Long term effects of whole tree harvesting on soil carbon and nutrient sustainability in the UK

Abstract

The practice of harvesting forest residues is rapidly increasing due to rising demand for renewable energy. However, major concerns have been raised about the sustainability of this practice and its net impact on long term soil ability to support forest productivity, particularly through second and subsequent rotations. In this study, soil chemical properties such as acidity, total N and C, available NO 3 -N and NH 4 -N and exchangeable cations were measured in all horizons in peaty gleys soils under one of the oldest experiments in Europe-a 28-year-old second rotation stand of Sitka spruce (Picea sitchensis), in Kielder forest, UK. Treatments included Whole Tree Harvesting (WTH-of all above ground biomass), Conventional stem-only harvesting (CH) of the first rotation crop, and repeated Fertilisation (FE) after the planting of the second rotation forest. This study demonstrates the soil changes underpinning the reduced second rotation tree productivity on these acidic upland sites under WTH, a further 18 years after the investigation by Proe and Dutch (1994). Overall, WTH increased soil acidity significantly (p \ 0.05) and reduced soil base saturation whilst FE reduced soil acidity (p \ 0.05) and increased soil base saturation as compared to CH. Soil moisture was significantly higher (p \ 0.01) under WTH compared to CH and FE plots. There was no evidence that WTH decreased soil organic carbon (SOC) and soil nitrogen (N), but to the contrary there were significantly (p \ 0.01) higher concentrations and stocks of total C and N in the WTH soils compared with CH and FE. The depletion of SOC and N in CH and FE plots was attributed to much higher soil mineralisation rates associated with the brash and fertilisation as compared to the WTH plots, where significantly less soil available NO 3 -N (p \ 0.01) was found. In the long term WTH on peaty gley soils appears positive for soil C and N storage. However, WTH had a long term negative impact on soil and tree nutrition of K ? and P, which are currently at deficient levels, but has had a stabilising effect on tree N nutrition as measured in twigs and needles. These results suggest that whilst WTH lead to a reduction in aboveground tree biomass compared to conventional harvest, these practices on selected soil types and certain sites may be beneficial for soil C and N sequestration. The overall findings of this study imply that cost benefit analyses for each site should be carried out before decisions are made on the appropriate type of forest operations (harvesting and replanting), considering both geology and soils in order to serve both environmental benefits, long term sustainability and the available biomass production for timber and biofuel.

Changes in the effects of whole-tree harvesting on soil chemistry during 10years of stand development

“…Probably as a consequence of this, lower growth rates of different conifer species have been observed in experimental stands subjected to WTH than in those subjected to CH (Proe et al, 1996;Egnell and Leijon, 1999;Egnell, 2011). Other effects of WTH include acidification of soil and water and depletion of soil nutrients (Nykvist and Rosén, 1985;Staaf and Olsson, 1991;Olsson et al, 1996b;Johnson and Todd, 1998;Belleau et al, 2006;Thiffault et al, 2006Thiffault et al, , 2011Wall, 2008;Walmsley et al, 2009;Saarsalmi et al, 2010;Vanguelova et al, 2010). Furthermore, leaching may be enhanced by the production of nitrate from decomposing harvest residues (Staaf and Olsson, 1994;Titus et al, 1998;Mahendrappa et al, 2006), which means greater nitrate leaching in CH stands than in WTH stands.…”

Harvest residue management and fertilisation effects on soil carbon and nitrogen in a 15-year-old Pinus radiata plantation forest

“…The ability of forest soils to act as sinks for atmospheric C, sustain commercial biomass production, and provide other environmental services will likely depend on how well these soils are managed (Fox, 2000;Lal, 2005;Vanguelova et al, 2010). Forest management practices affect soil C and nitrogen (N) storage by changing the quantity or quality of organic matter inputs to the soil, causing physical disturbance of the soil profile, or by modifying the soil environment (temperature and moisture regimes) and nutrient levels (Johnson, 1992;Johnson and Curtis, 2001;Jandl et al, 2007;Nave et al, 2009Nave et al, , 2010Vanguelova et al, 2010). In-line with the increasing demand for renewable energy, interest in the use of planted forests for bioenergy production is growing in New Zealand (Hall et al, 2009) and elsewhere (Vanguelova et al, 2010).…”

“…Forest management practices affect soil C and nitrogen (N) storage by changing the quantity or quality of organic matter inputs to the soil, causing physical disturbance of the soil profile, or by modifying the soil environment (temperature and moisture regimes) and nutrient levels (Johnson, 1992;Johnson and Curtis, 2001;Jandl et al, 2007;Nave et al, 2009Nave et al, , 2010Vanguelova et al, 2010). In-line with the increasing demand for renewable energy, interest in the use of planted forests for bioenergy production is growing in New Zealand (Hall et al, 2009) and elsewhere (Vanguelova et al, 2010). This demand could lead to the intensification of forest management with associated reductions in the quantities of residues returned to the site following harvesting and the need to apply fertilisers to maintain site productivity.…”

Using Macronutrient Distributions within Trees to Define a Branch Diameter Threshold for Biomass Harvest in Sugar Maple-Dominated Stands

“…Several studies have also identified P as possibly limiting the productivity of temperate hardwood forests [36,37] and multiple sources of evidence indicate that WTH significantly reduces P soil pools [25,38,39]. Estimated P annual budgets in SM-YB forests are between 0.02 [25] and 0.10 kg·ha −1 ·year −1 [35].…”