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!