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Shrub Species (shrub + species)
Selected AbstractsImpact of the invasive alien grass Melinis minutiflora at the savanna-forest ecotone in the Brazilian CerradoDIVERSITY AND DISTRIBUTIONS, Issue 2 2004William A. Hoffmann ABSTRACT Exotic grasses are a serious threat to biodiversity in the cerrado savannas of central Brazil. Of particular concern is the possible role they may have in impeding tree regeneration at gallery (riverine) forest edges and increasing fire intensity, thereby driving gallery forest retreat. Here we quantify the effect of roads and distance from gallery forests on the abundance of the African grass Melinis minutiflora Beauv. and test for an effect of this species on woody plant regeneration and leaf area index. Melinis was present at approximately 70% of the sites near gallery forest edges, with its frequency declining sharply at greater distances from the edge. Melinis frequency was 2.8 times greater where roads were present nearby. Leaf area index (LAI) of the ground layer was 38% higher where Melinis was present than where it was absent. LAI was strongly correlated to fine fuel mass (r2 = 0.80), indicating higher fuel loads where Melinis was present. The abundance of tree and shrub species in the ground layer was negatively related to LAI and to the presence of Melinis. The greater fuel accumulation and reduced tree regeneration caused by Melinis may cause a net reduction in forest area by increasing fire intensity at the gallery forest edge and slowing the rate of forest expansion. [source] Xylem root and shoot hydraulics is linked to life history type in chaparral seedlingsFUNCTIONAL ECOLOGY, Issue 1 2010Robert B. Pratt Summary 1.,Shrubs in fire prone chaparral communities have evolved different life history types in response to fire. A key to understanding the evolution of life history type differences is to understand how physiological traits are linked to differences in life history type. Vascular adaptations are important for delivering an efficient and stable water supply to evergreen chaparral shrub leaves. This study tested for a link between vascular physiology and life history type in chaparral shrubs. 2.,Chaparral shrub species along the south-western coast of North America survive wildfire by three different life histories. Non-sprouters are killed by fire and re-establish exclusively through germination of fire-stimulated seeds, facultative sprouters re-establish by a combination of vegetative sprouting and fire-stimulated seeds, and obligate sprouters re-establish exclusively by vegetative sprouting because their seeds do not survive fire. Non-sprouters and facultative sprouters establish seedlings in the open canopy post fire environment, whereas obligate sprouters establish seedlings in the shady understory of the mature chaparral canopy. 3.,Seedlings of nine species (Rhamnaceae) representing three each of the different life history types were grown in deep containers in a common garden under treatments of sun and shade. Hydraulic conductance was measured using a high-pressure flow meter for all organs, and a vacuum technique was used to measure conductance of fine and woody roots. We predicted that non-sprouters would exhibit greater hydraulic efficiency than the sprouting species, and that facultative sprouters would be more efficient than the shade tolerant obligate sprouters. 4.,Non-sprouters had the greatest hydraulic conductance per unit leaf and sapwood area at the whole seedling level, whereas facultative and obligate sprouters were not different. Comparing hydraulic conductance across major organs (from fine roots to leaves) showed that the hydraulic system was well coordinated. At the whole seedling level, the root system was more of a bottleneck than the shoot system. This pattern was consistent with high resistance extraxylary pathways in roots and differences in root architecture. 5.,The greater hydraulic efficiency of the non-sprouter life history type is attributed to its post-fire pioneering habit and may partially explain the relatively high speciation in the non-sprouters. Lower hydraulic efficiency is associated with a sprouting life history and greater shade tolerance. The seedling root systems represent a hydraulic bottleneck that may place roots under especially intense selection. [source] Patterns and consequences of differential vascular sectoriality in 18 temperate tree and shrub speciesFUNCTIONAL ECOLOGY, Issue 2 2006A. E. ZANNE Summary 1Resource delivery within plants depends on supply pathways. Some species have relatively constrained (sectored) vascular connections, while others have relatively unconstrained (integrated) vascular connections. 2In this study, patterns of vascular hydraulic sectoriality, anatomy and ecological tolerance were examined for 18 Northern Hemisphere temperate woody species growing at Arnold Arboretum, Jamaica Plain, MA, USA. A hydraulic technique was used to measure axial and tangential conductivity on branch segments. From a ratio of these values, a sectoriality index was calculated. 3Species that were more hydraulically sectored had greater vessel size, variation in vessel area and tangential nearest-neighbour distance, as well as lower vessel density, than did integrated species. 4Ecologically, higher tolerance to drought and wind was correlated with being sectored, while higher tolerance to flood and shade was correlated with being integrated. 5These results suggest that sectored species should be especially prominent in xeric environments where sectoriality may reduce embolism spread by minimizing vessel-to-vessel contact and pitting, and integrated species should be especially prominent when resources are spatially patchy or heterogeneous. [source] Leaf size and foraging for light in a sclerophyll woodlandFUNCTIONAL ECOLOGY, Issue 5 2002J. G. Bragg Summary 1It has been suggested that leaf size may represent a foraging scale, with smaller-leaved species exploiting and requiring higher resource concentrations that are available in smaller patches. 2Among 26 shrub species from a sclerophyll woodland community in New South Wales, Australia, species with smaller leaves tended to occur in better light environments, after controlling for height. The dark respiration rates of small-leaved species tended to exceed those of larger-leaved species. 3However, the higher-light environments where smaller-leaved species tended to occur had a patch scale larger than whole plants. There would not have been any foraging-scale impediment to large-leaved species occupying these higher-light patches. An alternative explanation for small-leaved species being more successful in higher-light patches, in this vegetation with moderate shading, might be that they were less prone to leaf overheating. 