Post on 04-Jan-2016
Spatial pattern of seed dispersal in a subtropical community in Dalaoling Mountains, Three Da
ms
Advisor: Zehao Shen, Associate ProfessorDepartment of Environmental Sciences, Peking University
Nan LuSep.9, 2005
Peking University
Seed dispersal
Primary/originaldispersal
Secondary/postdispersal
ParentPlant
SeedRain
Seedling
Soil SeedBank
Dispersal is the departure of a diaspore (seed or fruit as the unit of the plant that is actually dispersed) from the parent plant.
Seed dispersal process:
Environmental Sieve
Environmental Sieve
Life history loop
Seed dispersal pattern
Previous studies on the seed dispersal pattern mainly focused on:
An individual plant or a single population (seed shadow) in the homogeneous environment.
Seed dispersal pattern at the community level in the heterogeneous environment is little understood.
Objectives Topography is one of the major sources of spatial heterogeneity. I aim to find out if the community-level seed dispersal pattern is affected
by topographic heterogeneity.
Pattern ofSeed rain
Pattern of soilSeed bank
Communityseed dispersal
patternLandform
PositionShapeExposureSteepness
* 1: To examine if topographic factors (slope position, shape, exposure, steepness) have unique influence on the spatial pattern of seed rain.
* 2: To examine if topographic factors (mainly position) have unique influence on the spatial pattern of soil seed bank.
Parent plant distribution Wind, Gravity
Surface soil runoff, erosion
Study Area
Dalaoling Mountains, northern bank of the Three Dams, Hubei Province
110º52'~111º01‘ E, 31º01'~31º08‘ N Subtropical region Ever-green and deciduous broadleav
ed mixed forest Middle range of the mountain: 1100~1
700 m
National Forest Park Elevation: 1440-1490 m Community structure:Dominant deciduous species: Fagus lucida
(Fagaceae), Sorbus folgneri (Rosaceae)
Dominant ever-green species: Cyclobalanopsis myrsinaefolia (Fagaceae).
Seed Rain
Collecting seeds every two days from Aug.1 to Dec. 31, 2001~2004
Plastic mesh cone (0.6 m deep, 1 m2 ) supported by a round wire frame 1 m off the ground.
Sampling Design : Exposure ( 1-3 ) Position ( 1-5 ) Shape ( 1-3 ) Steepness 10 topographic positions(sites),
each site has 10 repetitions, 100 plots in total.
Methods
ridge
mid-slope
Two collections were operated on May 1 and Oct. 1, 2002.
Sampling design : Position (top-ridge, slope, valley)
Litter-fall layer 0-5 cm layer 5-10 cm layer 0.2 m * 0.2 m 40 subplots in total
Seed Identification:• Arboreal seeds (>0.85 mm) : Filtering with sieves (No. 6, 10, 20), picking out. • Herbaceous seeds (<0.85 mm): Germination, Illuminated incubator, 25 ( ±1 )℃ , 60 days.
Soil Seed Bank
Methods
Data Analysis
Parameters:
Seed Rain Density = seed number ( Ind. ) / m2
Species Richness = number of species / m2
Reserves of Soil Seed Bank = seed number ( Ind. ) / m2
Sorenson Coefficient , SI = 2C/ ( A+B )
Statistical Test: Non-parameter Kruskal Wallis Test
Results – pattern of seed rain(1) Pattern of the seed rain density
Table 1 Kruskal Wallis Test of seed rain density difference among groups divided by the three types of topographic factors
grouping factor
Position Shape Exposure Year
H P H P H P
2001 5.216 0.074 4.759 0.093 0.088 0.957
2002 20.043 0.000 12.615 0.002 0.995 0.608
2003 1.458 0.482 0.457 0.796 1.490 0.475
2004 8.035 0.018 8.790 0.012 12.263 0.002
Average 19.706 0.000 16.253 0.000 15.849 0.000
Figure 1 Comparison of seed rain density (average of 2001 to 2004) on different topographic positions, shapes and exposures.
Topographic Grouping Factors
See
d d
ensi
ty (
Ind
. /m
2 )
Position Shape Exposure
0
40
80
120
10 20 30 40 50
Steepness (°)
See
d d
ensi
ty (
Ind
. /m
2 )
Figure 2 Seed rain density (average of 2001 to 2004) on the slope gradient
(2) Pattern of species richness of the seed rain
Table 2 Kruskal Wallis Test of species richness difference among groups divided by the three types of topographic factors
grouping factor Parameter
Position Shape Exposure
H 13.2534 10.5817 6.3742
P 0.0013 0.0050 0.0413
Steepness ( °)Figure 3 Species richness of seed rain on the slope gradient
Number of species
0
2
4
6
8
10 20 30 40 50
Conclusion Seed rain density and the species richness are greatly affected by slope position,
shape and exposure; steepness has no effect on seed rain density and the species richness.
