Turning a rice paddy into a natural forest ǀ Mortality rate ǀ 5 months after planting
Endangered Trees community organization engaged in a reforestation project in Baan Cha Niang Village, Surin (Thailand) together with Onetreeplanted.org.
Six planting sites were selected and the planting took place between April and August 2021. One of the six planting sites, an expired rice field belonging to a local farmer (Ean Promsri), was selected for statistical analysis.
The other planting sites were a natural forest, a rubber tree plantation, a piece of land in front of the house of a local farmer and two sites belonging to the municipality (around the lake).
On 23rd April 2021, a total of 547 trees were planted on the land of Ean Promsri. Five local tree species and two alien species were selected for the planting purpose. The two alien species were Mahogany, originally from the Caribbean and Ceylon Ironwood, originally from Sri Lanka. We use abbreviations throughout the analysis as shown in below list:
MAH Mahogany (Swietenia macrophylla King).
RES Resin Tree (Dipterocarpus alatus).
ROS Siamese Rosewood (Dalbergia cochinchinensis).
AMB Amboyna (Pterocarpus indicus)
TEA Teak (Tectona Grandis)
IRO Ceylon Ironwood (Hopea odorata)
M1 One month after planting
One month after planting, we lost 77 trees among which were 29 Rosewood trees, making Dalbergia cochinchinesis the worst performing tree species.
The second month, 83 trees were lost among which 42 Burmese ironwood. With 46 dead trees of a total of 108, survival rate of Ironwood was only 57% two months after planting.
By mid June, 71% of the trees were still alive with teak the best performing trees (only 5% mortality).
Between the 4th and 5th month after planting, 34 teak trees perished, a surprisingly high number. So teak was no longer the best performing species, but in fact the second worst performing, by M5. Only Ceylon Ironwood had a higher mortality rate (54%).
By 23rd September, five months after planting, total mortality rate was 41%, with Amboyna the best performing species (60% survival rate).
Mortality rates starts with 14% one month after planting, is highest the second months after planting (15%), then it declines during M3 and M4 (as low as 1%) and peaks again during heavy monsoon, when rice paddies become flooded (9%).
Different planting sites and mortality rate
Among 6 planting site, only one site was an expired rice paddy, and without having publishing statistical evidence, we can conclude that the rice paddy planting project of Ean Promsri had the second highest mortality rate of all planting sites. The planting site with the highest mortality rate was the public lake, with very bad soil quality. The two sites with the highest survival rate were the community forest, and the rubber tree plantation.
The challenges to turn an expired rice paddy into a forest?
To make a rice paddy, about 1.5 m of topsoil is removed, making the paddy lower in elevation compared to the roads and houses around it. With the top soil removed, the paddy supposed to fill with water during the rainy season, which is necessary for a good rice harvest.
However, since rain is less abundant in Isaan (Thailand) in the last 20 years, and with an aging population and the new generation not wanting to take over the farming business of their parents, many rice fields become expired. The farmers call them too dry. A dry rice field is no longer good for a rice harvest, since it doesn't flood during rainy season.
Lowering tree mortality rate when planting on a rice paddy
For an expired rice paddy to turn into forest more efficiently, we believe filling up the soil that has once been removed is recommended, with better soil quality for the young saplings and lower chance of flooding during the two months of monsoon (September and October). This would cost between 15,000 to 50,000 Baht, depending on the size of a paddy, and this has not been done in our case, due to budget constraints.
A rice paddy is typically completely barren, without any trees in the vicinity for providing shade to the younger trees. A way of providing shade is planting a few sun-loving trees the year before, such as Banana or the Rain tree.
Before planting the trees, we tilled the soil, which in retrospect was a mistake, since the top soil was being destroyed. Best practice would be no tilling at least 1 year before the tree planting project, ensuring a solid soil structure, and natural grasses to grow.
When should planting begin?
We started planting in April, the hottest time of the year, with temperatures reaching 40 degrees or more. Rain was abundant in the beginning of the month, yet a dry spell occurred just after our planting effort, with 10 days of relentless sun, no rain and blue sky. This right away killed about 15% to 20% of the saplings.
For the other planting sites, we waited till June, when the temperatures are typically lower than April between 30 and 35 degrees, and rain more abandoned.
How old or tall should the saplings be?
Because we have never done tree planting before, we didn't have a nursery, and bought the trees from the garden shop. We were promised they were 6 month old, but they were still small, no taller than knee height, and they suffered from transportation and sudden change of location and direct sun intake.
Trees that have been in the nursery under shade, should be put in semi-sun for about 2 weeks to 1 month before planting, and watered every second day (instead of daily), to help the tree acclimatize to the natural conditions.
For the 2022 planting season, we grow the trees in our own nursery, and if grown from seeds, we suggest to plant 9 to 12 month old trees, and from cuttings (cloning), about 3-month old trees. Older trees are stronger and will have higher survival rates.
Other techniques to improve survival rate?
Having larger trees nearby to provide shade definitely helps and we built a small bamboo construction with a netting roof top, to provide shade to some of the trees. In this tiny sample of about 32 trees, we still have over 80% survival rate compared to 59% without shade.
Mulching techniques, or hey and other fibers to be put around the trees help with evaporation and keeping the soil moist.
We also watered the trees every once in a while during the first two months, especially during the long dry spell.
Which tree species is best for Isaan / Thailand?
Till just recently, we believed that teak is the best performing tree species, however, between M4 and M5 a whopping 34 trees died in a single month (about 40% of all teak planted), which is a mystery to us. The teak trees were more subject to being eaten by insects, you can see this from the leaves, yet Amboyna were also terribly eaten by insects.
The rice field was flooded for just about 2 weeks in September, and interestingly the flooding may have caused damage to the teak (which we believed are water loving trees), while not at all to the Mahogany or Amboyna.
So five month after planting, the best performing trees were Amboyna (survival rate 70%), followed by the Resin tree (69%), Siamese Rosewood (60%), Mahogany (57%), Teak (53%) and Ceylon Ironwood (46%).
For information about tree planting initiatives in Thailand, please contact us under email@example.com or call +66 84 629 50 07.
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