4Such relationships of leaf size to light across species at a given height may be important contributors to the wide spread of leaf sizes among species within a vegetation type, along with patterns down the light profile of the canopy, and effects associated with architecture and ramification strategy. [source] The effects of elevated CO2 on root respiration rates of two Mojave Desert shrubsGLOBAL CHANGE BIOLOGY, Issue 5 2010NAOMI M. CLARK Abstract Although desert ecosystems are predicted to be the most responsive to elevated CO2, low nutrient availability may limit increases in productivity and cause plants in deserts to allocate more resources to root biomass or activity for increased nutrient acquisition. We measured root respiration of two Mojave Desert shrubs, Ambrosia dumosa and Larrea tridentata, grown under ambient (,375 ppm) and elevated (,517 ppm) CO2 concentrations at the Nevada Desert FACE Facility (NDFF) over five growing seasons. In addition, we grew L. tridentata seedlings in a greenhouse with similar CO2 treatments to determine responses of primary and lateral roots to an increase in CO2. In both field and greenhouse studies, root respiration was not significantly affected by elevated CO2. However, respiration of A. dumosa roots <1 month old was significantly greater than respiration of A. dumosa roots between 1 and 4 months old. For both shrub species, respiration rates of very fine (<1.0 mm diameter) roots were significantly greater than those of fine (1,2 mm diameter) roots, and root respiration decreased as soil water decreased. Because specific root length was not significantly affected by CO2 and because field minirhizotron measurements of root production were not significantly different, we infer that root growth at the NDFF has not increased with elevated CO2. Furthermore, other studies at the NDFF have shown increased nutrient availability under elevated CO2, which reduces the need for roots to increase scavenging for nutrients. Thus, we conclude that A. dumosa and L. tridentata root systems have not increased in size or activity, and increased shoot production observed under elevated CO2 for these species does not appear to be constrained by the plant's root growth or activity. [source] A 10-year decrease in plant species richness on a neotropical inselberg: detrimental effects of global warming?GLOBAL CHANGE BIOLOGY, Issue 10 2009EMILE FONTY Abstract The census of vascular plants across a 10-year interval (1995,2005) at the fringe of a neotropical rainforest (Nouragues inselberg, French Guiana, South America) revealed that species richness decreased, both at quadrat scale (2 m2) and at the scale of the inselberg (three transects, embracing the whole variation in community composition). Juvenile stages of all tree and shrub species were most severely affected, without any discrimination between life and growth forms, fruit and dispersion types, or seed sizes. Species turnover in time resulted in a net loss of biodiversity, which was inversely related to species occurrence. The most probable cause of the observed species disappearance is global warming, which severely affected northern South America during the last 50 years (+2 °C), with a concomitant increase in the occurrence of aridity. [source] Habitat shifts of endangered species under altered climate conditions: importance of biotic interactionsGLOBAL CHANGE BIOLOGY, Issue 11 2008KRISTINE L. PRESTON Abstract Predicting changes in potential habitat for endangered species as a result of global warming requires considering more than future climate conditions; it is also necessary to evaluate biotic associations. Most distribution models predicting species responses to climate change include climate variables and occasionally topographic and edaphic parameters, rarely are biotic interactions included. Here, we incorporate biotic interactions into niche models to predict suitable habitat for species under altered climates. We constructed and evaluated niche models for an endangered butterfly and a threatened bird species, both are habitat specialists restricted to semiarid shrublands of southern California. To incorporate their dependency on shrubs, we first developed climate-based niche models for shrubland vegetation and individual shrub species. We also developed models for the butterfly's larval host plants. Outputs from these models were included in the environmental variable dataset used to create butterfly and bird niche models. For both animal species, abiotic,biotic models outperformed the climate-only model, with climate-only models over-predicting suitable habitat under current climate conditions. We used the climate-only and abiotic,biotic models to calculate amounts of suitable habitat under altered climates and to evaluate species' sensitivities to climate change. We varied temperature (+0.6, +1.7, and +2.8 °C) and precipitation (50%, 90%, 100%, 110%, and 150%) relative to current climate averages and within ranges predicted by global climate change models. Suitable habitat for each species was reduced at all levels of temperature increase. Both species were sensitive to precipitation changes, particularly increases. Under altered climates, including biotic variables reduced habitat by 68,100% relative to the climate-only model. To design reserve systems conserving sensitive species under global warming, it is important to consider biotic interactions, particularly for habitat specialists and species with strong dependencies on other species. [source] Advanced snowmelt causes shift towards positive neighbour interactions in a subarctic tundra communityGLOBAL CHANGE BIOLOGY, Issue 8 2006SONJA WIPF Abstract Positive and negative species interactions are important factors in structuring vegetation communities. Studies in many ecosystems have focussed on competition; however, facilitation has often been found to outweigh competition under harsh environmental conditions. The balance between positive and negative species interactions is known to shift along spatial, temporal and environmental gradients and thus is likely to be affected by climate change. Winter temperature and precipitation patterns in Interior Alaska are rapidly changing and could lead to warmer winters with a shallow, early melting snow cover in the near future. We conducted snow manipulation and neighbour removal experiments to test whether the relative importance of positive and negative species interactions differs between three winter climate scenarios in a subarctic tundra community. In plots with ambient, manually advanced or delayed snowmelt, we