Consumer-grade UAV imagery facilitates semantic segmentation of species-rich savanna tree layers

Conventional forest inventories are labour-intensive. This limits the spatial extent and temporal frequency at which woody vegetation is usually monitored. Remote sensing provides cost-effective solutions that enable extensive spatial coverage and high sampling frequency. Recent studies indicate that convolutional neural networks (CNNs) can classify woody forests, plantations, and urban vegetation at the species level using consumer-grade unmanned aerial vehicle (UAV) imagery. However, whether such an approach is feasible in species-rich savanna ecosystems remains unclear. Here, we tested whether small data sets of high-resolution RGB orthomosaics suffice to train U-Net, FC-DenseNet, and DeepLabv3 + in semantic segmentation of savanna tree species. We trained these models on an 18-ha training area and explored whether models could be transferred across space and time. These models could recognise trees in adjacent (mean F1-Score = 0.68) and distant areas (mean F1-Score = 0.61) alike. Over time, a change in plant morphology resulted in a decrease of model accuracy. Our results show that CNN-based tree mapping using consumer-grade UAV imagery is possible in savanna ecosystems. Still, larger and more heterogeneous data sets can further improve model robustness to capture variation in plant morphology across time and space

Abiotic conditions shape the relationship between indigenous and exotic species richness in a montane biodiversity hotspot

Montane ecosystems are more prone to invasions by exotic plant species than previously thought. Besides abiotic factors, such as climate and soil properties, plant-plant interactions within communities are likely to affect the performance of potential invaders in their exotic range. The biotic resistance hypothesis predicts that high indigenous species richness hampers plant invasions. The biotic acceptance hypothesis, on the other hand, predicts a positive relationship between indigenous and exotic species richness. We tested these two hypotheses using observational data along an elevational gradient in a southern African biodiversity hotspot. Species composition data of indigenous and exotic plants were recorded in 20 road verge plots along a gradient of 1775–2775 m a.s.l. in the Drakensberg, South Africa. Plots were 2 × 50 m in size and positioned at 50 m elevational intervals. We found a negative correlation between indigenous and exotic richness for locations with poorly developed mineral soils, suggesting biotic resistance through competitive interactions. A strong positive correlation for plots with very shallow soils at high elevations indicated a lack of biotic resistance and the possibility of facilitating interactions in harsher environments. These results suggest that biotic resistance is restricted to the lower and mid elevations while biotic acceptance prevails in presence of severe abiotic stress, potentially increasing the risk of plant invasions into montane biodiversity hotspots

Climate change impacts on the availability of anti-malarial plants in Kenya

In many rural East African areas, anti-malarial plants are commonly used as first-line treatment against malaria. However, spatially explicit information about the future availability of anti-malarial plant species and its relation to future suitable habitat for malaria vectors is limited. In this study we (1) model the distribution of anti-malarial plant and malaria vector species and assess the drivers of their distributions taking the example of the Samburu dryland in Kenya, (2) map the modeled overlap in this area, (3) assess the impact of future climate change on anti-malarial plant and malaria vector species and (4) report their future overlaps. Our results show that mean temperature of warmest quarter, precipitation of wettest quarter and mean temperature of coldest quarter were the most important environmental variables that affected the distribution of anti-malarial species. The effects of climate change will vary, with some areas characterized by huge losses in anti-malarial species habitat while others gained or remained stable under both SSP2-4.5 and SSP5-8.5 climate change scenarios by 2050s and 2070s. According to most of our scenarios, more than half of the anti-malarial species will become vulnerable or threatened by 2050s and 2070s. A comparison between distribution patterns of future anti-malarial species richness and malaria vector species suitable habitat suggests that the former will decrease considerably while the later will increase. Because the availability of anti-malarial species will decrease in the areas affected by malaria vectors, geographically targeted conservation strategies and further control measures against malaria vectors are all the more important

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

Bush thickening is amajor concern to farmers of arid and semi-arid rangelands; reactive intervention remains the norm. Herewe compared some of the short-termecological 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. Fromeach 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.Project no. RVO 67985939 (The Czech Academy of Sciences).http://www.elsevier.com/locate/sajb2017-01-31hb2016Geography, Geoinformatics and Meteorolog

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

Early detection ofemerging invasive plants depends onmaximizing the probability of detecting newpopulations. 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-termmonitoring programmes as an effective means for early detection of new invasive species.DST-NRF Centre of Excellence for Invasion Biology, the University of Johannesburg and the University of Pretoria. JMK is currently supported by the long-term research development project no. RVO 67985939 (Academy of Sciences of the Czech Republic). The MazdaWildlife Fund.http://www.elsevier.com/locate/sajbhb201

