Biomass and nutrients in tree root systems–sustainable harvesting of an intensively managedPinus pinaster(Ait.) planted forest

Abstract

To develop sources of renewable energy and to reduce greenhouse gas emissions, increasing attention has been given to the extraction of forest biomass, especially in the form of harvest residues. However, increasing the removal of biomass, and hence nutrients, has raised concerns about the sustainability of site fertility and forest productivity. The environmental cost of harvesting belowground biomass is still not fully understood. The objectives of this study were to (i) estimate the stocks of belowground biomass that potentially can be collected; (ii) measure the nutrient (N, P, K, Ca, Mg) concentrations of the different root compartments (stumps, coarse and thin roots); and to (iii) quantify the biomass and nutrient exports under different scenarios, including harvests of above and belowground compartments. The study was carried out on Pinus pinaster stands located in southwestern France. Results showed that roots could be a significant fuelwood resource, particularly at forest clear cutting. Negative relationships between root diameter and root nutrient concentration were observed, independently of root function or tree age. Such relationships can be used to accurately simulate nutrient concentrations in roots as well as nutrient exports. Combining our original results on roots with previously published data on the aboveground compartments showed that nutrient losses were higher in canopy harvest scenarios than in root harvest scenarios. This was mainly due to high nutrient concentrations of needles. We concluded that stump and root harvest could be sustainable in our study context, conversely to foliage harvest. Because thin roots have higher nutrient concentrations than coarse roots and the proportion of thin roots increased with an increase in the distance from the tree, collecting roots only in the close vicinity of the stumps should limit nutrient exports (particularly N) without unnecessarily reducing fuelwood biomass.

Descendant root volume varies as a function of root type: estimation of root biomass lost during uprooting in Pinus pinaster

“…In the L12 dataset, the sample consisted of seven of the largest DBH trees, as well as five trees that spanned the range of DBH values in the stand (Danjon et al, 2007). In L19, only the largest, most dominant trees were sampled (Augusto et al, 2013). In L12 and L19, trees were uprooted after removing soil from shallow roots with an air-lance, loosening the soil between the shallow roots with the bucket of a mechanical shovel, and then pulling the stem vertically.…”

Soil Degradation and Soil Quality in Western Europe: Current Situation and Future Perspectives

“…It was also observed that after 23 years of growth of the next rotation of trees, the plots where whole trees were harvested had a significantly lower basal area on average [36]. Furthermore, the removal of tree stumps and coarse roots from felling sites as a source of woody biomass for bioenergy generation is being established in parts of WE such as Aquitaine (France) [37]. However, harvesting roots may be unsustainable if soil fertility is reduced, with consequences for future forest production [37,38].…”

“…Furthermore, the removal of tree stumps and coarse roots from felling sites as a source of woody biomass for bioenergy generation is being established in parts of WE such as Aquitaine (France) [37]. However, harvesting roots may be unsustainable if soil fertility is reduced, with consequences for future forest production [37,38].…”

Sequential Management of Commercial Rosewood (Aniba rosaeodora Ducke) Plantations in Central Amazonia: Seeking Sustainable Models for Essential Oil Production

“…If a biomass harvest is totally removed then no material remains at the planting site, and so no further contribution decomposition-mediated nutrient cycling is possible [27][28][29]. For the first harvest, reduction of nutrient exports by pruning management compared to full-cut management was 43% for N, 54% for P, 57% for K, 46% for Ca, 31% for Mg, 49% for Fe, 30% for Zn and 41% for Mn.…”

“…As a result, biomass accumulation under such management may be limited by negative impacts on soil fertility [28,29]. In consequence, interactions between such tree crops and nutrient cycling need to be studied if sustainable forest management is to be guaranteed.…”