Forest Guild Report on Biomass Retention and Harvest

For foresters and landowners, one of the top concerns about the rise of the wood bioenergy industry over the last five years has been the effect of biomass removal on the health of the forest. The retention of biomass (logging slash, small-diameter trees, tops, limbs, and trees not considered merchantable in traditional markets) nourishes the soil, prevents erosion and provides wildlife habitat.

To date, this does not seem to have been much of an issue primarily because 1) in most states, not enough biomass is currently being removed to negatively impact forests and 2) many states have developed biomass harvesting standards in order prevent degradation of forest health.

As the bioenergy industry expands, however, as it is expected to do, the importance of understanding just how much biomass can be removed before forest health begins to suffer increases.

In an effort to “identify how expanding markets for bioenergy can enhance forests while meeting the social and economic needs of society,” the Forest Guild Southeast Biomass Working Group recently published Forest Biomass Retention and Harvesting Guidelines for the Southeast. For this publication, the Guild investigated best practices for four types of Southeast forests: Southern Appalachian hardwoods, Upland hardwoods and Mixed pine–hardwoods, Bottomland hardwoods and Piedmont and Coastal Plain pinelands. (Read our post outlining state guidelines for biomass harvesting.)

Based on their review of best practices for each of these forest types, the Forest Guild formulated recommendations for both the retention of 1) logging slash and other downed woody material (DWM) that provide soil nutrients and 2) forest structures that provide shelter for wildlife and promote biodiversity.

Downed Woody Material

The ideal biomass retention rate for a forest is specifically tied to the nutrient status of that forest. According to the Forest Guild report, “On sites where large quantities of DWM already exist, less retention is necessary.”  In general, however, the Guild makes the following recommendations:

• On an average site, 1/3 of the harvest slash should be left on site. The number of tons per acre can be found by forest type in the table below.
• DWM of all sizes should be left on site (fine, coarse and whole log).
• Slash should be distributed evenly over the site, not left in a pile at the landing.

Forest Structures

For forests with existing structures:

• Leave and protect roots, stumps and large DWM.
• Leave and protect live cavity trees, den trees, live decaying trees and dead standing trees (snags).

For forests without existing structures:

• Select live trees to become structures in the future.
• Retain a variety of species.
• When salvaging logging after a disaster, retain material and snags as indicated in the  table below.

The following table quantifies the amounts and types of material that should be retained based on the type of forest:

About the Forest Guild and the Report:

“The Forest Guild is a professional organization of forest stewards, associated natural resource professionals, and affiliates who are passionate about restoring and sustaining the integrity of our nation’s forests while meeting the needs of the communities that rely on them.” The group “developed these guidelines to assist several audiences: field foresters, loggers, state policy makers, biomass facilities wishing to assure sustainability, third-party certifiers, and members of the public interested in protecting forests. This report focuses on post-harvest forest conditions and not on the type of harvest.  The goal is to ensure the forest can support wildlife, maintain biodiversity, provide clean water, sequester carbon, protect forest soil productivity, and continue to produce income after a biomass harvest or repeated harvests.”