assessed the relative importance of neighbours for survival, phenology, growth and reproduction of two dwarf shrub species. Under ambient conditions and after delayed snowmelt, positive and negative neighbour effects were generally balanced, but when snowmelt was advanced we found overall facilitative neighbour effects on survival, phenology, growth and reproduction of Empetrum nigrum, the earlier developing of the two target species. As earlier snowmelt was correlated with colder spring temperatures and a higher number of frosts, we conclude that plants experienced harsher environmental conditions after early snowmelt and that neighbours could have played an important role in ameliorating the physical environment at the beginning of the growing season. [source] Assessment of vegetation effects on hydraulics and of feedbacks on plant survival and zonation in ephemeral channelsHYDROLOGICAL PROCESSES, Issue 6 2010P. J. Sandercock Abstract The interaction of vegetation and flow in channels is important for understanding the influences of forces in channels and effects on erosion, sediment flux and deposition; it has implications for channel habitats, channel instability and restoration schemes. Methods are needed for calculating forces on plants and data are required on thresholds for plant destruction and survival. A simple method of calculating the effect of hydraulics on vegetation and its zonation within ephemeral channels is described. Detailed cross section surveys of channel morphology, vegetation and estimates of Manning's n are input into the software program WinXSPRO to calculate the hydraulics of flows across the channel for a given event or flow level, incorporating subdivision into zones of differing morphology and vegetation across the section. This was applied to a number of cross sections on ephemeral channels in SE Spain and typical roughness values for Mediterranean vegetation types in channels were assessed. The method is demonstrated with reference to two well-documented floods in SE Spain, in September 1997 on the Torrealvilla and in October 2003 along the Salada. These flows led to the mortality of herbs, reed and smaller shrub species. Some damage to larger shrubs and trees occurred, but trees such as Tamarisk (Tamarix canariensis) were shown to withstand high forces. Some grasses were highly resistant to removal and induced sedimentation. Significant erosion was limited to areas with little vegetation covering the channel floor. Further quantification of resistance of vegetation to flows and upper threshold values for removal is continuing by relating calculated hydraulic conditions using the methods outlined to measurements of vegetation responses in events at monitoring sites. Copyright © 2009 John Wiley & Sons, Ltd. [source] Gradients in vegetation cover, structure and species richness of Nama-Karoo shrublands in relation to distance from livestock watering pointsJOURNAL OF APPLIED ECOLOGY, Issue 2 2006SIMON W. TODD Summary 1Gradients of animal impact known as piospheres tend to develop around artificial watering points, particularly in arid zones. Such grazing gradients represent a potential opportunity for differentiating the long-term effects of livestock activity from other environmental patterns. In this study, the impact of watering point provision on the plant cover, species richness and community structure of Karoo shrublands, South Africa, was investigated in the context of the evolutionary history and current grazing management practices of the region. 2The impacts of watering point provision were investigated by sampling plant cover and composition along transects placed at set distances, ranging from 10 m to 2200 m, from 11 watering points. 3Karoo vegetation cover and structure are relatively resilient to livestock grazing. Karoo plant diversity, as measured by species richness, evenness and dominance, was not as resilient. Twice as many species decreased as increased near watering points. The majority of species that decreased were regarded as being highly palatable to livestock. Heavy grazing, leading to death or repeated reproductive failure, is the most likely mechanism leading to the decline of such species. 4The highly disturbed area immediately adjacent to watering points was dominated by forbs and contained a large proportion of alien species. Adjacent to this was a zone dominated by widespread shrub species of medium to low palatability. Areas most distant from watering points contained a greater proportion of species known to be highly palatable to livestock. The ability of dominant Karoo shrubs to tolerate heavy grazing may have allowed rangeland managers to maintain stocking rates above that which can be tolerated by the majority of species but which are supported by a minority of grazing-tolerant species. 5Synthesis and applications. Highly palatable species are more abundant in areas distant from water points. Larger paddocks therefore provide a refuge for sensitive species that might otherwise be lost from the rangeland as a whole. Species that tend to occur away from watering points represent potentially useful indicators of grazing pressure. The use of these species as indicators of rangeland condition among landowners should be promoted. [source] Aboveground biomass estimation of the shrubs, Echiochilon fruticosum (Desf.) and Helianthemum kahiricum (Del.) in the arid zone rangelands of TunisiaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Abdelkader Idi Abstract The knowledge of the plant biomass is very important for the assessment of the rangeland productivity. It could help to select the appropriate species for the improvement of natural ecosystems (rehabilitation, restoration and seedling). By examining different correlations between the biomass production and the volume parameters of two North African shrub species of high range value (Echiochilon fruticosum Desf. and Helianthemum kahiricum Del.), we aimed to establish the appropriate regression models, which could be useful for the prediction of the productivity of these species. The data showed a significant relationship between the total biomass (TB) production and the mean diameter (MD) of the studied species (R2 = 0.65 for Echiochilon and R2 = 0.75 for Helianthemum). Likewise, annual fresh production (leaves and current-year shoots) was well correlated with MD of Helianthemum (R2 = 0.82). However, the correlation between these two parameters was relatively low for Echiochilon (R2 = 0.42). Résumé Il est très important de connaître la biomasse végétale pour évaluer la productivité d'un territoire. Il peut être utile de sélectionner les espèces appropriées pour l'amélioration d'écosystèmes naturels (restauration, réhabilitation, plantations). En analysant différentes corrélations entre les paramètres de production de biomasse et de volume de deux espèces d'arbustes nord-africains de grande distribution (Echiochilon fruticosum Desf. et Helianthemum kahiricum Del.), nous avons voulu établir les modèles de régression appropriés qui pourraient servir pour prédire la productivité de ces espèces. Les données ont montré un lien significatif entre la production totale de biomasse et le diamètre moyen des espèces étudiées (R2 = 0.65 pour Echiochilon, et R2 = 0.75 pour Helianthemum). De même, la production annuelle de matière fraîche (feuilles et rameaux de l'année) était bien liée au diamètre moyen pour Helianthemum (R2 = 0.82). Cependant, la corrélation entre ces deux paramètres était relativement faible pour Echiochilon (R2 = 0.42). [source] Abiotic and biotic drivers of seedling survival in a hurricane-impacted tropical forestJOURNAL OF ECOLOGY, Issue 6 2009Liza S. Comita Summary 1. ,Many forests experience periodic, large-scale disturbances, such as hurricanes and cyclones, which open the forest canopy, causing dramatic changes in understorey light conditions and seedling densities. Thus, in hurricane-impacted forests, large variations in abiotic and biotic conditions likely shape seedling dynamics, which in turn will contribute to patterns of forest recovery. 2. ,We monitored 13 836 seedlings of 82 tree and shrub species over 10 years following Hurricane Georges in 1998 in a subtropical, montane forest in Puerto Rico. We quantified changes in the biotic and abiotic environment of the understorey and linked seedling dynamics to changes in canopy openness and seedling density, and to spatial variation in soil type, topography and tree density. 3. ,Canopy openness was highest when first measured after Hurricane Georges and dropped significantly within c. 3 years, while seedling densities remained high for c. 5 years post-hurricane. When all species and census intervals were analysed together, generalized linear mixed effects models revealed that canopy openness, seedling and adult tree densities were significant drivers of seedling survival. 4. ,The relative importance of abiotic and biotic factors changed over time. Separate analyses for each census interval revealed that canopy openness was a significant predictor of survival only for the first census interval, with lower survival at the highest levels of canopy openness. The effect of conspecific seedling density was significant in all intervals except the first, and soil type only in the final census interval. 5. ,When grouping species into life-history guilds based on adult tree susceptibility to hurricane damage, we found clear differences among guilds in the effects of biotic and abiotic factors on seedling survival. Seedlings of hurricane-susceptible and intermediate guilds were more strongly influenced by canopy openness, while seedlings of the hurricane-resistant group were less affected by conspecific seedling density. Individual species-level analyses for 12 common species, however, showed considerable variation among species within guilds. 6. ,Synthesis. Our results suggest that hurricanes shape species composition by altering understorey conditions that differentially influence the success of seedlings. Thus, predicted increases in the intensity and frequency of hurricanes in the Caribbean will likely alter seedling dynamics and ultimately the species composition in hurricane-impacted forests. [source] Developmental changes in habitat associations of tropical treesJOURNAL OF ECOLOGY, Issue 3 2007LIZA S. COMITA Summary 1Recent studies have documented local-scale associations between tree species and topographic and edaphic habitat types in forests worldwide. To determine whether such associations form at early life stages, we compared species' positive associations with five habitat types (high plateau, low plateau, slope, streamside, and swamp) at two life stages for 80 tree and shrub species in a Panamanian lowland forest. 2Nineteen significant, positive habitat associations were detected at the small tree stage (seedlings and saplings , 20 cm tall and < 1 cm d.b.h.), and 18 at the large tree stage (individuals , 1 cm d.b.h.), according to results of torus-translation randomization tests. The majority of species did not show consistent associations at the two stages. Of the 30 species significantly associated with a habitat, only five were associated with the same habitat at both stages. Overall, more species were associated with the wetter slope habitat at the large tree stage compared with the small tree stage. 3For a subset of species, we examined the relationship between observed habitat associations and seed dispersal and seedling establishment patterns by using species-specific seed dispersal kernels to predict seed rain into each habitat. 4Two-thirds of species associated with a habitat at the large tree stage had higher predicted seed densities in the associated habitat relative to other habitat types, indicating that limited seed dispersal acts to reinforce habitat associations for most species. In contrast, only one-third of the species associated with a habitat at the large tree stage showed evidence of higher seedling establishment rates in the associated habitat compared with other habitats, and an equal number of species appeared to have lower rates of establishment in the habitat that large trees of the species were associated with. 5Overall, our results indicate that habitat associations of large trees typically do not form at early life stages. Rather, many species appear to exhibit different ecological habitat preferences across life stages. Future studies of species' habitat associations should therefore include multiple life stages in order to detect developmental shifts in ecological preferences. [source] Xylem density, biomechanics and anatomical traits correlate with water stress in 17 evergreen shrub species of the Mediterranean-type climate region of South AfricaJOURNAL OF ECOLOGY, Issue 1 2007ANNA L. JACOBSEN Summary 1Climate change in South Africa may threaten the sclerophyllous evergreen shrubs of this region. Available data suggest that they are not as tolerant of water stress as chaparral shrubs occurring in climatically similar California, USA. 2Seventeen species from nine angiosperm families, including both fynbos and succulent karoo species, were studied at a field site in Western Cape Province, South Africa. Minimum seasonal pressure potential (Pmin), xylem specific conductivity (Ks), stem strength against breakage (modulus of rupture, MOR), xylem density, theoretical vessel implosion resistance () and several fibre and vessel anatomical traits were measured. 