IN GUANACASTE National Park, in Costa Rica, the native tropical dry
forest is becoming established again after years of felling, thanks to the
efforts of an American ecologist, Dan Janzen. He is playing a leading part
in restoring this type of forest, and encouraging local people to become
involved in its maintenance.
On a small island in Panama, Nancy Garwood of the Field Museum of Natural
History, in Chicago, and I are tackling the same problem 鈥� that of replacing
lost forest 鈥� but approaching it from a different angle. We are focusing
on the growth of seedlings of the trees, shrubs, lianas and herbs found
in the lowland tropical wet forest on Barro Colorado Island in Lake Gatun.
The end product of our project will be an illustrated manual that provides
a practical guide to restocking and maintaining tropical forests. At present,
there is a large gap in our knowledge of how to germinate seeds of native
species in tropical wet forests. Our knowledge of the structure of seedlings
and their rates of survival is also incomplete.
Advertisement
Barro Colorado Island is an ideal place for examining the conditions
in which a tropical forest matures. It became an island in 1914, when engineers
dammed the Chagres river to form Lake Gatun. The governor of the Canal Zone
designated the island as a nature reserve in 1923, and it later came under
the direction of the Smithsonian Tropical Research Institute. There is a
busy field station, with excellent laboratory facilities, and a herbarium
containing some 2000 specimens of plants collected on the island.
About 1300 species of vascular plants grow on Barro Colorado, a good
number of which also grow in similar conditions in other parts of tropical
America. We are gathering seeds from such plants and cultivating them in
specially constructed growing houses on the island. The houses are made
from net rather than glass, so that they are open to the tropical weather.
The netting keeps out large insects, birds and snakes. Narrow moats around
the houses serve the same purpose.
The houses have two tiers of staging so that we can grow seeds in either
full light or shade. Netting placed around the lower tiers further reduces
the light intensity, recreating the deep shade found in the forest. In this
way, we can establish which species thrive as seedlings in sunlight, and
which in shade.
After collecting the seeds, we clean away any pulp and plant them in
peat pots. Most seeds grow well in ordinary forest soil, but we are finding
that some, such as the figs, grow better in a gritty mixture (about a ratio
of 3:1 of sand to soil). Regular watering is essential, even in the wet
season, because tropical heat dries the soil very quickly. Once the seeds
have germinated, we begin to record their growth.
An important part of the manual will be illustrations. We decided to
use pen and ink drawings (because they are more flexible than photographs
for showing details of the plants), and to produce them on the spot from
living seedlings to ensure accuracy (dried specimens lose too much of their
natural shape).
Eventually, we will have illustrations for each species, showing several
stages, from germination through to juvenile seedling. There will be detailed
drawings of cotyledons and first-leaf stages, and large-scale drawings to
show features such as glands and hairs, which are helpful in identifying
a species.
By the time the cultivation stage of our project is finished, we should
have grown at least 700 species. The next stage will be to prepare taxonomic
descriptions, graphs and tables of measurements. The manual will also include
useful notes for would-be tree growers, such as details of animals that
eat the fruit or seeds of a species, whether seeds need to be digested by
animals before they will germinate, and which fruits are edible and which
poisonous. This work, together with a key to species and a glossary in English
and Spanish, will probably take us two or three years.
The result, we hope, will be a manual that is an important source of
information with many practical applications. Foresters and conservationists
will be able to identify plants in their juvenile stages and to recognise
those which could be transplanted to other suitable locations. They will
be able to spot, and deal with, introduced species that are troublesome
or might displace native plants, and conserve rare or threatened species.
The insight into tropical biology and into the diversity of the forest and
plant populations will help in developing forestry techniques that are suitable
for tropical wet forests. In poor regions, properly managed forests could
help to provide a sustainable source of income.
Margaret Tebbs works in the Department of Botany at the British Museum
(Natural History) in London, which will publish the manual. The project
is funded by grants, including from the Natural Environment Research Council,
NATO and the US National Science Foundation.
