As Timberland Converts to Cannabis, Spotted Owls and Barred Owls Test Positive for Rat Poison
70 percent of northern spotted owls and 40 percent of barred owls tested positive for poison
Issue expected to intensify with Proposition 64 recreational marijuana law in effect
Wildlife species are being exposed to high levels of rat poison in northwest California, with illegal marijuana farms the most likely source point, according to a study led by the University of California, Davis, with the California Academy of Sciences.
The study, released Jan. 11 in the journal Avian Conservation and Ecology, showed that seven of the 10 northern spotted owls collected tested positive for rat poison, while 40 percent of 84 barred owls collected also tested positive for the poison.
The study is the first published account of anticoagulant rodenticide in northern spotted owls, which are listed as a threatened species under federal and state Endangered Species acts.
The study area encompasses Humboldt, Mendocino and Del Norte counties. It supports previous accounts that rat poison is contaminating the food web in this region, as the primary food source for owls — rodents — is being contaminated.
Timberland converting to marijuana farms
Driving the issue is the increasing conversion of private timberland into private, illegal and unpermitted marijuana cultivation sites. These sites often overlap with designated critical habitat for northern spotted owls, and the owls feed at their edges.
“Spotted owls are inclined to feed along forest edges. Because grow sites break apart these forest landscapes, they are likely source points for exposure,” said lead author Mourad Gabriel, a research faculty member with the UC Davis Karen C. Drayer Wildlife Health Center within the School of Veterinary Medicine's One Health Institute. He's also executive director of nonprofit Integral Ecology Research Center.
Gabriel's studies in 2012, 2013 and 2015 were the first to link rat poison and illegal marijuana farms to the deaths of fishers, a weasel-like mammal living in remote forests of California and the Pacific Northwest, bringing broad attention to the issue.
Abundance of grow sites, lack of oversight
Proposition 64, which legalizes recreational marijuana in the state, took effect this month. With its arrival, resource managers expect the number and size of unpermitted, private cultivation sites to grow, which could exacerbate the problem.
The study authors note that an estimated 4,500 – 15,000 private cultivation sites are in Humboldt County alone, yet the county has seen legal permits for only a small fraction of them. That means there are thousands of unpermitted private grow sites with no management oversight.
“When you have thousands of unpermitted grows and only a handful of biologists that regulate that for multiple counties, we're deeply concerned that there aren't sufficient conservation protective measures in place,” Gabriel said. “If no one is investigating the level at which private marijuana cultivators are placing chemicals out there, the fragmented forest landscapes created by these sites can serve as source points of exposure for owls and other wildlife.”
Anticoagulant rodenticides inhibit the ability of mammals and birds to recycle vitamin K. This creates a series of clotting and coagulation problems, which can lead to uncontrollable internal bleeding.
Barred owls and added stressors
Barred owls are a physically larger group of owls currently competing for resources and space in critical habitat designated for northern spotted owls. Forty percent, or 34 of 84, of the barred owl tissue samples collected for this study tested positive for anticoagulant rodenticide. The owls are being exposed through the prey they eat.
Environmental contamination, when coupled with ongoing competition from barred owls, poses an additional stressor on northern spotted owls, the study said. The fact that barred owls are contaminated as well shows that the species may be used as potential surrogates for detecting these contaminants in northern spotted owls.
“Access to these owl specimens allows us to explore the health of the entire regional forest system,” says Jack Dumbacher, curator of Ornithology and Mammalogy at the California Academy of Sciences. “We're using our collections to build a concrete scientific case for increased forest monitoring and species protection before it's too late to intervene.”
This study's researchers did not kill any owls for this study. Northern spotted owls were opportunistically collected when found dead in the field, while barred owl tissue samples were provided by outside investigators conducting an unrelated barred-owl project.
The necropsies for this study were conducted at the California Academy of Sciences and the California Animal Health and Food Safety Laboratory System, which is part of the UC Davis School of Veterinary Medicine.
