Weed Management after Wildfires

Written By: By Stephanie Larson, Ph.D, Livestock & Range Management Advisor
Published: April 3, 2019

Severe fires can substantially affect the environment. Lack of vegetation on burned hillsides increases the likelihood of soil erosion from rain; in turn, the water quality of streams and rivers is degraded. However, the most environmentally and economically damaging impact of wildfires is the post-fire invasion and aggressive reestablishment of noxious weeds, which compete aggressively with desired native species for space and nutrients. Minimizing the impact of noxious weeds requires good post-burn weed management. Many kinds of native plants will survive and reinitiate growth soon after a fire. The ability of these plants to reestablish, thrive, and reseed in subsequent years will be reduced by the presence of noxious weeds. Unfortunately, noxious weeds can thrive in recently burned areas as fires expose ground surfaces, reduce shade and increase light, and create a flush of nutrients. All of these conditions favor weeds. Wildlife habitat, livestock grazing, watershed stability, and water quality may be compromised, and large-scale infestations of noxious weeds are difficult, and costly, to manage.

To assist in reducing the impacts and invasion of unwanted species, you should develop a rangeland and pasture weed management plan. A successful plan will integrate several control methods, combined with a well-planned strategy to reduce the impact of weeds on rangelands and pastures. The following steps outline such a complete, integrated strategy.

Inventory and mapping – Before a management program, you should assess the extent of the problem. An inventory provides information on the weed species present, the size and density of the infestation, and the characteristics of the site including soil and vegetation complexes. This information is used to identify areas of potential invasion or possible routes of introduction to a specific land area. Once the information is gathered, you can prioritize critical areas for best results when implementing control measures.

Planning and implementation – During the planning and implementation phase, problem areas identified, prioritized and then paired with appropriate solutions. The economic feasibility of the plan should be evaluated to ensure there are adequate resources to implement all phases of the weed management plan, including post-treatment monitoring and evaluation.

Preventing weed encroachment – By far the most cost-effective method of weed management is to prevent the introduction of weeds in the first place. Prevention programs involve limiting weed seed introduction and dispersal, minimizing disturbance, and practicing proper management. Specific ways to prevent new weed introductions are these:
• Create a grazing plan that provides for rotation and rest of desired forage species;
• Manage for diverse vegetative communities, increase species biodiversity;
• Avoid driving through weed-infested areas
• Clean undercarriage of vehicles that have been in weed-infested areas;
• Reduce weeds’ abilities to further spread seeds;
• Minimize soil disturbance when possible; and
• Improve soil health.

Early detection and eradication – Early detection of new weed infestations can facilitate complete eradication of a serious noxious weed before it has a chance to establish on rangelands and  pastures. Understanding the weed’s life cycle will help identify the best control methods.

Containment of large infestations – Once weed infestations become too large to eradicate, containment is the most cost-effective strategy. You should prioritize the areas of most concern. Containment of large-scale infestations is beneficial because it preserves uninfested rangeland by treating the borders of existing infestation and preventing the infestation from spreading beyond its existing boundaries.

Select appropriate control techniques – No single weed control technique is appropriate for all areas in a management unit. Chose control techniques according to available economic resources and the environmental considerations of the area. Specific things to consider when selecting the most appropriate control technique include the target weed species, effectiveness of the control technique, availability of control agents such as insects or grazing animals, land use, timeline of control, environmental considerations, and relative cost of the control techniques. A combination of control techniques may provide better control than a single technique.

Revegetation and proper grazing management – Revegetation with desirable plants may be necessary on sites without an understory of desirable species. These newly established species can minimize the invasion of rangeland weeds and improve the forage quality of the site. A grazing plan, with the goal of moderate grass utilization, will allow ample recovery time between grazing periods for plants to recover and to promote litter accumulation. This is important for maintaining a healthy plant community.

Monitoring and evaluation – Any time a management program is initiated, monitoring and evaluation are key to determining program success and identifying needs for change in the program. Ideally, monitoring will detect changes in both weeds and desirable plants, as well as biological control agent populations and soil characteristics such as erosion, bare ground, and compaction. Many rangeland weeds are difficult to control and require a long-term commitment on the part of the land manager to suppress or eradicate them. The adoption of integrated weed management strategies is the best way to protect uninfested rangeland and pastures and reclaim land with existing weed populations.

To create a landscape resilient to future disasters such as fire, drought or flooding, begin by identifying weed concerns and develop a weed management plan. For further information, contact Stephanie Larson, slarson@ucanr.edu or 707-565-2621.

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