Overstory #19 - Selected Tree Seed
Selected Tree Seed: improved returns in the short-term, viable populations for the long run
For generations, people all over the world have unwittingly been depleting the gene pool of many important trees by cutting down trees with the best characteristics, and leaving behind the inferior ones. Hundreds of forestry and agroforestry tree species have also suffered from severe genetic loss due to indiscriminant deforestation.
It is crucial that reforestation, forestry and agroforestry projects make strides to improve the gene pool by propagating seed from carefully selected trees. By utilizing the highest quality selected seed and plant material available, you can begin to reverse the trends of genetic degradation while improving the productivity and health of your plantings.
The genetic quality of tree seed used in plantings is a major factor in the economic success and productivity of a project. Select seed will produce plants that are more productive, better adapted to local site conditions, and better suited to achieve the results planned for the project. The long-term ecological viability and future contribution of a planting is also at stake, as projects should contain enough diversity to reproduce healthy and productive offspring for future generations, while remaining resilient to environmental stresses. The short and long term impacts of genetic seed quality warrant careful consideration and planning when collecting or purchasing seeds.
Five main criteria in selection (or, What are we selecting FOR?)
There are five main criteria in selecting tree seed for a particular species:
- Characteristics of the tree products/services. Tree characteristics such as form, wood quality, or biochemical traits are likely to be passed on to the offspring of a tree. Select trees that are representative of the qualities that are desirable for your project.
- Adaptation to site conditions such as soils, wind, elevation and rainfall. Different populations of a species have varying tolerances to environmental conditions and stresses. Select from populations that are adapted to conditions similar to yours.
- Tree growth rate. Studies have shown that you can readily achieve a 20-100% increase in overall growth rate for a species by selecting seed from trees that are the best performers.
- Resistance to pests and diseases. Minimize collections from trees that are obviously prone to harmful pests and diseases.
- Genetic diversity of the seed. Diversity is an important factor. Create a local population with sufficient diversity and vigor in the gene pool to allow for viable populations and offspring into the future as well protect against loss to unforeseen biological and environmental stresses in the near term.
Three Tips for Collecting Select Seed
Here are three important standards to keep in mind when collecting seeds. If you're purchasing seeds collected by someone else, ask if they follow these standards too.
- Collect from trees with the best form, vigor, and health--the offspring of such trees will tend to have similar qualities. When you are out collecting, keep in mind that seed selection is definitely an area where "quality over quantity" has to be the standard. Distressed and stunted trees tend to produce the most abundant seed, and usually low to the ground where it is easier to access. AVOID collecting from such trees, as you will pass on their undesirable traits. Often the trees with the most desirable characteristics are also the most challenging to collect seed from because they are the tallest and most difficult to access. Rise to the challenge! The extra effort you make now will pay off many times over, for your purposes and for the future.
- At a minimum, be sure to collect from at least 30 individual trees. To reduce the chance of collecting from closely related individuals, take seed from trees separated by 70 meters (200 feet) or more. If you can pick from more than 30 trees, do so. Pick from throughout the canopy of each tree to ensure that a range of pollinators is represented in the seeds. Pick similar quantities of seeds from each tree so that no one tree is over represented. This can help prevent inbreeding in future generations.
- Collect from wild stands and within the native range wherever possible. Many plantings done by people have too narrow a genetic base to be a viable source of seed, and the offspring of such populations may be inbred. (Also, be sure to leave enough seed in the wild to allow that population to regenerate naturally.)
By collecting from a broad diversity of specimens selected for superior qualities, your will improve the productivity of your planting now, and its ecological viability into the future.
Ian Dawson and James Were, "Collecting germplasm from trees--some guidelines," Agroforestry Today, Vol 9, No 2, ICRAF House, United Nations Avenue, Gigiri, PO Box 30677, Nairobi, Kenya. Email: email@example.com.
Simons, A.J. 1996. Delivery and improvement for agroforestry trees. IN: Dieters MJ, et al, eds. 1009. Tree improvement for sustainable tropical forestry. QFRI-IUFRO conference, 27 October-1 November, Queensland, Australia. See Agroforestry Today issue referenced above.
Seed Collection Technical Bulletin Forests & Forestry. 1992. The World Bank, Asia Technical Department, Room F3055, 1818 H St. NW, Washington, D.C. 20433, USA.
About the Authors
Kim M. Wilkinson is the Education Director for Permanent Agriculture Resources and editor of The Overstory. She has B.A. degrees in Anthropology and Ecology from Emory University.
Craig R. Elevitch is an agroforestry specialist with more than ten years of public and private sector experience in tropical agroforest and forest management. He has a M.S. degree in Electrical Engineering (Dynamical Systems) from Cornell University.
Related Editions to The Overstory
- The Overstory #59--Choosing Species for Timber Production and Multiple Benefits
- The Overstory #54--The Agroforester's Library, Part Three--Species
- The Overstory #31--Tree Domestication
- The Overstory #16--Multipurpose Trees