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In 1986, equations to estimate site index in loblolly and slash pine plantations in East Texas were published. These equations were developed using data collected from East Texas Pine Plantation Research Project (ETPPRP) permanent plots distributed throughout East Texas. The site index prediction equations were designed to estimate tree height 25 years from planting, ie., index age = 25 years.

In the 1986 study, only data recorded during the first measurement cycle of the ETPPRP (1982- 1984) were available for analysis. Pairs of observed plantation age and a'verage !otal height of the ten tallest trees values were accessible from 150 permanent plots in loblolly pine plantations and 75 sample plots in slash pine plantations. For both species, approximately 85% of the data pairs were 1 o years or younger.

In this update, new versions of site index prediction equations are presented for these two pine species based on information from repeated measurements of the ETPPRP permanent plots during 1982-1992. To date, almost all the ETPPRP plots have been measured four times. The loblolly pine site index equation is based on the analysis of 608 age-height pairs, and the slash pine site index prediction equation is derived from 264 age-height pairs. Original data pairs from the 1986 study are included in this new expanded data set. which represents a 3 to 4 fold increase in data size.

As a result, the updated equations should quantify the productivity of the East Texas planted areas in a more accurate and reliable manner.





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