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Analysis
A framework for classifying and quantifying the natural capital and ecosystem
services of soils
Estelle Dominati
a,b,
⁎, Murray Patterson
a
, Alec Mackay
b
a
Ecological Economics Research New Zealand, c/-Landcare Research Building, Private Bag 11052, Palmerston North 4442, New Zealand
b
AgResearch, Grasslands Research Centre, Tennent Drive, Private Bag 11008, Palmerston North 4442, New Zealand
abstractarticle info
Article history:
Received 30 October 2009
Received in revised form 28 April 2010
Accepted 4 May 2010
Available online 27 May 2010
Keywords:
Soil ecosystem services
Soil properties
Processes
Capital formation
Degradation
Human needs
The ecosystem services and natural capital of soils are often not recognised and generally not well
understood. This paper addresses this issue by drawing on scientific understanding of soil formation,
functioning and classification systems and building on current thinking on ecosystem services to develop a
framework to classify and quantify soil natural capital and ecosystem services. The framework consists of five
main interconnected components: (1) soil natural capital, characterised by standard soil properties well
known to soil scientists; (2) the processes behind soil natural capital formation, maintenance and
degradation; (3) drivers (anthropogenic and natural) of soil processes; (4) provisioning, regulating and
cultural ecosystem services; and (5) human needs fulfilled by soil ecosystem services.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Nowadays industrial and post-industrial economies seem less
dependent on their environment; however, to meet the basic needs of
a growing global population (food, fibre, clean air, clean water), the
extreme importance of the natural capital stocks and ecosystem
services they provide needs to be recognised. Accordingly, since the
late 1960s there has been a growing interest in the analysis of the
services provided by ecosystems and the need to include them in
decision-making processes in order to achieve sustainable develop-
ment. Several studies have provided frameworks for the description
and valuation of ecosystem services (Costanza et al., 1997; de Groot
et al., 2002; MEA, 2005) but all too often soils, the basic substrate for
many ecosystems and human activities, have been considered a black-
box within these frameworks, because their focus is on what happens
above ground. Many authors (Balmford et al., 2002; Daily et al., 1997;
Kroeger and Casey, 2007; Swinton et al., 2006, 2007; Turner and Daily,
2008) agree that our ability to understand soil natural capital and the
ecosystem services it provides is incomplete, despite a good
understanding of soil formation and functioning. Because soils are
an important determinant of the economic status of nations (Daily
et al., 1997), it is essential to include them in ecosystem service
frameworks that inform decision-making and environmental policies.
One of the difficulties while constructing a coherent “natural
capital-ecosystem services”framework for soils is the confusion
created by the use of different terminologies borrowed from at least
three disciplines: ecology, economics and soil science. Many of the
terms used have multiple definitions. For sake of clarity, we define
here the terms as used in this paper, that are applied to soils —fully
recognising that a particular term may be used differently in a
different discipline or field. Fig. 1 presents an example of each term
defined here in the context of the provision of an ecosystem service:
flood mitigation. Natural capital refers to the extension of the
economic idea of manufactured capital to include environmental
goods and services. Natural capital, like all other forms of capital, is a
stock as opposed to a flow. Natural capital consists of “stocks of
natural assets (e.g. soils, forests, water bodies) that yield a flow of
valuable ecosystem goods or services into the future”(Costanza and
Daly, 1992, p. 38). Soils are considered here as natural capital and
provide services such as recycling of wastes or flood mitigation
(Fig. 1).
To describe soils, pedologists use different concepts like soil
components and soil properties. A soil component is defined here as a
biogeochemical species (e.g. nitrate NO
3
−
) or an aggregation of
biogeochemical species (e.g. clays, Fig. 1) that make up soils. Soils
consist of four major categories of soil components: mineral, organic,
liquids, and gases. Soil properties are the physical (e.g. porosity,
texture), chemical (e.g. pH, readily available phosphate), and
biological (e.g. microbial biomass) characteristics of a soil. Soil
properties are often measurable quantities that allow soil scientists
to place soils on relative scales. For example (Fig. 1), clays are soil
Ecological Economics 69 (2010) 1858–1868
⁎Corresponding author. Ecological Economics Research New Zealand, c/-Landcare
Research Building, Private Bag 11052, Palmerston North 4442, New Zealand. Tel.: +64 6
356 9099x81513.
E-mail address: E.J.Dominati@massey.ac.nz (E. Dominati).
0921-8009/$ –see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ecolecon.2010.05.002
Contents lists available at ScienceDirect
Ecological Economics
journal homepage: www.elsevier.com/locate/ecolecon
components which play an important role in the formation of soil
structure. Clay content is a property informing the amount of clay in a
soil.
Authors (Costanza and Daly, 1992; Daly and Farley, 2003; de Groot
et al., 2002; Ekins et al., 2003a) agree that natural capital yields
ecosystem services but the nature of these ecosystem services is still
debated in the literature (Costanza 2008; Fisher & Kerry Turner 2008;
Wallace, 2007). Controversy revolves around the definitions of the
terms “function”and “processes”used to define ecosystem services
and the boundaries between them. In ecology, the traditional
definition of an ecosystem function was the role the ecosystem
plays in the environment, but in recent years, the term “ecosystem
function”has been used as a synonym for “ecosystem process”
(Wallace, 2007), as in soil science. In this paper, the term “process”is
used rather than “function”and is defined as the transformation of
input into outputs. Some processes are chemical (e.g. oxidation),
some physical (e.g. diffusion), others are biological (e.g. denitrifica-
tion). For example (Fig. 1), flocculation is a process leading to the
formation of soil structure. At the molecular level, water molecules
and cations link negatively charged clays together. When the soil dries
out the clays are brought together into more stable aggregates.
The existing literature on ecosystem services tends to focus
exclusively on the ecosystem services rather than holistically linking
these services to the natural capital base from which they arise. To
avoid this, ecosystem services are defined here as the beneficial flows
arising from natural capital stocks and fulfilling human needs. We
argue that ecosystem services are not processes but flows (amount
per unit time), as opposed to stocks (amount). For example (Fig. 1),
soil structure presents pores able to store water. The provision of the
ecosystem service ‘flood mitigation’depends on the amount of water
a soil can store (stock) and also the timing of the availability of the
storage volume regarding a rainfall event.
