Tree seed supply chains

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


Location of the countries and survey areas

KenyaUganda

Tanzania

Kabale

Mabira

Arusha

Meru

Nairobi

Location of nursery survey sites



Nursery sites


Why bother about genetic diversity?

• adaptation to changing environments• direct use of genetic resources• viability of populations in short term• - seed production• - inbreeding depression


Inbreeding depression in Acacia mangium in Sabah

Seed source

1st generation2nd generation

3rd generation

Seedling height (cm)32.520.718.1

Sim, 1984


Theory• direct impacts

• decrease population size

• increase spatial isolation

• decrease densities

• change local environment

genetic processes

genetic drift

gene flow

mating - inbreeding

selection


Bottleneck genetic drift


Isolated trees– mating patterns?


Altered mating patterns in farm trees?

• Predictions: increased inbreeding• greater pollen dispersal• fewer sires

• Isolated farm tree Continuous forest

inbreedingdispersal

sires


How many trees to collect from?


Data collected in a survey of seed-propagated tree species in tree nurseries from five areas in East Africa

Survey area (country) All areasKabale (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] 15 [8] 26 [16] 31 [25] 17 [10] 54 [54] 143 [113]All species 11 14 16 7 16 43Indigenous species 3 6 6 1 3 15Cases indigenous species 4 10 6 2 5 27Cases five most common species

2 3 11 10 40 66

Cases of unique species occurrence

3 6 6 2 5 22

Single tree collections all species

7 4 8 7 5 31

Single tree collections indigenous species

2 1 2 0 1 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)

Seedlings per nursery lot, Ns: mean (SD)

871 712 (1408)

2060 1408 (3661)

787 432 (1228)

1339 1011 (2127)

1543 676 (2535)

1378 401 (2446)

Clients per nursery lot, Nc: mean (SD)

12 14 (20)

41 27 (55)

17 9 (22) 81 92 (149)

22 5 (20) 28 10 (53)



Cupressus lusitanica

Wind pollinatedHermaphrodite, self compatible100,000 seed produced per tree


Calliandra calothyrsus

Bat/moth pollinatedHermaphrodite and male flowers, Mainly outcrossing1,000 seed produced per tree


Dovyalis caffra

Bird?/insect pollinatedDioecious270-470 seed produced per tree


Sclerocarya birrea – male tree being cut as not producing fruits


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


Senna siamea

• Insect pollinated• Hermaphrodite• Self–compatible?• High seed production per

tree


Procurement pathwaysNGOs compared with CBOs


Distribution pathways


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?


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)

Tree seed supply chains

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