sub-systems: Garden and Gardener (see Diagram 1). The System in turn, interacts
with the Enviroment through its output and through the fixed constraints. Quoting
Churchman (cf.) : "When we say that something lies outside the system, we mean that the system can do relatively little about its characteristics or its behaviour. Environment in effect, makes up the things or people that are fixed or given from the system's point of view".
From all those things or people that are relevant to the Gardening system we have to decide which ones are to be placed inside the system and which ones outside.
According to Churchman the decision may be based on the answers to the following
two questions:
1) Can the system do something about it ? ( i.e. to modify it ?)
2) Does it matter relative to the system's objectives ?
If the answer to 1) is NO and to 2) is YES the the item is placed in Environment.
A clear example is total budget: the system can do nothing, or relatively little, about its
amount, since its fixed by the funding organization according to its priority amoong the
organization other commitments. On the other hand the budget size is of paramount
importance in reaching the systems objectives.
On the basis of questions 1) and 2) we can build a truth table with four different
Classes, originating from the four pair-answers to the questions, that is:
Classs 1) 2) Decision Example
====================================================
A NO YES ENVIRONMENT Fixed Budget
B NO NO IRRELEVANT Structures at suff.distance
C YES NO IRRELEVANT ? ??
D YES YES SYSTEM Allocation of work
======================================================
The above table may be taken to represent a simple computer program designed
to classify variables in two classes: system variables or environmental variables and to
reject all the rest( classes B and C) as irrelevant variables.
the Observer is clearly placed in the Environment since a) the system cannot modify
it to any appreciable extent and b) it clearly matters relative to the system's objectives.
As a matter of fact the main system objective is defined in terms of the Observer.
Other items to be placed in the Environment or Surroundings (both words
will be used indiscriminately) are listed below; each item or compartment may give rise
to one or more variables according to the level of the analysis. (We will design by
Ei a set of env. variables and by Eii individual variables within the set )
E2 : Total Budget (including salaries and expenses; in many funding organizations
the budget is allocated to items that cannot be modified by
the system. In that case this item is broken down in several
ones).
E3: Climate (including variables such as temperature,humidity,evapotranspiration
solar radiation,etc.) The set of E3 is sometimes represented as
climate zone when selecting plants.
E4: Water resources (including rainfall and water bought, in special cases
also water quotas)
E5: Soil type or types,( i.e. clayish or sandy,acid,basic, salinity level,organic
content,etc.etc.)
E6: Topography.
E7: Infrastructure (including buildings,internal roads, water supply,drainage
structures,etc)
E8,E9,E10: reserved for any other items that kind readers would care to suggest.
E20: Layout of Garden. I have set this item apart because its position in
Surroundings may be controversial. If we work
under the assumption that the rules of the game(or premises of the model)
are such that the Garden layout is set initially by the Landscape Architect (LA)
and the Gardener is not at liberty to change it then this item is clearly in
Environment [answers to questions 1) and 2) above are NO and Yes].
This implies that the position and type of trees,bushes and other elements,
the limits of lawns and garden covers,flower beds,garden paths,etc. cannot
be modified by actions of the System. For instance if a dead tree has to be
replaced, the new tree should be of the same shape(columnar,rounded,etc)
and be planted in the same position; the type of annual flowers at the
discretion of the Gardener but the size and position of the flower bed are
fixed. I am aware that in practice this is not often the case; either we
gardeners are convinced that "we know better" or our budget is such that
decisions have to be made bet. the Architect's fees or replacing an old
piece of equipment. Since in my modest opinion the design of extensive
gardens is the domain of qualified professionals, I am leaving the Garden
Layout and hence the L.A. in the environment. More about this in:
The Landscape Architect in relation to the Model(Annotation,empty)
The sets of env. variables listed above set up the
constraints of the system. Within the context of systems analysis we are looking
for optimum performance within the constraints imposed by the env. variables.This
implies that within the model we have adopted the best performance of our system is not to attain the maximum Signal to Noise Ratio, but the maximum value possible under
the constraints imposed by total budget, climate, soil type, etc. The following example
may help to clarify the point:
In a given Garden there is a number N of lawn blocks with
a total area AT, which are kept under sprinkler irrigation. For each lawn we have the
management choice of "high maintenance level" (HML) or "low maintenance level"
(LML). Under HML we have to irrigate with Q cubic meters per unit area per unit time
so as to arrive to an SNR of 80; under LML we require only 0.7*Q but SNR will not
be higher than 50 because of yellowish patches most of the time. If our water quota,
E43, per unit time, is such that E43 > Q*AT that is, no constraint = no problem;
we keep all our lawns under HML. If, as is sadly the case in most temperate or dry
climates, E43< Q*AT , we'll have to decide which fraction of AT will be be kept
under HML or LML, consistent with performance requirement that the overall value
of SNR will be the highest possible. (the overall value being the summation of
(SNR)j*Ai for the N lawnblocks). The relevant set of equations are not complex
even if we include cost of water constraints and are shown in the Linear programing
of Lawns chapter (C.E.,empty)
The most usual constraints imposed by the Surroundings are those arising from
total budget (E2), particularly when budget is clearly inadequate in relation to the
constraints ( E20) imposed by the layout of the garden. This is a no-win situation and
the best solution for a wise Gardener is to try to find himself another job in a garden with
more generous patrons. Otherwise look for some partial solutions in the Section: Management .
.
