Reaching new heights: can drones replace current methods to study plant population dynamics?

Spatially explicit data on heterogeneously distributed plant populations are difficult to quantify using either traditional field-based methods or remote sensing techniques alone. Unmanned Aerial Vehicles (UAVs) offer new means and tools for baseline monitoring of such populations. We tested the use of vegetation classification of UAV-acquired photographs as a method to capture heterogeneously distributed plant populations, using Jacobaea vulgaris as a model species. Five sites, each containing 1–4 pastures with varying J. vulgaris abundance, were selected across Schleswig–Holstein, Germany. Surveys were conducted in July 2017 when J. vulgaris was at its flowering peak. We took aerial photographs at a 50 m altitude using three digital cameras (RGB, red-edge and near-infrared). Orthomosaics were created before a pixel-based supervised classification. Classification results were evaluated for accuracy; reliability was assessed with field data collected for ground verification. An ANOVA tested the relationship between field-based abundance estimations and the supervised classifications. Overall accuracy of the classification was very high (90.6%, ± 1.76 s.e.). Kappa coefficients indicated substantial agreement between field data and image classification (C 0.65). Field-based estimations were a good predictor of the supervised classifications (F = 7.91, df = 4, P = 0.007), resulting in similar rankings of J. vulgaris abundance. UAV-acquired images demonstrated the potential as an objective method for data collection and species monitoring. However, our method was more time consuming than field-based estimations due to challenges in image processing. Nonetheless, the increasing availability of low-cost consumer-grade UAVs is likely to increase the use of UAVs in plant ecological studies

Landscape corridors: Possible dangers?

Ctr Invas Bio

Alien plant species that invade high elevations are generalists: support for the directional ecological filtering hypothesis

Questions: The richness of invasive alien plant species tends to decrease with increasing elevation. This pattern may be due to alien plant species requiring traits allowing survival at high elevations (the Abiotic Limitation Hypothesis; ALH). In contrast, the more recent Directional Ecological Filtering Hypothesis (DEFH) suggests that only species with broad environmental tolerances will successfully spread from lowlands (where most introductions occur) to high elevations. Here we test support for the DEFH and ALH along an elevational gradient by asking: (1) are alien species that occur at higher elevations generalists; and (2) do alien species occurring at higher elevations exhibit traits that distinguishes them fromlowland alien species? Location: Sani Pass, Maloti-Drakensberg Transfrontier Conservation Area, South Africa. Methods: A nestedness analysis was conducted to test whether alien species were nested along the elevational gradient, and ANOVA and Chi2 tests (supplemented by resampling procedures) were used to determine if functional traits differed between high- and low-elevation alien species. Results: Significant nestedness of the alien flora indicates that alien species occurring at high elevations are generalists, being widespread across the elevational gradient. Compared to low-elevation aliens, plant height was lower and cold toleranceweaker for high-elevation species. Conclusion: We found support for the DEFH, with the majority of high-elevation aliens being widespread generalists. Overall only two of the 11 functional traits differed between high- and low-elevation alien species, with only one trait supporting the ALH: shorter plant stature at higher elevations. Therefore, complementing nestedness analyses with trait data provides a more nuanced insight into the determinants of alien richness patterns along elevational gradients, and highlights how the two contemporary hypotheses might not be mutually exclusive

Worden rijkswegbermen goed beheerd? Een botanische evaluatie

Wegbermen kunnen een belangrijke bijdrage leveren aan flora en vegetatie van Nederland. Bermen van rijkswegen worden al lang ecologisch beheerd. Het effect van dit beheer was nog niet eerder landelijk beoordeeld. In dit artikel een beschrijving van de botanische veranderingen na 15 jaar. Aan ieder vegetatietype is een vegetatiekundig waardeoordeel gegeven in een vijfdelige schaa

Some ecological side-effects of chemical and physical bush clearing in a southern African rangeland ecosystem

Bush thickening is a major concern to farmers of arid and semi-arid rangelands; reactive intervention remains the norm. Here we compared some of the short-term ecological implications of chemical and physical removal of the bush encroacher Acacia mellifera in the central Highland savanna of Namibia.We selected 21 invaded sites, 7 had been chemically cleared, 7 had been physically cleared and 7 had never been cleared. From each site,we recorded grass species composition, as well as the densities of A. mellifera, the undesired perennial shrub Pechuel-loeschea leubnitziae and a non-targeted tree Acacia erioloba, 24–30 months post-treatment. We fitted one-way ANOVA models to test for the effect of treatment on grass species richness and density of targeted and non-targeted tree species. A canonical correspondence analysis was used to determine how treatment affected grass species composition. While both treatments reduced the density of the bush encroacher, P. leubnitziae effectively replaced A. mellifera in chemically treated sites, where die-back presumably happened faster and nutrient and water competition decreased more rapidly. In such sites, perennial grass species were effectively outcompeted by P. leubnitiziae

Repeated monitoring as an effective early detection means: first records of naturalised Solidago gigantea Aiton (Asteraceae) in southern Africa

Early detection of emerging invasive plants depends on maximizing the probability of detecting new populations. Repeated surveys along a gradient of environmental conditions or in areas exposed to high propagule pressure provide a potentially efficient strategy for early detection of alien species. The long-term monitoring of such an area resulted in the documentation of the first naturalised Solidago gigantea Aiton (Asteraceae) population for southern Africa. This population consisted of c. 45 individuals growing in two locations on unmanaged grassland in the Drakensberg Mountains at an elevation of 1619 m a.s.l. Solidago gigantea readily invades unmanaged European grasslands, altering biomass and transforming habitats. Moreover, since goldenrods (Solidago spp) are perennial species reproducing through a large number of wind-dispersed seeds and belowground rootstocks, these species appear well pre-adapted to the fire-prone grassland biome of South Africa. We therefore suggest early-stage eradication of S. gigantea before it potentially becomes an unmanageable and costly invasive species in this region. This study supports long-term monitoring programmes as an effective means for early detection of new invasive species

Worden rijkswegbermen goed beheerd? Een botanische evaluatie

Wegbermen kunnen een belangrijke bijdrage leveren aan flora en vegetatie van Nederland. Bermen van rijkswegen worden al lang ecologisch beheerd. Het effect van dit beheer was nog niet eerder landelijk beoordeeld. In dit artikel een beschrijving van de botanische veranderingen na 15 jaar. Aan ieder vegetatietype is een vegetatiekundig waardeoordeel gegeven in een vijfdelige schaa