Download The role of herbivores in the ecosystem and management of

The role of herbivores in the ecosystem and
management of Miombo woodlands
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Heikki Roininen, Timo Veteli and Tiina Piirainen (University of
Joensuu, Finland)
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Research on plant animal interaction (ecology and evolution)
– Insects, voles, hares, moose, reindeer and willow ptarmigan
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Similar methods for research might be applicable for Miombo
woodlands
Research in Miombo and other systems may help to understand
plant/animal relationships in general
Presentation: to review literature on the effect herbivores in Miombo
woodlands (excluding human)
Reindeer and Willow ptarmigan
Reindeer and willow ptarmigan
browsing on willows
Interactions between mammals, plants and environment
(Cumming 1982)
Effects of herbivores in relation to other
influences (Sankaran 2005 et al.)
• What are the primary factors driving the
existence of Miombo (Savanna)?
– Precipitation
– Fire
– Herbivore
Relationship between MAP (Mean Annual
Precipitation) and woody cover
No herbivore effect on woody cover of dry savanna (MAP <
650mm)
Relationship between MAP (Mean Annual
Precipitation) and woody cover
Two generally accepted influences in plant/animal
interaction
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Clear pattern between plant
species richness and
grazing/browsing intensity
Effects on species richness of plants
• Negative effect of grazing/browsing in nutrientpoor systems
• BUT positive in nutrient-rich systems
Comparing the influences of
domestic and natural herbivores
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Sustainable densities versus overgrazing
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Overgrazing and with episodic droughts has caused
widespread rangeland degradation and loss of
floristic and faunal diversity (reviewed by du Toit
and Cumming 1999)
Livestock and game in similar densities
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Very few studies done
No difference in species richness (woody plants)
Some indication that relative abundances changed
In some cases game caused more evenness of
woody plant species (it means higher diversity)
Methods in Richardson-Kageler
(2003) study
• Both sites of fences (cattle or game)
– Expected to be equal in the beginning
– 18 cases studied (good replication!)
• Densities known (equal in most cases)
• More than 10 years time period
• Woody plants measured
Effects of livestock and game on woody
plants in sustainable systems
• No differences in species richness
• Some indication that relative abundances of tree
species changed (but similarities of tree
assemblages are not analysed)
• Is the effect of domestic animals equal with
game?
– More diverse fauna of feeders should caused more
diverse tree community
– More research needed!
Studies on effects of large
herbivores on woody plants
• Ford (1987); elephants decreased higher woody plants
but did not change species richness
• Smart et al. (1985): species richness did not differ inside
or outside of enclosures, but evenness decreased in
enclosures
• Cumming (1997); Heavy elephant effect (woody canopy
removed). No difference in woody plant species richness
less than 3 meters height
• Augustine and McNaughton (2004): Native browsers
(elephant and did-dik) provide important ecosystem
services by suppressing rates of shrubs encroachment
on commercial rangeland
Herbivory on seedlings
• General herbivory impacts on seedlings “not well
known” (Shaw et al. 2002), mammals are
causing high mortality
• Invertebrates and rodents largely unstudied
• Relative role of different herbivores is important
to know
– Observation studies; livestock and game effects
overrun others
• If fenced insect herbivores cause similar effects
• Rodents?
Study on A. drepanolobium
seedling (Shaw et al. 2002)
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Invertebrates more important than rodents
Invertebrates and rodents together may compensate removal of
large herbivores
Especially removal of cotyledon increased if large mammals
excluded
Indirectly study shows that invertebrate community (herbivorous
insect) differ on areas with mammals and no mammals
Hypothetically invertebrates can have big effect
– In our experiment: increase of invertebrates and there impacts inside
enclosures
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Rodent populations are highly cyclic or variable in rain forests,
boreal and arctic zone
– Difficult to demonstrate temporally variable effects (every 4th years)
Historical evidence for impacts of
herbivores, even aged stands of Acacia
(Prins 1993)
• Seedling establishment is difficult under
natural browsing condition
• Anthrax epidemics of impala population in
Manyara NP
– 1984, 1977, 1961, 1880 (rinderpest)
– After these epidemics new even aged stand
were established
– Predictions for our experiment?
Exclosure studies on the effect of
(large) herbivores
• In general most studies are unreplicated or
poorly replicated enclosure studies in
natural parks
• Species richness and diversity measured,
but for some reason similarities of species
composition between treatments are not
analysed
• Usually long lasting, 10 or more years
• Nothing is known about harvesting effects!
What has been the role of herbivores (large)
in the evolution of Miombo tree??
• Indirect evidence support the few that
herbivores has been important selective
factor
– Defence structures, defence chemicals etc.