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Report Summary: Climate Change and Plants; Which Future?

1: An overview of current climate change

There is unequivocal evidence that the Earth’s climate is warming at an unprecedented rate. Temperature increases are geographically inequitable. Some regions, particularly at high altitudes and latitudes, are warming more than other areas. Other climatic effects, including prolonged droughts in arid and semi-arid regions, increased flooding in mid to high latitudes, and more extreme weather events are also increasing. Sea levels are rising. Climates are changing more rapidly than species can adapt and there is a high risk of mass extictions of biodiversity as the planet warms.

There is very good evidence that human activities that increase the concentration of greenhouse gases (GHGs) in the atmosphere are driving climate change. The Fourth Assessment Report (AR4) of the intergovernmental Panel on Climate Change (IPCC) stated that: “continued GHG emissions at or above current rates would cause further warming and induce changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century. For the next two decades a warming of about 0.2°C per decade is projected for a range of emission scenarios. Afterwards, temperature projections increasingly depend on specific emission scenarios.”

In other words, the future world climate depends on us and our ability to curb GHG emissions.

2: The physiological responses of plants to climate change

The diversity and distribution of the world’s terrestrial vegetation is the product of a complex suite of interactions between individual plants and a multitude of climatic and environmental variables. Plants are major regulators of the global climate, and their collective responses to increased atmospheric CO2 concentrations have clearly played an important role in mitigating climate change up to this point. The uptake of CO2 by plants during photosynthesis is the major pathway by which carbon is stored.

In looking to the future, it is increasingly critical to understand how plants respond on a basic level to the changes imposed upon them by continued increases in atmospheric CO2, as well as the cascade of climatic and environmental changes triggered by this increase. While plant responses to changes in single variables, such as CO2 or temperature, are increasingly well-understood, we have only just begun to understand how the interaction of these changes impacts plants and their role in regulating the global climate. Recent discoveries reveal just how much remains to be learned while illustrating the many ways in which the world’s plants can all-too-easily loose their ability to act as a global carbon sink, becoming instead yet another carbon source.

3: Observing and predicting plant responses

Understanding the effects of climate change on plant species and communities is a fairly recent conservation concern, but requires long-term data sets. Some such data sets exist, such as longterm phenological records for a few plant species, but analysis can be hampered because data collection protocols and species selection generally were not set up to answer contemporary questions. Similarly, experimental approaches can be prohibitively expensive and lengthy, so research in this field relies heavily on modeling. Models can be used for predicting responses of single species, multi-species assemblages, global vegetation patterns, and climate or hardiness zones. Models are only as good as the data and assumptions on which they are built and are continually improving as we refine and test them using data from past climate changes. While it remains important to scrutinise climate change predictions adequately, the scientific debate must not divert us from taking timely and appropriate action on both mitigation and adaptation.

The extent of global change is still IN OUR HANDS and scientific rigour should not replace action.

4: Plant community interactions

It is clear that different plant species will respond differently to climate change. Some species will stay in place but adapt to new climatic conditions through selection or plasticity. Other species will move to higher latitudes or altitudes. Some species may become extinct. Because of this, plant community composition will be reorganised, new communities will emerge and others will be lost. One of the biggest concerns of this community reshuffling is the disruption of food webs and coevolved mutualisms, such as the relationships between a plant and its pollinator or seed disperser. If species that rely on each other no longer co-occur in the same time or space, both may be driven to extinction. Diseases, pests, and invasive species may spread into new ranges putting more pressure on fragile communities. Maintaining biodiverse communities will become an even greater conservation priority.

5: Plant species at risk

In an era of rapid climate change, species have three basic alternatives, they can: 1) migrate to appropriate environmental conditions; 2) adapt to the new environmental conditions; or 3) become extinct. In a changing environment, ‘weedy’ species with fast generation times and wide ecological tolerances are more likely to adapt or migrate quickly and are more likely to flourish. Conservative species with specific habitat requirements or long generation times are more prone to the threat of extinction. At present an estimated one-quarter of vascular plant species are under threat in the wild.

With predicted temperature increases, changing hydrological cycles and other factors of climate change, as many as half of all plant species may be lost over the next century. This is a catastrophic scenario given the fundamental importance of plants to life on earth. As yet there is a lack of published information on plant extinctions directly due to climate change but with baseline information now being collected on the distribution, threat status and ecology of various plant groups, monitoring schemes can be established. Plant species restricted to high-risk habitats, including montane, island or coastal habitats are likely to be the first casualties of climate change. Plant conservation action needs to be increased now to ensure that options are available for the future.

6: Ecosystems at risk

An ecosystem is an array of living things (plants, animals and microbes) and the physical and chemical environment in which they interact. Healthy ecosystems provide the conditions that sustain human life through the provision of a diverse range of ecosystem services. Plant diversity underpins terrestrial ecosystems and they are often described according to the major vegetation type they consist of. Many ecosystems will be highly vulnerable to projected rates and magnitudes of climate change and the services lost through the appearance or fragmentation of ecosystems will be costly or impossible to replace. Forest ecosystems are particularly important, containing as much as two thirds of all know terrestrial species and storing about 80% of above-ground and 40% of belowground carbon. Deforestation is a major source of greenhouse gas emissions and contributes to loss of species as well as changes in regional and global climate. Reducing deforestation is herefore one of the most effective ways of reducing greenhouse gas emissions. Ecosystem responses to climate change will be complex and varied. Climatic changes will essentially affect all ecosystem processes but at different rates, magnitudes and directions. Responses will vary from the very short term response of leaf-level photosynthesis to the long-term changes in storage and turnover of soil carbon and nitrogen stocks.

7: Linkages between climate change, plants and livelihoods

Agroecosystems face many of the same threats from climate change as species in natural cosystems, including the spread of diseases, pests and invasive species and problems adapting to new extremes in temperature and rainfall. Ecosystems managed for agriculture are dependant on the goods and services provided by natural ecosystems. As with natural ecosystems, the key to adaptation is maintaining genetic diversity and it is crucial to conserve crop diversity and crop wild relatives to meet the needs of agricultural breeding programmes. Biofuels have been touted as one way to reduce greenhouse gas emissions but they are far from a panacea. Increased biofuel production may drive up food costs for many staple foods, including maize, decreasing food security. 

Even if non-food crops are used for biofuels, the carbon footprint of fuel production can be significant if intact plant communities are cleared for plant production. Many of the world’s poor depend directly on harvesting non-timber forest products, edible, medicinal and aromatic plants for livelihoods and sustenance. With increasing human pressure and loss of natural vegetation, many of these species are under threat. Climate change will further threaten these species and, as a consequence, the people who depend on them.

8:  Managing the impacts of climate change on plant diversity

It is clear that many species of wild plants are likely to become extinct within the next century, and, at least for some communities and ecosystems, climate change is already imposing huge costs. Uncertainty about how climate change will unfold or what the response of species and habitats will be, must not prevent us from taking urgent action now. Conserving plant diversity will help in the maintenance of carbon sinks and will ensure options for future plant use under different climatic conditions. The Global Strategy for Plant Conservation (CBD, 2002), and achieving its 16 plant conservation targets for 2010, becomes even more important in the light of climate change. It also provides a useful framework for amending or developing additional plant conservation targets post- 2010, many of which are outlined below. The richness of future biodiversity depends on how we act and what we conserve today.

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