Keeping in mind these concepts, this paper undertakes to assess
the importance of soils as natural capital and provider of ecosystem
services. It draws on scientific understanding of soil formation,
functioning and classification systems and builds on current thinking
on ecosystem services to develop a framework to conceptualise,
classify and quantify soil natural capital and ecosystem services. The
paper first discusses existing ecosystem service frameworks, then
presents a new framework that introduces soils as natural capital,
illustrates natural capital formation, maintenance and degradation
and the drivers impacting on these processes. Finally, the paper
describes the ecosystem services provided by soils, and outlines how
soil ecosystem services fulfil human needs.
2. Existing Classification Schemes for Ecosystem Services
Before presenting our framework, we examine the strengths and
limitations of the general ecosystem service frameworks found in the
literature, as well as agro-ecosystems service frameworks which
include soils.
2.1. General Ecosystem Service Frameworks
With heightening awareness of the importance of ecosystem
services, over the last two decades general typologies and classifica-
tion systems have emerged (Table 1). De Groot's classification system
(1992), one of the first, defined ecosystem functions as “the capacity
of natural processes and components to provide goods and services
that satisfy human needs, directly or indirectly”and grouped these
functions into four primary categories: regulation, habitat, production
and information functions (Table 1). Costanza et al. (1997) detailed
seventeen goods and services, including most of de Groot's (1992)
functions. Noël and O'Connor (1998) classified “the specific roles or
services provided by natural systems that support economic activity
and human welfare”into five categories —“the five S's”(Table 1).
Daily (1999) also produced an “ecosystem services framework”
including five services (Table 1). A common thread through all
these classification systems is the recognition of the diversity of roles
played by ecosystems (Table 1). The concepts proposed in different
classifications tally with each other (Table 1), for instance de Groot's
(1992) production functions correspond to what Noël and O'Connor
(1998) called the “source”role of ecosystems.
More recently, de Groot et al. (2002) identified 23 functions in the
four primary categories established in earlier work (de Groot, 1992)
and detailed the corresponding processes and services, noting that
“ecosystem processes and services do not always show a one-to-one
correspondence”(de Groot et al., 2002, p. 397). To the four categories,
they later introduced a fifth, a carrier function (Table 1) and specified
that the “regulation functions provide the necessary pre-conditions
for all other functions”(de Groot, 2006, p. 177). As part of the CRiTiNC
project, Douguet and O'Connor (2003) and Ekins et al. (2003b) used a
similar classification (Table 1) to that of Noël and O'Connor (1998) to
argue that the principles of environmental sustainability must be
based on the maintenance of the important life-support “functions of
nature”that form the basis on which the “functions for people”are
fundamentally dependent.
The novel idea that de Groot et al. (2002), Douguet and O'Connor
(2003) and Ekins et al. (2003b) advanced is that some ecosystem
functions –or processes as we call them here –support others.
Ecosystem processes insure ecosystems health and functioning,
whereas ecosystem services are flows coming from these ecosystems.
The Millennium Ecosystem Assessment (MEA, 2005) took up this idea
in a “framework of ecosystem services”(Table 1). It assessed the
consequences of ecosystem change for human well-being, defining
ecosystem services as “the benefits people obtain from ecosystems”
(MEA, 2005, p. 40). It classified ecosystem services in four categories:
provisioning, regulating, cultural and supporting services. The first
three categories of services directly affect people, whereas the
supporting services are there to maintain the other services. It is
interesting to point out that the MEA's four categories are close to the
categories of functions of de Groot (1992) with the difference that de
Groot's “regulation functions”seem to include both of the MEA's
Fig. 1. Illustration of the use of the key terms employed in this paper.
1859E. Dominati et al. / Ecological Economics 69 (2010) 1858–1868
“supporting and regulating services”(Table 1). The approach set out
in the MEA has been adopted and used widely (Barrios, 2007; Lavelle
et al., 2006; Sandhu et al., 2008; Swinton et al., 2007; Zhang et al.,
2007).
Some roles of ecosystems are mentioned unanimously by the
authors cited above (Table 1), including the production (or source)
role —the capacity of ecosystem to produce resources of interest for
humans; the regulation role —the capacity of ecosystems to auto-
regulate themselves, absorb human emissions, recycle them, and
remain stable; and the information role —the capacity of ecosystems
to inspire people and produce non-material goods. However, as has
been reported by a number of authors (Boyd and Banzhaf, 2007;
Costanza, 2008; Fisher and Kerry Turner, 2008; Wallace, 2007), some
common challenges are still found with existing frameworks.
First, not all existing frameworks recognise that some processes
sustain others. Of the classification systems covered (Table 1), only
Ekins et al. (2003b), de Groot (2006),andtheMEA (2005)
acknowledge that some processes “support”other processes. Failure
to make the distinction can lead to double accounting in the valuation
and measurement of ecosystem services. Once it has been recognised
that some processes support others, the challenge is to identify
precisely the ecosystem services provided and the processes directly
supporting them and to base the valuation of the services on these
processes.
Second, the definitions and use of terms to describe ecosystem
services vary across the published classification systems. The
ecosystem services literature often refers to groups of processes
such as, for instance, “nutrient cycling”(MEA, 2005) as a service. It has
been argued (Balmford et al., 2008; Boyd and Banzhaf, 2007; Fisher
and Kerry Turner, 2008; Wallace, 2007) that doing so mixes up the
“means of production”, the processes, with the actual services.
Photosynthesis, for example, is an essential process for plant growth
and should not be confused with the ecosystem service it supports,
which is the provision of food and fibre.
Third, as different authors (Boyd and Banzhaf, 2007; Wallace,
2007) have pointed out, in valuing ecosystems it may be more helpful
to focus on ecosystem components, and use them as proxies for
services, rather than on processes, because science gives us much
more information on the structure and composition of ecosystems
than on the processes involved in their functioning.
The general ecosystem service frameworks (Table 1) do little
justice to the roles of soils in the provision of ecosystem services and
as a consequence fail to recognise the large differences that exist
between soils in their ability to provide services. For instance, the MEA
mentions “soil formation”as a supporting service and recognises that
“many provisioning services depend on soil fertility”(MEA, 2005,p.
