3 Results

3.1 Sex ratio shifted from female-biased to male-biased during ontogeny

In 2017, a total of 297 D. morrisiana trees on the plot flowered, 181 males and 116 females, giving a male-biased operational sex ratio (OSR) of 0.61 (95% CI: 0.56–0.65). Among flowering trees, 45.3% of males and 34.5% of females were observed flowering again the following year. In contrast, among the 2,255 tagged individuals >1 cm DBH, the molecular sexing technique identified 1,068 male and 1,187 female trees (Figure 1), giving a significantly female-biased population sex ratio of 0.47 (95% CI: 0.46–0.49) (Figure 2a).
The flowering OSR of D. morrisiana was male-biased in each size class from small to large trees (Figure 2a). Although more male saplings (1–2cm) flowered, the number of total flowering individuals (n = 4) at this stage was too small to give a significant result (Table S1). In contrast, molecular sexing revealed that the population sex ratio shifted from female-biased in saplings to male-biased in large trees (Figure 2b).
The sex ratio of seedlings followed this same general pattern. Of the 2,203 seeds we collected from 16 mother trees, only 359 seeds from 12 mother trees germinated and survived to produce leaves. We were able to determine the sex of 349 seedlings. The overall sex ratio of seedlings from all the mother trees was strongly female-biased (0.38, 0.34–0.43) (Table S2). Because of the low numbers of seedlings from each mother tree, most sex ratios were statistically insignificant, except for seedlings of one mother tree (C) which were significantly female-biased.

3.2 Sexual dimorphism in life-history traits

We found significant differences in flowering proportion, tree size (DBH), and growth (RGR) between the two sexes (Figure 3). Male trees exhibited a higher flowering proportion than females (Figure 3a). Model results also showed that male trees had higher probability of flowering than female trees (Figure S1). When comparing all individuals together, male trees had a larger DBH than females, although this difference was not statistically significant (D = 0.05, p= 0.07) (Figure 3b, S2b). In contrast, the DBH of flowering female trees was slightly, but not significantly, larger than the DBH of flowering males (D = 0.07, p = 0.92) (Figure 3b, S2a).
Across all individuals, there was no significant difference between the RGR of males and females (D = 0.03, p = 0.70) (Figure 3c, S2d). However, in flowering individuals only, RGR was significantly higher in males than in females (D = 0.19, p < 0.01) (Figure S2a). The RGR of flowering females was significantly lower than that of non-flowering females (D = 0.20, p < 0.01), whereas the RGR of flowering and non-flowering males did not differ significantly (D= 0.07, p = 0.46). In the comparison of RGR at each life stage for flowering individuals, flowering male trees had higher RGR than flowering females at the medium-sized stage (D = 0.27, p< 0.01), while there was no significant difference between RGR of males and females in small flowering trees (D = 0.18, p= 0.78) (Figure S3). The RGR of male trees was also higher than that of females in flowering large-sized trees, but it was not significant (D = 0.20, p = 0.45) (Figure S3). Model results also showed that the RGR of male trees was higher than that of females only in flowering individuals but not in all individuals pooled (Figure S4).
During the period between the two censuses, 465 trees died, but only 43 of these trees were sexed, 21 of which were females and 22 of which were males, yielding a mortality rate of 1.77% for females and 2.06% for males.

3.3 Spatial segregation of sexes

For all tagged individuals of D. morrisiana in the HSD plot, we found that males and females were spatially segregated only at small scales (Figure 4, S5). The mark connection functionpMF (r ) was below the simulation envelopes within 2 m, which indicated that the probability of both female and male trees appearing together at this scale was lower than the expectation of the random labeling null model (Figure 4b). On the other hand,pMM (r ) andpFF (r ) lay well inside the global simulation envelopes for all distances r , exhibiting no repulsion or attraction within the sexes.