Pattern of seed rain
—light/energy/water/nutrient
—wind speed/direction; gravity Topography
Pattern of the parent tree density, productivitySeed dispersal in horizontaland vertical directions
Gravity
Wind
0 110 220 330 440 550
LY
MZX
TSL
Com
mun
ity ty
pe
Spring
0 110 220 330 440 550
LY
MZX
TSLABC
**
Autumn
**
0 60 120 180 240 300
LY
MZX
TSLABC
*
Autumn
0 60 120 180 240 300
LY
MZX
TSL
Com
mun
ity ty
pe
*
Spring
(1) Vertical distribution of reserves of soil seed bank
Figure 4 Reserves of herbaceous seeds (Ind./m2)
Figure 5 Reserves of arboreal seeds (Ind./m2)
Kruskal Wallis Test, *p <0.05, **p < 0.01
A: Litter-fall layerB: 0~5cmC:5~10cmLY: Fagus lucida forestMZX: Capinus fagesii forestTSL: Tsuga chinensis forest
Results – pattern of soil seed bank
(2) Reserves of soil seed bank on different slope positions
Type of communityFigure 6 Reserves of herbaceous seed bank on three slope positions
Kruskal Wallis Test, *p <0.05, **p < 0.01
LY: Fagus lucida forestMZX: Capinus fagesii forestTSL: Tsuga chinensis forest
0
400
800
1200
1600
LY MZX TSL
Rese
rves
of
seed
s(In
d./m
2)
Spr i ng
0
400
800
1200
1600
LY MZX TSL
Topr i dge顶脊 Sl ope山坡 Val l ey沟谷
Autumn
**
Top-ridgeSlopeValley
0
700
1400
2100
2800
LY MZX TSL
Rese
rves
of
seed
s(In
d./m
2)
Spr i ng
**
0
700
1400
2100
2800
LY MZX TSL
Topr i dge顶脊 Sl ope山坡 Val l ey沟谷
Autumn
Type of communityFigure 7 Reserves of arboreal seed bank on three slope positions
Top-ridgeSlopeValley
Per
cent
0. 0
0. 2
0. 4
0. 6
0. 8
1. 0
T S V
A
T S V
C
T S V
ABC
E
0. 0
0. 2
0. 4
0. 6
0. 8
1. 0
T S V
B
T S V
D
T S V
A
BC
F
0. 0
0. 2
0. 4
0. 6
0. 8
1. 0
T S V
G
T S V
I
T S V
A
BC
K
0. 0
0. 2
0. 4
0. 6
0. 8
1. 0
T S V
H
T S V
J
T S V
ABC
L
(3) Comparison of vertical distribution of arboreal and herbaceous soil seed bank reserves on different slope positions
Figure 8 Distribution of soil seed bank in soil profiles
T: Top/ridge S: Mid-slope V: Valley
A~F: Arboreal seeds: LY Autumn(A)Spring(B); MZX Autumn(C) Spring(D); TSL Autumn(E) Spring(F)G~H: Herbaceous seeds: LY Autumn(G) Spring(H); MZX Autumn(I) Spring(J); TSL Autumn(K) Spring(L)
Slope position
Lower slope positions have relatively frequent disturbances, which make it easier for seeds to move into the earth; At the same time, seeds on lower positions are buried by the surface soil transported from higher positions. Seeds are accumulating at lower positions!
The pattern of the community soil seed bank is greatly affected by position factor.
Conclusions
Results - analysis of arboreal seed dispersal : Comparing seed rain and soil seed bank
Comparison of quantity:
Table 3 Seed rain density (Ind./m2)
Table 4 Seed bank reserves (Ind./m2)
SPR
15
17
189
AUT
11
21
19
B/R Ratio
Comparison of spatial pattern:
The average seed rain density of 4 years are significantly different at three slope positions: P01~04 = 0.0087 ( α= 0.05 ), Top-ridge>Mid-slope>Valley.
The seed bank reserves are not significantly different at three slope positions: P Spring = 0.9551 , P Autumn= 0.8141 ( α = 0.05 ) .
The result indicates : More seeds input did not lead to more seeds accumulation in the soil on higher slope positions.
Soil layer 2001 2002 2003 2004 Average
Top-ridge 35.90 52.50 1.45 37.55 31.85
Slope 9.00 34.33 1.30 41.97 21.65
Valley 4.60 2.20 2.43 13.67 5.73
Spring Autumn
497.50±671.80 370.00±296.46
388.24±352.68 462.50±380.23
1085.71±1401.85 970.00±757.58
B seed rain density
R seed bank reserves
Discussion From the primary to the secondary dispersal processes, the spatial
pattern of community seeds was greatly changed.
The pattern of parent trees, which is highly correlated with topography was still the determinate factor of seed rain pattern. Seeds tended to distribute within the range close to their mother plants; On the other hand, the primary seed dispersal was affected by wind, which is also related to topographic characteristics.
In the secondary seed dispersal process, soil erosion and soil accumulation from high positions to low positions led to the seed flux along the aspect gradient, re-shaping the spatial pattern of the seeds on different positions and in different soil depth. This process weakened the seed rain pattern after the primary seed dispersal.
Light, temperature, nutrients,waterWind
GravityTransmission地表搬运
ConclusionsTopography and geomorphological processes played significant roles in the
process of seed dispersal from three aspects:
1) Controlling the distribution pattern of parent trees;
2) Affecting the important dispersal force – wind;
3) Driving the erosion, transmission and deposition of soil flux with seeds carried in it.
Thank you!