The Dangers of Indicators and the need Models
in the Assessment of Forest Sustainability
Keith Rennolls
School of Computing and Mathematical Sciences, University of Greenwich,
Park Way, London SE10 9LS, UK.
Email: k.rennolls@gre.ac.uk
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Abstract
It is argued that biodiversity and nutrient status are essential factors in any
meaningful assessment of sustainability. Criteria and indicators are the
dominant current methodology for the assessment of forest sustainability. Some
dangers involved in complete reliance on indicators are discussed. It is
suggested that model-based sustainability assessment is often more
appropriate for changing environments. However, there are also dangers in the
use of models for sustainability assessment. Criteria on the suitability of models
for this task are needed. The various meanings of “sustainability” are
considered. Finally it is suggested that a repository of definitions and and criteria
for model-based sustainability assessment is needed, and that the Forest
Model Archive1 might be a suitable repository.
Keywords: Sustainability, C & I, stability, monitoring, biodiversity, models, FMA.
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Introduction: ‘Change & Evolution’ versus ‘Sustainability & Conservation’
Global climate change has a number of causes. A primary cause is the excessive use of
fossil fuels, leading to a build up of CO2 in the atmosphere. The progressive clearance of
tropical forests is another major contributory factor in this process. Hence global
temperatures are rising due to the greenhouse effect. Existing ecosystems will change,
move locations and even disappear. As a result the biodiversity structure of the planet will
change, with some biodiversity resources being lost. The globe is not in a steady state.
There has long been concern over these processes, since it seems a natural that we should
aim to conserve such biodiversity resources that exist.
“The current worldwide climatic deterioration may provide the tests (of a
possible general theory of biodiversity that) we need; it may plunge us all into a
vast, though undesired, ecological field experiment. If we observe the
concomitant changes in the biosphere we may end up sadder and wiser in a
very literal sense.”
Pielou, Ecological Diversity, 1975.
Mankind’s current activities are clearly not sustainable, in the sense that the current state is
not maintainable under current practices. Within the above evolutionary view of global
change it is seen that while such changes proceed on global spatial scales, the concept of
“sustainability” has no meaning. The issues of sustainable forestry and biodiversity
conservation hinge on aspects of scale, both spatially and temporally. Attempts to “conserve
forest biodiversity” in the short to medium term, and locally, are important in order to mitigate
1
www.forestmodelarchive.info
the effects of rapid climate change. Forest management programmes which aim to be
“locally sustainable” do not necessarily have any impact in conserving biodiversity resources,
and even if they attain local sustainability in the short term, they cannot negate the long term
effects of climate change either locally or globally.
The Importance of Monitoring Biodiversity Sustainability
Biodiversity is an important aspect of the global environment in which we live.
However, biodiversity has a wide range of definitions, through a range of scales and
levels of detail, and there is no consensus. Even the simpler concept of species
diversity at one tropic level has many definitions, the simplest of which is species
abundance (Peliou, 1975, Margurran, 1988).
Sustainability of a forest management process is even more variously defined than
biodiversity, and most definitions include the conservation of biodiversity in some
form. The definition and usage depends on aims and context, and hence
inconsistency is inevitable and conflicting aims likely.
The Indian Institute of Forest Management (2005) in their “Criterion 2: Maintenance,
Conservation and Enhancement of Bio- Diversity” state the following:
“Only 20% of Indian biodiversity has been documented. More than 5150 species
of plants, 16214 species of insects. 44 mammals, 42 birds, 164 reptiles, 121
amphibians and 435 fish species are endemic to the ecosystem of the country:
However, in recent times, heavy biotic pressure has started exerting tremendous
stress on natural resources and hence, many of the plant and animal species are
under various degrees of threat. According to the Botanical Survey of India, there
are about 45 000 species of plants in the country: The vascular flora, that forms
the conspicuous vegetation cover, comprises of 15000 flowering plant species, of
which more than 33% (or 5150 species) are endemic. About 15000 endemic plant
species and an unknown number of endemic fauna species are facing varying
degrees of threat. Biodiversity conservation is important to ensure that the
underlying components of living resources, i.e., habitat, species and genetic
diversity are maintained. Loss of genetic resources accentuated by forest
degradation not only poses a grave threat to food security in the region, but also
close off various little understood options for the future generations. Destroying a"
keystone species" triggers off the deadly "domino effect" whereby other species
and genes along with the entire ecosystem crumble to extinction. Also, once
genetic resources and their variability are lost, the promises of biotechnology will
be aborted.”
