Searsia (Anacardiaceae) in perspective, part 2
...continued from https://www.inaturalist.org/journal/milewski/67776-searsia-anacardiaceae-in-perspective-part-1#
Some thoughts on the ecology of Searsia laevigata:
This species straddles the distinction between strandveld (which is relatively exempt from intense fire) and fynbos (which depends on fire).
Searsia laevigata deviates from the typical small shrubs of fynbos in a) being semi-deciduous, b) being relatively non-flammable, c) tending to be semi-prostrate, and d) having bright-hued fruits and endozoochory.
However, its semi-deciduousness may not conform to the drought-deciduousness well-documented under mediterranean-type climates in California and Chile. Instead, it may reflect an easily overlooked relationship to herbivory.
Searsia laevigata seems to retain a dependence on defoliation by fire, becoming bedraggled-looking in stands unburnt for more than a few years.
I noticed this in the winter of 2001, when I observed S. laevigata
- near Olifantsbos in the Cape Point section of Table Mountain National Park, in mature fynbos/strandveld (in a condition similar to https://www.inaturalist.org/observations/89056617 and https://www.inaturalist.org/observations/57867958 and https://www.inaturalist.org/observations/88925450), and
- at Fairhill Nature Reserve near Gansbaai, in fynbos/strandveld 8 months after an overdue fire (in a condition similar to https://www.inaturalist.org/observations/143859147 and https://www.inaturalist.org/observations/157994752 and https://www.inaturalist.org/journal/milewski/81213-field-notes-from-fairhill-nature-reserve-western-cape-province-south-africa-part-1-the-common-eland-taurotragus-oryx#).
In the former situation it looked more bedraggled than the rest of its community, as if semi-senescent despite a low stature, or as if drought-stricken despite this being the rainy season. In the latter situation it looked vigorous and 'refreshed', having regenerated vegetatively from the base.
I infer that the regime natural to S. laevigata is a 'pastoral' one in which frequent, mild fire (of the sort formerly promoted by Khoekhoe pastoralists) is accompanied by considerable folivory by ungulates.
Also please see
https://www.inaturalist.org/journal/milewski/68664-searsia-has-dense-wood-unusual-for-family-anacardiaceae-part-1#
https://www.inaturalist.org/journal/milewski/68675-searsia-has-dense-wood-unusual-for-family-anacardiaceae-part-2#
https://www.inaturalist.org/posts/68676-searsia-has-dense-wood-unusual-for-family-anacardiaceae-part-3-related-genera-in-kruger-national-park#
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https://www.inaturalist.org/observations/80521132
SEARSIA UNDULATA
Searsia undulata (https://www.inaturalist.org/observations/9228216 and https://www.inaturalist.org/taxa/575088-Searsia-undulata) is fully evergreen and non-spinescent.
Its stem-configuration suggests some adaptation to folivory by ungulates, at a genetic level.
This species tends to have a branching pattern, at the scale of its twig-size stems, that forms perpendicular barriers to any herbivore attempting to strip the leaves (https://www.inaturalist.org/observations/145088817 and https://www.inaturalist.org/observations/93584409).
This adaptation makes little sense w.r.t. Diceros bicornis, which simply clips stems of twig-size by means of its premolars.
However, it does make sense w.r.t. Taurotragus oryx and Loxodonta africana, because a) both might strip the foliage, and b) the stems are likely to be extremely non-brittle, even when subject to the pull-force exerted by the proboscis of elephants.
Searsia burchellii is similar (https://www.inaturalist.org/observations/81036567).
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