Stands Of Vegetation Research Articles

Quantification of forest stock using remote sensing and gis

Forest stock is key information required in forest mensuration, forest utilization and forest management. The present study highlights the application of the state-of-the-art technology of satellite remote sensing, Geographical Information System (GIS) and Global Positioning System (GPS) in quantification of forest growing stock. The stratification of forest in to various forest cover types and structural canopy density classes and use of sampling procedures facilitate in obtaining the required information in the shortest time and cost effective manner. In general, the forest areas refer to natural stands of woody vegetation in which trees predominate. Forests are known to be one of the very important renewable natural resources which change with time and space. The direct benefits from forests are mainly timber and non-timber minor forest products. The list of indirect benefits is quite huge, including the amelioration of climate, soil and water conservation, biodiversity conservation, habitat for a variety of fauna, tourism and recreation, etc. Broadly, there are six major groups in h,dian forests, namely tropical moist forests, tropical dry forests, montane sub-tropical forests, montane temperate forests, sub-alpine forests and alpine forests. These have been further divided into 16 types, 46 sub-types and 221 ecologically stable formations (Champion and Seth, 1968). The information about the size of forest areas and the growing stock are the two important parameters of forest inventory. Forest inventory, therefore, makes an attempt to describe the quality and quantity of forests. It is undertaken at the national or state levels for knowing the location, extent, nature, condition and productive capacity of forests. The outputs are used for formulating the policies, plans/projects and monitoring purposes.

Ecological strategies for managing tamarisk on the C.M. Russell National Wildlife Refuge, Montana, USA

Tamarisk ( Tamarix ramosissima) is an introduced shrub or small tree associated with the loss of biological diversity in riparian habitat throughout much of western North America. Control measures are often expensive and ineffective, so land managers need site-specific information to guide cost-effective integrated management strategies. We sampled 12 randomly selected tamarisk-infested inlets on Fort Peck Reservoir on the C.M. Russell National Wildlife Refuge stratified by stream basin size. At each site we sampled 2–5 stands of riparian vegetation, recording plot elevation, canopy cover of vascular plants, density of woody species and age estimates for representative woody plants. Tamarisk plants 1–3 years old were abundant in the drawdown zone along the shore of Fort Peck Reservoir. The lack of plants older than three years indicates that tamarisk in the drawdown zone were destroyed during a recent two summers of inundation and suggests that three months of inundation will kill tamarisk plants. The oldest (17–22 years) and largest tamarisk plants in the study area were found in the full-pool zone and were recruited in periods of significant drawdown following high-water years. Tamarisk was uncommon in cottonwood and silver sagebrush stands on stream terraces above full pool. Only the largest streams in our study area appeared capable of supporting tamarisk and significant native riparian vegetation. Tamarisk plants at or above full pool level should be removed in these drainages to prevent upstream invasion and loss of native species. The level of the reservoir should be raised to the level of full pool for three consecutive months during the growing season every 3–5 years to prevent development of extensive stands of tamarisk in the drawdown zone capable of producing large quantities of seed.

