Baseload, Bioenergy

Bio-energy Forest Plantations for the Southeastern United States

Bio-energy forest plantations will supplement woody biomass from other sources such as logging residues. In the southern U.S., projections are for an increase of up to 25 million “new” tons of woody biomass demand for bioenergy. To supply this woody biomass demand will require purpose grown plantations of various species including pine, eucalypts, sweetgum, hybrid poplar and cottonwood, amongst others. Forest plantation yields can be 8-15 green tons/acre/year on rotations of 5-12 years. Utilization of this renewable and sustainable biomass resource will be as feedstock “designed” for a large number of bio-energy applications.

Demand for renewable energy sources is increasing in the Southeastern United States. There are few opportunities in this region to achieve this with sources such as solar, wind and hydroelectric. Biomass from agriculture and forestry are available for bioenergy feedstock. In the particular case of forestry, purpose grown plantations for biomass feedstock give an opportunity for cost savings, a sustainable resource for bio- energy and an economic opportunity for forest landowners.

Bio-energy plantations include, amongst others, pine, cottonwood, hybrid poplar, sweetgum and eucalypts. Much of the emphasis has been on hardwood plantations due to their ability to coppice, continued genetic improvement programs as well as the opportunity to combine fast growth and wood properties in selected clones. In the specific case of Eucalyptus and Populus, there are a large number of commercial planting programs in countries outside the U.S.

A number of feedstock characteristics are important in bio-energy hardwood plantations. Firstly, the plantation hardwood species has to be adapted to the soil and climate conditions. The hardwood feedstock has to be acceptable in harvesting, field processing and ultimately for conversion to bio-energy. Lastly, the growing (stumpage), harvest, haul and preparation costs have to be favorable compared to other biomass options. In the Southeastern US there are a limited number of hardwood species that can be competitive for forest plantation biomass for bio-energy production. The most important species would be from genera such as Eucalyptus, Populus and Liquidambar.

Hardwood Comparisons

Published data on commercial growth rates and final harvest yields for hardwood bio- energy plantations in the southeastern U.S. are relatively scarce. In Table 1, a sample of published growth rates are provided.

Growth rate differences are large and will depend on multiple factors including species, soils and harvest methods. In several states including Florida, eucalypt plantations are being considered for pellets (Pirraglia et. al., 2011), bio-fuel (Gonzalez et. al., 2011a,b) and combined heat and power (Dougherty and Wright, 2010, 2012).

Conclusions

Publication of commercial growth rates and final harvest yields for hardwood bio-energy plantations would be useful for those forestry and energy organizations seeking to invest in this renewable asset. It is surprising, to some, that after more than seventy years of research there are less than ten refereed publications with harvest yield values

though certainly the grey “unscanned” literature contains more. In addition, including stand management details as well as stating in the publication whether it is green versus dry tons, whole tree chips versus wood chips would also assist the investors. 

Lead image: Forest trees via Shutterstock