Conifer Root Proliferation after 20 Years of Soil Compaction

Soil compaction is known to limit plant growth by reducing soil macroporosity and restricting gas, water, and root movement. Recent evidence from study sites across the United States and Canada, however, suggests that tree growth is not universally affected by soil compaction from forest harvesting practices. Our observational study examined rooting patterns in mixed conifer plantations in the central Sierra Nevada of California to determine whether tree roots use continuous pathways or channels to overcome the physical restrictions of compacted soil. Replicate plots were established 20 –25 years earlier to compare compacted and uncompacted treatments after clearcut harvesting. Fine and lateral root counts were taken at multiple depths in soil trenches. Rooting was extensive in compacted plots despite consistently high soil strength values (3 MPa). No differences in rooting patterns or in fine or lateral root numbers were detected between compaction treatments. The results indicated long-term tolerance by conifer roots to soil compaction without clear use of preferential channels or uncompacted zones.