Forest Genetic Resources Training Guide
Tree seed supply chains
Tree planting on farms in East
Africa: how to ensure genetic
diversity?
David Boshier,
Ian Dawson &
Ard Lengkeek
Forest Genetic Resources Training Guide
Location of the countries and survey
areas
Uganda
Mabira
Kenya
Meru
Kabale
Nairobi
Arusha
Tanzania
Location of
nursery survey
sites
Forest Genetic Resources Training Guide
Forest Genetic Resources Training Guide
Nursery sites
Forest Genetic Resources Training Guide
Why bother about genetic
diversity?
• adaptation to changing environments
• direct use of genetic resources
• viability of populations in short term
•
- seed production
•
- inbreeding depression
Forest Genetic Resources Training Guide
Inbreeding depression in Acacia
mangium in Sabah
Seed source
1st generation
2nd generation
3rd generation
Seedling height
(cm)
32.5
20.7
18.1
Sim, 1984
Forest Genetic Resources Training Guide
Theory
• direct impacts
genetic processes
• decrease population size
genetic drift
• increase spatial isolation
gene flow
• decrease densities
mating - inbreeding
• change local environment selection
Forest Genetic Resources Training Guide
Bottleneck  genetic drift
Forest Genetic Resources Training Guide
Isolated trees
– mating patterns?
Forest Genetic Resources Training Guide
Altered mating patterns in farm trees?
• Predictions: increased inbreeding
•
greater pollen dispersal
•
fewer sires
sires
inbreeding
dispersal
• Isolated farm tree
Continuous forest
Forest Genetic Resources Training Guide
How many trees to collect from?
1
Allelic richness (frequency>0.05)
Wind pollinated species
Insect pollinated species
0.9
0.8
0.7
0.6
0.5
0.4
0
5
10
15
20
Number of trees to collect from
25
30
35
Forest Genetic Resources Training Guide
Data collected in a survey of seed-propagated tree
species in tree nurseries from five areas in East Africa
Survey area (country)
All areas
Kabale
(Uganda)
Mabira
(Uganda)
Nairobi
(Kenya)
Meru
(Kenya)
Arusha
(Tanzania)
Nurseries [client data*]
7 [6]
9 [7]
21 [16]
12 [8]
22 [22]
71 [59]
Cases [client data]
All species
Indigenous species
Cases indigenous species
Cases five most common species
Cases of unique species
occurrence
Single tree collections all species
Single tree collections indigenous
species
15 [8]
11
3
4
2
3
26 [16]
14
6
10
3
6
31 [25]
16
6
6
11
6
17 [10]
7
1
2
10
2
54 [54]
16
3
5
40
5
143 [113]
43
15
27
66
22
7
2
4
1
8
2
7
0
5
1
31
6
Seed trees per nursery lot, Nm:
mean (SD)
3.7  1.8
(3.6)
5.1  2.3
(6.0)
5.8  3.1
(8.9)
5.7  3.1
(6.5)
8.2  3.8
(14.1)
6.4  1.7
(10.3)
2060  1408
(3661)
787  432
(1228)
1339  1011 1543  676
(2127)
(2535)
1378  401
(2446)
41  27 (55)
17  9 (22)
81  92
(149)
28  10
(53)
Seedlings per nursery lot, Ns: mean 871  712
(SD)
(1408)
Clients per nursery lot, Nc: mean
(SD)
12  14
(20)
22  5 (20)
Forest Genetic Resources Training Guide
Forest Genetic Resources Training Guide
Cupressus lusitanica
Wind pollinated
Hermaphrodite, self compatible
100,000 seed produced per tree
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Calliandra calothyrsus
Bat/moth pollinated
Hermaphrodite and male flowers,
Mainly outcrossing
1,000 seed produced per tree
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Dovyalis caffra
Bird?/insect pollinated
Dioecious
270-470 seed produced per tree
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Sclerocarya birrea – male tree being
cut as not producing fruits
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Grevillea robusta
• Self incompatible with protandry
• Fruit set cross-pollination (5.9-17.5%)
>open-pollination on farms (0.1%-3.3%)
• Open-pollinated flower stigmas – most no
pollen or only self-pollen
• Lack of cross-pollen may limit seed
production
Forest Genetic Resources Training Guide
Senna siamea
•
•
•
•
Insect pollinated
Hermaphrodite
Self–compatible?
High seed production per
tree
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Procurement pathways
NGOs
compared with
CBOs
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Distribution pathways
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Think about and discuss
• Where are bottlenecks to genetic diversity? How to overcome
these?
• In 5 main species, how does seed production per tree influence
number of trees seed collected from? How species biology affects
genetic diversity in seed collections?
• How can mixing seed ensure use and maintenance of existing
genetic diversity? mean Ns/Nc vs mean Ns/Nm.
• Advice/training to improve situation? Figs 2-4; to NGOs and/or
directly to communities? What specific advice/training?
• How does seed collection and plant production occur?
• Are seeds and plants transferred and if so how? Does this provide
limitations or opportunities?
Forest Genetic Resources Training Guide
Plan objective: ensure maintenance of genetic diversity
in the collection & supply of seed, & improved nursery
practice
• Plan should identify:
• influences on genetic diversity(bottlenecks, selection,
genetic drift) associated with current seed collection and
distribution paths
• key actors (individuals, institutions), processes (what actors
do), social limits in seed supply chain (policy, trade,
institutional, capacity). Communication/training needs
related to key actors.
• Specific actions to improve situation, addressing diversity
issues in seed system (e.g. practical ways to collect &
distribute seed/seedlings to ensure genetic diversity in
nurseries & material planted in field)