Donald L. Rockwood

Short-rotation woody crops and phytoremediation: Opportunities for agroforestry?

Worldwide, fuelwood demands, soil and groundwater contamination, and agricultures impact on nature are growing concerns. Fast growing trees in short rotation woody crop (SRWC) systems may increasingly meet societal needs ranging from renewable energy to environmental mitigation and remediation. Phytoremediation, the use of plants for environmental cleanup, systems utilizing SRWCs have potential to remediate contaminated soil and groundwater. Non-hyperaccumulating, i.e., relatively low contaminant concentrating, species such as eucalypts (Eucalypts spp.), poplars (Populus spp.), and willows (Salix spp.) may phytoremediate while providing revenue from fuelwood and other timber products. Effective phytoremediation of contaminated sites by SRWCs depends on tree-contaminant interactions and on tree growth as influenced by silvicultural, genetic, and environmental factors. Locally adapted trees are essential for phytoremediation success. Among the different agroforestry practices, riparian buffers have the greatest opportunity for realizing the SRWC and phytoremediation potentials of fast growing trees. Agroforestry that combines SRWC and phytoremediation could be an emerging holistic approach for sustainable energy, agricultural development, and environmental mitigation globally.

Energy Product Options for Eucalyptus Species Grown as Short Rotation Woody Crops

Eucalyptus species are native to Australia but grown extensively worldwide as short rotation hardwoods for a variety of products and as ornamentals. We describe their general importance with specific emphasis on existing and emerging markets as energy products and the potential to maximize their productivity as short rotation woody crops. Using experience in Florida USA and similar locations, we document their current energy applications and assess their productivity as short-term and likely long-term energy and related products.

Micropropagation of field tested superior Eucalyptus grandis hybrids.

Three superior clones of Eucalyptus grandis hybrids were micropropagated through several steps. Five-year-old trees were girdled to induce juvenile sprouts. Cultures were attempted from mature branches and sprouts. Branches from mature trees were 100% contaminated while sprouts were only 40% contaminated. Pre-initiation hormone free medium and dark environment were used to screen for contaminants and to reduce production of phenolic compounds. Initiation of auxillary buds was achieved with modified MS plus 0.05 mg/l NAA and 0.5 mg/l BAR High multiplication rates were obtained on auxin-free medium with 0.6 mg/1 BAR Elongation of shoots was best on media with high auxin (2.5 mg/l of IBA) and cytokinin (1–1.5 mg/l of zeatin). Continual subculture on the multiplication medium improved rooting significantly. Up to 98% rooting was achieved on 1/4 MS with 2 mg/l IBA. Rooted propagules were successfully transferred to a mist greenhouse with 82% survival, and then to greenhouse conditions.

Field performance of micropropagated, macropropagated, and seed-derived propagules of three Eucalyptus grandis ortets.

Tree size, survival, and coppicing of micropropagated plantlets, macropropagated cuttings, and seedlings of Eucalyptus grandis Hill ex Maiden were monitored through 57 months in a study in southern Florida to assess propagation options. Two plantlet lines developed by direct micropropagation and orchard open-pollinated seedlings from three ortets were compared in the main study. Rooted cuttings from up to four ramets of each of the three ortets and another ortet were examined in an adjacent supplemental study. Freezes at six and 16 months killed most initial and first-coppice stems to the ground. Most developmental differences in the main study were consistent from ages 2 to 57 months. Propagation by ortet interactions were observed beginning at 21 months, due to the poor performance of seedlings of one ortet after the second freeze. At 57 months, no differences in tree height, DBH, volume, or survival were detected between plantlet lines and between rooted cuttings and plantlets, but seedlings were inferior to plantlets and cuttings. Vegetative propagules had more uniform tree size at every age, with typically less than one-half the variability observed among seedlings. Even though plantlets and cuttings may be more expensive to produce, they have numerous advantages over seedlings for E. grandis plantation establishment in Florida.

Development of Eucalyptus clones for a summer rainfall environment with periodic severe frosts

Eucalyptus grandis, E. grandis hybrid, and E. saligna hybrid trees, developed through as many as four generations of selection in southern Florida, were naturally exposed to exceptionally low winter temperatures. In a genetic base population and related field studies, 100 phenotypically superior cloning candidates were selected after an 8-h freeze with a low of −11 °C. Following propagation as rooted cuttings, 55 clones (typically 11–42 ramets per clone) were outplanted in a single-tree plot design and evaluated for 3.8 years which included two additional severe freezes. Significant clonal variation was observed in frost resilience, vigor, and quality. After composite evaluation for frost resilience, size, and form, only three clones were considered suitable for operational planting. Selection of further clones for outplanting requires major commitments to locate candidates and to test them. Field testing for frost resilience requires considerable investment, much beyond the requirements for developing fast-growing clones alone. Clones identified by testing will not be resistant to freezing conditions but will be resilient and greatly reduce the risks now associated with plantation culture in southern Florida.

