Die-back of kiaat (Pterocarpus angolensis) in southern Africa: a cause for concern?

Abstract

Pterocarpus angolensis (kiaat) is a well-known southern African tree species of commercial importance that occurs in several vegetation types in the Zambezian regional centre of endemism. The most prominent of these vegetation types are the Zambezian miombo woodland and undifferentiated woodland. A diverse range of ecosystems within these vegetation types necessitate adaptation by tree species to survive extremes of drought, temperature, altitude, soil nutrition and tolerate fire in order to compete with other plant species. There are several reports of a die-back disease of P. angolensis in Zambia, Zimbabwe and South Africa, but very little is known regarding the cause or significance of this problem. In this review, we provide details regarding the history of the disease and consider its possible causal agents. A pathology study conducted at three locations in South Africa on diseased and dying trees resulted in the collection of 199 fungal isolates; comprising saprophytic species such as Candida, Penicillium and Humicola, and potentially pathogenic species such as Lasiodiplodia theobromae, Cytospora spp. and Fusarium spp. Drought, during several years preceding disease, along with a lack of fire management may have contributed to both the present and past reports of tree die-back and death. Finally, an analysis is made of the importance of the problem and actions that might be taken to alleviate it.

Nitrogen Cycle Patterns During Forest Regrowth in an African Miombo woodland Landscape

“…Combining data on canopy structure, foliar tissue, and soils, we evaluated indicators of ecosystem N availability across regrowth and mature forest sites, and between wet and dry seasons, over a 400‐km 2 region. Our hypothesis was that ecosystem N availability would remain low relative to tree demand in regrowing forests in this landscape, and reflect broad influences of low N inputs from woody vegetation productivity, frequent disturbance, and edaphic factors linked to sandy soils and fire that limit accumulation of plant‐available N. To explore evidence for N fixation across regrowth sites, we focused our foliar sampling to compare foliar N concentrations and N stable isotope composition (δ 15 N) among a canopy tree species shown to actively fix N in Miombo ecosystems ( Pterocarpus angolensis ; Högberg, ; Mehl et al, ), and two non‐N‐fixing trees, a canopy dominant ( Brachystegia spiciformis ) and a pioneer species ( Terminalia sericea ).…”

Decline and Die-Back of Woody Plants in a Physiognomic and Floristically Complex Sebungwe Region and the Factors Modifying Mosaic Patch Landscapes at Sengwa Wildlife Area, Zimbabwe

“…F. oxysporium is a contributing factor in stand dieback and that drought, frost, fire, insects and infections by mistletoe Loranthus spp were seen as predisposing or inciting factors. Mycorrhizal fungi leads to tree population decline in mukwa [36,37]. Epidemic dieback is not a common feature in the study area.…”

Studies on Mukwa (Pterocarpus angolensis, D. C.) Dieback in Chobe Forest Reserves in Botswana

“…The highest fire and elephant damage was observed in the Chobe Forest Reserve which also showed the highest diameter range with aging trees. Mehl et al (2010) reported that the occurrence of dieback was related to fire damage. McGregor and O'Connor (2002) reported that dieback may also be influenced by vegetation structure, soil surface structure and soil chemistry.…”

“…The effects of dieback on natural populations of P. angolensis on the Miombo woodlands in general have been reported by several authors (Anon, 1985;Banda et al, 2006;Kikula, 1986;Rampart, 2007;Rampart, Cahalan, Mmolotsi, & Kopong, 2010). The major factors causing dieback of P. angolensis include elephants (Ben-Shahar, 1993;Ben-Shahar, 1996;Rampart et al, 2010) and diseases (Mehl, Geldenhuys, Roux, & Wingfield, 2010). P. angolensis has been reported to be on decline in the Chobe Forest Reserves due to dieback (unpublished reports).…”