Bemigisha, Jane 
  
Inundation/flooding:. Between 1967 and 1984 the Lake Naivasha water increased in extent, and most of the Northern 
papyrus swamp was flooded, as well as part of the natural vegetation and agricultural fields in the lower areas. Most of the 
north papyrus swamp changed to water, leaving a little concentration to the northeast. The rest of the natural vegetation types 
decreased in extent as well. On a study about papyrus response to flooding, Gaudet (1977) found that the survival got 
minimal especially the young papyrus plants, which could tolerate flooding only after reaching a certain stage of 
development. On the other hand, some herb species could succumb to the flood like Sphaeranthus which has shown a 
high percentage of survival due to its cell structure that is adaptable to both flood and dry conditions (Gaudet, 1977). 
Drawdown: Between 1984 and 1995 the lake water levels dropped even below the 1967 level. According to Gaudet (1977), 
the drawdown succession should eventually succeed to a papyrus swamp. Indeed papyrus overtook the water ward 
immediate shore but it continued to decrease in the extent (table 3). By 1995, the strikingly evident north swamp decreased 
further still below the 1984 area (1). The zonation changed with woodland which had followed papyrus by the 1967 status, 
having its position taken over by shrubland after the flood in 1984. 
There was an extensive interference of agricultural fields on all sides which could be that farmland expansion took advantage 
of the receding water because of improved drainage condition for cultivation. Between 1967 and 1984 100.8 ha of papyrus 
was converted into agricultural fields; between 1984 and 1995 this was 387.5 ha. It was found that dykes and channels were 
made to limit flooding on the farmlands. This process could be practically irreversible. Once a field is established, it will be 
hardly abandoned, and even if so, the conditions might be no longer suitable for papyrus. Shrub species like conyza 
floribunda which seem to have high reproductive rates and wider tolerances (Gaudet , 1977) stand a higher chance to out- 
compete papyrus on abandoned fields. 
Other forms of human interference, though not included in the model were grazing and burning observed during 
fieldwork for the same study. In addition, Gaudet (1977) indicate that cattle graze the papyrus especially the young ones 
on the study area. The after-effects of grazing on vegetation have been studied by Verweij (1995) who found that short herb 
species benefited from increased light moisture and nutrients after the higher structural vegetation are grazed especially by 
cattle. On the other hand, burning has been found to encourage bush encroachment (Luttge, 1997) so that shrub species 
could have an advantage of flourishing against papyrus after the burn. Build-up area so far had no direct effect on the 
distribution of papyrus cover. 
5. CONCLUSION 
Lake water levels (open water) have a high impact on the distribution of the papyrus swamp with shrubland taking the most 
advantage of both drawdown and flooding conditions to overtake the swamp. If the water level is high, papyrus is flooded 
and dies , particularly the juvennaile stands. If the lake water level goes down again, papyrus recovers and new plants can be 
established from seeds stored in the muddy soils. However, during flooding, shrub species like conyza floribunda get higher 
chances to survive due to their high tolerance to flooding. In the case of drawdown, human activities exert further influence 
for example the reclamation of riparian land by agricultural fields or grassland for grazing, or burning. Once more, shrub 
species take advantage due to their high reproductive rates. 
Considering the highest influence of the water levels, the integration of related factors like climatic regime, ground water 
level, soil drainage/depth, and topography would improve on the explanations. Anthropogenic factors as grazing and 
burning should also be considered for the model improvement. Appropriate temporal and spatial scale remote sensed data 
should be given particular attention. 
6. REFERENCES 
Bizuayehu, A. A., 1994. GIS based decision support system for development intervention planning, a case study in 
irrigation planning, Wageningen Agricultural University / ITC Msc. Thesis. 
Chandria , P. G., Surendra, S., 1995. Land cover Assessment and Monitoring at UNEP/EAP-AP: A RS and GIS Approach . 
Edited by Shizuo Shindo and Ryutaro Tateishi, In : Proceedings of International Symposium on Vegetation Monitoring 
(Japan : Centre for Environmental Remote Sensing, Chiba University) pp 40 - 49. 
Denny, P.(ed) 1985. The ecology and management of Africa wetlands vegetation. Geobotany 6 
(DORDRECHT/BOSTON/LANCASTER: Dr. W. Junk publishers , Kluwer academic) 
  
172 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.