Gichuki, J.1, 2, 3, L. Triest2 & F. Dehairs3

1Kenya Marine and Fisheries Research Institute, P. O Box 1881, Kisumu Kenya.
E-mail:gichukij@yahoo.com
2Laboratory of Plant Science and Nature Management, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium.
3Laboratory of Analytical Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium.

Estimating the regenerative potential, production capacity and optimum harvest intervals of papyrus (Cyperus papyrus L.) in the papyrus dominated wetland ecosystems of Lake Victoria, Kenya

Cyperus papyrus above ground biomass was estimated non-destructively from regressions between culm girth and culm dry weight. Initially 100 subsamples (representing 34% juvenile, 33% mature and 33% senescent plants) were randomly selected from the wetland. Using data from culm girth and dry weight, the regression curve described by the equation, Log10G=2.995 Log10W-0.6489, R2=0.9464, p< 0.05; n = 100, was obtained. From the regression the mean above ground biomass from four plots in the wetland was estimated as 3.48 ± 0.95 kg m-2 dry weight.

Regarding the assessment of the regenerative potential, production capacity and optimum harvests, 9 quadrats (3*3 m) were marked out but only the inner (1*1 m) were sampled. This was undertaken to minimise edge effects. Harvesting was carried out at two positions (the culm base and the detritus level). Harvesting was carried out at an interval of 6 months (0, 6 and 12 months) for the culm base and detritus harvested plots. The control plots were left intact until the end of the study (12 months)

We found a significant decrease (ANOVA; p = 0.037) in the number of new juveniles for the detritus level harvested plots after six months harvesting interval and a further significant decrease ANOVA; p = 0.02) in the number of juvenile culms after twelve months interval. The number of new culms after the first and second harvests in the control and culm base plots remained the same. We observed a significant decrease (ANOVA; p = 0.002) in the above ground (standing) biomass for the culm base harvested plots after six months harvest interval and also further decrease (ANOVA; p = 0.01) for the six to twelve months interval. There was further decrease (ANOVA; p = 0.0001) from the first harvest to the harvest twelve months later. Similar decreases were observed in the detritus level harvested plots after six months (ANOVA; p = 0.00018), between six and twelve months (p = 0.00064) and from the first harvest to the harvest twelve months later (ANOVA; p = 0.000006). Overall, these results suggest that large scale harvesting of papyrus at six months interval is unsustainable. In this regard the harvest intervals should exceed 6 months.