Deriving Biomass Models for Small-Diameter Loblolly Pine on the Crossett Experimental Forest

Foresters and landowners have a growing interest in carbon sequestration and cellulosic biofuels in southern pine forests, and hence need to be able to accurately predict them. To this end, we derived a set of aboveground biomass models using data from 62 small-diameter loblolly pines (Pinus taeda) sampled on the Crossett Experimental Forest in southeastern Arkansas. Of the 25 equations initially evaluated, we chose 17 that best fit our dataset and compared them using a suite of conventional test statistics, including pseudo-R2 , root mean squared error (RMSE), and bias. Because most of the 17 models varied little in pseudoR 2 (ranging between 0.96 and 0.99), bias (all were within ± 0.01), and RMSE, an additional comparison was done using Akaike’s Information Criterion corrected for small sample size (AICc). This test statistic produced considerably more discrimination between the biomass models. Of the 17 models evaluated, six produced ΔAICc scores that met or exceeded the threshold for substantial support. To recommend a single preferred model, we then extrapolated beyond our actual data and qualitatively compared model predictions with those from the National Biomass Estimator. Our “best” model did not have the minimum AICc score, but rather predicted logically consistent aboveground biomass values at both the upper and lower ends of our extrapolation

Comparing Aboveground Biomass Predictions for an Uneven-Aged Pine-Dominated Stand Using Local, Regional, and National Models

Sequestration by Arkansas forests removes carbon dioxide from the atmosphere, storing this carbon in biomass that fills a number of critical ecological and socioeconomic functions. We need a better understanding of the contribution of forests to the carbon cycle, including the accurate quantification of tree biomass. Models have long been developed to predict aboveground live tree biomass, but few of these have been derived from Arkansas forests. Since there is geographic variability in the growth and yield of pine as a function of genetics, site conditions, growth rate, stand stocking, and other factors, we decided to compare aboveground tree biomass estimates for a naturally regenerated, uneven-aged loblolly pine (Pinus taeda)-dominated stand on the Crossett Experimental Forest (CEF) in southeastern Arkansas. These predictions were made using a new locally derived biomass equation, five regional biomass equations, and the pine model from the National Biomass Estimators. With the local model as the baseline, considerable biomass variation appeared across a range of diameters—at the greatest diameter considered, the minimum value was only 69% of the maximum. Using a recent inventory from the CEF’s Good Farm Forty to compare each model, stand-level biomass estimates ranged from a low of 76.9 Mg/ha (a different Arkansas model) to as much as 96.1 Mg/ha (an Alabama model); the local CEF equation predicted 82.5 Mg/ha. A number of different factors contributed to this variability, including differences in model form and derivation procedures, geographic origins, and utilization standards. Regardless of the source of the departures, their magnitude suggests that care be used when making large-scale biomass estimates

Five Years of Change in an Old-Growth Pine-Hardwood Remnant in Ashley County, Arkansas

The Levi Wilcoxon Demonstration Forest near Hamburg, Arkansas is an industrially-owned remnant of old-growth pine and hardwoods. Some of the loblolly (Pinus taeda L.)and shortleaf (Pinus echinata Mill.)pine in this stand are over 200 years old, and numerous individuals exceed 90 cm in diameter and 30 m in height. A2000 survey of a portion of this tract found that 27 tree species contributed an average of387.5 live stems/ha and 31.8 m2 /ha of basal area. An inventory of the same plots in2006 yielded noticeable declines in density (now down to 342.5 stems/ha) and basal area (now 28.2 m2 /ha). Much of this loss came in the aftermath of a windstorm in May 2003, which felled a number of overstory pines. Loblolly pine decreased from 49.6 stems/ha and 13.2 m2 /ha in2000 to 42.1 trees/ha and 11.2 m 2 /ha in2006, while shortleaf pine declined from 21.7 trees/ha and 5.0 m2 /ha to 14.6 trees/ha and 3.5 m 2 /ha. Further pine mortality came from smaller-scale windthrow, lightning, and bark beetle infestations. Some hardwoods were also toppled by storms or crushed by falling trees, but most appear to have succumbed to drought, competition, and salvage logging. However, hardwood basal area remained virtually unchanged over this period, signifying adequate diameter growth and midstory recruitment. In particular, shade-tolerant hardwood species showed notable gains. Even though most overstory pines currently appear healthy, natural catastrophes and the lack of new canopy recruits may eradicate virtually all pines from this stand within 30 to 50 years

Checklist of Major Plant Species in Ashley County, Arkansas Noted by General Land Office Surveyors

The original General Land Office (GLO) survey notes for the Ashley County, Arkansas, area were examined to determine the plant taxa mentioned during the 1818 to 1855 surveys. While some challenges in identifying species were encountered, at least 39 families and approximately 100 species were identified with reasonable certainty. Most references were for trees used to witness corners or lines. Prominent arboreal genera recorded in these early survey records included Quercus, Pinus, Carya, Liquidambar, Nyssa, Ulmus, Acer, Fraxinus, and Taxodium. A number of shrubs, vines, graminoids, and herbaceous species were also reported, including notable genera like Vaccinium, Lindera, Crataegus, Myrica, Rubus, Smilax, Vitis, Arundinaria, and Bidens. Even though very few GLO surveyors had formal training in plant identification, their familiarity with local and regional floras (undoubtedly supplemented by their field crew\u27s knowledge) contributed to the relative accuracy of the effort. Taxonomic discrepancies (e.g., shifting species names, delineation of new taxa since the survey was completed, obscure common names) have obscured a number of identifications in this study. Nevertheless, the GLO records are a valuable and systematic (statewide) source of information from a period of time that predates most formal botanical investigations

