Effects of habitat, burial, age and passage through birds on germination and establishment of chinese tallow tree in coastal South Carolina

Journal of the Torrey Botanical Society, Apr-Jun 2001 by Renne, Ian J, Spira, Timothy P, Bridges, W C

We monitored seedling emergence on 21 March, 5 April, 19 April, 13 May, 22 June, 8 August and 20 September 1996 (n = 7 dates) by marking newly emerged seedlings with a toothpick with dated masking tape. On 20 September 1996, the number of surviving seedlings was counted and differences in emergence and survival rate were tested as a function of habitat and planting date. Seedling survival for each plot was calculated by dividing the number of surviving seedlings by the total number of seedlings that emerged. A seedling was considered a survivor if it had at least one fully expanded leaf and a living shoot apex.

FIELD TRANSECT STUDY. Tallow tree population growth rates differ in the five coastal forest types described above (Renne, unpubl. data), so we investigated whether seedling emergence and survival were different in these habitats. Because herbivory, trampling by mammals and microsite differences can create spatial and temporal differences in seed germination and seedling survival (Howe et al. 1985; Oswald and Neuenschwander 1993), seeds were sown along unfenced transects where no litter or vegetation was removed.

On 15 March 1998, 6000 seeds were collected from ca. 100 tallow trees. Seeds were sown 0.5 cm deep at 20 cm intervals along five randomly placed 20 m transects in all five habitats (n = 100 seeds per transect and 500 seeds per habitat). On 23 May, 23 June and 31 July 1998, newly emerged seedlings were marked with a plastic straw and their transect position was recorded so that emergence and survival history could be determined for each seedling. Because seedlings may emerge from a seed bank, seedling emergence was also monitored along transects without sown seeds. These were located I m away from those with sown seeds. Final seedling number was estimated by subtracting numbers of surviving seedlings from transects without sown seeds from ones with sown seeds on 9 October 1998. This experiment was repeated on 18 March 1999, but freshly collected seeds were sown at 40 cm intervals along 20 rn transects located 1 rn away from those used the previous year (n = 50 seeds per transect and 250 seeds per habitat). Numbers of surviving seedlings were recorded on 10 October 1999 only.

SEED BANK STUDY. On 15 March 1998, the potential for a one- and two-year soil seed bank was assessed by burying two packs of 100 tallow tree seeds at a depth of 4 cm in each of three randomly selected, fenced locations in each of the five forest types (n = 3000 seeds). Seeds were placed in panty hose pouches surrounded with 0.5 cm mesh hardware cloth to prevent seed predation by rodents. One seed pack was recovered from each plot after one and two years. We assumed seeds with split seed coats had germinated. Ungerminated seeds were tested for viability with 1% TC. Actual sampling of the soil seed bank did not occur.

Six thousand seeds from one collection event were used in the seed bank, 1998 transect and second greenhouse experiment (1997-1998 seeds only). To obtain a baseline for initial seed viability, we split 101 of these seeds, counted the number of intact embryos, and placed cut embryos in 1% TC before any experiments were done.