Site index estimation in Scots pine (Pinus sylvestris L.) stands in the High Ebro Basin (northern Spain) using soil attributes

Site index curves and an edaphic discriminant rule for Scots pine stands in the High Ebro Basin (northern Spain) are presented to estimate site index under different silvicultural situations. High-grading practices strongly modify the forestry structure by the means of bias in the dominant height and stand density. In order to achieve the silvicultural and site variability of Scots pine stands in the studied area, 75 plots from the National Forest Inventory of Spain (NFI) were selected. In these plots 46 dominant trees were cut down and 104 trees were bored at stump and at breast height (1.3 m). In each plot a soil sample from the first 10 cm of soil was taken and signs of dimensional cutting were recorded. Site index curves and the edaphic discriminant rule were developed. The site index curve model used is an extension of the Richards model. The site factors selected in the discriminant rule represent the most important edaphic parameters for forest productivity (texture and the assimilability of the nutrients). Site quality of the studied stands was medium-low as compared with other site index curves for Scots pine around the world. The edaphic discriminant rule presented is useful for estimating site index classes in stands exposed to dimensional cutting and in young stands of Scots pine in the the High Ebro Basin (northern Spain). Site index curves were fitted to allow an estimate of the site index of undisturbed and stands which were not high-graded.