III. Characteristics of Lodgepole Pine Forests

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In Crater Lake National Park there exists a wide variety of plant communities presently dominated by lodgepole pine. Some communities have only a single age-class of lodgepole pine, which includes almost all the trees. Others have several distinct age-classes, or have age structures that indicate that reproduction occurs more or less continuously rather than as a short-term response to disturbance. Some communities include other species of trees in the overstory or understory; others are essentially pure lodgepole pine. From this type of information we inferred what type of succession occurs in the various forests.

Some forests are obviously seral, with lodgepole eventually being replaced by other tree species. In some seral communities, lodgepole pine reproduces little and the replacement is rapid, with only one generation of lodgepole occupying a site before the more shade tolerant trees take over almost complete dominance. Of course, some catastrophe may at any time destroy the forest, allowing lodgepole pine to return.

In one seral community the complete replacement of lodgepole pine is delayed, apparently indefinitely, by periodic light ground fires which burn the area incompletely. In two others, invasion of other tree species is slow even without fire, requiring two or more generations of lodgepole pine before the invaders gain dominance.

The lodgepole communities also vary in their understory layers, from almost absent to relatively dense. In two communities, at least, we think the understory plays an important role in delaying tree invasion. Managers can use understory composition to determine the type of forest by using the key in Appendix B; this is more accurate than the maps (Fig. 2, Appendix C) in most situations and can be applied to unmapped areas. Knowing the community, one can determine our management recommendations from section VIII below.

The environments of the various communities are very similar in many ways. Lodgepole forests usually occur on glowing avalanche deposits on relatively gentle topography. Soils are almost all of the Steiger series. We found no evidence of serious moisture stress in any lodgepole forest. Elevations range from the lowest in the Park to over 2000 m.

However, we have identified some differences reflecting the pattern in the forest communities. Topographic basins usually support climax lodgepole forests toward the center, the more sparse and species-poor ones being closest to the middle. These very depauperate forests have the lowest moisture stress but do not usually include small streams and usually seem to be the farthest from outcrops of rocks other than pumice or scoria. In contrast the seral forests with the densest ground vegetation have considerable andesite, dacite, or weathered material in the parent material or nearby upslope, include many streams, have the greatest soil profile development but yet have the greatest moisture stress on the saplings of lodgepole pine. Elevation correlates with some community differences, and continuity with ponderosa pine forest is characteristic of some types.