Wood Biomass Production from a 10-Year Old Plantation of Fraxinus Angustifolia Vahl in Greece

National Agricultural Organisation, Forest Research Institute, Greece

Abstract: The native species Fraxinus angustifolia Vahl. (narrow-leaf ash) is a fast growing noble hardwood and it is an interesting and important tree species for the country. It has high sprouting ability, relatively heavy wood (700-750 kg/m3 - air dried) and it is recommended for energy plantations. Under the frame of the European research program FRAXIGEN (EVK2-CT-2001-00180), eight natural populations were identified all over continental Greece and selected for research. In March 2006, an experimental plantation was established using provenances (13-20 trees/provenance) with 2 year-old seedlings in a planting density 1,110 plants/ha (3 x 3 m), in the area of Messia (Kilkis) near the banks of Axios river. In December 2016, biometric parameters (height, diameter at breast height/DBH, diameter at the base/DB, total height) as well as the production of fresh and dry wood biomass, based on the mean tree of each provenance, were recorded. In the recording, each provenance was represented with 13-20 trees, depending on the availability of the plants established. The mean tree of each provenance was cut and then the fresh and dry weight and the moisture content were measured. The moisture content was calculated by oven drying of fresh samples. Four categories of woody biomass were defined based on diameter/thickness of trunks/branches, as following: category (Ι) >12 cm (mainly stem wood), category (ΙΙ) 8-12 cm (thick branches), category (ΙΙΙ) 4-8 cm (medium branches) and category (ΙV) <4 cm (thin branches). In relation to diameter (DBH), results showed significant differences between provenances: provenance 14FAN developed the largest diameter (15.9 cm) whereas provenance 09FAN the smallest (12.6 cm). In relation to the basal diameter (DB), significant differences were also found: provenance 14FAN gave the largest diameter (20.6 cm) whereas provenance 09FAN the smallest (16.5 cm). However, despite of these differences, at this stage, almost all provenances depicted significant diameter growth. In relation to the total height, results did not show much difference between provenances probably due to the high competition between trees. The moisture content was calculated and ranged between 30.8-33.7% (of the fresh weight), depending upon provenance and biomass category. Regarding the total fresh biomass, it was ranged from 82-157 kg/tree while the dry biomass from 54-107 kg/tree (or 60-118.8 tns/ha), depending on provenance. Assuming an average colorific value 19 MJ/kg ξύλου, the total thermal energy of the produced biomass per ha ranged from 1,140,000 MJ (or 316,920 kWh) for the provenance 08FAN up to 2,249,600 MJ (or 625,000 kWh) for the provenance 14FAN. Regarding biomass categories, important is that the category of thin branches (ΙV/<4 cm) gave relatively high values of dry biomass ranged from 34.20% to 39.92% of the total dry weight. The correlation between diameter at breast height (DBH) and total dry weight (T.D.W.) was not found significant (p = 0.079) with r2 = 0.427. On the other hand, the correlation between diameter at base (DB) and the T.D.W. was significant (p = 0.020) with r2 = 0.624 and the linear model was: T.D.W. = -109.104 + 9.983 DB. Based on this model the T.D.W. of a standing plantation can be estimated. The research keeps on, while the plantation acts as pilot experiment (the first in the country) for production of woody biomass of the tested species.