Spatial pattern of seed dispersal in a subtropical community in Dalaoling Mountains, Three Dams Advisor: Zehao Shen, Associate Professor Department of Environmental Sciences, Peking University Nan Lu Sep.9, 2005 P eking University

Seed dispersal Primary/original dispersal Secondary/post dispersal Parent Plant Seed Rain Seedling Soil Seed Bank 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 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 of Seed rain Pattern of soil Seed bank Community seed dispersal pattern Landform Position Shape Exposure Steepness * 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 broadleaved mixed forest Middle range of the mountain: 1100~1700 m National Forest Park Elevation: 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 m 2 ) 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, 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. ） / m 2 Species Richness = number of species / m 2 Reserves of Soil Seed Bank = seed number （ Ind. ） / m 2 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

Figure 1 Comparison of seed rain density (average of 2001 to 2004) on different topographic positions, shapes and exposures. Topographic Grouping Factors Seed density (Ind. /m 2 ) Position Shape Exposure

Steepness (°) Seed density (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 Steepness ( °) Figure 3 Species richness of seed rain on the slope gradient Number of species

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, productivity Seed dispersal in horizontal and vertical directions Gravity Wind

(1) Vertical distribution of reserves of soil seed bank Figure 4 Reserves of herbaceous seeds (Ind./m 2 ) Figure 5 Reserves of arboreal seeds (Ind./m 2 ) Kruskal Wallis Test, *p <0.05, **p < 0.01 A: Litter-fall layer B: 0~5cm C:5~10cm LY: Fagus lucida forest MZX: Capinus fagesii forest TSL: Tsuga chinensis forest Results – pattern of soil seed bank

(2) Reserves of soil seed bank on different slope positions Type of community Figure 6 Reserves of herbaceous seed bank on three slope positions Kruskal Wallis Test, *p <0.05, **p < 0.01 LY: Fagus lucida forest MZX: Capinus fagesii forest TSL: Tsuga chinensis forest Top-ridge Slope Valley Type of community Figure 7 Reserves of arboreal seed bank on three slope positions Top-ridge Slope Valley

Percent (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./m 2 ) Table 4 Seed bank reserves (Ind./m 2 ) SPR AUT B/R Ratio Comparison of spatial pattern: The average seed rain density of 4 years are significantly different at three slope positions: P 01~04 = （ α= 0.05 ）， Top-ridge>Mid-slope>Valley. The seed bank reserves are not significantly different at three slope positions: P Spring = ， P Autumn = （ α = 0.05 ）. The result indicates ： More seeds input did not lead to more seeds accumulation in the soil on higher slope positions. 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,water Wind Gravity Transmission 地表搬运 Conclusions Topography 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.

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