What's in a soil name?

By Thembi Borras

You may be familiar with local forest soil names such as Bearwallow, Kibesillah, Ornbaun and/or Zeni. Soil names, also referred to as series names, are commonly used to connect to useful information such as soil descriptions that include potential annual production, permeability, erodability, depth and color, which may inform management decisions. Series names are easy to remember, pronounce and recognize. However, dig a little deeper and you learn behind each series name is a soil order, suborder, great group, subgroup and family, which when combined form a long and complex taxonomic classification that is brimming with information, such as particle size, temperature regime, moisture regime, characteristic soil horizons and origin.

For example, the Zeni series is a fine-loamy, mixed, isomesic Ultic Haplustalf. From this, I can glean that it is in the Alfisol order, an order that in part may be characterized by clay from upper horizons leaching to lower horizons where the clay accumulates in films. The moisture regime is ustic, which means moisture is limited, but is present at a time when conditions are suitable for plant growth. The temperature regime, is isomesic, which means the annual soil temperature is between 46 degrees F and 59 degrees F, measured at approximately 20" below the surface. Finally, I can glean something about the particle size; fine-loamy may be translated to clay loam. A loam is a mixture of sand, silt and clay that exhibits the properties of each in approximately equal proportions.

There are twelve orders of soils, Entisols are young soils with little or no morphological development. Inceptisols, Alfisols, and Ultisols are in ascending order in the development continuum, all of which locally can support timber. Mollisols are soils with a dark horizon rich in organic matter and can often be found supporting grasslands. Aridisols are desert soils. Vertisols are truly amazing as they invert themselves through the shrinking and swelling of the clays contained within them in response to soil moisture. Oxisols are highly weathered soils in subtropical or tropical environments; you can experience Oxisols in Florida. Andisols are soils formed in volcanic ash and are prevalent in the Andes. Spodosols are acid forest soils with a subsurface accumulation of metal-humus complexes. In our area, the pygmy forest grows from a Spodosol. Histosols are organic soils, peats are an example. Finally Gelisols are soils with a permafrost within 2 meters of the surface.

A portion of this production was gleaned from Keys to Soil Taxonomy published by the USDA and the Natural Resources Conservation Service, The Nature and Properties of Soils by Nyle Brady, the University of Idaho Soil Science Division website at http://soils.ag.uidaho.edu/soilorders/orders.htm and The Soil Survey Report for the western part of Mendocino County, available at http://www.ca.nrcs.usda.gov/mlra02/wmendo.html.

Increasing Timber Inventory to a Sustained Yield Goal

By Thembi Borras

Developing a sustained yield goal is in part based on site quality, which conveys the relative productivity of a land area. According to the Soil Survey Report for the western part of Mendocino County, the potential annual production from a fully stocked stand can be as low as 245 board feet (bf) per acre per year to as high as 2,050 bf/acre/year. Although different for each soil complex, often the potential annual production from a fully stocked stand of redwood and Douglas-fir is closer to 750 bf/acre/year. The sustained yield goal can be determined given the potential annual production and a selected long-term annual growth rate that can be maintained while protecting forest related values.

For example, if the potential annual production on the Jones Family Forest is 800 bf/acre/year and the Jones Family selects a long-term annual growth rate of 4%, the sustained yield goal is 20,000 bf/acre. This is determined by the following formula: 800 bf/acre/year = (.04/year)*X; X=20,000 bf/acre. The Jones Family Forest is 200 acres. Therefore, the sustained yield goal is 4,000,000 bf on the entire Jones Forest.

Critical to this exercise is to compare the sustained yield goal to the current standing volume and the current annual growth rate to the long term annual growth rate.

Continuing with this example, based on information from a timber cruise, the Jones Family Forest supports a current standing volume of 2,000,000 bf or 10,000 bf/acre. The Jones Family now knows the starting point, which is 2,000,000 bf, and the goal, which is 4,000,000 bf. At this point, a Potential Harvest Schedule can be developed, which will reflect how quickly this goal is reached based on the volume harvested at each entry, the responding growth rate and the frequency of entries.

By cutting less than growth over several cycles, the inventory of the stand will build and eventually the sustained yield goal will be attained, at which point, the periodic growth can be harvested without ever depleting the inventory.

The inventory can be viewed as “principle” and the growth as the “interest” earned on that principle. A truly sustainable forest allows the perpetual harvest of the interest without ever having to touch the principal.

The Soil Survey Report for the western part of Mendocino County is available at http://www.ca.nrcs.usda.gov/mlra02/wmendo.html. A portion of this production was gleaned from an unpublished paper by Craig Blencowe entitled, Craig Blencowe: Building up the Forest.