̽��ֱ�� of Cambridge - Mangrove

Mangroves could survive sea-level rise if protected

tdk25 — Wed, 31 Jul 2013 07:44:32 +0000

Mangroves, which provide a natural coastal defence to communities around the world, may be able to withstand a future rise in sea levels far more than previously thought, scientists have found.

Their report should serve to allay fears that many mangrove areas could be lost in the coming decades as sea levels go up because of global warming.

It comes, however, with a cautionary note: ̽��ֱ��authors, who have carried out a rare and detailed survey of how mangroves adapt to their environment, also argue that it is vital that they are managed and conserved so that they can continue to provide this protection.

̽��ֱ��survey warns that human activity on land – such as the damming up of rivers or the felling of trees to create shrimp ponds – is currently a far greater threat to many mangrove habitats than the effects of climate change on sea level.

Mangroves – trees and shrubs which grow in saltwater, coastal environments – play a critical role in protecting thousands of shoreline communities in tropical and subtropical regions from floods, storms, and other hazards.

Their densely-packed, overground root systems can absorb wave energy and reduce the velocity of a sudden surge of water. In the 2004 tsunami, for example, mangroves were sometimes the difference between life and death for people whose homes lay in the path of the giant waves which crashed into shorelines around South Asia.

For some time, scientists have been concerned that if sea levels rise as predicted, they will kill off mangroves – removing these natural coastal defences at the very time they are expected to be needed most.

̽��ֱ��new study suggests that this is far less likely than previously thought, however. Dr Anna McIvor, from the ̽��ֱ�� of Cambridge, and the report’s lead author, said: “Although we can expect some mangrove areas to be lost as sea levels rise, many of them appear to be able to withstand it.”

“In fact, changes to mangrove habitats through human activity are likely to pose a bigger threat to these coastal defences than sea level rise as it stands. Our research has enabled us to find out more about how mangroves continue to flourish in spite of a rise in sea levels – but that information should be used as the basis for better management of these important ecosystems.”

̽��ֱ��study was carried out by a team from ̽��ֱ��Nature Conservancy, Wetlands International, and the Cambridge Coastal Research Unit (based in the ̽��ֱ��’s Department of Geography). ̽��ֱ��researchers examined both recent reports looking at surface elevation in mangrove areas, and the historical reasons why mangroves have, in some places, persisted for thousands of years.

They found that the height of the soil surface in mangrove areas is often “surprisingly dynamic”, and in some cases appears to be building up at rates of between one and 10 millimetres every year. ̽��ֱ��global mean sea level rise is currently 3mm per year, meaning that many mangrove areas build up soil at a rate which keeps pace with the sea.

There are several reasons for this, but chief among them appear to be the ability of mangroves to trap sediment as it is carried down to them by rivers, and the work of their roots beneath the surface. “Mangroves provide much of the organic sediment matter that makes up the soil, their complex roots help to bind and trap the sediments on the soil surface, while the unseen growth of roots beneath helps to build up the soil from below,” McIvor said.

Despite this resistance to changes in sea level, however, the report cautions that the future stability of mangroves is by no means guaranteed. “Threshold rates of sea level rise are likely to exist, beyond which mangrove surfaces are no longer able to keep up,” the authors point out.

Perhaps more urgently, in some regions human activities like agriculture and construction are being authorised regardless of their impact on the ecosystems which enable mangroves to thrive.

In some countries, for example, rivers which play a vital role by carrying sediment to the mangrove areas so that the soil can be built up are being dammed or diverted. Another common threat is aquaculture: in Indonesia, and other South Asian countries, mangroves are often cut down without restriction to make way for shrimp ponds.

̽��ֱ��report also warns that mangroves may need room to expand landward, especially where conditions are such that sea level rise may still be a threat to their growth. Communities which rely on them for coastal defence need to leave space to ensure that this can happen, the authors advise.

Dr Mark Spalding, from ̽��ֱ��Nature Conservancy and the Department of Zoology, ̽��ֱ�� of Cambridge, said: “This report shows that well-managed mangroves in many places will continue to support and safeguard many vulnerable communities as sea levels rise. We still have lots to learn about them, but the sensible, precautionary approach is to look after them and restore them as a critical first line of defence.”

̽��ֱ��full report can be downloaded at: http://coastalresilience.org/science/mangroves/surface-elevation-and-sea...

For more information about this story, please contact Tom Kirk, Tel: 01223 332300, thomas.kirk@admin.cam.ac.uk

Human activity is currently a bigger threat to mangroves, and the natural defences they provide against storm surges and other coastal disasters, than rising sea levels, according to a new study.

Although we can expect some mangrove areas to be lost as sea levels rise, many of them appear to be able to withstand it.

Anna McIvor

Wikimedia Commons.

Mangrove trees along a coastline, Everglades National Park.

This work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page.

Yes

Climate change: can nature help us?

Anonymous — Wed, 08 May 2013 11:05:19 +0000

Flooding, landslides, crop failure, water shortages. Across the globe, the frequency with which humans are suffering the ill effects of climatic variability and extreme weather events is on the increase. Can natural environments be used effectively to help people adapt to the effects of climate change? ̽��ֱ��first systematic review of this question – facilitated by the Cambridge Conservation Initiative (CCI) Collaborative Fund for Conservation – finds much evidence of their effectiveness.

" ̽��ֱ��delays in international agreements on ways to reduce global greenhouse gas emissions mean that planning to counter the impacts of climate change is a necessity,” said Robert Munroe, Climate Change Officer at BirdLife International. “Governments of all countries should be making plans to protect us against these impacts.”

