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Riparian Habitats (riparian + habitat)
Selected AbstractsA new index of habitat alteration and a comparison of approaches to predict stream habitat conditionsFRESHWATER BIOLOGY, Issue 10 2007BRIAN FRAPPIER Summary 1. Stream habitat quality assessment complements biological assessment by providing a mechanism for ruling out habitat degradation as a potential stressor and provides reference targets for the physical aspects of stream restoration projects. This study analysed five approaches for predicting habitat conditions based on discriminant function, linear regressions, ordination and nearest neighbour analyses. 2. Quantitative physical and chemical habitat and riparian conditions in minimally-impacted streams in New Hampshire were estimated using United States Environmental Protection Agency's Environmental Monitoring and Assessment Program protocols. Catchment-scale descriptors were used to predict segment-scale stream channel and riparian habitat, and the accuracy and precision of the different modelling approaches were compared. 3. A new assessment index comparing and summarizing the degree of correspondence between predicted and observed habitat based on Euclidean distance between the standardized habitat factors is described. Higher index scores (i.e. greater Euclidean distance) would suggest a greater deviation in habitat between observed conditions and expected reference conditions. As in most biotic indices, the range in index scores in reference sites would constitute a situation equivalent to reference conditions. This new index avoids the erroneous prediction of multiple, mutually exclusive habitat conditions that have confounded previous habitat assessment approaches. 4. Separate linear regression models for each habitat descriptor yielded the most accurate and precise prediction of reference conditions, with a coefficient of variation (CV) between predictions and observations for all reference sites of 0.269. However, for a unified implementation in regions where a classification-based approach has already been taken for biological assessment, a discriminant analysis approach, that predicted membership in biotic communities and compared the mean habitat features in the biotic communities with the observed habitat features, was similar in prediction accuracy and precision (CV = 0.293). 5. The best model had an error of 27% of the mean index value for the reference sites, indicating substantial room for improvement. Additional catchment characteristics not readily available for this analysis, such as average rainfall or winter snow-pack, surficial geological characteristics or past land-use history, may improve the precision of the predicted habitat features in the reference streams. Land-use history in New Hampshire and regional environmental impacts have greatly impacted stream habitat conditions even in streams considered minimally-impacted today; thus as regional environmental impacts change and riparian forests mature, reference habitat conditions should be re-evaluated. [source] Temporal fluctuation in abundance of Brown-headed Cowbirds and their hosts in riparian habitat in the Okanagan Valley, British Columbia, CanadaJOURNAL OF FIELD ORNITHOLOGY, Issue 4 2006Tawna C. Morgan ABSTRACT We tested the hypothesis that the abundance of Brown-headed Cowbirds (Molothrus ater) and their hosts, as well as parasitism rates, changed between 1992,1993 and 2001,2003 in riparian habitats in the Okanagan Valley, British Columbia, Canada, where riparian habitat has been reduced in area by more than 85% over the past 60 years. Cowbird abundance declined from a mean of 2.1 and 1.9 individuals per census plot in 1992 and 1993, respectively, to 0.66 individuals per plot in 2001,2002. The mean number of potential host individuals per census plot was also lower in 2001,2002 (5.5) than in 1992 (7.0) and 1993 (7.8). Although the percentage of Yellow Warbler (Dendroica petechia) nests parasitized declined (77% in 1992,1993 to 50% in 2002,2003), Yellow Warblers and Song Sparrows (Melospiza melodia) in the Okanagan Valley continue to be parasitized at high rates and have low nesting success. Host species and the distance of nests from the edge of nest patches were the strongest predictors of both nest success and parasitism, indicating the importance of large continuous patches of shrubs that allow nests to be located further from edges. SINOPSIS Se expuso a pruebas la hipótesis de la abundancia de tordos (Molothrus ater) y sus huespedes y como la tasa de parasitismo cambiaron durante el 1992,1993 y el 2001,2002 en un hábitat ripario en el valle Okanagan, Columbia Británica, Canada. En dicha localidad el hábitat ripario se redujo en un 85% en los últimos 60 años. La abundancia de tordos se redujo en un promedio de 2.1 y 1.9 de individuos/censo en 1992 y 1992, respectivamente, a 0.66 individuos en 