40). It also mentions the role of soils in the provision of regulating
services like erosion regulation, water purification and waste
treatment, but does not explicitly identify the part played by soils in
the provision of these services and more generally in the provision of
services from above ground ecosystems. This is why we need to
examine ecosystem service frameworks that accord more importance
to soils and their different roles.
2.2. Soil Ecosystem Service Frameworks
Many agree (Daily, 1997; Dale and Polasky, 2007; de Groot et al.,
2003; Straton, 2006) that a better characterisation of ecosystem
services supplied by soils is overdue. Daily (Daily et al., 1997, p.128)
indicated that “research is needed to better characterise the
ecosystem services supplied by soils”, along with a better under-
standing of the “interrelationships of different services supplied by
soils and other systems”. While a few authors (Daily et al., 1997; Wall
et al., 2004; Weber, 2007) have proposed soil specific frameworks for
ecosystem services, others (Barrios, 2007; Lavelle et al., 2006; Porter
et al., 2009; Sandhu et al., 2008; Swinton et al., 2007; Zhang et al.,
2007), mainly working on wider agro-ecosystems, have detailed
services provided by soils (Table 2). These studies enable us to start
identifying where and in which way soils affect the provision of
ecosystem services. When comparing the different soil ecosystem
service frameworks in the literature (Table 2), the following roles of
soils in the provision of services can be identified:
•Fertility role: soil nutrient cycles ensure fertility renewal and the
delivery of nutrients to plants, therefore contributing to plant
growth,
•Filter and reservoir role: soils fix and store solutes passing through
and therefore purify water. They also store water for plants to use
and take part in flood mitigation,
•Structural role: soils provide physical support to plants, animals and
human infrastructures,
•Climate regulation role: soils take part in climate regulation through
carbon sequestration and greenhouse gases (N
2
O and CH
4
) emis-
sions regulation,
•Biodiversity conservation role: soils are a reservoir of biodiversity.
They provide habitat for thousands of species regulating for instance
pest control or the disposal of wastes,
•Resource role: soils can be a source of materials like peat and clay.
To progress the recent advances made in soil specific ecosystem
service frameworks, several remaining limitations need to be
addressed. Extending the existing frameworks to show the links
between soil natural capital stocks and ecosystem services to provide
a more holistic approach would be one of the major challenges. Like
general ecosystem service frameworks, existing soil ecosystem
service frameworks fail to recognise that some processes support
other processes which lead to confusion in the wording of the
services. For instance, Wall et al. (2004) mention as services the
“retention and delivery of nutrients to plants”and the “contribution to
plant production for food”(Table 2). The first one is a group of
processes, whereas the second one is the service. Moreover, existing
frameworks tend to ignore a great deal of scientific knowledge that
Table 1
Ecosystem roles mentioned by different classification systems.
Authors Ecosystem roles
a
Life-support Production Regulation Habitat
provision
Physical
support
Information and culture
De Groot (1992), de Groot
et al., (2002)
Regulation functions Production functions Regulation functions Habitat functions NC Information functions
Noël & O'Connor (1998) Life-support Source Sink NC Site Scenery
Daily (1999) Regeneration processes Production of goods Stabilising processes NC NC Life filling functions,
preservation of options
Ekins et al. (2003a,b) Life-support Source Sink NC NC Human health and welfare
MEA (2005) Supporting services Provisioning services Regulating services NC NC Cultural services
De Groot (2006) Regulation functions Production functions Regulation functions Habitat functions Carrier functions Information functions
a
Roles as described by the original authors. NC: not considered.
1860 E. Dominati et al. / Ecological Economics 69 (2010) 1858–1868
has been acquired about soils and do not acknowledge the complexity
of soil functioning. When applying the existing frameworks for
valuation, some authors tend to use a one-to-one correspondence
between processes and services without acknowledging the com-
plexity of soil processes. Sandhu et al. (2008) and Porter et al. (2009)
used similar methodologies for the valuation of ecosystem services
from agro-ecosystems, including some soil ecosystem services. For
each one of the services they valued, they identified one soil process
underlying the service (e.g. soil formation), using one indicator to
measure that process (e.g. the population of earthworms). The
economic valuation was then based on that single indicator. While
the methodology used in both studies helps illustrate the links
between soil processes and properties and the provision of services
from soils, limiting each service to one indicator fails to recognise that
each soil service is the product of multiple properties and processes.
Nevertheless, Porter et al. (2009) did consider a more sophisticated
function when dealing with nitrogen regulation, showing that it is
necessary to acknowledge that soils are very complex ecosystems.
Services are underpinned by more than one process or property and
the use of process-based models that capture the scientific knowledge
available is required to fully comprehend them. Dale and Polasky
(2007) argued about general ecosystem service frameworks that “a
thorough understanding of how ecological systems function”is
needed and that “ideally, it would be useful to have the ability to
accurately measure the flow of ecosystem services from agro-
ecosystems at several scales of resolution”(Dale and Polasky, 2007,
p. 287). Existing frameworks also pay little attention to those factors
over which managers of soils have control and therefore have had
limited utility as tools to explore the impacts of land uses and
practices on the provision of soil ecosystem services.
The limitations of existing frameworks mentioned above highlight
the need for a better framework. In the following section, we present a
framework for the provision of ecosystem services by soil that
addresses some of these limitations.
3. Proposed Framework for Soil Ecosystem Services
The conceptual framework for classifying, quantifying and mod-
elling soil natural capital and ecosystem services (Fig. 2) provides a
broader and more holistic approach than previous attempts to identify
soil ecosystem services by linking soil ecosystem services to soil
natural capital. It shows how external drivers impact on processes
that underpin soil natural capital and ecosystem services and how soil
ecosystem services contribute to human well-being. The framework
consists of five main interconnected components: (1) soils as natural
capital; (2) natural capital formation, maintenance and degradation;
(3) the drivers of soil processes; (4) provisioning, regulating and
cultural soil ecosystem services; and (5) human needs fulfilled by soil
ecosystem services.
