AGRE-0057 Mechanised Logging and On-Site Debarking of Short Rotation Coppice and Stands of Eucalyptus and Poplar: Impact on Silviculture, Environment and Economy

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Crops for Paper/Pulp : ECLAIR Cluster II - Lignocellulose : Paper/Pulp : Separation/Fractionation : Wood (Lignocellulose)

Short rotation forest mechanised harvesting system

SUMMARY

This project looked at the yields, economics, quality and performance of stands of short rotation coppice of Eucalyptus or poplar produced for the production of paper pulp in specific regions of Spain and France. The main objective was to develop and justify from an economic and environmental basis a mechanised harvesting system which included on-site debarking. The traditional method of manual logging and debarking at the mill was taken as a base line. Benefits were found to vary with stand density, the volume of trees, uniformity of stands, season of logging and other related parameters. Mechanical harvesting was competitive only on denser stands of larger trees. Debarking had some advantage in pest control, but could lead to lower pulp yield and quality.

INTRODUCTION

The general objective of this project is to develop a mechanised harvesting system for short rotation forest (SRF) coppice of Eucalyptus and poplar which includes on-site debarking; and to assess and quantify its effects on the economics and the environmental aspects of this system. The traditional method of manual logging and debarking at the mill was taken as a base line.

OBJECTIVES

In order to reach the overall goal, the main objective was divided into several areas, as follows:

• use of trial plots of Eucalyptus (ENCE) and poplar (AFOCEL, ARMEF), to evaluate the mechanical system in comparison with the traditional in relation to the characteristics of the stands and site parameters (stand, density, understoreys, sanitary situation, ground features, logging date etc.);
• evaluation of the relationship between felling time and stump height and stump and shoot survival and growth;
• assessment of the effects of the bark remaining at the site, on the soil fertility;
• study of the phytosanitary condition of the shoots, stumps and piled wood, either with or without bark, to evaluate the timing of disease and insects in relation to the logging season, the site quality and different methods used;
• to determine whether the wood quality (with regard to pulping) differs with time, after piling at the site with bark or without bark;
• finally to design and produce harvesting heads adapted for debarking.

These are considered separately in terms of work carried out on Eucalyptus and poplar. During the period from April 1991 to January 1993, 12 experimental plots of Eucalyptus globulus aged from 10 to 14 years were selected in Huelva (SW Spain). These were used to evaluate a mechanical harvesting system including on-site debarking in order to compare it with the traditional method of manual logging with debarking at the mill. The experimental sites were selected from three developing zones (Arenas, Andevalo and Sierra) at four production rates (more than 50 m3/ha, between 40-50 m3/ha, between 30-40 m3/ha, less than 30 m3/ha) divided on the basis of the four seasons. This provided 4 plots per zone, 3 plots per quality and 3 per season. The size of an experimental area varied from 3 to 10 ha. Accessibility was good in the Arenas plots, intermediate in Andevalo plots and difficult in Sierra plots. Soil conditions are always good. The harvested material consisted of stems of diameter 5 cm in 2.2 m billets. For poplar, 6 plots were selected over the period from 1991 to 1993. The first harvest was of 7 to 8 year SRC of 3 clones, with an average of density to 2800 stems per hectare. Sites were very homogeneous on rich soils which favoured poplar cultivation, producing from 10.1 to 13.5 tons of total dry matter/ha/year with 78% of pulp wood billets (2m). Average stem volume (at diameter 7 cm) was 0.084 m3 from material of average height of 17.8 m and diameter 12.3 cm. Three experimental conditions were used during the logging trials: hand felling, or mechanical felling with and without barking. For this, two heads (SIFER-ARMEF design) were tested in order to improve debarking on the site. The heads have worked in Spain on Eucalyptus and in France on poplar. The poplars stands were homogeneous as far as stocking and density parameters are concern and the logging conditions were favourable. For manual felling, the organisation of work was found to be the most important parameter affecting productivity, whereas for the harvester, it was the unit volume of the trees. Barking reduces productivity of the harvester from 30 to 45 %. It is not justified on the felling site because in France poplar timber is debarked in the mill. For Eucalyptus the yield (measured in m3/productive hour) for the manual harvest did not depend on the factors considered in these trials, being on average 0.86 m3/productive hour.

Where mechanical harvesting is concerned, site quality is very important with the most important parameter concerning productivity being the unitary volume of the average tree in the stand. The most significant parameters as far as economics are concerned are the stocking rate of the stand and the unitary volume of the average tree. In those stands where the average tree has a volume less than 0.06 m3, exploitation costs are lower for manual harvesting; in those stands where the stock is lower than 35 m3/ha, manual harvesting is also the most appropriate from an economic point of view. In all cases, the cutting height was found to have no influence on the shoot death rate or on growth. The site quality, zone and season was found to have a significant influence on both parameters. To minimise the negative effects and increase the positive ones, it is recommended that logging is avoided in Arenas and Andevalo in the Spring. If this is not possible then spring logging in Arenas should be performed in stands over 40 m3/ha and in Andevalo in stands over 50 m3/ha. The height at which the cut is performed has no effect on the sprouting capacity, nor on the growth and death rate of the shoots, so the advice is to perform the cut as low as possible. The main chemical parameters of the soil were found to be stable, whether or not bark was left on the ground. However, it was difficult to reach a firm conclusion during the short period of the project. The wood piled with bark can be a source of Phorachanta semipunctata, a boring insect that attacks Eucalyptus globulus wood. However, the extent of the problem varies with the season of logging, the zones and the time the piles remain as stock. Therefore, in order to control the population of this insect, the recommendations are to debark the wood where possible, otherwise the piles must be split within three months after logging to avoid the emergence of adult insects. However, wood logged in winter and autumn can remain piled with bark for one month longer. No degradation was observed on the wood piled with or without bark, on the density of wood, sodium hydroxide solubility or viscosity of pulp. There were significant differences in cooking yield after three months storage of piled wood without bark, which showed losses bigger than 1 %. This yield loss was related to a lower delignification capacity, measured as Kappa number for Kraft pulp, with a significant increase of 0.5 points in Kappa number in the wood piled without bark.

EXPLOITATION

Two new debarking-delimbing-bucking heads have been designed by ARMEF, taking into account debarking constraints. A modified 400 head is being used at ENCE, a 500 head has been commercialised with the logo SIFOR 500.

PARTICIPANTS

Association Forêt - Cellulose (AFOCEL), and Association pour la Rationalisation et la Mecanisation de l'Exploitation Forestière (ARMEF), both in France.