# Mapping Wild Leek through the Forest Canopy Using a UAV
## 1 Introduction  
_Allium tricocum_, commonly known as wild leek, is a spring ephemeral species of Eastern North America. Wild leek is also present in many parts of Europe, although it is not the same species (sp. _Allium ampeloprasum_). The bulbs of wild leek are edible and widely harvested within its native range in the Eastern United States, Ontario, and Southern Quebec [1; 2; 3]. Due to overharvesting, wild leek is now in decline in many areas; in the province of Quebec only 47 out of 370 populations are considered healthy and in most locations the number of plants harvested remains unregulated, which contributes to the sustained decline of the species [4; 5; 6]. Efforts have been made to identify extinction thresholds and sustainable levels of harvest for wild leek, and to implement guidelines to achieve recovery of the species [5; 7; 8]. In Quebec, wild leek was designated a vulnerable plant species through the Regulation Respecting Threatened or Vulnerable Plant Species and Their Habitats, under which the annual per-person limit to harvest was set to 50 plants for personal consumption [9]. Understory vegetation has been shown to provide food and habitats for wildlife and influence ecosystem functions [10; 11]. Therefore, tracking the distribution of sensitive understory species to document long-term trends is of critical importance [12; 13; 14]. The occurrence of selected species, usually vulnerable and rare species, is currently used as an environmental indicator to assess changes in the ecological integrity of some parks in Southern Quebec [15]. Using rare and endangered species as ameasure of environmental integrity requires the collection and analysis of occurrence data to establish the baseline condition and detect trends of decline or recovery. In Gatineau Park, which contains one of Quebec's largest populations of wild leek [16], wild leek is among a suite of indicators from which broader inferences can be made on the condition of the park. However, due to the lack of an effective and affordable methodology for monitoring wild leek, change in the distribution of the population cannot be assessed [17]. For that reason, developing a method for long-term monitoring of wild leek is important to make better inferences on the health of Gatineau Park's ecosystems and to detect changes in the distribution of this species at risk in protected areas. Dense patches of wild leek are found in deciduous forests dominated by maple and beech, whose branches are bare in early spring (Figure 1). They grow in a variety of environments, on slopes and flat terrain, where they are generally well exposed to light, and on the edges of streams with soils that are humid and rich in minerals [4; 18]. The leaves of the wild leek emerge shortly after the snowmelt, develop and broaden for photosynthetic activity, and senesce in mid-late June with tree canopy closure [19; 20]. The dependency of wild leek on light for growth allows a short time period where the differences in phenology between forest floor species and forest canopy species makes wild leek visible from the air through the canopy. 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]. In those studies, land surface phenology metrics were extracted, where pixels dominated by specific understory vegetation types exhibited distinct signals throughout the course of a year. Such methods require the acquisition of repeated remote sensing information throughout the year, which is more commonly available at coarser spatial resolutions.