Invasive plants

The invasion of the exotic dioecious shrub
Baccharis halimifolia is transforming the estuarine
communities of Southern Europe. Large scale gradients
of salinity and flooding regime determine B.
halimifolia zonations in salt marshes where the
subhalophilous sea rush communities are the most
affected by invasion. In this study we aim to (1) assess
the invasion level and influence of B. halimifolia on
native flora and to (2) quantify the performance of the
exotic shrub in rush communities across fine-scale
salinity and waterlogging gradients. Using floristic
data collected in estuaries in Northern Spain we
identified 3 sea rush community subtypes: low,
medium and high salinity communities. B. halimifolia
cover decreased from low to high salinity communities.
Native species cover, richness and diversity and
herbaceous-subshrub layer cover was significantly
lower in invaded rush communities than in uninvaded
ones. The reduction of the singular native estuarine
species cover and richness was higher in the high and
medium salinity community than in the low salinity
community. Growth and reproductive traits measured
on two consecutive years in invaded rush communities
in Urdaibai Biosphere Reserve indicated that increased
edaphic stress reduced B. halimifolia individual performance
and enhanced attack by natural enemies.
Moreover, leaf drop was more responsive to salinity in
female than in male individuals.Weconclude that finescale
variations on edaphic stress played an important
role in the invasibility of rush communities by
affecting the individual performance of B. halimifolia,
and might generate sex specific responses. The implications
for rush marsh conservation are discussed.

Alien invasive species are a significant threat to biodiversity and ecosystems in nonnative geographical ranges. Ulex europaeus is one such shrub introduced to the montane grasslands of Sri Lanka. We conducted this study with the objective of evaluating the U. europaeus removal programs focusing on both positive and negative impacts that arose. Three months of pre-removal and three months each of two post-removal time periods were selected for sampling. We evaluated the changes in the density of U. europaeus, Calotes nigrilabris, spatiotemporal variation of vegetative structure and pollinator abundance. Initially, the removal of U. europaeus was mostly successful in terms of reduced shrub density. However, the prevalence and emergence of live shrubs after the removal program raises concerns regarding the viability of the project. Furthermore, the drastic population density reduction of endemic and threatened lizard C. nigrilabris following the removal of U. europaeus can be considered a negative impact of high conservation concern. However, we observed an increase in pasture availability and re-establishment of natural vegetative structure. It can be concluded that proper knowledge regarding the invasive species and understanding their ecological linkages is important for the success of management programs. Continuous and long term, control and monitoring are recommended.

Invasive plant species represent a serious threat to biodiversity and landscape as well as human health and socio-economy. To successfully fight plant invasions, new methods enabling fast and efficient monitoring, such as remote sensing, are needed. In an ongoing project, optical remote sensing (RS) data of different origin (satellite, aerial and UAV), spectral (panchromatic, multispectral and color), spatial (very high to medium) and temporal resolution, and various technical approaches (object-, pixel-based and combined) are tested to choose the best strategies for monitoring of four invasive plant species (giant hogweed, black locust, tree of heaven and exotic knotweeds). In our study, we address trade-offs between spectral, spatial and temporal resolutions required for balance between the precision of detection and economic feasibility. For the best results, it is necessary to choose best combination of spatial and spectral resolution and phenological stage of the plant in focus. For species forming distinct inflorescences such as giant hogweed iterative semi-automated object-oriented approach was successfully applied even for low spectral resolution data (if pixel size was sufficient) whereas for lower spatial resolution satellite imagery or less distinct species with complicated architecture such as knotweed, combination of pixel and object based approaches was used. High accuracies achieved for very high resolution data indicate the possible application of described methodology for monitoring invasions and their long-term dynamics elsewhere, making management measures comparably precise, fast and efficient. This knowledge serves as a basis for prediction, monitoring and prioritization of management targets.

The rapid spread of invasive plants makes their management increasingly difficult. Remote sensing offers a means of fast and efficient monitoring, but still the optimal methodologies remain to be defined. The seasonal dynamics and spectral characteristics of the target invasive species are important factors, since, at certain time of the vegetation season (e.g., at flowering or senescing), plants are often more distinct (or more visible beneath the canopy). Our aim was to establish fast, repeatable and a cost-efficient, computer-assisted method applicable over larger areas, to reduce the costs of extensive field campaigns. To achieve this goal, we examined how the timing of monitoring affects the detection of noxious plant invaders in Central Europe, using two model herbaceous species with markedly different phenological, structural, and spectral characteristics. They are giant hogweed (Heracleum mantegazzianum), a species with very distinct flowering phase, and the less distinct knotweeds (Fallopia japonica, F. sachalinensis, and their hybrid F. × bohemica). The variety of data generated, such as imagery from purposely-designed, unmanned aircraft vehicle (UAV), and VHR satellite, and aerial color orthophotos enabled us to assess the effects of spectral, spatial, and temporal resolution (i.e., the target species' phenological state) for successful recognition. The demands for both spatial and spectral resolution depended largely on the target plant species. In the case that a species was sampled at the most distinct phenological phase, high accuracy was achieved even with lower spectral resolution of our low-cost UAV. This demonstrates that proper timing can to some extent compensate for the lower spectral resolution. The results of our study could serve as a basis for identifying priorities for management, targeted at localities with the greatest risk of invasive species' spread and, once eradicated, to monitor over time any return. The best mapping strategy should reflect morphological and structural features of the target plant and choose appropriate spatial, spectral, and temporal resolution. The UAV enables flexible data acquisition for required time periods at low cost and is, therefore, well-suited for targeted monitoring; while satellite imagery provides the best solution for larger areas. Nonetheless, users must be aware of their limits.

Freshwaters are not only used locally in many developing countries but they are often over exploited for domestic purposes, agriculture and disposal of industrial wastes which result in an overload of excess nutrients, harmful chemicals and heavy metals. Plant species together with sediments and water samples collected from eleven aquatic water bodies in the vicinity of industrial units in Kolkata were studied for their potential to uptake Pb, Cd and Cr under field conditions. Cd and Cr concentrations in the sediments were higher than background values considered to be toxic. Alternanthera philoxeroides and Eichhornia crassipes were the two invasive species present, with the former being more widely distributed. Among native plants, Ipo-moea aquatica was the most abundant. Metal uptake in the plants differed among species, tissues and sites. Pb and Cd accumulation in root tissues for all plants in most sites suggested an exclusion strategy for metal tolerance. Since I. aquatica is widely consumed in many parts of SE Asia, its metal content should be checked before use since it was found to efficiently translocate both Pb and Cd from roots to shoots. The potential of A. philoxeroides as a metal excluder needs to be explored further since it translocates less to its shoots as compared to E. crassipes and I. aquatica.