An odd case of scenery shaped by natural mega-masculinity

Many thanks to @zarek for help with this Post.

Everyone knows that flat-topped trees occur in African savannas, as epitomised by the Serengeti ecosystem.

However, how many realise that one of the most photogenic of these would not be flat-topped but for planar pruning by giraffes and the bush elephant (Loxodonta africana)? And that this has a sexual dimension?

Balanites aegyptiaca (https://www.inaturalist.org/observations/34646560 and https://fineartamerica.com/featured/savanna-sentinel-maasai-mara-kenya-stephen-stookey.html and https://en.wikipedia.org/wiki/Balanites_aegyptiaca) has a flat top the lower margin of which is always at precisely the height of maximum reach of fully mature male giraffes (https://www.alamy.com/stock-photo-masai-giraffe-feeding-on-acacia-tree-masai-mara-national-reserve-kenya-26388262.html and http://localcode.org/2021/05/why-giraffes-have-anxiety/ and https://www.travelblog.org/Photos/8132188 and https://www.shutterstock.com/nb/image-photo/giraffe-eatting-acacia-tree-leafs-grumeti-1672550830).

Vegetation characterised by flat-topped B. aegyptiaca is particularly associated with the Maasai Mara National Reserve in southwestern Kenya, which constitutes the northernmost part of the Serengeti ecosystem (e.g. https://fineartamerica.com/featured/1-reticulated-giraffe-kenya-mint-images-art-wolfe.html and https://fineartamerica.com/featured/acacia-trees-of-masai-mara-csilla-florida.html and https://www.inaturalist.org/observations/32535668 and https://www.gettyimages.com.au/detail/photo/acacias-masai-mara-national-reserve-royalty-free-image/594906082?adppopup=true and https://www.inaturalist.org/observations/92778234).

However, it is recorded also from semi-arid central Kenya, where a different species of giraffe occurs: https://www.inaturalist.org/observations/6820525 and https://www.gettyimages.com.au/detail/photo/kenya-meru-np-desert-date-tree-in-savannah-royalty-free-image/200522407-001?adppopup=true.

In giraffes, foraging postures are surprisingly dimorphic along sexual lines. Whereas adult females forage mainly with the neck horizontal, mature males forage mainly with the neck upright (http://www.miketaylor.org.uk/tmp/giraffes/Simmons_96_giraffe-sex.pdf and https://www.researchgate.net/publication/229562000_Sexual_segregation_by_Masai_giraffe_at_two_spatial_scales and https://www.researchgate.net/publication/312385422_Sexual_segregation_in_foraging_giraffe).

The following shows that, even when stretching vertically, females of the Maasai giraffe (Giraffa tippelskirchi) would be far too short to reach the 'browse-line' set by mature males on B. aegyptiaca: https://es.123rf.com/photo_97831866_three-giraffes-under-acacia-tree-in-the-african-savannah.html.

What this means is that a conspicuous feature of the Serengeti is maintained quasi-horticulturally by mature male giraffes. Here, B. aegyptiaca is shaped at the scale of the scenery by not only megaherbivory but also fully erect masculinity.

The following, marginally influenced by megaherbivores at the northern edge of the Serengeti ecosystem, shows the form of the crown of B. aegyptiaca free of recent pruning: https://www.inaturalist.org/observations/47865466. Where megaherbivores are absent, the following is representative: http://tropical.theferns.info/image.php?id=Balanites+aegyptiaca.

The following, of ecologically similar Balanites maughamii in and near Kruger National Park in South Africa, confirm that the crown in this genus is not intrinsically broader than it is deep: https://www.inaturalist.org/observations/96987381 and https://www.inaturalist.org/observations/10803334 and https://www.inaturalist.org/observations/28544857.

Even in the Maasai Mara National Reserve, B. aegyptiaca would not be flat-topped were it not for a fortuitous limitation on the height of the trees. This is shown by the following of B. maughamii in Kruger National Park, which grows tall enough to give some depth to the crown above any 'browse-line': https://www.inaturalist.org/observations/84345825.

The following show that females of the Maasai giraffe can reach the crown of B. aegyptiaca only when the trees are still young: https://www.gettyimages.com.au/detail/photo/masai-giraffes-feeding-on-a-great-acacia-tree-masai-royalty-free-image/975235594?adppopup=true and https://www.gettyimages.com.au/detail/photo/masai-giraffe-feeding-on-a-great-acacia-tree-masai-royalty-free-image/975235622?adppopup=true and https://www.shutterstock.com/nb/image-photo/african-giraffegiraffa-camelopardalis-on-masai-mara-153384374.

The 'browse-line' is about 6 metres above ground level (see https://www.guinnessworldrecords.com/news/2020/7/say-high-to-forest-guinness-world-records-reveals-the-worlds-tallest-giraffe-625257 and https://www.inaturalist.org/observations/35337181 and https://fineartamerica.com/featured/masai-giraffes-monika-bhm.html). Balanites aegyptiaca thus provides a natural scale in any photo containing flat-topped individuals of this species (e.g. https://www.istockphoto.com/photo/giraffe-walking-on-the-plains-of-the-masai-mara-national-park-gm1277799866-376914862).