The Strength of Biological Control in the Battle against Invasive Pests: a Reply

The Strength of Biological Control in the Battle against Invasive Pests: a Reply MARK S. HODDLE Department of Entomology, University of California–Riverside, Riverside, CA 92521, U.S.A., email mark.hoddle@ucr.edu Nontarget Impacts of Biological Control Louda and Stiling (2004 [this issue]) state that biological control is not a simple matter of community re-assemblage because deliberate introductions of exotic natural ene- mies for suppression of exotic pest populations can have reticulate impacts that are difficult, if not impossible, to predict a priori. In an insightful retrospective study, Hawkins et al. (1999) analyzed 68 life-table studies of native insects and introduced insect pests to determine whether biological control is analogous to naturally oc- curring control (i.e., the action of native natural enemies on native hosts). Hawkins et al. (1999) show that suc- cessful biological control programs result in less reticulate trophic relationships than those seen in natural food webs of native insects. The most successful biological control programs are those that do not have “natural” food-web structures because biological control food webs consist of short, linear food chains that are devoid of complex reticulate trophic interactions. This result occurs because biological control systems often consist of exotic species that share few ecologi- cal or evolutionary links with native biota. Furthermore, control is enhanced in simplified habitats characteristic of agroecosystems and, arguably, native systems invaded by exotic plants because both often consist of vast mono- typic stands of exotic vegetation. Host-specific natural en- emies that cause population declines of the target pest are themselves subject to density-dependent population regulation as the biological control agent’s food source is depleted, and they are unable to adequately exploit other hosts in the environment to maintain high population densities because they lack significant trophic linkages to other hosts. The more specialized the natural enemy the less likely it is to infiltrate native communities and attack nontarget native species (Hennemen & Memmott 2001). Generalist natural enemies that have low levels of host and habitat fidelity and exploit a wide range of hosts in a vari- ety of habitats are more likely to cause unwanted collat- eral damage to nontarget species either directly through direct attack or indirectly through apparent competition because of reticulate food-web linkages. Two plant-feeding insects (Rhinocyllus conicus [inten- tionally released; Gassmann & Louda 2001] and Larinus planus [an accidental arrival in the United States that was eliminated as a potential biological control agent because of broad host breadth on Carduinae thistles in its home range; Louda & O’Brien 2002]) mentioned by Louda and Stiling as having “unexpected levels of nontarget feeding” were anticipated from host-specificity tests because both weevils were known to feed and reproduce on a variety of thistle species in their home and introduced range. As Louda and Stiling point out, both insects are “thistle specialists,” but thistles are a speciose group with repre- sentatives in genera that occur in Europe and North Amer- ica, and these weevils, due to their broad dietary breadth within the thistle group, have greater numbers of signif- icant food-web linkages than desirable, thereby making significant nontarget impacts more likely. The real issue here concerns legislation (i.e., redistribution of L. planus and R. conicus) and changing social values (i.e., what con- stituted acceptable damage to nontarget species, and the value of native flora and fauna in the 1960s versus 2003), as opposed to an inherent flaw in the theoretical prin- ciples underlying concepts of host specificity and host range assessment as they pertain to biological control. The moth Cactoblastis cactorum, a native of Argentina and “poster child” of biological control (Stiling 2002) has invaded the continental United States from the Caribbean and is attacking native cactii. Louda and Stiling consider C. cactorum a “specialist” on the cactus genus Opuntia, a group with approximately 200 species in the new world but no representatives in Australia, making C. cactorum a specialist on this continent when it was released in Paper submitted April 15, 2003; revised manuscript accepted May 23, 2003. Conservation Biology, Pages 61–64 Volume 18, No. 1, February 2003

Effects of host plant species on the development of Dysdercus cingulatus (Heteroptera: Pyrrhocoridae)

The survivability and the developmental rates of Dysdercus cingulatus when fed various cultivated and wild host plant species were compared in the laboratory. On this basis, Chorisia speciosa was regarded as a better-than-adequate host plant for D. cingulatus. Abelmoschus moschatus, A. esculentus, Hibiscus makinoi, Thespesia populnea and Gossypium arboreum were adequate, H. tiliaceus was relatively poor, and Abutilon indicum was very poor. Although D. cingulatus developed faster when fed cultivated species than when fed wild species, host plant properties such as the weight of seeds and habit (arboreal or herbaceous) could not explain the survivability and developmental rate of D. cingulatus when fed the different species. Estimations of a lower threshold temperature for the development of D. cingulatus nymphs fed with plant species except for A. indicum fell within a range of 0.5 degrees (13.9 to 14.4°C). However, the estimated total effective temperature for development varied so widely among food plant species that its value for A. indicum was more than twice that for Ch. speciosa. Developmental parameters obtained here may be applied to the design of control programs for D. cingulatus in cotton fields adjacent to or near vegetative stands containing alternative wild host plants.

Midsummer spatial variation in methane efflux from stands of littoral vegetation in a boreal meso‐eutrophic lake

