Abstract
While reclaimed loblolly pine (Pinus taeda L.) plantations in east Texas, USA have demonstrated similar aboveground productivity levels relative to unmined forests, there is interest in assessing carbon (C) and nutrients in aboveground components of reclaimed trees. Numerous studies have previously documented aboveground biomass, C, and nutrient contents in loblolly pine plantations; however, similar data have not been collected on mined lands. We investigated C, N, P, K, Ca, and Mg aboveground contents for first-rotation loblolly pine growing on reclaimed mined lands in the Gulf Coastal Plain over a 32-year chronosequence and correlated elemental rates to stand age, stem growth, and similar data for unmined lands. At the individual tree level, we evaluated elemental contents in aboveground biomass components using tree size, age, and site index as predictor variables. At the stand-level, we then scaled individual tree C and nutrients and fit a model to determine the sensitivity of aboveground elemental contents to stand age and site index. Our data suggest that aboveground C and nutrients in loblolly pine on mined lands exceed or follow similar trends to data for unmined pine plantations derived from the literature. Diameter and height were the best predictors of individual tree stem C and nutrient contents (R ≥ 0.9473 and 0.9280, respectively) followed by stand age (R ≥ 0.8660). Foliage produced weaker relationships across all predictor variables compared to stem, though still significant (P ≤ 0.05). The model for estimating stand-level C and nutrients using stand age provided a good fit, indicating that contents aggrade over time predictably. Results of this study show successful modelling of reclaimed loblolly pine aboveground C and nutrients, and suggest elemental cycling is comparable to unmined lands, thus providing applicability of our model to related systems.
Highlights
Reclaiming forests on surface mined lands serves as a springboard for carbon (C) sequestration, restoration of composition and ecological function, and provides economic opportunities such as timber and bioenergy production (Zipper et al 2011)
Our objectives were to: (1) examine C and macronutrient (N, P, K, Ca, Mg) concentrations in two aboveground biomass components of first-rotation reclaimed loblolly pine plantations across a full rotation chronosequence; (2) evaluate the relationship of individual tree C and nutrient contents by biomass component to more measured predictor variables; (3) assess the impact of stand age and site index on stand-level C and nutrient contents; and, (4) compare data from this study to unmined lands derived from the literature to determine the impact of surface mining on aboveground loblolly pine C and nutrient accumulation
Elemental concentrations for individual tree stem and foliar biomass components were referenced to unmined concentrations reported for 12-year-old loblolly pine plantations growing in the Upper Coastal Plain and Piedmont regions in Georgia (Zhao et al 2014), first-rotation 22-year-old loblolly pine growing in the Upper Coastal Plain in Alabama (Rubilar et al 2005), and for loblolly pine plantations from several studies across the southeastern USA (Albaugh et al 2010)
Summary
Reclaiming forests on surface mined lands serves as a springboard for carbon (C) sequestration, restoration of composition and ecological function, and provides economic opportunities such as timber and bioenergy production (Zipper et al 2011). These benefits are universal to several avenues of land restoration following human-caused disturbances (Nave et al 2018). Surface mine reclamation creates potential for additional soil organic C sequestration and storage over longer periods of time, especially on high quality forested sites (Amichev et al 2008; Ussiri and Lal 2005). Amichev et al (2008) demonstrated that ecosystem C sequestration on mined lands are capable of meeting pre-mining levels. Published allometric relationships for loblolly pine trees growing on reclaimed mined lands in the Gulf Coastal Plain showed increased biomass and volume growth over time, with growth rates similar to non-mined lands (Priest et al 2015)
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