Bunchgrass Ridge

Ecology and restoration of conifer-invaded meadows:
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2A. Effects of conifer encroachment: a chronosequence approach
 
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A. Effects of conifer encroachment
 
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B. Effects of tree age & species
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From the thesis of
Ryan Haugo
Ryan Haugo
 
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Introduction

In this study, we used a chronosequence approach to explore the process of vegetation change as meadows are replaced by forests. Bunchgrass Ridge provides an ideal setting for this approach: open meadows and forests of vary age (young to old) lie in close proximity, sharing similar topography and soils. We asked the following questions:

  • How do the composition, abundance, and richness of meadow and forest understory species change during the transition from open meadow to old forest?
  • How rapidly, and to what extent, are meadow species lost from these systems?
  • How quickly do forest species colonize and how does composition change with forest age?
  • Which attributes of forest structure (light availability, tree density, basal area) exhibit the strongest controls on meadow and forest species?
Methods

Field sampling. Sampling was conducted within the 1-ha plots used to reconstruct tree invasion history at Bunchgrass Ridge, and in adjacent meadow openings. We sampled a total of 356, 10 x 10 m subplots. (See subplot sampling design, below.) Within each subplot we measured the following:

  • forest structure (density and basal area by tree species)
  • light availability (hemispherical photos)
  • cover of all plant species (1m2 quadrats)

Analyses. We grouped subplots into seven encroachment classes by similarity in age structure, using an agglomerative, hierarchical classification. (See box, right)

Plant species were classified into two groups, based on habitat affinity (see Plant species list):

  • meadow species (n = 43)
  • forest understory species (n = 48)
For each group of species, we calculated total cover and richness of each of the seven encroachment classes.
Subplot sampling design
Veg subplot sampling design
Encroachment classes
Tree-encroachment classes
Haugo, R. D., and C. B. Halpern. 2007. Vegetation responses to conifer encroachment in a dry, montane meadow: a chronosequence approach. Canadian Journal of Botany 85:285-298. Download PDF
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