FEATURE: Rehabilitating degraded lands in Cambodia through the cluster method
11 Aug 2021
This article briefly highlights the achievements of the regional project on ‘Performance of Modified Cluster Method in Rehabilitating Degraded Lands in Siem Reap, Cambodia (AFoCO/021/2021)’, which is a research-based project jointly implemented with the National Institution of Forest Science (NIFoS) of the Republic of Korea.
Cambodia is rich in forest resources, but most of the forest lands have degraded and are in need of rehabilitation. Restoring degraded lands, particularly in Siem Reap is very challenging since the soils have been exposed to physical elements due to slash-and-burn farming, excessive logging, and the consequent slash produced. The low survival rate of plants in dry and sandy areas was caused by quick drying of the topsoil, resulting in a water-stressed condition, while the rate was also influenced by its microclimate. Such issues are mitigated through the utilization of water-retaining agents that will store moisture and gradually release it to the plants. AFoCO recently supported the Institute of Forest and Wildlife Research and Development (IRD) in Cambodia by conducting a study ‘Performance of Modified Cluster Method in Rehabilitating Degraded Lands in Siem Reap, Cambodia (AFoCO/021/2021)’. The study investigated the benefits of using coconut husks as a moisture retaining agent and the Miyawaki method on the survival and restoration of degraded lands. It was found that coconut husks offer numerous advantages as a retaining agent because of their affordability and biodegradability. The Miyawaki method has also been successfully tested in Cambodia. Despite the fact that the conventional Miyakwai method is costly due to the large number of seedlings required, this study has successfully made improvements by reducing the costs of establishment using the cluster planting approach.
This study was conducted with the goal of overcoming challenges such as limited knowledge on the appropriate species to plant due to lack of site suitability study of major species; the high cost of planting and maintenance; and the high mortality rate of seedlings in the dry season due to poor water retaining capability of the soil.
This project aims to: (1) evaluate the cost-effectiveness of cluster planting combined with the Miyawaki method in rehabilitating degraded lands; (2) determine the survival rate of test species (Dalbergia cochinchinensis) planted together with other species in a cluster using the Miyawaki method; and (3) demonstrate the effectiveness of local materials (coconut husks) as a water-retaining agent on the survival of seedlings.
This project will be implemented for 2 years. It will examine the following variables: (1) growth (diameter, total height, and crown diameter) of the planted seedlings; (2) survival of the planted seedlings particularly the test species, D. cochinchinensis; (3) biomass of the competing grasses; (4) seedlings recruitment or tree seedlings that grow naturally in each plot; (5) the cost of establishment and maintenance.
The experiment is conducted in Siem Reap Province covering an area of 2.25 Ha. The 2.25 hectares were allocated to the three treatments (at 0.25 Ha each) and 3 blocks (3 blocks x 3 treatments x 0.25 Ha. /treatment = 2.25 Ha.). There are three treatments that were compared: (1) plants planted using the Miyawaki-cluster planting method; (2) using coconut husks as a retaining agent; and (3) using the conventional planting method (control). The experiment follows a Randomized Complete Block Design, with three blocks. Each block is subdivided into three plots, where the treatments are randomly assigned. The area per plot is 0.25 hectares making one block covering 0.75 hectares.
In Treatment 1, four cluster plants were established measuring 10m x 10m. The species panted is a mix of climax, pioneer or fast-growing species, and fruit trees planted at 2m x 2m. There were 120 fast-growing species that were planted: Albizzia lebbeck (Chres); Diospyros sp. (Troyeung) and Lagerstroemia speciosa (Trobaek Prey). There were 72 fruit tree seedlings planted: Chrysophyllum caimito (Tekdos Kor); Syzygium cumini (Pring); Annona squamosa (Tep); Annona muricata (Tep Barang); Psidium guajava (Tro Bek); and Averrhoa carambola (Speu). For climax species, the following seedlings were planted: Anisoptera costata (Pdaek); Dalbergia oliveri (Neang Nuon); Dipterocarpus alatus (Chheuteal); Hopea odorata (Kokir); Pterocarpus macrocarpus (Thnong); and Sindora cochinchinensis (Kokor).
Treatment 2 plot was planted with D. cochinchinensis applied with water retainer (Coconut husk). The seedlings were planted at 3m x 3m. Treatment 3 serves as control – D. cochinchinensis were planted at 3m x 3m but without the water retainer.
The project started implementing the field activities in June 2021. The activities include the following:
- Site assessment, mapping and layout, and land preparation
The field staff conducted an ocular assessment on the study site before the land preparation was conducted. The design of the experimental plots was finalized based on the configuration of the area. Preparation of materials such as coconut husks (approximately 20 bags) was purchased ahead. The planting areas were cultivated using a four-wheel tractor to clear the site from weeds. The boundary of the experimental plots and the planting spots were marked using stakes in June, 2021.
- Seedling preparation and planting
The project has planted 120 seedlings of fast-growing species (A. lebbeck: 40 seedlings; Diospyros sp.: 40 seedlings; and L. speciosa: 40 seedlings); 72 fruit tree seedlings (C. caimito: 12 seedlings; S. cumini: 12 seedlings; A. squamosa: 12 seedlings; A. muricata:12 seedlings; P. guajava:12 seedlings; and A. carambola: 12 seedlings); and 72 climax species seedlings (A. costata: 12 seedlings; D. oliveri:12 seedlings; D. alatus:12 seedlings; H. odorata:12 seedlings; P. macrocarpus:12 seedlings; and S. cochinchinensis:12 seedlings).
Some of the seedlings that were not available in the Khun Ream nursery were purchased from other nurseries. The seedlings were first hardened in Khun Ream nursery before they were out planted in the experimental plots.
- Field monitoring
The project team is now on the stage of monitoring the project site to check for any insects. The measurements are yet to be conducted.
Although the planned activities were implemented according to schedule, the project has encountered some challenges due to a recent spike of CoVID 19 cases. The situation has worsened in the past months which has prompted the government to impose stricter measures in the movement of its staff. In Siem Reap, the local government has restricted the entry of people coming from other provinces. As a result, the staff from Phnom Penh were unable to participate in the layout and establishment of plots. Close online coordination was made between the field personnel and the national staff to address such challenges.
Contributed by Dr. Sokh Heng, Project Manager of AFoCO/021/2021, Director of Institute of Forest and Wildlife Research and Development, Cambodia; Sokleap Khiev, AFoCO Fellowship Official from Cambodia; and Cha Ji Yea, Team Assistant