Soil‐Core Break Method to Estimate Pine Root Distribution

Root‐distribution studies are tedious and time consuming; there‐fore, 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, siliceous, hyperthermic Ultic Haplaquod). 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 = 2 N . 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.