Summary1. Spatial variation of methane (CH4) efflux from the littoral zone of a meso‐eutrophic boreal lake was studied with a closed‐chamber technique for three summer days in 22 vegetation stands, consisting of three emergent and three floating‐leaved species.2. Between‐species differences in CH4 emission were significant. The highest emissions were measured from the emergent Phragmites australis stands (0.5–1.7 mmol m−2 h−1), followed by Schoenoplectus lacustris > Equisetum fluviatile > Nuphar lutea > Sparganium gramineum > Potamogeton natans. Within‐species differences between stands were not significant.3. In P. australis stands, the stand‐specific mean CH4 emission was significantly correlated with solar radiation, probably indicating the role of effective pressurised ventilation on CH4 fluxes. The proportion of net primary production emitted as CH4 was significantly higher in P. australis stands (7.4%) than in stands of S. lacustris and E. fluviatile (both 0.5%).4. In N. lutea stands, CH4 efflux was negatively correlated with the mean fetch and positively with the percentage cover of leaves on the water surface. There were no differences in CH4 efflux between intact N. lutea leaves and those grazed by coleopteran Galerucella nymphaeae. In S. graminaeum and P. natans stands, CH4 effluxes were not related to any of the measured environmental variables.5. For all vegetation stands, the biomass above water level explained about 60% of the observed spatial variation in CH4 emission, indicating the important role of plants as gas conduits and producers of substrates for methanogens in the anoxic sediment.

Fetch and Footprint of Turbulent Fluxes over Vegetative Stands with Elevated Sources

In this study, Raupach's localized near-field (LNF)theory is combined with appropriate parameterizations ofthe turbulence inside a canopy to investigate how airstability and source configuration influence the fluxfootprint and flux adjustment with fetch in theroughness sublayer. The model equations are solvednumerically. The flux footprint from the LNF predictionis in general more contracted than the prediction basedon the inertial sublayer similarity functions. Invery unstable conditions, the near-field effect causes thefootprint of the elevated canopy source to locatefurther upwind than that of the ground-level source, andthe combined footprint can become negative in situationswhere the two sources are of opposite sign. The fluxfootprint and flux adjustment with fetch in theroughness sublayer are sensitive to source configurationand the parameters specifying wind speed and theLagrangian time scale inside the canopy.

Experimental Study of Bed Load Transport through Emergent Vegetation

Vegetation is an important agent in fluvial geomorphology and sedimentary processes, through its influence on the local hydraulics that determine sediment transport. Within stands of emergent vegetation, bed shear is substantially reduced through the absorption of momentum by drag on the stems. This stimulates deposition of sediment and reduces capacity for bed load transport. The effect of emergent vegetation on hydraulic parameters (including equilibrium bed gradient, flow depth, and velocity) and on bed load transport rate has been investigated experimentally for one sediment size, stem diameter, and stem spacing. Bed load transport rate was found to be closely related to bed-shear stress, which must be estimated by partitioning total flow resistance between stem drag and bed shear.

First Field Studies of an Endangered South African seahorse, Hippocampus capensis

South Africa's endemic Knysna seahorse, Hippocampus capensis Boulenger 1900, is a rare example of a marine fish listed as Endangered by the IUCN because of its limited range and habitat vulnerability. It is restricted to four estuaries on the southern coast of South Africa. This study reports on its biology in the Knysna and Swartvlei estuaries, both of which are experiencing heavy coastal development. We found that H. capensis was distributed heterogeneously throughout the Knysna Estuary, with a mean density of 0.0089 m−2 and an estimated total population of 89 000 seahorses (95% confidence interval: 30 000–148 000). H. capensis was found most frequently in low density vegetation stands (≤20% cover) and grasping Zostera capensis. Seahorse density was not otherwise correlated with habitat type or depth. The size of the area in which any particular seahorse was resighted did not differ between males and females. Adult sex ratios were skewed in most transects, with more males than females, but were even on a 10 by 10 m focal study grid. Only three juveniles were sighted during the study. Both sexes were reproductively active but no greeting or courtship behaviours were observed. Males on the focal study grid were longer than females, and had shorter heads and longer tails, but were similar in colouration and skin filamentation. The level of threat to H. capensis and our limited knowledge of its biology mean that further scientific study is urgently needed to assist in developing sound management practices.

Assessing the quality of native vegetation: The ‘habitat hectares’ approach

Summary Assessments of the ‘quality’, condition or status of stands of native vegetation or habitat are now commonplace and are often an essential component of ecological studies and planning processes. Even when soundly based upon ecological principles, these assessments are usually highly subjective and involve implicit value judgements. The present paper describes a novel approach to vegetation or habitat quality assessment (habitat hectares approach) that can be used in almost all types of terrestrial vegetation. It is based on explicit comparisons between existing vegetation features and those of ‘benchmarks’ representing the average characteristics of mature stands of native vegetation of the same community type in a ‘natural’ or ‘undisturbed’ condition. Components of the index incorporate vegetation physiognomy and critical aspects of viability (e.g. degree of regeneration, impact of weeds) and spatial considerations (e.g. area, distribution and connectivity of remnant vegetation in the broader landscape). The approach has been developed to assist in making more objective and explicit decisions about where scarce conservation resources are allocated. Although the approach does not require an intimate botanical knowledge, it is believed to be ecologically valid and useful in many contexts. Importantly, the index does not provide a definitive statement on conservation status nor habitat suitability for individual species. It purposefully takes a ‘broad‐brush’ approach and is primarily intended for use by people involved with making environmentally sensitive planning and management decisions, but may be useful within environmental research programmes. The ‘habitat hectares’ approach is subject to further research and ongoing refinement and constructive feedback is sought from practitioners.

