The investigation was carried out at the College of Forestry, Navsari Agricultural University, Navsari (20.95N latitude, 75.90E longitude with an altitude of 10 m amsl), Gujarat, India, during 2014-2019. Climate of area is characterized humid and warm with monsoon rainfall of around 1500 mm (June- September), moderately cold in winter (November- February) and fairly hot and humid in summer (March-May). Soils of experimental site is deep black originated from old alluvium of basaltic material, taxonomically placed under the group of Ustochrepts, sub group of verti Ustochrepts, sub order of orchrepts and order of inceptisols, characterized by clay, deep, moderately drained with good water holding capacity. The soil cracks heavily on drying and expands on wetting and predominant clay mineral found to be montmorillonite. Soil pH and average available nitrogen, phosphorus, potassium, and organic carbon of experimental site was 225.79 kg ha-1, 32.81 kg ha-1, 310.34 kg ha-1, 7.67 and 0.87%, respectively.

The study-1 was conducted in randomized block design with 17 open pollinated Melia dubia Cav. progenies as treatments with three replications (three individuals in each replication). The seeds of 16 families were supplied by Division of Genetics and Tree Improvement, Forest Research Institute Dehradun, Uttarakhand, India and family named GJ09 was local source (collected from Northern most tip of Western Ghats), which were collected from South Gujarat, India. Planting was carried out in January, 2014 at 3x3 m spacing with boundary row to avoid edge effect.

The study-2 was comprised of Melia dubia plantations at with spatial geometries of 2×2, 3×2, 3×3 and 4×2 m. Both the experiments managed following normal tree management practices. No additional fertilizer (organic or inorganic) was applied throughout the period and trees were allowed to natural pruning after 2nd year onwards.

The tree height and diameter at breast height (DBH; at 1.37 cm above ground) were recorded (from 1st to 5th years of age) periodically following standard methods in each replication (3 tree/replication in progeny evaluation and 5 trees per replication in spatial geometry evaluation) of each family. Standing tree fresh biomass was calculated following regression equations B=0.0299(HD2)+7.48 (Thakur et al., 2021), Where, B =total tree fresh biomass, H=height (m) of the tree and D= DBH (cm). Estimated fresh biomass was converted to dry mass i.e. 50 per cent of the fresh biomass (Laxmai et al., 2021).

Below ground biomass (BGB) of the tree includes live root biomass, excluding fine roots and was calculated using 0.26 factor of root: shoot ratio (Ravindranath and Ostwald, 2008).

BGB (t ha-1) = AGB (t ha-1) × 0.26

Sum of AGB and BGB gives total biomass (TB) of the tree (Ravindranath and Ostwald, 2008).

TB (t ha-1) = AGB (t ha-1) + BGB (t ha-1)

Then biomass was converted to total carbon stock by multiplying factor of 0.51 (Dury et al., 2002) and carbon sequestration by multiplying the carbon stock by factor of 3.67 (Van-Kooten, 1999).

The data generated were subjected to the statistical analysis following randomized block design (RBD) and ANOVA was constructed. Further, Duncan's multiple range test (DMRT) was used to compare the sets of means of each treatment following Sheoran (n.d.). OPSTAT - Online Statistical Analysis Tools. CCS HAU, Hisar. http://14.139.232.173/opstat/ default.asp.

Biomass productivity

The results indicated that biomass production (kg/tree and ton/ha; dry weight basis) varied significantly (p<0.05) amongst the 17 progenies (Table 1). In the 1st, 2nd and 3rd year the maximum biomass production (9.05, 24.3 and 37.00 kg/tree and 10.05, 27.00 and 41.10 t/ha, respectively) was put up by progeny number 259. At the age of two years, biomass production (21.83 kg/tree and

24.25 t/ha) by progeny 260 was at par with that of 259. At the age of 4 years, highest biomass production (53.85 kg/tree and 59.83 t/ha) was of progeny GJ09, which however was statistically at par with progeny 260. However, at the age of 5 years (Table 1), GJ09 put up maximum biomass (86.06 kg/tree and 95.61 t/ha) with average maximum productivity of 17.21 kg/tree/year and 19.12 t/ha/year (Fig. 1a and b). The minimum biomass production and productivity was of progeny 270 at the age of 5 years.

