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Abstract
The horizontal and vertical stand structure in three alluvial flat old-growth redwood forests located in Northern California were quantified in an attempt to develop targets for old forest restoration. Additionally, thinning scenarios were simulated in two second-growth coast redwood stands.
Many structural attributes were common to the three old-growth study sites and could serve as targets or reference conditions in old forest restoration efforts. Redwood density ranged from 118-148 trees ha-1 and an upper canopy density of 45-74 trees ha-1. The frequency distribution of redwood tree diameters was right-skewed and broad at the three study sites. The mean crown ratio was 0.64. The percentage of canopy gap area ranged from 17-25%.
Spatial patterns for trees (≥ 15 cm dbh) in different size classes were analyzed separately with Ripley's K(d) function. Results revealed two patterns. At two sites, trees were randomly distributed throughout the stand and size classes were spatially independent of each other at scales of 0-50 m. At one site, a clumped spatial pattern was revealed for small and medium-sized tree groups at small scales while a random spatial pattern was detected for large trees at scales of 0-50 m. In addition, significant positive deviation from spatial independence at small scales suggested an attraction between tree groups. The spatial pattern of regeneration (trees < 15 cm dbh) was examined using quadrat-based analyses. Regeneration was clumped at all three sites.
The influence of stand density on second-growth stand structure and growth over a 100 year time period was examined in terms of meeting the management objective of accelerating the development of old forest characteristics and approaching the reference conditions for alluvial flat old-growth redwood forests. Simulated thinning regimes accelerated individual tree growth and produced uneven-aged stands. Results suggested that some old forest characteristics can be restored within 100 years. Predicted overstory average diameter and crown ratio at the end of the 100-year time horizon was greatest for thinning regimes with the lowest overstory density.
