Optimising the use of biomass can contribute to a more sustainable and increased production of bioenergy as well as bio-based chemicals and fuels. A new study by PhD student Sruthy Vattaparambil Sudharsan and her research colleagues shows that thinning method on second-rotation poplars affect the quality of the wood and bark.
Forest management can improve and actively shape the feedstock qualiity and quantity of biomass according to the study by Sruthy Vattaparambil Sudharsan, PhD student at Luleå University of Technology (LTU) and within Trees For Me, and her fellow researchers at LTU and SLU.
Effects of thinning method and intensity
”One of the more surprising results was how clearly stem thinning improved biomass quality and not just growth, compared to row thinning”, says Sruthy Vattaparambil Sudharsan.
The study was conducted on second rotation poplar trees, of clone OP42, at a plantation located near Skurup in southern Sweden. The trees were harvested after 15 years, then left for resprouting. Seven years after the first harvest, thinning of rows and stems was carried out with different thinning intensities. In row thinning, the stems in every other row were removed, while in the second method, only the largest stem of each stump was kept.
”We initially expected heavier thinning to always result in higher overall yields, but we found that moderate thinning outperformed heavy thinning in total structural biomass yield”, says Sruthy Vattaparambil Sudharsan.
Quality of raw material
The results showed that the yields of both total biomass and structural components, e.g. hemicellulose and lignin, were highest for single-stem trees thinned via stem thinning. The thinning method and stem diameter affected the fuel and lignocellulosic composition, which in turn has effects on bioenergy conversion, material and chemical production.
”Seeing consistently lower ash content and more favorable ratios of high volatile matter to fixed carbon in single-stem trees, especially at higher stump density, was striking. A high ratio of high volatile matter to fixed carbon is beneficial when using industrial boilers. Another unexpected finding was that the composition of carbon, hydrogen, and nitrogen remained stable across treatments. The high extractive content in the bark of heavily thinned trees was also surprising”, Sruthy Vattaparambil Sudharsan explains.
The results are useful for industrial actors since variations in lignin, hemicellulose, and extractive content indicate that management strategies can help align biomass supply with specific end uses, such as biofuels, bio-based chemicals, or chemical extraction from bark.
The results also provide practical guidance to forest owners on how management choices influence not only biomass volume but also quality of the raw material.
--------
Do you want to learn more about the effect of forestry on biomass for energy and materials?
Welcome to Trees For Me's webinar on 20 March at 14.00-15.00 when PhD student Sruthy Vattaparambil Sudharsan will share the latest updates from the research project.
Registration link and more about the webinar.