Geoscience Reference
In-Depth Information
Figure 16-45.
Rumpo habitat/species management area of the Vormsi Maastikukaitseala (landscape reserve).
Southern coast of the island of Vormsi plus the adjacent Väinameri shallow seal oor and islets, western Estonia. Kite
aerial photo by S.W. Aber and J.S. Aber.
1999). Other small historical islands have disap-
peared completely.
The western mainland, islands, and northern
margin of Estonia are parts of the Baltic Coast
Bog Province (Fig. 16-45), which corresponds
roughly to the region that was submerged in the
Baltic Ice Lake following deglaciation in the
latest Pleistocene (Valk 1988; Ilomets 1997).
Eastern Estonia, on the other hand, remained
above the Baltic Ice Lake and is part of the East
Baltic Bog Province (Fig. 16-46). Bogs in these
two regions have distinct l ora; for example,
Trichophorum cespitosum
(tufted bulrush) and
Myrica gale
(sweetgale) grow only in the
western region, whereas
Chamaedaphne caly-
culata
(leatherleaf) is found only in the eastern
region (Valk 1988).
The oldest known peat in Estonia is dated
nearly 10,000 radiocarbon years ago (Ilomets
1997). Paludii cation (rising ground water)
leading to substantial peat accumulation began
around 8500 years ago, and the next phase took
place about 7100 to 6500 years ago, which cor-
responded to transgression of the Littorina Sea
in the Baltic basin. The i rst signii cant phase of
peat initiation by terrestrialization (lake ini ll-
ing) happened some 6500-4500 years ago
during the i rst half of the Atlantic period, and
paludii cation reached a peak between 5100 and
4100 years ago. For the most part, basal peats
accumulated in fens and are rich in
Bryales
(mosses) and
Carex
species.
The initiation of raised bogs, characterized
by
Sphagnum
peat, was somewhat later. Three
minor phases of bog formation occurred around
7000, 6000 and 5000 years ago, each lasting
about half a millennium. The major time for bog
development was between 4000 and 2000 years
ago, however, when more than 40 percent of
modern Estonian bogs came into existence as a
result of hydroseral succession (Ilomets 1997).
A few younger bogs formed between 1500 and
500 years ago. Given approximately 12,000
years since deglaciation of Estonia, several mil-
lennia were required for the processes of paludi-
i cation and terrestrialization to initiate fens in
which peat could begin to accumulate, which
took place generally between 7000 and 4000
years ago during the mid-Holocene climatic
optimum (Fig. 16-47). At least one or two more
millennia were then necessary for raised bogs
to appear via hydroseral succession. Within
these general time frames, bogs and fens dis-
played distinct differences in the timing of their
Holocene development between eastern and
western Estonia (Ilomets 1997).
Human activities have inl uenced bog devel-
opment during the past few centuries (see
