Modelling Soil Organic Matter Dynamics – Global Challenges - Sustainable Management of Soil Organic Matter - page 41

Fig. 2.1. Structure for regional modelling and integrated assessment of SOM dynamics.
Ecosystem/SOM models, based on fundamental process studies, are driven by spatially distributed
databases of driving variables and validated by regional networks of long-term experimental sites.
For climate change impact assessment, climate models provide projected climatic driving variables
for the region. Economic decisions influence the type and distribution of management systems, and
the ecosystem responses to changes in management and climate provide a feedback to economic
and management decision models.
to encompass geographic and political units which are relevant to decision
and policy makers.
However, significant challenges remain, particularly considering the
potential impact of decisions based on these types of applications. A num-
ber of authors (e.g. Elliott and Cole, 1989; Paustian et al ., 1995; Powlson,
1996) have emphasized the importance of linking such applications to
regionally distributed experimental databases for model validation
purposes, as described earlier in this chapter. As of yet, there are few studies
that have examined the influence of spatial and temporal scale on model
predictions at the regional scale. Depending on the properties of the driving
variables and the model functions that utilize them, aggregation errors may
be more or less severe, depending on the linearity of their scaling properties
(Paustian et al ., 1997). Similarly, there is a need to develop and apply
formalized methods for uncertainty analysis of regionalized SOM models,
including differentiating between uncertainty associated with input data
and uncertainty in model predictions. Decision-makers utilizing the infor-
mation generated by regional modelling systems will accept uncertainty
as long as they have an idea as to the degree of uncertainty and that the
estimates are unbiased.
In intensively managed ecosystems, such as agriculture, management
decisions by farmers have a profound influence on the structure and
functioning of the ecosystem, including the amount and dynamics of soil