Trees outside of forests
Devising options for
conservation of two tree
species outside of forests
David Boshier
What are the impacts of human
interventions on trees?
What are the genetic impacts of
human interventions on trees?
Examples from other classes
impacts of human interventions on trees?
fragmentation, afforestation, silviculture,
deforestation, agriculture, shifting cultivation,
premature death, clear fell
genetic impacts of human interventions on trees?
hybridisation, inbreeding depression, dysgenic
selection, loss of genetic diversity, species loss,
increase variance between populations, genetic
loss/erosion
Genetic impacts of human
interventions on trees
Humans impact forests in a variety of ways, eg
• conversion of forest to agriculture & other uses
• forest fragmentation
• logging, harvesting of different types
• domestication/breeding
Need to consider influence of interventions on
functionality of tree populations & relevance to
conservation
Genetic impacts of human
interventions on trees
All interventions influence genetic diversity of trees
to greater or lesser extent
In many circumstances impacts on genetic diversity
may not be a priority
Foresters/conservation managers need to be able
to identify – how patterns of genetic variation are altered
– under what sort of circumstances genetic diversity
and its loss may become limiting
Where & how should we conserve?
In situ - Ex situ
In situ - reserve system of undisturbed,
protected areas within natural distribution
(ecosystem based)
Ex situ - artificial maintenance of populations
outside natural distribution (species based)
6
Impacts of human disturbance
not random
• often
superimposed on
habitat
heterogeneity
• may lose species
and populations
adapted to
lowlands/good
soils
Conservation of biodiversity in
situ: trees as a paradigm
ideal reserve model
emphasis: large, continuous, protected areas
limitations: location, size, security, biology:
–
–
–
–
movement of animals
extensive distribution of many species
gene flow between populations
upland, non agricultural areas
essential but not sufficient
Where should we conserve?
In situ - Ex situ
In situ - reserve system of undisturbed,
protected areas within natural distribution
(ecosystem based)
Ex situ - artificial maintenance of populations
outside natural distribution (species based)
10
Conservation of biodiversity ex situ:
methods and limitations
seed banks - problems of regeneration
plantations - changes in gene frequencies, few
populations
botanical gardens - deficiencies for gene pool
conservation
11
© RBG Kew
© RBG Kew
© DH Boshier
a large number of individuals of many species have
long ago ceased being ecologically (and
evolutionarily) reproductive; they flower but set no
These
are the
deadnever lead to
seed, or if they
set seed,
theliving
seedlings
12
Janzen 1986
recruitment of adults.
© DH Boshier
Issues of concern – conservation
of tree genetic resource outside of
forests
• Conservation of species and genotypes
• Conservation paradigms – in situ, ex situ,
through use on farms – circa situm
• Fragmentation – gene flow patterns and
maintenance of viable populations
• Reproductive materials: source and collection
Theory
direct impacts
genetic processes
decrease pop. size
genetic drift
increase spatial isolation
gene flow
decrease densities
mating - inbreeding
change local environment
selection
A: Low genetic structure
Low genetic differentiation (Gst)
y
x
y
z
xy
z
xy
z
x
y
x
z
y
xy
z
xy
z
z
xy
z
x
z
Fragmentation
xy
z
y
x
xy
z
xy
z
High genetic differentiation (Gst)
B: High genetic structure
yy
y
yy
zzz
zz
z
yy
y
xx
x
Fragmentation
zz
xx
x
yy
y
xx
x
zz
xx
zz
yyy
yy
y
xx
x
yy
y
A: Drift and extinction: loss of genetic
diversity
xy
z
xy
z
xy
z
xy
z
Drift – no
gene flow
zz
z
xx
x
Increased genetic differentiation
(Gst)
yy
y
yy
y
Extinction
xx
x
xx
x
B: Gene flow reduces loss of genetic
diversity
xz
xy
z
xy
Drift
z
xy
z
z
gene flow
xx
xy
y
xy
z
xy
y
z
xy
z
Extinction
xx
y
Reduced genetic differentiation
(Gst)
A: fragmentation with drift among isolates
y xy
z
x
xy
y z
z
z
x
y xy
z
y
xx y
z
x y
zz
z
xz
z
z
yy
x
xx
y
z
High genetic differentiation (Gst)
yy
y
xx
x
xx
x
xx
z
x
B: fragmentation with gene flow via ‘isolated’ trees
y xy
z
x
xy
y z
z
z
y xy
z
xx y
z
x y
x
y
z
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z
y
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xy
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z
x
x
x
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z
y
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z
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z
x
Low genetic differentiation (Gst)
Range of land-use systems may be important for
long term genetic viability of some tree species
through
– conservation of particular genotypes not found in
reserves
– facilitation of gene flow between existing reserves
– maintenance of MVPs (Minimum Viable Populations)
– intermediaries & alternate hosts for pollinators & seed
dispersers
Broad vision of corridors - mosaic of land-uses
that promote connectivity & conservation of
biodiversity more generally
Isolated trees
– can we collect seed?
