Thomas R. Fox

Sustained productivity in intensively managed forest plantations

Abstract Because of the rapid increase in the world’s population, demand for forest products is increasing while large amounts of forest land are being lost or degraded. In addition, timber harvest is being restricted in many of the world’s natural forests. The use of plantations managed for timber production must increase to meet the world’s increasing demand for wood and fiber from this reduced land base. Concentrating timber production on the best-adapted sites will allow the world’s demands to be met on fewer acres. Intensive management of plantation forests is perhaps the only way to meet the increasing demand for forest products and still reserve large areas of native forests for conservation and preservation purposes. Maintaining long-term soil productivity in these intensively managed plantations is critical. The impacts of intensive management on soil quality and subsequent tree growth can be positive, neutral or negative; the direction and magnitude of the impact depends on the specific management practice soil physical, chemical and biological properties. In order to understand and predict the impacts of intensive management, the factors limiting productivity on each specific site must be understood. Forest harvesting by itself tends to have minor impacts on soil quality and long-term site productivity. Compaction during timber harvesting can degrade the soil quality. However, tillage during site preparation can in most cases restore soil physical properties to pre-disturbance levels. Site preparation practices that remove large quantities of organic matter and surface soil can detrimentally impact soil quality, most notably on sandy soils. Intensive management practices such as fertilization can improve soil quality and increase site productivity by ameliorating factors limiting growth. The increased growth rates in intensively managed stands can indirectly improve soil quality by increasing organic matter. The increased production of coarse roots in intensively managed plantations is particularly important in this regard. These changes can lead to long-term improvement in soil quality and site productivity, especially on the degraded soils on which many forest plantations are established. Based on the available data, intensive management can be practiced sustainably on many soils. Land classification systems are needed to identify soils that are suitable for intensive management. Site-specific management regimes must then be developed to insure that intensive management is practiced sustainably on these soils.

Effects of site preparation on nitrogen dynamics in the southern Piedmont

Abstract The impact of three mechanical site preparation treatments, chop-burn, shear-disc, and shear-pile-disc, on nitrogen dynamics was examined on gauged watersheds in the Piedmont of Virginia. Samples from soil solution and streamwater and a series of soil incubations, both laboratory and in situ, were used to monitor changes in the treatment areas following site preparation. Available nitrogen reserves were lowest in the shear-pile-disc watershed where the logging slash had been piled into windrows. Larger nitrogen reserves were found in the shear-disc and the chop-burn watersheds. Nitrogen mineralization was greater in the site prepared areas than in the uncut stand and mineralization generally increased as site preparation intensity increased. Between 58 and 95 kg/ha of nitrogen were mineralized in the site prepared areas during the first year following treatment compared to only 38 kg/ha during the same period in the uncut stand. Streamwater nitrogen export increased following site preparation with the largest losses of nitrogen occurring in the shear-pile-disc watershed.

Genetically engineered trees for plantation forests: key considerations for environmental risk assessment

Forests are vital to the worlds ecological, social, cultural and economic well-being yet sustainable provision of goods and services from forests is increasingly challenged by pressures such as growing demand for wood and other forest products, land conversion and degradation, and climate change. Intensively managed, highly productive forestry incorporating the most advanced methods for tree breeding, including the application of genetic engineering (GE), has tremendous potential for producing more wood on less land. However, the deployment of GE trees in plantation forests is a controversial topic and concerns have been particularly expressed about potential harms to the environment. This paper, prepared by an international group of experts in silviculture, forest tree breeding, forest biotechnology and environmental risk assessment (ERA) that met in April 2012, examines how the ERA paradigm used for GE crop plants may be applied to GE trees for use in plantation forests. It emphasizes the importance of differentiating between ERA for confined field trials of GE trees, and ERA for unconfined or commercial-scale releases. In the case of the latter, particular attention is paid to characteristics of forest trees that distinguish them from shorter-lived plant species, the temporal and spatial scale of forests, and the biodiversity of the plantation forest as a receiving environment.

