Amazonia: Characterization - Biotic - Epiphytes
Epiphytes or arboreal flora constitute an integral
part of the rainforest ecosystem and are the most sensitive among
the flora to climatic change. Vascular epiphytes (such as those
living on bark), residing primarily in pre-montane to mid-montane
forests, comprise 10% of epiphyte species, yet the majority of those
in the forest canopy1. Non-vascular epiphytes (mosses, liverworts,
and lichens) require specific timing on wet dry cycles to flourish,
and are much more acutely affected by variations in climate (such
as changes in the patterns of annual and seasonal rainfall) than
their vascular counterparts. All epiphytes, however, are distributed
throughout the canopy on the basis of water supply. Within vascular
epiphytes, there are:
which are the most tolerant to adverse moisture conditions|
Bark users, that
prefer more humidity|
knotholes and rotting wood, that are more sensitive to drought and require
hosts of rooting media|
Humus, which are
also very sensitive to drought|
Non-vascular epiphytes include:
crustose lichens, that peak in the mid-altitudes|
that prefer cloud forests|
The availability of moisture affects the diversity,
abundance and distribution of non-vascular and vascular epiphytes
(although the latter is less sensitive).1
Hypothetical tree illustrating how vascular epiphytes
in humid forests tend to partition substrates illustrating
sensitivity to micro climate, particularly humidity, and
associated development of
the organic rooting media required by some populations.1
Epiphytes play a key role in the rainforest ecosystem. They
provide nectar, pollen, fruit and seed for harvest, and their moisture and
nutrient retaining properties are essential to many of the terrestrial
invertebrates and lower vertebrates. Some epiphytes have developed coevolved
mutualisms with fauna, for example within an ant-nest garden, the ants
provide a home for the epiphytes, while the epiphytes remove harmful excess
moisture from the nest. They also provide an important source of biomass
Epiphytes are important in rainforest hydrology and
mineral cycles. They are well equipped to absorb the prevailing
horizontal precipitation (in the form of fog water). They also vastly
increase the canopy foliage surface area which absorbs ions and
moisture (some data indicates that up to half of the canopy's macronutrients
may be contained in epiphytes1). Epiphytes behave as storage facilities
and capacitors for other rainforest biota, as they release certain
ions at some points in the year, and absorb the same ions at others.
Dead epiphytes contribute to the soil-recharging litter of the forest
Adaptation to drought:
Epiphytes are not as well equipped to deal with drought as other
flora, because they donít have access to the ground, but they still
have some mechanisms to help them cope. Many epiphytes exhibit CAM
(crassulacean acid metabolism), which involves taking in CO2 at
night, and photo-fixing it during the day with closed stomata to
reduce water loss by transpiration.1 They also contain
absorptive foliage that are efficient at quickly taking up water
when it is available and preventing desiccation when water is scarcer.
However, CAM can be impeded by higher night-time temperatures, dehydrated
tissues, and high saturation deficits in the surrounding air, which
lower the "stomatal conductance" of the epiphytes, reducing
the CO2 uptake, which in turn reduces growth and reproduction and
even induces net carbon losses.1 Higher temperatures, demands on
evaporation, and exposure to light cause CAM-idling, which is basically
the epiphyte closing its stomata when it becomes stressed, that
narrows the range of habitats a species can inhabit.
In general, epiphyte species composition and biomass are much
more sensitive to different relative moisture levels than those of other
The effects on different forests and certain regions of the
same forest due to change in climate vary according to the types of
epiphytes in these regions. Higher CO2 concentrations allow C3 and CAM
epiphytes to fix carbon with less transpiration, but the scientific
community is still not sure of exactly how this would change competitive
patterns between species.
A change in the climate large enough to only affect epiphytes would
nonetheless change the entire forest in terms of its "physical structure,
biodiversity, and patterns of energy, water, and nutrient flux" in addition
to "ecosystem stability and resiliency."1
Epiphytes and Fragmentation:
Basic Info on Fragmentation:
Habit fragmentation is defined as "the simultaneous reduction of the area of
the focal habitat and increased isolation of the remaining habitat patches." 5
In short, fragments are areas of forest surrounded by deforested area.
Many species are lost during and immediately following fragmentation, but
there are also many long-term effects which can be caused by changes in
processes such as pollination, predation, territorial behavior and feeding
habits, in addition to changes in microclimate affecting solar radiation,
humidity and wind pattern. In general, fragments have a much greater
proportion of edge zone (in comparison to closed forest), which is
physically different from interior forest, thus changing ecological
properties of the fragment. Fragments usually can not support many species
assemblages that exist in closed forest, and smaller fragments suffer more
loss in biodiversity.
Effect of fragmentation on Epiphytes:
Survival of epiphytes subsequent to fragmentation is largely dependent on
the size of the tree in which a species resides, the size of the fragment
and also the relation of the fragment to closed forest (distance). In
fragmented forest, there is a much greater loss in biodiversity of epiphytes
than loss of presence in the fragment. The size and shape of a fragment will
determine the exchange rate of diaspores and pollen within and between
fragments, and can lead to isolation of subpopulations.
