Cutting to the Chase: Conifer Removal Success Depends on Cutting AND Burning
The following is a segment of an Ask an Expert article written by the USDA’s Working Lands for Wildlife Sage Grouse Initiative republished here with permission.
Tree encroachment is one of the biggest threats facing sagebrush and grassland landscapes. Even as few as one or two trees per acre cause sage grouse and lesser prairie-chickens to abandon otherwise suitable habitat. Additionally, encroaching conifers suck up water that sustains native forbs and grasses, reduce biodiversity, and increase fire severity in sagebrush and prairie landscapes.
New research done in partnership between the USDA’s Agricultural Research Service (USDA-ARS), Oregon State University and The Nature Conservancy explored the question: What are the most effective methods for removing conifer trees? Specifically, the researchers examined whether burning encroaching conifers or removing them mechanically proved more effective for long-term sagebrush-steppe restoration.
To better understand this study and its conclusions, the Sage Grouse Initiative reached out to two of the study’s principal authors, Kirk Davies and Chad Boyd, both from the USDA-ARS.
ASK AN EXPERT:
What was the main goal of your research?
Our goal was to compare cutting and prescribed fire as juniper management tools with respect to how long it takes juniper to return following treatment and the effects of treatment on non-target vegetation like shrubs and grasses.
Your paper notes that fire played a key role in maintaining healthy sagebrush landscapes historically because it prevented woody species like juniper trees from expanding into sagebrush-steppe landscapes. That’s no longer happening. Why not?
A couple of things. First, historical grazing during the latter 1800’s and early 1900’s was very different than the seasonal grazing and periodic rest practiced today. Records from the northern Great Basin indicate that historical stocking levels often exceeded carrying capacity and grazing often took place on a year-round basis. Additionally, historical grazing on public domain lands was first-come-first-served, which created a competitive environment for forage resources among grazers. These historical practices created a severe reduction in fine fuels which decreased fire frequency within the juniper zone.
Published data indicate that it was during this relatively fire-free period that juniper establishment increased dramatically. Following World War II, an influx of surplus vehicles, aircraft, and equipment greatly increased the effectiveness of fire-suppression operations, further diminishing the presence of fire within the juniper zone and allowing for reproduction and expansion of juniper populations. Continued effective fire suppression has allowed even more juniper expansion in sagebrush communities.
Are there potentially negative impacts from using fire to control woody plants in sagebrush country?
We see fire as one tool in the toolbox. In rangeland management, silver bullets don’t exist, and all tools need to be applied within a context that makes sense relative to a management objective. For example, if patches of juniper are encroaching into otherwise intact plant communities within priority sage-grouse habitat, and if management has the logistical and financial capacity to control juniper with cutting, then cutting might make more sense than fire. Alternatively, if a larger landscape has been encroached by juniper to the extent that it no longer functions as sage-grouse habitat, then fire might make more sense. Bottom line, keep all the tools in the tool box and use those tools where they make most sense relative to management objectives.
Managers who are considering using prescribed fire to control juniper have to think carefully about the condition of the understory and what that might mean to post-fire recovery dynamics. For example, in areas where juniper woodland development has proceeded to the point of closed juniper stands, the understory conditions are diminished. When this diminished understory experiences a severe fire (due to heavy woody fuel loading from the dense juniper stands), extended post-fire recovery periods are often the result, making prescribed fire a potentially risky proposition. These types of situations may require additional treatments such as seeding understory species and possibly weed control.
Exotic annual grasses like cheatgrass, medusahead, and ventenata are a real threat to the sagebrush sea, and I’ve read that they can infest areas following fires. Is there a way to use fire without exacerbating the annual grass problem facing our western rangelands?
The ecology of the sagebrush biome has been fundamentally altered relative to the pre-European period. Probably the biggest change has been the increase in exotic annual grasses in low to mid elevations. Thus, managers have to consider the risk of post-treatment increases in exotic annual grasses. Managers should evaluate local site factors such as elevation, aspect, and understory conditions when considering the use of prescribed fire or cutting for controlling juniper. Generally speaking, hotter and drier sites will have increased potential for post-treatment annual grass expression. In areas at risk of post-treatment increases in exotic annual grasses, research has shown that seeding perennial understory species (particularly bunchgrasses) can greatly limit exotic annual grasses.
Why do fire treatments produce longer-lasting results that simply cutting conifers?
Two reasons. First, fire decreases the juniper seedbank and cutting does not. If fires burn completely, juniper seeds are effectively removed from the area. The net effect is to delay the onset of juniper succession and increase effective lifetime of fire-treated areas relative to cut areas. Second, cutting often misses very small juniper seedlings, fire generally does not. Following cutting, these small seedlings are released from competition with larger trees and often grow at accelerated rates which decreases the treatment lifetime.
Were there any surprises that came from your research?
Yes, one surprise was the lack of an increase in exotic annual grasses with fire compared with cutting. This is probably because site conditions and perennial bunchgrass abundance largely determine exotic annual grass response to juniper removal, not individual treatments.