By Rob Finlayson

The benefits of harnessing scientific and local knowledge to enhance tree cover in farming landscapes are being overlooked primarily due to a lack of comprehensive data

The authors of the recent book, How trees and people can co-adapt to climate change: reducing vulnerability in multifunctional landscapes (World Agroforestry Centre 2011), argue that the micro-climatic effects of trees influence the properties assessed in climate-change prediction models, for at least as long as 30 years. These properties include shifts in daily average temperature, day–night temperature differential, humidity and wind speed. However, existing climate maps and climate-change projections are based on data and models that refer to ‘landscapes without trees’. This is the standard instruction for synoptic World Meteorological Organization (WMO) weather stations: avoid locations where tree effects influence the results. Explicitly adding the effects of trees to climate maps will expand the range of adaptation options.

The effects of trees at micro- and meso-climatic scales can be modelled as radiation, water balance and wind speed and compared to synoptic WMO data with various types of tree cover. With such information, scientists would be able to produce more accurate predictions and governments would be able to more realistically plan for climate changes. However, because trees are currently absent from WMO data, the task becomes much more complex.

“Recognition of the opportunities and limitations of these effects and respect for local knowledge systems that relate to them could lead to more locally appropriate adaptation planning,” argues the book’s lead author, Meine van Noordwijk, Chief Science Advisor with the World Agroforestry Centre.

Modifying tree cover in agricultural landscapes to adjust micro-climates for crops has a long history and should be acknowledged by governments in their planning for change, he claims. In the parklands of the Sahel, trees protect grain crops from excessive heat and maintain crop-zone soil moisture in critical periods; in the coastal zones of Southeast Asia, intercropping under coconut has a long tradition; on the mountain slopes where coffee, cocoa or tea provide farmers' incomes, manipulating 'shade trees' depending on elevation and local climate is relatively well studied but its use for vegetables and local food crops is less well understood. Temperatures measured under tree cover and in the open can vary around 2 ˚C. But, asserts van Noordwijk, none of this experience has yet made it into WMO data collection nor any nation’s climate-adaptation planning.

“We should acknowledge farmers' ecological and climatic knowledge and how they respond to changes, and test this knowledge,” he said. “If we learn how farmers use trees to modify their local climates and include tree effects in WMO data, then we are really starting to see the big picture from both perspectives, for the long-term benefit of us all.”