Summary

Emile Mwenge, PhD studentship, University of Reading (2010-2015)

Background

Biomass use for energy is rapidly growing as result of policies promoting greater use of renewable energy. Policies aiming at mitigating climate change and insuring energy security encourage the use of alternative energy sources, cheap and locally available such as forest wood and forest residues. However, intensive harvesting of forest biomass can be damaging for the environment so that in many countries this is prevented from environmentally sensitive sites by guidelines based on local conditions.

In relation to brash and stump removal four principal risks are acknowledged as threats to both sustainable forest management and the wider environment in the United Kingdom:

  • Increased soil damage due to compaction, rutting and disturbance leading to erosion and increased turbidity and siltation of local watercourses.
  • Removal of essential major and micronutrients (e.g. nitrogen, phosphorus, potassium and boron), leading to lower soil fertility, and potential loss of tree growth in subsequent rotations.
  • Removal of base cations (calcium, magnesium, sodium and potassium) reducing soil buffering capacity and leading to increased soil and stream water acidification.
  • Increased carbon loss from disturbed soil after stump harvesting leading to reduced soil carbon stock” (Forest Research, 2009).

Research objectives

The project aims to investigate the above threats in regard to brash removal and stump harvesting and assess the long term nutritional effects of brash removal and stump removal on UK forest soils, especially in terms of soil fertility and acidification which could form a limiting factor for forest growth, restricting the long term forest sustainability and affecting the forest’s carbon dioxide mitigation approach.

The objective is to increase understanding of environmental impacts of stumps removal. A full understanding, particularly how stump extraction influences the forest soil carbon balance and forest nutrient stocks, is central in producing guidance on good practices for a sustainable forest management.

The project will also verify, how relevant are the warnings given in the current UK interim guidance, in order to help policymakers in setting up updated guidelines and recommendations of sustainable stump removal in the UK. A nutrient budgeting is a useful approach in determining long-term sustainability of harvesting practices.

This project will calculate nutrients balance at forest stand level, through determination of nutrients fluxes, and then upscale this to national level using a GIS (Geography Information System) approach. Output and input fluxes of nutrients will be measured and a balance calculated.