Asian Journal of Environment & Ecology

Aims: The study was conducted to analyze the wood density for three conifer tree species (Juniperus recurva, Picea spinulosa, and Abies densa) which are widely used in Bhutan for house construction, incense making and firewood purposes. The wood density for these species is exhibited according to physiographic regions of the country (West, West-Central, East, and East-Central).

Study Design: This study investigates the wood density of Juniperus recurva, Abies densa, and Picea spinulosa across Bhutan's physiographic zones. A total of 32 trees per species were sampled, with eight trees selected per zone. Due to its limited distribution, Picea spinulosa was sampled from only three zones. Sampling was stratified across different physiological conditions, with trees classified into eight diameter classes and four crown categories. Destructive randomized branch sampling (RBS) was employed, wherein trees were felled to extract stem disc samples at four positions along the main bole. Standard measurements of tree height, stump height, and basal diameter were recorded. Samples were dried in an oven at 80°C until a constant dry weight was achieved. Wood density was determined using the ratio of dry mass to green volume, with the latter measured via the water displacement method. This methodological approach ensures accurate wood property quantification, providing valuable insights into species-specific density variations.

Place and Duration of Study: The study was conducted across Bhutan’s four physiographic zones, covering a range of environmental conditions to ensure comprehensive regional representation. Field sampling took place over multiple locations where Juniperus recurva, Abies densa, and Picea spinulosa are naturally distributed.

Methodology: This study was conducted across four physiographic zones of Bhutan—western, west-central, east-central, and eastern—at elevations ranging from 2800 to 5000 meters above sea level to capture regional variations in wood density. Sample collection focused on three conifer species: Juniperus recurva, Picea spinulosa, and Abies densa. A total of 96 trees (32 per species) were sampled, with trees categorized into eight diameter classes and four crown classifications to ensure a representative dataset. Destructive randomized branch sampling (RBS) was employed, involving tree felling and extraction of stem disc samples from different height strata of the main bole. Fresh samples were labeled, cleaned, and transported to the laboratory for analysis following standardized protocols.

In the laboratory, the green volume of each wood sample was determined using the water displacement method, while the dry mass was recorded after oven-drying the samples at 80°C until a constant weight was achieved. Basic wood density was calculated as the ratio of dry mass (g) to green volume (cm³). The density values were analyzed across different physiographic zones to identify regional variations. Additionally, the results were compared with the Global Wood Density Database to assess differences between Bhutanese conifers and global averages. The findings provide baseline wood density values for these species, supporting sustainable forestry practices and contributing to ecological and climate-related research.

Results: The analysis revealed significant variation in wood density across the different physiographic zones and conifer species. Abies densa exhibited the highest average wood density across all zones, with values ranging from 0.46 to 0.56 g/cm³. Picea spinulosa showed intermediate density values, ranging from 0.40 to 0.48 g/cm³, while Juniperus recurva had the lowest average density, between 0.34 and 0.42 g/cm³. Wood density generally increased with elevation, with the highest densities found in the eastern and west-central zones, which have higher altitudes and more challenging environmental conditions.

When grouped by diameter classes, the data revealed that larger trees typically had higher wood densities than smaller trees within each species. Crown classification also played a role, with trees exhibiting a fuller canopy tending to have slightly higher density values than those with less developed crowns. The results also showed a notable difference between Bhutanese conifers and the global wood density averages, with Abies densa and Picea spinulosa having slightly higher densities compared to global values for similar species, while Juniperus recurva was comparable. These findings suggest that local environmental conditions in Bhutan, including altitude and climatic factors, contribute to variations in wood density, which could inform forest management and conservation strategies

Conclusion: This study highlights the significant variation in wood density among Bhutanese conifers, with species such as Abies densa showing higher densities compared to Picea spinulosa and Juniperus recurva. Elevation and crown classification were key factors influencing wood density, with higher altitudes and fuller crowns generally associated with increased density. These findings contribute valuable insights into the wood properties of Bhutanese conifers, providing essential data for forest management and conservation strategies, as well as offering a comparative perspective against global wood density norms.