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Ecology and restoration of conifer-invaded meadows:
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Home > Research > 3. Gopher disturbance > 3B. Community structure
     
3B. Contributions of gopher mounds and castings
to meadow community structure
 
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From the senior thesis of

Maddy Case

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Introduction

This work extends our earlier, chronosequence-based study of mound succession to address effects at larger spatial scales and to assess the role of winter castings (figure, right)—largely ignored in previous studies of gopher disturbance and plant community structure.

We hypothesized that patterns observed at the scale of mounds would extend to larger spatial scales. Specifically,
  • greater disturbance would reduce plant cover, graminoid dominance, and species richness, but increase heterogeneity (spatial variation in species composition)
  • both mounds and castings would contribute to these effects, but castings less so, due to their smaller size and ephemeral nature
Methods

Sampling

Four plots (5 x 20 m) were established in three meadows of differing composition. All plots had moderate but variable levels of gopher disturbance. Each plot was sampled with twenty 5 m transects; each transect consisted of 25 contiguous 20 x 20 cm quadrats (see photos, below).

Following snowmelt we estimated cover (%) of mounds (>1 yr old) and castings. Several weeks later, we estimated cover of forb and graminoid species.

Analyses

Mixed-effects models were used to assess the relationships between disturbance (cover of mounds, castings, or their sum) and three measures of community structure:
  • Plant cover (total, forbs, graminoids, and forb:graminoid ratio)
  • Richness (number of species per transect)
  • Heterogeneity (mean Bray-Curtis dissimilarity between pairs of quadrats)
    Top
Types of gopher disturbance
Mounds
Mounds
Gophers form mounds as they dig tunnels and push loose soil to the surface.
Castings
Soil castings form under winter snowpack. Gophers move soil into snow tunnels which are then exposed by spring snowmelt.

Sampling
Plot with transect flags Sampling quadrat
One of four sample plots after snow melt. Pink flags mark the ends of the twenty 5-m transects.
Sampling a quadrat (20 x 20 cm).
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