The site-specific context of flat-topping in B. aegyptiaca is shown by comparison with a far more widespread flat-topped tree, the acacia Vachellia tortilis (https://en.wikipedia.org/wiki/Vachellia_tortilis).

Vachellia tortilis extends from the range of the reticulated giraffe (Giraffa reticulata) in northeastern Africa (https://www.istockphoto.com/photo/giraffes-eat-leaves-from-the-acacia-trees-gm1145171139-308148025 and https://www.dreamstime.com/giraffes-eat-leaves-acacia-trees-image145927594 and https://www.istockphoto.com/photo/giraffe-and-the-sahara-gm145927660-5898831) to southern Africa, where Balanites is present (albeit not flat-topped) in the form of the species B. maughamii (https://www.inaturalist.org/observations/96987302).

The difference between these flat-tops is that the shape of the crown in certain subspecies of V. tortilis is intrinsic, i.e. genetically 'hardwired', and produced independently of any pruning by megaherbivores.

This is easily proven by many photos showing individuals of V. tortilis close to giraffes but so tall as to be completely out of reach of their foraging (e.g. https://www.istockphoto.com/photo/giraffes-and-tree-gm471562500-62851392 and https://www.istockphoto.com/photo/four-giraffes-stand-under-the-acacia-tree-gm1095915896-294204080 and https://www.istockphoto.com/photo/two-giraffes-gm187666654-28988606 and https://www.gettyimages.com.au/detail/photo/group-of-giraffes-below-an-acacia-tree-royalty-free-image/1043213214?adppopup=true and https://www.gettyimages.com.au/detail/photo/young-maasai-giraffe-royalty-free-image/1170328810?adppopup=true and https://www.gettyimages.com.au/detail/photo/giraffe-under-an-acacia-tree-royalty-free-image/1297807624?adppopup=true and https://www.gettyimages.com.au/detail/photo/group-of-giraffes-below-an-acacia-tree-royalty-free-image/1043212864?adppopup=true and https://www.agefotostock.com/age/en/details-photo/umbrella-thorn-acacia-vachellia-tortilis-previously-acacia-tortilis-and-masai-giraffe-or-maasai-giraffe-giraffa-camelopardalis-tippelskirchi/WR2669234 and https://www.freeimages.com/premium/giraffe-under-acacia-tree-1451292 and https://www.gardenguides.com/12512303-facts-about-umbrella-thorn-acacia.html and https://www.gettyimages.com.au/detail/photo/elephant-under-umbrella-acacia-tarangire-national-royalty-free-image/1227143022?adppopup=true).

The following gives a misleading impression that the upper surface of this well-grown sapling of V. tortilis is being shaped by the Maasai giraffe (of which a mature male is pictured): https://www.robertharding.com/preview/741-5768/masai-giraffe-giraffa-camelopardalis-tippelskirchi-ndutu-serengeti-unesco/. In fact this shape is spontaneously adopted in V. tortilis regardless of pressures by either giraffe or elephant.

The following show how the crown of B. aegyptiaca is shaped as soon as it overtops mature males of the Maasai giraffe: https://fineartamerica.com/featured/nibbling-the-treetop-lindley-johnson.html and https://www.alamy.com/stock-photo-giraffe-feeding-from-an-acacia-tree-15304538.html and https://www.gettyimages.com.au/detail/photo/masai-giraffes-feeding-on-a-great-acacia-tree-masai-royalty-free-image/975235426?adppopup=true and https://www.sciencephoto.com/media/389403/view/giraffe-giraffa-camelopardalis-eating-from-tree and https://www.gettyimages.com.au/detail/photo/masai-giraffes-feeding-on-a-great-acacia-tree-masai-royalty-free-image/975235458?adppopup=true and https://www.gettyimages.com.au/detail/photo/masai-giraffes-feeding-on-a-great-acacia-tree-masai-royalty-free-image/975235392?adppopup=true.

Publicado por milewski milewski, 01 de diciembre de 2021

Comentarios

I'll come back to read it when you're finished! :D

Publicado por mbwildlife hace 9 meses (Marca)

When Vachellia is a sapling, it can be suppressed and hedged for several years by megaherbivores. Eventually a few shoots 'get away' to form a crown above the reach of mature males of both giraffe and elephant, resulting in a 'duplex' shape: mahttps://fineartamerica.com/featured/reticulated-giraffes-eat-from-tree-steve-somerville.html.

Publicado por milewski hace 9 meses (Marca)

The following is a different genus of tree, but shows that the 'browse-line' corresponds to the maximum reach of mature males of the Maasai giraffe: https://fineartamerica.com/featured/giraffe-kenya-africa-keith-levit.html.