One adaptation option is to invest in costly, large-scale structures such as sea walls, irrigation systems and dams. But while their short-term impact is clear, these solutions lead to ever-increasing maintenance costs and often have negative impacts on local ecosystems and biodiversity.

“International policy makers are having to think about the different approaches they could take, but the problem is that they don’t have enough information to make informed decisions,” said Munroe.

“Hard-engineered sea walls have a limited life span, and we know that they change wave and tidal currents, often to the detriment of saltmarshes or mangroves that act as a natural buffer to storm surges and coastal erosion. Do we really want to lose these buffers and face increasing costs of sea wall maintenance?” asked Dr Iris Möller, Deputy Director of the Cambridge Coastal Research Unit in the Department of Geography.

“There’s anecdotal evidence from events like the 2004 Indian Ocean tsunami that villages surrounded by mangroves were significantly less affected by the tsunami than more exposed areas,” she added. ̽��ֱ��mangroves may have saved thousands of lives and properties by absorbing a large proportion of the energy in the waves.

But local anecdotal evidence is not enough to provide a reliable measurement of the effectiveness of an approach. Now a review has been completed of the effectiveness of natural approaches to buffering the effects of climate change. Termed Ecosystem-based approaches for Adaptation (EbA), this relatively new concept incorporates approaches that have been used for a long time to address climatic variability, but not necessarily in the context of adaptation to climate change.

“We wanted to understand what the research evidence tells us, in terms of the relative importance of ecosystems as opposed to hard-engineering solutions to the same problem,” said Dr Bhaskar Vira in the Department of Geography. Vira, Möller, Dr Tom Spencer (Director of the Cambridge Coastal Research Unit) and Dr Andreas Kontoleon (Department of Land Economy) worked with climate change policy expert Munroe at BirdLife and climate change expert Dr Nathalie Doswald at the United Nations Environment Programme World Conservation Monitoring Centre, as well as with the International Institute for Environment and Development in London. They looked at published studies from around the world in which a wide range of EbA had been assessed. ̽��ֱ��step-by-step detail of their systematic review method was published in Experimental Evidence in 2012, which will enable it to be replicated for consistency in future studies.

“ ̽��ֱ��systematic review is very specific: we sifted out the most relevant published studies and compiled evidence from them on the different interventions being used and how effective they have been,” said Vira. ̽��ֱ��team found that activities related to EbA have been used across the globe to address a broad range of climatic hazards and impacts.

Interventions include the sustainable management of wetlands and floodplains to act as floodwater reservoirs and provide important water stores for times of drought, and the conservation and restoration of forests and natural vegetation to stabilise slopes and regulate water flows, preventing flash floods and landslides due to increased rainfall. Most of the approaches were reported by the studies to be effective in reducing human vulnerability to the effects of climate change, climatic variability or natural hazards.

“ ̽��ֱ��results are providing general guidance on the circumstances in which an EbA may be useful,” said Vira. “There are cases where it isn’t necessarily going to be helpful – if you live in Gloucestershire and you’re about to get flooded, you can’t start planting trees, you have to use sandbags. These interventions take time, and there are limitations to their effectiveness.”

“It’s important to work towards fully informed decision-making between alternative adaptation approaches,” said Munroe. “Large-scale infrastructural solutions may tend to be pursued because the financial costs are clear and their short-term effectiveness at buffering hazards has been tested by engineers. But by constraining natural ecological cycles, they may increase social vulnerability in the medium to long term. We found some discussions on the comparison between ecosystem-based and other kinds of approaches to adaptation, which are valuable for policy makers.”

“We also realised there are some real knowledge gaps,” added Möller. “We need information on the costs as well as the benefits, and on whether monitoring systems have been put in place to assess the long-term effectiveness of these approaches. With respect to ecosystems as coastal protection, for example, we need to know exactly how much energy mangroves and marshes absorb and what we can do to maximise and maintain the effect.”

̽��ֱ��project collaborators recognise that the divide between scientific research and policy making must be bridged if governments are to make the best decisions for long-term adaptation to climate change. “Our partnership with NGO colleagues meant the project has both academic rigour and a built-in pathway to impact,” said Vira. ̽��ֱ��Collaborative Fund for Conservation, which was established with the generous support of the Arcadia Fund, was set up explicitly to foster these innovative partnerships.

̽��ֱ��team’s collective range of contacts has enabled them to disseminate their results and recommendations. Their presentations at the United Nations Climate Change Conference in Durban in December 2012, and the distribution of briefing papers and guidance documents, have drawn the attention of decision-makers at the highest levels to the possibilities of ecosystem-based approaches.

“A technical workshop on EbA, likely to involve 70 countries, was recently convened by the Climate Change Convention,” said Munroe. “Our work contributed to the momentum that resulted in this decision. It’s really exciting as it’s the first time the Convention has met to discuss this approach.”

“EbA is an important tool in the adaptation toolkit, which has often been ignored because the evidence base had not been made clear,” said Munroe. “Employing it alongside other adaptation options will result in much more sustainable responses to the effects of climate change in both developed and developing countries.”

Hard-engineered sea walls have a limited life span. Could saltmarshes and mangroves offer a different approach to buffering against storm surges and coastal erosion?

Do we really want to lose these buffers and face increasing costs of sea wall maintenance?

Iris Moller

Saltmarshes starting to be inundated by the tide at Abbots Hall, Cumbria, UK

This work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page.

Yes

Licence type:

Attribution