SOIL-CORE BREAK METHOD TO ESTIMATE PINE ROOT DISTRIBUTION

Root-distribution studies are tedious and time consuming; therefore, root systems of forest ecosystems are one of the least studied components. Yet they are essential in order to assess belowground effects of forest-management activities. This study used the soil core-break method to measure the number of roots crossing a horizontal unit area (N, expressed in no. cm-2) as an alternative to measuring the more time consuming root-length density (Lv, expressed as cm root length cm-3 soil volume). Soil core samples were taken from the surface horizon of a 7-yr-old slash pine (Pinus elliottii Engelm.) stand growing on a Pomona sand (sandy, silliceous, hyperthermic Ultic Hapiaquod). Soil cores, 15.2-cm diameter by 30 cm long, were extracted from two microsite locations within the check and complete-weed-control plots. Root-length density and roots per square centimeter were measured at 2-cm depth increments. The roots-per-square centimeter measure was a useful predictor of root-length density only when treatment means were used, and even then the data did not fit the theoretical relationship of Lv = 2N. An Lv/N slope of = 1 suggested that roots have a preferential vertical orientation in the A horizon. However, depth trends of root-length density and roots per square centimeter were similar regardless of management practices or microsite. Roots measured as roots per square centimeter was also a less variable measure of root quantity than was root-length density. Although roots per square centimeter can only be used to calculate root-length density on an empirical basis, the more easily obtained value of roots per square centimeter can be used to depict root response to belowground competition.