A Model to Estimate Leaf Area Index in Loblolly Pine Plantations Using Landsat 5 and 7 Images

Vegetation indices calculated from remotely sensed satellite imagery are commonly used within empirically derived models to estimate leaf area index in loblolly pine plantations in the southeastern United States. The data used to parameterize the models typically come with observation errors, resulting in biased parameters. The objective of this study was to quantify and reduce the effects of observation errors on a leaf area index (LAI) estimation model using imagery from Landsat 5 TM and 7 ETM+ and over 1500 multitemporal measurements from a Li-Cor 2000 Plant Canopy Analyzer. Study data comes from a 16 quarter 1 ha plot with 1667 trees per hectare (2 m × 3 m spacing) fertilization and irrigation research site with re-measurements taken between 1992 and 2004. Using error-in-variable methods, we evaluated multiple vegetation indices, calculated errors associated with their observations, and corrected for them in the modeling process. We found that the normalized difference moisture index provided the best correlation with below canopy LAI measurements (76.4%). A nonlinear model that accounts for the nutritional status of the stand was found to provide the best estimates of LAI, with a root mean square error of 0.418. The analysis in this research provides a more extensive evaluation of common vegetation indices used to estimate LAI in loblolly pine plantations and a modeling framework that extends beyond the typical linear model. The proposed model provides a simple to use form allowing forest practitioners to evaluate LAI development and its uncertainty in historic pine plantations in a spatial and temporal context

Vegetation control and fertilization in midrotation Pinus taeda stands in the southeastern United States

- We quantified Pinus taeda L. plantation response to vegetation control (VC) applied using site specific methods including chemical (glyphosate, imazapyr, metsulfuron methyl, and triclopyr) and mechanical means and nitrogen and phosphorus fertilization on a variety of sites ranging in age from ten to twenty-two years old at treatment initiation in the Piedmont and coastal plain of the southeastern United States. We examined pine and hardwood (the primary competing vegetation) basal area and pine volume and foliar nutrient responses in a 2 $\times$ 2 factorial combination of a one time application of VC and fertilization in a randomized complete block design with three or four replications at each site. Vegetation control reduced hardwood vegetation at least 70% at all sites. On average, annual pine volume growth response was greatest on the combined treatment (6.1 and 11.0 m3 ha–1 yr–1) followed by fertilization alone (5.5 and 7.9 m3 ha–1 yr–1) and then VC alone (1.1 and 4.5 m3 ha–1 yr–1) for years one and two and years three and four, respectively. The range in pine volume response across all treatments for the sites examined here was –3 to 12 m3 ha–1 yr–1. There may be sites, not represented here, with greater water deficits, more competing vegetation, or where nitrogen and phosphorus are not the primary limiting factor that would be more responsive to VC. Fertilization alone did not significantly affect hardwood basal area at year two or four and the proportion of hardwood vegetation (as basal area) was about the same before treatment (12%) and up to four years after treatment (11%) in the check and fertilized treatments. We hypothesize that the combined treatment may provide the best pine response in later measurement periods as fertilization responses diminish because added nutrients are utilized and VC responses increase from increased nutrient and moisture availability to the pines provided the competing vegetation does not recover.- Contrôle de la végétation et fertilisation de peuplements de Pinus taeda à mi-révolution dans les états du Sud-Est des USA. Nous avons évalué l’effet sur des plantations de Pinus taeda L. de différentes méthodes de contrôle de la végétation (VC) à savoir des traitements chimiques (glyphosate, imazapyr, metsulfuron, methyl et triclopyr) , des interventions mécaniques et une fertilisation phosphatée, ceci sur un ensemble de stations situées en plaine et en piedmont des Etats du Sud Ouest, portant des peuplements allant de 10 à 22 ans en début d’expérience. Nous avons étudié la surface terrière des pins et des feuillus (principale végétation concurrente) ainsi que le volume et la composition foliaire en nutrients des pins dans un dispositif en bloc complet à 2 ou 3 répétitions, avec une combinaison factorielle 2 $\times$ 2 d’une seule application de VC et de fertilisation. Le contrôle de la végétation réduit l’importance des feuillus de 70 % au moins, sur toutes les stations. En moyenne, c’est le traitement combiné qui a l’effet le plus important sur le volume de pin (6,1 et 11,0 m3 ha–1 an–1) suivi par la fertilisation seule (5,5 et 7,9 m3 ha–1 an–1) et par le VC seul (1,1 et 4,5 m3 ha–1 an–1), les deux nombres entre parenthèses correspondant aux années 1 et, puis 3 et 4. L’amplitude de l’effet sur le volume des pins pour l’ensemble des traitements et des stations va de –3 à 12 m3 ha–1 an–1. Il est possible que certains stations, non représentées ici, caractérisées par un plus grand déficit en eau, une concurrence plus importante et des disponibilités suffisantes en azote et phosphore, puissent réagir de manière plus importante aux traitements de contrôle de la végétation. La fertilisation seule n’a pas d’effet significatif sur la surface terrière des feuillus aux années 2 et 4 ; la proportion de feuillus en surface terrière est à peu près la même avant et après traitement (12 et 11 %) dans les parcelles témoins et fertilisées. Pour expliquer la supériorité du traitement combiné sur la croissance des pins au bout de 4 ans, nous émettons l’hypothèse suivante : l’effet fertilisation tend à diminuer, les nutrients apportés ayant été utilisés, mais l’effet VC augmente compte tenu de l’augmentation des disponibilités en nutrients et en eau au profit des pins, la végétation concurrente ne pouvant pas se développer

