Trade and harvesting impacts on Merwilla plumbea
V.L. Williams*, D. Raimondo†, A.B. Cunningham§ & T. Ticktin¤
* University of the Witwatersrand, Johannesburg † SANBI, Pretoria § People and Plants International, Australia ¤ University of Hawaii
Funded by: IDRC and People & Plants International Introduction
• Merwilla plumbea (inGuduza) is one of the most popularly traded medicinal plant species in South Africa • Mander (1998) estimated 95.5 tonnes sold in Durban markets • Study aimed at getting a better insight into the species’ population dynamics for resource management purposes • Objectives: i. Re-assess the extent of trade ii. Develop methods for bulb age assessments Æ essential for population matrix modelling & bulb production economies Species description & distribution
• Typically mistbelt & montane grassland from 300–2500 m.a.s.l. • Variable species (bulb & leaf size, flower & leaf colour etc) •Variation Î varying taxonomic treatments and the recent ‘lumping’ of 3 previously distinct taxa (incl. Scilla natalensis) into M. plumbea based on molecular phylogenetic analysis
Market Survey and Trade Data Survey Methods
• Structured interviews based on a fixed set of questions (2006)
• Questionnaire designed to capture info on volume & value of the trade, bulb sizes sold, etc.
• Sample size: – 30 traders in Faraday market, Johannesburg – 46 traders in Warwick market, Durban Results
Proportion of traders selling inGuduza • 63 traders (38%) in Faraday • 430 traders (90%) in Warwick
M. plumbea bulbs as a market component • ≈10.6% ± 5.7% (SD) of the total volume of plant material for sale at a traders’ stall Prevalence of size-classes
1 – 5 cm 5 – 10 cm > 10 cm Faraday 2006 36.3 ± 18.7% 40.8 ± 23.6% 34.1 ± 13.9% Warwick 2006 26.7 ± 19.3% 48.5 ± 22.5% 26.0 ± 24.1%
(Mean ± SD)
• From previously studies: increase in the prevalence of bulbs in 1 – 5 cm class since 1994
• 46% and 70% of the volume of bulbs in Faraday & Warwick respectively were ‘singletons’ (i.e. not clusters of ≥2 joined or previously joined bulbs) Number of bulbs sold per annum
Faraday Warwick Per trader Mean no. of sales/day 4 sales 4.6 sales Min. no. bulbs/sale 3 bulbs 3 bulbs ∴ no. bulbs sold/day 12 bulbs 13.8 bulbs ∴ no. bulbs sold per year 3,744 bulbs 4,306 bulbs
No. M. plumbea traders in the market 63 traders 430 traders
∴ no. bulbs sold per annum in the 235,872 1,851,580 markets bulbs bulbs Assuming a mean mass of 0.394g per 92.9 729.5 M. plumbea bulb tonnes/a tonnes/a Min. estimated value of sales to customers in 2006
Faraday Warwick Per trader Mean no. of sales/day 4 sales 4.6 sales Cost per sale R10 R5 ∴ Mean value/day R40 R23 ∴ Value per year R12,480 R7,176
No. M. plumbea traders in the market 63 traders 430 traders
∴ Value of sales to customers per R786,240 R3,085,680 annum Population Structure & Bulb age Methods
5 sites: 2 heavily harvested by gatherers; 2 not harvested; 1 experimentally harvested once (1993)
3 x 20m2 plots per site Seedling class 1: single bulb; leaf length <2cm
Seedling class 2: Bulbs allocated to single bulb; leaf length >2cm size-classes (7Æ4 Juvenile class: classes, <7 leaves; leaf length >20cm March 2006)
Adult class: >7 leaves; leaf length >35cm Results: Population structure: unharvested populations; different burn regimes
200 Mbona power curve 2 Mbona (3 yr burn rotation) 180 (r = 0.77)
160 Merthley Lake (Annual burn)
140 Royal Natal (3.5 yr burn rotation) 120
100
80
60 Mean no.individuals Mean plot per
40
20
0 Seedling 1 Seedling 2 Juvenile Adult Population structure: Merthley Lake (non-harvested site) vs Mweni (continually harvested site); annual burn rotation
70.0
60.0 Merthley Lake (non-harvested site)
Mweni (harvested site) 50.0
40.0 size at which plants first appear in markets
30.0
Meanno. individuals per plot 20.0
10.0
0.0 Seedling 1 Seedling 2 Juvenile Adult Impact of a once-off harvest at Mbona in 1993 (13 yrs later)
40
Not harvested 35
Light harvest 30
Heavy harvest 25
20
No. of individuals of No. 15
10
5
0 Total Adult 1 (Single bulb) Adult 2 (<6 bulbs) Adult 3 (>6 bulbs) Bulb aging
• Merwilla plumbea produces new whorl of leaves each spring from bulb centre.
• Bulb scales move outwards as bulbs age Æ scales can be used to age the bulbs
• Plants of known age were dug up from the wild, sliced in half and the leaf scales counted
• Individuals from plants planted as seeds at Mbona in 1993, 2002 and 2003 were dug up
• 30 known age cultivated bulbs also counted (11 & 25 yrs old) 11 bulbs scales
Cultivated bulbs all 11 years old; Different sizes due to differing available resources Widest point bulb diameter vs no. of bulb scales
16
14
Approximate 12 size of bulbs in muti 10 markets
8
y = 0.4633x - 0.3813 6 r2 = 0.82 n = 63
Widest point bulb diameter (cm) 4
2
0 0 5 10 15 20 25 30 35 Number of bulb scales Implications & Conclusions Implications
Widest bulb diameter 1 – 5 cm 5 – 10 cm > 10 cm
Predicted no. bulb scales <12 >12 to ≤22 >22 (& hence estimated age) scales scales scales
Faraday 1995 0% 93.8% 6.3%
Faraday 2006 36.3% 40.8% 34.1%
Warwick 2006 26.7% 48.5% 26.0% Conclusions
• Decline in the availability of bulbs in the larger size classes in the markets
• Increase in the prevalence of smaller size classes may indicate a pressure on the resource
• Harvested populations have few adults and a marked decline in recruitment Next Step: 1
• Continue studies on age/size relationships in the markets Î relate this to flowering and bulb predation Î surrogate for population info 14.4cm diam
~ 14 yrs ~ 18 yrs
~ 12 yrs ~ 15 yrs From sample of 15 bulbs bought in Faraday: • 27% had inflorescences • 47% signs of predation
• regression equation (previous graph) predicted number of scales from the diameter to within 2-3 scales
Inflorescence
≈ 15 bulb scales Next Steps: 2 - 4
2. Continue with the construction of the matrix model to determine population viability with harvesting pressure
3. Assess this species threat status using results from this study
4. Provide recommendations for management of the resource Acknowledgements
• Keith Cooper who provided access to Mbona Nature Reserve and who conducted harvesting experiments in the 1990’s
• Michele Payne for conducting the field work component on wild populations
• Ezemvelo KZN Wildlife for access to work in the Royal Natal Nature Reserve
• Luci Coehlo from Fakisandla Consulting, Durban, for facilitating the Warwick market study
• Students Sbongile and Simphiwe Khuluse for interviewing the traders
• IDRC are thanks for their financial support to People and Plants International (PPI)