2001,2002. El número promedio de hospederos potenciales por localidad censada (5.5) fue menor para el mismo periodo en comparación con el 1992 (7.0) y el 1993 (7.8). Aunque el porcentaje de nidos parasitados (77% en el 1992,1993 a 50% en 2002,2003) en Dendroica petechia, se redujo, tanto la especie como Melospiza melodia, tuvieron un alto grado de parasitismo y un bajo éxito de anidamiento. Tanto las especies hospederas y la distancia del nido al borde del parcho de anidamiento resultaron ser los elementos de predicción más fuertes con respecto al parasitismo y el éxito de anidamiento. Esto es un indicativo claro de la importancia de parchos de arbustos amplios y contínuos, que permitan el anidamiento lejos del borde. [source] Effects of physical disturbance and granivory on establishment of native and alien riparian trees in Colorado, U.S.A.DIVERSITY AND DISTRIBUTIONS, Issue 1-2 2001Gabrielle L. Katz In western North America, the alien Elaeagnus angustifolia L. invades riparian habitats usually dominated by pioneer woody species such as Populus deltoides Marshall ssp. monilifera (Aiton) Eckenwalder. We conducted manipulative field experiments to compare the importance of physical disturbance and granivory for seedling establishment of these two species. We planted seeds of both species in disturbed and undisturbed study plots, and used exclosures, seed dish trials and live-trapping to assess the role of granivory. Seedling establishment of both species was increased by physical disturbance and seeds of both species were subject to granivory. However, the relative importance of these two factors differed between species. For P. deltoides, lack of physical disturbance prevented seedling establishment in uncleared subplots, but granivory did not prevent seedling establishment outside of exclosures. For E. angustifolia, granivory prevented seedling establishment outside of exclosures, but lack of physical disturbance did not prevent establishment in uncleared subplots. The lesser dependence on disturbance may enable E. angustifolia to invade areas characterized by low levels of fluvial disturbance, such as floodplains along regulated rivers, where P. deltoides recruitment does not occur. Populations of granivorous rodents may affect the susceptibility of riparian ecosystems to invasion by E. angustifolia. [source] The effects of the invasive Argentine ant (Linepithema humile) and the native ant Prenolepis imparis on the structure of insect herbivore communities on willow trees (Salix lasiolepis)ECOLOGICAL ENTOMOLOGY, Issue 6 2008JULIE P. NYGARD Abstract 1.,We examined the relative effects of the invasive Argentine ant, Linepithema humile, and a common native ant, Prenolepis imparis, on the community of herbivorous insects occurring on willow trees, Salix lasiolepis in Northern California, U.S.A. 2.,Using paired control and treatment branches from which we excluded ants and other non-volant predators, we found that effects of Argentine ants on the herbivore community were generally similar to those of P. imparis. Argentine ants and P. imparis suppressed the damage by skeletonising insects by 50%, but had little effect on most other external-feeding or internal-feeding guilds. 3.,The abundance of aphids was 100% greater in the presence of Argentine ants, but there was no effect on aphid numbers in the presence of P. imparis. Late season aphid numbers were substantially higher in the presence of Argentine ants, but not P. imparis. 4.,The effects of Argentine ants on skeletonising insects and aphids combined with the overwhelming abundance of Argentine ant workers, suggests that they may have substantial, but often overlooked, effects on the herbivore communities on other plant species in or near riparian habitats in which they invade. [source] Assemblages of soil macrofauna across a Scottish land-use intensification gradient: influences of habitat quality, heterogeneity and areaJOURNAL OF APPLIED ECOLOGY, Issue 6 2005PAUL EGGLETON Summary 1Land-use intensification strongly influences biodiversity by altering habitat heterogeneity, the distribution of habitat types and their extent. This study explores these effects within mixed semi-natural/agricultural mosaic habitats in Scotland, examining the effect of land-use intensification on the soil macrofauna at point (m2), landscape (km2) and regional (> 1 km2) scales. 2The soil macrofauna in six 1-km2 sampling areas (land-use units; LUU) were sampled using a combined hand-sorting and Winkler bag extraction technique. Within each LUU, 16 1-m2 samples were taken in each of 2 successive years. Each LUU had a mixture of land-use types, representing an agricultural intensification gradient. 