Eucalyptus beyond Its Native Range: Environmental Issues in Exotic Bioenergy Plantations

The genus Eucalyptus is native to Australia and Indonesia but has been widely planted in many countries. Eucalyptus has proven to be particularly successful in tropical and subtropical regions. Several species are also successful in some temperate regions, but problems with sudden and severe frosts pose limitations. Current plantations around the world are dominated by the “big nine” species (E. camaldulensis, E. grandis, E. tereticornis, E. globulus, E. nitens, E. urophylla, E. saligna, E. dunnii, and E. pellita) and their hybrids, which together account for more than 90% of Eucalyptus planted forests. Much of current tree improvement efforts focus on the use of hybrids and clones, and development of genetically modified Eucalyptus is already underway. For many reasons, there is increased interest in using wood for energy, and short-rotation plantings of Eucalyptus will likely be an important source of feedstock [1]. Many Eucalyptus species have desirable properties for bioenergy plantations, including rapid growth rates and high wood density. The indeterminant growth pattern and evergreen foliage allow eucalypts to grow whenever climatic conditions are suitable.The sclerophyllous leaves of eucalypts allow them to withstand very dry conditions and may also be an adaptation to low nutrient conditions. However, the same traits that make Eucalyptus attractive for bioenergy and other bioproducts, such as rapid growth, high fecundity, and tolerance of a wide range of climatic and soil conditions, also make them potentially invasive. The prospect of widespread planting of these nonnative species for commercial purposes in the southern United States has again arisen, prompting questions about potential environmental effects. In response, a conference was held in Charleston, South Carolina, in February of 2012 to review the history of Eucalyptus research and culture in the USA and around the world and to examine potential environmental issues surrounding their expanded introduction in the southern USA. Environmental issues addressed included invasiveness potential, fire risk, water use, and sustainability. Papers from that conference, as well as contributions from other countries that shed light on these issues, are the subject of this special issue.

Does Plethodon cinereus affect leaf litter decomposition and invertebrate abundances in mixed oak forest

Abstract Although investigators have determined that some anurans can influence nutrient availability in terrestrial systems, ecological interactions among salamanders, invertebrates, and leaf litter decomposition in the detrital ecosystem are poorly understood. We examined the effects of the Eastern Red-Backed Salamander (Plethodon cinereus) on leaf litter decomposition rates and invertebrate populations in the mixed oak forests of southwestern Virginia from May 2006 to June 2008. We constructed 12 in situ mesocosms with 0, 1.0, or 2.0 P. cinereus/m2 (4.0 P. cinereus/m2 in year 2). We quantified decomposition rates of leaf litter and numbers of invertebrates with litter bags that were removed from mesocosms monthly throughout the experiment. Further, we assessed what taxa of invertebrates were preyed upon by salamanders with gastric lavage. Across our 2-year experiment, we were unable to detect an effect of salamander abundance on rates of leaf litter decomposition, numbers of broad invertebrate taxonomic groupings, or functional guilds of invertebrates. Stomach analysis confirmed that salamanders were euryphagic, but they consumed more herbivores than detritivores or predators. Although we are unclear why these results conflict with earlier work indicating that salamanders can influence invertebrates and leaf litter decomposition, variability of canopy trees or microclimate may have contributed to a lack of control of invertebrate populations or litter decomposition by salamanders in the complex mixed-oak forests of the Appalachian Mountains.

Phosphorus Nutrition of Forest Plantations: The Role of Inorganic and Organic Phosphorus

Fertilization with P is a common silvicultural practice in forest plantations where large and sustained growth responses frequently occur following P fertilization. Inorganic P is tightly sorbed in many forest soils and, consequently, labile P is low. Trees have evolved a variety of mechanisms to acquire P in soils with low P availability. This includes release of low molecular weight organic acids into the rhizosphere. Significant quantities of organic P also exist in the forest floor and mineral horizons of forest soils that can contribute to P nutrition of forests. There are several mechanisms whereby organic P in the forest floor and the mineral soil may become available to forest trees. These include uptake of organic P by mycorrhizae and mineralization of organic P.

Predicting Forest Regeneration in the Central Appalachians Using the REGEN Expert System

REGEN is an expert system designed by David Loftis to predict the future species composition of dominant and codominant stems in forest stands at the onset of stem exclusion following a proposed harvest. REGEN predictions are generated using competitive rankings for advance reproduction along with other existing stand conditions. These parameters are contained within modular REGEN knowledge bases (RKBs). To extend REGEN coverage into hardwood stands of the Central Appalachians, RKBs were developed for four site classes (xeric, subxeric, submesic, mesic) based on literature and expert opinion. Data were collected from 48 paired stands in Virginia and West Virginia to calibrate the initial RKBs. Paired stands consisted of one mature uncut hardwood stand adjacent to a regenerating clear-cut stand with similar site characteristics that was harvested within the previous 20 yr. Data from 17 additional paired stands was collected a year later to validate the performance of REGEN. Predicted values were within 4 percentage points of measured values on average, and model error was typically less than 20 percentage points for species groups. These results confirmed the suitability of REGEN to predict the future species composition of stands regenerated using the clear-cut method in the Central Appalachians of Virginia and West Virginia.