3.1. Soil Natural Capital
Soil natural capital is capital is defined here as a stock of natural
assets yielding a flow of either natural resources or ecosystem services
(Costanza and Daly, 1992). Since the flow of services from ecosystems
requires that they function as whole systems, the structure,
composition and diversity of the ecosystem are important compo-
nents of natural capital. By incorporating the idea of soils as natural
capital into the conceptual framework, we provide a more complete
picture, as well as infuse soil science knowledge into the discussion.
Doing so creates the opportunity to value the natural capital of soils
and also to track the changes in these values for a given human use.
The natural capital of soils can be characterised by soil properties. The
idea of soil properties is central to soil science and it is the way in
which soil scientists and agronomists describe and characterise soils.
As measurable quantities, soil properties enable soil scientists to
compare soils on different criteria. The concept of soil properties can
be traced back to the 1840s when scientists studied the chemical
properties of soils: first, soil's weak-acid properties and the capacity to
absorb and exchange cations (Way, 1850) and anions, and later the
colloidal properties of soil clays and their mineralogy (Schloesing,
1874). In parallel, soil physics was developed as a discipline about soil
moisture and water physics, based on the work of Darcy (1803–1858)
but also the principles and determination of the grain-size distribu-
tion in soils (i.e. clay, silt and sand fractions) that influences both
physical and chemical properties. Understanding mechanical proper-
ties of soils came later (beginning of the 20th century) with rheology
(study of deformation and flow of matter) informing us of the
behaviour of soils under stress (Yaalon, 1997).
A soil property can refer to any soil componentthat can be measured
and used to compare or assess soils. For instance, when soils contain
stones, the properties related to stones can be size, percentage of stones
in soil volume or percentage of stones in soil mass. Soil properties are
routinely evaluated in terms of three broad dimensions —physical,
chemical or biological. For example, texture is a physical soil property
representing the relative proportion of sand, silt and clay in the soil.
Texture isa determinant factor of aggregatesize and soil structure and is
also an indicator of other soil properties like water storage capacity and
drainage class. Cation exchange capacity (CEC) is a chemical property. It
is a quantitative measure of the soil's ability to hold cations, and
indicates the quantity of negative charges present per unit mass of soil.
CEC is influenced by the amount of organic matter (OM), the types and
amounts of clays, and pH (Fig. 3). Microbial biomass and its activity are
biological soil properties. It refers to the size and diversity of microbial
populations associatedwith organic matter decomposition and nutrient
transformations.
Soil properties are interrelated with each other and with soil
components (Fig. 3). For example, physical properties influence soil
moisture content and water movements, which then influence soil
chemical and biological properties. In return, soil chemical and
biological processes and properties influence physical properties by
the production of precipitates and colloids for example. Properties
influence the intensity at which the processes occur and are at the
same time products of these processes. It is very important when
quantifying and valuing the natural capital stocks of a soil that double
counting of soil properties does not occur and there is a clear
understanding of the influence soil properties have on soil processes
and how they collectively contribute to ecosystem services.
Most of the modern soil classifications are based on the properties
of horizons within the soil. Soil classification provides a framework
that facilitates communication and understanding amongst pedolo-
gists, when there is a prior agreement on concepts. They also make
information more accessible to non-specialists. The properties chosen
to build-up classification schemes are those that can be observable or
measured in the field or measured in the laboratory. Those linked
directly to use are of particular interest. In the past, climate
parameters were utilised in the classification of soils. The World
Reference Base for Soil Resources (WRB) is the international standard
taxonomic soil classification system endorsed by the International
Union of Soil Sciences (IUSS), replacing the previous Food and
Agriculture Organisation (FAO) soil classification. The WRB is inspired
by modern soil classification concepts, including the United States
Department of Agriculture (USDA) soil taxonomy, the legend for the
FAO Soil Map of the World, the French Référentiel Pédologique, and
Russian concepts. The WRB classification is based mainly on soil
morphology as an expression of soil formation conditions. Soil
classifications and associated properties alone cannot be used for
compiling an inventory of soil natural capital stocks and their value.
Human use (land use) or purpose must be added to soil classifications
before a value can be assigned to the natural capital stocks by
quantifying the ecosystem services they provide. For example, a deep
stony soil will be suited for grape growing, average for sunflower
1861E. Dominati et al. / Ecological Economics 69 (2010) 1858–1868
cropping, and unsuitable for arable cropping because these different
crops require different optimal water and drainage conditions. Land
use is therefore a very important component of the relationship
between soil natural capital stocks, ecosystem services and human
welfare. Notwithstanding the difficulties and intricacies of applying
soil classification schema to a “natural capital-ecosystem services”
framework, the existence of soil classification systems does provide a
rigorous way of considering soil's stocks, on which ecological
economists and others concerned with managing soil ecosystem
services can draw on as a basis for recognising differences between
soils.
When describing soil natural capital stocks and the sustainable
productive capability of soils, it is useful to make the distinction
between inherent soil properties derived from soil formation
conditions and those properties that respond to active management
(Fig. 2). Lynn et al. (2009, p. 86), make the distinction between
“permanent, removable and modifiable limitations”.Robinson et al.
(2009, p. 1906) made a similar distinction between “inherent and
dynamic properties”. In this paper, we make the distinction between
inherent and manageable soil properties (Fig. 2). Inherent soil
properties typically include slope, depth, cation exchange capacity,
and clay types. They cannot readily be changed without significant
modification of the soil, its environment, or without involving
prohibitive costs. Manageable soil properties typically include soluble
phosphate, mineral nitrogen, organic matter contents and macro-
porosity (Fig. 2). In an ecosystem services management framework,
although recognising and taking account of inherent soil properties,
the manageable properties assume more practical importance as they
provide the opportunity for agronomists, farmers and other stake-
holders to optimise the provision of ecosystem services from soils.
Knowing what type of properties is involved in the processes and the
services they support is therefore essential. For this reason, in putting
forward the conceptual framework of soil natural capital and
ecosystem services, we put major emphasis on recognising and
distinguishing the differences between inherent and manageable soil
properties within soil natural capital stocks. The ability to track
changes in the inherent properties of soils provides a tool for both
industry and policy to separate the effects of short-term management
practices from the long-term changes in our soil resources.
