Josef Brůna1, Jana Müllerová1, Tomáš Bartaloš1 and Petr Dvořák2
1Institute of Botany of the Czech Academy of Sciences, Průhonice, Czech Republic
2Institute of Aerospace Engineering, Brno University of Technology, Brno, Czech Republic
Tree of heaven (Ailanthus altissima) belongs to the 100 worst European invasive species with further potential to spread due to climate change. Ailanthus is particularly limited by late spring frost which damages the buds and young leaves. In the Czech Republic and other Central and Northern European countries, Ailanthus is still mostly present in urban areas serving as heat islands. However, with increasing temperatures and enough propagules from already established populations, its invasion is expected to grow rapidly. Means of early detection as well as detailed knowledge on the species potential to spread across Europe are therefore urgently needed. In the Czech Republic, the species is currently on the northern edge of its distribution range, being present only in the warmest parts of the country and in urban areas. Examples of Ailanthus escaping into the open landscape are still rather rare here, unlike in neighbouring countries, such as southern Hungary or southern Austria where it has already massively increased in the last decades. But we can expect similar scenarios.
In our study, we focused on possibilities of early detection using custom built fixed wing UAV and identified the best phenology phase for detection. We generated an orthoimage and digital model of the canopy using Structure from Motion method in Agisoft Photoscan. Subsequently, we applied object-oriented image analysis and automatic classification of segments and achieved high accuracies using spring multispectral imagery (RGB+NIR). Our results from several years show that the accuracy also depends on frostwhich can lower the accuracy, especially if the frost appeared only in part of the area (e.g. valley bottoms).
Consequently, we produced a model of the current and potential distribution of Ailanthus, using data on species distributions in the Czech Republic and identified environmental and climatic constrains shaping the current distribution, as well as potential spread with regard to expected future climate change.