BOTTLE REFORESTATIONA new method to combat desertification

Willem VAN COTTHEMUniversity of Ghent (Belgium)

All over the world tree nurseries use plastic bags (mostly black ones) to grow tree seedlings. Generally speaking, these seedlings are taken to the plantation site in their plastic bags, where the bags are cut open and the root ball is positioned in the planting pit. During that generally rough handling, the root ball is usually broken and the roots damaged, causing a lot of difficulties to get the seedlings growing due to transplant shock.

It is well known that many people, after tree planting in the field, do not take care of those useless pieces of plastic bags, which are then left (littered) at the planting site. That is one of the reasons why one can find plastic nursery bags almost everywhere at plantation sites, polluting the environment (trees are blooming with colored bags).

Considering the heavy pollution load of plastic bags on the environment, and considering that billions of plastic bags are used every year at the global level, we have been looking for a more efficient and cheap alternative.

Experiments with plastic bottles showed that this can be an interesting solution to:

(a) Reduce the damage to the root system at planting time.(b) Reduce the volume of irrigation water needed to keep the seedlings alive (higher

water use efficiency WUE) before and after transplantation.(c) Enhance biomass production in a shorter period (stronger seedlings).(d) Enhance survival rate of the tree seedlings.(e) Enable reforestation at the most hostile locations.(f) Avoid pollution of the earth’s surface with plastic nursery bags.

Tree seedlings grown in bottles can very easily be transported to the plantation site without significant damage to the plants and their root system. This makes this method very interesting for large-scale afforestation or reforestation programmes. Therefore the method is called “bottle reforestation” or “bottle afforestation”.

Different variants of growing tree seedlings in bottles can be used. The first will be described below, others will follow.

Growing seedlings in plastic bottles – Variant 1

The simplest method is illustrated in a few steps:

2010 - Fruit juice bottle 15 cm (6 inches) high

2010 - Two perforations 2,5 cm (1 inch) above the bottom let a possible surplus of irrigation water run out of the bottle (to avoid acidification of the potting soil inside and to avoid asphyxiation of the roots)

2010 - Willow tree (Salix matsudana) cuttings, rooting in water for 1-2 weeks

2010 - Rooted willow cutting planted in plastic bottle filled with potting soil. Only a minimal quantity of water is needed to keep the potting soil moistened for a very long period (almost no evaporation).

2010 - Soon after planting the cutting in the bottle new shoots are formed and many new roots are growing towards the bottom of the bottle.

2010 - In less than 1 month a young willow is developed, ready to be planted.

One can also plant 2-3 willow cuttings in a bottle filled with potting soil (left). A lot of irrigation water is saved, because evaporation is low (percolating water stocked at the bottom 2,5 cm and evaporation occurs only at the surface of the potting soil in the bottle, thus less influence of the wind).

Once the young trees have developed a good root system, with a bunch of roots sitting at the bottom, the bottles can be transported to the plantation site. One can expect less damage to the roots than with the classical plastic bags, because the root ball sits well fixed inside the bottle.

Planting the young trees

At the plantation site, plant pits with a diameter of 2-3 times the diameter of the bottles are prepared. Each bottle is placed close to a plant pit.

With a pair of scissors the lower part of the bottle (e.g. 2,5 cm or 1 inch) is cut off, leaving the bottom part of the root ball hanging out of the bottle (again less damage to the root ball than with plastic bags).

After pouring some water in the plant pit, the bottle with its young tree is placed at the bottom of the plant pit so that the lower part of the root ball touches the humid soil and the top of the bottle is level with the surface of the plantation site.

The plant pit is filled with the surrounding soil and some additional water is poured in the bottle. That water will run through the bottle, where is makes the root ball completely moistened and the surplus will run into the local soil, moistening the bottom part of the root ball hanging outside the bottle.

Thus, the young tree will not get a serious transplant shock and it will swiftly continue its growth in the local soil, keeping survival rate very high, even if post-plantation irrigation is difficult or impossible.