Leaf physiology and stem growth were assessed in loblolly pine ( Pinus taeda L.) in response to 10 to 11 years of treatment with weed control (W), weed control plus irrigation (WI), weed control plus irrigation and fertigation (WIF), or weed control plus irrigation, fertigation, and pest control (WIFP) to determine whether increased resource availability can push productivity of loblolly pine closer to its biological growth potential expressed in favorable, exotic environments. Maximum basal area and stem biomass were 41 m²·ha^–1 and 172 Mg·ha^–1, respectively, in response to fertigation. Stemwood biomass production was positively and linearly related to basal area. Belowground woody biomass was highest in the WIF and WIFP treatments and averaged 50 Mg·ha^–1, but the W and WI treatments exploited a greater area of soil with low-density coarse roots. Fertigation increased foliar nitrogen concentration and foliage biomass, but treatment had no effect on leaf physiological parameters or growth efficiency. Comparison with growth rates reported for loblolly pine in Hawaii revealed that loblolly pine grown in its native range can produce the high yields observed in exotic environments when stands are below maximum carrying capacity.

Forests can partially offset greenhouse gas emissions and contribute to climate change mitigation, mainly through increases in live biomass. We quantified carbon (C) density in 20 managed longleaf pine (Pinus palustrisMill.) forests ranging in age from 5 to 118 years located across the southeasternUnited Statesand estimated above‐ and belowground C trajectories. Ecosystem C stock (all pools including soil C) and aboveground live tree C increased nonlinearly with stand age and the modeled asymptotic maxima were 168 Mg C/ha and 80 Mg C/ha, respectively. Accumulation of ecosystem C with stand age was driven mainly by increases in aboveground live tree C, which ranged from <1 Mg C/ha to 74 Mg C/ha and comprised <1% to 39% of ecosystem C. Live root C (sum of below‐stump C, ground penetrating radar measurement of lateral root C, and live fine root C) increased with stand age and represented 4–22% of ecosystem C. Soil C was related to site index, but not to stand age, and made up 39–92% of ecosystem C. Live understory C, forest floor C, downed dead wood C, and standing dead wood C were small fractions of ecosystem C in these frequently burned stands. Stand age and site index accounted for 76% of the variation in ecosystem C among stands. The mean root‐to‐shoot ratio calculated as the average across all stands (excluding the grass‐stage stand) was 0.54 (standard deviation of 0.19) and higher than reports for other conifers. Long‐term accumulation of live tree C, combined with the larger role of belowground accumulation of lateral root C than in other forest types, indicates a role of longleaf pine forests in providing disturbance‐resistant C storage that can balance the more rapid C accumulation and C removal associated with more intensively managed forests. Although other managed southern pine systems sequester more C over the short‐term, we suggest that longleaf pine forests can play a meaningful role in regional forest C management.

The future climate of the southeastern USA is predicted to be warmer, drier and more variable in rainfall, which may increase drought frequency and intensity. Loblolly pine (Pinus taeda) is the most important commercial tree species in the world and is planted on ~11 million ha within its native range in the southeastern USA. A regional study was installed to evaluate effects of decreased rainfall and nutrient additions on loblolly pine plantation productivity and physiology. Four locations were established to capture the range-wide variability of soil and climate. Treatments were initiated in 2012 and consisted of a factorial combination of throughfall reduction (approximate 30% reduction) and fertilization (complete suite of nutrients). Tree and stand growth were measured at each site. Results after two growing seasons indicate a positive but variable response of fertilization on stand volume increment at all four sites and a negative effect of throughfall reduction at two sites. Data will be used to produce robust process model parameterizations useful for simulating loblolly pine growth and function under future, novel climate and management scenarios. The resulting improved models will provide support for developing management strategies to increase pine plantation productivity and carbon sequestration under a changing climate.

Currently, little information is available to estimate individual tree attributes for longleaf pine (Pinus palustris Mill.), an important tree species of the so

Long-term hydraulic acclimation to resource availability was explored in 3-year-old Populus deltoides Bartr. ex Marsh. clones by examining transpiration, leaf-specific hydraulic conductance (G_L), canopy stomatal conductance (G_S) and leaf to sapwood area ratio (A_L:A_S) in response to irrigation (13 and 551 mm year⁻¹ in addition to ambient precipitation) and fertilization (0 and 120 kg N ha⁻¹ year⁻¹). Sap flow was measured continuously over one growing season with thermal dissipation probes. Fertilization had a greater effect on growth and hydraulic properties than irrigation, and fertilization effects were independent of irrigation treatment. Transpiration on a ground area basis (E) ranged between 0.3 and 1.8 mm day⁻¹, and increased 66% and 90% in response to irrigation and fertilization, respectively. Increases in G_L, G_S at a reference vapor pressure deficit of 1 kPa, and transpiration per unit leaf area in response to increases in resource availability were associated with reductions in A_L:A_S and consequently a minimal change in the water potential gradient from soil to leaf. Irrigation and fertilization increased leaf area index similarly, from an average 1.16 in control stands to 1.45, but sapwood area was increased from 4.0 to 6.3 m² ha⁻¹ by irrigation and from 3.7 to 6.7 m² ha⁻¹ by fertilization. The balance between leaf area and sapwood area was important in understanding long-term hydraulic acclimation to resource availability and mechanisms controlling maximum productivity in Populus deltoides.