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Pure Appl. Chem., Vol. 70, No. 11,
pp. 2114, 1998
Diversity and conservation of epiphytes in a changing
environment*
Peter Hietz
Institut für Botanik, Univ. f. Bodenkultur, Gregor-Mendel-Str.
33, A-1180 Vienna, Austria
E-mail: [email protected]
Abstract: About 10 % of the world's total vascular flora are
epiphytes, and in some humid tropical forests they may be the most diverse
life form. Growing on trees, their fate is tied to that of their hosts
and they are threatened by deforestation. Without contact to the soil,
they rely on atmospheric input of water and in part nutrients. This
makes many species susceptible to changes in forest microclimate caused
by human activities and they may serve as indicators for biodiversity
and forest disturbance. Some effects of human activities on the diversity
of epiphytes and possibilities for conservation are considered.
Forest conversion As epiphytes depend on their host plants,
usually trees, any conversion to a vegetation without trees will obviously
result in a complete loss of epiphytes in the affected area. Diversity
in young secondary vegetation will be lower than in oldgrowth forests
because small trees do not offer the variety of microsites. Many species
require rooting substrates that only accumulates on large branches of
old trees, and young forests do not provide the stable and humid microclimate
prevailing in the lower strata of mature forests. A plantation of alder
in eastern Mexico had little more than half the number of vascular epiphytes
(21 species) than an adjacent oldgrowth cloud forest (39). Of these
only eleven were present with fertile individuals while ten were infertile
and only present because of seed or spore input from the nearby mature
forest. Especially species requiring either the humid lower canopy or
thick branches were missing from the plantation. Large trees, such as
old shade trees in coffee plantations, may host a very diverse epiphyte
flora and two coffee plantations studied were about as rich in epiphytes
as mature forests in the area. While some trees are good hosts, others
appear hostile to epiphytes and plantations of mango have a very low
diversity of epiphytes.
Forest disturbance Almost nothing is known on the effect
of forestry and forest disturbance on vascular epiphytes. However, studies
on epiphytic lichens and bryophytes in temperate forests showed that
diversity is generally highest in oldgrowth and heterogeneous forests.
Vascular epiphytes with slow growth and long generation cycles will
be negatively affected by repeated disturbance caused by logging operations
that remove most of the large trees, which usually are the best hosts.
Additionally, opening the forest and makes the interior drier, which
may result in the disappearance of drought-sensitive species.
Fragmentation With long-living individuals and mobile
diaspores epiphytic species that support the drier and sunnier microclimate
in small fragments and along fragment edges may be better able to survive
in a fragmented landscape than other plants. Survival of zoophilous
and zoochorous species over many generations will also depend on the
ability of their pollinators or dispersers to cross between fragments.
Pollution Many non-vascular epiphytes are known to be
highly sensitive to atmospheric pollution and lichens have long been
used as indicators of air quality. Deriving most of their nutrients
directly or indirectly from the atmosphere and without the buffering
capacity the soil provides for ground-rooted plants, vascular epiphytes
are also likely to suffer from atmospheric pollution and may serve as
bioindicators in tropical countries.
Global climate change If global climate change leads
to a geographic shift in climate zones, epiphytes with mobile seeds
and shorter life cycles may be better able to follow their suitable
climate than trees. On the other hand, if seasonality of precipitation
in tropical countries increases, the perhumid forests now supporting
the highest epiphyte diversity will decline.
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- PDF file (81KB)
* Invited lecture presented at the International
Conference on Bioversity and Bioresources: Conservation and Utilization,
23-37 November 1997, Phuket, Thailand.
Back to Invited Lectures
Contents
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Page last modified 5 March 1999.
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