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  • Writer's pictureRolf Graf

Tree planting in Thailand (Surin), a statistical analysis about mortality rate

On 23rd April 2021, Endangered Trees foundation planted 547 trees as part of the 8,000-trees-contract with

Endangered Trees has just recently been founded and has a charitable mission, to increase Thailand's forest area, reduce global warming and to save endangered trees from extinction. This tree planting event was their first in such a scale, and this in April, Thailand's hottest time of the year.

"There are still hundreds of things we don't know about tree planting, dozens of unanswered questions and very little data is available online, so I'm here to change all of this", says Rolf Graf, the enthusiastic founder of Endangered Trees.

"Some of the most burning questions we are eager to find out", continues Onanong Promsri, Chairman and CEO of the foundation, "are...

  • "how tall the saplings should be before they can endure the burning heat of Thailand's April weather,

  • how old they should be before taking them out of the nursery,

  • how frequently they need watering,

  • whether they need watering at all during the dry season, and

  • the mortality rate of different species."

The rainy season started unusually early this year, with lots of rain in April. Still the temperatures rose to a peak of 38 degrees Celsius, and a 10-day streak without rain was not unusual.

"Let's give it a try and do something crazy", proposed Onanong Graf. "Let's plant the first lot in April, and monitor the data closely. We can learn from our mistakes, and make gradual improvements. We will publish the first set of data one months after." All agreed unanimously at Endangered Trees.

So the trees were planted on the land of a local Farmer on a hot Friday morning in April, two days after heavy rain. The soil was thoroughly soaked. The land was an expired rice patty, with no trees around and exposed to the sun.

Six types of trees were planted in rows, with a total of 17 rows. The trees were:

  • Siamese Rosewood (Dalbergia cochinchinensis) ROS

  • Teak (Tectona Grandis) TEA

  • Amboyna (Pterocarpus Indicus) AMB

  • Burmese Ironwood (Xylia xylocarpa) IRO

  • Mahogany (Swietenia mahagoni) MAH, and

  • Resin tree (Dipterocarpus alatus) RES

One week after planting, the teakwood trees lost all their leaves, supposably a shock effect of too much sun. The small delicate root may not absorb the amount of energy the large leaves capture during photosynthesis. "This is a total disaster", the founder cried out, "all my lovely trees are going to die."

Endangered Trees immediately started building little tree umbrellas to shade some of the trees from the sun.

"The last three nights I couldn't sleep", said Rolf Graf, "I was excited to count the trees and monitor the data". So on Friday the 21st May, in the morning, the trees were counted and the mortality rate reported on a notebook.

Regarding mortality, a tree is considered dead when there is no more green leaves around, and please note, they may come back to life at a later stage.

Indeed, the trees didn't look good at all two week after planting. Yet, after the first rain, the leaves grew back and many of the plants have recovered.

The teakwood, as the below table show, are the best performing tree species, with just one dead tree out of 73 planted, followed by the resin tree (3 dead) and ironwood (4).

One month after planting, with 29 dead out of 93, Siamese Rosewood is the worst performing species, followed by Amboyna (21 dead) and Mahogany (19).

The average mortality rate one month after planting is 14.3%, with three well-performing trees (Teak, Burmese Ironwood and Resin Tree) and three rather mediocre performing trees (Rosewood, Mahagony and Amboyna).

The trees were watered daily starting four days after the last rain, until the rain returned.

One row of Amboyna trees were planted on a little dam dividing two rice fields from each other, a bit further away from the rest. Those trees did not receive water except rain. It is a small sample but still meaningful data. Out of 27 trees, 21 died, and only six survived. Mortality rate of this small sample of unwatered trees is 77%.

Subtracting those 21 unwatered Amboyna trees from the larger sample group (21 dead of 92 planted), no Amboyna trees died, making Amoboyna possibly the best performing species. Amboyna may be the unexpected high-performer, and further monitoring is necessary.

Out of a total of 547 trees, 460 trees were still alive one month after planting, and Endangered Trees team is in a jubilant mood.

"The average survival rate is above the benchmark", reported a near hysterical Onanong Graf, "and this in spite of planting during the hottest time of year, and in spite of having no shade for the trees, and in spite of being still a greenie to this trade".

"There is still a long way to go, and we are not there yet", warned the the founder of Endangered Trees, "this is just the first month". "We may not reach 80% survival rate by the end of the rainy season." "And what about beyond?" There are still a lot of unanswered questions.

For the time being, Champagne bottles remain unopened at Endangered Trees, yet there is reason for cautious optimism.

"We started with the most difficult planting plot", commented Rolf Graf. "This plot is fully exposed to sun, and any further trees will be planted on partly shady grounds, and with the data gathered and the necessary steps taken, the future looks promising at Endangered Trees."

In addition to the trees already under the umbrella, another 30 trees were planted under a large net. The sample data contains about 60 trees partly or fully shaded. It is too early to conclude, yet it looks like all trees under the net have survived.

All trees were purchased from a local nursery, without age indication. They were between 10 and 40 cm tall. It is unclear whether taller trees really have higher survival rate, as one of our best performing trees, the teak, was one of the smallest (just 20 cm tall).

What have we learned from this? Steps to be taken for future tree-planting event:

  • Trees exposed to the sun need watering daily, if not mortality rate goes through the roof.

  • There are better and worse-performing tree species. For the coming tree planting events, we increase the number of high-performing trees (Teak, Resin Tree, Ironwood and possibly Amboyna), reduce the number of low-performing trees (Mahogany and Rosewood).

  • Plant trees in more shaded areas or under nets / umbrellas.

  • Find out how old your trees are before you plant them, therefore grow them from seed in your own nursery.

  • Find out if larger trees of the same species really perform better than smaller trees (common sense would predict they should), yet there is no data available.

Little umbrellas were built to shade the trees from the midday sun.

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