Abstract
Research Highlights: Bark thickness (BT) in coastal redwood (Sequoia sempervirens (D.Don) Endl.) varies in accordance with tree size, crown ratio, position within the canopy, height along the tree stem, genetic identity and latitude. However, current BT predictive equations do not account for such variability, leading to inaccurate BT estimations. We present improved BT models to increase the accuracy of BT estimates for coastal redwood in northern California. Background and Objectives: BT is an important metric that has many practical applications in forest management. However, BT varies substantially across species and environments, as well as across individuals and populations. Our objectives were to investigate BT along various gradients of change, with factors accounting for genetics, tapering of BT along the tree bole, differences in BT according to tree crown position within the stand, and the latitude. Materials and Methods: We collected BT data throughout most of redwood’s natural range along a north–south latitudinal gradient. Subsets of these data were used to examine the influence of particular variables on BT while holding the other variables constant. Results: Regionally, the bark was thicker among more xeric southern redwoods and thinner among more mesic northern redwoods. We found that the BT of codominant, intermediate and suppressed trees was around 8%, 14%, and 18% thicker, respectively, than bark of the same size dominant tree. Redwood trees growing in the partial shade of an overstory had thicker bark than trees growing in even-aged stands and incorporating genetic identity yielded major improvements in the BT model estimates, suggesting that BT is under genetic control. Bark thickness decreased with increasing height along the tree stem, with notable differences in the BT above and below breast height. Conclusions: We recommend utilizing the best available BT equations (over standard ‘bark factors’) in forest science, modeling and management applications. We also recommend the adoption of our drilling method for BT measurement on larger trees due to the potential for error associated with traditional bark gauge measurements.
Highlights
Understanding how the thickness of tree bark varies within and among trees has practical application in forest science and management
The best model indicated that redwood trees growing in the partial shade of an overstory had thicker bark than trees growing in even-aged stands, after accounting for the effects of tree size and crown ratio on Bark thickness (BT) (Table 10)
Redwood BT was most strongly associated with diameter at 1.37 m breast height (DBH), but was found to be negatively correlated with the crown ratio (CR)
Summary
Understanding how the thickness of tree bark varies within and among trees has practical application in forest science and management. Bark thickness (BT) informs fire science research topics such as modeling post-fire tree mortality because trees with thicker bark are generally more resistant [1]. Forest managers contemplating commercial thinning in young stands need estimates of the inside-bark diameter of logs to ensure that cut trees will yield logs meeting merchantability specifications for minimum small-end diameter [6]. In these instances, to derive inside-bark dimensions of wood in trees, we can subtract predictions from BT equations from outside-bark data or model estimates [7,8]
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