Significant trees of Sierras de Cordoba, nearest woodland to the treeless Pampas

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Readers, please come with me on a brief photo-tour of the woody vegetation of the Sierras de Cordoba (https://en.wikipedia.org/wiki/Sierras_de_C%C3%B3rdoba), the nearest mountain range to the Pampas (https://en.wikipedia.org/wiki/Pampas).

This may provide some hints as to what the vegetation of the Pampas might be like, were the grasses not so overwhelmingly dominant (https://www.inaturalist.org/journal/milewski/55189-the-empty-pampas-epitome-of-a-biogeographical-mystery-part-1#).

The topic should be of particular interest to those naturalists familiar with the Highveld (https://en.wikipedia.org/wiki/Highveld) of South Africa.

The Pampas of Buenos Aires province of Argentina, and the Highveld of Free State (https://en.wikipedia.org/wiki/Free_State_(province)) and adjacent provinces of South Africa, are the most extensive areas of treeless grassland in the southern hemisphere. However, the Pampas is unrivalled in its extreme treelessness (https://www.sciencedirect.com/science/article/pii/S0254629915003051).
 
The Sierras de Cordoba of Cordoba Province (https://en.wikipedia.org/wiki/C%C3%B3rdoba_Province,_Argentina), located northwest of the Pampas, are not to be confused with the foothills of the Andes. Although they may seem overshadowed by the Andes far to the west, the Sierras de Cordoba form an upland considerable in its own right.

The highest altitudes of this range are indeed treeless (= above the tree line). However, the lower slopes are wooded, forming vegetation that can loosely be described as chaco (https://www.researchgate.net/publication/202000227_What_is_the_Gran_Chaco_vegetation_in_South_America_I_A_review_Contribution_to_the_study_of_flora_and_vegetation_of_the_Chaco_V). And the composition of the dominant trees is intriguing, as I show below using just three example species.
 
Anacardiaceae are particularly prominent in these woodlands/dry forests. The examples I illustrate below are Schinopsis haenkeana (dominant on relatively dry, west-facing slopes) and Lithraea molleoides.
 
In southern Africa, naturalists cannot long overlook Anacardiaceae (Searsia, Harpephyllum, Ozoroa, Sclerocarya, Lannea, etc., https://www.inaturalist.org/observations?place_id=6986&taxon_id=48874&view=species).

However, anacardias do not naturally dominate woodland/dry forest anywhere in Africa (https://www.inaturalist.org/journal/milewski/68007-new-interpretations-around-the-marula-sclerocarya-birrea#). This is because the tree members of the family tend to be mesic and subordinate to other taxa, while the dominant forms tend to be shrubs of Searsia, in dry climates.

In Argentina and Chile, anacardiaceous trees seem to be naturally more prominent than in southern Africa.

Of course, many naturalists in various countries are familiar with anacardias in the form of Schinus molle (https://www.inaturalist.org/taxa/57354-Schinus-molle) and Schinus terebinthifolia (https://www.inaturalist.org/taxa/130872-Schinus-terebinthifolia). One can perhaps think of these Argentinian trees as essentially enlarged, arborescent counterparts for many searsias.
 
Then, another particularly prominent tree in the Sierras de Cordoba is the rutaceous species, Zanthoxylum coco (https://www.inaturalist.org/taxa/887202-Zanthoxylum-coco).

This is noteworthy, because it is as spinescent as any member of its cosmopolitan genus.

Prepare to be surprised at the spinescence of the rachis (https://en.wikipedia.org/wiki/Rachis) in Z. coco: https://noalatala.miraheze.org/wiki/Archivo:Zanthoxylum_coco_04.jpg and https://en.wikipedia.org/wiki/Zanthoxylum_coco#/media/File:Fagara_coco_leaves.jpg.

This, technically, may qualify as foliar spinescence. However, it is functionally equivalent to a form of caular spinescence that penetrates the leaf. This anti-herbivore adaptation might be unsurprising in a land of giraffes. However, it does surprise in central Argentina, where large arboreal herbivores - including even monkeys - are absent.

My most memorable encounter with Zanthoxylum was in shrubby form, among rocks just south of Suikerbosrand Nature Reserve (https://en.wikipedia.org/wiki/Suikerbosrand_Nature_Reserve) on the Highveld.

Well, here is the same strange, widespread genus again, this time in full tree form: https://www.inaturalist.org/observations/87438621. There are congeners similar to this in Africa, but the difference is – again – that in Africa this genus tends to get lost among the dominant trees belonging to other families and genera.
 
To summarise:
The dominant trees of the mountain range closest to the pampas belong to families and genera familiar to naturalists on the Highveld. However, they take an unusual prominence for these taxa.
 
Please entertain the following thought-experiment:
If one reduced these trees to tall shrubs, and let them grow in the pampas of one’s mind, what would the vegetation be like?

Well, I suppose, a bit like the vegetation of rocky outcrops on the Highveld, where Zanthoxylum is present in shrubby form, and anacardias are patchily common in the form of Searsia spp.

However, in reality these taxa have not achieved even the stature of tall shrubs in the Buenos Aires province. Instead, as far as I know, they are virtually absent in the Pampas.
 
Anacardiaceae: Schinopsis haenkeana, dominant on west-facing slopes:
https://3.bp.blogspot.com/-CjovMRUYNJ0/UWYCcYGfJ2I/AAAAAAAAOfI/4vcc4tuPW34/s1600/Schinop+haenkea.jpg
https://alchetron.com/Schinopsis-haenkeana

Anacardiaceae: Lithraea molleoides:
https://www.inaturalist.org/observations/115610242
http://subidaimagen.infojardin.com/subes/images/rgh1378133642r.jpg
http://www.tierranativa.com.ar/coco1.html

Rutaceae: Zanthoxylum coco:
https://www.inaturalist.org/observations/91481843
https://c2.staticflickr.com/8/7019/6661162439_de55962091_z.jpg
http://2.bp.blogspot.com/-lVHqcOkT__E/UDcj4HEHmAI/AAAAAAAABAk/iiV0VjEi6gQ/s640/Fotos+Macro+Macrografia+Photos+pictures+images+Macrography+hojas+hoja+plantas+leaf+plants+leaves.JPG

Publicado el julio 30, 2022 02:00 MAÑANA por milewski