Evaluating Hackberry Sites

Abstract

Site-index curves are presented for evaluating the growth potential of hackberry in native timber stands in Kansas. A single guide curve was computed from data gathered in the 1964-1965 Kansas forest inventory and harmonized curves were calculated. Hackberry (Celtis occidentalis L.) is one of the most widely distributed tree species in the woodlands of Kansas. Hackberry ranks third in total standing biomass and harvested sawtimber from commercial forest land (Raile and Spencer, 1984), and is used principally for furniture and containers. Although found on a variety of sites, hackberry grows best on rich soil along streams. In the eastern third of the state it grows in mixture with other hardwood species but occurs in almost pure stands in the central part of the state. Hackberry is drought resistant and has survived extremely dry periods in the Great Plains (Fowells, 1965). Evaluation of site productivity (wood producing potential of an area) is an important aspect of management for attaining maximum benefits from forest lands. The site-index method is the most widely accepted means for determining site quality. It uses tree height/age relationships and correlates well with timber yields. By definition, site index is the average height at age 50 years of dominant (overstory) trees in a fully stocked, even-aged stand. Curves or tables have been published for many commercial tree species in the United States. In Kansas, only curves for black walnut (Juglans nigra L.) have been published (Geyer and Lynch, 1987). The purpose of this paper is to provide another in a series of site-index equations, curves, and height tables for important tree species growing in natural stands in Kansas. PROCEDURE Forest survey data from Kansas (Chase and Strickler, 1968) provided the basic input for the construction of the site-index curves. As part of a stand inventory and analysis program, 776 temporary, variable-radius plots randomly located in the forest areas of the state were established at 10 points uniformly placed over each sample. This content downloaded from 157.55.39.43 on Fri, 30 Sep 2016 05:29:42 UTC All use subject to http://about.jstor.org/terms VOLUME 91, NUMBERS 3-4 159 Table 1. Distribution of sample trees by age and height classes. Height classes Age classes 25 35 45 55 65 75+ Totals 20 2 9 5 1 1 18 30 2 13 19 14 1 1 50 40 5 13 6 1 25 50 3 6 5 4 18 60 1 1 7 2 11 70+ 4 4 8 Totals 4 22 33 35 24 12 130 Tree measurements included height and age of the first tree in each plot that was one of the major species represented and whose crown was in the upper canopy. Total tree height to the nearest foot was measured with a relascope, and age to the nearest year was determined by increment borings at breast height (4.5 ft.). Additional years were added for seedling development to estimate total age. Hackberry was found at 130 sample areas. The distribution of these trees by height and age classes is shown in Table 1 and by geographic location and physiographic site classes in Table 2. A non-linear growth model (Richards, 1959) was used to express heightgrowth patterns. The model used was H = bo + bl(1l e-b2Age), where: H = dominant and codominant height (feet), Age = total age in years, b = coefficients of the model estimated by the iterative method of least squares, e = base of natural logarithms. A guide curve was calculated using SAS (Barr et al., 1976) and a family of site-index curves was developed utilizing the harmonized curve approach (Spurr, 1952). This approach assumes that additional curves are proportional to the guide curve, differing only by a fixed percentage. Aspen in the Central Table 2. Distribution of sample plots by geographic location and physiographic sites. Physiographic sites Geographic location Upland Lower slope Intermittent Bottomland Totals Northeast (22 counties) 4 15 28 16 63 Southeast (21 counties) 5 26 18 49 Western (62 counties) 3 12 3 18 Totals 4 23 66 37 130 This content downloaded from 157.55.39.43 on Fri, 30 Sep 2016 05:29:42 UTC All use subject to http://about.jstor.org/terms 160 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE Table 3. Estimated total height (ft.) of upper canopy hackberry trees in Kansas with base age 50 years.