The Forest Restoration Research Unit


Learning from Nature to Restore Northern

Thailand’s Degraded Forest Ecosystems

“In the planting of the seeds of most trees, the best gardeners do no more than follow nature, though they may not know it…So, when we experiment in planting forests, we find ourselves at last doing as Nature does. Would it not be well to consult with Nature in the outset?…for she is the most experienced planter of us all…”


Extract from “On the Succession of Forest Trees” by Henry David Thoreau (1817-1862), American writer, philosopher and naturalist.

The forests of northern Thailand are one of the kingdom’s most important natural resources. They are habitat for numerous wildlife species, including 150 mammal species, 383 birds and at least 3,450 vascular plants, of which 1,116 are trees. Northern villagers still rely on forest products such as firewood, bamboo, edible fruits, mushrooms, medicinal plants, honey etc. to meet some of their basic needs. Furthermore, the northern forests protect extensive mountainous watersheds that feed the Chao Phraya River, irrigate the rice fields of the central plains and supply water to the nation’s capital.

However, despite their importance, these forests have been widely degraded or destroyed in recent years. In 1961, forests covered 116,280 km2 (or 68.5%) of the 17 provinces which comprise the northern region, but by 1995, logging, fire and agricultural expansion had reduced this figure by 36.4% to only 73,886 km2 (or 43.5% of the region’s area). Although a ban on commercial logging since 1989 has helped slow the rate of destruction, illegal logging, agricultural expansion and various development projects maintain the deforestation rate for the region at approximately 0.9% per year.

The consequences of deforestation are particularly serious in the mountainous north. As watersheds become eroded, flash floods occur in the rainy season, streams dry up in the dry season and rivers become choked with silt. Large mammals such as elephants, tigers, bears and wild cattle have been mostly extirpated and populations of smaller animals such as gibbons and hornbills have become perilously small and isolated. Rural poverty increases when villagers have to buy products in the market that they used to collect from forests.

In the past, people accepted deforestation as an inevitable consequence of economic development. Now, however, attitudes are changing. Since 1993, various tree-planting projects to celebrate the Golden Jubilee of His Majesty King Bhumibol Adulyadej have encouraged people from all walks of life to become involved in restoring the region’s forests. Such activities have raised hopes that deforestation might be reversible. However, the success of tree-planting projects is often limited by lack of skills and knowledge about how to grow, plant and take care of native forest trees, which have never before been planted on a large scale. Forest ecosystems contain a very wide diversity of tree species, many of which have never been studied in detail. Often, the tree species grown for planting projects are unsuited to the sites being planted. Methods of growing and planting native forest trees need to be improved and appropriate methods to care for the trees after planting (e.g. fertiliser application, weeding etc.) need to be developed.

The Forest Restoration Research Unit (FORRU)


It was to address some of these technical aspects of tree planting that the Forest Restoration Research Unit (FORRU) was established in 1994. FORRU is a joint initiative between Chiang Mai University (CMU) and Doi Suthep-Pui National Park Headquarters (under the Royal Thai Forest Department (RFD)). The main unit comprises a research tree nursery and office at Doi Suthep-Pui National Park Headquarters. In addition the unit has established a community tree nursery and demonstration plots at Ban Mae Sa Mai, an Hmong hill tribe village in the north of the national park.

The aim of the unit is to develop effective methods to complement and accelerate natural forest regeneration on deforested sites within conservation areas, to increase biodiversity and protect watersheds. Specific objectives include:

i) development of tools for studying the restoration of natural forest ecosystems, such as this book;

ii) research to investigate the ecological processes of natural forest regeneration, to determine ways in which these processes might be accelerated;

iii) identification of tree species suitable for planting to complement natural tree establishment;

iv) development of appropriate methods to propagate such tree species and test their performance after planting out and

v) training of interested groups in the new forest restoration techniques developed by the unit.

