Integrating Bioenergy Harvesting with Silviculture - A California Example
Although the revenue obtained from the biomass does not always cover all harvesting and transportation costs, Sierra Pacific Industries (SPI) in northern California has integrated bioenergy harvesting into their forest management plans. According to SPI management, they do this because the removal of the biomass substantially reduces the costs of other forest operations and reduces the risk and liabilities associated with forest fires.
Many of their forests in inland northern California are degraded natural ponderosa pine (Pinus ponderosa) stands with a history of high-grading. Their practice for regenerating these stands is to clearcut small blocks which are planted with genetically improved seedlings and managed as even-aged plantations using intensive silviculture. Establishment typically includes ripping and weed control. Since fire is a high risk and carries large liabilities if it spreads to adjacent land, it is important to reduce residual biomass on the site. If bioenergy harvesting were not carried out, the slash would need to be piled and burned, a practice that itself carries considerable risk, causes smoke pollution, and can be safely undertaken only a few days each year. Thus biomass harvesting at clearcutting:
- improves access to the site for ripping, planting, and weed control;
- removes the necessity to pile and burn residues;
- reduces costs of establishing the new crop by as much as $150 per acre (2006 data); and
- is more environmentally friendly than other alternatives.
Because of the cost savings, the operation can be justified on sites where the direct costs of removing residue, chipping, and transportation are not fully covered by the payment made by the energy company.
The company often harvests the biomass at clearcutting in a two stage process. Prior to logging the valuable sawlogs, small trees are removed with a feller-buncher. This material is left in piles within the forest for transpiration-drying for several weeks prior to being forwarded to landings for chipping. Some nutrient-rich foliage is shed from the trees during this process.
This pre-harvest biomass removal also improves logging access. After logging the merchantable trees, the remaining residue is also collected and chipped (at right). The amount of chipped residues removed from the site for the combined operations varies from 15-25 dry tons per acre.
Sierra Pacific Industries also uses bioenergy harvesting to ensure timely thinning operations and when establishing fuel breaks as part of their fire prevention operations. Harvesting small trees during thinning operations ensures growth is concentrated on the valuable crop trees, while again reducing the risk of fire. A normal first commercial thinning is often about age 15 years in ponderosa pine plantations. The supply of biomass for energy allows for earlier thinning and reduced overall costs by about $50 per acre (2006 data) compared with chainsaw non-commercial thinning.
The biomass operations are limited to sites where:
- the transport distance is under 100 miles,
- slopes are <40%,
- access is suitable for chip vans, and
- there is a minimum of about 7 dry tons of chips per acre available for an operation.
Encyclopedia ID: p1333
