31 December 2015 [BR for Everyone]
2015 Mediareview

With our best wishes to our readers for the coming 2016, here we provide a brief account of some biotic pump discussions that took place in the second half of 2015. These discussions reflect how successful (or unsuccessful) we and our colleagues have been in spreading the biotic pump message and explaining its importance.

Quote: "An essential point is that the biotic pump moisture transport is a very complex mechanism that is controlled by vegetation. A great variety of biochemical substances emitted by plants and the associated biota change the dew point (which depends on how clean the atmosphere is). This gives a physical possibility to the forest to switch condensation on/off at different amounts of atmospheric water vapor. These forest properties are different at different stages of forest succession. E.g. in our boreal zone early successional species are all leafy, so they cannot provide a significant evaporation flux early in spring when the foliage has not yet developed. Primary coniferous species like spruce start photosynthesis and transpiration immediately with the onset of warm weather. Therefore, large-scale destruction of primary forests and their successional re-growth via the stage of deciduous trees can trigger continent-scale biotic pump disruption and associated climatic shifts that will last for decades.
This is to emphasize that reforestation must really be SMART, i.e. it should take into account the stability of the forest ecosystem itself. Reforestation seen just as re-planting (as done in China) is a dead-end. Lots of territories that are now occupied by what we city-dwellers would call a "forest" is in fact just a slowly or rapidly degrading tree-covered land, not self-sustainable forest ecosystems with a high climate mitigation potential as they used to be. We need a totally new, cutting-edge science of forest medicine to start returning our land to a self-sustainable state."

This policy brief was presented on the Global Landscape Forum in Paris 6 December 2015. Quote: "In June 2015, over 30 experts in the fields of Earth and plant sciences convened in Leuven, Belgium, to discuss the latest scientific findings related to forest, water, soil and atmosphere interactions. They consolidated research showing how forests regulate water and climate, not only at local,watershed and catchment scales, but also at regional, continental and global scales. This policy brief reflects these findings.

What forests do

  1. Forests promote precipitation.
  2. Trees and forests are natural cooling systems.
  3. Forests generate air and moisture flows.
  4. Trees and forests can improve groundwater recharge.
  5. Forests can moderate flooding."

Quote: "One way forests may move water is known as "biotic pumping." As water transpires into the atmosphere above the forest, the theory holds, it creates a low-pressure system that sucks in air surrounding it, eventually and continually pumping moisture inland from the ocean. Cutting down forests degrades these low-pressure systems, essentially turning off the pump."

Quote: "Reputed experts will address diverse questions as: how does tropical deforestation and land degradation influence rainfall patterns, temperature and atmospheric dynamics; what are the myths and realities of the roles forests on water and in watersheds; how important are forests work as a rainfall recycler or as a biotic pump bringing moisture from oceans to the inlands; what do we know about the impact of climate change on microclimate? Are we on the right track in translating the newest insights into research agendas, policies and management practices of forested landscapes?"
See a more detailed report on the meeting here.

Quote: "Antonio Nobre: You know, it's like love. Love is the only quantity that increases the more you give. And so the trees do this, lower the pressure during a drought, pull the moisture from the oceans and counter the droughts... When you come with the chainsaw and the bulldozer and fire, then forest doesn't know how to handle this. That's what I call the Achilles' heel of the rain forest..."

Compare this view of the biotic pump as love to its description as an investment:
Native species that form natural forest communities have evolved a complex set of genetically encoded biophysical and morphological traits that make the biotic pump possible. These traits took hundred million of years to evolve and are different in different regions of the world. The need to keep evaporation high for running a rich water cycle explains one of the long-standing biochemical puzzles - why plants appear to be "wasteful" of water during photosynthesis. The apparently low water use efficiency of plants has been traditionally interpreted as an "unavoidable evil", "land plants dilemma" etc. This implies that biological evolution was unable to produce a more efficient biosynthesis process that would use water more sparingly (Cramer et al., 2009). However, there are many plants, especially in the arid environments, that have a much better water use efficiency than the global average, so the evolutionary explanation ("bad luck") is apparently not valid. The biotic pump explains that plants benefit from spending more water vapor as moisture returns to them with surplus owing to the moisture convergence initiated in a moist atmosphere by high evaporation. The biotic pump is a clever investment of moisture: the forest must spend it wisely to gain more in return than it has spent.

Trees meet the ocean

See also our photogallery "Five days in the rainforest" (Colombia, November 2014).