FORRU's initial priority was to gather basic ecological data about the very large number of tree species which grow in northern Thailand, to determine which ones might be useful for restoring damaged forest ecosystems. With more than 600 tree species growing on Doi Suthep, there were plenty to choose from. Apart from a few commercially valuable tree species, very little was known about seed production, germination and seedling growth of the vast majority of wild forest trees. Without such information, it was impossible to make sensible choices as to which tree species to use in forest restoration projects. Therefore, FORRU collected and germinated the seeds of as many species as possible and developed criteria to assess their potential to restore damaged forest ecosystems.


Seed Production and Collection

To determine when ripe seeds can be collected, FORRU’s researchers recorded the abundance of flowers and fruits of 94 native tree species in the forests of Doi Suthep, every 3 weeks, over 4 years.

Data on the characteristics of fruits and seeds (e.g. colour, size, shape, weight etc.) have been entered into a computer database that can be used to help identify species and provide clues as to their seed dispersal mechanisms. Different fruit or seed types vary in their potential to be naturally dispersed into deforested areas. Some are more likely to attract wildlife into planted sites than others, so it is important that fruit and seed characteristics are considered among the criteria used to select tree species for planting.

Research currently underway is determining how to identify superior parent trees for seed collection. Maintaining genetic diversity is an essential element of any tree-planting program with conservation objectives. Therefore, in collaboration with Horticulture Research International in the U.K., genetic variation within selected tree species is being assessed to ensure that genetic diversity is maintained among the seedlings grown for planting.


Seed Germination

Seed germination trials have been carried out on nearly 400 tree species to provide basic data on germination rates and dormancy. The results enable nursery managers to estimate how many seeds to sow and the time required to produce a required number of seedlings. Initially, experiments compared seed germination in partial shade (similar to that in deforested gaps) and deep shade (similar to that beneath a forest canopy), to eliminate shade dependent species that are unsuitable for planting in sunny deforested sites. The results showed that many so-called primary or climax forest tree species could germinate and grow well in the sunny conditions of deforested sites. Therefore, including such species in tree-planting programmes can greatly accelerate forest regeneration.

Using both trial and error and controlled experiments FORRU researchers and CMU students have determined the best methods to clean seeds and treat them to accelerate germination and increase the final germination percentage. Treatments have included soaking the seeds in water, scarification and various heat treatments. Further research is currently underway on seed storage, improving the seed germination medium and preventing fungal diseases that cause damping-off during germination.


Seedling Growth in the Nursery


Producing a wide range of native forest tree species for forest restoration is beset with nursery scheduling problems. Different species produce seeds at different times of the year and they have different seedling growth rates. Yet, all the trees must reach a suitable size by the planting season i.e. June. Research on the growth of seedlings at FORRU is helping to develop production schedules that will enable nursery managers to plan nursery operations (such as that shown in the poster accompanying this volume). After germination, seedlings are monitored in the nursery through all stages of production, until they are ready for planting out. Mortality and growth rates, responses to fertiliser and pruning, and any signs of pests or diseases are routinely monitored.

Experiments to test different container types have shown that root trainers; rigid plastic pots, with vertical grooves to prevent root spiralling, are ideal. However, if such containers are not available, excellent results may also be obtained with 9” x 21/2” plastic bags, if roots are prevented from growing out of the bottom of the bags by frequent pruning. Recently experiments have begun to test the effectiveness of air pruning. Seedling containers are raised off the ground on a wire grid. As the roots grow out of the bottom of the containers, they are killed when exposed to air. This stimulates the formation of a compact root-mass within the container that increases the chances that the trees will survive after planting. Other experiments currently underway are examining the effects of container size on seedling growth in the nursery and testing different types of fertilizer and methods of application.


Tree-planting Experiments

In collaboration with Doi Suthep-Pui National Park authority and with sponsorship from the Biodiversity Research and Training Programme, FORRU has established experimental field trials in the degraded upper watershed above Ban Mae Sa Mai. These trials have three main objectives:


i) to assess the relative performance of different tree species,

  1. to determine the most appropriate treatments to enhance tree performance after planting and
  2. to assess whether tree planting encourages the return of biodiversity to degraded areas.