A distinction also needs to be made between soil natural capital
and added capital, with the latter associated with technologies
employed to lift the productive capacity of soils (e.g. irrigation to
overcome limited water holding capacity). For this reason, variations
in the soil natural capital can lead to very marked differences in land
use and farming systems and associated environmental footprint
(Mackay, 2008).
3.2. Soil Natural Capital Formation, Maintenance and Degradation
Soil natural capital, like any type of capital (manufactured, social,
human), is formed, maintained and degraded over time. The following
section details the processes involved in these phenomena.
3.2.1. Soil Natural Capital Formation and Maintenance:
Supporting Processes
Soils are complex dynamic systems consisting of soil components
(abiotic and biotic) interconnected by biological, physical and
chemical processes. Soil processes support soil formation, which is
the development of soil properties and soil natural capital stocks. Soil
processes also form the core of soil functioning and allow the
establishment of equilibria and the maintenance of natural capital
stocks (Fig. 2). What we call here “supporting processes”(Fig. 2) are,
strictly speaking, categories of processes driving soil natural capital
formation and soil functioning. We chose this denomination to relate
to the Millennium Ecosystem Assessment framework (MEA, 2005)
but we depart from the MEA by talking about supporting processes
rather than services. The definitions of the terms given in this paper
allow us to make that distinction since these processes do not directly
affect human well-being.
The following supporting processes are included in the conceptual
framework (Fig. 2):
•Nutrient cycling, which refers to the processes by which a chemical
element moves through both the biotic and abiotic compartments of
soils. Nutrient cycles are a way to conceptualise the transformations
of elements in a soil. The transformation, or cycling, of nutrients into
different forms in soils is what maintain equilibria between forms,
e.g. soil solution concentrations of nitrate drive many processes
such as plant uptake, exchange reactions with clay surfaces or
microbial immobilisation.
•Water cycling, which refers to the physical processes enabling water
to enter soils, be stored and released. Soil moisture is the driver of
many chemical and biological processes and is therefore essential in
soil development and functioning. The continuous movements of
water through soils carrying nutrients disturb chemical equilibria,
and thereby drive transformations.
•Soil biological activity: soils provide habitat to a great diversity of
species, enabling them to function and develop. In return, the
activity and diversity of soil biota are essential to soil structure,
nutrient cycling, and detoxification. Biological processes include
predation, excretion and primary production among others.
These processes are at the core of soil formation (pedogenesis),
building up the physical, biological and chemical stocks of soils.
Pedogenesis is the combined effect of physical, chemical, biological,
and anthropogenic processes on soil parent material. Soils are formed
from the rock materials that make up the earth's crust. Soils can be
formed from the underlying bedrock, from material moved relatively
small distances (e.g. down slope) or even considerable distances from
where the bedrock was originally exposed to the environment. The
formation of a soil in these mineral deposits is a complex process. It
may take centuries for a developing soil to acquire distinct profile
characteristics. Minerals derived from weathered rocks undergo
chemical weathering creating secondary minerals and other com-
pounds that vary in water solubility. These constituents are
translocated through the soil profile by water and biota. In addition
to chemical weathering, physical weathering also takes place. It refers
to the disintegration of mineral matter into increasingly smaller
fragments or particles. Pedogenic processes, driven by nutrients and
water cycles and biological activity, include the accumulation of
organic matter, leaching, the accumulation of soluble salts, calcium
carbonate and colloids, nutrient redistribution, gleying and the
deposition and loss of materials by erosion, and are very important
in soil development and defining soil properties.
Five factors control soil development and natural capital forma-
tion: parent material, climate, vegetation, topography, and time
(Jenny, 1941). The mineralogy of the parent material influences
weathering products and the mineral composition of the soil. Rainfall
influences the intensity of weathering and the leaching of weathering
products, while temperature will change the speed of chemical and
biological reactions. Some indirect climatic effects are through
biomass production and rates of organic material decomposition.
Species of flora and fauna have a significant effect on the type of soil
formed but in time the distribution of flora and fauna depends on
climate, topography, and parent material. Landscape relief affects soil
formation in different ways, including soil depth, modification of local
climate, and available water.
Thus, we saw how, with time, supporting processes gradually
build up and create soil properties and ensure the maintenance of the
dynamic equilibria underpinning soil natural capital. However, soil
natural capital is also degraded over time.
1862 E. Dominati et al. / Ecological Economics 69 (2010) 1858–1868
Fig. 2. Framework for the provision of ecosystem services from soil natural capital.
1863E. Dominati et al. / Ecological Economics 69 (2010) 1858–1868
3.2.2. Soil Natural Capital Degradation: Degradation Processes
The MEA (2005) brought to attention the degradation and loss of
ecosystems, but there has been very little recognition of degradation
processes in the soil ecosystem services literature (Palm et al., 2007).
However, the idea of ecosystem “dis-services”has begun to emerge
(Swinton et al., 2007). The notion of dis-service refers to an adverse
change in a stock or in a process leading to a loss of ecosystem services.
There is a real need to consider the degradation of soil natural capital,
and the degradation of natural capital stocks in general, and to identify
and quantify the processes behind this degradation because losing
natural capital stocks means losing ecosystem services. By limiting soil
natural capital degradation, we can act on ecosystem services provision.
Soils can be qualitatively (e.g. salinisation) and quantitatively (e.g.
erosion) degraded over time. Again, this is analogous and conceptu-
ally the same as the degradation (or depreciation) of manufactured
capital used in national economic accounts and macro-economics.
There are a number of types of soil degradation processes: physical,
chemical and biological. Physical degradation processes refer to the
structural breakdown of the soil through aggregates disruption. This
results in the loss of pore function, which leads to a reduction in
surface infiltration, increased water run-off and decreased drainage,
in time leading to a decrease in gases availability to plants and biota.
Physical degradation processes include (Fig. 2):
•Erosion: the loss of soil material. Soil particles from disrupted soil
aggregates or even soil horizons are removed from site by gravity,
water, ice or wind. Erosion causes the loss of soil profile, which
impacts on soil depth and therefore on the levels of stocks of
nutrients and organic matter, for example.
