Removing forest, grasslands, or other existing habitats for cannabis cultivation can cause wide-ranging impacts on terrestrial and aquatic ecosystems. These impacts include loss and fragmentation of sensitive habitat due to road construction, grading and burying of streams, increased sediment delivery, and erosion.
Tree and vegetation removal reduces habitat availability, nutrient cycling and moisture retention. In addition, removal of trees and root structures destabilizes surrounding soil, increasing the likelihood of landslides and stream sedimentation. These changes cause wildlife to move considerable distances to find food, shelter, and breed. Clearing landscapes or placement of fencing disconnects habitats (habitat fragmentation) and disrupts fish and wildlife behavior. In the short-term, loss of connectivity between habitats causes problems for migratory animals. Long-term, loss of habitat connectivity reduces fish and wildlife's ability to adapt to climate change.
Well-planned cannabis cultivation sites can minimize habitat loss and habitat fragmentation, avoid sensitive habitats, and protect fish and wildlife.
Water is a precious resource that fish and wildlife species rely on for survival. Cannabis cultivation can significantly affect water availability. Additionally, cannabis cultivation occurs during California's dry season when water availability is significantly decreased. In many areas, water demand for cultivation already exceeds the amount of water available. As climate change progresses, California can expect increases in water scarcity and drought.
Reduced or altered stream flows can threaten fish and wildlife. Water demands for cultivation can significantly reduce spring flows, which are critical to migrating fish. In addition, loss of spring flows and agricultural water use in summer can quickly reduce water available for fish and wildlife. Reduced stream flows may cause many issues:
- Interference with salmon spawning, migration, and rearing;
- Reduction in sensitive species habitat availability and habitat complexity;
- Loss of watering holes for wildlife;
- Decrease in food supply, food production, and dissolved oxygen for aquatic wildlife;
- Increase in water temperature, disease transition, and physiological stress; and
- Increase in turbidity, suspended sediment, and algal blooms.
Cultivators can take actions to protect streams, and wildlife and their habitats. Ensure you are using best practices for water conservation and water storage. Screen your diversion point to protect fish and wildlife. Use drip irrigation and store winter water for use in summer to conserve water.
Contact the State Water Quality Control Board for additional information on water conservation.
Construction of dams and stream crossings used for cannabis cultivation can cause erosion and degrade water quality and associated wildlife habitats (Santucci et al., 2005). For example, breeding populations of foothill yellow-legged frogs are five times smaller in streams that have dams (Kupferberg et al., 2012). Also, these constructions can impact the flow regime of the streams which can have a negative impact on salmonid species.
Pesticides and fertilizers can have significant impacts on the environment. All agriculture, including cannabis cultivation, must use legal pesticides as directed by the manufacturer, CDFW, or California Department of Pesticide Regulation (CDPR). Improper pesticide use can cause pollution, destruction of sensitive habitats, and fish and wildlife injury or death.
Cultivators can protect California's natural resources by choosing legal pesticides and using them as directed by the manufacturer, CDFW, or CDPR. Cultivators can avoid pollution, wildlife loss, and other environmental impacts by minimizing pesticide use, using appropriate pesticide application according the the manufacturer's label, and ensuring proper pesticide storage. A list of legal pesticides (PDF) approved for use in cannabis cultivation, as well as a list of pesticides that cannot be used (PDF) on cannabis are available from CDPR.
One of the biggest threats to wildlife associated with cannabis cultivation is the use of banned pesticides, or the misuse of legal ones. Anticoagulant rodenticides and other pesticides can bioaccumulate in tissues, often taking weeks to reach lethal concentrations, leading to a longer exposure period for predators (Franklin et al., 2018). Consumption of these pesticides may not always kill the animal, but even low doses can lead to reduced immune response, decreased reproductive potential, and increased susceptibility to predation (Thompson et al., 2014). Use of rodenticides also cause adverse impacts to soil and water quality. To learn more about rodent control that is safer for wildlife, visit CDFW's rodenticide page and Raptors are the Solution.
Insecticides and Herbicides
Insecticides and herbicides can also threaten wildlife. Some species are directly poisoned by them (Berny, 2007; Pimentel, 2005). But even when pesticides are not lethal, they can cause numerous problems like compromising the immune system, altering the development of reproductive organs, and slowing growth rates (Kiesecker, 2002; Tiemann, 2008; Relyea and Diecks, 2008). Similarly to rodenticides, wildlife may also be poisoned when they consume prey or plants that have been treated with insecticides or herbicides (Berny, 2007; Freemark and Boutin, 1995).
Fertilizers can help your plants grow, but they can also increase the abundance of pests and pathogens, including diseases. When excess fertilizers run-off into watersheds, they can have negative consequences for wildlife. They can cause algae outbreaks which deplete the water of oxygen, suffocating fish and other aquatic life.
Light pollution can have negative ecological impacts. Light pollution from artificial light refers to direct glare, increases in light intensity and duration, and unexpected fluctuations in light (Gaston, 2013). Artificial lights are often on at times that are normally dark and can be brighter than moonlight. Changes in light and dark cycles can influence plants, insects, fish, birds, and wildlife, causing changes to species life cycles as well as changes to terrestrial and aquatic ecosystems (Longcore, 2004). Specifically, artificial lights:
- Interfere with detection of circadian, lunar, and seasonal cycles (Gaston, 2013);
- Interfere with food and predator identification (Gaston, 2013);
- Interfere with navigation and orientation (Gaston, 2013);
- Cause changes in movement, foraging, reproduction, communication, and other critical behaviors (Longcore, 2004); and
- Cause physiological changes.
Frogs and salamanders are particularly susceptible to artificial light pollution. Light pollution "may affect physiology, behavior, ecology, and evolution of frog and salamander populations" (Wise, 2007). For example, artificial light levels and timing influences melatonin production in salamanders. Melatonin regulates hormones, reproductive development and behavior, skin coloration, an animal's ability to regulate body temperature, and night vision (Gern, 1983).
Changes in individual frogs, such as timing delays in transitioning from tadpole to frog, can affect that individual's ability to survive. Remaining a tadpole longer may result in waterbodies becoming dry before metamorphosis can occur, increased predation, and reduced survival. Reduced survival at the population level can result in smaller populations or populations that disappear altogether. Ecological light pollution affects entire communities, not just individuals, and puts many species at risk.
Take steps to reduce light pollution from your cultivation site. Consider using black-out curtains in greenhouses and reducing non-essential lighting.
Cannabis cultivation sites often have substantial amounts of noise pollution resulting from road use, generators, and other equipment. This is a concern because wildlife may respond to noise at exposure levels as low as 55-60 dB (Barber et al., 2009). For reference, normal conversation is approximately 60 dB. Noise pollution can disrupt the communication of many wildlife species like birds and frogs (Patricelli and Blickley, 2006; Parris et al., 2009). It can also increase levels of stress hormones in species such as the Northern spotted owl (Hayward et al., 2011). Bats have reduced foraging success in areas with chronic noise, and this has been correlated to the decline of 12 species of bat in California that are either endangered or of special concern (Schaub et al., 2008).