3The following hypotheses were tested: (i) the study area sustains a number of distinct habitats as defined by soil macrofaunal composition; (ii) a greater number of restricted range species are found in semi-natural habitats; (iii) local (point) species density is related to habitat type; (iv) overall levels of species richness per habitat at regional scales are related to species-area effects; and (v) landscape-level species density is correlated with habitat heterogeneity. 4Initial analysis revealed five distinct habitat types: Caledonian forest (semi-natural pine forest), closed canopy woodland (pine plantation and broadleaved woodland), riparian habitats (wet woodland and grassland), pasture (improved grassland) and arable (crop fields). 5As hypothesized, the Caledonian habitat contained a greater number of restricted-range species than the other habitats. However, conifer plantations contained more restricted range species than expected, given their anthropogenic origin. Species density per m2 was most strongly affected by habitat type. At the regional level, the size of the species pool was correlated with the size of habitat areas. There were more species overall in LUU with greater habitat heterogeneity. 6Synthesis and applications. Caledonian pine forests have high species densities and contain species of conservation value. Mixed conifer plantations also appear to have a surprisingly high invertebrate conservation value. In contrast, intensively managed agricultural habitats have low species densities and conservation value. Generally, mixed land-use areas have higher species densities than single land-use areas. This emphasizes the need for careful management of forest systems within the matrix of agricultural habitats to maximize landscape diversity. [source] Patterns of population genetic diversity in riparian and aquatic plant species along riversJOURNAL OF BIOGEOGRAPHY, Issue 9 2010Olivier Honnay Abstract Aim, The downstream hydrochoric spread of seeds of aquatic and riparian plant species, without upstream compensation, can be expected to result in downstream accumulation of population genetic diversity. This idea has been termed the ,unidirectional dispersal hypothesis' and is the genetic equivalent of the more generally known ,drift paradox'. Our aim was to test this unidirectional diversity hypothesis, and to present a general synthesis of the patterns of population genetic variation across different riparian and aquatic plant species along rivers. Location, The Meuse River (Belgium) and rivers world-wide. Methods, First, we used amplified fragment length polymorphism markers to compare patterns of within- and between-population genetic diversity among three riparian plant species (Sisymbrium austriacum, Erysimum cheiranthoides and Rorippa sylvestris), typically occurring in different habitats along a gradient perpendicular to the Meuse River. Second, we performed a meta-analysis on studies reporting on the population genetic structure of riparian and aquatic plant species along rivers. Results, Along the Meuse River, we found significant genetic differentiation among populations of all three riparian species, and significant isolation by distance for one of them (R. sylvestris). There was no clear association between the typical habitat of a species and its population genetic structure. None of the three species provided evidence for the unidirectional dispersal hypothesis. The meta-analysis, based on 21 data records, did not support the unidirectional dispersal hypothesis either. Average weighted population genetic differentiation across species was significant. Main conclusions, Important mechanisms of upstream seed dispersal, probably through zoochory, together with higher seed recruitment opportunities in upstream habitats due to density dependence of recruitment, may explain the absence of downstream accumulation of genetic diversity. Also, it seems difficult to find consistent patterns in genetic variation in species from aquatic and riparian habitats. We argue that this is due to the recurrent extinctions and colonizations characteristic of these habitats, resulting in complex genetic patterns. Our results strongly support previous suggestions that stream ecology should consistently embrace metapopulation theory to be able to understand patterns of genetic diversity, as well as species diversity. [source] Contrasting patterns of nuclear microsatellite genetic structure of Fraxinus mandshurica var. japonica between northern and southern populations in JapanJOURNAL OF BIOGEOGRAPHY, Issue 6 2010Li-Jiang Hu Abstract Aim, The aim of this study is to detect extant patterns of population genetic structure of Fraxinus mandshurica var. japonica in Japan, and to provide insights into the post-glacial history of this species during the Holocene. Location, Hokkaido and Honshu islands, Japan (including the Oshima and Shimokita peninsulas). Methods, We examined nine polymorphic nuclear microsatellite loci to assess genetic variation within and among 15 populations across almost the entire range of the species in Japan. Extant patterns of