Assessment of growth and productivity of Aquilaria malaccensis Lam. (Agarwood) growing under different agroclimatic zones 8, 9 and 10 of Karnataka

Introduction

Aquilaria malaccensis Lam. syn. Aquilaria agallocha which is commercially well known for its resinous heartwood, commonly known as agarwood belongs to family Thymelaeceae. It is locally known as 'Agaru, also refers to as the "Wood of the Gods" because of its frequent use in religious, fragrant, and medicinal contexts and is endemic to Indo-malayasian region. It is widely distributed in South and South-East Asian regions. A. malaccenis is found in ten countries viz. Bangladesh, Bhutan, India, Indonesia, Iran, Malaysia, Myanmar, Philippines, Singapore and Thailand (Barden et al., 2000) [3] . In India, it occurs in the natural woods of evergreen and semi evergreen regions of North East India (Hajra, 2000) [6] . Agar is an evergreen tree, grows upto a height of 18 to 40 m with a diameter of 0.6 to 0.8 m and grows well at an altitude of 500 m above sea level but can grow upto 1000 m. The wood of tree is soft, light, elastic and the colour is white to yellowish-white (Chakrabarty et al., 1994) [4] . Due to its high demand both government and private agencies are promoting agarwood cultivation. In recent years, Karnataka witnessed a surge in agarwood cultivation as farmers tap into burgeoning market for its resinous heartwood. Several farmers have planted agarwood in different parts of the Karnataka especially in agroclimatic zone 8, 9 and 10. Vanadurgi Agarwood India Limited, headquartered at Sringeri, Karnataka started its operations in 2007, is closely associated with the farmers and grower associations of the Karnataka. It aimed at promoting the agarwood cultivation in different parts especially in hilly and coastal districts by providing seedlings, agrotechniques and also sharing information on inoculation technologies for agarwood. As per the company, currently 10,176 farmers from Karnataka are growing in 9,670 acres of land (Anon, 2007) [2] . As the tree growth rates are influenced by external environmental factors like rainfall and site conditions like altitude and other extrinsic factors. The present study aimed to assess the growth and productivity of agarwood grown under different agroclimatic zones.

Materials and Methods

Study site: The field experiments were carried out in Uttara Kannada and Haveri districts of Karnataka. This region exhibits a wide range of climate and topographic situations. The experimental sites are situated in Coastal Zone-10 (Zone A), Hilly Zone-9 (Zone B) and North Transition Zone-8 (Zone C), The rainfall in these site ranges between 1000-3700 mm per year and the elevation ranges between 20-622 MSL. The details of the study area are depicted in Table 1. Over the few years farmers have been growing Agarwood (Aquilaria malaccensis) as an intercrop in arecanut plantations. Trees having age gradations of 12 to 14 years were selected. The selected plantations have spacing of 2.75 × 5.5 m. In this selected plantations, 20 trees per plantations were selected for recording growth parameters. Growth parameters such as total tree height (m), girth at breast height (GBH), canopy diameter (m) were recorded in the field and calculated the basal area (m 2 ) and tree volume (m 3 /ha). The experiment was laid out in two Factorial Randomized block design with 6 main factors (Agro climatic zones), 2 sub factors (Sampling sites) and 4 replications. The growth parameters such as tree height, Girth at breast height (GBH) and Girth at Base (GAB) was measured using the measuring tape. The crown diameter of a tree refers to the horizontal distance from one side of the tree's canopy to the other side, measured at the widest point of the tree's foliage. Crown diameter was calculated using the formula (Chaturvedi and Khanna, 1984) [5] .

Where, D 1 is diameter of crown at major axis and D 2 is diameter of crown at minor axis. Basal area is measured as the cross-sectional area of tree stems at breast height (usually at a height of 4.5 feet or 1.37 meters above the ground) per unit area of land. Basal area was calculated using the formula (Chaturvedi and Khanna, 1984) [5] .

Basal area = G 2 /4 ∏ Where, G is girth at breast height and expressed in meter (m) ∏ is constant equal to 3.14

The Form factor is a numerical value that represents the shape or form of a tree's stem or trunk. Form factor was calculated by using the formula (Chaturvedi and Khanna, 1984) [5] .

(Girth at breast height) 2 Form factor = (Girth at base) 2 The volume of a standing tree was determined by using the various growth parameters, including tree height, diameter at breast height (DBH), form factor and basal area. Total tree volume was calculated by using the formulae (Chaturvedi and Khanna, 1984) [5] .

