Abstract
Scots pine (Pinus sylvestris L.) grows from sea level up to 2700 m as small groups or individually in Türkiye. Cone and seed production is the main tool in sustainability of forest tree species. However, many biotic and abiotic factors such as stand structure and forestry practices could impact production. The impact of thinning levels (unthinned or known control, moderately thinned, and heavily thinned in 2021) together with growth characteristics on mature cone production was examined based on two-year cone data (2024 and 2025) in natural stands. Stands and individuals within stands were evaluated for both cone production and growth. Heavily thinned stands had higher cone production for both years (16.8 and 96.6) than moderately thinned (9.7 and 40.7) and unthinned (9.5 and 32.6). The year 2025 produced more abundant cones (55.4) than 2024 (11.9). Significant (p < 0.05) differences were found with respect to thinning level for growth characteristics and cone productions except for tree and crown heights. Years showed significant (p < 0.05) differences among grades and within grade for cone productions. Additionally, growth characteristics had generally significant (p < 0.05) impact on cone production in both grade and years.
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Impact of Thinning Levels on Cone Production in Natural Stands of Scots Pine (Pinus sylvestris L.)
Ercan Oktan 
*
Scots pine (Pinus sylvestris L.) grows from sea level up to 2700 m as small groups or individually in Türkiye. Cone and seed production is the main tool in sustainability of forest tree species. However, many biotic and abiotic factors such as stand structure and forestry practices could impact production. The impact of thinning levels (unthinned or known control, moderately thinned, and heavily thinned in 2021) together with growth characteristics on mature cone production was examined based on two-year cone data (2024 and 2025) in natural stands. Stands and individuals within stands were evaluated for both cone production and growth. Heavily thinned stands had higher cone production for both years (16.8 and 96.6) than moderately thinned (9.7 and 40.7) and unthinned (9.5 and 32.6). The year 2025 produced more abundant cones (55.4) than 2024 (11.9). Significant (p < 0.05) differences were found with respect to thinning level for growth characteristics and cone productions except for tree and crown heights. Years showed significant (p < 0.05) differences among grades and within grade for cone productions. Additionally, growth characteristics had generally significant (p < 0.05) impact on cone production in both grade and years.
DOI: 10.15376/biores.21.2.3506-3517
Keywords: Forestry; Growth; Population; Reproductive; Tending; Variation
Contact information: Department of Forest Engineering Karadeniz Technical University, Trabzon, Türkiye; *Corresponding author: oktan@ktu.edu.tr
Graphical Abstract
INTRODUCTION
Scots pine (Pinus sylvestris L.) is one of the most important forest tree species in Europe and Asia. It is also an exotic species in various countries such as Korea, China, Mexico, and New Zealand (Boratyński 1991). Turkish Scots pine (Pinus sylvestris ssp. hamata), which is one of five sub-species, is an important tree species in 23.36 million ha of Turkish forest area and by 1.41 million ha natural distribution, according to the latest forestry inventory (OGM 2025). It is classified as one of the economically and ecologically important tree species for Turkish forestry and for “National Tree Breeding and Seed Production Programme” (Koski and Antola 1993). It grows up to 45 m height, 2.0 m diameter and can be found between sea level and 2700 m, sometimes up to 3125 m at different environmental conditions (Anşin and Özkan 1996).
Various climatic conditions affect reproductivity of the species, which affects its sustainability. Scots pine is wind-pollinated and has both male and female cones on the same tree. Female cones develop approximately after 15 years on solitary trees or 25 to 30 years. Abundant male cones appear some years later (Mátyás et al. 2004). The female cones convert to mature cones in two years after fertilization.
A good seed year occurs every two years in Scots pine (Saatçioğlu 1976). However, there could be many biotic (i.e., Eriksson et al. 1973; Hedegart 1976; Odabaşı 1990; Kang et al. 2003; Zobel and Talbert 2003; Bilir et al. 2008, 2023, 2025; Yazıcı and Bilir 2023) and abiotic (i.e., Boydak 1977; Odabaşı 1990; Zobel and Talbert 2003; Bilir and Yazıcı 2024) factors that affect reproductive characteristics in forest tree species (i.e., Eriksson et al. 1973; Hedegart 1976; Boydak 1977; Odabaşı 1990; Kang et al. 2003; Zobel and Talbert 2003; Bilir et al. 2008, 2023, 2025; Yazıcı and Bilir 2023; Bilir and Yazıcı 2024).
Reproductive traits of plant species and their populations are not easily changed. It is known that common forest tending practices included thinning are mainly focused on increasing the amounts of wood products. Thinning, which has become an established forestry practice, could also have different impacts on reproductive traits. However, while the impact of some biotic and abiotic factors on cone production were investigated in Scots pine (i.e., Jonsson et al. 1976; Boydak 1977; Nikkanen and Velling 1987; Kang et al. 2003; Bilir et al. 2008), there has been a need for study on the impact of thinning grades relative to cone production. Cone production is one of the main tools for both sustainable forestry, and cones are used in various industries (Hendek Ertop and İncemehmetoğlu 2021).
This study was carried out to estimate whether forest thinning levels (unthinned, moderately thinned, and heavily thinned) have an impact on cone production, and to estimate relations among growth characteristics and cone production in natural stands of P. sylvestris to contribute to silvicultural and other forestry practices of the species.
EXPERIMENTAL
Materials
Study area
Studied areas/grades were selected to be close to each other (~150 m.) at similar conditions to minimize impacts of other changeable factors such as altitude, climatic, and edaphic. Trees were sampled from natural stands that were either unthinned (UT, also known control), moderately thinned (MT), and heavily thinned (HT) of the species (Fig. 1). The vertical stand profiles of the areas depending on size and position of tree crowns during data collection are shown in Fig. 1. These were drawn using TreeDraw (Staupendahl 2003). The following data were collected from 300 m2 (30 ×10 m) plot size of each grade (Fig. 2). The thinning was practiced in the areas in year 2021. Additionally, a regional good/rich seed year was 2023. Some details of the areas are given in Table 1.
Table 1. Some Details and Number of Trees of the Sampled Areas