Absolute and relative changes in tree growth rates and changes to the stand diameter distribution of Pinus taeda as a result of midrotation fertilizer applications

Silvicultural treatments have the potential to change the diameter distribution of a stand, which can alter the final product mix of the stand. Growth and yield models need to account for these changes in the diameter distribution to assess the economic viability of the silvicultural operations. We investigated how the diameter distribution of Pinus taeda L. stands changes as a result of midrotation fertilization. Data from 43 installations of a nitrogen and phosphorus midrotation fertilizer trial series established in the southeastern United States were used in the study. The results indicated that both the absolute growth response and the relative growth response of individual trees were greater among the larger trees. A three-parameter Weibull distribution fitted at each study site was used to investigate how the parameters of the distribution changed with time and treatment. The location and scale parameters of the Weibull distribution were both affected by fertilization. Stand variables, such as site...

Estimating leaf area index at multiple heights within the understorey component of Loblolly pine forests from airborne discrete-return lidar

ABSTRACT Airborne discrete-return light detection and ranging (lidar) can be used to estimate leaf area index (LAI) with relatively high accuracy. This capacity was explored with regard to assessing the capability of estimating LAI at different heights at the plot level, in the presence of understorey vegetation, within intensively managed Loblolly pine forest in North Carolina, USA. Field measurements utilized the LI-COR LAI-2200 plant canopy analyser for field-based estimates of effective LAI at three elevations within each plot; these were on the ground (0.0 m) and 1.0 m and 2.5 m above the ground within the various understorey heights and densities. A number of new and previously existing lidar metrics and indices were calculated from the distribution of return heights, which have been identified as potentially strong predictors of LAI. A bivariate and stepwise regression approach was then applied to create models for the estimation of LAI from lidar-derived height distribution metrics. The results show that specific logarithm transformed laser penetration indices calculated using a height threshold (e.g. the number of returns below 2.5 m ratioed against all returns) as close to field LAI measurement height (e.g. 2.5 m) was more effective than other lidar metrics. LAI can be estimated for each of the three measurement heights within the understorey component explaining 67 to 76% of the variance (root mean square error 0.42–0.57). The indices that produced the highest correlations and which were selected in stepwise regression analysis were calculated using all returns. The results indicate that LAI can be estimated accurately using lidar data in pine plantation forest over a variety of stand conditions.

Microbial nitrogen cycling response to forest-based bioenergy production.

Concern over rising atmospheric CO2 and other greenhouse gases due to fossil fuel combustion has intensified research into carbon-neutral energy production. Approximately 15.8 million ha of pine plantations exist across the southeastern United States, representing a vast land area advantageous for bioenergy production without significant landuse change or diversion of agricultural resources from food production. Furthermore, intercropping of pine with bioenergy grasses could provide annually harvestable, lignocellulosic biomass feedstocks along with production of traditional wood products. Viability of such a system hinges in part on soil nitrogen (N) availability and effects of N competition between pines and grasses on ecosystem productivity. We investigated effects of intercropping loblolly pine (Pinus taeda) with switchgrass (Panicum virgatum) on microbial N cycling processes in the Lower Coastal Plain of North Carolina, USA. Soil samples were collected from bedded rows of pine and interbed space of two treatments, composed of either volunteer native woody and herbaceous vegetation (pine-native) or pure switchgrass (pine-switchgrass) in interbeds. An in vitro 15N pool-dilution technique was employed to quantify gross N transformations at two soil depths (0-5 and 5-15 cm) on four dates in 2012-2013. At the 0-5 cm depth in beds of the pine-switchgrass treatment, gross N mineralization was two to three times higher in November and February compared to the pine-native treatment, resulting in increased NH4(+) availability. Gross and net nitrification were also significantly higher in February in the same pine beds. In interbeds of the pine-switchgrass treatment, gross N mineralization was lower from April to November, but higher in February, potentially reflecting positive effects of switchgrass root-derived C inputs during dormancy on microbial activity. These findings indicate soil N cycling and availability has increased in pine beds of the pine-switchgrass treatment compared to those of the pine-native treatment, potentially alleviating any negative effects of N competition between pine and switchgrass. We expect that reduced soil C in the pine-switchgrass treatment, effects of pine and switchgrass rooting on soil C availability, and plant N demand are major factors influencing soil N transformations. Future research should examine rooting architecture in-intercropped systems and the effects on soil microbial communities and function.