Fur seal populations facilitate establishment of exotic vascular plants

The cessation of seal harvesting has prompted a recovery of previously decimated fur seal (Arctocephalus gazella and Arctocephalus tropicalis) populations across the Southern Ocean region. Although the associated increase in seal-related soil disturbance is known to impact indigenous vegetation, the effect of increasing fur seal numbers on exotic plant species is not yet clear. Here, we compare plant species composition and cover between 26 sites with high fur seal impact paired with nearby control sites on sub- Antarctic Marion Island. Seal-affected sites had a significantly higher number and cover of exotic plants, specifically of the widespread sub-Antarctic invaders, Poa annua and Sagina procumbens, than control sites. Furthermore, some of the native species, most notably the disturbance-sensitive species, Blechnum penna-marina, were significantly less abundant in seal-affected sites compared to controls. We propose that this is a result of both physical trampling, which opens up niches for exotics by damaging natives, and nutrient enrichment of the soils, giving exotic species a competitive advantage over natives. While other studies have noticed associations between exotic plant species and indigenous animal disturbance, this is, to the best of our knowledge, the first study to empirically show that the successful recovery of fur seal populations can have undesirable side-effects such as the enhanced persistence of exotic plant species. We recommend that alien plant management plans specifically include areas of increased animal disturbance into their programmes.http://www.elsevier.com/ locate/bioconhb201

QUANTIFYING DISPERSAL AND ESTABLISHMENT LIMITATION IN A POPULATION OF AN EPIPHYTIC LICHEN

Dispersal is a process critical for the dynamics and persistence of metapopulations, but it is difficult to quantify. It has been suggested that the old-forest lichen Lobaria pulmonaria is limited by insufficient dispersal ability. We analyzed 240 DNA extracts derived from snow samples by a L. pulmonaria-specific real-time PCR (polymerase chain reaction) assay of the ITS (internal transcribed spacer) region allowing for the discrimination among propagules originating from a single, isolated source tree or propagules originating from other locations. Samples that were detected as positives by real-time PCR were additionally genotyped for five L. pulmonaria microsatellite loci. Both molecular approaches demonstrated substantial dispersal from other than local sources. In a landscape approach, we additionally analyzed 240 snow samples with real-time PCR of ITS and detected propagules not only in forests where L. pulmonaria was present, but also in large unforested pasture areas and in forest patches where L. pulmonaria was not found. Monitoring of soredia of L. pulmonaria transplanted to maple bark after two vegetation periods showed high variance in growth among forest stands, but no significant differences among different transplantation treatments. Hence, it is probably not dispersal limitation that hinders colonization in the old-forest lichen L. pulmonaria, but ecological constraints at the stand level that can result in establishment limitation. Our study exemplifies that care has to be taken to adequately separate the effects of dispersal limitation from a limitation of establishment

Vagrant birds as a dispersal vector in transoceanic range expansion of vascular plants

Birds are thought to be important vectors underlying the disjunct distribution patterns of some terrestrial biota. Here, we investigate the role of birds in the colonisation by Ochetophila trinervis (Rhamnaceae), a vascular plant from the southern Andes, of sub-Antarctic Marion Island. The location of O. trinervis on the island far from human activities, in combination with a reconstruction of island visitors’ travel history, precludes an anthropogenic introduction. Notably, three bird species occurring in the southern Andes inland have been observed as vagrants on Marion Island, with the barn swallow Hirundo rustica as the most common one. This vagrant displays long-distance migratory behaviour, eats seeds when insects are in short supply, and has started breeding in South America since the 1980s. Since naturalised O. trinervis has never been found outside the southern Andes and its diaspores are incapable of surviving in seawater or dispersing by wind, a natural avian dispersal event from the Andes to Marion Island, a distance of >7500 km, remains the only probable explanation. Although one self-incompatible shrub seems doomed to remain solitary, its mere establishment on a Southern Ocean island demonstrates the potential of vagrancy as a driver of extreme long-distance dispersal of terrestrial biota

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 the support for the DEFH and the ALH along an elevational gradient by asking: First, are alien species that occur at higher elevations generalists? Second, do alien species occurring at higher elevations exhibit traits that distinguishes them from lowland 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 tolerance weaker 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 found 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.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1654-11032018-03-31hb2017Plant Production and Soil Scienc