Download FFI briefing: Why biodiversity matters for carbon storage

FFI briefing: Why biodiversity matters for carbon storage
Is carbon protection the same as biodiversity protection?
Protection of forests for their carbon value through Reduced Emissions from
Deforestation and Degradation (REDD) schemes has been increasing in recent
years. These schemes concentrate on preserving forest cover, and thus have
great potential for the conservation of natural biodiversity. Some (REDD+)
initiatives already specifically take biodiversity protection into account.
There has been debate about the potential impacts of REDD schemes on
biodiversity, given its potential to protect natural forests1. However, where REDD
projects are not well designed, they could fail to effectively protect the
biodiversity within the forest itself; protecting these areas for their carbon value
may not necessarily conserve their biodiversity value. Furthermore, relatively
little is known about how such reductions in biodiversity may in turn affect the
ability of a forest to store carbon2.
The carbon storage value of a forest is essentially dependent on the trees within
it photosynthesising and storing carbon. Different plant species are more efficient
at sequestering and storing carbon from the atmosphere. In general, large, slow
growing trees with high wood densities tend to store the most carbon in the long
term. When such a tree dies, much of the carbon stored within it will be released
back into the atmosphere. Changes in biodiversity may directly, and indirectly,
affect the likelihood of tree survival and thus carbon storage.
Potential impacts on biodiversity in carbon forests
Although habitat destruction remains a key global threat to biodiversity, simply
protecting forest cover does not necessarily prevent a loss of the species within.
If not managed effectively then threats such as uncontrolled hunting, selective
logging or collection of non-timber forest products may alter both biodiversity
levels and species composition. This will have direct impacts, but may also have
indirect impacts on the resilience of the ecosystem, and thus its ability to store
carbon in the long term3. For example, one study suggested “Even forests
whose trees received full protection from a program such as REDD could, over
decades, lose carbon stocks through the ripple effects of bushmeat hunting on
species interactions” 4.
Direct effects of biodiversity loss on carbon storage
REDD initiatives are designed to control threats related to trees, such as
selective logging, fires or destructive collection of tree products. However, they
may not necessarily protect against the loss or destruction of non timber plants or
collection of animals. One of the most interesting examples of the potential
impact of biodiversity loss on carbon storage is the case of hunting – be it for
bushmeat or for commercial use – activities that are widespread across many
forested areas.
Poaching often focuses on large bodied vertebrates, and thus removes species
which tend to play critical functional roles in an ecosystem. Where top predators
(such as tigers) are removed from a forest, this can result in an increase in
herbivore abundance5 and in a forest context this may lead to over browsing of
seedlings and prevent regeneration of trees. Similarly the removal of large
herbivorous species (such as elephants), which would normally create small
clearings as a result of their feeding behaviour, has been linked to a decline in
tree regeneration6.
Bushmeat hunting of species which act as seed dispersers may result in a shift in
tree species composition, and could ultimately alter carbon storage potential although this process is still the subject of debate. Field studies in Thailand,
Cameroon and Panama have found that 70%-90% of tree species rely on animal
seed dispersal and that bushmeat hunting has a direct impact on tree species
composition4,6,7. In Cameroon and Thailand, the removal of large bodied seed
dispersers was linked to the loss of larger seeded trees, which are often those
that store the most carbon. However, others have questioned the impact of
bushmeat hunting on carbon storage, given an associated reduction in seed
predation8.
Changes in species composition – implications for carbon?
There is evidence that the loss of vertebrate seed dispersers can shift plant
species composition towards those with wind dispersed seeds, such as lianas.
This can result in a reduction in the net carbon stored in the forest.
For example, lianas grow quickly and are able to out-compete slower growing
trees for both light, water and soil nutrients9,10. This inhibits tree growth and
regeneration, and increases tree mortality. An increase in lianas within a forest
has been shown to negatively affect both the rate and volume of carbon storage.
This occurs for two reasons: firstly while lianas out-compete trees, their thin
stems and low wood density mean that they store relatively little carbon
compared to the trees which they replace10. Secondly, lianas will infest certain
species preferentially, causing a shift in species composition to faster growing
tree species, which often have lower wood density and store much less carbon11.
One model predicts a 34% decrease in carbon storage of a forest following liana
infestation2.
