Silva, L., Alves, M., Elias, R. & Silva, L. (2017) Comparison of T-Square, Point Centered Quarter and N-Tree sampling methods in Pittosporum undulatum invaded woodlands. International Journal of Forestry Research, 2818132, 1-13. DOI:10.1155/2017/2818132
Tree density is an important parameter affecting ecosystems functions and management decisions, while tree distribution patterns affect sampling design. Pittosporum undulatum stands in the Azores are being targeted with a biomass valorization program, for which efficient tree density estimators are required. We compared -Square sampling, Point Centered Quarter Method (PCQM), and -tree sampling with benchmark quadrat (QD) sampling in six 900 m2 plots established at P. undulatum stands in São Miguel Island. A total of 15 estimators were tested using a data resampling approach. The estimated density range (344–5056 trees/ha) was found to agree with previous studies using PCQM only. Although with a tendency to underestimate tree density (in comparison with QD), overall, -Square sampling appeared to be the most accurate and precise method, followed by PCQM. Tree distribution pattern was found to be slightly aggregated in 4 of the 6 stands. Considering (1) the low level of bias and high precision, (2) the consistency among three estimators, (3) the possibility of use with aggregated patterns, and (4) the possibility of obtaining a larger number of independent tree parameter estimates, we recommend the use of -Square sampling in P. undulatum stands within the framework of a biomass valorization program.
