Fig. 2

a The original near-infrared (NIR) spectra and b the second derivative spectra for each species based on wood block samples. Encircled one 7000 cm⁻¹ assigned to the amorphous regions in cellulose, encircled two 5980 cm⁻¹ aromatic skeletal due to lignin, encircled three 5800 cm⁻¹ furanose or pyranose due to hemicellulose, encircled four 5464 cm⁻¹ semi- or crystalline region in cellulose, encircled five 5220 cm⁻¹ water, encircled six 4890–4620 cm⁻¹ cellulose, encircled seven 4404 cm⁻¹ cellulose and hemicellulose, encircled eight 4280 cm⁻¹ semi- or crystalline regions in cellulose