Biodiversity loss and ecosystem resilience
Unpredictable disturbances such as fires, natural disasters and invasive species
introductions - and the ongoing changes to temperature or precipitation caused
by climate change - all require ecosystems to adapt. Resilience of an ecosystem
(its ability to recover from such impacts) is a key concern – as a degraded forest
ecosystem quickly ceases to be a carbon sink and becomes a carbon source.
High levels of biodiversity can provide ‘biological insurance’ against losses from
disturbances, making the ecosystem more resilient and likely to recover, and
allowing it to continue storing carbon in the long term2. A 2009 report by the CBD
supported this, stating that “within a given biome, diverse forests are more
biologically productive and provide larger and more reliable carbon stocks,
especially in old-age stable forest systems...Hence, protecting and restoring
biodiversity serves to maintain resilience in forests, in time and space, and their
ongoing capacity to reliably sequester and store carbon”12
For example, a large fire may destroy several dominant trees and plants, but
quickly colonising plant species will take their place, producing the appropriate
environment to enable the subsequent recovery of larger, dominant species2.
This recovery is only possible if a diversity of species co-exist in the first place.
Similarly a biodiverse ecosystem is less likely to be severely damaged by the
introduction of an invasive, exotic species. For example, an ecosystem with
several natural predator species and a variety of plant species is likely to be less
susceptible to the introduction of a non-native pest species13,14. In a forest
context this may help to prevent large insect invasions, which are often linked to
tree die back. In a system of reduced biodiversity, invasions of pests may be a
serious threat – and may result in tree mortality and loss of carbon storage
function.
Resilience to the changing climate is also becoming a more important issue and
biodiversity is likely to strengthen an ecosystem’s ability to survive without
significant loss of above-ground carbon storage. One study concluded that
biodiverse ecosystems in Panama are likely to show greater resilience to a
drying climate as the presence of several drought tolerant species provides
‘biological insurance’ to counter the loss of other species2.
Additional indirect benefits of protecting biodiversity
Building biodiversity protection within REDD schemes adds extra value, beyond
enhanced carbon protection15. Maintaining biodiversity maintains other noncarbon functions of forests – for both local communities and wider ecosystem
service benefits - including opportunities for sustainable harvests, but also
maintenance of services such as water quality and pollination and erosion
prevention.
Text and research by Amy Hinsley
Literature cited:
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Reviews, 17: 1-19.
2 Bunker, D.E., DeClerck, F., Bradford, J.C., Colwell, R.K., Perfecto, I., Phillips, O.L., Sankaran, M., Naeem, S. (2005)
Species loss and aboveground carbon storage in a tropical forest. Science 310 (5750), pp. 1029-1031
3 Diaz, S., Hector, A., and Wardle, D.A. (2009) Biodiversity in forest carbon sequestration initiatives: not just a side
benefit. Current Opinion in environmental Sustainability 1: 55-60.
4
Brodie JF, Helmy OE, Brockelman WY, Maron JL. (2009) Bushmeat poaching reduces the seed dispersal and
population growth rate of a mammal-dispersed tree Ecological Applications, 19(4), 2009, pp. 854–863
5 Lyons, K., Brigham, C., Traut, B., Schwartz, M. (2005 )Rare Species and Ecosystem Functioning. Conservation Biology,
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6 Maisels, F., Keming, E., Kemei, M., Toh, C. (2001) The extirpation of large mammals and implications for montane
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Seeds, and Seeds Dispersed by Bats, Birds, and Wind BIOTROPICA 39(3): 363–371
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Vargas, P.N., Alexiades, M., Ceron, C., Di Fiore, A., Erwin, T., Jardim, A., Palacios, W., Saldias, M. and Vinceti, B. (2002)
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10 Wright, S., Hernandez, A., Condit, R. (2007) The Bushmeat Harvest Alters Seedling Banks by Favoring Lianas, Large
Seeds, and Seeds Dispersed by Bats, Birds, and Wind BIOTROPICA 39(3): 363–371
11 van der Heijden, G. M. F. and Phillips, O. L. (2009). Liana infestation impacts tree growth in a lowland tropical moist
forest, Biogeosciences Discuss., 6, 3133-3158,
12
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Change. A synthesis of the biodiversity/resilience/stability relationship in forest ecosystems. Secretariat of
the Convention on Biological Diversity, Montreal. Technical Series no. 43, 67 pages.
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(2000). Consequences of changing biodiversity. Nature 405 (6783), pp. 234-242
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contributions to invasion resistance and persistence of natives Oecologia 162 (3), pp. 709-718
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benefit. Current Opinion in environmental Sustainability 1: 55-60.