Total volume = Total height (m) × Basal area (m 2 ) × Form Factor (m)

Results and Discussion

The influence of agroclimatic zones and sites on Aquilaria malaccensis growth parameters and productivity are depicted in Table 2 and Figure 1(a-e). Different growth parameters like mean total tree height (m), mean girth at breast height (GBH, m), mean crown diameter (m) and form factor (m), mean basal area (m 2 ) and mean volume (m 3 ha -1 ) are presented below. Among the growth parameters of A. malaccensis, all parameters such as GBH, crown diameter, basal area and volume showed statistically significant difference between agro climatic zones except for tree height but none of the parameters showed statistical difference between sites and interaction.

Among the agroclimatic zones, mean tree height was varying from 10.1 to 10.5 m. Highest tree height was recorded in Zone A (10.5 m) followed by Zone C (10.3 m) and least in Zone A (10.1 m). Mean GBH was varying from 0.535 to 0.673 m and highest was recorded in Zone B (0.673 m) followed by Zone A (0.624 m) and least in Zone C (0.535 m). Mean tree crown diameter was varying from 1.7 to 2.8 m with Zone B recorded highest with 2.8 m followed by Zone A (2.1 m) and least was in Zone C (1.7 m). Mean tree basal area was in the range of 0.025 to 0.039 m 2 with Zone B having highest with 0.039 m 2 followed by Zone A (0.032 m 2 ) and least was in Zone C (0.025 m 2 ). Mean tree volume was varying from 103.12 to 230.83 m 3 per ha. Highest mean tree volume was recorded in Zone B (230.83 m 3 ha -1 ) followed by Zone A (138.33 m 3 ha -1 ) and least in Zone C (103.12 m 3 ha -1 ).

In the present study, in a 13 to 14 years old agarwood plantation under mean annual rainfall range of 1000-3500 mm it was observed that mean tree height ranged from 10.1 to 10.5 m, mean girth at breast varied from 0.535 to 0.673 m, crown diameter ranged from 1.7 to 2.8 m, basal area ranged from 0.025 to 0.032 m 2 and volume ranged from 103.12 (m 3 ha -1 ) to 230.83 (m 3 ha -1 ). The observed variations in growth and productivity of agarwood was also reported by Hossen and Hossain (2016), who studied growth and productivity of 12-16 year old agarwood plantation in Bangladesh. They reported that, tree height range from 9.90 to 14.67 m, the girth size range was 0.41 to 0.465 m, basal area varies from of 0.014 to 0.019 m 2 and volume range from 72.59 to 307.08 (m 3 ha -1 ) under the mean annual rainfall range of 2735 to 3634 mm. In the present study the observed tree height was not influenced by site conditions, however, they reported that height was found to be significantly varying. Other growth parameters like girth at breast, crown diameter, basal area and tree volume were found to be higher than observed in Bangladesh. The current results showed the higher growth and productivity in Zone B with high altitude and high rainfall whereas, Zone A showed moderate growth and productivity having low altitude and high rainfall and least growth and productivity was observed in Zone C having high altitude and low rainfall (Fig. 1). In all the study sites, the soils were found to be of acidic nature and it seems that rainfall having the significant influence on growth and productivity but not the altitude of the region. Positive influence of acidic soils on growth and productivity of agarwood are reported by various workers. Akter and Neelim (2008) [1] also reported higher growth and productivity of agarwood in soils having pH range of 5.5 to 6.5.

In the present investigation, it was observed that, influence of altitude on growth and productivity of agarwood was found to be insignificant. Several workers have reported that, agarwood grows very well in different altitudinal zones like Mat et al. (2012) [8] who reported agarwood species grows extremely well at the altitudinal range of 300 to 850 m. Similarly Rabgay et al. (2020) [9] reported that agarwood tree grows best in altitudinal limits of 143 to 1037 m. Hence, the growth was found to be good in different altitudes. However, present study indicated that, rainfall was found to have significant influence on growth and productivity of agarwood. Agarwood grown in high rainfall region (1800 to 3500 mm) reported with higher growth and productivity with Zone A having 3000 to 3700 mm and Zone B in the range of 2500 to 3600 mm when compare to Zone C with low rainfall (1100 to 1500 mm). Suharti et al.

(2011) [10] reported that 1,800 to 3,500 mm of precipitation is best suited for agarwood growth. It seems that, for good growth and productivity of agarwood, it requires high rainfall coupled with acidic site conditions.

In the present study, the temperature range of 20 to 24 °C was found to be more suitable for growth and productivity of agarwood. Similar positive influence of temperature on agarwood growth was reported by Mat et al. (2012) [8] , higher growth was observed at daily temperature range of 20 to 22 °C. Similar findings by Rabgay et al. (2020) [9] who reported that agarwood tree grows best in mean temperature range of 19.68 to 24.31 °C. Mean annual range of precipitation, 2,127 to 5,441 mm and they concluded that agarwood grows well in areas with slightly acidic soil having good rainfall. Hence, agarwood growth is significantly influenced by rainfall but not by altitude as it has reported good growth both at low and high altitudes. However, poor growth was observed in low rainfall area.

References

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