Options for Optimizing the Drying Process and Reducing Dry Matter Losses in Whole-Tree Storage of Poplar from Short-Rotation Coppices in Germany

Abstract

For sustainable production of wood in short-rotation coppices and agroforestry systems, it is necessary to optimize the storage processes to achieve low dry matter losses together with low-cost drying. The harvesting of the trees can be carried out very efficiently with modified forage harvesters or tractor-powered mower-chippers. The wood chips produced can be dried naturally at low cost in open-air piles. However, this type of storage is connected with high dry matter losses of up to about one fourth in the course of seven-month storage. Although harvesting whole trees is connected with significantly higher costs, lower dry matter losses are to be expected from storing the trees in piles. Consequently, in this study, the storage and drying behavior of poplar under different German weather conditions and depending on the structure of the storage piles has been examined in detail. After a seven-months storage period, the trees still displayed moisture contents of 41–44% following an initial moisture content of 56% but achieved very low dry matter losses of only 4–7%. Moisture contents of 35–39% could only be achieved in October after a further two-months drying period under favorable weather conditions. All storage piles were built up on approximately 30 cm high support timbers for better ventilation. Additionally, covering the ground with a fleece did not have any influence on the drying behavior, nor did different pile heights. Smaller tree trunk diameters are not only connected with a higher share of bark or ash, but also thinner trunks tend to become damp again more quickly after rainfall. That is why whole-tree storage is suitable above all for medium or longer rotation periods with which, under favorable conditions, the higher harvesting costs can be compensated by a higher wood chip quality and lower storage losses.

Impact of Storage Method on the Chemical and Physical Properties of Poplar Wood from Short-Rotation Coppice Stored for a Period of 9 Months

“…The components of the gas atmosphere (CO 2 and O 2 ) were regularly measured using the Geotechnical Instrument gas analyser (Anagas CD 95, model: 1/9; manufactured by Geotechnical Instruments, Leamington Spa, UK) [13,26].…”

“…Overall losses depend on the used compartments of the tree, whereby consistently higher reductions can be expected for chips from stems than for those from crown wood [21]. Large differences in mass losses for 7-month open air storage period of poplar were found between wood chips and logs and ranged between 17 to 19% and 4 to 7%, respectively [13,22].…”

“…Numerous studies were carried out for wood chips [7,8], whereas storage of logs from SRCs received less attention in research [9,10]. The majority of recent investigations about log storage methods relate to calamity wood from forests, which leads to a focus on other wood species than poplar [10][11][12][13]. The main goal for the application of an adequate storing method is to preserve the physical properties (e.g.…”

“…wood density) and other quality-related characteristics (e.g. colour) of wood for its further utilization [10,13,14].…”

“…A general differentiation is made between procedures for short-term (a few weeks) and medium-to long-term storage (a few months to several years) [13].…”