Altered mating patterns in fragments
Predictions:
increased inbreeding
greater pollen dispersal
fewer sires
sires
inbreeding
dispersal
Isolated tree
Continuous forest
Can valuable tree genetic
resources persist outside of forests
and if so what measures need to
be taken to ensure they persist?
Swietenia humilis – IUCN listed as vulnerable,
also on CITES appendix II
monoecious flowers, self-incompatible, bee
pollinated, wind dispersed
Swietenia humilis
White, Boshier & Powell, 2002
trees sampled at Punta Ratón, Honduras
Pollen flow into fragments
Swietenia humilis
Fragment
Las Tablas*
El Jicaríto
Cerro El Jiote
Tablas Plains
Tree 501**
Fragment
“size”
97
44
22
8
1
% pollen from
outside
36.0
47.0
38.3
68.4
100.0
* part of continuous forest, surrounded by unsampled trees
** an “isolated” tree
White, Boshier & Powell, 2002
Frequency of pollen flow to S. humilis trees in
Cerro Jiote fragment and to an “isolated” tree,
Honduras
Pollen donors
C. Jiote
0.8
0.4
0
0.3-0.6
0.9-1.2
Distance, km
>1.5
Pollen donors
‘Isolated’ tree
0.8
0.4
White, Boshier & Powell, 2002
0
0.9-1.2
2.1-2.4
Distance, km
3.3-3.6
4.5
>20 trees selfed no seed
Pachira quinata
Central + South America
Deciduous tree
Hermaphrodite flowers
Self-incompatible
Bat (& moth) pollinated
Seed + ‘kapok’
wind dispersed
Costa Rica: Forest vs Pasture
Lomas Barbudal Reserve
Stewart Property
Forest
1000
Stewart Property
SP13
SP12
SP07
SP14
SP08
800
Pasture
North (m)
SP09
SP15
SP16
600
SP11
SP06
SP04
400
SP01
SP02
SP18
SP03
SP05
SP19
200
SP10
SP17
SP20
0
0
200
400
600
800
1000
West (m)
1200
1400
1600
1800
Results: Forest vs Pasture
Site
Forest
Outcrossing Correlation
rate (SE)
of tm (SE)
0.926
(0.021)
0.117
(0.045)
Number
of sires
Dispersal
distance
3.3 - 4.1
48 metres
Results: Forest vs Pasture
Site
Outcrossing Correlation
rate (SE)
of tm (SE)
Number
of sires
Dispersal
distance
Forest
0.926
(0.021)
0.117
(0.045)
3.3 - 4.1
48 metres
Pasture
0.828
(0.085)
0.636
(0.148)
2.9 - 4.4
158 metres
Lower outcrossing & greater dispersal but not
fewer sires in the pasture
Results: Forest vs Pasture
Site
Outcrossing Correlation
rate (SE)
of tm (SE)
Forest
0.926
(0.021)
Fuchs
Forest
0.915
(0.043)
Pasture
0.828
(0.085)
Fuchs
Pasture
0.777
(0.114)
0.117
(0.045)
Number
of sires
Dispersal
distance
3.3 - 4.1
48 metres
1.8 - 2.6
0.636
(0.148)
2.9 - 4.4
158 metres
1.2 - 1.6
Fuchs et al 2003 suggest isolated (>500m)
pasture trees receive less outcrossed pollen
Costa Rica: Pasture
1000
Stewart Property
SP13
SP12
SP07
SP14
SP08
800
Isolated by 350m
North (m)
SP09
SP15
SP16
600
SP11
SP06
SP04
400
29%
SP01
SP02
SP03
82%
51%
71%
SP18
SP05
SP19
200
SP10
SP17
SP20
29%
20%
0
0
200
400
600
800
1000
1200
West (m)
Predict that selfing will increase with isolation
But it doesn’t!
1400
1600
1800
Self-incompatibility system
Reduced germination of self pollen
–Slower growth rate of self pollen
Pollen reaching ovary
Self
Cross
48 hours
15%
56%
72 hours
64%
90%
120 hours
89%
90%
Ability to self varies among trees
–
–
50% non-selfers
12.5% selfers
WCMC World List of Threatened Trees
(IUCN Red List categories of threat)
http://www.wcmc.org.uk/trees/Background/intro.htm
9% of world's tree flora globally threatened with extinction
accuracy of assessment?
S. humilis P. quinata -
IUCN
vulnerable
not listed
this study
?
?
Your task
Derive an action plan to ensure
effective conservation and use of
both species outside of forests