Efficacy of Ficus Hydroseeding for Forest Restoration in an Abandoned Limestone Quarry

ABSTRACT: Reforestation of limestone quarries is more challenging, compared to other degraded sites, due to rocky conditions, steep cliffs and lack of top-soil. Trees species of the genus Ficus can survive well under various conditions; from riparian zones to dry cliff faces. Therefore, this genus may have high potential to survive in the harsh conditions of limestone mine substrates. Hence, this study tested a hydroseeding technique to germinate seeds of Ficus spp. in a limestone quarry of Siam Cement (Lampang). The seeds of Ficus benjamina, F. hispida and F. semicordata were tested with a hydrogel, comprised of sodium carboxymethyl cellulose (NaCMC) mixed, in various proportions, with agar or corn starch. NaCMC (1% w/v) was used as a base component (0, 25, 50, 75 and 100% v/v) with added agar (0.45% w/v) or corn starch (5% w/v) to investigate the gels’ chemical and physical properties.

The pH of the hydrogel mixes did not vary significantly (pH 5.82 to 6.08, ANOVA, p < 0.05). Corn starch significantly increased hydrogel viscosity (p < 0.05), whilst adding agar significantly reduced it (p < 0.05). Increased NaCMC content increased both the equilibrium water content and the swelling ratio. Moreover, adding corn starch had better results on equilibrium water content, swelling ratio and water vapor permeability (WVP) than agar did, in the same proportions. Agar with NaCMC had insignificant WVPs, but WVPs increased with increasing proportion of corn starch (p < 0.05). At high relative humidity, film blending with NaCMC and agar had higher moisture sorption than film with corn starch and equilibrium moisture contents (Mo) from a GAB model were ranged from 0.573 to 0.998 g water/g dry film.

Hydroseeding was tested in the nursery. A syringe was used to deliver exactly 50 seeds, mixed with 50 ml of hydrogel, into mine substrate spread on germination trays. High NaCMC content inhibited germination of Ficus spp. seeds. Per cent germination differed significantly among the gel formulae (p < 0.05). Germination in control was highest on the 10th day. Per cent germination, median length of dormancy (MLD) and per cent survival did not differ significantly among treatments (p < 0.05). However, differences among species were significant (p < 0.05). F. benjamina had the lowest germination percentage, MLD and survival percentage, whilst F. hispida and F. semicordata had high values.

Hydrogels of 50:50 NaCMC with agar or corn starch, were tested for Ficus hydroseeding on limestone mine slopes, at the beginning of rainy season in 2013. All treatments, including the control, resulted in very low germination and survival percentage. In conclusion, hydrogel was not effective for establishing Ficus seedlings on mines.