title: Effects of sample size on sap flux-based stand-scale transpiration estimates.
abstract: In this study, we aimed to assess how sample sizes affect confidence of stand-scale transpiration (E) estimates calculated from sap flux (F(d)) and sapwood area (A(S_tree)) measurements of individual trees. In a Japanese cypress plantation, we measured F(d) and A(S_tree) in all trees (n = 58) within a 20 x 20 m study plot, which was divided into four 10 x 10 subplots. We calculated E from stand A(S_tree) (A(S_stand)) and mean stand F(d) (J(S)) values. Using Monte Carlo analyses, we examined the potential errors associated with sample sizes in E, A(S_stand) and J(S) using the original A(S_tree) and F(d) data sets. Consequently, we defined the optimal sample sizes of 10 and 15 for A(S_stand) and J(S) estimates, respectively, in the 20 x 20 m plot. Sample sizes larger than the optimal sample sizes did not decrease potential errors. The optimal sample sizes for J(S) changed according to plot size (e.g., 10 x 10 and 10 x 20 m), whereas the optimal sample sizes for A(S_stand) did not. As well, the optimal sample sizes for J(S) did not change in different vapor pressure deficit conditions. In terms of E estimates, these results suggest that the tree-to-tree variations in F(d) vary among different plots, and that plot size to capture tree-to-tree variations in F(d) is an important factor. The sample sizes determined in this study will be helpful for planning the balanced sampling designs to extrapolate stand-scale estimates to catchment-scale estimates.
authors.affiliation: School of Forestry and Resource Conservation, National Taiwan University, Taipei 106-17, Taiwan. kumett@ntu.edu.tw
authors.forename: Tomonori
authors.initials: T
authors.lastname: Kume
authors.forename: Kenji
authors.initials: K
authors.lastname: Tsuruta
authors.forename: Hikaru
authors.initials: H
authors.lastname: Komatsu
authors.forename: Tomo'omi
authors.initials: T
authors.lastname: Kumagai
authors.forename: Naoko
authors.initials: N
authors.lastname: Higashi
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Shinohara
authors.forename: Kyoichi
authors.initials: K
authors.lastname: Otsuki
mesh_terms: D029781:Cupressus / Q000502:physiology*; D007564:Japan; D009010:Monte Carlo Method; D018526:Plant Transpiration / Q000502:physiology*; D011156:Population Density; D011891:Rain; D015203:Reproducibility of Results; D018401:Sample Size; D014197:Trees / Q000502:physiology*