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TROPICAL VEGETATION AND CROPS, DISCUSSION 135 
temperate regions with that in the tropics. The 
tropical conditions are so different, that when 
comparing the two, I would like to say that plant 
ecology in the tropics can only be applied in a 
very general sense. As Mr Miller indicated, we 
are only able to guess congregations on the 
aerial photographs. These congregations are an 
indication for the occurrence of possible plant 
associations and the information obtained from 
the aerial photographs gives an indication for 
local plant conditions. Based on this informa- 
tion an extended survey programme can be 
made and executed in the field. As far as I am 
informed forestry inventory methods in several 
tropical regions are based on this system. 
CHAIRMAN: I presume that Mr Schwarck 
from Venezuela would like to make some 
comments. 
Mr SCHWARCK: I would like to ask whether 
it has been tested, in how far these congrega- 
tions in tropical forests can be identified as 
major groups. If so, what would be the order 
of the approximate number of these different 
congregations, that you would have to cope with 
or establish in new areas. 
CHAIRMAN: I think it will be rather difficult 
to give a direct answer to this. 
Mr MILLER: There is a useful classification 
of African visitation on a physiognomic basis 
drawn up at a meeting at Yangambi and pub- 
lished a few years ago. This classification is 
given in terms of structure and is illustrated by 
a number of diagrams of vegetation types, and 
as a whole, we try to use that as a reference on 
structural terms. I use the word “congregation” 
as a non-committal sort of category; I just want 
to make sure that there is no confusion with 
other systems of classification. 
CHAIRMAN: In addition to this remark I 
would like to say that one should be very care- 
ful with general classification systems, as I am 
not quite sure whether systems valid for African 
conditions can be applied to countries in South 
America, where conditions may be quite 
different. 
Mr MILLER: I should say here, having quite 
recently seen photographs of vegetations in 
Brasil, particulary in Southern Brasil, that I 
Was greatly impressed by the similarity with 
Africa. It seems to me that I could have taken 
comparable photographs in Africa with exactly 
the same appearance, although composed of 
very different species. 
CHAIRMAN: I give the word to Mr Curtis 
from Bristol. 
Mr CurTIs: This is Curtis speaking of the 
University of Bristol. I am a geographer with 
special interests in Soil Survey. I have found 
that the text of a practical classification system 
in soil survey is not always a suitable classifica- 
tion for mapping purposes. That is to say when 
you apply photogrammetric methods for your 
mapping work, you may find that you wish to 
define your soil group in a way quite different 
from the classical soil classification systems. 
This problem seems to arise also when one is 
attempting to interpret soils from aerial photo- 
graphs. 
The question I would like to put to Mr 
Miller is this: Are there similar problems of 
grouping and classification of vegetation units 
in tropical areas and does he find that this 
classification which may be related to existing 
ground surveys are suitable for photographic 
interpretation purposes? 
Mr MiLLER: Actually a photograph is not 
always a complete record of what is on the 
ground. Sometimes photography will show you 
more than you can detect on the ground but it 
is quite possible, of course that it will show you 
less, so you have to establish any correlation by 
field work. I would say in most cases photo- 
interpretation gives only the possibility to 
demarcate main vegetation groups. I think that 
soil people would probably prefer a more 
detailed classification. But I am not a soil ex- 
pert and I would not like to go far into that 
subject. 
Mr CURTIS: Do you feel that you are able, 
in fact, to detect groups, certain groups of 
species in tropical areas and that you are able 
to give a name in terms of species for a certain 
area with satisfactory results? I am thinking 
now, not in terms of congregations but of asso- 
ciations, where you have a great mixture of 
species as, I understand, is the normal situation 
in the tropics. 
Mr MILLER: The less it is interfered with by 
human occupation the more the character of 
the vegetation will be controlled by the soil con- 
ditions. In both West and East Africa there is 
often a situation where the mature character of 
the forests is not yet fully developed; in such