Although the slow growth and long cycles of epiphytes make them more
vulnerable to high rates of disturbance, they allow them to survive better
in the mid-term if they can get past initial conditions. This increases
their chance of success for colonization of second-forest in deforested
areas as long as these reforested patches are not to far from larger
fragments. In addition, their sensitivity makes them "suitable indicators of
changes in local climate, forest structure and ecosystem health"2.
Epiphytes as Bioindicators
Epiphytes and orchids are well suited to be indicators of the
health and biodiversity of the rainforest, not only because they are an
important source of nutrients for other flora and fauna, but because they
are very sensitive to shifts in microclimate and they have slow growth. The
performance, survival, and distribution of epiphytes is dependent on stand
density, microclimate, distance from seed source, tree size and species,
type and history of disturbance, population dynamics of epiphytes and trees,
and epiphyte physiology.2
Epiphytes are far more vulnerable to deforestation than other
flora. For example, 26% of vascular plant species present in 1900 are now
extinct, but 62% of epiphyte species are extinct.2
Epiphytes are completely dependent on their host plants, so if a tree is cut
down, all of the epiphytes residing on that tree will die. In addition, they
have very specific zoning constraints, so secondary vegetation might not
have all of the necessary microsites for different epiphyte species.
illustrates the loss of species and biodiversity in a plantation as compared
with oldgrowth forest. While the number of species for the two groups is not
very different, there is considerable loss of biodiversity, because only
epiphytes residing in some of the locations on a tree are present.
TABLE 1. Epiphyte
Richness and Occurrence of Ecological Groups in an Oldgrowth Forest and an
Figures in parentheses for the plantation are fertile species; all
species in the oldgrowth forest were found with fertile individuals.
Epiphytic Species Living on:
stem and thick branches
thick and thin branches
In addition to deforestation, epiphytes are affected adversely by increased
CO2 levels in the atmosphere. Raised CO2 levels shift climate zones, forcing
flora and fauna to migrate. Although epiphytes could migrate more easily
than trees, many models of the effect of fluctuating CO2 levels predict
increased seasonality of precipitation, and thus a reduction of the perhumid
area containing the highest epiphyte diversity.2
Below are a couple of specific species or groups have been
identified as good bioindicators.
The hemiepiphytic Ficus is a keystone species
because of its "numerical abundance, intra-crown synchrony of fruit
ripening, relatively short intervals between fruiting, large crop sizes
and intrapopulation fruiting asynchrony" and the fact that it is often
available as a food source for birds when other fruits are scarce.4|
Lichens are often used as an indicator of air quality:
Tillandsia, for example, is particularly sensitive to lead pollution.
Epiphyte N concentration:
Epiphytes obtain their Nitrogen either from canopy soil or
from nutrients in rainwater. Nitrogen-15 concentration is much higher in
ground-rooted plants than in epiphytes with access to canopy soil, pointing
to a much richer source of Nitrogen in terrestrial soil versus canopy soil.
In addition, N-15 concentration is much higher for those epiphytes in canopy
soil than those on smaller branches, indicating that epiphytes on smaller
branches have to rely almost exclusively on rainwater as a source of
Nitrogen.3 This means that
these epiphytes (on small branches) are much more susceptible to drought and
thus would be better bioindicators.
Next: Brazilian Society->
Benzing, David H. "Vulnerabilities of Tropical Forests to Climate Change:
the Significance of Resident Epiphytes." Climatic Change. 1998.
Volume 39: Issue 2-3, pgs 519-540.
Peter. "Diversity and Conservation of Epiphytes in a Changing Environment."
Pure and Applied Chemistry (IUPAC).
1998. Volume 70: Issue 11.
Available at: http://www.iupac.org/symposia/proceedings/phuket97/hietz.html
Hietz, Peter; Wanck, Wolfgang; Wania, Rita; Nadkarni, Nalim M. "Nitrogen-15
natural abundance in a montane cloud forest canopy as an indicator of
nitrogen cycling and epiphyte nutrition." Oecologia. 2002. Volume
131, pgs. 350-355.
Lambert, Frank R. and Marshall, Adrian G. "Keystone characteristics of
Bird-dispersed Ficus in a Malaysian lowland Rain Forest." Journal
of Ecology. 1991. Volume 79, pgs. 793-809.
Ranta, Pertti; Blom, Tom; Niemela, Jari; Joensuu, Elina and Siitonen, Mikko.
"The fragmented Atlantic rain forest of Brazil: size, shape and distribution
of forest fragments." Biodiversity and Conservation. 1998. Volume 7,
Turner, I.M.; Chua, K.S.; Ong, J.S.Y.; Soong, B.C.; Tan, H.T.W. "A century
of plant species loss from an isolated fragment of lowland tropical
rainforest." Conservation Biology. August 1996. Volume 10: Issue 4,