Searsia has dense wood, unusual for family Anacardiaceae, part 2: comparison with Californian shrubs, including Rhus and Malosma

@tonyrebelo @jeremygilmore @wynand_uys

continued from https://www.inaturalist.org/posts/68664-searsia-has-dense-wood-unusual-for-family-anacardiaceae-part-1#

In part 1, I pointed out that Searsia has dense wood for an anacardia.

But, how dense is its wood, compared with a typical shrub in chaparral vegetation (https://en.wikipedia.org/wiki/Chaparral) in California, as well as coastal sagebrush and semi-desert scrub in the same region?
 
Please see the information in http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2008.02554.x/epdf.
 
The pattern is intriguing.
 
For reference, a species of Lycium (https://www.inaturalist.org/observations?place_id=14&taxon_id=58333&view=species) has wood density of 0.7. This is greater than I expected, based on the light wood of South African congeners.

Similar to this North American species of Lycium in wood density are the typical shrubs of the California chaparral, e.g.

• Adenostoma (https://www.inaturalist.org/observations?place_id=any&taxon_id=47147&view=species),
• Arctostaphyllos (https://www.inaturalist.org/observations?place_id=14&taxon_id=47179),
• Ceanothus (https://www.inaturalist.org/observations?place_id=14&taxon_id=49674&view=species), and
• Artemisia (https://www.inaturalist.org/observations?place_id=14&taxon_id=52855&view=species).

All have wood densities of 0.7 or less.

So does Quercus (https://www.inaturalist.org/observations?place_id=14&taxon_id=47851&view=species) in its chaparral shrub form, despite the reputation of oak wood.

Atriplex (https://www.inaturalist.org/observations?place_id=14&taxon_id=58112&view=species) differs from this standard of 0.7. Its wood has density 0.8.

Saltbush may look soft and weedy, but it has rather dense wood. This is borne out in the Karoo of South Africa. Here, farmers suffer punctures in their tyres, when they drive over the broken remnants of the stems at ground level, after ripping out former plantations of Atriplex nummularia (https://www.inaturalist.org/taxa/75711-Atriplex-nummularia).

The densest wood in this data-set is that of Larrea (0.85). This is a plant capable of living for hundreds or perhaps thousands of years (https://www.inaturalist.org/taxa/68205-Larrea-tridentata).
 
As for anacardias, there are two genera of shrubs in these ecosystems: Rhus (https://www.inaturalist.org/observations?place_id=14&taxon_id=54765&view=species) and Malosma (https://www.inaturalist.org/taxa/64122-Malosma-laurina), the latter now containing several spp. formerly allocated to true Rhus.

The point is that all these shrubby anacardias in the Californian shrublands have REMARKABLY LIGHT WOOD, about 0.5.

This is even lighter than that of Lycium, and more like Salvia (which resembles a herbaceous plant as much a woody plant, in some respects).

In this data-set, Salvia has wood density of about 0.5 (https://www.inaturalist.org/observations?place_id=14&taxon_id=50644&view=species).
 
Bottom line:
Shrubs in chaparral and adjacent semi-arid vegetation have unremarkable wood densities. Most spp. are similar resemble the average arborescent anacardia, elsewhere in the world, in wood density. The values approximate 0.7.

Larrea, which is an extreme plant in various ways, has somewhat denser wood.

However, Rhus and closely related Malosma have remarkably light wood, at only ca 0.5. This is is remarkably different from Searsia in Africa and Asia - which, as far as I know, always has wood density >0.7, and often >0.9.
 
Putting these findings a different way, in summary:

Show me an anacardia anywhere on Earth, and I will expect its wood density to be an unremarkable 0.7.

This would be in line with diverse floras of trees called 'hardwoods' in the Northern Hemisphere, that actually have far lighter wood than those of

• the average eucalypt,
• typical trees and large shrubs of Afromontane forest/semi-arid thicket in southern Africa, and
• various acacias, including Australian wattles (genus Acacia).

However, there are two divergences, in opposite directions, from this general average of unremarkable wood (density about 0.7) in anacardias and 'hardwoods'.

On one hand, we have Searsia. This has dense wood, and probably the densest wood in the whole family Anacardiaceae.

On the other hand, we have Rhus and Malosma. These have remarkably light wood, despite their former lumping with Searsia into a single genus, Rhus (sensu lato, https://www.sciencedirect.com/science/article/pii/S0254629916302605).
 
So:
Yes, Searsia has dense wood, and in this way differs from Rhus.

Searsias, in the mediterranean-type climate in South Africa (in and near the Fynbos Biome), also have much denser wood than expected for chaparral-type shrubs, under similar climates in California.

to be continued in https://www.inaturalist.org/journal/milewski/68676-searsia-has-dense-wood-unusual-for-family-anacardiaceae-part-3-related-genera-in-kruger-national-Park...

Posted on July 31, 2022 03:24 AM by milewski