Shifts in Biomes!

Hello everyone!

I was going through some articles yesterday and I found this diagram on the right that nicely summarize some ideas I intend to focus on in my blogs. It shows a range of ‘climate’ change mechanisms that are likely driving responses from biodiversity (pink box), and potential impacts/responses from different levels of biodiversity (blue box).  The reason why I highlighted ‘climate’ because there are other factors that we must never forget, such as land use change, exploitation of resources and so on…. that are also driving recent responses observed!

Today I’ve chosen to focus on the bottom of the diagram (ironically at the very top of the biodiversity chain) – BIOMES. Unlike last week, I am going to explore at a higher level of biodiversity, and how climate change is affecting vegetation communities worldwide that can potentially be devastating enough to have an impact on biome integrity.

 Predicted aspects of Climate Change (Pink box) 

and examples of potential effects on different levels of biodiversity (Blue Box) 

What are Biomes?

For those that haven't crossed paths with this term, biomes are essentially large geographical areas with flora and fauna (plants and animals) that have common characteristics due to similar climates over a range of different continents. They are often defined by abiotic factors, such as soil types, climate patterns, relief, and vegetation. Here’s a simplified map version of major biomes on earth:

                                             Simplified version of major biomes on earth

Importance of Biomes

One of the main concerns of anthropogenic climate change has been the potential response from terrestrial biosphere. It is not surprising owing to its importance for us, such as supplying us with timber, food and other life essential… as well as for ecosystem around the world. It plays a large role in maintaining biodiversity, carbon sequestration and feedbacks in the biosphere. Changes in vegetation structure will largely influence the balance and equilibrium of the ecosystem; for example, it could influence runoff and hence the amount of seasonal streamflow; as well as habitats that will modify species interaction and trigger widespread responses from the ecosystem.   

Climate changes and its impacts on biomes

There are considerable evidence that suggest anthropogenic climate change is already driving changes in vegetation structure, distribution and productivity. The underlying effect of global warming on vegetation structure mainly resides in the biochemical and physiological influences of temperature, atmospheric CO2 concentration and water availability on terrestrial plant growth. In warmer regions, it is predicted that forest dieback may occur and terrestrial plants may face water stress due to the increases in temperature (causing faster evapotranspiration) and a potential reduction in precipitation in certain regions. Whereas, in mid-to-high latitude areas that are more chilly, predicted rise in temperatures will cause a longer growing season and an increase in vegetation productivity (NPP).  But also, other factors such as increases in wildfire and changes in climate that exceed the physiological thresholds for vegetation may alter plant mortality and recruitment in an area. The replacement of more dominant and resilient species that are able to tolerate the changing conditions can result in an entire shift in biome of an area. Therefore, as global warming continues to take place, how vegetation patterns will change is expected to vary considerably amongst different regions.

Current Shifts

It is clear that climate change is shifting vegetation both latitudinally and elevationally worldwide. Researchers at University of California, Berkeley estimated that between 1901-2002, mean temperatures increased significantly on 76% of land worldwide, especially in subarctic, temperate and boreal ecosystems. Biome shifts that have been noticeable include dieback of trees and retracting of woodlands to grasslands in the Sahel, reducing ecosystem services it brings to many people (forest wood for cooking / supply of water) in that region. Nevertheless, the noticeable process of shrublands encroaching onto Arctic tundra is also a huge problem for many endangered species.

Picture showing a mixture of grassland
 and woodland - shifts observed in Sahel

Map showing the Sahel region

However, one of the main concerns that ecologist and scientists have raised are ‘tipping points’, where exceeding ecosystem thresholds may potentially cause irreversible shifts and changes in major biomes. A study showed that tropical biomes, such as rainforest, desert and savanna in Africa and South America are tied to certain climate tipping points, where when climate thresholds exceed they don't gradually shift through intermediate states, but rather ‘tip over’ where they suddenly switch to other ecosystems.

Future predictions

In terms of future predictions, Alo and Wang (2008) simulated 8 different GCMs climate projections with a global vegetation model to estimate changes in vegetation near 2100. They found a consistent pattern of poleward expansion and treeline shift of boreal and temperate forests towards higher latitudes at the expense of tundra and alpine ecosystems across all the GCM scenarios. They also suggest that a widespread vegetation degradation in the tropics will occur, especially in South Africa and South America due to an increase in drought deciduous trees at the expense of evergreen trees due to changing moisture conditions.

Similarly, Lapola and his colleagues’ analysis on potential future distribution of biomes in tropical South America suggests that increases in carbon dioxide concentration and/or drier season persists longer than four months, then Amazonian rainforest could likely be replaced by drier biomes, such as shrublands, tropical savannahs and even semi-deserts.

Picture showing Amazonian Rainforest.... that in the future could potentially look different from a shift to drier biomes

… To avoid this we need to manage!

To avoid this, adequate adaptation measures must be put in place according to vulnerability by ecologist. But also a significant reduction in greenhouse gas emission must be made to avoid the potential devastating consequences to global vegetation – which also will have potential impacts on wildlife, species interaction, biosphere feedbacks and last but not least...our (human) well-being! 

Personally I think that instead of focusing on individual species (not saying that they aren't important), but maybe we should focus more on researching/mitigating/managing biomes and ecosystems. If we can't secure ecosystems and habitats that are deemed as essentials for species, then many species without adequate adaptability mechanism will lose out giving that some ecosystems are tied to certain 'tipping points'. What do you think? 

Anyways! Have a great week and see you all in a few days :)