POPULATION-ENVIRONMENT DYNAMICS:  TOWARD BUILDING A THEORY


INTRODUCTION
This volume is a collection of separate but related studies focusing on
the relationship between human populations and the environment. The effort
consists of this introduction, a set of abstracts, a set of thirteen chapters each written
by a seminar participant which investigates a different aspect and
geographic setting of the population-environment dynamic, and a concluding
set of statements, by the seminar participants as a group, examining the relationships among the chapters.
 
In this introduction we present a synopsis of the common framework, which
we call a family of transitions. In addition to the common framework, this
introductory chapter presents the abstracts for each ensuing chapter.  
Readers of the monograph reporting work from prior years should note that
the material in the following section on a family of transitions is
repeated here for background and therefore can be skipped.

1.    A FAMILY OF TRANSITIONS  
One way of viewing the complex dynamic relationships between population
and the environment is to visualize them as a family of transitions. That
is, not only is there a demographic and epidemiologic transition but also
a deforestation, toxicity, agricultural, energy and urbanization
transition as well as many others. In this chapter it is argued that for
each transition there is a critical period when society is especially
vulnerable. During that period, rates of change are high, societal
adaptive capacity is limited, in part, due to this rapid change, and there
is a greater likelihood that key relationships in the dynamic become
severely imbalanced. The trajectory society takes through a transition
varies, depending upon many factors operating at local and national
levels. Transitions not only are occurring in many different sectors but
also at different scales, both temporal and spatial. At times, a society
experiences several transitions simultaneously, which can raise social
vulnerability because of how they amplify each other.


1.1 TYPES OF TRANSITIONS
The Demographic Transition
Let us begin with a review of the ideas behind the widely accepted
demographic transition. At the onset of this transition, births and deaths
are both high and are in relative equilibrium with each other.
Historically, births exceed deaths by small amounts so total population
rises only very gradually. Occasionally, famine or an epidemic causes a
downturn in total population but in general, changes in rates are low.
During the transition, however, death rates drop dramatically, usually due
to a change in the health condition of the population. This change in
health is caused by many, often interrelating factors. After some time
lag, the birth rate begins to drop and generally declines until it is in
approximate balance with the death rate again.

The Epidemiological Transition
The term epidemiologic transition was coined to describe the changing
source of mortality and morbidity from infectious diseases occurring
primarily in the younger age groups to degenerative diseases in older age
groups.  As with the demographic transition, there is considerable
volatility during the transition.  At the onset, infectious diseases begin
their decline usually due to extensions of health care and sanitation by
the national or local government. Single vector programs such as malaria
control and immunization programs are often the first implemented because
they are capable of ready extension and do not require as heavy a
commitment to education and other sustained infrastructure - especially in
rural areas. These single vector programs are then followed by
broader-based health care which demand heavier investment in
infrastructure. But an entirely successful move through this transition
does not always happen. At times, other sectors in transition overpower
the health care delivery system. 

The Agricultural Transition
For several hundred years, worldwide agricultural production has been
rising in relative harmony with population. Overall, increases in
production have kept up with and even outpaced growth in population. The
two factors that have been responsible for these increases are 1)
extensions of land under cultivation and 2) improvements in productivity.
At times changes have been dramatic. Formulating an agricultural
transition reflects the condition that, in general, sources 
of increase in production shift from extending land to intensifying
production on land already under cultivation. 

The Forestry Transition
At the onset of the forestry transition generally a large percentage of a
region is under forest cover. Rapid deforestation occurs during the
transition and finally forest cover stabilizes at a lower level determined
by many factors such as the local region's needs, the state of the local
and national economy, climate and soil characteristics. In most settings
this transition will end in a steady state equilibrium balancing growth
and harvest. Again, how society handles the vulnerable transition period
often determines in a profound way the quality of life for the region.

The Toxicity Transition
The toxicity transition can be considered a composite of many transitions:
global atmospheric, local air pollution, surface water, ground water and
solid waste to name a few. Again, there are at least two sets of factors
operating in tandem. The transition begins with low levels of industrial
or agricultural production and correspondingly low levels of toxins. As
production and population increase, toxic byproducts increase to levels
which eventually become unacceptable to the general public. This in turn,
causes a public demand for pollution abatement. After an environmentally
costly time lag, remediation steps are taken which helps to bring
pollution under control.