geographical structure were analysed using Bayesian clustering, Monmonier's algorithm, analysis of molecular variance, Mantel tests and principal coordinates analysis. Recent bottlenecks within populations and regional genetic variation were also assessed. Results, Northern populations (Hokkaido Island and the Shimokita Peninsula) formed a single homogeneous deme, maintaining the highest level of allelic diversity on the Oshima Peninsula. By contrast, southern populations (Honshu Island) demonstrated strong substructure on both coasts. Specifically, populations on the Pacific side of Honshu exhibited significant bottlenecks and erosion of allelic diversity but preserved distinct subclusters diverging from widespread subclusters on the Japan Sea side of this island. Main conclusions, Genetic evidence and life history traits suggest that F. mandshurica occupied cryptic northern refugia on the Oshima Peninsula during the Last Glacial Maximum, which is reflected in the species' extant northern distribution. Strong geographical structure in southern populations, in agreement with fossil pollen records, suggests geographical isolation by mountain ranges running north,south along Honshu. Given that this tree species is cold-adapted and found in riparian habitats, populations on the Pacific side of Honshu probably contracted into higher-elevation swamps during warm post-glacial periods, leading to a reduction of effective population sizes and rare allelic richness. [source] Tertiary relict trees in a Mediterranean climate: abiotic constraints on the persistence of Prunus lusitanica at the eroding edge of its rangeJOURNAL OF BIOGEOGRAPHY, Issue 8 2008Fernando Pulido Abstract Aim, To investigate the ecophysiological traits allowing persistence of a subtropical relict tree (Prunus lusitanica L.) under a dry Mediterranean climate at the eroding edge of its range. Location, A glasshouse for the study under controlled conditions and two marginal populations located in riparian forests of central Spain and exposed to summer drought, in contrast to subtropical populations that grow in mountain cloud forests. Methods, Two experiments were conducted to assess tolerance to the abiotic conditions found in riparian habitats. In a glasshouse experiment, gas-exchange and light-use parameters were measured to evaluate seedling responses to a factorial combination of irradiance (60%, 10%, 2% and 0.5% full sun) and moisture (well watered control and drought stress). In a parallel field experiment, irradiance and soil moisture were measured as predictors of seedling survival at two sites in which half the seedlings were subjected to a threefold increase in summer precipitation by adding water every 10 days. Results Soil moisture strongly determined survival both in the glasshouse and in the two field sites. In the field, periodic addition of water failed to increase survival. Water-use efficiency (WUE) increased with drought. Seedlings did not tolerate deep shade (2,0.5%) and their performance and survival were better when exposed to moderate (10%) or high (60%) irradiance. The effect of water stress on seedling performance was stronger at moderate irradiance, moderate at high irradiance and negligible at very low light. Seedling size (height and number of leaves) attained after 1 month of experimental treatments had a positive effect on survival at the end of the summer, hence greater survival was not achieved at the expense of vertical growth. Main conclusions, While studies in Macaronesia have shown that P. lusitanica occupies a wide range of moisture conditions along mountain slopes, it behaves as an obligate riparian species in dry peripheral populations. Intolerance to deep shade and tolerance to moderate and high irradiance allow the species to grow in small and moist gaps, or in treeless river sections. Despite the species' low range filling in marginal, drought-prone regions, long-term persistence might have been achieved through shifts to riparian habitats serving as local refuges. [source] Nesting behavior and breeding success of HoatzinsJOURNAL OF FIELD ORNITHOLOGY, Issue 4 2007Antje Müllner ABSTRACT Hoatzins (Opisthocomus hoazin) are the only member of the family Opisthocomidae and are found only in forests in the Amazon and Orinoco river basin of South America. Although locally common in riparian habitats, information about their natural history is based almost exclusively on observations from gallery forests in the "llanos" (savannahs) of Venezuela. We investigated the nesting activities of Hoatzins in a primary rainforest in Amazonian Ecuador from 1995 to 2000. At our study site, Hoatzins live and breed in the inundated forests that surround lakes and river channels. Egg laying occurred from February to July and from September to November, but always peaked in April, May, and June. The mean clutch size was 2.4 ± 1.1 eggs (N= 291; range = 1,7), but 51% of all