Dynamics of stump sprout regeneration after transformation to multiaged management in coast redwood forests

Abstract

There is considerable interest in multiaged management as a silvicultural and restoration tool in redwood forests of California. For multiaged silviculture to be successful, a new cohort of trees must first be able to regenerate underneath the residual overstory. We used annual re-measurement data from a replicated manipulative experiment in coastal northern California to determine how understory light, stand density, and spatial arrangement of residual trees affected coast redwood (Sequoia sempervirens) and tanoak (Notholithocarpus densiflorus) stump sprouts regenerating after partial harvest of conifers and felling-to-waste of tanoak. Four treatments (group selection, aggregated retention, low-density dispersed retention, and high-density dispersed retention) were applied at each replicate on redwood-dominated sites. Height growth of redwood sprouts was 49% greater than tanoak sprouts across all treatments. Redwood and tanoak sprouts were sensitive to overstory density. Redwood sprouts were marginally taller under high-density aggregated versus dispersed overstory trees at the same residual stand density (39.5 m2/ha BA). Sprout growth correlated with understory light; redwood sprouts exhibited a significant increase in sensitivity to light availability from year 2 to year 6. No differences in redwood sprout growth were detected when retaining a residual tree on the same root system versus sprouts growing on a root system where all redwood stems were cut. Our finding that cutting unwanted hardwoods in tandem with partial harvesting of merchantable conifers can maintain a competitive advantage for redwood sprouts versus tanoaks is an important consideration for maintaining redwood dominance when transitioning to multiaged management.