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Seed rain dynamics in temperate forestB. Li et al.Table 3. The response variables, predictive variables retained after the step-wise procedure and other related information for the autoregressive models.S in eq 1: seedrain densityk ineq(1)M in eq 1:meteorological measureVariables retainedafter step-wise procedureR 2PNUM 1 T NUM i 1 ;T i 1 0.417 1.01E-05NUM 2 T NUM i 1 ;T i 1 0.416 1.39E-05NUM 3 T NUM i 1 ;T i 2 ,NUM i 3 0.491 4.61E-06NUM 1 P NUM i 1 ;P i 1 0.365 5.42E-05NUM 2 P NUM i 1 ;P i 2 0.534 1.87E-07NUM 3 P NUM i 1 ;P i 2 0.534 2.75E-07WEI 1 T T i 1 0.281 0.000613WEI 2 T T i 2 0.332 4.84E-05WEI 3 T T i 2 0.323 7.73E-05WEI 1 P WEI i 1 ;P i 1 0.238 0.001867WEI 2 P P i 2 0.435 1.64E-06WEI 3 P P i 2 0.433 2.40E-06The abbreviations in the table are components in eq 1. NUM, number of seeds; WEI, weight of seeds; T, temperature; P, precipitation; k represents monthlylag used in the autoregressive models.Fig. 4. Similarity in species composition between species in the seed rainand species occurring within different radii (1–20 m) from each seed trap.Both patterns for all species and species grouped according to dispersalmode and growth form are shown. Similarity was measured with theJaccard coefficient.slowing down the process of competitive exclusion (Seidler& Plotkin 2006). Our research implies strong dispersal limitationin the studied forest. In our study, no seed was collectedfor 52% of the species. A similar phenomenon wasobserved in the BCI 50-ha plot, where no single seed wastrapped for 10% of the species during 10 yr (Hubbell et al.1999). Hubbell et al. (1999) also showed that most seedtraps captured about 50 (16.7%) species and that morethan 50% of species were distributed among no more thansix seed traps (Hubbell et al. 1999). We also observed similaraggregated distribution of species among seed traps.Besides dispersal limitation, the relatively short time ofseed collection may also contribute to the small number ofspecies collected because seed production is influenced bymasting years (Kelly & Sork 2002). Yet, dispersal limitationappears to be stronger in our plot than in BCI, given thatthe seed traps in our plot are so arranged that the largestdistance from a seed trap for all trees in the plot is only31 m (Fig. 1).It is widely recognized that seeds from forests that aredispersed by wind can disperse over a longer distance thanthose dispersed in other ways (Greene & Johnson 1995;Fragoso 1997; Qian 2009). In the study, we foundevidence for longer dispersal distance of wind-dispersedspecies: we collected a larger proportion (16/21) of winddispersedspecies than those dispersed by gravity (3/11)or gravity and animals combined (6/20) (Table 2); theJaccard coefficient of species dispersed by wind was consistentlylarger than for species dispersed by gravity, indicatingthat a larger proportion of wind-dispersed seeds in theneighbourhood arrive at seed traps than those dispersed bygravity. However, because our seed traps were erected 1 mabove the surface, the chances of collecting wind-dispersedand animal-dispersed seeds may differ and receives furtherinvestigation.In addition, our study indicated that dispersal distance isalso related to growth form of the species. In primary seeddispersal stages, tree height and large crown size facilitateseed dispersal. With the inverse modelling method, Muller-Landauet al. (2008) found that tree height is positivelycorrelated with dispersal distance; Tackenberg et al. (2003)further confirmed the effect of tree height on dispersal distance.Shrubs are much shorter and have smaller crownareas. This may explain why they have the smallest Jaccardcoefficients among growth forms. However, furtherwork is necessary because the seed trap arrangement couldbe even finer in this plot, although this arrangement isalready superior to similar research in other forest dynamicsplots (e.g. BCI).Dispersal distance can have an impact on subsequentseedling recruitment processes. For example, it is very difficultfor seeds near parent trees to thrive because of possiblespecies-specific pests and pathogens (Janzen 1970;Connell 1971) and other forms of inhibition. Therefore,Journal of Vegetation Science276 Doi: 10.1111/j.1654-1103.2011.01344.x © 2011 International Association for Vegetation Science89