performance of savanna simulation models over a range of woody,herbaceous mixtures. Savanna structure and productivity are the result of complex and dynamic interactions between climate, soils and disturbances, notably fire and herbivory. Such factors are difficult to isolate or experimentally manipulate in order to evaluate their impacts at spatial and temporal scales appropriate for assessing ecosystem dynamics. These factors can, however, be evaluated with simulation models. Existing savanna models vary markedly with respect to their conceptual approach, their data requirements and the extent to which they incorporate mechanistic processes. Model intercomparisons can elucidate those approaches most suitable for various research questions and management applications. Conclusion Theoretical and conceptual advances could be achieved by considering a broad continuum of grass,shrub,tree combinations using data meta-analysis techniques and modelling. [source] The irreversible cattle-driven transformation of a seasonally flooded Australian savannaJOURNAL OF BIOGEOGRAPHY, Issue 5 2003Ben R. Sharp Abstract Aim ,Anecdotal historical and photographic evidence suggests that woody vegetation is increasing dramatically in some northern Australian savanna habitats. Vegetation change in savannas has important implications for pastoral land-use, conservation management, and landscape-scale carbon storage, and informs theoretical debates about ecosystem function. This study seeks to determine the nature, extent and cause(s) of woody vegetation change in a seasonally flooded alluvial savanna habitat. Location ,The study area is located within the seasonally inundated alluvial zone of the tidal portion of the Victoria River, Northern Territory, Australia. The study area has been grazed by domestic stock since c. 1900, prior to which the area was inhabited and more likely regularly burnt by Aboriginal people for thousands of years. Methods ,Digital georeferenced aerial photographic coverages were used to examine and quantify woody vegetation change between 1948 and 1993. Transect surveys of woody and herbaceous vegetation were carried out to ground-truth air-photo results and determine the nature and causes of observed vegetation changes. Results ,There has been a dramatic increase in woody vegetation cover throughout the study area. Vegetation change patterns are roughly uniform across the full range of edaphic habitat variation and are unrelated to the depositional age of fluvial sediments. Two woody species, Eucalyptus microtheca and Excoecaria parvifolia, are predominantly responsible for observed increases. Demographic analyses reveal that woody invasions have been episodic and indicate that in most locations peak woody species establishment occurred in the mid-1970s. Grasses are almost absent in a majority of habitats within the study area. Instead, large areas are covered by scalded soil, dense invasive weed populations, and unpalatable forbs and sedges. What grasses do occur are predominantly of very low value for grazing. The condition of the herbaceous layer renders most of the study area almost completely non-flammable; what fires do burn are small and of low intensity. Main conclusions ,Multiple working hypotheses explaining observed patterns of woody vegetation increase were considered and rejected in turn. The only hypothesis consistent with the evidence is as follows: (1) observed changes are a direct consequence of extreme overgrazing by cattle, most likely when stocking rates peaked in the mid-1970s; (2) prolonged heavy grazing effected the complete transformation of much of the herbaceous vegetation to a new state that is not flammable; and (3) in the absence of regular fire mortality, woody vegetation increased rapidly. The relatively treeless system that existed in 1948 was apparently stable and resilient to moderate grazing levels, and perhaps also to episodic heavy grazing events. However, grazing intensity in excess of a sustainable threshold has forced a transition that is irreversible in the foreseeable future. Stable-state transitions such as this one inform debates at the heart of ecological theory, such as the nature of stability, resilience, equilibrium and carrying capacity in dynamic savanna ecosystems. [source] Sacoglottis gabonensis, a keystone fruit for forest elephants in the Réserve de Faune du Petit Loango, GabonAFRICAN JOURNAL OF ECOLOGY, Issue 2 2009Bethan J. Morgan Abstract This study suggests that the fruits of Sacoglottis gabonensis (Baill.) Urb. (Humiriaceae) are a keystone resource for forest elephants (Loxodonta cyclotis Matschie) in a coastal rain forest, the Réserve de Faune du Petit Loango, Gabon (now part of Loango National Park). Faecal counts demonstrated that forest elephants used Sacoglottis -dominated forest more when Sacoglottis was abundant and electivity indices suggest that Sacoglottis is a preferred food. The flora of Petit Loango is characterized by the absence of herbaceous vegetation such as Marantaceae and Zingiberaceae, and during the prolonged dry season few fleshy fruits are present other than Sacoglottis fruits, which are produced in a glut during this time. While inter-annual fruiting reliability remains to be confirmed, fruit production in 1998 and high stem density relative to other study sites provide indirect evidence that Sacoglottis fruits are a reliable inter-annual resource at Petit Loango. It is thus proposed that Sacoglottis gabonensis fruits fulfil an important role as a keystone ,fallback' resource for forest elephants during the dry season at Petit Loango. Résumé Cet article suggère que les fruits de Sacoglottis gabonensis (Baill.) Urb. (Humiriaceae) sont une ressource primordiale pour l'éléphant de forêt (Loxodonta cyclotis Matschie) dans une forêt pluviale côtière, la Réserve de Faune du Petit Loango, au Gabon, qui fait partie du Parc National de Loango. Le comptage des excréments a montré que les éléphants de forêt fréquentent les forêts dominées par Sacoglottis davantage lorsque les Sacoglottis sont abondants, et les indices d'électivité suggèrent que c'est leur nourriture préférée. La flore de Petit Loango se caractérise par l'absence de