Hydraulic conductivities of competing root systems of Grevillea robusta and maize in agroforestry

Models of water uptake in mixed stands of vegetation commonly assume that water is partitioned among competing root systems in proportion to relative root length densities. Such an approach assumes implicitly that roots of different species have equivalent hydraulic properties. This was tested for root systems of Grevillea robustaA. Cunn. and maize (Zea maysL.) at a semi-arid site in Kenya. The hydraulic conductances for roots of both species were measured in situat the scale of the whole root or root system using a high pressure flow meter (HPFM). Hydraulic conductivities (κr) were expressed per unit root length. Root lengths were estimated for maize plants by soil coring and for G. robustausing a fractal branching model calibrated against soil coring. Mean κr was 1.88×10−7 ±0.28×10−7kg s−1 MPa−1 m−1 for G. robustaand 1.25×10−7 ±0.13×10−7kg s−1 MPa−1 m−1 for maize. Values of κr were not significantly different (P<0.05), suggesting that the assumption of hydraulic equivalence for root systems of the two species may be valid, at least when hydrostatic gradients are the major driving force for water uptake. Differences in conductivities between these species could arise, however, because of variation in the hydraulic properties of roots not accounted for here, for example because of root age, phenology or responses to the soil environment.

Characteristics that determine carbon gain in dense stands of vegetation

Characteristics that determine carbon gain in dense stands of vegetation

Acute toxicity associated with the use of South African traditional medicinal herbs

Traditional medicines, mainly of plant origin, are regularly taken in South Africa by 60–80% of the population. The materia medica that underpins this ancient practice is drawn almost entirely from natural stands of vegetation, and large volumes of plant material are traded annually on informal markets, some 750 species being in common use. These medicines are at present neither regulated nor subject to formal quality control measures. The World Health Organisation (WHO), the South African Health Ministry and its regulatory body, the Medicines Control Council, require that traditional remedies be subject to the same criteria applied to all medicines: those of quality, safety and efficacy. Medicines safety is of paramount concern and toxicological studies are necessary to establish safety profiles of indigenous traditional remedies. This paper reviews some of the available data, which suggest that indigenous traditional medicines are mostly without harmful side effects, but that some 40 plant species may be a cause for concern. Inappropriate use of these species is associated with a high mortality rate, particularly among paediatric patients. There is also a need to give attention to possible interactions between traditional and Western allopathic medicines taken concurrently, as well as to infraspecific variation in plant secondary biochemistry, with the occurrence of particularly potent biotypes. Pending the outcome of toxicological studies, interim preventive measures, aimed at reducing the number of hospital admissions due to poisoning by traditional remedies, are suggested.

Evolutionarily Stable Leaf Area Production in Plant Populations

Using an analytical model, it was shown that for a given amount of nitrogen in the canopy of a stand ( N T ), there exists an evolutionarily stable leaf area index (ES-LAI), and therefore an evolutionarily stable average leaf nitrogen content ( n ES av ; n ES av = N T / ES− LAI), at which no individual plant in the stand can increase its photosynthesis by changing its leaf area. It was also shown that this ES-LAI is always greater than the optimal LAI that maximizes photosynthesis per unit N T of the stand. This illustrates that the canopy structure that maximizes photosynthesis of a population is not the same as the canopy structure that maximizes photosynthesis of individuals within a population. It was further derived that the ES-LAI at given N T increases with the ratio between the light-saturated photosynthesis and the N content per unit leaf area (leaf-PPNUE) and that it decreases with the canopy extinction coefficient for light ( K L ), the light availability and the apparent quantum yield ( Φ). These hypotheses were tested by comparing calculated ES-LAI and n ES av values to actual LAIs and leaf N contents measured for stands of a large variety of herbaceous plants. There was a close correspondence between the calculated and measured values. As predicted by the model, plants with high leaf-PPNUEs produced more leaf area per unit nitrogen than those with low leaf-PPNUEs while plants with horizontal leaves, forming stands with higher K L values, produced less leaf area than those with more vertically inclined leaves. These results suggest that maximization of individual plant photosynthesis per unit of nitrogen plays an important role in determining leaf area production of plants and the resulting canopy structure of stands of vegetation. They further suggest this optimization to be a mechanism by which leaf traits such as leaf-PPNUE and leaf inclination angle are causally related to structural characteristics of the population, i.e. the leaf area index of the stand.