•Sealing and crusting: the formation of a structural seal at the soil
surface that crusts once dry. The impact of raindrops causes physical
disintegration of surface aggregates. The physico-chemical disper-
sion of clay particles into pores results in decreased porosity and
infiltration. Surface sealing and crusting also prevent seedling
emergence.
•Compaction: loss of soil structure leading to lower infiltration
decreased drainage and increased surface run-off. It also reduces the
movements of soil gases (O
2
,CO
2
). Farming practices including high
cattle stocking rates or tillage destroy soil aggregates and can lead to
the formation of a compacted layer at depth.
Chemicaldegradation refers to the processes leading to soil chemical
imbalances. Main chemical degradation processes include (Fig. 2):
•Salinisation: the accumulation of salts like sodium or magnesium
chloride. It lowers the water potential, making water harder to take
up by plants. Salt crystals can also destroy roots and breakdown soil
aggregates.
•Loss of nutrients by leaching and run-off. It decreases the levels of
macronutrients on exchange sites (clays, OM) and in soil solution.
•Acidification: it occurs when cations are excessively leached from
soils, when the application of fertilisers is not balanced or when
mineralisation is too intense because of soil structure perturbation.
•Toxification: the excessive build-up of some elements (e.g. alumin-
ium, iron) and heavy metals (e.g. mercury, chromium, lead). It can
be caused by excessive weathering or industrial activities.
Biological degradation processes can also degrade the natural
capital of soils. The artificial disruption of soil structure (tillage, cattle
Fig. 3. Simplified relationships between some soil components (hexagons) and properties (rectangles).
1864 E. Dominati et al. / Ecological Economics 69 (2010) 1858–1868
Table 2
Soil ecosystem services and agro-ecosystem services classifications and the concordances between them.
Reference Type of
framework
Services attributable to soils
Nutrients Water Structure
Provision to plants Contribution to
plant production
Renewal through
soil formation
Cycles regulation Movements Provision
to plants
Filtering Flood control Support
provision
Erosion
control
Daily (1997) Soil specific Retention and
delivery of nutrients
to plants
NC Renewal of
soil fertility
Regulation of
major element
cycles
NC NC NC Buffering and
moderation of
the hydrological cycle
Physical support
of plants
NC
Wall et al. (2004) Soil specific Retention and
delivery of
nutrients
to plants
Contribution to
plant production
for food, fuel
and fibber
Generation and
renewal of soil
and sediment
structure and
soil fertility
Regulation of
major
biogeochemical
cycles
Translocation of
nutrients, particles
and gases
NC Provision of clean
drinking water
Mitigation of floods
and droughts
Contribution
to landscape
heterogeneity
and stability
Erosion
control
Lavelle et al. (2006) Soil specific NC Enhancement
of primary
production
Soil formation Nutrient cycling NC Water supply NC Flood control NC Erosion
control
Barrios (2007) Soil specific Nutrient uptake NC NC Nutrient cycling NC Water flow NC Storage of water NC Regulation of
soil erosion
Weber (2007) Soil specific NC Production
function
NC Reactor function NC NC Filter function Buffer function Carrier function NC
Swinton et al. (2007) Agro-
ecosystems
NC Food, fibre NC NC NC NC Water pollution NC NC NC
Zhang et al. (2007) Agro-
ecosystems
NC Food, fibre
production
Soil formation Nutrient cycling NC Water
provision
Water
purification
NC NC Soil
retention
Sandhu et al. (2008) Agro-
ecosystems
Soil fertility Food Soil formation Mineralisation of
plants nutrients
NC Hydrological
flows
NC NC NC NC
Porter et al. (2009) Agro-
ecosystems
NC Food
production
Soil formation N regulation NC Hydrological
flow
NC NC NC NC
Reference Services attributable to soils General agro-ecosystems' services
Climate regulation Biodiversity Resources Pollination Culture
General Carbon
sequestration
GHGs
production
General habitat Populations
regulation
Recycling actions General Recreation Aesthetics
Daily (1997) NC NC NC NC NC Disposal of wastes
and dead OM
NC NC NC NC NC
Wall et al. (2004) Modification of
anthropogenically
driven global
change
NC Regulation of
atmospheric
trace gases
Vital component of
habitats important
for recreation and
natural history
Control of potential
pests and pathogens
Bioremediation
of wastes and
pollutants
NC NC NC NC NC
Lavelle et al. (2006) Climate regulation NC NC NC Regulation of animal
and plant populations
NC NC NC NC NC NC
Barrios (2007) NC Carbon
sequestration
NC NC Biological control of
pests and diseases
NC NC NC NC NC NC
Weber (2007) Climate regulating
function
NC Habitat function NC NC Resource
function
NC Cultural and
historical function
NC NC
Swinton et al. (2007) NC Carbon
sequestration
NC Biodiversity
conservation
NC Odours Health
risks
NC NC NC Recreation Aesthetics
Zhang et al. (2007) Climate regulation NC NC Genetic diversity Pest control NC NC Pollination NC NC Aesthetic
landscapes
Sandhu et al. (2008) NC Carbon
accumulation
NC NC Biological control
of pests
NC Raw
materials
Pollination NC NC Aesthetics
Porter et al. (2009) NC Carbon
accumulation
NC NC Biological control
of pests
NC Raw material
production
Pollination NC NC Aesthetics
NC: not considered.
1865E. Dominati et al. / Ecological Economics 69 (2010) 1858–1868
treading) can lead to excessive activity of the soil biota due to
oxygenation and therefore excessive mineralisation of organic matter
leading to the loss of structure and nutrients.
All the processes mentioned above add to, maintain or degrade soil
natural capital. One needs to acknowledge that they can be influenced
by a number of drivers, natural and anthropogenic.
3.3. External Drivers
Soil processes are influenced by many drivers more or less external
to the system where the processes take place. These drivers can come
from natural origins or be anthropogenic, influencing soil processes in
different ways, including the nature and speed of the processes. The
drivers impacting on the inputs to, or outputs of, a system will influence
the type of reactions taking place. By influencing soil processes, external
drivers willtherefore also impact on the levels and nature of soil natural
capital stocks (Fig. 2). Natural drivers influencing soil processes and
natural capital stocks include climate, natural hazards, geology and
geomorphology and biodiversity (Fig. 2). Climate has a very significant
impact on soil processes and therefore on the provision of ecosystem
services from soils. The characteristics of local climate (rainfall intensity,
temperature, sunshine) influence supporting processes, degradation
processes and biodiversity by driving soil moisture and temperature.
