Hjelm, Birger
- Institutionen för växtproduktionsekologi, Sveriges lantbruksuniversitet
Sammanfattning
In Sweden hybrid poplar has been in focus as future bio- energy supplier and has been planted on former farmland, yet on limited areas, (<2 000 ha-1). After harvest of the first generation, most poplar clones produce a large number of self-generated shoots. Volume or biomass models are usually based on total height (TH) and diameter at breast height (DBH). Experience tells us that diameters are easy to measure in field but height is not. A function to predict coppice heights will therefore be useful. The objective of this study was to investigate if a linear mixed height model can improve height predictions compared to a traditional model. Data of fifty coppices with observed DBH and TH in each of five harvested poplar sites in the province of Skåne in South Sweden, was used. The traditional linear model was expressed as TH = b0 + b1DBH, with transformation log (TH) = b0 + b1* log(DBH). For calculations of the transformed models, the retransformation equation TH=exp(b0)*DBHb1 was used. In the mixed effect model “Site” was the random group effect level. The transformed traditional model reduced the absolute bias with 3.2 %, yet with a small tendency to underestimate height (0.9 dm). However, the main improvement was observed when we used a linear mixed effect model, where we had an absolute bias reduction from 9 dm down to 6 dm resulting in a remarkable lower span between Min and Max values. A mixed model will give a reduction of absolute bias up to almost 30 % compared to a traditional linear model.
Publicerad i
Utgivare: International Poplar Commission
Konferens
International Poplar Commission. Environmental Applications of Poplar and Willow Working Party
SLU författare
UKÄ forskningsämne
Skogsvetenskap
Permanent länk till denna sida (URI)
https://res.slu.se/id/publ/53594