clutches contained two eggs. The mean duration of the incubation period was 32 ± 1.5 d (N= 20) and, overall, 17% of Hoatzin nests fledged at least one young. The main cause of nest failure was predation, with birds and snakes being the most frequent predators. Hoatzin reproduction was closely linked to the rainy season, and such timing may be influenced by increased food availability (high water levels cause leaf fall and the subsequent growth of new leaves coincides with the beginning of the feeding period of the young) and reduced risk of nest predation by mammalian predators when water levels are high. Our results indicate that the breeding biology of Hoatzins in tropical rainforest habitat, including small clutch sizes and low annual reproductive success, is similar to that of tropical passerines and provides further support for the existence of typical life history characteristics for tropical birds. SINOPSIS Las hipótesis relacionadas con la variación altitudinal en los ciclos de vida de aves están basadas en una gran cantidad de datos de aves de zona templada, mientras que para el trópico inclusive se desconoce la biología básica. Esto aplica en particular para aves que no son paserinos. Investigamos las actividades de anidamiento de Hoatzin (Opisthocumus hoazin) en un bosque pluvial primario de la amazonia ecuatorial. En nuestra área de estudio, los hoatzines viven y se reproducen en bosques inundados que bordean lagos y canales. Los intentos reproductivos estuvieron asociados a la época de lluvias y se agruparon en unos meses del año. Normalmente, estas aves anidan una vez al año. El reanidamiento solo ocurrio cuando hubo pérdidas durante la época de puesta. Los nidos fueron construidos en los árboles y arbustos más comunes en el hábitat. El número de huevos por camada vario de uno a siete, aunque el 51% de las camadas consistieron de dos huevos. El tiempo promedio de incubación fue de 32 días. El exito promedio de eclosionamiento (para todos los nidos) fue de 34% y el 50% de los pichones dejaron el nido, lo que dio un éxito de anidamiento en general de 17%. La causa principal de pérdida de nidos lo fue la depredación, en donde otras aves y culebras resultaron ser los principales depredadores. La pequeña ventana de tres meses para reproducirse parece ser el resultado de un fuerte constreñimiento para una reproducción exitosa, debido a una mejor protección de los nidos y mayor abundancia de alimentos durante la época de inundación. El hoatzin exhibe un ciclo de vida similar al de paserinos tropicales. Esto indica la efectividad de las presiones ambientales de selección que deben estar envueltas en la formación de dichos trasos. [source] Temporal fluctuation in abundance of Brown-headed Cowbirds and their hosts in riparian habitat in the Okanagan Valley, British Columbia, CanadaJOURNAL OF FIELD ORNITHOLOGY, Issue 4 2006Tawna C. Morgan ABSTRACT We tested the hypothesis that the abundance of Brown-headed Cowbirds (Molothrus ater) and their hosts, as well as parasitism rates, changed between 1992,1993 and 2001,2003 in riparian habitats in the Okanagan Valley, British Columbia, Canada, where riparian habitat has been reduced in area by more than 85% over the past 60 years. Cowbird abundance declined from a mean of 2.1 and 1.9 individuals per census plot in 1992 and 1993, respectively, to 0.66 individuals per plot in 2001,2002. The mean number of potential host individuals per census plot was also lower in 2001,2002 (5.5) than in 1992 (7.0) and 1993 (7.8). Although the percentage of Yellow Warbler (Dendroica petechia) nests parasitized declined (77% in 1992,1993 to 50% in 2002,2003), Yellow Warblers and Song Sparrows (Melospiza melodia) in the Okanagan Valley continue to be parasitized at high rates and have low nesting success. Host species and the distance of nests from the edge of nest patches were the strongest predictors of both nest success and parasitism, indicating the importance of large continuous patches of shrubs that allow nests to be located further from edges. SINOPSIS Se expuso a pruebas la hipótesis de la abundancia de tordos (Molothrus ater) y sus huespedes y como la tasa de parasitismo cambiaron durante el 1992,1993 y el 2001,2002 en un hábitat ripario en el valle Okanagan, Columbia Británica, Canada. En dicha localidad el hábitat ripario se redujo en un 85% en los últimos 60 años. La abundancia de tordos se redujo en un promedio de 2.1 y 1.9 de individuos/censo en 1992 y 1992, respectivamente, a 0.66 individuos en 2001,2002. El número promedio de hospederos potenciales por localidad censada (5.5) fue menor para el mismo periodo en comparación con el 1992 (7.0) y el 1993 (7.8). Aunque el porcentaje de nidos parasitados (77% en el 1992,1993 a 50% en 2002,2003) en Dendroica petechia, se redujo, tanto la especie como Melospiza melodia, tuvieron un alto grado de parasitismo y un bajo éxito de anidamiento. Tanto las especies