Among the characteristics of site that most influence white pine growth is the depth of the surface soil horizon. The deeper this zone of vigor-sustaining roots, the better the growth. Roots are most abundant in finer-textured strata, regardless of the depth to which they must grow to reach that zone. Root extension also depends on the availability of soil nitrogen, organic matter, and soil moisture. Poor root growth in mottled soils indicates poor drainage.
Good seed germination and seedling establishment occur on old fields because the soil is warm, stimulating cotyledon development and root growth. In contrast, soil under a dense forest canopy is cool, because little solar radiation reaches the floor. Low soil temperature, inhibiting white pine growth, encourages replacement with later successional species.
Soils under pure white pine forests deteriorate because decomposition of organic matter is retarded. The humus layer that develops lacks incorporation of organic matter with the mineral soil. Fungi and microfauna intrude and reproduce in this accumulated raw humus, consuming
available nitrogen as they do. The organic matter to nitrogen ratio then widens, providing less available nitrogen for the trees. Over several rotations this could be detrimental. However, the chances for pure stands to continue for more than a couple of rotations are so improbable, because of disturbances and natural succession, that the occurrence of a low nitrogen problem is unlikely. Species either proceed toward the ecological climax or successional degressions occur.
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