Title:
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Plant community change in the Montgomeryshire Canal in relation to succession theory
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The water physico-chemistry, hydrology and plant
communities in the Montgomeryshire Canal were examined
for evidence of successional phenomena over a five
year period and comparisons were made with previous
studies.
Plant communities changed in a manner which
suggested that classical successional ideas were
applicable to canals. The changes were readily
distinguishable when a period of twenty years had
passed but as the examined period was decreased the
complexity of the sequence became more apparent. In a
single year there were changes in the plant
communities. A later stage of succession was indicated
as the number of changes increased and the available
energy and habitat niches were filled. Succession did
not take place in a slow orderly manner but progressed
as a series of jumps when the plants were released
from inhibitory factors. These sudden changes were
promoted by changes in the habitat due to climatic
variation, removal of grazers or alterations in the
water level. Where the most important inhibitory
factors were unchanging, the succession proceeded to a
climax community decided by those factors.
The physico-chemical factors affecting the canal
changed during the study period. The canal became more
acidic due to the effects of a cold wet spring. The
underwater light climate in un-navigated lengths was
determined more by the amount of shade upon the water
surface than by any other factor. Levels of suspended
solids were relatively unimportant. Established plant
communities showed a great resistance to change,
despite being subjected to traumatic perturbations.
Skim dredging of a site with a well established
community structure did not change the course of the
succession, but removed inhibiting factors such as
anoxic material or grazing and promoted a more rapid
change to reedswamp.
In the .long term falling water levels had the
same effect as raising of the bottom due to infill,
but in the two routes towards a less aquatic system
were different. Infill led to a moving band of depth
sensitive plants whilst loss of water encouraged rapid
creation of a reedswamp. The study confirmed that
limited navigation is not detrimental to the species
composition or the productivity. Eutrophication was a
limiting factor creating an unique climax community.
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