3Species displayed great variability in Pmin, similar to the range reported for chaparral and karoo shrub species, but in contrast to previous reports for fynbos shrubs. 4More negative Pmin was associated with having greater xylem density, MOR and . There was no relationship between Pmin and traits associated with increased water transport efficiency. 5Xylem density integrates many xylem traits related to water stress tolerance, including Pmin, MOR and , as well as percentage fibre wall, parenchyma, vessel area and fibre lumen diameter. 6Xylem density may be an integral trait for predicting the impact of climate change on evergreen shrubs. [source] Ecological aspects of seed desiccation sensitivityJOURNAL OF ECOLOGY, Issue 2 2003John C. Tweddle Summary 1The ability of seeds to survive desiccation is an important functional trait and is an integral part of plant regeneration ecology. Despite this, the topic has received relatively little attention from ecologists. In this study, we examine the relationships between seed desiccation tolerance and two important aspects of plant regeneration ecology: habitat and dormancy. This is done by comparative analysis of a data set of 886 tree and shrub species from 93 families. 2The proportion of species displaying desiccation sensitive seeds declines as the habitat becomes drier, and possibly also cooler, although the latter observation requires cautious interpretation. Desiccation sensitivity is most common in moist, relatively aseasonal vegetation zones, but is infrequent in, though not absent from arid and highly seasonal habitats. 3The highest frequency of desiccation sensitivity occurs in non-pioneer evergreen rain forest trees, although 48% of the species examined have desiccation tolerant seeds. In contrast, all pioneer taxa within the data set have drying tolerant seeds. 4Desiccation sensitivity is more frequent in seeds that are non-dormant on shedding (c. 31%), than dormant (c. 9%). Highest frequencies of drying tolerance occur in seeds with physical or combinational dormancy, at 99% and 100%, respectively. 5Although there is an association between non-dormancy and desiccation sensitivity in both tropical and temperate zones, the relationship does not appear to be causal. 6Working from the hypothesis that seed desiccation sensitivity represents a derived state in extant species, we use the results to investigate and discuss possible ecological trade-offs and associated fitness advantages. These may explain the hypothesized repeated loss of this trait. The frequent association between large seed size and desiccation sensitivity is also considered. [source] A hybrid zone dominated by fertile F1s of two alpine shrub species, Phyllodoce caerulea and Phyllodoce aleutica, along a snowmelt gradientJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2008Y. KAMEYAMA Abstract In alpine ecosystems, the steep environmental gradients produced by the difference in snowmelt timing create a dynamic selective regime for alpine plants. As these gradients directly alter flowering phenology, they can affect pollen-mediated gene flow among populations of single and related species. In northern Japan, we found a hybrid zone dominated by fertile F1s of two alpine shrub species, Phyllodoce caerulea and P. aleutica, along a snowmelt gradient. Seed germination confirmed the fertility of F1 hybrid, making the rarity and absence of backcross and F2 plants puzzling. The long-term clonal perpetuation of F1 hybrids (at least a few thousand years ago) contributes the maintenance of this unique hybrid zone. The distribution patterns of chloroplast DNA haplotypes suggest that F1 formation might be caused by directional pollen flow between parental species along the snowmelt gradient. Based on these results, we discuss the ecological and evolutionary significance of this unique hybrid zone. [source] Pollen Morphology of Tundra Shrubs and Submarginal Plants from Barrow, AlaskaJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 7 2006Ling-Yu Tang Abstract Investigation of plant morphological features, pollen, and habitat have been made for two shrub species from Barrow, Alaska, namely Dryas integrifolia M. Vahl and Salix rotundifolia Trautv., both of which are endemic to the Arctic floristic area. The former species has small lanceolate or plate leaves, whereas the latter has rounded leaves with distinct veins, rich in vitamin C. Both have dwarf and sprawling habits. Pollen studies showed that the pollen grains of the two species are spheroidal to sub-spheroidal or prolate. The type of aperture was tricolporate; pollen size 26.3,31.3 ,m; ornamentation finely reticulate under a light microscope (LM) and striate-reticulate under a scanning electron microscope (SEM) for D. integrafolia and finely reticulate under the LM and SEM for S. rotundifolia. Comparisons were made between the pollen from the same species from Arctic collections with those from China and Japan. Investigation of pollen morphology of tundra plants can provide significant data for comparative studies of fossil pollen and for the reconstruction of paleovegetation and paleoclimate in the Barrow area. (Managing editor: Ya-Qin Han) [source] Post-fire regeneration of Mediterranean plant communities at a regional scale is dependent on vegetation type and drynessJOURNAL OF VEGETATION SCIENCE, Issue 1 2007Xavier Arnan Abstract Question: We tested whether (1) the change in composition and structure of whole plant communities after fire is directly related to regeneration of the dominant tree species in the canopy; (2) the change in structure and composition of plant communities several years after fire decreases with the proportion of obligate seeders and (3) the proportion of obligate seeders in plant communities increases with the dryness gradient. Location: Catalonia (NE Spain) Methods: We measured floristic differences between burned and long-since burned sites in eight vegetation types across a climate gradient. We compared 22 sites burnt in 1994 in paired plots with 22 sites that had not been burnt since the 1940s. In each site we placed plots in burned and long-since burned areas, where we identified the presence and abundance of all plant species. Results: When the tree canopy recovers, structure and composition of the vegetation also return to the long-since burned community; when tree canopy does not recover, composition of the post-fire community varies compared to the long-since burned one. A higher proportion of obligate seeders in the pre-fire community promotes quicker regeneration of the original community. The proportion of obligate seeders increased along the dryness