The Japanese in Brazil: From Immigration to Dekassegui

June 2002 · Historically Speaking Mieko Nishida The Japanese in Brazil: From Immigration to Dekassegui In 1980 the first Japanese-Brazilian woman film director, Tizuka Yamasaki, made her international debut with Gaijin: os caminhos da liberdade. Gaijin, a Japanese word literally translated as "foreigner " that usually refers to white foreigners in Japan, is the term with which Japanese-Brazilians have always referred to non-Japanese-Brazilians. But as Yamasaki says, "It is indeed the Japanese who have been gaijin in Brazil. They had been abandoned by their native country, and have been alienated in a new land." Yamasaki, born in 1949 to an Issei father and a Nisei mother, based this movie on the life of her maternal grandmother. It captures various aspects ofJapanese immigration to Brazil, including the hardships of coffee plantation life. It is widely believed that JapaneseBrazilians have enjoyed success as a model minority group in urban Brazil. Dedicated to educating their children, highly motivated immigrant parents left the coffee plantations for the city. Brazilian-born children attended the University of Säo Paulo and became lawyers, medical doctors , and dentists. But is diis picture ofdie Japanese-Brazilian elite a social reality or a cultural myth? The state of Säo Paulo has the second largest concentration of persons of Japanese descent outside Japan (Hawaii is first). In Brazil as a whole, the total number of persons ofJapanese descent amounts to some 1.3 million, almost 1% of the entire Brazilian population of 155 million. Japanese immigration to Brazil was a response to the great demand for labor on the coffee plantations in the Southeast following the abolition of slavery in 1888. At first, European immigrants filled this demand. But the flow of workers from Europe came to a halt by the beginning of the 20th century. Japanese immigration to Brazil began in 1908 and, after the enactment ofanti-Asian immigration laws during the 1920s in the United States, the number of immigrants quickly rose to more than 100,000 by the 1930s. During the late 1930s and early 1940s, Japanese-Brazilians were faced with two drastic changes. One was Brazilian nationalism ; the other,Japan's involvement in World War ?. Brazil's President Getulio Vargas stricdy enforced the country's immigration laws and its assimilation policy. Schools taught by aliens and in foreign languages were suppressed in 1938; almost allJapanese schools, numbering about 600 at the time, shut down. Beginning in 1940, foreign language newspapers were subjected to censorship . After Pearl Harbor, Japanese immigrants were no longer permitted to publish newspapers, even in Portuguese. Furthermore, Brazil severed diplomatic relations with Japan in January 1942, and Japanese-Brazilians lost all freedom to travel inside the country. The Brazilian government prohibited Japanese immigration in 1943, although immigration was allowed to resume a decade later. The urbanization of the JapaneseBrazilians did not take place until after Japan's defeat By then, most had given up hope ofreturning toJapan with a substantial fortune; instead they decided to settle in Brazil with their Brazilian-born children. During the 1950s, they began to move to major cities on a large scale. Rapid urbanization did not mean that Japanese-Brazilians moved up the social ladder. On the contrary , most abandoned positions as landowners and independent farmers to work in small family businesses—laundries , vegetable stands, grocery stores, beauty salons, and craft shops. Without sufficient capital to invest in these businesses , Japanese-Brazilian entrepreneurs relied heavily on the unpaid labor of family members, particularly Nisei children. Thus a typical Japanese-Brazilian family strategy was created: older children worked for the family business, while younger children, particularly sons, were sent to college. Two classes ofJapaneseBrazilians emerged: college-educated, assimilated, white-collar professionals; and members of the working-class who continued both to speakJapanese and preserve Japanese values and customs. In the mid-1980s many South Americans ofJapanese descent—not only from Brazil but also Peru, Argentina, and Paraguay—began emigrating to Japan. In the case ofJapanese-Brazilians there had always been a cultural factor motivating them to move "back" to Japan. Despite the image of Japanese-Brazilians as a successful urban middle class, they had been consistendy exposed to the larger society's pejorative racial and ethnic...

