Best Management Practices for Silvicultural Chemicals and the Science Behind Them

Abstract

Silvicultural chemicals include fertilizers and pesticides applied for forest management. All states east of the Rockies have at least some form of silvicultural chemical best management practices (SCBMPs) and it is widely accepted that SCBMPs effect some protection of water quality. All SCBMPs recommend handling and application precautions and a minimum width streamside management zone (SMZ) on each side of streams for protection of water quality and aquatic ecosystems. Typically these zones increase in width as stream width increases. In areas where cold-water fish are present, additional widths are designated for their protection. Minimum SMZ widths range from 8 to 91 meters on each side of the stream bank for intermittent and perennial streams. Most SMZ recommendations do not cover ephemeral drainages, ditches or canals. SMZs are generally described as being site specific with width dependent on slope, soil type and other conditions as well as the stream's designation as perennial or intermittent. The science behind SCBMPs is often elusive. Spray drift can be controlled through proper selection and use of application technology while considering site specific conditions. SMZs greatly reduce the amount of herbicides reaching streams. Available toxicological data and research on aquatic ecosystem impacts from herbicide use suggest that additional protection from silvicultural chemicals may not be necessary. However, there is evidence to suggest that protection of ephemeral and intermittent channels can further reduce entry of silvicultural chemicals into streams and also reduce sedimentation. This may be the most fruitful area of research we can pursue in light of the knowledge gaps listed.