The Urbanization Transition
The urbanization transition is driven by the dual forces of rural to urban
migration and central city population growth. The early stages of the
transition are characterized by rapid growth of urban population; however,
in later stages, growth declines and may reverse. Rural to urban migration
is a product of many forces - both  "pull"  and "push". In terms of the
population-environment dynamic, the urbanization transition often acts as
an amplifier as it interacts with other transitions.

The Fossil Fuel Transition
The fossil fuel transition is a special case of the energy transition.
Historically, many energy transitions have already occurred in different
regions and time periods. Significant transformations began in the
sixteenth century brought about by sail and later, by steam power. Today,
we are now in the most universal and perhaps critical energy transition:
fossil fuels. Studying this transition is especially instructive because
the record on different societies' passage through the vulnerable period
is varied and appears to be heavily influenced by public policy. 


1.2  GENERAL CHARACTERISTICS OF TRANSITIONS
Similarity of Trajectory Across Sectors
We have attempted to show in the seven example sectors discussed earlier
that the notion of transitions apply across all sectors of investigation.
Each class of transition, whether it be demographic, toxicity, forestry,
agriculture, urbanization, energy or epidemiological have similar 
patterns. It is this perception that has caused us to posit the existence
of a family of transitions possessing some common attributes useful in
analysis. The first common attribute of all  transitions is their
trajectory. They all begin in reasonable stability, then move to the
volatile transition period where change is rapid, and finally return again
to relative balance. Analytically, these are clearly nonlinear systems but
ones which have properties that lend themselves to well-understood
mathematical functions. 

Applicability of Transitions Across Scales
The second attribute has to do with scale. One of the most interesting and
at the same time vexing aspects of studying population-environment
dynamics is that many phenomena manifest themselves at all levels of
geographic and temporal scale. For example, data depict one  demographic
transition for an entire continent, a different one for a country within
that continent and still other different transitions at the regional
level. Local conditions may delay or advance the onset and or completion
of the transition in relation to the larger body. Thus, moving through the
demographic transition can take more or less time as the scale changes.  
This same variation seems to exist in all other population-environment
transitions that have been investigated. True, national or regional-level
determinants often set the stage for the local dynamic, but in the end it
is these local conditions which determine the timing, magnitude and
specific trajectory of the overall transition. 

One can think of our world, seeming to be chaotic, but instead consisting
of a multitude of well defined transitions in many sectors, each with its
own local characteristic. Different transitions begin at different times
and places, but ebb and flow in an overlapping way, sometimes reinforcing
one another and at other times dampening their dynamic. As adjustment
occurs, occasionally useful niches are created which are then exploited by
stressed elements of the ecosystem. Unfortunately, at other times,
different sectors interact with each other in a harmful way to broaden and
extend the susceptible period.

Societal Vulnerability
During transitions there seems to be a special vulnerability borne by
society. Ample evidence indicates that key relationships are most likely
to become out of balance during the transition. A primary cause of this
vulnerability is the rapidity of change during the high velocity portion
of the transition. Adaptive capacity is impeded because there is little
time for systems to adjust and often there are limited feedback mechanisms
operating which otherwise could help this process. Another contribution to
social vulnerability during a transition is the amplifying effects created
by transitions occurring simultaneously in several sectors.  Rapid rates
of change in several sectors could more easily overpower the available
infrastructure which leads us to the next source of vulnerability during
transitions: capital availability.
 
Capital or investment capacity can either amplify or reduce societal
vulnerability during a transition. If there are financial resources
available to deal with the effects of rapid change, remediation is easier
to implement. Africa which is trying to deal with a difficult demographic
transition has almost no capital available for its use and will therefore
undergo great hardship. The Soviet Union and Eastern Europe are struggling
to find financial resources to deal with their flawed toxicity transition.
Another dimension of transitions which affects societal vulnerability is
the degree of interconnectedness. How closely is the local village
connected to the regional and national economy? How much does what happens
in one location determine what happens in another? There is no question
that interconnectedness is increasing worldwide. We also know that under
some circumstances linkage creates dependencies which in turn, increase
vulnerability. However, it can work in the opposite direction as well.
These very same links to a larger domain can also act as a safety net. If
there are connections, resources can be brought to the stressed area more
easily to mitigate the local adversity. The final and perhaps most
important dimension of transitions affecting vulnerability is feedback.