Hence, it is important in considerations of biodiversity conservation, to take into
account those very rare species (of which there are a large number) which may be
only rarely observed.
Diversity has wider connotations when considered in the context of sustainability at
the regional, national or global levels, and when it involves social and economic as
well as biological dimensions. In such multi-dimensional situations, in which there
exist multiple inter-related sustainability criteria, Multiple Criteria Analysis (MCA) and
Cognitive Mapping for structuring the participatory process of conflict resolution have
been used by Mendoza & Prabhu (2003) and Mendoza et al. (2004). In this paper
no attempt is made to address the sustainability issue at this level. Rather, we
restrict consideration to the level of the sustainability of management of forest stand.
The Various Meanings of Sustainability (at Stand Level)
Sustainability criteria at the level of stand management should include aspects of biodiversity
conservation or maintenance. Often the measurement of a biodiversity is a non-trivial task,
and measures are sought which are thought to be causally related to the biodiversity and
sustainability. There is currently much policy-driven measurement of the status of the
managed forest systems, and the resultant collation of databases of sustainability data by
supra-national bodies, such as the MCPFE, for the purpose of central evaluation and
comparison of national and regional performances, possibly as part of a carbon account.
What is meant by sustainable forest management? The policy MCPFE definition is:
"The stewardship and use of forests and forest lands in a way, and at a rate,
that maintains their biodiversity, productivity, regeneration capacity, vitality and
their potential to fulfil, now and in the future, relevant ecological, economical
and social functions, at local, national and global levels and that does not
cause damage to other ecosystems."
Third Ministerial Conference on the Protection of Forests in Europe,
Helsinki, 1993.
We might ask the following questions…
•
•
•
Maintain biodiversity?… 100%, at all locations?
Is new speciation envisaged?
Future ecological functions?…What are they?.
We consider a sequence of rather more restricted definitions than that of the MCPFE, and
consider how they maybe assessed.
Forest Stand Steady-State Sustainability, and the “Normal Forest”
Sustainability could be taken to mean that there should be a steady-state for all
measurable (and immeasurable) variables. State variables would have to include all
biodiversity measures. Of course no forest can be steady-state in the strict sense, since
trees grow and die. Hence the steady state has to be an average steady state, where
variation is present, but the variation is essentially unchanging. The only ways that such
an average steady-state is achievable is if:
(i) the forest is in a naturally evolved state, or
(ii) the forest is a managed “normal” forest, in the sense of Susuki (2005) and Von Gadow
(2002).
We term such a concept of sustainability as “steady state”; Susuki says “that the normal
wood in the wide sense’ is indispensable to the future of sustainable forest management”.
A “broad-band” forest steady state forest sustainability definition would include the
conservation of heritage, the continued access to traditional landscapes, the survival and
maintenance of the species-mix and biodiversity measures in the ecosystem, and the
potential use of uniquely evolved bio-genetic resources for a range of scientific and
medical purposes.
Rotational (Stand) Sustainability.
The unchanged status in all state-variables is a stringent a condition for forest managers,
who will often aim to manage previously unmanaged forest resources for quantifiable
financial outputs. Most managed forest stands are managed on a rotation basis, and hence
the minimal requirement for sustainability would be a definition in terms of one time-point
within each rotation cycle at which to define the unchanged status of the forest. This would
normally be the status immediately prior clear-cut, and/or just after re-planting/
regeneration.
Strong Rotational (Stand) Sustainability
This is meant to include sustainability of the forest biomass production, but also the
sustainability of the soil minerals which will allow such long term biomass production, as
well as the maintenance of biodiversity. It includes the “steady state” sustainability. This is
an ideal sustainability target, but one which is very difficult, and proably impossible to
attain, and certainly very expense to monitor.
