Modes of regeneration in the southernmost patches of rainforest and vine thicket in Africa

(writing in progress)

The southernmost point of Africa is Cape Agulhas (https://en.wikipedia.org/wiki/Cape_Agulhas).

The vegetation hereabouts is mainly shrubby and prone to wildfire. However, there are several patches in which non-flammable trees dominate to the degree of producing wildfire-free vegetation over small areas (https://journals.co.za/doi/pdf/10.10520/AJA00423203_1660 and https://open.uct.ac.za/bitstream/handle/11427/26351/Kruger_Dynamicsconservation__1.pdf?sequence=1). Three of these patches are called Grootbos (https://www.inaturalist.org/places/grootbos-private-nature-reserve), Platbos and Steynsbos.

The question arises of how the trees and tall shrubs in these rainforests and vine thickets - which are periodically scorched at their edges - regenerate.

Celtis africana (https://www.inaturalist.org/taxa/133950-Celtis-africana and https://www.inaturalist.org/observations/40028876 and https://www.inaturalist.org/observations/33329789), the tallest species of indigenous tree in the region and dominant in one patch of forest, regenerates germinatively (e.g. https://www.inaturalist.org/observations/65430694). This species is also exceptional in being the only winter-deciduous tree in the Cape Floristic Region.

Apodytes dimidiata (https://www.inaturalist.org/taxa/489301-Apodytes-dimidiata), common in the same patch, also regenerates largely germinatively, and has a relatively even distribution of size-classes.

Sideroxylon inerme (https://www.inaturalist.org/taxa/362175-Sideroxylon-inerme), the dominant species of tree in the largest patch, is remarkably in its emphasis on vegetative regeneration. Virtually no seedlings or saplings can be found despite the fact that the seeds are dispersed and sown by fruit-eating birds. The species is long-lived and clonal.

Among the less common species:

Olinia ventosa (https://www.inaturalist.org/taxa/557509-Olinia-ventosa) has a similar pattern of regeneration to S. inerme, but is not as extreme. Furthermore, when planted in gardens it grows rapidly, in contrast to S. inerme which grows slowly.

Euclea racemosa ssp. racemosa (https://www.inaturalist.org/taxa/526223-Euclea-racemosa) regenerates mainly vegetatively, but seedlings can be found.

Pterocelastrus tricuspidatus (https://www.inaturalist.org/taxa/526208-Pterocelastrus-tricuspidatus), Chionanthus foveolatus (https://www.inaturalist.org/taxa/582167-Chionanthus-foveolatus), Afrocanthium mundianum (https://www.inaturalist.org/taxa/579167-Afrocanthium-mundianum) and Kiggelaria africana (https://www.inaturalist.org/taxa/119178-Kiggelaria-africana) can all be found in the form of seedlings as well as mature individuals.

The occurrence of the various species in the various patches is as follows.

Platbos only: Celtis africana (apart from two individuals at Grootbos), Apodytes dimidiata, Olinia ventosa, Afrocanthium mundianum, Kiggelaria africana (rare even here)

All the patches: Sideroxylon inerme, Euclea racemosa ssp. racemosa, Chionanthus foveolatus, Gymnosporia buxifolia (https://www.inaturalist.org/taxa/586670-Gymnosporia-buxifolia)

Grootbos and Platbos: Pterocelastrus tricuspidatus

Steynsbos only: Olea europaea ssp. cuspidata (https://www.inaturalist.org/taxa/57140-Olea-europaea)

Rare throughout: Ilex mitis (https://www.inaturalist.org/taxa/133559-Ilex-mitis), Ocotea bullata (https://www.inaturalist.org/taxa/557940-Ocotea-bullata)

(writing in progress)

Posted on February 23, 2022 10:03 PM by milewski