Bunchgrass Ridge

Ecology and restoration of conifer-invaded meadows:
Research and adaptive management

     
Home > Research > 4. Restoration experiment > Results: Question 2
     
4. Experimental restoration of meadow communities
 
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1. Conifer invasion
2. Vegetation responses
3. Gopher disturbance
4. Restoration experiment
 
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  Q1. Tree removal
> Q2. Fuel-reduction methods
  Q3. Duration of tree influence
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Gopher disturbance

Western pocket gopher photo courtesy UW Burke Museum
 
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Question 2. Are there adverse effects of fuel-reduction methods (broadcast burn or pile-and-burn)
on soil properties or on establishment of undesirable species?

Soil physical or chemical properties

Effects of fuel-reduction methods

Broadcast burning resulted in signficant exposure of mineral soil (figure below: Bare ground), but the predominance of charred litter indicated low-severity fire (top-right photo) indicated low-severity fire. The only substantial change to soil chemistry was a transient increase in available N (figure below: Total available N). In contrast, tree removal alone (unburned) did not affect soil properties.
Soil properties
Effects of treatments on bare ground, total N over time
Effects of fuel-reduction methods on soil properties, one and three years after treatment. Values are plot means (+1 SE, n = 3). Letters denote significant differences among means within years.

Local effects of burn piles

Pile burning created intense, but localized scarring (white ash and reddened mineral soil; photos, right), but only the centers of scars showed signs of severe burning. Initially, the concentration of available N was more than twice that of broadcast-burned plots and four times that of unburned plots (figure below: Total available N). By year 3 (2009), however, available N was markedly reduced.

Similarly, plant recovery within scars was rapid around the edges and dominated by meadow species (figure below: Plant responses).
Local effects of burn piles
Local effects of burn piles on bare ground, meadow and forest species, and total N
Effects of burn piles on soil properties and plant responses, one and three years after treatment. Values are plot means (+1 SE, n = 3). Letters denote significant differences among means within years.

Effects of soil disturbance by gophers on recovery from burning

Tunneling and mounding by gophers (Thomomys mazama) are disturbances that are integral to the community structure of these herb-dominated habitats (see Gopher disturbance). Far less active in the forest, gophers readily disperse into openings created by tree removal and fire. Evidence of their disturbance (mounds and castings) increased over time (figures, below).

Mixing of sub-surface and surface soils led to rapid healing of burns scars, dampening the physical and chemical effects of fire in both broadcast- and pile-burned plots (photos, right; figures, below). Deposition of mineral soil on the surface may benefit plant establishment.

Thus tree removal, through its influence on gopher populations, may be more critical to the restoration of these meadows than any short-term benefit (or adverse effects) of fire.
Soil disturbance by gophers
Cover of gopher disturbance among treatments and within burn piles over time
Soil disturbance by gophers among treatments (left) and in and adjacent to burn piles (right), one and three years after treatment. Values are means (+1 SE). For both comparisons, gopher disturbance increased over time, but did not differ among treatments or by position (Pos) within burn scars.

TopEstablishment of undesirable species

Ruderal or exotic species

Ruderals were surprisingly sparse in the post-treatment vegetation, despite their abundance in the seed bank, and the potential for fire to promote their establishment.

However, Rumex acetosella (present prior to disturbance), has expanded in several scattered locations (photo, right), and should be monitored in the future.

Conifer seedlings

We anticipated greater recruitment of conifers in burned than in unburned plots, due to a preference for mineral soil as a substrate for germination.

However, seedlings densities were low (<0.05 seedlings/m2 in 2009) and comparable between treatments, suggesting limited importance of re-invasion by conifers in the short-term.

However, where conifers have established (primarily near the edges of experimental plots), height growth has been substantial (photo, right). Because propagule pressure remains high and potential germination sites are plentiful, conifer recruitment should be monitored in the future.

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On this page:
Soil properties
  Fuel-reduction methods
  Burn-pile scars
  Gopher disturbance
Undesirable species
  Ruderal/exotic species
  Conifer seedlings

Ground-surface conditions
following fuel reduction
Broadcast burning
Ground surface-broadcast burning
Note charred litter and absence of unburned ground.
Pile burning
Ground surface-pile burning
Note burn-pile scars and predominance of unburned ground.
Burn-pile scar
Burn-pile scar
Note white ash and reddened mineral soil (center) and blackened litter (edges).

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Gophers mediate
effects of prescribed fire
Broadcast burning
Gopher mounds in broadcast-burned plot
Year 1
Burn piles
Burn pile scar year 1
Year 1
Burn pile scar with gopher disturbance year 3
Year 4
 
Undesirable species
Exotic species--Rumex acetosella
Rumex acetosella
Grand fir seedlings year 5
Grand fir seedlings, year 5 (2011)
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