Plots are planted with 20-30 different tree species and then subjected to different treatments including different methods of fertilizer application, weeding and mulching. In addition, trees are planted at different densities and saplings propagated using different nursery methods are compared with those transplanted from directly from forest. The performance of the planted trees is monitored 3 times per year. In addition, the attractiveness of the planted trees to seed-dispersing birds is monitored, as well as the species diversity of the ground flora and the establishment and subsequent performance of none-planted tree seedlings. Planted plots are compared with non-planted control plots.

These experiments have identified several top-performing tree species including, Melia toosendan, Erythrina subumbrans, Sapindus rarak, Spondias axillaris, Hovenia dulcis, Gmelina arborea, Prunus cerasoides, Ficus subulata, Ficus microcarpa and Ficus altissima.


Working with a local community

FORRU is not a social development project. Its aim is not to persuade individuals or communities to plant trees, but to provide technical advice to those who decide for themselves that they would like to become involved in restoring the nation's disappearing forests. One such community is Ban Mae Sa Mai on the northern slopes of Doi Suthep-Pui.

The villagers wanted to restore forest to abandoned agricultural land above their village to protect the watershed and celebrate the King’s Golden Jubilee. Their initial attempts at tree planting were disappointing, so in 1996 Doi Suthep-Pui National Park HQ asked FORRU staff to provide the villagers with technical assistance. Since FORRU needed an area to establish experimental plots, a partnership was formed.

FORRU helped the villagers build a community tree nursery and trained and employed two villagers to run it. The Ban Mae Sa Mai community tree nursery now produces most of the trees needed for the villagers’ tree-planting programme as well as some planted in FORRU’s experimental plots. It is also used to test the feasibility of new techniques developed at FORRU's research nursery within a local community. The nursery also has an education and training function. School children in the village visit the nursery during their classes and many workshops and training sessions have been located there. It has also become a focal point for village’s conservation group, the "Mae Sa Mai Resources Conservation Volunteer Group". This group organises tree planting, the cutting of firebreaks and fire lookouts to protect the planted areas.


Sharing Results

All results of FORRU’s research programme are freely available to any individuals or groups interested in restoring forests. In addition to hosting many visits from a wide range of different organisations throughout the year, FORRU organises workshops to share information generated by the project with participants. Furthermore, the project has produced several publications, details of which are provided in the list of references at the end of this book. FORRU’s first training manual “Forests for the Future: Growing and Planting Native Trees for Restoring Forest Ecosystems” is particularly useful for those starting tree-planting projects. It provides more details of nursery and tree-planting techniques than can be described in this book.

For Further Information….

FORRU has produced three publications for general distribution. They are distributed free to tree-planting groups within Thailand and are available for purchase by any other individuals or organizations:

Forests for the Future:

Growing and Planting Native Trees for

Restoring Forest Ecosystems

(1998 in Thai or Englsih)


“The recent surge in public enthusiasm for planting native forest trees, has not been supported with sound technical advice. Seedlings planted are often of poor quality, or are of inappropriate species and care for them after planting is often insufficient. This book, based on the work of the Forest Restoration Research Unit since 1994, offers a basic introduction to growing and planting native trees to restore natural forest ecosystems. It provides practical advice on which tree species to plant; how to grow them in a nursery and how to organize a tree planting event. If you are already involved in reforestation activities or if you are thinking of starting a new tree planting group, this book will be of interest to you.”


Tree Seeds and Seedlings

for Restoring Forests in Northern Thailand


(in press 2000, Thai and English editions)



A field guide to the seeds and seedlings considered most useful for the restoration of seasonally dry tropical forests in northern Thailand


Forest Restoration for Wildlife Conservation


(in press 2000, only available in English)


Procedings of a regional workshop held in Chiang Mai in January-February 2000 that established a research agenda for the restoration of degraded. seasonally dry tropical forests in SE Asia.

To order copies or for further information please email:

Dr. Stephen Elliott at