Seedlings established continuously after tree removal, but density did not differ between treatments (see figures at right). Late-seral grand fir was dominant; lodgepole pine and Douglas-fir were far less abundant.

Density declined steeply with distance from edge in many plots (see seedling density maps, below left); local density in the 5-m outer band averaged 682 seedlings/ha vs. 140 seedlings/ha in the remainder of the plot.

Grand fir seedlings were more abundant along S than along N edges (see upper figure, below right). Plot-level density of grand fir seedlings correlated strongly with basal area of grand fir in the adjacent forest (but not with its density or height) (see lower figure, below right).

Seedling density maps

Grand fir seedling density

Burned plot Unburned plot Spatial distributions of total seedling density in two 1-ha experimental plots. North is at the top.

Orientation and distance from edge Mean density (+1 SE) of grand fir seedlings along S vs. N edges of plots. Densities are shown to distances of 10, 20, and 30 m from the edge. P values are from t-tests. Abundance in adjacent forest Relationship between grand fir seedling density and basal area of grand fir in the adjacent forest. Values are plot-level values coded by treatment (burned vs. unburned).

Conclusions

Despite low density of seedlings after 8 years, continuous establishment over time suggests the need for periodic re-entry and removal of seedlings. Fortunately, slow-growing grand fir remains small and can be cut efficiently with hand tools.

Spatial patterns of seedling establishment indicate strong influences of adjacent forests on the reinvasion process. Positive associations with forest edge, shaded N-facing exposures, and tree size (basal area) suggest that removal treatments should be configured to minimize edge effects and to maximize distances to seed sources (particularly larger trees).

Absence of a treatment effect suggests that burning—critical for reducing woody residues following tree removal—does not increase the probability of seedling establishment, at least where late-seral species such as grand fir are the principal colonists.