TOWARD UNDERSTANDING ECOBY8TEMB
29
desert. Fiowever, a stand of well-watered gram will lose substentiady
more water by evapotranspiration into the windy, dry desert air than
.the same grass stand would lose into windy, humid air. Very careful,
detailed estimatea of these comparisons can be easily worked out b d
on the aethoda outlined here providing one can adequately deeoribit
the vegetation of a given region.
The p i n t to be made by the examplee given in Figs. 8, 9, and 10 is
that orle cannot conclude that wind will increnae or decreaee water
wage unless all the other environmental factors which act simultaneoualy are specified. The question of competition for water among
neighbwing plants will depend upon a11 of these simdtaneous factors
and u p n whether the plant is near the ground whsre there is little wind
or whether it is higher up exposed to more prevalent winds. Competition for water will depend upon whether one plant is exposed to full
sun ana hence haa a high amount of radiation absorbed or is shaded
and he8 s low amount of radiation absorbed.
2. Other Fador8
To Ltudy competition in the field is exceedingly difficult, exoept in a
few obvious instances, until one can actually demonstrate through
physical laws precisely how a given environmental factor affects a plant
in the simultaneous context of all other fectors. What can be$done is to
use thc Bystems approach and work out mathematical models of plants
arrangod very much aa they actually are growing in the natural plant
community.
One can specify the climate for each plant, leaf by leaf, and demonstrate by computation the water usage by the plant for the prevailing
mnditions. One can permit the climate to change in any realistic tamporal manner and compute the water usage of each individual plant
with its individual characteristics and its climate. One can change the
density or arrangement of the plants, change the degree of shading
of one plant by another, or change the wind prome in the stand aa a
result of the density, and demonstrate by ccrlonlation what these
changes will mean in terms of the water usage. Having done this one is
then juRtified in going into the field in order to verifs or deny the predicted results. This is exoeedingly difficult and muat be done with great
carb. It is difficult because of the fact that in the field nearly all variables may change at the same time and continuously. But this is
precisely the reawn why it is basically impossible to go into the field
first in an attempt to understand just how it is that the various individual plants of a community me competing for water or for any other
factor. This does not mean that some field work ahould not be undertaken prior to making vaut and complex donlatiom. Indeed it must
29
desert. Fiowever, a stand of well-watered gram will lose substentiady
more water by evapotranspiration into the windy, dry desert air than
.the same grass stand would lose into windy, humid air. Very careful,
detailed estimatea of these comparisons can be easily worked out b d
on the aethoda outlined here providing one can adequately deeoribit
the vegetation of a given region.
The p i n t to be made by the examplee given in Figs. 8, 9, and 10 is
that orle cannot conclude that wind will increnae or decreaee water
wage unless all the other environmental factors which act simultaneoualy are specified. The question of competition for water among
neighbwing plants will depend upon a11 of these simdtaneous factors
and u p n whether the plant is near the ground whsre there is little wind
or whether it is higher up exposed to more prevalent winds. Competition for water will depend upon whether one plant is exposed to full
sun ana hence haa a high amount of radiation absorbed or is shaded
and he8 s low amount of radiation absorbed.
2. Other Fador8
To Ltudy competition in the field is exceedingly difficult, exoept in a
few obvious instances, until one can actually demonstrate through
physical laws precisely how a given environmental factor affects a plant
in the simultaneous context of all other fectors. What can be$done is to
use thc Bystems approach and work out mathematical models of plants
arrangod very much aa they actually are growing in the natural plant
community.
One can specify the climate for each plant, leaf by leaf, and demonstrate by computation the water usage by the plant for the prevailing
mnditions. One can permit the climate to change in any realistic tamporal manner and compute the water usage of each individual plant
with its individual characteristics and its climate. One can change the
density or arrangement of the plants, change the degree of shading
of one plant by another, or change the wind prome in the stand aa a
result of the density, and demonstrate by ccrlonlation what these
changes will mean in terms of the water usage. Having done this one is
then juRtified in going into the field in order to verifs or deny the predicted results. This is exoeedingly difficult and muat be done with great
carb. It is difficult because of the fact that in the field nearly all variables may change at the same time and continuously. But this is
precisely the reawn why it is basically impossible to go into the field
first in an attempt to understand just how it is that the various individual plants of a community me competing for water or for any other
factor. This does not mean that some field work ahould not be undertaken prior to making vaut and complex donlatiom. Indeed it must