Stump and Root Biomass of Poplar Stands

Abstract

Abstract:Today there is an increasing demand for biomass for use in energy production. In this study we investigated stumps and roots from six poplar (Populus sp.) stands growing on former farmland in Sweden, situated between latitudes 55 and 60°N. The mean age of the poplar was 20 years (range 16-23), the mean stand density 1151 stems ha −1 (range 361-3279), and the mean diameter at breast height (over bark) 288 mm (range 81-574). All poplar stands were on clay soils (light and medium clay and light clay tills).The mean dry mass weight of the 72 excavated stumps was 45 ± 39 kg (range 1-185), with the roots ≥ 50 mm weighing 14 ± 16 kg (range 0.2-87). Dry mean stump weight represented 21% (by dry weight) of the stem. The mean total dry weight per hectare for stumps amounted to 34.9 ± 21.8 (range 12.9-66.9) tons and the equivalent value for roots was 12.0 ± 9.6 (range 4.7-10.9) tons. The excavation of below-ground biomass can either focus on the stump or the stump and parts of the root system. Depending on the combination of soil type and soil moisture the weight of soil adhering to stumps and the cleaning requirements will vary.

Plastic Allometry in Coarse Root Biomass of Mature Hybrid Poplar Plantations

“…Large roots have particularly slow decay rates, and they can contribute to the belowground biomass C pool over a century after harvest [97], while having a short-term positive effect on soil organic C stocks once incorporated into the soil [98]. Lastly, more accurate coarse root biomass estimates are also be needed, as coarse root biomass may eventually represent a valuable bioenergy feedstock in some countries [19].…”

“…Being the largest biomass C pool after stems and branches, poplar coarse root biomass needs to be more accurately quantified [96]. Until now, only general allometric relationships had been developed for poplar coarse root biomass [24,26,22,23,19,27,25], with no consideration for the potential effect of plantation environment on allometric trajectory. In this study, using the general allometric relationship developed across the four sites (Fig.…”

“…Tap root volume was calculated using the Smalian formula [59]. Tap root biomass was obtained by multiplying its volume by the mean density of hybrid poplar coarse roots (0.313 g/cm 3 ) [19]. All coarse roots (diameter>2 mm) in excavated pits were hand cut with a saw, removed, cleaned and air dried for 2 months.…”

“…Yet, the potential effects of environmental conditions on coarse root biomass growth and allometry have received little attention over the years. In poplar plantations, a few studies have developed allometric relationships between diameter at breast height (DBH) and coarse root biomass in different plantation environments [22,23,19,24,25]. These relationships have also been developed in natural poplar stands [26,27].…”

“…From an economic perspective, there is also a need for a better quantification of belowground biomass. The growing demand for bioenergy in many parts of the world has stimulated the exploitation of new sources of feedstock, such as stump and coarse root biomass that can be extracted following harvest [18,19].…”