Assessment of the effects of thinnings in scots pine plantations in Mongolia: a comparative analysis of tree growth and crown development based on dominant trees

Abstract

The post-thinning stand density and spacing in forest plantations influence individual tree growth and crown development, and the changes detected in dominant tree growth are a good indication of the thinning effect. The objective of this study was to determine the effects of different thinning intensities on diameter and height growth in a Scots pine (Pinus sylvestris L.) plantation. The field measurements were carried out between 2016 and 2020 on a Scots pine plantation, growing in Selenge province of northern Mongolia. Following this, experimental thinnings were carried out with different intensities. Thinning treatments comprised thinning with very low, low, medium, and high intensities, as well as an unthinned control stand. Stem analyses were performed to calculate the annual and cumulative diameter, height, and volume growth. For tree crown measurements several parameters were analyzed: crown diameter, crown projection area, and crown index. A total of 300 trees (5 treatments à 3 replications à 20 dominant trees from each plot) were subjected to the comparative analyses. This study revealed that thinning showed a stronger positive effect on diameter and volume growth of dominant trees in the plantation. Our results showed a gradual increase in diameter, basal area, and volume growth depending on the thinning intensity. An ANOVA test for growth analyses of dominant trees showed a significant difference in diameter (p < 0.0001) and height (p < 0.0001) growth performance following experimental felling with different thinning intensities. Finally we elaborated linear mixed effect models (LMM) for tree growth between 2016 and 2020 of selected dominant trees. With the help of the LMM we analyzed and described the thinning impact on DBH, BA, height, volume and crown diameter. The models confirmed that higher thinning intensity triggered growth of the response variables except for height. A greater height growth was found in very low (10%) and low (15%) intensity treatments. Due to reduction of competition and optimization of the distance between individuals, thinnings contributed to a relatively faster development of the tree crown in radial directions. Based on our analysis results and comparative graphs representing post-thinning dominant tree growth in diameter, height, basal area, and volume, we recommend medium-(30%) and high-intensity (45%) thinnings as at the beginning stage of plantation establishment.

Effects of radial growth rate on juvenile wood properties of Pinus sylvestris planted in Mongolia

“…The plantation was established in 2002 using two-year-old seedlings with an initial spacing of 4.0 × 1.0 m. The experimental thinning treatment was conducted in 2016 in half of the area. Detailed information about the plantation was reported in a previous paper (Ganbaatar et al 2021). In 2020, dominant, medium, and suppressed trees (three trees in each growth category) were selected from non-thinned and thinned sites (nine trees in each site).…”

“…Thus, wood properties have mainly been assessed in coniferous species found in natural forests, such as Larix sibirica, Pinus sylvestris, Pinus sibirica, Picea obovata, and others (Ishiguri et al 2018, Sarkhad et al 2022. On the other hand, efforts have also been made to establish plantations in Mongolia (Sukhbaatar et al 2020, Ganbaatar et al 2021. Ganbaatar et al (2021) reported the effects of thinning on tree growth and crown development in P. sylvestris plantations in Mongolia.…”

“…On the other hand, efforts have also been made to establish plantations in Mongolia (Sukhbaatar et al 2020, Ganbaatar et al 2021. Ganbaatar et al (2021) reported the effects of thinning on tree growth and crown development in P. sylvestris plantations in Mongolia. However, the available information about wood properties remains limited for planted trees in Mongolia.…”

Thinning Effects on Stand Structure and Carbon Content of Secondary Forests

“…This is not the case with A-index (Formula ( 2)) where a different approach to constructing classes was been chosen. The value of A describes the size of the upper space occupied by the trees [25]. The W-index describes the horizontal distribution pattern of trees [26].…”