The results expressed that carbon stocks varied significantly among the progenies and the age gradations (Table 2). Among the 17 progenies, 259 progeny acquired maximum carbon stock amounting to 4.61, 12.39 and 18.87 kg/tree and 5.13, 13.77 and

20.96 t/ha from 1st to 3rd year of age. At 2nd year progeny 260 had at par carbon stock with 259. Progeny GJ09 showed highest carbon stock amounting to 27.47 and

43.89 kg/tree and 30.51 and 48.76 t/ha at 4th and 5th year, respectively. However, at 4th year progeny 260 was at par with GJ09 (Table 2). Minimum carbon stocks were of family 270 at 5 years of age.

Further, owing to maximum carbon stock, progeny 259 sequestered maximum carbon of 16.94, 45.49 and

69.25 kg/tree and 18.82, 50.53 and 76.94 t/ha at age of 1st, 2nd and 3rd year (Table 3). However, at 4th and 5th year, the maximum carbon sequestration (100.80 and

161.07 kg/tree and 111.99 and 178.95 t/ha) was of GJ09. Progeny 260 sequestered statistically at par carbon to that of GJ09. Progeny 270 sequestered minimum carbon at the age of 5 years.

The results pinned out that the carbon stock and carbon sequestration potential of M. dubia progenies varied significantly at the age of 5 years (Fig. 2, 3). Maximum carbon stock (8.78 kg/tree/year and 9.75 t/ha/year) and carbon sequestration (32.21

Table 1. Variation in biomass production of M. dubia progenies in South Gujarat

Means with different superscript letter in the same column indicate significant difference (p<0.05) according to Duncan's Multiple Range Test

Table 2. Variation in carbon stocks of M. dubia progenies in South Gujarat

Means with different superscript letter in the same column indicate significant difference (p<0.05) according to Duncan's Multiple Range Test

Table 3. Variation in carbon sequestration of M. dubia progenies in South Gujarat

Means with different superscript letter in the same column indicate significant difference (p<0.05) according to Duncan's Multiple Range Test

kg/tree/year and 35.79 t/ha/year) potential was of progeny Gj09. Progeny 260 showed statistically at par carbon stock (7.32 kg/tree/year and 8.13 t/ha/year) and carbon sequestration potential (26.87 kg/tree/year and 29.85 t/ha/year) to progeny Gj09. Minimum carbon stock and carbon sequestration rate was of progeny 270 (Fig. 2, 3).

The results expressed that biomass production and productivity of M. dubia differed significantly (p<0.05) under different spatial configurations (Table 4). At 1- year of age, maximum individual tree biomass (7.39 kg/tree), carbon stock (7.77 kg/tree) and carbon sequestration (13.84 kg/tree) was maximum in 3x2 m spaced plantations. In 2nd, 3rd and 4th years of age maximum per tree biomass (15.90, 26.10 and 37.24 kg), carbon stock (8.11, 13.31 and 18.99 kg) and carbon sequestration (29.76, 48.85 and 69.70 kg) was recorded under 3x3 m planting geometry (Table 4). At 5 years' age of trees in 4x4 m spatial geometry provided highest biomass, carbon stock and carbon sequestration to the tune of 53.30, 27.18 and 99.77 kg/tree, respectively.

