particular for continuous sequences that have been correlated
over 500 000 years (Tzedakis et al. 1997). To verify this
assumption, pollen samples are taken from modern or recent
moss and their pollen spectra are compared with current
vegetation. From a qualitative point of view, we can already
sketch the relationship between the abundances of pollen
and the composition of the vegetation. For example, the
study of an altitudinal transect provides an impression of
what happened during a cooling climate. Many published
articles are based on this approach. But if current pollen
spectra are collected from vegetation as diverse as possible,
the problem can be treated quantitatively and objective keys
to interpretation can be established. We develop this perspective below.
Figure 12.1 shows that the vegetation around Lake Rotsee, Switzerland (Lotter and Zbinden 1989) was dominated
by herbaceous vegetation before 11,000 years BP: sagebrush
(Artemisia) and grasses (Poaceae), indicating an open
environment with few trees. Around 11,500 years BP, birch
(Betula) and, a century later, pine (Pinus) flourished until
they occupied nearly 80% of the assemblage. This pioneer
arboreal vegetation thrived due to a warmer climate. Around
Fig. 12.1 Simplified pollen
diagram of Lake Rotsee (8.33° E,
47.08° N, 419 m) in the Swiss
Alps (Lotter and Zbinden 1989).
The time period covered is from
12 000 years before now (BP) in
calendar age to the present day.
AP is the sum of all the arboreal
pollen abundances
152
J. Guiot
over 500 000 years (Tzedakis et al. 1997). To verify this
assumption, pollen samples are taken from modern or recent
moss and their pollen spectra are compared with current
vegetation. From a qualitative point of view, we can already
sketch the relationship between the abundances of pollen
and the composition of the vegetation. For example, the
study of an altitudinal transect provides an impression of
what happened during a cooling climate. Many published
articles are based on this approach. But if current pollen
spectra are collected from vegetation as diverse as possible,
the problem can be treated quantitatively and objective keys
to interpretation can be established. We develop this perspective below.
Figure 12.1 shows that the vegetation around Lake Rotsee, Switzerland (Lotter and Zbinden 1989) was dominated
by herbaceous vegetation before 11,000 years BP: sagebrush
(Artemisia) and grasses (Poaceae), indicating an open
environment with few trees. Around 11,500 years BP, birch
(Betula) and, a century later, pine (Pinus) flourished until
they occupied nearly 80% of the assemblage. This pioneer
arboreal vegetation thrived due to a warmer climate. Around
Fig. 12.1 Simplified pollen
diagram of Lake Rotsee (8.33° E,
47.08° N, 419 m) in the Swiss
Alps (Lotter and Zbinden 1989).
The time period covered is from
12 000 years before now (BP) in
calendar age to the present day.
AP is the sum of all the arboreal
pollen abundances
152
J. Guiot