Weak Rotational (Stand) Sustainability
This expression is used to characterise systems of forest management which can
demonstrate of forest biomass production, but assume that the various other soil and
biodiversity features are sustained, without explicit verification. Many schemes to monitor
sustainability, and in particular many forest-production model-based methods only attempt
to demonstrate weak rotational sustainability.
Use of Conservation and Sustainability Measures, Indices and Indicators
Forest Status Measures
Science and technology is based on measurement. Simplistically, it might be thought that to
characterize a system it is merely necessary to define or develop suitable measures of the
state variables of the system, and then to measure them. Similarly, it might be thought that
the stability, conservatism, and sustainability of the system may then be monitored by
repeated measurement of the system. The problem with such a simplistic view arises for
dynamically varying forest ecosystems; for such systems a full characterization of the system
requires knowledge of the ‘equations of motion’ (i.e. a model) of the system, as well as a
measurement of state. It is then possible to investigate if the system is dynamically stable,
either steady-state, or rotational, and possibly to predict the potential system collapse.
Forest Status Indices
The forest state, including forest biodiversity and forest species diversity are multi-factorial
constructs which can only be completely characterized by multiple measurements. Indices
are weighted combinations of measures, with the weights chosen so that the index reflects
some important feature of the overall forest ecosystem. Determination of a suitable index
involves an analysis of the correlational structure of multivariate measures of the system.
The validity of their use as monitoring tools depends on the system not undergoing structural
changes.
Criteria & Indicators of Sustainability
The common approach to sustainability monitoring has been a number of key criteria, with
associated indicators, and are generally concerned with the weak (rotational) sustainability
which maintains these indicators over the long term. This C & I approach of using
“indicators”, instead of a broad spectrum measurements, arose originally from the “Rapid
Appraisal” approach to environmental assessment, based on the principle: “measure what
you can, cheaply and quickly, as long as it is correlated with what you are interested in”.
However, there is some risk of not really seeing what is going on by using indicators as
biodiversity measures. Within the “indicator paradigm” it might be argued that any changes
that might occur to other variables of the system would not be of importance, since they are
not amongst the listed indicators of importance.
An assumption of the C & I approach is that current satisfaction of a sustainability criterion,
through a monitored indicator, will ensure the future sustainability of the natural resource
management system. But even full mensurational cross-sectional approach does not
provide the same information as longitudinal (dynamic) data. It is not possible directly to
infer future dynamic stability (and sustainability) from current static measurements and datacollection activities.
For example, the MCPFE strategic statement given above has resulted in C & I guidelines
which require that the “number percentage of threatened species” be noted. However, the
guidelines do not require the statement of the species concerned, and hence there is no
way that any possible loss of species can be monitored. Similarly, the ITTO monitoring table
of indicators for biodiversity sustainability require the statement of “the number of
endangered, rare and threatened forest dependent species”, without the requirement to
state the species concerned.
In tropical forests there are many very rare and possibly threatened species that are not
routinely observed in inventory and monitoring studies. Estimates of unseen species
proportions needs the use of various statistical estimation methods. See the vast species
abundance estimation literature!
In a world of limited resources, monitoring resources are limited. Hence, the use of
Sustainability C & I. However, to avoid clear dangers of missing dangerous trends it is
important that such an indicator based monitoring should have embedded within it a
continual monitoring of the indicator validity through a properly designed statistical validation
scheme.
When the context of sustainability is regional, national or global, and involves social and
economic as well as biological dimensions, Multiple Criteria Analysis (MCA) and Cognitive
Mapping for structuring the participatory process of conflict resolution have been used by
Mendoza & Prabhu (2003). In this paper no attempt is made to address the sustainability
issue at this level. Rather, we restrict consideration to the level of the sustainability of
management of forest stand.
The only way to move from data collected atone time to statements about what will happen
in the future is by a forecasting system. Hence, systems process models applied to natural
resource management processes are an essential part of a proper sustainability evaluation.
