Introduction
Begin by watching the video below to hear Jeremy Maestas (Sagebrush Ecosystem Specialist, USDA Natural Resource Conservation Service) introduce tools available to land managers for addressing conifer encroachment.
There are a variety of tools available to address the problem of conifer encroachment, both on the desktop and in the field. From the desktop or before going out into the field, very important data layers are now readily available from the Sage Grouse Initiative (http://map.sagegrouseinitiative.com/).
Select a tab below to learn about some of the available layers.
This product provides a high-resolution estimate of tree canopy cover on a per acre basis. Data are in 1m spatial resolution suitable for analysis in a GIS.
Thematic raster data represents tree canopy cover (% cover per acre) in the following classes:
- less than 1% or absent
- 1 - 4%
- 4 - 10%
- 10 - 20%
- 20 - 50%
- greater than 50%
Click to view larger.
Thematic raster data represent resilience and resistance in the following classes:
- 0: Wetland/Riparian
- 1: High
- 2: Moderate
- 3: Low
- Null: Not Available
Click to view larger.
This product represents the probability of cultivation relative to climate, soils, and topography. Independent models were produced for each county and county-level predictions were merged for state coverage. Thematic raster data represents risk in seven classes from low to high.
Click to view larger.
Determining what areas to treat
The Field Guide for selecting the most appropriate treatments recommends considering the following questions to determine which areas to treat (Miller et al. 2014). Click on each question for additional detail.
Generally speaking, areas with higher resilience and resistance have a higher probably of success of any given treatment compared to areas with lower resilience and resistance. Lower resistance and resilience sites may require additional treatments or follow-up.
Areas in PACs or near occupied habitat, specially designated areas such as focal areas, sage-grouse leks, brood-rearing habitat, or winter range should be higher priorities for treatment. Local knowledge on which areas are important can also be very useful in identifying the importance of an area.
Using conifer treatments to create areas of suitable habitat that link otherwise isolated populations is very helpful on a landscape scale.
Leaving juniper debris on the ground after mechanical treatments can intercept runoff and increase infiltration, as well as reduce evaporative loss of soil water (Miller et al. 2007).
Examples of cost-benefit matrices are Table 1 from GBFS #4, “Common conifer treatment options, costs, and trade-offs” or SageSTEP “Guide to Vegetation Treatment Costs for Land Management in the Great Basin Region".
Retreatment is more likely on low resistance and resilience sites.
Many restoration treatments by either mechanical means or prescribed fire require adequate post-treatment grazing management to be successful.
Identifying Treatment Sites
Begin by watching the video on the right to hear advice on conifer removal from Jeremy Maestes.
- When determining which sites should undergo treatment for removal of conifers it is important to prioritize sites that have an understory composition that is sufficient for shrub-steppe plant communities to recover without requiring additional seeding or weed control.
- Conifer removal treatments should be focused on early encroachment stands in and around landscapes that have existing sage-grouse leks (Science to Solutions #1, Baruch-Mordo et al. 2013).
- Prioritizing Phase I stands for complete removal of conifers will likely prove the most effective for restoring and sustaining habitat.
- Treating early Phase II stands can also prevent conversion to conifer woodlands and help functionally restore sagebrush habitat for several decades.
- Warmer and drier sites, later phase conifer stands, and sites with depleted perennial grasses, are less resilient to disturbance and may be good candidates for post-treatment weed control and seeding.
- Prescribed fire or slash pile burning may increase the likelihood of invasive plant introduction so the need for weed control and seeding of slash piles should be evaluated, especially when fire severity is high.
- After fire or seeding, at least two years of rest is recommended; warmer and drier sites may require even longer periods of rest or growing season deferment during the critical perennial grass growth period (April-July).
- Planning a maintenance cut five years after the initial treatment is a cost-effective approach that will extend the lifespan of projects for many decades.
To help with determining treatment sites consider using maps of tree cover, combined with lek locations to help identify areas to target.
For example, this figure shows a map delineating potential treatment areas in central Oregon (from Great Basin Fact Sheet #4). Areas with high conifer cover are shown in purple and dark blue and known lek locations are indicated with a green dot. Potential treatment areas, outlined in the black and white lines, have been specifically delineated to be near known lek locations and to encompass areas with a low % of conifer cover. The references cited earlier suggested these areas will have the highest probability of success in terms of restoring habitat value for sage-grouse.
Field Tools And Techniques
Once the treatment areas have been identified, there are a variety of tools that may be used for treatment of conifer encroached areas.
Before exploring the various tools, listen to Rick Miller describe the tools for managers dealing with conifer encroachment.
Mechanical tools that surgically remove trees while retaining the shrub community and understory cover are the best options. Mechanical tools include chipping, shredding, and combinations of these tools. In general chaining is not recommended as it often causes sagebrush removal as well.
