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Tree Evaluation at Station: Objectives, Advantages, and Disadvantages

This article explores the objectives, advantages, and disadvantages of conducting tree evaluations on a station. It covers trial types, specimen trials, species/provenance trials, provenance tests, and family trials. The text emphasizes factors to consider when planning trials and highlights the significance of such evaluations.

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Tree Evaluation at Station: Objectives, Advantages, and Disadvantages

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  1. Tree evaluation on station Tony Simons, ICRAF, Kenya

  2. Tree evaluation on station • Objectives of evaluation • Advantages of work on station • Disadvantages of work on station • Types of trials

  3. 1. Objectives of evaluation • Trials cost in terms of both time and money, so: • Why is the trial needed? • What hypothesis are you testing? • How many treatments do I need/have? • What do you plan to measure? How often? • Has anyone else researched this before? • (CSIRO, CIRAD, CATIE, EMBRAPA, DFSC, OFI, ASEAN, Winrock) • How long is the trial envisaged to last? • What will the trial lead to? • Can it be done satisfactorily on farm? • Are you trying to get too much/too little from it?

  4. 2. Advantages of work on station • Ease of access, more frequent monitoring • Nursery is usually closer, planting done quicker • Better control of the conditions (water, weeds, etc) • Need for fewer replicates as less variable site • Better security (theft, interference, fire) • Fewer constraints on what is permissible • Gain understanding before going on farm • Trials can be larger and/or more complicated • Visitors can see many trials in one place • Often historical records (field and climate) • May have a conservation role (don’t over play)

  5. 3. Disadvantages of work on station • May be unrepresentative of farmers’ conditions • - lead to false conclusions for on farm work • - farmers don’t relate to it • - the control treatment may be misleading • Can be expensive to maintain • Researchers can be reluctant to close trials • Default time fillers for labourers

  6. 4. Types of trials • Species trials • Species/provenance trials • Provenance tests • Provenance/family trials • Family (progeny) tests • Clonal trials • Management trials

  7. A. Species trials • Four kinds - Elimination (> 10 species, arboreta) • - Comparative (2-10 species) • - Proving trials (1-2 species) • - Modelling (e.g. WaNuLCaS) • What is the species required for? • How many species are available? • What is likely to grow well? (species-site matching) • Exotic/indigenous? • Does the seedlot represent the species? (# prov.) • Careful if species have contrasting growth

  8. A. Species trials (cont.) • Appropriate plot designs: (usually with border trees/rows) • - blocks (square, rectangular) • - lines • Plant at final spacing or thin? (50% diagonally) • What is the control? • Beware of confounding (species x management) • Problems arise if survival is moderate to low • Need sufficient number of trees (>50 trees) • Although often suggested, few species mixtures • Encourage correct botanic nomenclature • Biosafety considerations (weediness, quarantine) • What is the species required for?

  9. Square plots (measured trees/total) 3 x 3 (1/9) 4 x 4 (4/16) 5 x 5 (9/25) 6 x 6 (16/36) 7 x 7 (25/49) 8 x 8 (36/64)

  10. Fodder yield per plot (kg) at 18 months, Embu, Kenya

  11. Diaminatou’s trial

  12. Patrick’s trial

  13. Telesphore’s trial

  14. Fodder yield per plot (kg) at 18 months, Embu, Kenya

  15. 36.8 40.1 Species A Species B Fruit yield (kg)

  16. 36.8 40.1 Species A Species B Fruit yield (kg)

  17. B. Species/provenance trials • Several provenances tested per species • Objective: (a) to identify best species • (b) to identify best provenance (s,xs) • Not necessary to have equal numbers of provenances per species, but if unbalanced be cautious with species comparisons • Design and analysis is more complex • What is the species required for?

  18. C. Provenance tests • expect 2-5 fold differences between provenances • ensure seedlot has broad genetic base • (>30 parent trees) • depending on objectives and species, then • need 100-400 trees • is the material well documented? • can you get more seed if it is needed? • do you plan to convert the trial to a seed stand? • where most G x E tests are done (interpret/use?) • to date few done on farm, more could be

  19. D. Provenance/family trials • Several families tested per provenance • Objective: (a) to identify best provenances • (b) to identify best families (p,xp) • (c) to calculate genetic parameters • Not necessary to have equal numbers of families per provenance, but if unbalanced be cautious with provenance comparisons • Require >30 families per provenance • Design and analysis is most complex • What is the species required for?

  20. E. Family (progeny) tests • Used for calculating genetic parameters (s.e.) • - these are age, site, population, trait specific • Used to identify best families (backward seln - cso) • Used to identify next parents (forward seln) • Used for phenology studies, breeding system • Can be full-sib (we know mother and father) or half-sib (we know only mother) • Require >30 families, many more for family seln • Generally require >20 trees per family • What is the species required for?

  21. Height (m) at 12 months for 30 families of Prunus africana Overall mean = 1.0

  22. Height (m) at 12 months for 3 (of 30) families of Prunus africana Overall mean = 1.0, mean of three = 1.4

  23. F. Clonal trials • To observe clonal differences for selection • To determine clonal repeatability • To determine any “c” effects • Can be used for clonal seed orchards, if rogue • Can be used to set up mother blocks, if rogue • Good for mating system experiments • What is the species required for?

  24. G. Management trials • careful to ensure relevance to on-farm conditions • can investigate individual factors and interactions: • - spacing • - thinning • - watering • - pruning • - fertilising • - shading • - microsymbionts • - topworking, grafting, budding • - nursery carry-over experiments

  25. Most published tree species and provenance trials are for commercial forestry species Caution needed in AF with: - different designs - replication - farmer’s objectives …especially if extrapolating from a temperate trial

  26. If you are going to do advanced • improvement then don’t shortcut • trials • Get your species right • Get your founder material • right

  27. It is desirable if you can carry your blocking through from the nursery to the field.

  28. Trials can be converted to seed stands, … composition, design, layout, numbers, management

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