Distribution of trespass cannabis cultivation and its risk to sensitive forest predators in California and Southern Oregon

Abstract

Illegal cannabis cultivation on public lands has emerged as a major threat to wildlife in California and southern Oregon due to the rampant use of pesticides, habitat destruction, and water diversions associated with trespass grow sites. The spatial distribution of cultivation sites, and the factors influencing where they are placed, remain largely unknown due to covert siting practices and limited surveillance funding. We obtained cannabis grow-site locality data from law enforcement agencies and used them to model the potential distribution of cultivation sites in forested regions of California and southern Oregon using maximum entropy (MaxEnt) methods. We mapped the likely distribution of trespass cannabis cultivation sites and identified environmental variables influencing where growers establish their plots to better understand the cumulative impacts of trespass cannabis cultivation on wildlife. We overlaid the resulting grow-site risk maps with habitat distribution maps for three forest species of conservation concern: Pacific fisher (Pekania pennanti), Humboldt marten (Martes caurina humboldtensis), and northern spotted owl (Strix occidentalis caurina). Results indicate that cannabis cultivation is fairly predictably distributed on public lands in low to mid-elevation (~800-1600m) forests and on moderate slopes (~30–60%). Somewhat paradoxically, results also suggest that growers either preferred sites inside of recently disturbed vegetation (especially those burned 8–12 years prior to cultivation) or well outside (>500m) of recent disturbance, perhaps indicating avoidance of open edges. We ground-truthed the model by surveying randomly selected stream courses for cultivation site presence in subsets of the modeling region and found previously undiscovered sites mostly within areas with predicted high likelihood of grow-site occurrence. Moderate to high-likelihood areas of trespass cultivation overlapped with 40 to 48% of modeled habitats of the three sensitive species. For the endangered southern Sierra Nevada fisher population, moderate-high likelihood growing areas overlapped with over 37% of modeled fisher denning habitat and with 100% of annual female fisher home ranges (mean overlap = 48.0% + 27.0 SD; n = 134) in two intensively studied populations on the Sierra National Forest. Locating and reclaiming contaminated cannabis grow sites by removing all environmental contaminants should be a high priority for resource managers.

Conservation of rare and cryptic species: Challenges of uncertainty and opportunities for progress

“…Many species are affected by chronic threats that are difficult to mitigate, emerging threats that are poorly understood, or the interaction of multiple threats that may have dire consequences (Brook et al, 2008). In our case study, contemporary threats to small and disparate Humboldt marten populations include disease outbreaks (e.g., Smith et al, 2006), reduced genetic diversity (e.g., Lino et al, 2019), habitat loss due to increased wildfire (e.g., Abatzoglou et al, 2021), and exposure to anticoagulant rodenticides (e.g., Martin et al, 2022; Wengert et al, 2021). Addressing threats and supporting species recovery is imperative, but difficult when faced with limited funding, complicated logistics, and regulatory hurdles.…”

Species Distribution ofCannabis sativa: Past, Present and future

“…As outdoor cultivation becomes the standard practice species distribution maps can help define and rank the importance of critical environmental properties and identify where these suitable environments may exist around the world currently and how they are likely to be affected by changing climate in the future. Further, there has been increased scientific interest in the last decade around understanding the soil determinants important for Cannabis cultivation (Wengert et al, 2021). Identifying the best climatic and soil conditions for growth informs nutrient and water management and approaches such as species distribution modeling (SDM) providing a means for more informed land selection that may facilitate minimizing negative environmental externalities (Mehrabi et al, 2019).…”