Assessing Competing Vegetation in Young Red Pine Plantations in Central Wisconsin

Abstract

Competing vegetation is a major factor in reducing the growth or causing the demise of red pine plantations in the Lake States. This research was undertaken to better understand the relationship between levels of competing vegetation and the performance of young red pine plantations in central Wisconsin. An evaluation of the effects of competing vegetation on red pine growth during the fifth year after outplanting revealed that there were major differences related to competition. Young trees growing under light competition grew over 520% more biomass than those growing under heavy competition. On a relative basis, the trees growing under light and moderate competition outgrew those growing under heavy competition in both volume and biomass. Competition levels did not affect pre-dawn needle water potentials; however, a single day diurnal measurement revealed that midday and late afternoon water potentials were lower than those made at pre-dawn. Young trees growing under light competition also had larger needle fascicles and more stored foliar nutrients. An assessment of competing vegetation in three-, five-, and six-year-old plantations showed that competing vegetation variables generally accounted for 30 to 50% of the variability in tree height, volume, and biomass. Although stepwise multiple regression equations were significant, the coefficients of determination were low enough to indicate that there are many other factors influencing tree growth besides competing vegetation. A logistic regression approach was used to quantify the relationship between tree performance and competing vegetation. Several regressions were developed for each plantation, using height, volume, and biomass success as the dependent variables and a suite of competing vegetation measures as independent variables. Most of the resultant equations were significant, with percent correct classifications of 80 to 85%. In general, the equations classified the poorer performing trees correctly about 90 to 100% of the time, but classified the better trees correctly only about half the time. In this respect, the equations would be considered conservative. This approach is useful in that it enables a forester to classify plantation performance as good or bad, as a function of the competing vegetation.