Anthropogenically driven climate change therefore impacts on both soil
natural capital stocks and ecosystem services. Natural hazards, like
earthquakes or volcanic eruptions for example, can change a soil's
environment (e.g. bury it or compromise the integrity of soil structure at
different scales), thereby modifying supporting and degradation
processes like water cycling or erosion. The geological origin of the
parent material determines the initial minerals in soils that will drive
soil development and properties. Geological history, as well as the
climate of the area, determines the morphology of landscapes, therefore
the undergoing intensity of degradation and supporting processes.
Biodiversity is the agent of biological reactions; therefore the type and
variety of species present in an area will influence the type and intensity
of the biological processes.
Anthropogenic drivers, such as land use, farming practices and
technologies, also influence soil processes (Fig. 2). The type of land use
(e.g. cropping, livestock) determines the type of disturbance (e.g.
tillage, treading, use of agrochemicals) as well as inputs (e.g.
excrements, synthetic fertilisers) applied to the soil. Farming practices
determine the level of intensity of the disturbances (e.g. organic
versus conventional cropping) and the amount of inputs to the soil
(e.g. quantity and timing of fertilisation). The evolution of technology
provides humans with more tools to manage soil processes and the
impacts of the pressures applied to the environment, for example, the
use of nitrification inhibitors can reduce nitrate leaching losses and
nitrous oxide emissions from soils. Soil scientists have been studying
the impacts of many of these drivers on soil processes and properties
for many years and some areas like the impacts of farming practices
and climate on soil properties, are therefore well understood and
documented.
We saw that soil natural capital stocks can be characterised by soil
properties, that the formation, maintenance and degradation of these
stocks are determined by soil processes and that soil processes can be
influenced by external drivers. By showing how soil properties and
processes link to soil natural capital, the large body of knowledge on
soil processes from the soil science literature can be included into the
framework for the provision of ecosystem services from soils. In the
following section, we detail soil ecosystem services.
3.4. Provisioning, Regulating and Cultural Ecosystem Services from Soils
Ecosystem services are defined here as the beneficial flows arising
from natural capital stocks and fulfilling human needs. Soils take part
in the provision of a number of ecosystem services that we identified
by talking with soil scientists and compiling the literature (Table 2).
We chose to classify these soil services according to the MEA (2005)
model, so the reader can relate to more general ecosystem service
frameworks. Soils provide three types of services: provisioning,
regulating and cultural services. Provisioning services are defined as
“the products obtained from ecosystems”(MEA, 2005, p. 40). Soils
specifically provide a number of products useful for humans:
•The provision of food, wood and fibre: Humans use a great variety of
plants for a diversity of purposes (food, building, energy, fibre,
medicines). By enabling plants to grow, soils provide a service to
humans. Soils physically support plants and also supply them with
nutrients and water. The natural capital stocks insuring the
provision of the service are embodied by soil structure, water
holding capacity and nutrients fertility.
•The provision of physical support: soils form the surface of the earth
and represent the physical base on which animals, humans and
infrastructures stand. Even an otherwise unproductive soil may
provide physical support to human infrastructures (e.g. stretches of
the Trans-Australia Railway across the Nullarbor Desert). Soils also
provide support to animal species that benefithumans(e.g.
livestock). The strength, intactness and resilience of soil structure
represent the natural capital stocks behind this service.
•The provision of raw materials: soils can be source of raw materials
like, for example, peat for fuel and clay for potting. These materials
stocks are the source of the service. However, renewability of these
stocks is questionable (de Groot et al., 2002).
Soils also provide regulating services which enable humans to live
in a stable, healthy and resilient environment. The regulation that
these services provide come from soil processes and their effect on the
establishment of equilibria between natural capital stocks. Soil
regulating services included in our framework are (Fig. 2):
•Flood mitigation: soils have the capacity to store and retain
quantities of water and therefore can mitigate and lessen the
impacts of extreme climatic events and limit flooding. Soil structure
and more precisely macroporosity, as well as processes like
infiltration and drainage will impact on this service.
•Filtering of nutrients: if the solutes present in soil (e.g. nitrates,
phosphates) are leached, they can become a contaminant in aquatic
ecosystems (e.g. eutrophication) and a threat to human health (e.g.
nitrate in drinking water). Soils have the ability to absorb and retain
solutes, therefore avoiding their release into water. Natural capital
stocks of clays and OM, as well as processes like adsorption and
precipitation regulate this service and therefore drive the quality of
run-off and drainage waters and wider water bodies such as ground
water, lakes and rivers.
•Biological control of pests and diseases: by providing habitat to
beneficial species, soils can support plant growth (rhizobium,
mycorrhizae) and control the proliferation of pests (crops, animals
or humans pests) and harmful disease vectors (e.g. viruses,
bacteria). Soil conditions (e.g. moisture, temperature) determine
the quality of the soil habitat and thereby select the type of
organisms present. This service depends on soil properties and the
biological processes driving inter- and intra-specific interactions
(symbiosis, competition).
•Recycling of wastes and detoxification: soils can self-detoxify and
recycle wastes. Soil biota degrades and decomposes dead organic
matter into more simple forms that organisms can reuse. Soils can
also absorb (physically) or destroy chemical compounds that can be
harmful to humans, or organisms useful to humans. This service
depends on biological processes like mineralisation and immobili-
sation and therefore is also related to the natural capital stocks of
nutrients available for soil biota or for chemical reactions.
•Carbon storage and regulation of N
2
O and CH
4
emissions: soils play an
important role in regulating many atmospheric constituents,
1866 E. Dominati et al. / Ecological Economics 69 (2010) 1858–1868
therefore impacting on air quality. Perhaps most important is the
ability of soils to store carbon as stable organic matter which is a
non-negligible benefit when talking about off-setting greenhouse
gases emissions. This service is mainly based on OM stocks and the
processes driving them but also on soils conditions (e.g. moisture
and temperature) which regulate soil biota activity and thereby the
production of greenhouse gases like nitrous oxide (N
2
O) and
methane (CH
4
).