Publicado por milewski hace 9 meses (Marca)

I have a large amount of field data (mainly phenological) on Balanites glabra (of which I suspect the following is an illustration in Nairobi National Park: https://www.gettyimages.com.au/detail/photo/giraffe-grazing-top-of-the-acacia-thorn-tree-at-royalty-free-image/1014423062?adppopup=true), collected on the Athi-Kapiti plains near Nairobi in 1986-1988. Most still awaits publication but the following has appeared: https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2028.2006.00665.x.

Publicado por milewski hace 9 meses (Marca)

@mbwildlife Let me know what you think...

Publicado por milewski hace 9 meses (Marca)

@milewski yes, all three of those images in the first comment where you tag me show Boscia angustifolia
However, this one (https://www.gettyimages.com.au/detail/photo/herd-of-cattle-under-acacia-tree-in-a-tanzania-royalty-free-image/462575663?adppopup=true) shows Vachellia tortilis
This one (https://www.gettyimages.com.au/detail/photo/giraffe-grazing-top-of-the-acacia-thorn-tree-at-royalty-free-image/1014423062?adppopup=true) is difficult to say, but almost certainly a Balanites, possibly B. glabra, depending on where the photo was actually taken.
This one (https://www.sciencephoto.com/media/389403/view/giraffe-giraffa-camelopardalis-eating-from-tree) is a Balanites aegyptiaca
This one (https://www.nathab.com/blog/the-giraffe-african-savanna-relationship-its-complicated/) has several photos with different species, most of which are not identifiable with any certainty.

Publicado por zarek hace 9 meses (Marca)

It would be great to see a journal/blog post like this on how Balanites aegyptiaca are shaped by megaherbivores in the Mara Serengeti ecosystem and how different they are to those you find elsewhere. From my understanding, most of the large, mature B. aegyptiaca trees in the greater Mara-Serengeti ecosystem are between 75-150 years old. Very few young saplings are allowed to survive, unless they're protected by an elephant-proof fence, in which case they're almost unrecognizable to most amateur naturalists here, who are only accustomed to seeing heavily browsed, very old trees.
Along with Boscia angustifolia, as fire resistant species, they're the only remaining remnants of a once-extensive woodland that covered most of the Mara and northern Serengeti in the late 1800's before the rinderpest outbreak, and subsequent fires & elephant population boom.

Publicado por zarek hace 9 meses (Marca)

@milewski Very good writing, as always! Thoroughly researched.

Publicado por mbwildlife hace 9 meses (Marca)

@zarek Hi Zarek, Many thanks for all the useful information. Could you give this Post another once-over with your practised eye, to spot any errors in my writing? With many thanks from Antoni.

Publicado por milewski hace 9 meses (Marca)

@milewski Looks good. I realize my comment above asking for exactly this blog post was SUPPOSED to be on your similar blog about the browsing pressures on Gardenia volkensii. I didn't even realize you'd already created this blog. I'm so confused as to how my comments showed up here. :D
Perhaps you could show more images of what Balanites aegyptiaca looks like with no browsing pressure in the main body of the blog text. The one example you show from the northernmost reaches of the Mara ecosystem is within a fence that keeps the elephants out, but not the giraffes, so it's still subject to SOME browsing pressure. It's also old enough that it would have definitely been subject to both giraffe & elephant browsing before the fence was put up.
Here are a few examples that show just how extremely different they can look when not browsed at all:

https://www.researchgate.net/figure/Photo-3-Balanites-aegyptiaca-L-Del-adult-Photo-OHMi-team_fig5_320021303
https://www.researchgate.net/figure/Balanites-aegyptiaca-in-Qatar_fig3_281069191
http://tropical.theferns.info/image.php?id=Balanites+aegyptiaca
http://www.fruitipedia.com/2018/11/hankalta_balanites-aegyptiaca/
https://www.alamy.com/stock-photo/jericho-balsam-tree-balanites-aegyptiaca.html

Publicado por zarek hace 9 meses (Marca)

What's amazing/sad for me to see is just how many of the images you posted with links above are misidentified as Acacia trees. It seems everyone assumes that all flat-topped trees with thorns/spines must be Acacia.

Publicado por zarek hace 9 meses (Marca)

@zarek Hi Zarek, Many thanks, particularly for the useful photos, which I will indeed insert into the Post. Specimens from the Persian Gulf have a different aspect, suggesting a possible subspecies. I agree that the incuriosity that leads to an assumption of acacia is disappointing; After all it is hardly as if Balanites is just another boring and nondescript plant. It also surprises me how few photos there are on this very platform, iNaturalist. This applies particularly to Balanites glabra, which is a photogenic plant frequently viewed in Nairobi National Park but with no observations at all in iNaturalist. I have a large amount of data on the phenology of that species, which I would cheerfully turn over to anyone who could analyse them and write up the results.

Publicado por milewski hace 9 meses (Marca)
Publicado por milewski hace 8 meses (Marca)

@milewski have a look at some images of Elaeodendron buchananii from the greater Mara ecosystem. The leaves are poisonous to livestock and most wildlife, but the giraffe and elephants love them. The resulting browse line is very interesting.

Publicado por zarek hace alrededor de 2 meses (Marca)

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