What is Subtropical Thicket?

Photo by Craig Sholto-Douglas

"In essence all the Thicket vegetation types originally start as a number of small bush clumps of woody species that establish in a particular environment. Under certain environmental conditions these individual bush-clumps are able to increase in size and density. In the absence of a disturbing regime these bush-clumps are ultimately able to link-up with each other, to displace the original matrix vegetation" (Vlok & Euston-Brown, 2002: 6)

Synonyms of the 'Lost Biome' in South Africa

Valley Bushveld

Defined by Acocks (1953), Valley Bushveld was a problematic veld type due to it's placement into Karoo affinities, barring Addo Bush derived from Forest affinities.

Subtropical Transitional Thicket

Coined by Cowling (1984), Subtropical Transitional Thicket was defined as:

A Tongaland-Pondoland origin with links to Karoo-Namib and Afromontane forms
Low regional endemism (relative to fynbos) comprising mostly succulent species
dominated by spinescent shrubs and high number of woody vines and succulents
Deep well-drained, fertile soils

Other notable points include fire-protected sites and a rainfall regime between 200-800 mm/yr, 20% of which falls in winter.

Albany Thicket Biome

Recognised formally by Low & Rebelo (1996) as a Thicket Biome, the Albany Thicket Biome was described as a chapter (Hoare et al, 2006) in the Vegetation of South Africa, Lesotho and Swaziland.

The "Albany" in the biome description limits it's geographical range to the Albany area of the Eastern Cape. However it is defined as a "dense, thorny scrub, 2-5 m in height'.

Origin of subtropical thicket

"...southern African thicket is an ancient formation ... derived initially from elements in the forest formation...however, it also includes many species derived from lineages associated with other biomes."

The Thicket Breakdown- Regional types, spekboom thickets and mosaics

The Subtropical Thicket Ecosystem Planning (STEP) Project was a crucial assessment highlighting patterns and processes of thicket vegetation, thicket degradation and transformation and conservation potential. The work of Vlok & Euston-Brown (2002) in defining the Subtropical Thicket Biome to better understand it's geographical range within the STEP planning domain and species distribution, composition and structure has provided a solid and detailed basis for further research.

The classification of thicket by Vlok & Euston-Brown (2002) is simplified below.

Distribution of Mainland thickets

Mainland Thickets which are different to Dune Thickets and have three structural forms namely Arid, Valley and Thicket. These are distributed from E-W along the major catchment systems as well as along the Escarpment.

Spekboom thicket vs spekboomveld

Spekboom Thicket is termed when there is a local abundance of spekboom in valley thicket. Spekboomveld is a local abundance of spekboom in Arid Thicket.

What is a mosaic?

A Thicket mosaic occurs when thicket exists within a matrix of another vegetation type such as Fynbos, Grassland, Savanna or Nama Karoo and is controlled by fire, frost or rainfall.