from Part VI - Terrestrial Forcings and Feedbacks
Published online by Cambridge University Press: 05 November 2015
Chapter Summary
This chapter examines the biogeophysical coupling between terrestrial vegetation and climate. Daisyworld is first introduced as a simple model of coupled climate–vegetation dynamics. The Daisyworld model illustrates the potential for regulation of climate by vegetation. More realistic examples of climate–vegetation interactions occur regionally in response to gradients in precipitation or temperature. The gradient from tropical rainforest to tropical deciduous forest to savanna to desert represents increasing aridity. This gradient is not only a response to soil moisture but also feeds back to affect climate, especially precipitation. An example of this is in northern and western Africa, where climate model simulations demonstrate that the expansion of vegetation into desert in response to increased rainfall feeds back to increase rainfall. Another example is the boreal forest–tundra ecotone. The transition from forest to tundra relates to cold temperature. Numerous studies show that the northward migration of trees in response to climate warming feeds back to accentuate the warming; loss of tree cover with a cold climate reinforces cold temperatures. These studies indicate widespread changes in vegetation structure and biogeography in response to climate change are likely to themselves change climate. Carbon cycle feedbacks are considered in Chapter 29.
Biogeophysical Feedbacks
The studies outlined in Chapter 26 highlight biogeophysical processes by which Earth's land and its vegetation affect seasonal-to-interannual climate variability. Changes in vegetation structure, composition, and biogeography in response to long-term climate change similarly feed back to influence climate change. This arises from differences among vegetation in albedo, surface roughness, leaf area index, rooting depth, and canopy conductance.
The albedo of land varies with surface characteristics (Table 12.1). Vegetation generally has a lower albedo than bare soil; forests have a lower albedo than pastures or croplands. As a result, changes in vegetation such as grassland degradation or expansion and forest loss or woody encroachment alter surface albedo. An increase in surface albedo decreases net radiation at the land surface and reduces heating of the atmospheric boundary layer as well as water vapor in the boundary layer. A positive feedback develops if these changes decrease precipitation because drier soil directly increases albedo and further reduces vegetation cover (Figure 27.1a).
To save this book to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.