hospederas y la distancia del nido al borde del parcho de anidamiento resultaron ser los elementos de predicción más fuertes con respecto al parasitismo y el éxito de anidamiento. Esto es un indicativo claro de la importancia de parchos de arbustos amplios y contínuos, que permitan el anidamiento lejos del borde. [source] USING MARYLAND'S STREAM CORRIDOR ASSESSMENT SURVEY TO PRIORITIZE WATERSHED RESTORATION EFFORTS,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2002Kenneth T. Yetman ABSTRACT: The Stream Corridor Assessment survey has been developed by the Maryland Department of Natural Resources as a watershed management tool to identify environmental problems and to help prioritize restoration opportunities on a watershed basis. Potential environmental problems commonly identified during the survey include: stream channel alterations, excessive bank erosion, exposed pipes, inadequate stream buffers, fish migration blockages, trash dumping sites, near stream construction, pipe outfalls, and unusual conditions. In addition, the survey records information on the location of potential wetlands creation sites and collects data on the general condition of instream and riparian habitats. Over the past several years, in collaboration with the Maryland Conservation Corps, watershed associations, and local governments, more than 3,293 km (2,046 miles) of Maryland streams have been surveyed. Overall, the survey has proven to be a cost effective starting point for many watershed restoration efforts. [source] Effects of a Severe Frost on Riparian Rainforest Restoration in the Australian Wet Tropics: Foliage Retention by Species and the Role of Forest ShelterRESTORATION ECOLOGY, Issue 4 2010Timothy J. Curran Restoration of ecological communities that can withstand future climate and land use changes requires information on species responses to various natural disturbances. Frost is an important disturbance that regulates plant species distributions, and although rare in tropical rainforest, it can occur in upland areas, especially where deforestation has occurred. We report the impacts of a severe frost that occurred in June and July 2007 on the Atherton Tablelands, Queensland, Australia and caused extensive damage to riparian restoration plots of upland rainforest species. We estimated proportion foliage retention to (1) compare impacts across 45 species; (2) examine the influence of plant height on frost effects; and (3) determine if plantings under shelterbelts of mature trees received less damage. Species exhibited different levels of foliage retention. Species that were particularly frost resistant included those from riparian habitats and a conifer. Some heavily impacted species are deciduous and may survive frost by shedding leaves; this warrants further investigation. Plant canopy height above ground level was only weakly correlated to foliage retention. Sheltered plants were much less damaged than unsheltered conspecifics, suggesting a useful way to mitigate frost impacts. These principles should help guide the development of resilient ecological communities in frost-prone areas. [source] Rosette Recruitment of a Rare Endemic Forb (Gaura neomexicana Subsp. coloradensis) with Canopy Removal of Associated SpeciesRESTORATION ECOLOGY, Issue 1 2002Linda M. Munk Abstract Gaura neomexicana subsp. coloradensis Munz (Onagraceae), (Colorado butterfly plant), a short-lived perennial forb, became listed as a threatened species by the U.S. Fish and Wildlife Service in October 2000 because of its small global range and population size. This endemic subspecies consists of only 18 extant populations within southeastern Wyoming, southwestern Nebraska, and northeastern Colorado. Wyoming occurrences are on private land with the exception of three occurrences on F. E. Warren Air Force Base, near Cheyenne. Gaura neomexicana subsp. coloradensis may be displaced by many competitors, including Cirsium arvense (L.) Scop. (Canada thistle), an invasive, noxious weed. In June 1998, three G. neomexicana subsp. coloradensis populations were examined for rosette establishment in the presence of and after removal of associated species. The four study treatments removed: (1) Cirsium arvense, (2) grass and forb canopy and associated litter, (3) grass and forb canopy, litter, and C. arvense, and (4) no removal of associated plant species (control). Mature G. neomexicana subsp. coloradensis plants were evaluated for height, number of leaves, and capsule production. The mature plant characteristics monitored in 1998 were not good indicators of subsequent G. neomexicana subsp. coloradensis rosette densities in the following spring. Recruitment was assessed by counting new rosettes in the fall 1999. Although both G. neomexicana subsp. coloradensis and the exotic C. arvense have comparable habitat, removal of C. arvense did not increase G. neomexicana subsp. coloradensis vegetative