Epsilon Archive for Student Projects

Abstract

This study evaluated the effects of varying intensities and spatial patterns of precommercial thinning on stand structure and economic outcomes in Norway spruce
(Picea abies) plantations established on former agricultural land in eastern Latvia. It was hypothesized that increased thinning intensity and spatial heterogeneity would lead
to improved stand structural diversity and enhanced long-term economic returns.

We hypothesized that :
· Thinning regimes with lower intensity (e.g., retaining 1500 trees ha⁻¹) will produce higher total stand volume and long-term economic return, whereas higher intensity thinning (e.g., 500 trees ha⁻¹) will promote faster diameter growth but lead to lower cumulative yield and reduced profitability.
· Selective thinning that retains the 1,000 largest-diameter trees per hectare (1,000 U) will result in greater total stand volume and higher long-term economic return at rotation age compared to uniform thinning with evenly spaced trees (1,000 E), due to the enhanced growth potential of larger, more vigorous trees.

To test these hypotheses, four silvicultural treatments were implemented using a randomized complete block design across 20 × 20 m plots:
· 1500 E – 1500 trees per hectare were retained with even spacing between them.
· 1000 E – 1000 trees per hectare were retained, also evenly spaced.
· 1000 U – 1000 trees per hectare were left, but these were selected based on having the largest diameters, not spaced evenly.
· 500 E – 500 trees per hectare remained, evenly distributed across the area.

Over 17 years, tree diameter at breast height (DBH) and height were measured, and stem volume was calculated using species-specific height–diameter and volume functions to fill in data gaps. Stand attributes were statistically compared using oneway ANOVA followed by Tukey’s Honest Significant Difference (HSD) test. Economic performance was evaluated through single-rotation net present value (NPV) and Faustmann’s land expectation value (LEV), applying a 2.5 % discount rate and accounting for establishment costs, reforestation subsidies, pre-commercial thinning revenues, and final harvest income.

Our results confirm that wider spacing (500 E) accelerates diameter growth but reduces total stand volume. Contrary to our second hypothesis, the 1000 U treatment did not outperform 1000 E Both intermediate density regimes yielded similar outcomes in terms of volume, basal area, and economic returns. This similarity is likely attributable to competition among the largest retained trees within the plots. Although these trees initially had a size advantage, their proximity may have intensified competition for light and resources, limiting their subsequent growth.

The economic analysis indicates that, although the 500 E treatment achieves harvestable dimensions earlier, it results in lower net present value (NPV) and land expectation value (LEV) compared to other treatments. In contrast, the 1500 E regime delivers the highest long-term profitability due to greater total volume production, which compensates for its higher establishment costs. While risks such as pests, windthrow, and market fluctuations may lead some managers to prefer lower initial densities for reduced exposure, our findings suggest that even spacing at 1500 trees ha⁻¹