Biology Reference
In-Depth Information
and growing in relatively moist habitats. There was
Equisetum
(horsetail),
Lycopodium
(ground “pine'), ferns (Little et al. 2006; Hernández-Castillo
et al. 2006; Vavrek et al. 2006; Stockey et al. 2006), tree ferns (e.g.,
Rick-
woodopteris hirsuta
, Cyatheaceae; late Campanian Spray Formation, Van-
couver Island; Stockey and Rothwell 2004), aquatic monocots (
Cardstonia
tolmanii
, Limnocharitaceae; Riley and Stockey 2004),
Cercidiphylum
-like
plants, and pollen similar to
Gunnera
(at present a warm-temperate to tropi-
cal plant; Jarzen 1980; Jarzen and Dettmann 1989). Overall, however, the
conspicuous feature of the forest was its prominent evergreen component.
Farther south, between paleolatitudes 50°N and 40°N, conditions were
transitional between mesothermal and megathermal climates (fi g. 2.10).
In the northern part of this zone, a few deciduous trees with moderately
developed growth rings were present. To the south evergreens became even
more abundant; they were larger in size and had no or poorly developed
growth rings. In Wolfe's system, this vegetation toward the southwestern
United States is called a paratropical rain forest, while a similar type with
some seasonal (winter) dryness in the southeast is designated a tropical
forest (fi g. 2.10). The distinctions are a bit fi ne, but essentially they are
both “not quite tropical rain forests” in terms of MAT, MAP, seasonality,
buttressing, lianas, drip tips, leaf texture, and entire-margined leaf percent-
ages. As is often the case with biological systems, the parameters have to be
numerically quantifi ed more precisely than befi ts reality for data entry into
computer programs such as CLAMP, and one feature earlier used to defi ne
a lowland tropical rain forest, a three-tiered canopy, is no longer considered
as important (cf. the 1952 and 1996 editions of Richards,
The Tropical Rain
Forest
). These two similar vegetation types may be defi ned as follows:
-
-
Paratropical rain forest may experience some frost (
3°C), MAT
from 20°C-25°C, precipitation may be seasonal but no prolonged dry
season; predominantly broad-leaved evergreen with some deciduous plants,
woody lianas diverse and abundant, buttressing present, some drip tips,
entire margined leaves 57-75 percent.
1°C to
Tropical forest has MAT of about 25°C, subhumid (slightly drier), MAP
estimated at less than 1600 mm, moderate seasonality, growth rings absent
to poorly developed, canopy somewhat open, mesophylls (megaphylls in the
substratum), few drip tips, entire-margined leaves 39-55 percent.
Among modern vegetation types, these would be described as subtropi-
cal to warm-temperate forests. The lowland tropical rain forest had not yet
