Growing Biomass: Hybrid Poplar

Introduction of the Crop:

The Hybrid Poplar is called such because of the cross pollination that has occurred (either naturally or more commonly artificially) between multiple members of the Salicaceae family (poplars). The cross breeding is common with around 30 species varying from native species, either regionally known (Trembling Aspen, Eastern Cottonwood), nationally known (Carolina Poplar) and non-native species (Black Poplar from Bulgaria, Japanese Poplar, or European Aspen). The primary reason cross breeding is done is to ?get the best of both species?. These desired attributes are most commonly tree vigor, growth potential, or yield.

Hybrid Poplars have been studied and grown in Minnesota and some in Wisconsin. The amount of study and research that has gone into hybrid poplars has led to the creation of many Best Management Practice ?how to? guides such as ?Hybrid Poplar Crop Guidelines? or ?Hybrid Poplar Handbook? (Isebrands J.G., 2007). In many cases these hybrids have many times outgrown native aspen species that would normally be planted.

In two separate Canadian studies, hybrid poplars planted on idle land produced 3.75 and 5.67 tons per acre year (Truax et.al. 2011, Fortier et.al. 2010, respectively). In the same studies, hybrids grown on less than ideal sites where many controlling factors existed (poor nutrient loads, elevation as a controlling factor, depth to hardpan/water table) noticeable decreases were seen being 2.27 to 0.57 tons per acre year were seen in the same studies respectfully.

Site selection:

The origin of all hybrid poplars traces back directly to the ?pioneer species? that do best in large openings with minimal competition from larger plants. The use of large open fields like idle farmlands as the basis for plantations provide this crop with stronger growing potential. Sites preferred by hybrids can vary depending on elevation, cold hardiness of the plant, and nutrients, but all hybrids have several attributes in common at the site or stand level. Preferred acidity of the soil is a pH of 5 to 7.8, meaning these sites are either slightly acidic to just barely alkaline. The soil itself should have an organic matter content of 3-8% with slopes less than 8%.

Site Preparation:

Prior to planting any variety of these hybrids, herbicide should be applied to vegetation already occupying the site and larger shrubs should be removed to eliminate the potential for competition of resources. Once preliminary herbiciding has been done, cultivation either with moldboard or chisel plow should be done in preparation to planting the poplar. Once planted, either by hand or via machine, the surrounding vegetation may require herbicide up to the third or fourth year after planting to remove competing weeds or shrubs. Once planted, the use of fertilizer may be required, depending on the site?s fertility, and is encouraged for successful harvest. Actual estimates of required fertilizer will vary between sites, however for Hybrid Poplars use during the third year after planting is suggested (Froese R., Abbot Z., 2012).

End Results:

This form of ?crop management? is being established with a plantation of Hybrid Poplar to provide the landowner with opportunities ranging from long-term stable investments to recreational values.

Pros:

  • Utilization of idle lands
  • Plantation grown (consistency)
  • Growth can be 5-6 feet per year with dry ton weight exceeding 5 dry tons per acre year (on ideal sites)
  • Stable long-term investment (ten year harvest: biofuels or 15-20 year harvest pulp logs)
  • Grown from sprouts/root suckers (re-establishment costs minimal to nonexistent) and/or cuttings depending on viability
  • Harvested with standard harvesting equipment
  • Recreational value
    • Poplars and their cross breeds provide habitat and food for: Deer, hares, porcupine, migratory birds, ruffed grouse
    • Management in Minnesota favors poplar (aspen) species across the State since it is the most successful habitat for this species, which has provided the State with large and healthy populations.

Cons:

  • Requires conversion to plantation; considered costly
  • Herbicide may be required through first 3-4 growing seasons depending on weed vigor
  • Long-term investment, no quick turn options
  • Conversion back to idle status costly and time consuming

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Best Management Practices

Yield in 8 year-old hybrid poplar plantations on abandoned farmland