Autecological studies on Audouinia capitata 4. Seed Banks

Autecological studies on Audouinia capitata (Bruniaceae). 4. Seed production, seed banks and seedling recruitment. de Lange, J.H.; Boucher, C. (1993). South African Journal of Botany, 59, 145–155. doi:10.1016/s0254-6299(16)30748-7

Audouinia capitata (Lt.) Brongn. has an average annual production of 98 seeds per plant, determined from a study on approximately 800 of the 1200 plants in 25 known populations. Most of the buried seeds occurred within a radius of 2 m from the parent, in the top 20 mm of soil. Following exposure to plant-derived smoke, 13% of the fresh seeds and more than 80% of the oldest seeds germinated. Thirty-nine percent of the germinated seeds were unable to emerge from a mere 5 mm soil depth under optimal laboratory conditions. Seventeen to 31 months after a burn, 148 seedlings were recorded in seven populations containing 332 plants, from an estimated total annual production of approximately 40 000 seeds. The natural occurrence of small numbers of seedlings is only partially explained by factors investigated in this study. Seed set in at least 14 of the populations, having less than approximately 10 mature plants each, is probably too low to sustain future population expansions or even to maintain present levels.

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"Conclusions
Facets about the life cycle of A. capitata discussed in this study, are probably of crucial importance in the population dynamics of the species. Seed set in at least 14 of the 25 populations, having less than approximately 10 plants each, is probably too low to sustain future population expansions or even to maintain present levels. Seed production and the seed store in the soil are considered to be most important criteria which determine the successful maintenance of population levels (Boucher 1981).
The question may be raised whether eventual extinction faces all the smaller populations and whether some of the larger populations might eventually be degraded to the 'small population' category facing similar prospects as the present smaller populations. Demographic changes are likely to be gradual because A. capitata is an effective resprouter from a large lignotuber after fire. "
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"According to Bond and Slingsby (1983), A. capitata seeds are dispersed by ants. This observation was not confirmed in the present study. No elaiosome is present. The fruits are indehiscent and at the time of dispersal from the plant, the fruits are dry and do not present any attraction to ants. Observation of ant activity near A. capitata plants for continuing periods of up to two hours on several occassions over four years did not reveal any interest by foraging ants in the fruits. "

Populations:
Table 1 Results of a survey of natural seed production in all 25 known populations.
Presented here is just the number of plants per population. (1987-1990) for other details see the paper

500~ Karbonkelberg
162 Bonteberg South
98 Sirkelsvlei North
90 Olifantsbos
73 Bonteberg East
72 Sirkelsvlei West
71 Teeberg
27 Sirkelsvlei East
22 Bonteberg West
15 Rooihoogte West;
10 Anvil Rock East
8 EJsespiek
8 Klaasjagers Plateau
7 Diaz Cross
7 Kobrakamp
6 Lean Rock North
6 Rooihoogte East
6 Sirkelsvlei South
5 Rooikrans
4 Restersdam
1 Anvil Rock South
1 Babilonstoring
1 Brightwater
1 Kanonkop
1 Muizenberg Caves

Total 1202

Publicado el junio 16, 2022 07:46 TARDE por tonyrebelo