Environment and tree size controlling stem sap flux in a perhumid tropical forest of Central Sulawesi, Indonesia

Table 3 Parameter estimates and coefficients of determination (R ²) of the relationship between environmental variables and daily transpiration rate (E, mm day⁻¹) per tree height class during 2008

Tree height class (m)	E vs. D_mean				E vs. R				E vs. SWC
	E = a (1-exp(−bD_mean))				E = E = b₀ + b₁R				E = b₀ + b₁SWC
									E = b₀ + b₁SWC + b₂SWC²
	a	b	R ²	P	b ₀	b ₁	R ²	P	b ₀	b ₁	b ₂	R ²	P
<10	0.009	1.762	0.86	<0.001	−0.0003	0.0003	0.55	<0.001	0.014	−0.0002	–	0.12	<0.001
10–20	0.086	1.629	0.75	<0.001	−0.0024	0.0025	0.47	<0.001	0.133	−0.0002	–	0.12	<0.001
20–30	0.114	2.894	0.80	<0.001	0.0039	0.0043	0.59	<0.001	−1.265	0.0586	−0.0006	0.07	<0.001
>30	0.763	5.159	0.69	<0.001	0.2364	0.0243	0.45	<0.001	−10.543	0.4807	−0.0052	0.07	<0.001

The relationship between E and vapour pressure deficit (D _mean, kPa) followed an exponential form for all tree height classes. The relationship between E and solar radiation (R, MJ m⁻² day⁻¹) was better fitted to a first-order polynomial in all tree height classes. The relationship between E and soil water content (SWC, %) was better explained by a first-order polynomial in the smaller tree height classes and by a second-order polynomial in the taller trees

ISSN: 1297-966X