Friday, July 27, 2012

The Desert Cloud Forests of Yemen and Oman

As I hinted to in my last post I had recently learned of a very unique forest ecosystem in, of all places, the Arabian countries of Yemen and Oman. Located on the southeast of the Arabian peninsula Yemen and Oman are dominated by dry desert conditions except for 1% of the land- and it is that 1% we will be looking at called the desert cloud forest.

© Sebastian Kennerknecht

What makes this habitat possible is a unique interplay of ocean, elevation and desert. While other cloud forests receive water from both rainfall and capturing moisture from clouds- they generally receive enough water from rainfall alone that even without the moisture from clouds they still would exist as forest of some type. However in desert cloud forests it is the added moisture from the clouds that really allows the habitat to cross the threshold from desert scrubland/grassland to true forest. The desert cloud forests of the Hawf and Dhofar regions of Yemen and Oman respectively achieve this remarkable feet in several ways. First of all, like all cloud forests, these desert cloud forests occur relatively close to the ocean at no more than 15 km from the Indian Ocean. Secondly the cloud forest occur on an escarpment about 300-700 meters above sea level. Past the escarpment is dry plateau morphing into desert.
After the meager rainy season ends the inland desert heats up. However in the zone of the cloud forest this is the time of maximum cloud coverage. During this season the vegetation literally "intercepts" moisture from the air which trickles down into the ground- ultimately adding more water to the environment than rainfall does. In addition, during this critical period of about 3 months transpiration rates are low because solar radiation is deflected by the cloud cover. After the cloud cover breaks the forest is poised to green up aggressively due to the bank of water the system has accumulated from the rainy season and the cloudy season. Eventually transpiration outstrips the capacity of the forest and the trees go through a deciduous dry season dormancy until the rains return.

   Dhofari Buttontree.  Anogeissus dhofarica
The most important member of this community is the Dhofari buttontree, Anogeissus dhofarica, which is the dominant canopy tree and also intercepts the majority of the water from passing clouds. Unfortunately the tree is a favorite browse of the camels which are brought into the forests by local Bedouins. Camels, in the local society, are much like cadillac escalades in American society- a sign of wealth above and beyond what is really necessary- and the more camels an owner can keep in his herd the more prestige he has.

© Sebastian Kennerknecht
Unfortunately camels in such numbers may ultimately over-browse the system to such an extent that the trees which intercept water from the clouds lose their capacity to do so. In this scenario the trees would give way to desert grassland.

© Sebastian Kennerknecht

Regular readers of da' salad should recognize that islands and the effects of large herbivores on an islands flora is a repeating riff here. What we have here in the desert cloud forest are various herbivores- camels, goats, cattle- brought into an isolated environment that is very vulnerable to minor perturbations.  When we look at the desert cloud forests of Yemen/Oman it can be seen that we are in fact dealing with "islands" of a different sort...

As seen in the above satellite photos the desert cloud forests (dark patches towards right) are literally small little islands in a sea of desert. This is an important concept to grasp. If this ecosystem disappears,  and it is the last remnant of a formerly more widespread forest habitat of the middle east, there is literally no where for it to go to.

An island need not be surrounded by water.

© Sebastian Kennerknecht


Many of the photos in this blog were graciously provided by Sebastian "Seabass" Kennerchnect
 he has a great blog you should check out at

(Miller and Morris 1988) Desert Cloud Forest: Adapting a Unique Ecosystem to Climate Change

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