Individual trees that establish in open meadows can exert strong effects on local vegetation. In a companion study to the chronosequence analysis, we posed the following questions:

• How does tree age (i.e., duration of influence) affect the cover and richness of meadow and forest understory species?
• Are effects of individual trees more pronounced on meadow or forest species?
• Do lodgepole pine and grand fir differ in their effects on meadow or forest species?

Field sampling. From areas of open meadow, we selected 39 lodgepole pine and 46 grand fir (>1.4 m tall) of a range of sizes and ages (20-70 yr).

From the base of each tree, ground vegetation was sampled with a transect extending to the SW and NE. Each transect was sampled in two equal lengths—under the canopy and in open meadow—(photo, above right), using a series of 20 x 50 cm quadrats (photo, below right). Within each quadrat, we estimated cover of each plant species.

Analyses. Plant species were classified into two groups, based on habitat affinity (meadow and forest understory; see Plant species list)

For each quadrat we tallied the number, and summed the cover of forest and meadow species. Effects of individual trees were expressed as the mean difference between under-canopy and open-meadow quadrats. General linear models were then used to test effects of tree age and tree species on each measure of response.