Effects of vegetation management in constructed wetland treatment cells on water quality and mosquito production

The impact of three vegetation management strategies on wetland treatment function and mosquito production was assessed in eight free water surface wetland test cells in southern California during 1998–1999. The effectiveness of the strategies to limit bulrush Schoenoplectus californicus culm density within the cells was also investigated. Removing accumulated emergent biomass and physically limiting the area in which vegetation could reestablish, significantly improved the ammonia–nitrogen removal efficiency of the wetland cells, which received an ammonia-dominated municipal wastewater effluent (average loading rate=9.88 kg/ha per day NH 4-N). We determined that interspersing open water with emergent vegetation is critical for maintaining the wetland's treatment capability, particularly for systems high in NH 4-N. Burning aboveground plant parts and thinning rhizomes only temporarily curtailed vegetation proliferation in shallow zones, whereas creating hummocks surrounded by deeper water successfully restricted the emergent vegetation to the shallower hummock areas. Since the hummock configuration kept open water areas interspersed throughout the stands of emergent vegetation, the strategy was also effective in reducing mosquito production. Decreasing vegetation biomass reduced mosquito refuge areas while increasing mosquito predator habitat. Therefore, the combined goals of water quality improvement and mosquito management were achieved by managing the spatial pattern of emergent vegetation to mimic an early successional growth stage, i.e. actively growing plants interspersed with open water.

A Phytosociological Study of Exotic Annual Brome Grasses in a Mixed Grass Prairie/Ponderosa Pine Forest Ecotone

The annual brome grasses, Bromus japonicus and B. tectorum, are common invaders of the Northern Great Plains. Our objective was to determine if these exotic plants were positively or negatively associated with particular plant species or functional types in a prairie/pine ecotone at Wind Cave National Park, South Dakota. We addressed this issue by sampling at two spatial scales—the landscape scale and the site scale. For the landscape we evaluated species associations across a 3800 ha ecotone using 90 transects. Annual bromes were positively associated with C3 grasses, particularly Agropyron smithii and Stipa viridula, in addition to the shrub Symphoricarpos occidentalis. Annual bromes were negatively associated with trees, C4 grasses, particularly A. gerardii, Bouteloua curtipendula and Schizachyrium scoparium, as well as the shrub Rhus aromatica. For the site scale we assessed relationships at a finer resolution within two 1 ha stands of grassland vegetation. Annual bromes were negatively associated with Poa pratensis in both stands. Results indicate that the bromes often dominate in portions of the landscape with C3 grasses and Symphoricarpos occidentalis. Within individual sites, the bromes appear most limited by a competitive interaction with P. pratensis, resulting from phenological overlap.

Replacement of littoral native vegetation with the ponded pasture grass Hymenachne amplexicaulis: effects on plant, macroinvertebrate and fish biodiversity of backwaters in the Fitzroy River, Central Queensland, Australia

Changes in plant and macroinvertebrate communities were found following replacement of extensive zones of floating-attached/submergent native vegetation within Fitzroy River backwaters by the major environmental weed Hymenachne amplexicaulis (Poaceae). Impacts of H. amplexicaulis on native littoral flora and fauna (macroinvertebrates and fish) were assessed by comparing three sites previously supporting native vegetation and now invaded by H. amplexicaulis with nearby stands of native backwater vegetation. Plant biomass of Hymenachne plant beds was 30-fold greater than native plant beds, whereas plant species diversity (richness) was significantly less. Macroinvertebrate communities of Hymenachne beds were significantly lower in abundance of insect orders Ephemeroptera, Hemiptera and Odonata, while Coleoptera were more abundant in Hymenachne beds. Non-metric multidimensional scaling ordination of macroinvertebrate family abundance and composition data showed that Hymenachne plant beds had a different assemblage to that in native plant beds. In common with other studies of weed invasions, an increased abundance of some vertebrate fauna was observed (in this case an introduced fish species Xiphophorus maculatus comprised 75% of fish captured in Hymenachne beds compared with 0% in native plant beds). Change in vegetation structure was implicated as an important factor influencing macroinvertebrate and fish faunal composition, and with potential to impact on waterbird habitat values of wetlands.