gradient. Conclusions: Regeneration of plant communities after fire depends on the vegetation type before the fire. Regeneration increases when the dominant tree or shrub species persists after fire and with a higher proportion of obligate seeders in the pre-fire community. The proportion of obligate seeders varies along the dryness gradient, which suggests that vegetation in drier areas (when seeders are more abundant) recovers earlier than in moister areas. [source] Woody population distribution and environmental heterogeneity in a Chaco forest, ArgentinaJOURNAL OF VEGETATION SCIENCE, Issue 5 2002Ignacio M. Barberis Burkart (1969,1987); Digilio (1971,1974); Pérez Moreau (1994) Abstract. In southern humid Chaco forests dominated by Schinopsis balansae, woody plants are clumped and species composition varies spatially over short distances. We examined how these spatial patterns are associated with local environmental heterogeneity for three size classes of woody individuals: adults, saplings, and seedlings. Our study was based on the detailed description of two forest plots (3200 m2 in total) in which we mapped all individuals of woody species, and delimited patches with different microrelief, soil moisture, and ground cover of terrestrial bromeliads. Our results showed that woody-individual distribution is related to local environmental heterogeneity. For all size classes, density of woody individuals was highest on convex patches. These convex patches were dominated by both tree (Acacia praecox and Achatocarpus praecox) and shrub species (Celtis pallida, Capparis retusa and Grabowskia duplicata), while level patches were dominated only by tree species (Schinopsis balansae, Prosopis spp. and Geoffroea decorticans). Drier patches contained all the woody species present in the forest, while wetter patches contained only a subset of them. Within convex patches, trees are likely to occur in places with bromeliad colonies and shrubs in patches without bromeliads. The results suggest forest structure is controlled by environmental heterogeneity associated with microrelief and soil moisture. [source] Plant traits as predictors of woody species dominance in climax forest communitiesJOURNAL OF VEGETATION SCIENCE, Issue 3 2001Fumito Koike Satake et al. (1989) Abstract. The dominance of a given tree or shrub species in a particular forest community may be determined by many ecological traits of the target species, as well as those of the surrounding species as its potential competitors. The present study was conducted to evaluate the possibility of predicting community status (species composition and dominance) on the basis of traits of local flora using statistical methods, and to visualize the mathematical function which determines species dominance. A general linear model and logistic regression were used for the statistical analysis. Dependent variables were designated as dominance and presence/absence of species in climax forest, with independent variables as vegetative and reproductive traits. Subalpine, cool-temperate, warm-temperate and subtropical climax rain forests in East Asia were studied. Quantitative prediction of climax community status could readily be made based on easily measured traits of local flora. Species composition and 74.6% of the total variance of species dominance were predicted based on two traits; maximum height and shade tolerance. Through application of this method, the capacity of an alien species to invade a climax forest community could possibly be predicted prior to introduction of the alien species. [source] Biology and establishment of mountain shrubs on mining disturbances in the Rocky Mountains, USALAND DEGRADATION AND DEVELOPMENT, Issue 5 2003M. W. Paschke Abstract The Rocky Mountains of the western United States contain many economically important natural resources. Increasing development of these resources has lead to land degradation, which often requires restoration efforts. A common type of disturbance in this region is mineral extraction and these activities often occur in zones of vegetation dominated by shrubs. These mined lands have proven to be particularly challenging to restore to native shrub cover. Mountain shrubland species such as big sagebrush (Artemisia tridentata), antelope bitterbrush (Purshia tridentata), Saskatoon serviceberry (Amelanchier alnifolia), black chokecherry (Prunus virginiana), mountain mahogany (Cercocarpus montanus), and snowberry (Symphoricarpos sp.) are crucial species for wildlife in this region due to the seasonal dependence of many wildlife species on the mountain shrubland zones. The development of successful restoration techniques for these key shrub species is therefore important for the continued and sustainable utilization of natural resources in the Rocky Mountains. The purpose of this literature review is to provide a reference to land managers working on woody plant establishment on mining disturbances in mountain shrublands in the Rocky Mountains. This review covers the biology, ecology, and propagation of six shrub species that are of primary importance for meeting regulatory compliance in this region. Based upon this survey of the published literature, we conclude that successful establishment of these species has most often involved: (1) utilization of local shrub ecotypes, varieties or subspecies in reclamation efforts, (2) protection from browsing during the establishment phase, (3) strategies for avoiding herbaceous competition, and (4) providing a source of mutualistic soil organisms. Additional specific recommendations for each of these species are discussed. Copyright © 2003 John Wiley & Sons, Ltd. [source] Microsatellite diversity and genetic structure of fragmented populations of the rare, fire-dependent shrub Grevillea macleayanaMOLECULAR ECOLOGY, Issue 6 2002Phillip R. England Abstract Recent habitat loss and fragmentation superimposed upon ancient patterns of population subdivision are likely to have produced low levels of neutral genetic diversity and marked genetic structure in many plant species. The genetic effects of habitat fragmentation may be most pronounced in species that form small populations, are fully self-compatible and have limited seed dispersal. However, long-lived seed banks, mobile pollinators and long adult lifespans may prevent or delay the accumulation of genetic effects. We studied a rare Australian shrub species, Grevillea macleayana (Proteaceae), that occurs in many small populations, is self-compatible and has restricted seed dispersal. However, it has a relatively long adult lifespan (c. 30 years), a long-lived seed bank that germinates after fire and is pollinated by birds that are numerous and