Additional co-authoring institutions include Green Diamond Resource Company, Hoopa Valley Tribe and Humboldt State University.
The study was funded by the United States Fish and Wildlife Service, Arcata and Yreka California Field Offices.
Soon after Van Butsic arrived in California in 2013 to join UC Agriculture and Natural Resources, he noticed a pattern. “Fire, water and weed are the three land-use issues that come up no matter who I talk to in this state,” he said. Fire and water were well-covered by UC and other researchers already. But cannabis looked to be an unexploited niche.
UCCE Assistant Specialist Van Butsic uses satellite imagery to analyze the environmental impacts of cannabis production.
So Butsic, a UC Cooperative Extension (UCCE) assistant specialist in land systems science in the UC Berkeley Department of Environmental Science, Policy and Management, decided to build part of his research portfolio around understanding the scope, intensity and landscape impacts of cannabis cultivation in California (a research paper from another area of his research, ecosystem service valuation, appears on page 81 of this issue).
While the environmental impacts of cannabis production have drawn substantial media attention, and though it is by many estimates the state's most valuable crop, data beyond anecdotes is scarce.
Butsic attacked the problem by visually analyzing satellite-based imagery, identifying remote plantations and greenhouses in Humboldt County and mapping them using GIS.
This approach required many hundreds of hours of manual inspection of satellite images, and one of the first challenges was figuring out how to do this labor-intensive work. It wasn't difficult to find UC Berkeley undergraduates interested in working for course credit. Nearly 25 students have now contributed to the project, and two (so far) have moved on to full-time GIS jobs after graduation. An anonymous nonprofit organization provided financial support for a part-time staff researcher and to purchase more recent high-resolution satellite data.
This series of satellite images shows the development of a greenhouse complex in a Humboldt County forest. Using satellite imagery in combination with GIS layers showing topopgraphy, watercourses, zoning and other variables, Butsic and his colleagues can characterize cannabis production sites in a variety of ways, such as average slope, proximity to streams, and whether they are located on land zoned for agriculture.
The team has built a GIS data layer for about half of Humboldt County's land area, identifying roughly 300,000 cannabis plants (equivalent to a wholesale value of perhaps $150 million) based on 2012 imagery, with an updated estimate now in the works. The data layer enables a variety of analyses — from the zoning of the land used by cannabis growers (only about a quarter of the 1,429 grows identified were on land zoned for agriculture); to the slope of cannabis production plots, a factor influencing erosion (almost a quarter are on very steep ground, with slope exceeding 30%); to proximity to salmon streams (more than 200 grows were found within 100 meters of critical habitat for steelhead and chinook salmon) (Butsic and Brenner 2016).
Butsic and his colleagues identified approximately 4,400 grow sites in their research. Five percent of those, including the site pictured above, were within 100 meters of salmon streams.
Butsic estimates the absolute volume of water used to irrigate cannabis to be fairly modest — on the order of a few thousand acre-feet. But that figure probably understates the habitat impact of water diversions; water is withdrawn from small watersheds during summer months when water is scarce, and some creeks are known to have been completely dewatered.
The information is helping to inform local debates. Humboldt County recently adopted an ordinance requiring all new cannabis grows to be developed on land zoned for agriculture (existing grows on nonagricultural land are grandfathered in). This policy raises concerns about rapid inflation of agricultural land, as cannabis growers bid up prices beyond what other farm or livestock operations can support. Butsic's work provides insights into the characteristics and geography of lands that are likely to be developed for cannabis production.
Forest fragmentation occurs when cannabis growers clear land and build roads to access their grow sites. The Butsic team's analysis indicates that 68% of grows were located more than 500 meters from developed roads.
Related to this issue, Butsic and several Humboldt County–based UCCE academics — County Director Yana Valachovic, Area Fire Advisor Lenya Quinn-Davidson, and Livestock and Natural Resources Advisor Jeffery Stackhouse — are currently surveying Humboldt County landowners about cannabis-related land use issues.