Owing to maximum number of trees under 2x2 m spaced plantations (table 4), from 1st till 5th year of age, provided significantly highest biomass (18.07, 25.42,

41.23, 69.09 and 101.46 t/ha), carbon stocks (9.21, 12.97, 21.03, 35.24 and 51.75 t/ha) and carbon sequestration (33.82, 47.59, 77.16, 29.31 and 189.91 t/ha). The data in figure 4a and 5a pinned out that the individual tree biomass productivity, carbon stock and carbon sequestration potential amounting to 10.66,

5.44 and 9.95 kg/tree was under 4x2 m spatial configuration. However, as a results of maximum tree stocking per hectare, 2x2 m spaced plantations provided highest biomass productivity (20.29 t/ha/year), carbon stocks (10.35 t/ha/year) and carbon sequestration potential to the tune of 24.94 t/ha/year (Fig. 4b and 5b).

The variation in growth and productivity of tree species varies from location to location due to edapho- climatic attributes and genetic worth of material (Lodhiyal et al., 2002; Luna et al. 2009; Luna et al. 2011; Thakur et al. 2023). The productivity of M. dubia in the present study is comparable with that reported in some of the released varieties of M. composita (Kumar et al., 2017).

Table 4. Variation in biomass production, carbon stock and carbon sequestration of M. dubia under different spatial geometries in South Gujarat

Means with different superscript letter in the same column indicate significant difference (p<0.05) according to Duncan's Multiple Range Test

Jinger et al. (2025) have reported carbon stocks of 16.39 t/ha to 58.30 t/ha, and carbon sequestration to the tune of 60.20 t/ha and 214.20 t/ha in sole M. dubia plantation and under agroforestry (M. dubia+Lemon grass) systems in central Gujarat India at the age of 5 years spaced at 3 × 3 m. These findings are in congruity with our range carbon sequestration at same spacing and age in M. dubia g e r m p l a s m a n d s p a t i a l geometry study plantations. Kumar et al. (2024), in dry zone of Karnataka, India, reported the carbon stocks of 40.10 to 118.80 t/ha and biomass CO2 147.10 375.90 t/ha to of different M. dubia progenies at the age of 6 to 7- year-old plantations spaced at 5 × 5 m. The carbon stock and carbon sequestration of some progenies at the age of 5 years in the present study fall within the range reported by these workers. Singh et al. (2022) have also reported carbon stock of 10. 96 t/ ha and Carbon dioxide sequestration amounting to 40.17 t/ha from 2-year-old M. dubia which are in accordance with that provide by some progenies a n d s p a t i a l g e o m e t r y evaluations in our study. Similar individual tree range of carbon sequestration from M. dubia (at 5 × 4 m spacing) at different age gradation (1 to 3 years) have been reported by Choudhury et al. (2025).

The plantation spacing is known to influence growth and morphology of individual trees as well as quantity and quality of wood produced. Narrower spacing decrease individual growth and increase tree mortality through excessive intraspecific competition al., 2024). Conversely though wider planting spacing favor diameter/girth growth, enhances stem taper substantially. Higher stem taper values tend to reduce merchantable volume of individual trees at a particular diameter at breast height. It has been reported that at stand level, volume increases with narrower planting plans to a reasonable levels (Cardoso et al., 2013) and hence the biomass. The biomass production and productivity in present study has been recorded to be higher in narrower spacing/highest tree density which is in agreement with these findings.

The analysis of teak spacing studies revealed negative coordination for planting spacing, volume production, basal area and other wood characters which increase with increased plantation spacing (Perez-Cordero and Kanninen, 2003). Similarly, teak height and DBH (diameter at breast height) at age of 14 years was significantly lower in spacing of 2x2 m compared spacing regimes of 3x3 m and 4x4 m (Eliakimu et al., 2015). Similar growth behavior was exhibited by M. dubia for present study, which might have contributed by microsite differences for height, as it is sensitive to differences in site quality. Reduced competition in wider planting spacing results in attaining higher DBH/GBH, which may be attributed to effective use of more growing space for crown and root development (Eliakimu et al., 2015). The higher individual stem biomass has been reported with widest plantation spacing, which is in line with results of several other studies (Zhang et al., 2013; Eliakimu et al., 2015) and hence the carbon stocks and carbon sequestration was higher.