Seeing the forest for the invasives: mapping buckthorn in the Oak Openings

Detecting understory plant invasion in urban forests using LiDAR

“…While some success has been achieved with high-to-moderate resolution imagery, hyperspectral imagery has demonstrated the most promising results (Huang and Asner, 2009). The growing number of invasions in forests pushes the limits of remote sensing performance, particularly in detecting exotic plant invasions in the understory where regeneration and recruitment are most impacted by invaders (Becker et al, 2013). Canopy cover closure, canopy gap shadowing, mortality of native plant species, and terrain variability in the understory of forest ecosystems limit accurate detection of understory invaders (Asner et al, 2008).…”

“…Canopy cover closure, canopy gap shadowing, mortality of native plant species, and terrain variability in the understory of forest ecosystems limit accurate detection of understory invaders (Asner et al, 2008). Successful detection often depends upon open views of the species of interest (Resasco et al, 2007) and the timing of remote sensing imagery to take advantage of phenological patterns in the overstory, i.e., after leaf abscission (Becker et al, 2013;Tuanmu et al, 2010). To date, detection of understory plant invasions is largely reliant on field surveys, but cost and data collection times limit the number of locations that can be assessed.…”

Mapping Wild Leek through the Forest Canopy Using a UAV

“…Previous research in Gatineau Park revealed that areas with large and continuous patches of vegetation can be detected with 30 m resolution Landsat 8 imagery acquired during the period when wild leek emerges [48], suggesting that this free source of satellite imagery may be suitable as the basis for wild leek monitoring in the park. The ability of Landsat imagery to detect understory species has been demonstrated before, where invasive bamboo species [22] and European buckthorn [21] were mapped under deciduous forests. An advantage of using a time series to capture phenological differences throughout the year, as achieved by these studies, is that prior knowledge or testing on the optimal dates is not needed.…”

“…Using a set threshold has the benefit of being easily implemented, but might lack the flexibility and precision to separate other species present on the forest floor. Therefore, this method is not easily applicable to different species, compared to other methods based on phenological differences [21,22]. Furthermore, improved accuracies might be achieved by using hyperspectral remote sensing data if available, to better discriminate wild leek from other forest floor species, which have been shown to display differences in spectral characteristics [18].…”

“…Knowledge on the phenological differences between vegetation types has been used to detect the presence of invasive exotic species from remote sensing platforms. A study in the Oak Openings Region in Ohio presented a method to map the European buckthorn, an invasive species that develops leaves earlier and remains green later than surrounding vegetation, using Landsat time series [21]. Another study also used Landsat imagery to successfully map the distribution of two understory bamboo species in the Wolong Nature Reserve in China [22].…”