347 
icity to 
?ully. These 
■acting all 
in height 
3 gradual 
gradually overgrow the Phalaris (between 1953 until 1970) that had largely 
replaced the Sairpus maritimus after 1960 and started to compete with each 
other. In this competition Typha angustifolia and Phragmites seem to defeat 
Typha latifolia. This is in accordance with the fact that the growing accretion 
is too small for a well-developed backswamp. We thus get a transitional 
ecause of 
situation between a backswamp and a levee, where Typha angustifolia used to 
e stand, 
be more frequent than Typha latifolia which prefers weaker mud. The Delta 
scheme has unfortunately stopped the free natural development of these three 
ts as an 
species in the tidal delta and thus the free duel between Typha angustifolia and 
le 
Phragmites ends in 1970 in stalemate position. The environment after 1970 was 
))). The 
much less suitable for all of them. Typha latifolia almost completely 
disappeared after 1970. According to H. DE BOOIS (who at present studies the 
>n 
Lation, 
2 k swamp- 
accretion 
changes in the whole area) a strong frost has accelerated the defeat of the species. 
Typha angustifolia also quickly degenerates due to a too dry habitat. Phragmites 3 
however, maintains its area and even gains slightly. This is partly due to fire 
' a more 
and cutting which favours Phragmites in competition with other invaders. 
of the 
Plants very much promoted by the new situation after 1970 are Epilobium 
other 
hirsutum 3 Calystegia sepium 3 Urtica dioioa, Galium aparine and others, the 
inuation 
same as we observed on the levee but not Angelica archangelica. The fact that 
eto sum 
Phragmites and the Typha's came into domination shows, however, that the 
alar is 
Scirpeto-phragmitetum had reached an optimum after about 10 years. The 
hen the 
occurrence of Stachys palustris after 1968 shows that the Stachys variant 
Д 
о 
a 
had then followed the "typical" variant. The altitude of the accretion was then 
Droximately 
50 cm. 
about 40 cm. below mean high water, which fits with the data given in ZONNEVELD 
1959(60). 
, at 
On the levee, some willow branches of Salix dasydados rooted and developed 
hne and 
into shrubs. Other willow shrubs and small trees of Salix alba originated from 
e to 
sticks we ourselves had planted to mark the gravel patches. There is nevertheless 
other 
an indication that the forest stage had already started before the delta scheme 
the 
disturbed the entire natural succession. In a quarter of a century, research has 
ften over 
proved that in the Biesbosch area the conclusions derived from the side by side 
Dhs. The 
development of the plant communities to an (allochtonic) succession in time were 
■r plants. 
levees. 
right. In addition, it shows that photographic recording reveals much more and 
enables one to study the dynamics both of geomorphology and vegetation in a 
kswamp 
detailed and (semi-) quantitative way. 
ses, 
эе plants