Assessment of JERS-1 SAR for monitoring secondary vegetation in Amazonia: I. Spatial and temporal variability in backscatter across a chrono-sequence of secondary vegetation stands in Rondonia

Quantification of the direct impact of land use in the tropics on net biotic carbon flux relies on estimates of rates of deforestation, pre- and post-disturbance biomass, and fate of the cleared land. While existing remote sensing applications are providing estimates of the rates of deforestation and the fate of the cleared land (pasture, croplands, or secondary vegetation), techniques for estimating biomass of natural systems with remote sensing are needed. Synthetic Aperture Radar (SAR) presents a unique opportunity for imaging tropical forests under most cloud conditions and potentially provides information on vegetation biomass. Models for estimating above-ground biomass from SAR data have been developed. In this paper we examine the temporal and spatial variability of mean normalized radar cross-section across a chrono-sequence of secondary vegetation stands and clearings in Rondonia, Brazil. We also assess the impact of the observed temporal and spatial variability in normalized radar cross-section on estimating biomass of secondary vegetation stands. Results indicate that, while quantitative estimates of biomass are not stable due to intrinsic texture, system noise, and environmental effects, JERS-1 data are still useful for categorizing relative differences in development of secondary vegetation stands. Merging Japanese Earth Resources Satellite 1 (JERS-1) SAR data with Landsat Thematic Mapper (TM) derived age information data provide improved characterization of clearings and secondary vegetation in Rondonia.

Aquatic macrophytes: restore, eradicate or is there a compromise?

Promoting indigenous submerged macrophytes is considered an important measure to restore shallow lakes. On the other hand, dense stands of aquatic vegetation often cause nuisance for boating, swimming and by obstruction of water flow. Consequently, the interests of recreational users may conflict with nature conservation. At first sight, aiming lake management at intermediate vegetation biomass seems a good solution for this controversy. However, as can be shown with a simple economical model, such a compromise may not always be an optimal solution in terms of total welfare across all users of a lake. Here, we show that a management strategy aimed at moderate plant biomass can also be unfeasible for ecological reasons. This is shown by applying two very different models: a minimal logistic model of plant growth which is easy to understand, and the relatively complex and realistic simulation model Charisma which, among other things, includes the seasonal cycle and a detailed description of the dynamics of light availability for macrophytes. The qualitative results of both models were remarkably similar. If the ecosystem has no alternative stable states, it is possible to set vegetation to any desired sustainable level using an appropriate harvesting strategy. However, if an intermediate vegetation biomass is to be realized the costs of harvesting are high, because the yield is predicted to be maximal in that case. If the ecosystem has alternative stable states, harvesting becomes risky because the vegetation may collapse entirely below a certain, in practice unknown, biomass. Also, even moderate harvesting may reduce the resilience of the vegetated state, making the ecosystem more vulnerable to adverse conditions such as unfavorable weather conditions or bird grazing.

Deposition, germination and spatio-temporal patterns of charophyte propagule banks: a review

Charophyte oospore banks have been studied in different habitat types, whereas only one detailed study of bulbil banks has been recorded from the literature. The density of oospore banks generally appears to be very high, dominating the propagule bank in many wetlands. Oospore banks are characterised by high spatial variability within and between the sites. Bulbils and oospores are not uniformly distributed with sediment depth, oospores being generally more numerous in the top few centimetres. Animal activities can mix the sediment, bury propagules and/or homogenise their distribution. Burial deeper than 2 cm limits oospore germination, but burial to a depth of 5 mm can improve their germination capacities. Oospore banks are highly variable between years. They are generally perennial, cumulating several generations of oospores, and buffering the risk of reproductive failure with time. The limited germination rates recorded for oospores from the bank could be related to this perennial strategy, whereas up to 100% of freshly harvested oospores may germinate. Germination rates and patterns and the conditions required for germination vary greatly from one study to another as a result of the large range of species and habitats investigated. Certain water birds consume charophytes and could be efficient dispersal agents for oospores. Various abiotic factors can affect the charophyte biomass and therefore the oospore production which then in turn could affect the propagule bank. The oospore bank density appears to influence charophyte abundance in the field, but above a threshold, its abundance is not related to the number of oospores in the soil. Below a threshold of density, charophytes may be unable to establish dense stands of vegetation.