Why poplar trees?
Poplar trees were chosen for the Biocycle Farm because they grow rapidly and consume large amounts of water and nutrients from either “liquid biosolids” (water mixed with processed biosolids) or dry biosolids and recycled water. Poplars absorb at least twice the amount of nutrients as rye grass per acre, which makes them a preferable crop for maximizing the amount of biosolids that can be applied to a field. This asset is not shared by crops like Christmas trees or mint. Additionally, poplar trees reach harvest maturity within 12 years, which makes them an agricultural crop. Forestry is not permitted on the Biocycle Farm’s agricultural lands.
What is hybrid poplar?
Poplar is a genus of tree in the willow family that includes aspen, cottonwood, and poplar. Hybrid poplar varieties are crosses of two different species to produce clones having desired characteristics – such as weather hardiness and straight trunk growth. The trees on the Biocycle Farm include hybrids of native cottonwood species as well as Eastern, European, and Asian poplars.
Is hybrid poplar genetically modified (GMO)?
No. The trees chosen for Biocycle Farm are not genetically engineered in any way. Unlike genetically-modified organisms (GMO) in which the genetic code is manipulated in a lab, hybrids are merely the result of age-old cross-fertilization. Hybrid reproduction is achieved through vegetative propagation (i.e., cuttings) in much the same way that roses, grapes, and similar plants are cultivated. Trees generated from cuttings are referred to as “clones” because they carry the same genetic attributes as the original parent plant.
What is harvested poplar used for?
Hybrid poplar have traditionally been grown by paper companies for pulp, as poplar has an strong, light-colored fiber ideal for paper and cardboard products. These same properties make poplar a good resource for plywood veneer, furniture frames, shipping boxes and molding and trim work. Poplar fiber is also an ideal raw material for biochemicals and biofuels as an alternative to petroleum products – in fact, passenger jets have been successfully tested to run on poplar biofuel.
Why does the MWMC grow poplar instead of a commodity crop like Christmas trees or hemp?
The MWMC’s Biocycle Farm is first and foremost an integral part of our regional wastewater management strategy. Poplar trees provide the nutrient uptake and other beneficial uses for biosolids. Furthermore, the poplars are well-suited to environmental conditions such as seasonal wetland flooding, which would not be conducive for other trees or crops.
Is poplar a useful wood like Douglas-fir?
Hybrid poplar is a softer, more rapidly-growing tree than Douglas-fir. Currently, local timber markets are primarily geared for manufacturing products from plentiful local Douglas-fir and similar conifer species, such as structural lumber. Poplar has its own unique characteristics that make it ideal for lightweight building materials, trim work and frames, and paper and fiber products. The MWMC is working with the wood products industry to achieve local market opportunities for poplar.
I see poplar boards at local supply stores – is that a market for Biocycle poplar?
Wood labeled “poplar” found in home improvement centers is typically not hybrid poplar, but is usually a tree called yellow-poplar (or tulip-poplar) harvested from eastern forests. Yellow-poplar is actually not a true poplar (similar to how Douglas-fir is not technically a fir tree).
Non-traditional uses of hybrid poplar are emerging, such as use in architectural ceiling panels and cross-laminated timber. Hybrid poplar is excellent for trims, non-structural boards, and similar uses due to its easily-stained light color and light weight.
Do the trees accumulate pollutants, like heavy metals, that impact its use?
Although the phytoremediation (pollutant reduction by plants) benefits of poplar is touted for cleaning up contaminated sites, the wood from Biocycle Farm poplar would not be impacted in any way. For one, biosolids contain only trace amounts of chemicals in very low concentrations, and secondly, the phytoremediation benefits largely occur in the root zone through bacterial action (as opposed to plant uptake and absorption).
How fast do the trees grow?
Under optimal conditions, poplars can grow as much as 8 feet per year, reaching heights of more than 70 feet and greater than 6 inches in diameter in 7- 10 years. Trees are harvested after 12 years. Many of the Biocycle Farm’s trees are 10-12 inches in diameter at harvest.
Why not grow the trees bigger – longer than 12 years?
The Biocycle Farm is an agricultural site, not a forestry site; therefore, poplar growth is limited by Oregon statute. After 12 years, the trees have reached 10- to 12-inch diameters and the growth rate slows down. While larger trees could be grown under forestry conditions, the optimal operational benefits of the poplar occur during years 4 to 12.
How much poplar is produced per harvest?
The MWMC expects poplar yields of approximately 50 bone-dry tons (BDT) of pulpwood per acre. This is based on optimally growing trees planted at a density of 222 trees per acre and harvested at Year 12. The suitable saw log material at harvest is expected to be approximately 30 to 33 thousand board-feet (MBF) per acre. The remaining pulp material yields approximately 17 to 20 BDT of chips. Additional material can be processed into hog fuel and used for mulch, compost, and bioenergy production.