Density reduction in loblolly pine (Pinus taeda L.) stands to increase tree C assimilation: an approach with the dual δ13C and δ18O isotope signatures in needles

Table 3 Observed DBH, height, specific leaf area, foliar N concentration, area-based foliar N content, δ¹³C, δ¹⁸O and WUE_i (mean ± 1SD) of sampled trees of eight different density manipulation (planting density and thinning intensity) treatments applied in loblolly pine (Pinus taeda) plantation in southeast USA

Planting density (stems ha⁻¹)	Thinning (% of removal)	DBH (cm)	Height (m)	Specific leaf area (cm² gm⁻¹)	Foliar N concentration (mg g⁻¹)	Foliar N content (g m⁻²)	Foliar δ¹³C (%)	Foliar δ¹⁸O (%)
494	0	25.6 ± 4.4	12.9 ± 1.2	32.3 ± 2.6	15.0 ± 1.6	0.47 ± 0.08	− 30.3 ± 0.7	27.5 ± 0.8
1111	0	21.7 ± 2.6	13.6 ± 0.8	36.1 ± 4.4	15.5 ± 1.9	0.44 ± 0.09	− 30.5 ± 0.3	27.1 ± 0.8
1111	55%	23.6 ± 1.5	14.0 ± 1.5	33.3 ± 3.4	15.3 ± 2.8	0.46 ± 0.10	− 30.2 ± 0.4	27.5 ± 0.4
1729	0	18.3 ± 2.6	13.2 ± 1.6	36.3 ± 3.0	17.3 ± 1.9	0.48 ± 0.06	− 30.5 ± 0.5	26.8 ± 0.6
1729	71%	23.9 ± 2.6	13.8 ± 1.4	33.2 ± 3.2	14.9 ± 1.6	0.45 ± 0.07	− 30.3 ± 0.5	27.6 ± 0.4
1729	36%	20.5 ± 2.3	13.2 ± 1.9	35.2 ± 2.6	15.0 ± 2.3	0.43 ± 0.04	− 30.6 ± 0.7	26.8 ± 0.9
2346	0	17.7 ± 2.5	13.6 ± 2.0	36.2 ± 8.7	16.0 ± 1.9	0.47 ± 0.14	− 30.8 ± 0.5	26.9 ± 0.5
2964	0	15.5 ± 2.8	13.3 ± 1.3	37.8 ± 5.3	15.5 ± 3.5	0.41 ± 0.10	− 30.5 ± 0.4	26.9 ± 0.3

Mean ± standard deviations are shown (n = 9; one tree of planting density treatment 494 tree ha⁻¹ was excluded due to measurement error)

ISSN: 1297-966X