Comparison of Pine Height Models for the Crossett Experimental Forest

Many models to predict tree height from diameter have been developed, but not all are equally useful. This study compared a set of height-diameter models for loblolly (Pinus taeda) and shortleaf (Pinus echinata) pines from Ashley County, Arkansas. Almost 560 trees ranging in diameter at breast height (DBH) from 0.3 cm (both species) to 91.9 cm (for shortleaf) or 108.2 cm (for loblolly) were chosen for measurement. Height equations were then fit to four different functions (Chapman-Richards, modified logistic, exponential, and Curtis-Arney) with weighted nonlinear least squares regression using DBH as the only predictor. Models were evaluated using a series of goodness-of-fit measures, including fit index (R 2 ), root mean square error (RMSE), bias, and corrected Akaike information criterion (AICc). All of the models fit the data very well, with 96 to 98% of the variation explained for loblolly pine, and 96 to 97% explained for shortleaf pine. Similarly, few differences were apparent in RMSE, bias, and AICc, although it was clear that the Curtis-Arney function fit both pine species slightly less well across the upper range of the diameters. Only subtle differences appeared in curve shape for small- to moderate-sized pines, with increasing departures predicted above 75 cm DBH. Given their overall similarity in performance, the modified logistic function was the preferred height diameter model because of its more intuitive allometry at the upper extreme of pine size, especially when compared to the original FVS height dubbing equation. A unified height-diameter model capable of predicting total tree height for either pine taxa was also developed with a modified logistic function

Stand Conditions Immediately following a Restoration Harvest in an Old-growth Pine-hardwood Remnant

Portions of the Levi Wilcoxon Demonstration Forest (LWDF), a privately owned parcel of old growth pine and hardwoods in Ashley County, Arkansas, were recently treated to restore conditions similar to some historic accounts of the virgin forest. Following a hardwood-only cut, a post-harvest inventory showed that the number of tree species in the sample area declined from 24 in 2006 (the most recent pre-harvest inventory) to 12 in 2009. Loblolly (Pinus taeda L.) and shortleaf (Pinus echinata Mill.) pine now comprise 59.2% of the remaining live trees, up from 16.2% in 2006. Between 2006 and 2009, basal area dropped from 28.2 to 16.4 m2 /ha and stem density declined from 349.2 to 72.4 stems/ha, respectively. Total live biomass also fell from 224.8 Mg/ha in 2006 to 130.1 Mg/ha in 2009. While most of the pines in the LWDF are between 100 and 200 years old, ring counts on 102 randomly selected hardwood stumps yielded only one greater than 100 years old. Two-thirds of these hardwoods were less than 70 years old, having originated after the stand was set aside by the Crossett Lumber Company. Historical documentation and recent research suggest that the LWDF is now more similar to presettlement pine-dominated forests of southern Arkansas, which generally had lower stocking and fewer hardwoods

Historical Reflections on the Arkansas Cross Timbers

Kiichler\u27s original map of potential natural vegetation suggested that the eastern-most extension of the Cross Timbers oak-dominated woodland reached into extreme western Arkansas. Recent investigations have found possible old-growth Cross Timber communities in narrow strips along steep, rocky sandstone and shale ridges near Fort Chaffee and Hackett. However, many decades of Euroamerican intervention have altered vegetation composition and structure in west-central Arkansas, making field evaluation difficult. Fortunately, historical accounts of the area provide considerable supporting documentation. General Land Office surveyors, for instance, traversed this portion of western Arkansas before 1850. They reported many ridges and slopes dominated by grassy, stunted oak woodlands, with extensive prairies and richer bottomland terraces. Early explorers, missionaries, and botanists also found similar conditions. For example, both the botanist Thomas Nuttall (in 1819) and the Reverend William Graham (in 1845) mentioned abundant oak woodlands interspersed with glades and grasslands on the stony hills south of Fort Smith. These historical accounts help show that, though far more restricted in their extent than comparable stands in Oklahoma or Texas, Cross Timber communities are possible in Arkansas

Notable Environmental Features in Some Historical Aerial Photographs from Ashley County, Arkansas

A collection of 1939 aerial photographs from Ashley County, Arkansas was analyzed for its environmental information. Taken by the US Department of Defense (USDOD), these images show a number of features now either obscured or completely eliminated over the passage of time. One notable feature is the widespread coverage of sand blows in the eastern quarter of the county, suggesting a major soil liquefaction field consistent with strong seismic activity (magnitude 6.0 on the Richter Scale). Also seen in these photographs are the vestiges of the large prairies once found on the Pleistocene terraces of southern and eastern Arkansas. The former extent of these prairies can be clearly discerned, as can the encroachment of surrounding forests. Numerous prairie mounds are also visible across much of the county, especially in areas cleared for agriculture. Finally, nearly 15,000 contiguous hectares of virgin bottomland hardwoods along the Saline and Ouachita rivers are still apparent, which may have sheltered Ivory-Billed Woodpeckers in the 1930s. This work illustrates the value of old aerial photographs in the description of historical features by providing a snapshot of conditions that can help us understand present and future landscapes

Role of graduate students in university education in natural resources: A view from within

Concern has recently arisen on the changing role graduate students play in natural resources education at the university level. For example, there is the perception that an M.S. degree is little more than a preliminary step towards a Ph.D., rather than having its own quantifiable merits. Questions have also been raised about the degree of professionalism exhibited by graduate students, the expectations faculty have of students and the expectations students have of faculty