In Part 2 of this series (The Three Rules of Land), we discussed the three main characteristics that help to determine the desirability and value of a tract of land. In this article, we’re going to focus on the physical properties of the land or “dirt” itself that affect value which include site index, soil texture, and soil chemistry. These are some of the biggest components that determine the difference between “dirt” and “good dirt” for timberland.

If you are interested in timberland investments, you may be familiar with the term “site index.” If you are not, site index is the average height of co-dominant stems of a given crop species at a specific base age (usually 50 years) when grown in natural conditions with unimproved stock. It is often used as the benchmark of determining site productivity for timberland. While site index is a very important component of determining the quality of the soil, there are other factors that come into play in determining not only how much timber a tract is capable of producing, but also what species are best suited for the property and how difficult it may be to harvest the timber at maturity.

The term “soil texture” refers to the coarseness of the soil. In other words: How big are the particles that make up the soil? Coarse sandy soils are going to drain better and hold up to the ground pressure of timber harvesting during wet weather. Fine, clay soils will become sticky and soft in wet weather.

Operating equipment during these conditions will cause a laundry list of problems from root damage to residual trees to severe rutting and damage to the property’s road system. Ideal soils have a balance of coarse and fine particles; these soils are known as loams. A good sandy loam can absorb and drain water from significant rain events after 1-3 days and be suitable for equipment to resume operation.

In my experience, timber buyers often pay a premium for timber on land that has good access and well-drained soils that are “wet weather loggable.” This is because they know that they should be able to operate on those tracts during the wet winter months whereas they may have increased “downtime” or even be forced to leave tracts with finer soils until the weather improves.

Soil texture can also affect the land’s ability to grow timber. Extremely coarse soils with nearly pure sand or sand and gravel usually have poor productivity because of their low moisture holding capacity. These soils also tend to have lower pH and low available nutrient content, making it more difficult for plants to thrive and grow rapidly. On the other hand, extremely fine soils with heavy clay content may have the opposite problem. These soils can hold too much water and drown the roots of most trees and plants, with the exception of a few, highly adapted species. Again, a more balanced soil is going to be ideal for plant and tree growth.

An acre of timberland is only as good as its ability to grow good quality timber. So, knowing the specific soil types, textures and chemistry on the timberland you’re looking at buying or the timberland you already have is crucial.

Read more: Timberland Investing From the Ground Up