EPOW - Ecology Picture of the Week

Forest Savanna of the Congo

Savanna grasslands in dense tropical forest
Democratic Republic of the Congo, Africa

Explanation:  What are these blank patches in this sea of tropical forest?  

These are grassland savannas of central Africa.  They look like holes punched in the forest canopy. 

In a previous EPOW episode, we explored the gallery forests of drainages and streams that run through broad savannas.  This time, though, it's reversed ... with the savannas being surrounded by forest.

What creates these forest savannas?  It may be a combination of factors.  Soils might be too thin or lack nutrients by which to support trees.  Perhaps these areas had been burned and that set back succession.  Perhaps these are ancient wetlands that have drained, dried, and are now incapable of supporting trees. 

Whatever the situation, they are interesting places to explore. 

In fact, in 2004, I observed a small population of birds -- Red-billed Queleas (Quelea quelea) -- in a savanna at Mobenzeno village along the Ubange River in western Democratic Republic of the Congo.  The savanna looked like the ones in the main photo above -- an anomalous inclusion totally bordered by old secondary forest.   

The significance of my bird sighting is this.  Red-billed Quelea is not shown in any field guide or distribution map (e.g., van Perlo 2002) to occur where I saw them.  This bird species occurs in utterly vast numbers and huge flocks, both further north and south in Africa, outside this west-central African equatorial belt.  Elsewhere, their flocks are so huge that than often wreak devastation on agricultural crops.  Indeed, they are the most abundant wild bird in all the world.  

I saw the birds only in savanna habitat in the Congo, where grasses ranged 0.5 to 1 meter tall.  Whether it is a recent invader, or has escaped previous detection, is unknown.  

But it deserved monitoring.  If it expands its range further, and increases its population density as it does elsewhere, it might become a very serious agricultural pest, decimating food resources for many local people.   

Red-billed Queleas along a stream 
(where I photographed them in southern Kenya).
  

      
Information:
      van Perlo, B. 2002. Collins illustrated checklist: birds of western and central Africa. Reprinted as Birds of western and central Africa, Princeton University Press, Princeton, New Jersey, 384 pp.