Survey to Evaluate Escape of Eucalyptus spp. Seedlings from Plantations in Southeastern USA

Interest in biomass-based energy in the southeastern Unites States has led to increased need for fast-growing tree species. Several Eucalyptus species exhibit characteristics that make them attractive in the bioenergy context. However, some of these also possess traits that suggest they could become invasive. To make a preliminary assessment of the risk of seedling establishment in the vicinity of Eucalyptus plantations, we conducted surveys at 3 sites in South Carolina and 16 sites in Florida. In South Carolina, no seedlings were detected in any sample transect. In Florida, we found seedlings within the boundaries of Eucalyptus plantations at 4 of the 16 sites surveyed. We also detected seedlings outside the boundaries of these same four plantations, but only two seedlings were detected at distances >45 m from plantation boundaries. All seedlings from Florida were either E. amplifolia, E. robusta, or E. grandis. The most predictive variable evaluated was latitude, with 27°N being the highest latitude at which seedlings established with regularity. Results of this survey indicate that, under current conditions, the spread of Eucalyptus spp. from plantations should be possible to manage with appropriate monitoring, but this should be evaluated further before Eucalyptus spp. are adopted for widespread planting.

On Polydispersity of Plant Biomass Recalcitrance and Its Effects on Pretreatment Optimization for Sugar Production

This paper discusses a property associated with plant biomass recalcitrance to enzyme and microbial deconstructions in sugar production from cellulose and hemicelluloses. The hemicelluloses are more readily hydrolyzed to sugars than is cellulose. As a result, optimization to maximize individual glucose and hemicellulose sugar recovery is not possible. This property is an inherent feature of plant biomass and is named polydispersity of plant biomass recalcitrance (PPBR) in this study. A set of pretreatment experiments using eucalyptus and sulfite pretreatment to overcome recalcitrance of lignocelluloses was conducted. The results were used to predict the conditions for individually maximizing enzymatic glucose and xylose yields. The predicted maximal yields were used to quantitatively illustrate the PPBR concept. The effect of PPBR on pretreatment optimization and strategies for maximal sugar recovery using two-stage pretreatment are discussed.

Comparative greenhouse study of Eucalyptus grandis in vitro plantlets and half-sib seedlings, I. Net photosynthesis

Tissue culture-derived plantlets from three superior five-year-old Eucalyptus grandis Hill ex Maid hybrids were compared to their related half-sib seedlings under greenhouse conditions. Net photosynthesis, chlorophyll a and b concentrations, and nitrogen concentration were sampled four times at 40-day intervals. Comparisons were started 40 days after plantlets and germinating seedlings were moved from mist to greenhouse conditions. Seedlings had higher net photosynthesis, chlorophyll and nitrogen concentration at early harvests. However, as the study progressed the difference between plantlets and seedlings decreased and reached similar values. No family differences were observed regardless of plant origin (seedlings or plantlets). Plantlets and seedlings showed similar general trends in all the measured parameters over the four harvests.

History and Status of Eucalyptus Improvement in Florida

The first organized Eucalyptus research in Florida was begun by the Florida Forests Foundation in 1959 in southern Florida. This research was absorbed by the USDA Forest Service and the Florida Division of Forestry in 1968. In the early 1970s, the Eucalyptus Research Cooperative formed to provide additional support emphasized E. grandis, E. robusta, E. camaldulensis, and E. tereticornis and developed cultural practices for commercial plantations in southern Florida. In 1978, this cooperative united with the Hardwood Research Cooperative at North Carolina State University until 1985 when the 14-year effort ended after three severe freezes from 1983 to 1985. Eucalyptus planting and research were continued with a Florida-wide focus by the University of Florida and collaborators starting in 1980. The collective accomplishments in terms of genetic resources and commercial planting are summarized. For example, fast-growing, freeze-resilient E. grandis seedlings are produced by advanced generation seed orchards, five E. grandis cultivars are commercially available, as are E. amplifolia and Corymbia torelliana seeds. Genetic improvement of these and other species is ongoing due to beneficial collaborations. Short Rotation Woody Crop systems are promising for increasing productivity and extending uses beyond conventional pulpwood to applications such as windbreaks, dendroremediation, and energy wood.

Qualitative evaluation of fuelwood in Florida - a summary report.

This report summarizes qualitative information on 5 potential Florida fuelwood species: slash pine, sand pine, melaleuca, eucalypt, and casuarina. The important factors affecting the quality of fuelwood for industrial applications are briefly discussed. Fundamental properties relating to the fuel quality of these 5 potential fuelwoods are synthesized from several published and unpublished reports. Based on the qualitative data shown in this report, it appears that the fuel characteristics of these 5 species are comparable or superior to those of many other woods evaluated in the literature.