Sentinel-2 Leaf Area Index Estimation for Pine Plantations in the Southeastern United States

Leaf area index (LAI) is an important biophysical indicator of forest health that is linearly related to productivity, serving as a key criterion for potential nutrient management. A single equation was produced to model surface reflectance values captured from the Sentinel-2 Multispectral Instrument (MSI) with a robust dataset of field observations of loblolly pine (Pinus taeda L.) LAI collected with a LAI-2200C plant canopy analyzer. Support vector machine (SVM)-supervised classification was used to improve the model fit by removing plots saturated with aberrant radiometric signatures that would not be captured in the association between Sentinel-2 and LAI-2200C. The resulting equation, LAI = 0.310SR − 0.098 (where SR = the simple ratio between near-infrared (NIR) and red bands), displayed good performance ( R 2 = 0.81, RMSE = 0.36) at estimating the LAI for loblolly pine within the analyzed region at a 10 m spatial resolution. Our model incorporated a high number of validation plots (n = 292) spanning from southern Virginia to northern Florida across a range of soil textures (sandy to clayey), drainage classes (well drained to very poorly drained), and site characteristics common to pine forest plantations in the southeastern United States. The training dataset included plot-level treatment metrics—silviculture intensity, genetics, and density—on which sensitivity analysis was performed to inform model fit behavior. Plot density, particularly when there were ≤618 trees per hectare, was shown to impact model performance, causing LAI estimates to be overpredicted (to a maximum of X i + 0.16). Silviculture intensity (competition control and fertilization rates) and genetics did not markedly impact the relationship between SR and LAI. Results indicate that Sentinel-2’s improved spatial resolution and temporal revisit interval provide new opportunities for managers to detect within-stand variance and improve accuracy for LAI estimation over current industry standard models

Juvenile Southern Pine Response to Fertilization Is Influenced by Soil Drainage and Texture

