Tree Islands

Material Required

• Native tree saplings and seedlings of other species that will be planted
• Shovels and gardening tools, basic tools for planting and maintenance
• Optional: Mulch and organic matter
• Optional: Watering cans or irrigation system

Steps of Implementation: 

1. 1. Site assessment: Determine whether the site is suitable for the establishment of tree islands. A prerequisite is that some natural regeneration should be possible. There should be some rainfall and it should be next to some remaining forest.
   2. Community engagement: Involve local communities in the decision-making process (fostering a sense of ownership and responsibility). The local community may be interested in making it a community-driven project and working on the establishment, monitoring, and maintenance.
   3. Tree island design: Deciding what the tree islands should look like, how they can be placed in the area, and how they will be most effective is an important next step. Think about size, spacing, shape, and number. See “Design of the tree islands” section below.
   4. Tree species selection: Choose native tree species that are well-suited to the local environment, ensuring biodiversity and adaptability. The best species to use are native tree species that grow well and have rapid canopy cover expansion. Besides this, it is preferred to plant trees that attract animals that function as seed dispersers for hastening natural regeneration. See “Species composition” section below for more information.
   5. Planting: Establish tree islands by strategically planting the clusters of trees. Mulching and watering techniques may be used to enhance sapling survival.
   6. Monitoring: Regularly monitor the growth and health of the planted trees and the overall ecosystem. This can involve community members in data collection and observation.
   7. Maintenance: Carry out regular maintenance such as weeding, watering, and pest control to ensure the long-term success of the tree islands. Maintenance could include clearing invasive non-native grasses (about 3-6 months after planting); protecting the area from e.g. grazing, illegal logging, and fire; replanting trees in the island if needed; and sometimes watering or fertilizing. Rows of new trees are likely to be visible about 25 months after planting.

Optional:

• Educational signage: Educational signage can be installed to inform the community about the importance of the project, the tree species selected, and proper maintenance practices.
• Community workshops: Organise workshops to educate community members about sustainable land management practices, the benefits of biodiversity, and the importance of tree conservation - and to learn from their experiences.

The design of the tree islands depends on the project goals, budget, and timeline. 

Tree island shape:

• Circles: A circle is a good shape because there will be fewer edge effects, meaning that the sides of the patches are exposed to more light, wind, weeds, and different temperatures. A circle will have the best edge-to-inner forest ratio. 
• Squares: A square is easier to maintain than a circle because it has clear and straight edges. 
• Strips: easiest to install and maintain. But there will be more edge effects. 
• Hexagon: A hexagon is like a circle, but with straight sides. Here they used hexagons for planting tree islands. 

Tree island size: 

• Larger (and more) islands will likely mean faster results but at a higher cost 
• A minimum size of 64 m2 is recommended for a high recovery rate
• Smaller islands of 30-50 m2 tend to have more grass and are more affected by the death of a tree in the island. It will generally take a bit longer to yield results but will work out in the end
• But even smaller islands, of  3-30 m2 (circular) show valuable forest recovery outcomes
• Tree islands  should be large enough to attract seed dispersers and provide habitat to these species
• It is also possible to  establish tree plots of different sizes

Distance between the islands:

• The shorter the distance, the higher the recovery, but also the higher the cost
• If there is a high degree of degradation or disturbance on the site,  more intensive tree planting and less distance between the islands is required to restore the site
• The growth rate of the trees planted and their canopy coverage can provide the grounds for   estimating the ideal distance between islands: fast-growing, larger distance; slow-growing, shorter distance
• In example cases, a spacing of ~8-20 m (Costa Rica) and 12 m (Honduras) produced promising  results

 Amount of trees:

• This depends on the resources available and the speed of natural regeneration desired
• Planting on 20% of the identified area is a good starting point, so also just 20% of the trees that would be used for a tree plantation are used. 
• In the islands themselves, trees can be planted with 1 – 4 m spacing:
• Wider spacing (i.e. 3m): fewer resources/trees needed, promotes taller and wider tree growth
• Closer spacing (>2m): faster canopy coverage, potentially more natural forest conditions and growth, reducing space for invasive species
  
  Source

Ideal Species composition:

• Fast-growing species
• Medium and slow-growing species
• Fruit trees to attract seed-dispersing animals
• Native species where possible
• Nitrogen-fixing species (e.g. Black Locust, Mimosa, Alder, Redbud, Autumn Olive, Kentucky Coffee Tree, Golden Chain Tree, Acacia, Mesquite, and others)
• If fires occur in the area, consider fire-resistant species, especially at the borders of the islands
• Consider shrubs and herbs as well
• Involve local people and ask them which species are suitable
• Consider species that are of economic or cultural value to local people

This intervention contributes to:

It is hard to estimate the costs of the implementation of tree islands because every case is different and depends on many factors including location, scale, and number of planted trees, tree island design, maintenance, monitoring abilities, and labour costs. However,  it is cost-effective in comparison with a whole tree plantation. For example, only around 20% of the number of trees of a plantation is used, therefore the costs for tree planting are around 5 times lower. 

