Tree age determination in the widespread woody plant invader Pittosporum undulatum

- Pittosporum undulatum is a widespread woody plant invader, including in the Azores.
- As a contribution for a management plan, we applied tree age determination methods.
- P. undulatum revealed typical annual growth rings, and tree ages up to 131 years.
- Diameter at breast height and total biomass were the best predictors of tree age.
- Biomass use in 65% of its dominated areas implied a rotation period of 26 years.

Pittosporum undulatum Ventenat (Pittosporaceae) is an invasive tree of forests and woodlands in several regions of the world. In the Azores archipelago it occupies about 30% of the forested areas and efforts to valorize its biomass are underway. Implementing sustainable forest management requires basic information on tree age and growth rate, yet this information was lacking. We used tree-ring analysis to obtain accurate age estimates and growth rates from a total of 982 live trees (1318 samples: 646 increment cores and 336 pairs of stem discs) that were sampled in São Miguel, Terceira and Graciosa islands. Pittosporum undulatum showed distinct annual growth rings with an increase in cell-wall thickness and a decrease in cell lumen of the Fibers, from early to latewood. We found trees with ages at base and at breast height ranging from 5/4 to 131/108 years, respectively. Samples taken at tree base and at breast height allowed to estimate a diameter growth rate of 0.38 cm.year−1, with an average of 8 years needed to attain breast height, and a rotation period of 26 years to reach the average diameter of 7 cm presently found at the stands. Allometric equations relating tree age and diameter at breast height, tree height, basal area and biomass were found to be significant. Among the models with lowest AIC, equations predicting tree age from diameter at breast height or from biomass showed the best fit (R2 = 0.65 and for R2 = 0.70, respectively). The developed methods and the obtained results can now be used to support management of biomass valorization projects but also to better understand invasion dynamics at conservation devoted areas.