highly mobile. These latter characteristics raise the possibility that populations in the past may have been effectively large and genetically homogeneous. Using six microsatellites, we found that G. macleayana may have relatively low within-population diversity (3.2,4.2 alleles/locus; Hexp= 0.420,0.530), significant population differentiation and moderate genetic structure (FST = 0.218) showing isolation by distance, consistent with historically low gene flow. The frequency distribution of allele sizes suggest that this geographical differentiation is being driven by mutation. We found a lack mutation-drift equilibrium in some populations that is indicative of population bottlenecks. Combined with evidence for large spatiotemporal variation of selfing rates, this suggests that fluctuating population sizes characterize the demography in this species, promoting genetic drift. We argue that natural patterns of pollen and seed dispersal, coupled with the patchy, fire-shaped distribution, may have restricted long-distance gene flow in the past. [source] Combined effects of arbuscular mycorrhizas and light on water uptake of the neotropical understory shrubs, Piper and PsychotriaNEW PHYTOLOGIST, Issue 2 2003Damond A. Kyllo Summary ,,Root hydraulic conductance (Kr) was measured for five understory shrub species of the neotropical moist forest to determine the effects of arbuscular mycorrhizas (AM) for both carbon-rich and carbon-limited host plants. ,,Kr was measured using a high pressure flow meter (HPFM) for potted plants grown in a factorial combination of AM fungi (presence/absence) and light (3.5 and 30% of full sun, low/high). ,,AM colonization improved Kr for the more shade-tolerant species plants when growing in low light. By contrast, water uptake efficiency of the light-demanding species was significantly decreased by AM fungi in high light. Regardless of AM colonization, light-demanding species had a lower capacity than shade-tolerant species to meet transpirational demands, and they allocated substantially more to fine root production relative to leaf area when colonized. ,,The differential effects of AM colonization and light on a species' root hydraulic conductance in relation to phylogeny and light adaptation demonstrate that AM fungi may be critical in determining early plant succession and community composition not only due to effects on nutrient uptake, but on water uptake as well. [source] Fire-mediated interactions between shrubs in a South American temperate savannahOIKOS, Issue 9 2009Fernando Biganzoli We examined spatial patterns of fire-caused mortality and after-fire establishment of two dominant shrub species, Baccharis dracunculifolia and Eupatorium buniifolium in a humid temperate South American savannah. Our objective was to determine whether fires mediate in interactions between these two species. After a natural fire burned a large tract of savannah, we established two plots (respectively 550 and 500 m2) within which we mapped all surviving and dead shrubs as well as all individuals of shrub species that recruited in the following year. We used techniques of point-pattern analysis to test specific null hypotheses about spatial associations in the distribution, mortality, and establishment of shrubs. Results support the notions that fire mediates interactions between these two species. Fire-caused death of E. buniifolium tended to occur selectively in the vicinities of Baccharis individuals, and recruitment of B. dracunculifolia tended to be concentrated in the places of dead shrubs. These responses, however, were contingent on local abundances of shrubs which depend in part from the recent fire history. Anthropogenic perturbation of the natural fire regime would have therefore distorted the role of fire mediated interactions as drivers of the dynamics of the vegetation of this temperate savannah. [source] Effects of permafrost degradation on woody vegetation at arctic treeline on the Seward Peninsula, AlaskaPERMAFROST AND PERIGLACIAL PROCESSES, Issue 2 2003Andrea H. Lloyd Abstract Permafrost degradation leads to substantial changes in soil thermal and hydrologic characteristics. We investigated the effects of changes in active layer thickness and soil drainage on vegetation distribution near the arctic treeline on the Seward Peninsula, Alaska. We measured active layer thickness, soil moisture, density of tall shrub species, cover of low shrub species, and reconstructed white spruce establishment history along transects across the banks of a network of thaw ponds. We found that active layer thickness did not vary along our transects, but soils on thaw pond banks were significantly drier than those on level tundra or in thaw-pond channels. Thaw-pond banks were the only sites in which trees successfully established, and shrub communities on thaw-pond banks were taller and more dominated by tall shrub species like willow and shrub birch. The data suggest that the establishment of tree and tall shrub species at the arctic treeline can be limited by the availability of well-drained microsites, and the response of these species to regional climatic changes will be constrained by the availability of such microsites and thus contingent upon further degradation of the permafrost. Copyright © 2003 John Wiley & Sons, Ltd. [source] The Reproductive Biology of Two Species of Diplusodon Pohl (Lythraceae) from Serra do Cipó, Southeastern BrazilPLANT BIOLOGY, Issue 6 2000C. M. Jacobi Abstract: The reproductive biology of two shrub species of Diplusodon (Lythraceae), D. hirsutus and D. orbicularis, was studied. Their distribution is restricted, mainly associated with "campos rupestres", a montane biome in SE Brazil. Both species proved to be self-compatible but because of herkogamy they are greatly dependent on visitors to effect pollination. The main pollinators are medium-sized bees. In experiments where pollinators were excluded or discouraged the percentage of abscised fruits was total or extremely high; most of these fruits dropped within the first two weeks after pollination in D. orbicularis and three weeks in D. hirsutus. The percentage of surviving fruits from control or manual pollination was higher in D. orbicularis (ca. 70 %) than in D. hirsutus (ca. 50 %). Seed set was very variable, with slightly lower means in D. hirsutus. Within each species the mean seed set was similar in self-, cross-pollinated fruits, and controls. In both species, the similarity between control and manual pollination fruit survival curves suggests that factors other than pollen limitation are the cause of abortion in the study area. The high rate of abscission, which was also observed in unmanipulated fruits, was attributed