Soil quality (SQ) and forest societal services

1. Soil quality (SQ) and forest societal services

The concept of soil quality (SQ) has been described through a variety of definitions in the literature (Andrews et al. 2004). The simplest definition of SQ is ‘the capacity (of soils) to function’ (Karlen et al. 1997) or it may be defined as ‘the capacity to accept, store, and recycle water, nutrients, and energy, sustain biological productivity, maintain environmental quality, and promote plant and animal health’ (Doran and Parkin 1994; Périé and Munson 2000). A committee within the Soil Science Society of America presented an expanded version of this definition that defines SQ as ‘the capacity of

a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation’ (Karlen et al. 1997).

As defined, the concept of SQ is both multidimensional and relative. The understanding of what is good SQ depends on the type of ecosystem and the purpose(s) for which it is managed (Patzel et al. 2000). In principle, SQ might be considered good for one purpose, but poor when assessed for another purpose. In practice, assessments of good SQ for one purpose will often coincide or overlap with assessments of good SQ for other purposes.

Within the limitations set by climatic conditions and parent material, the soil provides nutrients and water to support the growth and health of the vegetation, and it acts as an anchor for roots preventing the soil from eroding. Forest soils thus support the production of a variety of services that are Within the limitations set by climatic conditions and parent material, the soil provides nutrients and water to support the growth and health of the vegetation, and it acts as an anchor for roots preventing the soil from eroding. Forest soils thus support the production of a variety of services that are

a prerequisite for the provision of all such services and special attention should be given to the question of good SQ when a forest is managed for a multiple of purposes since trade-offs with regard to good SQ potentially exist.

The demand for forest products, mainly timber and pulp wood, has increased, and this has led to an intensified forest management with more mechanised operations, shorter rotations, draining, soil scarification, fertilisation, weed control, selection of more productive species, and breeding for faster growth (e.g. Moffat 2003; Johnston and Crossley 2002). These practices affect SQ. Soil erosion, nutrient removal, soil compaction and changes in soil organic matter (SOM) and soil water status are identified as the most important affected features (Haines et al. 1975; 215,230, Johnston and Crossley 2002] when we describe SQ.

Maintaining SQ is the key to maintaining healthy and productive forests. Negative impacts are naturally counteracted by soil formation and nutrient input from soil weathering and deposition. A fundamental requirement for sustainable management is that the impacts of forest management practices should not exceed the long-term site recovery [230]. Therefore, also SQ must be retained in the long-term [166, 156]. For example, erosion losses should not exceed soil formation rates and nutrient removals should Soils differ in vulnerability, not exceed nutrient inputs by weathering, N fixation and atmospheric deposition [230]. If the long-term self restoration capacity is exceeded, the impacts will cause soil degradation and lead to a reduction in SQ [230] and a permanently impair of the productivity of the land (Powers 2006).

Soils differ in vulnerability, resilience and recovery time, and the degree to which forest SQ can be restored following degradation depends on the reversibility of individual impacts. Additionally, impacts need to be aggregated over at least one tree rotation before significant statements regarding for example nutrient sustainability can be made [230]. Recovery of the soil resource is possible to a smaller or larger degree, either by introducing less intensive management and letting the recovery processes act over long periods with no intervention or by improved treatments [230].

If intensively managed forests should continue to provide a wide range of societal services, forest management-induced changes in SQ should be detected before the long-term self restoration capacity of the soil is exceeded. This obligation is fundamental in international principles for sustainable forest management as outlined in the Montreal and Helsinki processes [186, Moffat 2003]. To fulfil these obligations, it should be clarified which management operations cause the largest or the most vital changes in SQ, and how these changes can effectively be detected and monitored. The need for quantitative tools and methods to assess and monitor SQ is apparent [7, 53] and flexible goals for SQ need to be established (Patzel et al. 2000) to allow for adaptation to different ecosystems and management strategies. These questions are addressed in this paper by:

i. identifying the most important indicators as a tool to estimate SQ in forests;

ii. identifying and describing the most important impacts of forest management strategies on forest soil processes;

iii. analysing which SQ indicators are suitable in relation to different management purposes; iv. comparing management-induced changes in SQ quantitatively (whenever possible); otherwise comparing the nature and scale of the changes in qualitative terms; v. giving an overview of on-going SQ monitoring, and discussing how monitoring of management- induced changes in SQ can be improved for better quantitative prediction of forest management impacts on SQ under various conditions.

We focus on temperate and boreal forests, and whenever possible on a long-term time perspective, i.e. one rotation period or approximately 50-120 years. Our analyses are based on existing data syntheses and reviews supplied with newer scientific research.