Christina Kappa, Elias Milios, and Kyriaki Kitikidou*

Department of Forestry and Management of the Environment and Natural Resources, Democritus University of Thrace, Pantazidou 193, 68200 Orestiada, Greece. E-mails: kappa_xristina@yahoo.com, emilios@fmenr.duth.gr, kkitikid@fmenr.duth.gr*

Although the relationship between site productivity and stand structure has been extensively studied, there is limited research specifically addressing how site productivity influences structural diversity in mixed stands. The aim of this work was to analyse the effect of site productivity on the structural diversity of the Pinus sylvestris–Fagus sylvatica stands in the central part of the Rhodope Mountains in north-eastern Greece. Data from 35 plots of 500 m2, established in mixed P. sylvestris–F. sylvatica stands, representing two site productivity types, were used. For each plot, the tree diameters were classified into 4-cm diameter classes. Using diameter at breast height (DBH) data, the following diversity indices were calculated for each sampling plot: Richness, Gini-Simpson, Gini-Simpson equitability, and Berger-Parker index. In most cases, the studied distributions exhibited high diversity. Overall, in P. sylvestris–F. sylvatica stands of the study area, F. sylvatica diameter distributions tended to exhibit higher structural diversity in good-productivity sites than in medium-productivity sites, although this trend was not consistent across all developmental stages. Further research in mixed P. sylvestris–F. sylvatica forests, as well as in different other species mixtures, is needed to draw more robust conclusions.

Received: 06 October 2025 / Accepted: 12 January 2026 / Available online: 26 January 2026

Open Access: This work is distributed under the Creative Commons Attribution 4.0 License.

M. Edi Armanto (1)*, Elisa Wildayana (1), and Bella Syakina (2)

1. Faculty of Agriculture, Sriwijaya University, South Sumatra 30820, Indonesia. E-mail:
mediarmanto@unsri.ac.id*, ewildayana@unsri.ac.id
2. School of Social Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia. E-mail:
syakinabella@student.usm.my

Peatlands in South Sumatra are increasingly degraded due to anthropogenic activities and climate change. Effective restoration therefore requires broad consensus on conserving biodiversity and carbon stocks through the planting of native peat species, such as rumbia palm (Metroxylon sagu Rottb.). This study aimed to evaluate the suitability of peatlands for rumbia palm cultivation and to identify the main limiting factors affecting its development. The research combined field observations, laboratory analyses, and environmental assessments to evaluate the physical and chemical characteristics of local peatlands. Results indicated that rumbia palm is closely linked to the cultural history of the Sriwijaya Kingdom in Palembang, yet has become marginalised due to widespread conversion of peatlands into industrial plantations. Soil acidity, nutrient levels, and peat depth were found to be the primary limiting factors influencing cultivation potential. Overall, the study shows that peatlands in South Sumatra have high potential for rumbia palm cultivation under proper management practices, such as soil improvement, fertilisation, and groundwater regulation. The novelty of this research lies in positioning rumbia palm cultivation as an indigenous, biodiversity-supporting, nature-based solution for restoring ecological functions of tropical peatlands.

Received: 06 October 2025 / Accepted: 16 January 2026 / Available online: 26 January 2026

Open Access: This work is distributed under the Creative Commons Attribution 4.0 License.

Angel Ferezliev (1), Kristiyan Kolev (2), and Tatiana Stankova (3)*

1. Experimental Station on Coniferous Forests – Velingrad, Department of Sylviculture, Forest
Research Institute, Bulgarian Academy of Sciences, 44 Khan Asparuh Blvd., 4600 Velingrad,
Bulgaria. E-mail: obig@abv.bg
2. Department of Ecology, Forest Research Institute, Bulgarian Academy of Sciences, 132 St.
Kliment Ohridski Blvd., 1756 Sofia, Bulgaria. E-mail: kris.kolev90@gmail.com
3. Department of Forest Genetics, Physiology and Plantation Forests, Forest Research Institute,
Bulgarian Academy of Sciences, 132 St. Kliment Ohridski Blvd., 1756 Sofia, Bulgaria.
*E-mail: tatianastankova@yahoo.com

Our study aimed to develop and provide forest practitioners with a reliable tool for estimating the breast height diameters of the plantation-grown Scots pine trees for restoration of their dimensions when the stems have been removed or destroyed. We applied a number of modelling approaches and developed a simple and a multiple fixed-effects models, a mixed-effects model, and a mixed-effects model with calibrated random parameter components. We compared their goodness of fit and contrasted the accuracy of their predictions with that of the currently applied table. A fixed-effects linear function of the basal tree diameter and the respective linear mixed-effects relationship showed an overall best model performance. Specifying the mixed-effects model to the particular stand by calibrating the random-parameter components with a breast height-basal diameter pair of measurements of one average-sized tree, was recommended. Our models perform better than the currently applied table, which systematically overestimates the breast height diameter, and consequently the volume of the largest portion of the tree trunk. Both model versions are executable in a few simple steps in the user-friendly environment of the MS Excel-based simulator DbhRestore, which is distributed free of charge on the Internet.

Received: 08 December 2025 / Accepted: 27 January 2026 / Available online: 03 February 2026

Open Access: This work is distributed under the Creative Commons Attribution 4.0 License.