Mapping Grey Willow (Salix cinerea) stand architecture using airborne laser scanning: implications for large‐scale tree weed control

We investigated the potential of airborne laser scanning (ALS) for mapping the stand architecture of Grey Willow (Salix cinerea), an invasive wetland weed in New Zealand. In particular, we focused on two metrics, tree height and canopy density, both of which influence the efficacy and nontarget impacts of herbicides aerially broadcast by helicopter to control tree weeds. We compared ground‐based measures of Grey Willow height and canopy density with ALS‐derived data, and the relationship between canopy density as estimated by each method and aerial herbicide deposition at three wetland sites in New Zealand. Analysis revealed strong linear relationships between ground‐based and ALS metrics, indicating that ALS data could be used to generate accurate, high‐resolution digital maps of Grey Willow height and canopy density. These maps coupled with computer‐guided variable flow rate technologies, which enable optimal placement of herbicide, could maximise Grey Willow mortality while reducing the mortality of nontarget indigenous plants. We recommend the application of ALS‐derived maps and computer‐guided variable flow rate technology is investigated for more targeted large‐scale tree weed control.     

Strategies for the biological control of invasive willows (Salix spp.) in Australia

Abstract  Willows ( Salix spp.) are Weeds of National Significance in Australia where a large number of taxa are naturalised in temperate regions and can cause serious environmental degradation of riparian and wetland habitats. Several species are of economic or ornamental value and conflicts of interest could arise with planning their suppression. Biological control of six willow species ( S. alba L., S. cinerea L . , S. fragilis L., S. nigra Marshall, S. viminalis L., S . x  rubens Schrank) is under consideration in Australia using three approaches based on targeting different morphological structures. A rich phytophagous biota associated with Salix in their regions of origin indicate a range of organisms are available for development as biological control agents. Implementation strategies will depend on the host species targeted for biological control, their reproductive strategies, the level of control required to reduce environmental impacts and the level of conflict of interest associated with a biological control program.     

Revegetation of a wetland following control of the invasive woody weed, Mimosa pigra, in the Northern Territory, Australia

Summary Methods for floodplain revegetation using native species were investigated, following clearance of the invasive shrub Mimosa pigra L. (Mimosaceae) in the Northern Territory of Australia. Prolific revegetation occurred naturally and several species were identified that have potential for revegetation at sites where natural regeneration is poor, namely: Spiny Mud Grass, Pseudoraphis spinescens, Awnless Barnyard Grass, Echinochloa colona, and an unidentified Panicum species. However, it may still be desirable to plant native perennial grasses, of which most species did not establish naturally. Stolons of the native floodplain grass Hymenachne acutigluma (Steud) Gilliland (Poaceae) established well when planted in wet mud and shallow water during the early dry season, as seasonal floodwaters subsided. Similar plantings during the early wet season were less successful. Sowing seed of several floodplain grasses and Eliocharis dulcis was unsuccessful in both seasons. Planting stolons of H. acutigluma as seasonal floodwaters subside may provide a reliable alternative to exotic floodplain grasses, Para Grass (Urochloa mutica), and Amity Aleman Grass (Echinochloa polystachya), which are also currently propagated vegetatively in Australia. However, planting H. acutigluma stolons had no tangible benefits in terms of suppressing Mimosa establishment, which was low in all treatments. Revegetation should not be considered an alternative to the diligent control of Mimosa seedlings; regenerating following control of Mimosa thickets.     

Interactions between national and local strategies for the management of aquatic weeds

Management of aquatic weeds is often handled primarily at the local level. However, both water and water weeds do not recognise political boundaries even when these coincide with rivers or catchment areas. Thus potentially effective management of a weed in one area may be undermined by absence of a complementary program of management in an adjacent area. Authorities in each of the eight States or Territories that make up Australia are separately responsible for managing water weeds in their own State or Territory. Originally there was little coordination of these programs, but during the 1980s a national strategy for control of Australian water weeds has been progressively devised and put into practice. This stresses prevention and includes policies on plant importation, nomination of noxious weeds, development of a research strategy, a public awareness campaign, guidelines on the use of herbicides in or near water, and a field guide. This strategy is currently being incorporated into a National Weeds Strategy.     