growth, seed capsule production, or rosette density. Removal of other forbs, grass, and litter, however, increased G. neomexicana subsp. coloradensis rosette density in the following two years, indicating that canopy removal of associated species can enhance rosette establishment of this rare native. The accumulation of dense vegetative cover and litter associated with the absence of herbivory and fire may contribute to the decline of rare species in rich riparian habitats. Return of herbivory and fire in mesic sites to reduce standing biomass accumulations should be considered in restoring recruitment potential to rare monocarpic species. [source] Alien and endemic flora at reference and non-reference sites in Mediterranean-type streams in PortugalAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2007Francisca C. Aguiar Abstract 1.A comparison was made between a variety of alien and endemic plant species from 272 aquatic and riparian habitats in Portuguese Mediterranean-type streams in reference condition , i.e. near-natural river corridors , and non-reference condition. The objective was to detect differences in relative proportion and cover between these species groups. The differences in endemic and alien flora from siliceous and calcareous river types were also analysed. Environmental and human disturbance factors were related with the richness and cover of both species groups. 2.A total of 568 species were found, of which 44 were alien and 28 were endemic. Alien species were present at 91% of the surveyed locations, and were consistently more widespread at non-reference sites than at reference ones for both river types, with calcareous sites having a higher invasibility. Endemic species occurred at 45% of the sampling sites and displayed a significantly lower richness and cover than their alien counterparts. 3.Alien richness and cover were positively related to direct human disturbance within the river systems, and with floodplain uses such as urban occupation, intensive agriculture, and nutrient inputs. Endemic species also respond to anthropogenic variables, rather than to climatic and geographical ones, with richness and cover increasing as human impacts on fluvial systems and related floodplains decrease. 4.Comprehensive control of alien invasive species and the protection of endemic plant populations will require attempts at monitoring ecological river integrity, and the achievement of ,good ecological status' , one of the goals of the European Union's Water Framework Directive. Portuguese riparian areas must be managed in such a way as to protect the relatively few preserved riparian habitats by lowering the direct and indirect pressures in fluvial corridors and thus preventing future alien plant invasions. Copyright © 2006 John Wiley & Sons, Ltd. [source] Seedling establishment, mortality, tree growth rates and vigour of Acacia nilotica in different Astrebla grassland habitats: Implications for invasionAUSTRAL ECOLOGY, Issue 3 2002Ian J. Radford Abstract A demographic study was conducted in the northern Australian Astrebla grasslands to determine the importance of habitat type in influencing invasion patterns of Acacia nilotica, an exotic leguminous tree from Africa and Asia. One of the repeated patterns observed for A. nilotica is that denser populations are often associated with riparian habitats. Data available on this species do not enable us to determine which of a number of processes has lead to the formation of this pattern. Several explanations were tested for patterns in tree abundance: (i) that more seedlings emerge in wetter habitats; (ii) that mortality is lower in wetter habitats; (iii) that growth rates are faster in wetter habitats; and (iv) that plants are more vigorous (as indicated by leaf cover, flowering intensity and predation rates) over longer periods in wetter habitats. The study was stratified across three habitat types, perennial and ephemeral riparian and non-riparian, which are characteristic of Astrebla grasslands and differentiated by the availability of water. In addition to testing for habitat-linked differentiation in demography, data were also used to test whether seedling emergence, mortality, growth and vigour varied between sites with cattle versus sheep. The data collected indicated that seedling emergence, determined primarily by livestock dispersal, was likely to be the dominant influence on patterns of A. nilotica invasion. Mortality and growth rates were similar in ephemeral riparian and non-riparian habitats, whereas perennial riparian habitats had more rapid growth rates, which may increase the rate of invasion in these areas. Plant vigour was also greater over longer periods in perennial riparian habitats with greater leaf cover, longer flowering season and fewer insect borer holes. Livestock species were found to have little influence on the demography of A. nilotica plants in