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Tropical botany researcher

2 Posts tagged with the kew_gardens tag
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When I joined Kew on secondment as a botanist last year I hadn't really expected to be negotiating the sourcing and planting of ca. 25,000 tree seedlings in the Bolivian Amazon. Many possibilities went through my mind, but not that one. That is what makes being a botanist so much fun! Contrary to the stereotype, you never know where your knowledge and contacts will lead you next.

 

Terry Pennington, Bente Klitgaard and myself are now in the Bolivian Amazon as part of a Kew Garden's Darwin Initiative project to reduce pressure on the incredibly biodiverse forests of the Bolivian Amazon, amongst the richest in Amazonia.

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The opening of new roads - an initiative by the Bolivian Government to give land to the landless rural poor of the Andes - and pressure on the land from Brazil are important threats to the future of much of the forest. Devising approaches to agriculture and forest use, and raising awareness of the economic and ecological value of these forests are tools that can reduce and mitigate some of these threats.

 

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View from the air of the Cobija area of the Bolivian Amazon.

 

As part of this aim we plan to introduce a very old but largely abandoned type of agroforest farming based on a group of trees in the bean family known as Inga. These trees grow very quickly (3m in the first year) and are able to tolerate very damaged and degraded soils such as those found in cattle farms or abandoned soya or pineapple plantations. These forms of farming are very profitable in the short-term but soon exhaust the ancient soils often found in the tropics and on which the tropical forest grows.

 

The result is that a farmer or agribusiness needs to clear forest on a regular basis to maintain an economic yield and leaves degraded pasture, a kind of grassy desert, in its wake. What we are aiming to do is provide a technique whereby farmers can restore this exhausted land to productivity, for growing food, fruit trees, cash crops, timber or even fodder and at the same time obtain a plentiful supply of fuelwood for cooking. This is known as Inga agroforest.

 

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Left: A two-year old Inga tree near Cobija. Right: Inga fruit with seeds below (click images to see them full size)
Inga has a pod within which are seeds (green) covered in a white, fluffy, very sweet and juicy flesh. The tree is commonly grown for its fruit but also has tremendous potential for the restoration of degraded land in Latin America, as it is very fast growing and tolerant of damaged soils.

 

The Inga agroforest approach involves planting dense alleys of Inga seedlings spaced several metres apart and letting them grow for 2 years, by which time they are about 6 metres tall (see photo above). Then all their branches are removed and a crop of beans, cassava, maize, Cacao or whatever is wanted is planted.

 

The Inga branches grow back very quickly and need to be cut every 6 months, providing a valuable source of fuel wood for cooking. The key to this system is that once the Inga trees are about 6 metres tall their side branches meet and so completely cover the alley, thereby suppressing weeds. And, just as importantly, they generate a rich leaf-litter that forms the basis of a nutritious soil for whatever crop is to be planted subsequently.

 

So far we have identified a number of trees that could act as sources of seed from three or four species, including one community that could probably provide all of the seed that we need, a good sign for our first day out in the field!

 

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Inga fruit with its seeds exposed to show their covering of edible white flesh.

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Since September 2012 Anaité López (Instituto Nacional de Bosques, Guatemala), Tim Marks (Millennium Seed Bank) and Wolfgang Stuppy (Millennium Seed Bank, do visit his amazing blog) have been working at the Millennium Seed Bank to develop a long-term storage protocol for the seed of the Maya Nut tree (Brosimum alicastrum).

 

This is important because Maya Nut is a significant famine food for the rural poor in northern Central America and is being actively used in reforestation projects as it is fast growing and relatively tolerant of disturbance.  At the moment, however, it is not possible to store the seed for more than a couple of weeks making it very difficult to deploy seed as and when it is needed outside of the fruiting season.

 

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Left: Maya Nut (Brosimum alicastrum) fruit - Fruit as it is when still on the tree

 

Right: Maya Nut (Brosimum alicastrum) seed - Seed once stripped of the fleshy outer layer by bats or birds (left), with both papery coverings removed (centre), with only the outer of the two papery covering removed (right)

 

The work involved collecting about 5,000 seeds from Maya Nut forests in the Peten of north eastern Guatemala. The seed was then shipped to the Millennium Seed Bank by courier where it was unpacked and studied by Anaité who had flown over from Guatemala for six weeks to undertake the work under the supervision of Tim Marks and Hugh Pritchard, specialists in seed research and storage. This was an opportunity for her to take back the skills and knowledge that she had learnt to Guatemala. The work has been funded by Defra through the Darwin Initiative (project 18-010) and is taking place incollaboration with the Maya Nut Institute.

 

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A batch of Maya Nut seeds being germinated following controlled storage. Image courtesy of Anaité López.

 

Our plan was to devise a regime of cooling and drying the seed that would enable it to be cryogenically stored (frozen) and so stored for many years. To do this we needed to identify the best rate at which to drop the temperature and humidity whilst keeping the seed viable. This involved storing the seed at different temperatures and humidities and taking a batch out and germinating it every month.

 

Given that this seed does not survive for long in the wild and that it is protected by two very thin, papery coverings (see above) we expected it to be very prone to dessication and so sensitive to low humidity. In fact we found quite the reverse. Six months later we are still germinating seed that has retained most of its moisture after having being stored in a dessicant for all this time!

 

In order to understand how this could happen we contacted seed morphologist Wolfgang Stuppy, world expert on seed morphology. He made the following images of sections through the seed which show a thin but dense layer of cells that control waterloss from the seed:

 

 

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Section through Maya Nut seed showing the dark outer layer that might reduce water loss. Image courtesy of Wolfgang Stuppy.

 

So we now have a partial explanation as to how the seeds can show such remarkable tolerance to drying out. It does, however beg two questions:

 

  1. Why do seeds not survive under the conditions of the forest floor?
  2. Why would a tropical tree that grows in the humid tropics develop such a remarkable resistance to drying out?

 

To be continued maybe...