to resource limitation. In D. hirsutus this was caused by drought during seed development. In D. orbicularis it was enhanced by nutrient drain by shoot-galling flies. The lack of selective abortion of either selfed fruits or fruits with a small number of seeds may be a useful mechanism to overcome this detrimental effect which is felt later during fruit development. [source] Chemical composition and construction cost for roots of Mediterranean trees, shrub species and grassland communitiesPLANT CELL & ENVIRONMENT, Issue 5 2002F. Martínez Abstract The construction cost of fine roots was studied in 23 woody species and two grassland communities, growing under natural conditions in southern Spain. Calculation of the energy (glucose) required for their synthesis was based on the quantification of chemical components present in tissues. Despite considerable differences in the chemical composition of the three life forms studied (trees, shrubs and herbaceous), detected differences in construction cost were non-significant (mean value: 1·64 ± 0·13 g glucose g,1). However, shrubs and herbaceous plants growing in more fertile habitats expended significantly less energy on root synthesis (1·58 ± 0·06 and 1·41 ± 0·05 g glucose g,1, respectively) than those growing in less fertile areas (1·80 ± 0·06 and 1·57 ± 0·1 g glucose g,1, respectively), because they contained smaller amounts of either waxes (shrubs) or lignins (herbaceous), both expensive to synthesize, and, proportionately, more cellulose; which is inexpensive to synthesize. Deciduous and evergreen tree species also differed mainly with regard to wax and cellulose contents, giving rise to a significantly higher construction cost in evergreens (1·57 ± 0·07 g glucose g,1 versus 1·78 ± 0·02 g glucose g,1). The differences observed in construction cost appeared to be due more to habitat-induced differences in chemical composition than to any intrinsic difference between the species studied. [source] Differences in the allocation patterns between liana and shrub Hydrangea speciesPLANT SPECIES BIOLOGY, Issue 3 2006YOHEI KANEKO Abstract Allometric analysis of four Hydrangea species (Hydrangea petiolaris, Hydrangea paniculata, Hydrangea macrophylla var. megacarpa and Hydrangea hirta) was conducted to test the hypothesis that the liana species (H. petiolaris) invests more in leaves and reproductive organs than the shrub species. We calculated the allocation ratios of leaves, supporting tissues (trunks and roots) and reproductive organs. Hydrangea petiolaris differed markedly from the three shrubs in terms of trunk and root allocations, while leaf allocation was not statistically different. The C/F ratios (the ratios of the dry weights of non-photosynthetic organs to photosynthetic ones) of the four species ranged from 9 to 12, and were not statistically different. These results did not support the hypothesis. The biomass of H. petiolaris was up to 100-fold greater than the biomass of the three shrubs. The growth form of H. petiolaris would minimize allocation to supporting tissue and produce a large biomass. The biomass of reproductive organs of H. petiolaris was up to 700-fold greater than the biomass of the three shrubs. This advantage might, therefore, serve as a driving force for the evolution of lianas. [source] Restoration of a Mediterranean Postfire Shrubland: Plant Functional Responses to Organic Soil AmendmentRESTORATION ECOLOGY, Issue 5 2010Marie Larchevêque We investigated the potential of plant functional responses to speed up restoration in a postfire ecosystem. The patterns of change in plant nutrient uptake and water potential after compost amendment were monitored for 2 years in a 7-year-old postfire shrubland in southeastern France. We studied four different stress-tolerant species with contrasting life traits: three shrub species and a perennial herb. Three treatments were applied: control, 50 and 100 Mg/ha of fresh cocomposted sewage sludge and green waste. In both compost treatments, concentrations of all the macronutrients increased. The amendment improved N and cation nutrition, but the positive effect of compost on plant nutrient status was most apparent on leaf P concentrations, indicating that P was a limiting nutrient in this shrubland. Compost had no significant short-term effect on trace metal concentrations in plants. The plant nutrition response of different species to the compost varied; the nutritional status of Brachypodium retusum and Cistus albidus improved the most, whereas that of Quercus coccifera and Ulex parviflorus improved the least. Woody species exhibited no increase in N stocks. Phosphorus accumulation was also about three times higher in plots amended at 50 Mg/ha than in control plots for B. retusum and C. albidus. The severe summer drought of 2003 altered the compost effect. Contrary to our expectations, plants on amended plots did not exhibit a better water status in summer: the effect of the summer drought had a greater effect on water status than did the compost treatment. [source] Seedling Establishment and Survival on Restored Campsites in Subalpine ForestRESTORATION ECOLOGY, Issue 3 2007David N. Cole Abstract This study experimented with common restoration techniques (scarification, soil amendments, mulch, and seeding) on six closed wilderness campsites in subalpine forests in Oregon. Effectiveness in encouraging seedling establishment, growth, and survival was assessed every year for the first 7 years following treatment. Closure and restoration of the campsites increased the density of plants established from seed. Despite an original density of virtually zero, mean density of perennial plants was 55 plants/m2 7 years after closure. All the treatments, with the exception of the biodegradable mulch mat, increased plant density. Seven years after treatment, seeding had increased plant density 5-fold, whereas scarification and soil amendments (organic matter, compost, and soil inoculum) had each increased density 3-fold. The organic and compost amendments also had the positive benefit of increasing growth rates and shortening the time-to-reproductive maturity. Results suggest that restoration of the herbaceous cover on these campsites can occur rapidly using the techniques employed. All but one of the species we seeded established in substantial quantities and survived at densities exceeding their density in the naturally sparse herbaceous cover on these sites. Thirty-six perennial species volunteered on these sites. The remaining challenge is reestablishment of the shrub species that comprise much of the ground cover in these forests. These species seldom establish from seed. [source] | ||||||||||||||||||||||||||||||||||