végétation herbacée comme les Marantaceae et les Zingiberaceae, et pendant la longue saison sèche, il y a peu d'autres fruits pulpeux que les Sacoglottis qui sont produits en abondance à cette saison. Même s'il faut encore confirmer que les fruits sont produits en continu d'une année à l'autre, la production des fruits en 1998 et la densité de hautes pousses, comparées aux autres sites étudiés, montrent indirectement que les fruits de Sacoglottis sont une ressource fiable tout au long de l'année à Petit Loango. On pose donc l'hypothèse que les fruits de Sacoglottis gabonensis jouent un rôle important comme aliment ressource pour les éléphants de forêt de Petit Loango pendant la saison sèche. [source] Photon flux partitioning among species along a productivity gradient of an herbaceous plant communityJOURNAL OF ECOLOGY, Issue 6 2006ANNE AAN Summary 1We studied light partitioning among species along the natural productivity gradient of herbaceous vegetation with an above-ground dry mass of 150,490 g m,2. The aim was to investigate how the light capturing ability per above-ground biomass and leaf nitrogen changes in an entire community and to reveal whether different species respond similarly to changes in soil conditions and competition. 2Species becoming dominant at high soil resources have intrinsically low leaf area ratios (LAR) and lower tissue nitrogen concentration, and hence relatively high nitrogen use efficiency. These traits lead to dominance when soil resources allow rapid growth so that benefits arising from the ability to locate leaves above neighbours and thereby increasing asymmetry of competition, become more crucial. 3In contrast to our expectations, above-ground efficiency of nitrogen use on the community level (aNUE) increased along the productivity gradient. Species level nitrogen use efficiency was unaffected by variation in site productivity; the increase in community aNUE was solely as a consequence of changes in species composition. 4Light absorption per unit of above-ground mass, ,M, declined significantly at the community level and also in most species, indicating that light use efficiency increased with increased site productivity and LAI. 5Light absorption per unit of leaf nitrogen, ,N, as an indicator of the ratio NUE/LUE showed no clear pattern on the community level because both NUE and LUE tend to increase with increased productivity. At the species level, ,N tends to decrease because NUE did not change with stand productivity. 6Some subordinate species responded by enlarging their LAR to increased competition. Additionally, these species were the most responsive in their leaf chlorophyll/nitrogen ratio to changes in light conditions, which shows that physiological plasticity is important for species that are unable to compete for light with the ability to position their leaves above those of other species. 7This study shows how plasticity in above-ground growth pattern and nitrogen allocation differs between species with respect to increased soil fertility and competition, leading to distinctive strategies of survival. Light partitioning analysis reveals that increased competition for light, resulting in changes in species composition, is the key factor that leads to decoupling of species and community level acclimation. [source] Predicting Root Density in Streambanks,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2008Candice Piercy Abstract:, Roots of riparian vegetation increase streambank erosion resistance and structural stability; therefore, knowledge of root density and distribution in streambanks is useful for stream management and restoration. The objective of this study was to compare streambank root distributions for herbaceous and woody vegetation and to develop empirical models to predict root density. Root length density, root volume ratio, soil physical and chemical properties, and above-ground vegetation densities were measured at 25 sites on six streams in southwestern Virginia. The Mann-Whitney test was used to determine differences in root density along stream segments dominated by either woody or herbaceous vegetation. Multiple linear regression was used to develop relationships between root density and site characteristics. Study results showed that roots were evenly distributed across the bank face with the majority of roots having diameters less than 2 mm. Soil bulk density and above-ground vegetation were key factors influencing root density. While significant relationships were developed to predict root density, the predictive capabilities of the equations was low. Because of the highly variable nature of soil and vegetation properties, it is recommended at this time that soil erodibility and root density be measured in the field for design and modeling purposes, rather than estimated based on empirical relationships. [source] Variation in leaf traits through seasons and N-availability levels and its consequences for ranking grassland speciesJOURNAL OF VEGETATION SCIENCE, Issue 4 2005Raouda Al Haj Khaled Abstract Question: Are leaf dry matter content, specific leaf area and leaf life span relevant plant traits to discriminate the fertility gradient in species-rich natural grasslands? In other words, is species ranking conserved when nitrogen availability or growing periods change? Location: Toulouse Research Centre, France; 150 m a.s.l. Methods: Fifteen grasses and nine dicotyledons were sown in pure stands in a random block design with three replicates. Each species was cultivated at two levels of nitrogen supply, limiting and non-limiting for growth, with three replications per nitrogen level. Leaf traits were measured across both levels of nitrogen supply and growing periods over the year. Results: Leaf dry matter content values separated the species into three life-form classes (grasses, rosette forbs and upright forbs, P < 0.001). This was not the case for specific leaf area and leaf life span. The three leaf traits were variable across growing periods and nitrogen levels, but the ranking of species was conserved over N-levels and growth periods. Furthermore leaf dry matter content was always less variable than the other leaf traits. Conclusion: We conclude that leaf dry matter content measured only on grasses could be used as an indicator to describe the N-richness of the habitat where native herbaceous vegetation develops. [source] Response of Trifolium repens to a mosaic of bare and vegetated patchesPLANT SPECIES BIOLOGY, Issue 1 2000Lizelotte Leeflang Abstract In herbaceous vegetation, plants are subjected to a spatial heterogeneous distribution of light. Trifolium repens was tested on its ability to avoid vegetated patches by change of stolon growth direction, reduced branching or reduced growth. Treatments consisted of a no grass control, grass on the west side and grass on the north side. When Trifolium was growing beside a grass patch on the west side, plants reduced branching but did not change direction nor was there reduced growth in stolons that were growing towards/in the vegetated patch compared to the control plants. When the grass patch was situated to the north of the plant, plants did not show reduced branching except of the primary stolon, nor was there change of growth direction or reduced growth. The biomass and number of ramets were reduced in the vegetated patch of the west treatment and the patch adjacent to the grass patch. In the north treatment biomass and number of ramets were only reduced in the vegetated patch. Compared to the control, total plant biomass was reduced in the west-grass-patch treatment but not in the north-grass-patch treatment. Reduced branching near grass patches could be an added mechanism by which to avoid vegetated patches; it is not very effective, however, because biomass production did not increase in the open patches but was only reduced in the vegetated patches. [source] Optimizing Hardwood Reforestation in Old Fields: The Effects of Treeshelters and Environmental Factors on Tree Seedling Growth and PhysiologyRESTORATION ECOLOGY, Issue 2 2008Etienne Laliberté Abstract Strong competition for water is largely recognized as the main factor explaining the resistance of herbaceous old fields to tree invasion. Therefore, site preparation as well as chemical and mechanical vegetation control are recommended when establishing hardwood tree plantations on such sites, but those methods are sometimes socially or ecologically inappropriate. The main objective of this study was to analyze whether treeshelters could improve early tree growth in herbaceous old fields, when mulching alone is used to partially control herbaceous competition. Our results indicate that treeshelters can facilitate tree growth in those conditions but that this was not caused by an improvement of tree water relations. Rather, it appeared to be related to an optimization of light levels inside the shelter, where light intensity was low enough to lead to a photosynthetic system less costly to maintain due to a greater specific leaf area but high enough to have no adverse effects on photosynthetic rates. Although treeshelters increased tree growth when surrounding herbaceous vegetation was low (either height or standing biomass), allowing high light levels, they reduced growth when surrounding vegetation was high and blocked a substantial quantity of light. Therefore, environmental factors such as light availability need to be considered to optimize the success of hardwood plantations when treeshelters are used in recently abandoned agricultural fields. [source] A new practical tool for deriving a functional signature for herbaceous vegetationAPPLIED VEGETATION SCIENCE, Issue 2 2004R. Hunt Abstract Hypothesis: For any one time and place a ,functional signature' can be derived for a sample of herbaceous vegetation in a way that concisely represents the balance between the different clusters of functional attributes that are present among component species. Methods: We developed a spreadsheet-based tool for calculating functional signatures within the context of the C-S-R system of plant functional types. We used the tool to calculate and compare signatures for specimen British vegetation samples which differed in management regime and location in time. Conclusion: The integrative power of the ,C-S-R signature' is useful in comparative studies involving widely differing samples. Movements in the signature can be used to indicate degree of resistance, resilience, eutrophication and dereliction. Systems of plant functional types other than C-S-R might also be approached in this way. Availability: The tool can be downloaded free of charge from the first author's web pages or from the journal's electronic archive. [source] Composition, size and dynamics of the seed bank in a mediterranean shrubland of ChileAUSTRAL ECOLOGY, Issue 5 2004Javier A. Figueroa Abstract Analysis was performed of the richness and abundance of woody species, forbs, and annual grasses in the easily germinating soil seed bank (henceforth seed bank) in a mediterranean shrubland of central Chile. The effects of successional development after fire and by microsite type (underneath or outside shrubs) on the density of seeds in the soil, and the relationship of species abundance in the seed bank with its abundance in the above-ground vegetation was examined. A total of 64 plant species were recorded in the seed bank, of which 44 were annual or biannual. Eight species were woody and another eight were perennial herbs. Four could not be identified to species level. The highest richness of established herbaceous species was recorded in late spring, with 31 species. The regeneration of the herbaceous vegetation was driven by the annual production of seeds and by a reserve of short-lived propagules in the soil. Density of all germinating seeds was significantly higher during late spring and late summer. Density of grass seeds was greater during late spring, while that of all other species was greater during late summer. Annual grass seeds accumulated in higher proportion at exposed microsites rather than under woody canopy, and in young (< 5 years old) and intermediate-age patches (10,20 years old) rather than in mature vegetation (30,50 years old). The abundance of established woody and herb species was uncorrelated with that of the seed bank. [source] | |||||||||||||