this study. Very low growth rates and high mortality in A. nilotica populations are likely to lead to net decline in ephemeral riparian and non-riparian habitats in the long term. The importance of episodic recruitment in the maintenance of A. nilotica populations is discussed. [source] Predicting potential impacts of environmental flows on weedy riparian vegetation of the Hawkesbury,Nepean River, south-eastern AustraliaAUSTRAL ECOLOGY, Issue 5 2000Jocelyn Howell Abstract Remnants of native riparian vegetation on the floodplain of the Hawkesbury,Nepean River near Sydney, have significant conservation value, but contain a large component of weeds (i.e. exotic species that have become naturalized). A proposal for the introduction of environmental flows required an assessment of potential impacts on 242 native and 128 exotic species recorded along 215 km of the river. The likely effects of frequency, season, depth and duration of inundation were considered in relation to habitat, dispersal season and tolerance to waterlogging. Overseas studies provided only limited information applicable to the study area; however, comparisons with similarly highly modified riparian habitats in New Zealand were instructive. Depth and season of inundation appear to be the variables with the greatest potential for differential effects on weeds and native plants. Because of likely spread of propagules and enhancement of growth under the present nutrient-enriched conditions, environmental flows that would cause more frequent flooding to higher levels of the riparian zone were judged to be of more benefit to weed species than native species, unless supported by bushland management including weeding. Predictions were limited by incomplete data on Hawkesbury,Nepean species, but two types of environmental flow were judged to be potentially beneficial for native water-edge plants, and worth testing and monitoring: first, flows that maintain continuous low-level flow in the river, and second, higher level environmental flows restricted to the river-edge habitat in autumn (the season in which a greater proportion of native species than weed species are known to disperse propagules). In summary, the presence of environmental weeds in riparian vegetation constrain the potential for environmental flows to improve river health. However, with ongoing monitoring, careful choice of water level and season of flow may lead to environmental flows that add to our knowledge, and benefit riparian vegetation along with other river system components. [source] Plant-Arthropod Associations from the Lower Miocene of the Most Basin in Northern Bohemia (Czech Republic): A Preliminary ReportACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2010Jakub PROKOP Abstract: Terrestrial plants and insects currently account for the majority of the Earth's biodiversity, and approximately half of insect species are herbivores. Thus, insects and plants share ancient associations that date back more than 400 Myr. However, investigations of their past interactions are at the preliminary stages in Western Europe. Herein, we present the first results of our study of various feeding damage based on a dataset of nearly 3500 examined plant specimens from the Lower Miocene of the Lagerstätte Bílina Mine in the Most Basin, Czech Republic. This site provides a unique view of the Neogene freshwater ecosystems. It has long been studied by scientists working in different branches of sedimentology, paleobotany, and paleozoology. The fossils are preserved in three characteristic horizons overlaying the coal seam (Clayey Superseam Horizon, Delta Sandy Horizon, and Lake Clayey Horizon), reflecting paleoenvironmental changes in a short time period of development. The trace fossils are classified as functional feeding groups or "guilds", without searching for a direct cause or a recent analog host relation. Approximately 23% of specimens of dicotyledonous plant leaves were found to be damaged and associated with some leaf "morphotypes". Deciduous plant-host taxa, and those with a chartaceous texture typical of riparian habitats, were frequently damaged, such as Populus, recorded with two species Populus zaddachii and Populus populina (57.9% and 31% herbivory levels, respectively), followed by Acer, Alnus, and Carya, averaging almost 30% of damaged leaves/leaflets. There has been evidence of 60 damage types (DT) representing all functional feeding groups recorded at the Bílina Mine, including 12 types of leaf mines and 16 gall-type DT. In total, Lower Miocene of the Lagerstätte Bílina Mine exhibits a high level of external foliage feeding types (23.7%), and a low level of more specialized DT, such as galls (4.3%) and leaf mines (<1%). A broader comparison based on DT of the main sedimentary environments shows significance supporting different biomes by frequency of damage levels and DT diversities. [source] | ||||||||||