Soil provisioning and regulating services arise at very different
scales ranging from microns (habit for micro-organisms) to landscape
(flood mitigation) to the globe (air quality).
Notably, none of the previous studies (Barrios, 2007; Daily et al.,
1997; Lavelle et al., 2006; Wall et al., 2004; Weber, 2007) on soil
ecosystem services cover or identify “cultural services”(Table 2). This
is a curious omission as soils alone, as part of landscapes that support
vegetation, have across many cultures been a source of aesthetic
experiences, spiritual enrichment, and recreation. Many deities and
religious beliefs refer specifically to the earth and its sacredness and
soils also have various cultural uses across the globe from being a
place to bury the dead, a material to build houses or a place to store
and cook food (Māori hāngi). The point here is not to detail all the
cultural services provided by soils but to acknowledge that these
services, even if almost always forgotten, are of tremendous
consequence.
We have examined services provided by soils and acknowledge
that they can be of a different nature, but to complete our framework,
in the following section we need to look at human needs and how
ecosystem services fulfil them.
3.5. Human Needs Fulfilled by Soil Ecosystem Services
Ecosystem services exist because they meet a human need. This is
the very essence of the anthropocentric concept of ecosystem
services. However, few studies in the ecosystem services literature
go as far as specifying how and what human needs are potentially or
actually fulfilled by ecosystem services. One very notable exception is
the Millennium Ecosystem Assessment (2005), which, although not
explicitly acknowledging it, shows how ecosystem services contribute
to human well-being by using a framework that resembles Maslow's
“Hierarchy of needs”(1943).Maslow's (1943) classic study of the so-
called “Hierarchy of needs”is the foundation study in this domain.
This hierarchy has five levels: the first four levels are deficiency needs:
physiological needs, safety and security needs, social (love and
belonging) needs, and esteem (psychological) needs; the last level
is self-actualisation needs. Deficiency needs must be met first, the
individual prioritises them; the higher needs can be considered only
when the lower needs are met. Maslow's framework has been widely
criticised (Wahba and Bridwell, 1976) on a number of grounds.
Probably the most persistent critique is that Maslow's framework is
based on a hierarchal structure for which there is a lack of strong
evidence. For example, a starving artist may be self-actualised while
his/her physiological needs (e.g. food) may be inadequately fulfilled.
In this context, Chilean economist Manfred Max-Neef's “matrix of
needs”(1992) is perhaps a better reflection of reality. In this
framework many needs are complementary and different needs can
be fulfilled simultaneously. Max-Neef classifies fundamental “axio-
logical categories”–subsistence, protection, affection, understanding,
participation, idleness, creation, identity, and freedom –that are split
into four “existential categories”(being, having, doing and interact-
ing), thereby forming a matrix of needs. Ecological economist Herman
Daly somewhat bravely presents an even broader contextualisation of
human needs, in terms of his “end-means”spectrum (Daly and Farley,
2003). This spectrum links ultimate ends (final cause and “God”)to
intermediate ends (health, safety, comfort) to ultimate means
(material cause, low entropy matter energy). However, whatever
philosophical construct of human needs is selected, it is inevitably a
poor representation of the complexity, subtlety or ever-changing
nature of human needs.
Even though Maslow's hierarchy of needs (1943) is an overly
simplistic picture, it's easy to comprehend and thereby enables us to
point out that ecosystem services relate to human needs on two
different levels. First, at the physical level, provisioning services
provide goods useful for the fulfilment of some physiological needs:
food, fibre for clothing, sources of energy, and support for infra-
structures (Fig. 2). Regulating services also fulfil some physiological
needs like clean air and clean water by regulating greenhouse gases
emissions and filtering water. Moreover, provisioning and regulating
services also fulfil safety and security needs by ensuring the stability
of human habitat through soil structure stability, flood mitigation, the
control of pests and the recycling of wastes (Fig. 2). Second, at the
non-physical level, ecosystems provide aesthetics, spiritual and
cultural benefits through cultural services, thereby fulfilling self-
actualisation needs. Again, the fulfilment relationships between
services and human needs are not a one-to-one correspondence.
As shown in Fig. 2, it should also be noted that some needs in
Maslow's hierarchy (1943) (social and esteem needs) cannot be
fulfilled by ecosystem services. This is because these needs are only
based on our own self-perception of emotionally-based relationships
with other human beings (or even animals).
4. Conclusion
This paper draws on soil science and builds on the current thinking
on ecosystem services to develop a framework for classifying and
quantifying the natural capital and ecosystem services of soils. The
framework shows how soil natural capital stocks can be characterised
by soil properties and how the provision of ecosystem services from
soils is linked to both manageable and inherent soil properties. We
argue supporting processes ensure the formation and maintenance of
soil natural capital and that degradation processes drive natural
capital depletion. These processes are influenced by both natural and
anthropogenic drivers. Including this scientific knowledge in the
framework opens the soil black-box and creates the opportunity to
value the natural capital of soils and also to track the changes in these
values for a given human use. It also allows, for the first time, the
inclusion of differences between soils into broader ecosystem service
frameworks.
The framework presented here is implemented in an on-going
study to quantify and value ecosystem services from soils at the farm
level. The framework concepts are used to incorporate the vast
scientific modern-day understanding of soil processes and taxonomy
into a model using pedotransfer functions to link the soil biophysical
processes and properties at the origin of the provision of each soil
ecosystem service to a biophysical measure of each service. The model
is then able to show how soil natural capital, farming practices and
soil management impact on the provision of ecosystem services.
Such a model paired with an economic valuation of soil services
provides a very powerful management tool for economists and policy
makers to better understand the provision of ecosystem services from
soils and weigh more carefully soil natural capital and soil services
values in rural development processes.
Acknowledgement
The research presented in this paper was funded by the
Foundation of Research Science and Technology's programme
“Sustainable Land Use Research Initiative”(Contract C02X0405). The
authors would like to thank anonymous reviewers for their useful
comments and suggestions.
1867E. Dominati et al. / Ecological Economics 69 (2010) 1858–1868
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