Trees for health – forever: Implementing sustainable medicinal bark use in Southern Africa




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Trees for health – forever: Implementing sustainable medicinal bark use in Southern Africa. Regional Workshop, Johannesburg, 1 – 3 November 2005.
Bark wound responses: Results from bark harvesting experiments

Stephen Syampungani



School of Natural Resources, Copperbelt University, Box 21692, Kitwe
Traditional medicines are still the main source of health care for the majority of the African population. Tree bark is an important component of the herbal medicine. It is normally removed and either used on its own or mixed with other herbal extractives. Bark removal has a wide range of effects ranging from coppicing to dying of trees. Within individual species, the recovery responses and rates vary from habitat to habitat, and also depend on the level of stress of the tree. Unfortunately, responses of individual species were not adequately known to provide for sustainable management of species of different ecophysiology. An experiment was carried out since July 2003 in Zambia (Miombo woodland), Malawi (Miombo woodland and Afromontane forest) and South Africa (Afromontane forest) to develop an understanding of species responses to bark harvesting. A number of target species for traditional bark harvesting were selected to represent a wide range of diameter class for each species. From each tree a vertical strip of bark of 1 m long and 10 to 15 cm wide (width depended on tree diameter) were removed in two different seasons: dry season treatment in July to August; and rainy season treatment in January to February. The removed bark was then used to determine the bark thickness, moisture content and bark density of individual species at time of removal.
Bark thickness, density and moisture content varied with vegetation type, season and species (Table 1).
Table 1. Bark thickness, density and moisture content for selected tree species during rainy and dry seasons (dry season values between brackets).

Species

Site

Bark thickness, cm

Bark density (wet) g/cm³

Moisture content, %

Miombo woodland, Zambia

Brachystegia spiciformis

Mwekera

1.95 (1.95)

0.95 (0.93)

38.75 (27.00)

Julbernardia paniculata

Mwekera

1.75 (3.12)

1.18 (0.63)

38.74 (29.60)

Pseudolachnostylis maprouneifolia

Mwekera

1.07 (1.96)

1.13 (0.56)

24.89 (26.78)

Parinari curatellifolia

Mwekera

1.66 (2.85)

0.73 (0.43)

29.85 (31.99)

Dalbergia nitidula

Mwekera

1.93 (1.54)

0.65 (0.87)

22.79 (32.79)

Afromontane forest, South Africa

Cryptocarya myrtifolia

Umzimkulu

1.14 (1.14)

1.20 (1.01)

58.17 (58.09)

Ilex mitis

Southern Cape

1.21 (1.20)

0.99 (0.89)

51.03 (-)

Ocotea bullata

Southern Cape

1.39 (1.12)

0.98 (0.92)

46.43 (-)

Prunus africana

Umzimkulu

1.49 (1.42)

1.01 (0.91)

49.52 (60.25)

Rapanea melanophloeos

Southern Cape

1.46 (1.49)

0.90 (0.92)

- (-)

Rhus chirindensis

Southern Cape

0.84 (0.61)

0.98 (1.04)

57.07 (74.36)

Zanthoxylum davyi

Umzimkulu

0.44 (0.53)

1.71 (1.29)

58.31 (65.35)

Bark recovery, if it occurred, either developed along the edge of the wound (edge growth) or on the wood (sheet growth) or a combination of the two. Many species exhibited a negative response to bark removal over the experimental period. In many species the bark around the wound lifted before the edge growth could be seen. In most of such cases edge growth developed underneath the lifted bark. Most species exhibited edge development, indicative of the ability to recover from bark wounding. For some species the study period was too short to show a conclusive response pattern for management prescriptions. The general response pattern of species from this study and related studies is shown in Table 2.


Table 2. Patterns of recovery by bark regrowth on the wound or coppice regrowth near base of the tree of different forest and woodland species.


Species

Vegetation

Country

Bark recovery*

Coppice regrowth+

Albizia adianthifolia

Woodland

South Africa

Very good

No

Balanites maughamii

Woodland

South Africa







Brachystegia bussei

Woodland

Malawi

Poor and slow

Poor

Brachystegia spiciformis

Woodland

Malawi, Zambia

Very poor & slow (Mal) to Good (Zam)

No

Cryptocarya myrtifolia

Forest

South Africa

No

No

Curtisia dentata

Forest

South Africa

Good

Good

Dalbergia nitidula

Woodland

Malawi, Zambia

Good (Mal), Poor (Zam)

No (Mal), Good (Zam)

Elaeodendron transvaalense

Woodland

South Africa

No

No

Ilex mitis

Forest

South Africa

Very good

Good

Julbernardia globiflora

Woodland

Malawi

No

No

Julbernardia paniculata

Woodland

Zambia

Good

No

Ocotea bullata

Forest

South Africa

Very good

Good

Parinari curatellifolia

Woodland

Malawi, Zambia

Poor & slow (Mal), Good (Zam)

No (Zam) to Good (Mal)

Prunus africana

Forest

Malawi, South Africa

Very good

Poor to good

Pseudolachnostylis maprouneifolia

Woodland

Malawi, Zambia

Good (Mal) to Very good (Zam)

No (Mal), Yes (Zam)

Pterocarpus angolensis

Woodland

Malawi

Good

No

Rapanea melanophloeos

Forest

Malawi, South Africa

No (RSA) Good (Mal)

No to Poor

Rhus chirindensis

Forest

South Africa

Good

Good

Warburgia salutaris

Forest

South Africa

Good

Good

Xymalos monospora

Forest

Malawi

Poor

Good ( but die later)

Zanthoxylum davyi

Forest

South Africa

Poor & slow

Poor
*Bark recovery: Very good: edge and/or sheet growth good and fast to cover the wound relatively quickly; Good: edge and/or sheet growth good but slow; Poor & slow: there is indication of edge and/or sheet growth but very slow; No: No recovery.

+Coppice regrowth: Good: good coppice regrowth at base of tree; Poor: some coppice regrowth at base of tree but development is slow, and/or may not survive; No: no coppice regrowth


Based on the information generated over the experimental period, the management of the selected species would fall into one or more of the following categories:


  • Species which produce agony shoots at the base of the stem and also on the wound sides but without sound edge or sheet growth. Management of such species for bark harvesting should involve full tree harvesting followed by coppice management, eg Dalbergia nitidula;

  • Species with good wound recovery and good coppice regrowth. The management could involve strip removal or coppice management, eg Pseudolachnostylis maprouneifolia and Ocotea bullata;

  • Species with good edge growth, poor shoot development and a high intensity of insect and fungal attack. The insect and fungal infestation will have negative future effects on the species. Their management should involve full tree harvesting with no coppice management because they do not produce any agony shoots, eg Brachystegia spiciformis and Julbernadia paniculata.

  • Species that exhibit edge growth and sheet development without agony shoots should be strip harvested.


These are preliminary recommendations. Observations should be continued to refine our understanding of the response patterns of the selected species, both on the wound and through agony shoots (around the wound) and coppice regrowth (from the base of the tree).


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