We examined three hypotheses in a nutrient dose and application frequency study installed in juvenile (aged 2–6 years old) Pinus stands at 22 sites in the southeastern United States. At each site, eight or nine treatments were installed where nitrogen was applied at different rates (0, 67, 134, 268 kg ha−1) and frequencies (0, 1, 2, 4 and 6 years) in two or four replications. Phosphorus was applied at 0.1 times the nitrogen rate and other elements were added as needed based on foliar nutrient analysis to insure that nutrient imbalances were not induced with treatment. Eight years after treatment initiation, the site responses were grouped based on texture and drainage characteristics: soil group 1 consisted of poorly drained soils with a clayey subsoil, group 2 consisted of poorly to excessively drained spodic soils or soils without a clay subsoil, and group 3 consisted of well-drained soils with a clayey subsoil. We accepted the first hypothesis that site would be a significant factor explaining growth responses. Soil group was also a significant factor explaining growth response. We accepted our second hypothesis that the volume growth-cumulative dose response function was not linear. Volume growth reached an asymptote in soil groups 1 and 3 between cumulative nitrogen doses of 300–400 kg ha−1. Volume growth responses continued to increase up to 800 kg ha−1 of cumulatively applied nitrogen for soil group 2. We accepted our third hypothesis that application rate and frequency did not influence the growth response when the cumulative nitrogen dose was equivalent. There was no difference in the growth response for comparisons where a cumulative nitrogen dose of 568 kg ha−1 was applied as 134 kg ha−1 every two years or as 269 kg ha−1 every four years, or where 269 kg ha−1 of nitrogen was applied as four applications of 67 kg ha−1 every two years or as two applications of 134 kg ha−1 every four years. Clearly, the sites examined here were limited by nitrogen and phosphorus, and applications of these elements to young stands effectively ameliorated these limitations. However, there were differences in the response magnitude that were related to soil texture and drainage. Juvenile fertilizer applications resulted in high stocking levels early in the rotation; this condition should be considered when undertaking juvenile fertilization programs

Tamm Review: Light use efficiency and carbon storage in nutrient and water experiments on major forest plantation species

International audienceWe used published data from nine sites where nutrient and water optimization studies had been installed in a 2 × 2 factorial design to determine maximum biomass production in response to a simple set of treatments. We tested for site and treatment effects on the relationships between stem, aboveground (stem, branches, foliage) and total (aboveground + roots) biomass production versus intercepted light (light use efficiency, LUE). We also estimated the additional carbon stored as a result of treatment. The sites were located in Australia (Pinus radiata), Brazil (Eucalyptus grandis × urophylla), France (Pinus pinaster), the United States in Georgia and North Carolina (Pinus taeda) and Hawaii (Eucalyptus saligna), Portugal (Eucalyptus globulus), South Africa (E. grandis), and Sweden (Picea abies). We hypothesized that site, treatment and their interaction would significantly affect LUE; however, we rejected our hypothesis because stem, aboveground and total LUE were not affected by site or treatment. The stem, aboveground and total LUE values were 1.21, 1.51, and 0.85 g MJ−1, respectively. The total LUE value was lower than that for stem and aboveground LUE because a different population was used for the analysis (only five of the nine sites had total production data), and the total LUE relationship had a zero intercept whereas the stem and aboveground LUE relationships had a negative intercept. The average amount of additional carbon that would be stored by the irrigation, fertilization, and fertilization plus irrigation treatments was 3.9, 6.8 and 13.4 Mg CO2 equivalents ha−1 yr−1, respectively. These additional carbon storage estimates, based on these research studies with annual nutrient and water applications, were similar to results obtained in operational settings with less intensive nutrient applications

Below-ground carbon input to soil is controlled by nutrient availability and fine root dynamics in loblolly pine

Availability of growth limiting resources may alter root dynamics in forest ecosystems, possibly affecting the land-atmosphere exchange of carbon. This was evaluated for a commercially important southern timber species by installing a factorial experiment of fertilization and irrigation treatments in an 8-yr-old loblolly pine (Pinus taeda) plantation. After 3 yr of growth, production and turnover of fine, coarse and mycorrhizal root length was observed using minirhizotrons, and compared with stem growth and foliage development. Fertilization increased net production of fine roots and mycorrhizal roots, but did not affect coarse roots. Fine roots had average lifespans of 166 d, coarse roots 294 d and mycorrhizal roots 507 d. Foliage growth rate peaked in late spring and declined over the remainder of the growing season, whereas fine roots experienced multiple growth flushes in the spring, summer and fall. We conclude that increased nutrient availability might increase carbon input to soils through enhanced fine root turnover. However, this will depend on the extent to which mycorrhizal root formation is affected, as these mycorrhizal roots have much longer average lifespans than fine and coarse roots