Undergraduate Thesis Or Project
 

Forestry in Argentina: the use of needle length as a site quality indicator of young ponderosa pine plantations in northern Patagonia

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  • Needle length in young ponderosa pine (Pinus ponderosa Dougl. ex Laws var. ponderosa) was assessed for its ability to estimate site quality of afforested land in Neuquén, Argentina. The objective was to determine the best aspect on the tree, number of needle age classes, and number of trees that would best predict top height in these plantations at age 20. Needles were sampled from thirty subplots representative of the geographical and productivity range of this species. On the fifth whorl of each sample tree, random groups of 10 fascicles were collected from various trees, aspects, and age classes and measured for average needle length. Total height, height to the first and sixth whorls above breast height and diameter at breast height were measured on each sample tree. Weighted simple linear regression models quantified the relationship between needle length and top height of the stand at 20 years, with top height specified as the mean height of four possible stand components. Mean needle lengths were computed as plot-level means for each age class-aspect combination as well as plot-level means for 2- to 5-consecutive years by aspect. To assess for the necessity of sampling from a fixed aspect, the null hypothesis of no differences between aspects was tested on a plantation-, plot-, and tree-level. Only the current year's needle lengths had a significant difference in needle lengths (NL) between NW and SE aspects. The stand component representing the 100-most dominant stems per hectare by diameter was selected for the final model because on average this dimension was more reliably predicted. Because precipitation is thought to have an effect on needle length, and because precipitation fluctuates widely between years, it is advisable to measure as many age classes of needles as possible to obtain accurate estimates of potential site productivity.
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