Analytic Properties of Transitions
We have seen that many characteristics of transitions are common across
all sectors and geographic scales. The question then, is whether there are
analytic techniques which might be useful in describing this family of
transitions. If so, these techniques may be helpful in portraying 
transitions in a way that facilitates comparison and thereby increases our
understanding. In this quest we are especially interested in techniques
and functions which reduce complexity and at the same time provide a
reasonably accurate portrayal of reality.
  
Functions which are candidates for consideration include exponential,
exponential to the limit L, logistic, Gompertz, and the power function.
Bounded functions which fit data more precisely but cannot be used for
predictive purposes may also be helpful in uncovering patterns.

1.3  POLICY IMPLICATIONS OF TRANSITION THEORY
But what does it gain us to fit an exponential or logistic or for that
matter any function to transition data? The answer lies in our ability to
gain insights by relating different transitions to each other. First,
consider the transitions within a given sector and at a given scale. We
know there are transitions in a sector which some societies have already
experienced while others have yet to endure. If the nature of these
experiences can be captured in general form, it is more likely that
knowledge can be transferred to other settings where a transition is first
starting. Of course, each civilization or local culture has its own unique
characteristics but any one emerging transition may be comparable to one
or more of those which have occurred before because conditions are
similar.

Second, there may be useful comparisons across different scales. We
already surmise that a national-level transition, perhaps now in process,
is actually comprised of a myriad of local transitions also in process or
which have recently occurred. But there may be other locales in the region
for which the transition has yet to happened. If similar patterns emerge
because of similar local conditions, a useful prediction could be made
about the nature of the passage through the transitions yet to appear.
Third, there may be insights gained simply by the process of fitting a
function to historical data. Different mathematical functions often have
very specific underlying characteristics which can provide useful ideas. 
The next potential use of transition theory is to facilitate analysis
across sectors. There is, of course, no good reason to expect the
trajectory of, say, a forestry or agricultural transition to mimic an
epidemiologic transition. However, for any society at a given time, there
may be similarities in the rates of change across sectors. Developed
economies have slower rates of change in their agriculture sector than
developing economies when conditions are favorable. Rural based cultures
may be expected to have urbanization transitions which are steeper than
non-rural cultures. In short, it is worth testing to see if patterns can
be empirically determined which would be helpful in predicting the shape
of future transitions, given a stated level of intervention.

We have already mentioned the special societal vulnerability associated
with several sectors being in rapid transition simultaneously.  From a
modeling perspective this simultaneity a very difficult condition to
describe and analyze, which may be why less progress has been made in 
this area to date. However, being able to portray these multiple
transitions with specific functions could be helpful. There is no question
that each transition interacts with the other. And to the analyst this
means that a reliable model must be structured as a set of simultaneous
relationships. Describing transitions as functions facilitates this
manipulation.

Another potential benefit of transition theory lies in the identification
of lead indicators. If success is achieved in fitting transition data to
an appropriate function, then for a given condition and point in time, the
future trajectory can be predicted more accurately. Identifying lead
indicators is facilitated because with an orderly function, only one, or
at most, two parameters need to be determined to define the trajectory.
This advantage is even more evident when several functions are considered
simultaneously.

Finally and perhaps most importantly, transition theory may permit more
informed public and private intervention. At one level we find ourselves
believing that the trajectory of a transition is somehow fixed by an
immutable law of nature. But at another level we know that this is not the
case. Public and private policy can make a difference as we have seen from
some of the cases discussed in this book. Rates of change can be
influenced by policy redirection and consequent resource allocation. To
the extent that we can link historical rate differentials with historical
policy implementation, a better determination can be made about which
intervention mix works best in dealing with problems facing society today.