Comparison of tree islands to a tree plantation and natural regeneration: 

Table 1 Implementation costs of tree islands, next to the costs of a plantation and only natural regeneration.  (Source)

Other estimates made for the total costs of Tree Islands:

• US$357-620 per ha, case: (1)* Costa Rica 
• US$4600 per ha, case: (2)* Colombia 
• US$2550 per ha, case (3)* Colombia

*See: Case studies

1. Tree islands in tropical premontane forest in southern Costa Rica. 

Description
A successful experiment and research on tree island planting by Karen Holl, in Costa Rica. This experiment was started in southern Costa Rica in 2004-2006 to compare the long-term ecological efficacy of applied nucleation to natural regeneration and to more intensive plantation-style tree planting (Wilson et al., 2021). A total of 18 1-hectare sites were originally established, with 12 still active as of 2020 (Wilson et al., 2021). The results of the study site shows tha applied nucleation is much more effective that the natural regeneration plots and similar to the plantation plots, in terms of canopy cover, species recruitment, and other key matrics. The case study’s implications are that applied nucleation can improve tree recruitment and species diversity.

2. Tree islands for restoring lowland rainforest in Madagascar 

Description
The project in Madagascar incorporates planting tree islands to restore a forest that is degraded by many wildfires. In this project, the tree islands were hit by wildfires as well and were vulnerable because of their greater amount of edge density. New designs for tree islands were made with fire-resistant tree species on the edges. The goals of the study are to restore native forests to four hectares of land that had been degraded by repeated wildfires resulting from tavy – a form of slash-and-burn agriculture, and to study the ability of native trees to suppress ruderal vegetation. This project was implemented by a non-profit organization, Green Again Restoration, on the private land of co-author Jean François Solofoniaina Fidy, the leader of Ambonivato fokontany (small village region). The entire project, from planning to execution, observation, and analysis, engaged the local community at every stage. Seeds were collected from trees grown on nearby farms, while tasks like weeding and watering in the nursery were managed by single mothers from Ambonivato during school hours. Young men from the village handled land clearance and tree planting, while local women were responsible for creating identification tags for the trees. All measurements and data recording were carried out by members of the local community.

3. Tree islands for Atlantic forest restoration in Brazil

Description
A research project on different tree-planting designs in Brazil. They compared tree island trips and squares to plantations. The trees are planted in strips, similar to the plantation style of planting, but leaving unplanted strips between the lines to recolonize naturally. The benefits of this design is that strip planting should result in reduced costs for planting and maintaining planted seedlings, and it could provide more habitat heterogeneity by providing both planted and unplanted areas. Additionally, there are fewer logistical obstacles for planting seedling for maintenance.

Guides 

• Applied nucleation restoration guide for tropical forests - please click here.

Videos 

• Restoring tropical forests with the use of tree islands - please click here.

Sources:

• Applied nucleation restoration guide for tropical forests
• Bechara, F. C., Trentin, B. E., Engel, V. L., Estevan, D. A., & Ticktin, T. (2021). Performance and cost of applied nucleation versus high-diversity plantations for tropical forest restoration. Forest Ecology and Management, 491, 119088.
• Corbin, J. D., & Holl, K. D. (2012). Applied nucleation as a forest restoration strategy. Forest Ecology and Management, 265, 37-46.
• Corbin, J. D., Robinson, G. R., Hafkemeyer, L. M., & Handel, S. N. (2016). A long‐term evaluation of applied nucleation as a strategy to facilitate forest restoration. Ecological Applications, 26(1), 104-114.
• Holl, K. D., Reid, J. L., Cole, R. J., Oviedo‐Brenes, F., Rosales, J. A., & Zahawi, R. A. (2020). Applied nucleation facilitates tropical forest recovery: Lessons learned from a 15‐year study. Journal of Applied Ecology, 57(12), 2316-2328.
• Holl, K. D., Zahawi, R. A., Cole, R. J., Ostertag, R., & Cordell, S. (2011). Planting seedlings in tree islands versus plantations as a large‐scale tropical forest restoration strategy. Restoration Ecology, 19(4), 470-479.