How Does Restoration of Native Canopy Affect Understory Vegetation Composition? Evidence from Riparian Communities of the Hunter Valley Australia

Restoration of native vegetation often focuses on the canopy layer species, with the assumption that regeneration of the understory elements will occur as a consequence. The goal of this study was to assess the influence of canopy restoration on the composition and abundance of understory plant species assemblages along riparian margins in the Hunter Valley, NSW, Australia. We compared the floristic composition (richness, abundance, and diversity) of understory species between nonrevegetated (open) and canopy revegetated plots across five sites. A number of other factors that may also influence understory vegetation, including soil nutrients, proximity to main channel, and light availability, were also measured. We found that sites where the canopy had been restored had lower exotic species richness and abundance, as well as higher native species cover, but not native species richness, compared with open sites. Multivariate analysis of plots based on plant community composition showed that revegetated sites were associated with lower total species diversity, light availability, and exotic cover. This study has found that the restoration of the canopy layer does result in lower exotic species richness and cover, and higher native species cover and diversity in the understory, a desirable restoration outcome. Our results provide evidence that restoration of native canopy species may facilitate restoration of native understory species; however, other interventions to increase native species richness of the understory should also be considered as part of management practice.     

外来杂草在我国的危害性及其管理对策

外来杂草已对我国的农作物生产、果园、草坪、环境和生物多样性等赞成了严重危害。外来杂草之所以能在传入地产生危害,与它们所具有的特性和当地缺乏环境阻力密切相关。对外来杂草的管理应从防止外来杂草传入和对现有的外来杂草初稿除两方面采取措施。防止传入的措施包括：（1）加强植物检疫;（2）建立外来植物引种驯化的风险性评价制度;（3）鼓励利用本土植物。对现有外来杂草的防除,则应采取综合性的防除措施：（1）防治生态破坏;（2）开展外来杂草的生物控制;（3）利用经济植物进行生境替代控制;（4）开展对外来杂草的利用。     

Effects of brassinosteroids on conditioning and germination of clover broomrape (Orobanche minor) seeds

Brassinolide [2, 3, 22R,23R-tetrahydroxy-24S-methyl-B-homo-7-oxa-5--cholestan-6-one] and its related compounds, brassinosteroids, applied at the early stages of conditioning shortened the conditioning period required before clover broomrape seeds would germinate after exposure to germination stimulants, such as dl-strigol and natural stimulants from red clover (Trifolium pratense L.) root exudate. Brassinosteroids applied after conditioning increased the rate of the seed germination induced by these stimulants. The inhibitory effect of light on seed germination when it was induced by dl-strigol could be overcome by brassinosteroids. Brassinosteroids also eliminated the inhibitory effects of light and dl-strigol applied at the early stages of conditioning. GA₃ was also effective in causing seed conditioning and increased the rate of the germination induced by these stimulants. There was a relationship between brassinosteroids and GA₃ in many of the experiments conducted. These findings may have practical implications in increasing the effectiveness of applying germination stimulants in the field to soils for suicidal germination of broomrape seeds.     

A palynological reconstruction of pre-European riparian vegetation at Wollombi, New South Wales and its application to stream bank management and revegetation

Summary A palynological investigation was conducted on sediments from three small floodplain swamps on upper Wollombi Brook in the Hunter Valley NSW in order to reconstruct pre-European riparian vegetation composition and community structure. Pre-European riparian plant communities on upper Wollombi Brook were characterized by wet sclerophyll forest associations with rainforest elements (most likely close to the channel). Major changes in both the nature and extent of riparian vegetation have been associated with European settlement. The pre-European pollen spectra assists the identification of a suite of native taxa potentially suitable for use in riparian revegetation operations, particularly in highly cleared streambank sites where protection of water quality and aquatic habitat is an important goal but where insufficient local remnants are available to indicate pre-existing plant species. The research emphasizes the use of palaeoenvironmental evidence as a tool for contemporary environmental management.