Advantages of Mechanical Treatments:
- Can maintain a desired level of the shrub component and be selective in which trees are targeted
- Some methods cause minimal soil disturbances
- Boundaries of the area treated are easily controlled and there is a broad time period when treatments can be applied
- Liability is minimal and mechanical treatments can be successfully used near the wildland urban interface
- Light surface disturbance also can enhance the seedbed for seedling establishment and have minimal impacts on soil biological crusts
Disadvantages of Mechanical Treatments:
- Can leave large amounts of woody debris
- Can result in high soil disturbance (compaction or soil surface movement) which can lead to increases in non-natives such as cheatgrass
- Typically have a high cost/acre, take longer to treat large areas, and some equipment is limited by steepness and roughness of the terrain
- Clearance costs on federal lands may be higher per acre, especially for archeological surveys if increased surface disturbance is expected
When to use Mechanical Treatments:
(Miller et al. 2014)
- Resilience and resistant scores are < 15 (very low or low) but sufficient perennial herbaceous species occur to promote recovery.
- It is desirable to retain the shrub layer.
- Species of concern will be more impacted by fire than mechanical treatment due to low fire tolerance or change in vegetation structure and composition.
- If the area being evaluated is cool (frigid) and aridic (10 to 12 inches ppt) or xeric (<12 inches ppt), then either low to moderate severity mechanical treatments can be considered when sufficient perennial herbaceous species exist to promote recovery.
Prescribed fire is a tool for controlling conifer expansion. Key considerations include the extent of treatment, site resilience, species composition, and spatial distribution of fire. While prescribed fire is a cost effective tool for greatly reducing woodland cover, the full restoration of shrub-steppe communities from mature woodland is a long-term process. Mechanical removal of conifers where sagebrush is still intact can produce more immediate benefits for sagebrush wildlife and should be considered first.
Watch Jeremy Maestas explain when to use prescribed fire as a treatment.
Advantages of Prescribed Fire:
- Often the most economical treatment and large areas can be treated
- Usually results in a longer time interval before retreatment is required
- Severity can be controlled somewhat by the prescription, which includes pre-fire fuel treatments and weather conditions at the time of the fire
- Conifer seedlings are typically killed by fire
Disadvantages of Prescribed Fire:
- Greater risk of invasive annual species dominance in low to mid elevation sites (mesic and dry-aridic soils)
- Reduces or eliminates shrubs, especially those that are fire intolerant (e.g., big sagebrush subspecies) with a lag time between fire and reestablishment
- Results in a significant reduction in soil biological crusts
- Includes potential liability issues and concerns such as smoke, wildlife, the urban interface, and increased costs
When to use Prescribed Fire:
(Miller et al. 2014)
- Resilience and resistance scores are > 20 (high); these are typically cool/moist ecological sites occupied by mountain big sagebrush.
- Large areas need to be treated.
- Funds are limited.
- If the area being evaluated is cool (frigid) and aridic (10 to 12 inches ppt) or xeric (> 12 inches ppt), then either low to moderate severity prescribed fires can be considered when sufficient perennial herbaceous species exist to promote recovery.
- If the area being evaluated is dry-aridic (< 10 inches ppt), the use of fire should be discouraged.
- If the area is aridic (10 to 12 inches ppt) and perennial herbaceous vegetation is depleted, the use of fire should be discouraged unless reseeding follows immediately after the fire and the soil temperature + moisture score is > 10.
- If the area is a priority area for conservation of sage-grouse but sagebrush cover is a limiting factor at the landscape scale, reseeding or transplanting sagebrush should be considered if prescribed fire is used.
- Burning is applied mindfully to retain sagebrush, such as treating slash piles or burning small patches of conifers. This can be described as “patch burning” as opposed to “broadcast burning.”
Deciding not to treat is an acceptable decision in some cases! For example:
- Chemical (herbicide) treatments may be needed or useful in some areas, especially for follow-up control of sprouting species; however, chemical treatment should only be used on sites where the herbicide will work as intended
- Seeding may be needed to fully restore a site after conifer treatments, but the decision to seed should be based on (1) ecological site characteristics that strongly contribute to degree of success, and (2) current composition and structure of native and invasive species. Seeding success varies across ecological sites:
- Native seeding success on severely depleted ecological sites with warm-mesic to mesic and dry-aridic (< 10 inches ppt) soil temperature/moisture regimes is extremely low. Using introduced wheatgrasses can slightly improve seeding success on these sites but may not meet management objectives.
- Seeding success on cool-me¬sic/aridic ecological sites (10 to 12 inches ppt) is usually mixed and is highly dependent on annual moisture in the first 2 to 3 years following treatment.
- Seeding success on frigid/xeric ecological sites (score = 14-17) is typically high.
- Environmental factors such as precipitation timing and amount, which cannot be controlled nor predicted, can affect seeding success even on cool-mesic/aridic and frigid/xeric ecological sites.
Click Case Studies to review land management actions in practice.