Monitoring Sustainability (of Biodiversity) using Models
It has stated above that longitudinal measurements (including rare species identification and
unobserved species number estimation) are needed to obtain an insightful evaluation of
sustainability prospects. Also, since sustainability is by its very nature a statement about the
long term future, predictive models are necessary in order to be able to make meaningful
statements about sustainability. No sustainability monitoring system can be truly effective
unless it monitors in detail the complexity of biodiversity and has available a soil-model with
associated data-drivers which monitors potential nutrient depletion resulting from any
particular forest management regime. However, a model-based system of forest
sustainability can also give misleading indications.
Monsuerud (2003) considers the suitability of various classes of forest model for their
suitability for use in the assessment of the sustainability of forest management. His
definition of (production) sustainability is concisely stated as:
“Sustainable productivity is therefore the ability of managers to maintain NPP within
the bounds of normal variation, without a permanent decline in the rate… The key is
that a useful metric like NPP must be both directly related to some fundamental
aspect of sustainability, and be at least a function of model outputs.”
The model classes considered by Monserud (2003) were Yield, Gap, Process, and
Vegetation distribution models. He concludes that each performs adequately on the aim for
which they were designed (i.e. yield, succession, scientific understanding, and response to
climate change), but that none performs adequately for all aims. Monserud concludes that
models which combine the best features of yield and process models (i.e. hybrid models) are
needed for the evaluation of forest sustainability. Similar considerations were expressed in
Rennolls & Blackwell (1988). Monserud’s definition of sustainability is in terms of NPP.
Clearly, other definitions and measures of sustainability are needed if biodiversity and
nutrient conservation is to be part of sustainability.
van Gardingen et al. (2003) is another example of a model-based evaluation of sustainability
of forest management practices in tropical forests. Even though their model does not have
state variables relating to (species) biodiversity, or any soil model, the authors say:
“The paper also indicates that the approach could be adapted to consider a wider
range of goods and services provided by forests to extend the analysis into a more
comprehensive economic analysis. A preliminary consideration of these issues
demonstrated that the system of management selected on the basis of timber yield
and financial performance will also provide benefits for the environment and local
communities.”
van Gardingen et al. (2003) have only been looking at weak (rotational) sustainability.
The Monsurud (2003) study considered a wide range of potential models, but only in
the context of the weak sustainability of NPP. The van Gardingen et al. (2003) study is
typical amongst many other similar model-based sustainability studies which focus
their considerations to the analysis of the financial sustainability of forest management
practices, but do not consider the biodiversity or nutrient dimensions of forest sites.
Discussion
It has been argued that there are dangers in an over-reliance on the use of indicators for the
monitoring of the sustainability of forest management practices. It has also been argued that
in changing situation of global climate change the use of model-based sustainability
assessment is the only viable option available. However, the few examples considered of the
state-of-the-art in model-based sustainability assessment indicates that there are also
potential limitations in the use of such model-based approaches.
It is suggested that a sequence/hierarchy of definitions/measures of sustainability in the
context of model-based sustainability assessment be formalized, somewhat on the lines
indicated above. Such a hierarchy would be a validation scale applicable to models that
might be considered for use in the evaluation of the sustainability of forest management. It
would be useful for such a model-based sustainability evaluation suitability scale were
included in a Forest Model Archive, (FMA) (Rennolls et al., 2002), a framework which could
potentially be used to evaluate model-based claims of sustainability.
Thornley (2005) provides an example of a state-of-the art physiological process based model
which includes a soil model component. Such a model can realistically evaluate claims that a
forest management regime is sustainable. Any model-based evaluation of strong (rotational)
sustainability must necessarily have such a soil model component if it is to be taken
seriously.
Biodiversity (and in particular species diversity) are paramount aspects that must be fully
taken into account in any fully satisfactory sustainability assessment. Use of indicator
species for this purpose are subject to the risk of not really noticing major losses in diversity,
especially when the environment is changing. What is really needed is a synthesis of models
of forest growth and productivity with full dynamic models of both soil and species diversity.
Unfortunately, at this point in time there are no fully evolved models of forest species
diversity. First steps have been made in this direction, (Hubble, 1997, 2001), but there is a
need for substantial further integrative model development across the whole spectrum of
forest modelling, to include production, soil, and diversity. There is much to be done, and it
needs to be done urgently!
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