Characterization of wood physical and anatomical featurs for the development of identification keys for twenty tree species of South India

Abstract

Wood has played a vital role in the history of human civilisation. Mankind have been using it as a building material, for making furniture, paper and fuelwood since time immemorial. The demand for wood continues to increase annually, even today. The rapidly expanding global population has created consumer demand for wood and wood products. This has led to unsustainable exploitation of forests globally, paving the way for illegal logging and resultant timber adulteration (UNODC, 2020). Illegal logging and global trade of such timber accounts for 51-152 billion U.S. dollars annually (INTERPOL, 2019). Accurate identification of timbers is therefore a need of the hour. Identifying the timber is also a necessity, even to determine its general end-use. In this backdrop, the present study was conducted to characterise the physical and anatomical features of 21 timber species and to develop a dichotomous Key and an IAWA (International Association of Wood Anatomists) Key for the accurate identification of the selected species. A survey was conducted, and wood samples were collected from different parts of Kerala. The procured samples were cut to the required dimensions (1x1x1 cm3 ). Gross features were recorded, and sections were prepared using a sliding microtome (Leica SM 2000R). Permanent slides were then prepared. The photomicrography of Transverse Sections (TS), Tangential Longitudinal Sections (TLS), and Radial Longitudinal Sections (RLS) were taken using a Catymage® image analyzer using a Catcam 500E series microscope camera, mounted on a Motic BA210 trinocular microscope. Physical properties like colour, odour, lustre, texture, basic density etc. and micro anatomical properties like vessel, ray and fibre morphology were studied. All the quantifiable parameters differed significantly between the species and characteristic features were identified. Wood specific gravity differed significantly. Highest specific gravity was observed in Hopea parviflora and Cocos nucifera, while the lowest specific gravity was observed in Ceiba pentandra. All the species studied (except Cocos nucifera) were categorised as diffuse porous. Small vessels were found in Aegle marmelos and comparatively larger vessels were observed in Ceiba pentandra. Vessels were solitary and in radial multiples of 2-3 in most of the species studied, except Casuarina equisetifolia which were exclusively solitary and in Alstonia scholaris they were in radial multiples of 4-8. Maximum vessel diameter was observed for Ceiba pentandra with 258.38 µm followed by Bombax ceiba with 232.11 µm and Acrocarpus fraxinifolius with 224.34 µm. The lowest vessel diameter was recorded in Aegle marmelos (93.82 µm) and Casuarina equisetifolia (99.11 µm). mm2 Vessel frequency was found to be highest in Aegle marmelos (37 per mm2 ) followed by Bridelia retusa (24 per mm2 ) and the lowest was recorded in Acacia nilotica, Albizia odoratissima, Hopea parviflora and Lagerstroemia lanceolata with a value of 3 per . Rays were observed to be variable, with a mixture of homocellular and heterocellular rays to exclusively homocellular rays. In Aegle marmelos, Albizia odoratissima and Cassia fistula, only procumbent rays were observed. Ray frequency was analysed in the present study and it was found that the highest ray frequency was found in Casuarina equisetifolia (15 per mm) Cassia fistula (13 per mm) and Neolamarkiana cadamba (13 per mm) and the lowest was recorded in Ceiba pentandra (4 per mm), followed by Bombax ceiba (5 per mm) and Melia dubia (5 per mm). Ray height was highest in Bombax ceiba (1.25 mm), followed by Bridelia retusa (1.50 mm) and the lowest was recorded in Cassia fistula (0.21 mm ) followed by Casuarina equisetifolia (0.22 mm). Paratracheal parenchyma is an advanced character and was observed in most of the species. Angular vessel outline was observed only in Alstonia scholaris. Utilizing all the physical and anatomical information obtained from the study, a dichotomous key and an IAWA key was prepared for the selected timbers species.