Bunchgrass Ridge

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

     
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2C. Composition and dynamics of the soil seed bank
 
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1. Conifer invasion
 
2. Vegetation responses
 
A. Effects of conifer encroachment
B. Effects of tree age & species
C. Seed bank composition
 
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From the thesis of
Nicole Lang
Nicki Lang
 
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Introduction

Soil seed banks contribute to the diversity and dynamics of many plant communities. In some systems they are critical for maintaining species’ populations or restoring native plant communities. [Conceptual model]

We examined the composition of the soil seed bank at Bunchgrass Ridge to determine whether meadow species maintain viable seeds in the soil, and by implication, whether the seed bank can contribute to meadow restoration if conifers are removed.

We addressed the following questions:
  • Do meadow species maintain viable seeds in the soil?
  • Do the density and diversity of seeds decline as meadow is replaced by forest?
  • What types of species dominate the seed bank?
  • What is the potential for seed banks to contribute to meadow restoration if trees are removed?
Methods
Collecting soil samples
Collecting seedbank samples

Field sampling. Samples of the soil seed bank were taken in May 2004 from subplots also sampled for forest age structure and ground vegetation. A total of 209 subplots was sampled.

Sampling was stratified, using a simplification of the chronosequence to represent three distinct stages of encroachment: open meadow, young forest, and old forest (see table, right).

In May 2004, three soil cores (6 cm in diameter and 10 cm deep) were extracted from each subplot and combined (~850 cm3/subplot). In Jul and Aug 2004, above-ground vegetation was sampled in the same subplots.

Analyses. Germinants were tallied into one of three groups defined by habitat affinity: ruderal, meadow, and forest understory species (see Plant species list). For each group, ANOVA or Kruskal-Wallis tests were used to assess differences in species richness (number of taxa per subplot) or germinant density among the three stages of encroachment.

Greenhouse methods
Germination flats
Germination flats
Soil samples were mixed with sterile potting soil and placed in germination flats in the University of Washington greenhouse. Seedling emergence was monitored for seven months.


Light availability, tree density, and basal area among open meadow, young forest, and old forest subplots.
Structural variable Open
meadow
Young
forest
Old
forest
Transmitted light (%)
46
22
17
Tree density (no./ha)
96
1,552
1,172
Basal area (m2/ha)
6
36
116
Lang, N. L., and C. B. Halpern. 2007. The soil seed bank of a montane meadow: consequences of conifer encroachment and implications for restoration. Canadian Journal of Botany 85:557-569. Download PDF
Conceptual model of seed accumulation and loss
during the transition from meadow to forest.
Conceptual model of seed accumulation and loss
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