DOI: 10.5061/dryad.44j0zpccw
title: Temporal nitrogen dynamics in intensively managed loblolly pine early stand development

description: Forest production is strongly dependent on nutrient uptake; however,
 sustainable management of intensively managed plantations requires an
 improved understanding of this relationship when fertilization occurs
 frequently across short rotations. Here, we studied temporal nitrogen (N)
 concentration ([N]) and content (Nc) dynamics under different
 silvicultural practices (herbicide, fertilization, and planting density)
 throughout early loblolly pine (Pinus taeda) stand development (5 years).
 We describe relationships of [N] and Nc of different stand components
 (foliage, branches, stem, roots, and competing vegetation) with carbon and
 biomass. Our results demonstrate that [N] of perennial loblolly tissues do
 not respond to silvicultural practices and progressively decrease through
 development. While foliar [N] was most responsive to resource
 availability, it was not consistent across time. Controlling competing
 vegetation was crucial to promote the use of site resources by the crop
 tree and increased loblolly Nc by &gt;500%. However, increased N
 uptake and expedited growth is dependent upon fertilization early in stand
 development. At age 5, herbicide plus reduced and
 full fertilization rates exhibited similar aboveground Nc, which
 was 32% higher than with herbicide only. Increasing planting density
 resulted in increased above- and belowground loblolly Nc; however,
 increases in Nc were not proportional with increases in planting density.
 Net primary productivity and N uptake were linearly related, but
 age/development strongly controlled N use efficiency. Our study helps to
 understand complex relationships between N, biomass, and silvicultural
 practices during early stand development and demonstrates that temporal
 evaluation of nutrient dynamics is crucial to better understand loblolly
 pine growth, carbon sequestration potential, and to inform sustainable
 silvicultural practices across short rotations.
description: All study details (e.g., site description, experimental
 design, planting density, fertilization timing, rates and sources, plot
 sizes, measurement protocols, and calculations) can be found in the
 manuscript linked to the data. Data is provided as plot means.
 Data file description: - Treatment
 coding:  1 – control: no herbicide and no fertilization
 (<i>C</i>) 2 - herbicide only
 (<i>H</i>) 3 - herbicide and half-reduced
 fertilization rate (<i>R</i>) 4 - herbicide
 and full fertilization (<i>F</i>) 5 -
 increased stand density (60+ %; 1346 <i>vs.</i> 2152 trees per
 hectare) with herbicide and full fertilization rate
 (<i>D</i>); Variable coding and
 units: *all
 properties are from loblolly pine trees but “cptveg”, which refers to
 competing vegetation   needlesperN – needles (foliage)
 nitrogen (N) concentration [N] – in % branchesperN – branch [N] in
 % stemperN – stem
 [N] in % rootsperN – root [N] in
 % cptvegperN –
 competing vegetation [N] in % need15N – foliage
 δ<sup>15</sup>N (‰) branch15N – branch
 δ<sup>15</sup>N (‰) stem15N – stem
 δ<sup>15</sup>N (‰) root15N – root
 δ<sup>15</sup>N (‰) cptveg15N – competing vegetation
 δ<sup>15</sup>N (‰) needlesN – foliage N content (kg
 N ha<sup>-1</sup>) branchesN – branch N content (kg
 N ha<sup>-1</sup>) stemN – stem N content (kg N
 ha<sup>-1</sup>) rootN – root N content (kg N
 ha<sup>-1</sup>) abvN – loblolly pine aboveground
 N content<sup>+</sup> (kg N
 ha<sup>-1</sup>) <sup>+</sup>sum of
 needle, branch, and stem N content cptvegN – competing vegetation N
 content (kg N ha<sup>-1</sup>) needlesCN – foliage
 Carbon:Nitrogen (C:N) ratio (unitless) branchesCN – branch C:N ratio
 (unitless) stemCN
 – stem C:N ratio (unitless) rootCN – root C:N ratio
 (unitless) abvCN
 – loblolly pine aboveground C:N ratio (unitless) abvg-biomass – loblolly pine
 aboveground biomass (needles + branches +stem) (Mg
 ha<sup>-1</sup>) "-" indicates no
 measurements or calculations were performed for this variable at this
 period.