Butsic's next steps include continued mapping of cannabis production in California, with Mendocino County to be completed by the end of 2017. Given the uncertainty around federal restrictions on cannabis production under the Trump administration, Butsic said it's difficult to predict what the most essential research questions surrounding cannabis will be. Nonetheless, “by continuing to document on the ground patterns of cannabis production, we will be in a position to answer those questions,” he said.
Google Earth Image of a cannabis grow site. The resolution of Google Earth images allowed the researchers to detect marijuana plants that were previously missed with other remote sensing techniques.
As policy liberalization rapidly transforms the multi-billion-dollar cannabis agriculture industry in the United States, the need for regulation and assessment of environmental impacts becomes increasingly apparent.
A recent study led by UC Cooperative Extension specialist Van Butsic used high resolution satellite imagery to conduct a systematic survey of cannabis production and to explore its potential ecological consequences.
Published this spring in Environmental Research Letters, the study focused on the “emerald-triangle” in northern California's Humboldt, Mendocino, and Trinity counties, which many believe is the top cannabis-producing region in the United States.
The UC Berkeley-based Butsic and his co-author Jacob Brenner used Google Earth imagery to locate and map grow sites (both greenhouses and outdoor plots) in 60 watersheds. Most cannabis grow sites are very small, and have gone undetected when researchers used automated remote sensing techniques, which are commonly used to detect larger changes such as deforestation.
“We chose to use fine-grained imagery available in Google Earth and to systematically digitize grows by hand, identifying individual plants. Most plants stand out as neat, clear, little circles,” said Brenner, who is on the faculty of the Department of Environmental Studies and Science at Ithaca College. “The method was laborious — it took over 700 hours — but it proved to be highly accurate.”
Butsic and Brenner paired their image analysis with data on the spatial characteristics of the sites (slope, distance to rivers, distance to roads) and information on steelhead trout and Chinook salmon, both of which are listed as threatened species under the federal Endangered Species Act. These and other species are vulnerable to the low water flows, soil erosion, and chemical contamination that can result from nearby agriculture.
Results of the study show 4,428 grow sites, most of which were located on steep slopes far from developed roads. Because these sites will potentially use significant amounts of water and are near the habitat for threatened species, Butsic and Brenner conclude that there is a high risk of negative ecological consequences.
“The overall footprint of the grows is actually quite small [~2 square kiliometers], and the water use is only equivalent to about 100 acres of almonds,” says Butsic, who is in the Department of Environmental Science, Policy, and Management at Berkeley. According to Butsic, California currently has more than one million irrigated acres of almonds.
He stresses that the issue lies in the placement of the sites: “Close to streams, far from roads, and on steep slopes — cannabis may be a case of the right plant being in the wrong place.”
Last year, California legislature passed laws designed to regulate medical marijuana production, and state voters will weigh in on whether to legalize recreational marijuana this coming fall. Given these changes as well as the profitability of cannabis production, Butsic expects that marijuana cultivation will expand into other sites with suitable growing conditions throughout the region. He and Brenner assert that ecological monitoring of these hotspots should be a top priority.
Bills recently signed into law by Governor Jerry Brown have made some advances in this direction — requiring municipalities to develop land use ordinances for cannabis production, forcing growers to obtain permits for water diversions, and requiring a system to track cannabis from when it is first planted until it reaches consumers.
But the researchers say that regulation will likely be a constant challenge because it will rely on monitoring procedures that are just now emerging, as well as voluntary registration from producers and budget allocation from the state for oversight and enforcement.
“Some of the same fundamental challenges that face researchers face regulators as well, primarily that cannabis agriculture remains a semi-clandestine activity,” says Brenner. “It has a legacy of lurking in the shadows. We just don't know — and can't know — where every grow exists or whether every grower is complying with new regulations.”