This research investigated a potential cost effective system for thinning small sized trees.

Thinning small sized trees is usually expensive and produces low value products. However, the potential for the thinned trees to be used as energy wood has created new opportunities. From a productivity and cost perspective, these thinning operations are often best suited to tree length systems. Raffaele Spinelli and Carla Nati have published an article in the Croation Journal of Forest Engineering (Croat.j.for.eng.30(2009)2 – pg 89-97) titled “A Low-Investment Fully Mechanised Operation for Pure Selection Thinning of Pine Plantations”. The research was carried out on Pinus halepensis.

The study tested a full tree system (extraction with branches and top intact) on relatively flat terrain with the following three specifications:

The system that was developed was as follows:

1. Feller buncher – A disc-saw with accumulating arms mounted on the universal implement hitch of a 58 kW, 4-tonne tracked skid-steer loader. It would reverse down every second inter row, selecting trees to fell on both sides and placing them in 3-5 tree bundles in the middle of the inter row.
2. Grapple skidder – a 44 kW farm tractor with a skidding grapple mounted on the three-point linkage. The skidder selected the bundles and dragged them to roadside to the chipper.
3. Chipper – Trailer mounted drum chipper powered by a 162 kW independent engine and its own loader. When sufficient material was available, the chipper was started up and the chips were blown directly into waiting transport trucks.

The site was thinned from 1670 to 1207 stems per hectare (463 trees removed per hectare = 28%) and the biomass yield per hectare was 27.5 oven-dry tonnes (odt). The felling and extraction was balanced at approximately 40 trees/hour, but the chipper productivity was nearly double.

The entire investment cost for the system amounted to €338,000 (including the truck and tractor to move the chipper). The feller buncher and grapple skidder cost was €98,000. With the price of chips being at €85/odt, the operation became profitable when harvesting trees of 19 cm DBH and larger. However, if the chip was increased to €100/bdt, then the breakeven point is at 15 cm DBH.

Please access the Croation Journal of Forest Engineering for a detailed and more complete account of the research.
Source:http://crojfe.sumfak.hr  Photo's: Raffaele Spinelli