Assessment of Plant Commnunity Structure in a Tropical Wetland Affected by Brick Making—The Case of Sironga Wetland, Kenya

Brick making is one of the major small-scale industries in Sironga which has been expanding due to the growing demand for urban expansion. Due to the increasing population pressure, brick-making is competing for the wetland resources. Sironga wetland is threatened with serious degradation and proba-ble loss of plant diversity. Conversion of this wetland for economic uses such as brick making has resulted in its loss. The objective of the study was to assess the effects of brick making on plant diversity in Sironga wetland. Nyamira County, Kenya. A one metre by one metre quadrat frame was laid down and perpendicularly recorded the percent cover for each species found inside the quadrant plus the percentage area covered by the bare ground litter. From each transect lines “diagonally” detailed vegetation under study was then done. The plant species were recorded and classified into three life-forms; herbs, sedges and grasses. The study revealed that grasses had the highest diversity H = 1.144. Diversity for herbs was H = 0.987 and H = 0.899 for reeds respectively. The study concluded that brick-making activities affected the plant diversity in Sironga wetland. This may be attributed partly to the li-mited information and awareness campaigns to the surrounding communities on the values and benefits of wetland ecosystem services and the lack of alternative livelihood sources. The study recommends that alternative live-lihoods are provided and awareness campaigns on the values and benefits of wetlands to the residents are done by the relevant agencies.


Introduction
Wetlands are habitats for animal and plant communities and have a vital function in maintaining ecosystem balance. The ecological functions of wetlands include maintaining micro-climate and conserving water reservoirs. Humans depend on wetland resources for their livelihood, thereby modifying the community structure of wetland flora and fauna. One of the anthropogenic activities associated with wetlands in developing countries is brick making. Brick making industry is the oldest industry in the history of mankind. Bricks are extensively used as the main input in construction because of their durability, reliability, low cost and easy availability [1]. In Kenya, bricks are still the preferred building material and hence brick making is a lucrative business and many areas are flouted by informal sectors of brick-making activities [2]. In Sironga wetland located in Nyamira County (Western Kenya), bricks are made using traditional kilns. Brick production in the wetland involves cutting of vegetation and draining the area which impacts directly on wetland biodiversity. Brick-making has immense disturbance potential to cause ecological alterations [3]. Disturbance has been recognized as one of the major factors influencing variations in species diversity [4] [5]. Brick-making activities cause significant disturbances on land [6] that adversely affect vegetation [7]. The disturbances alter the physico-chemical properties and habitats of soil which are likely to influence species diversity [3].
Due to the increasing human population, the demand for bricks for housing within and outside the study area has been increasing which poses a threat to the plant species and diversity. Although production of bricks in the study area has risen in the last decade [8], there is insufficient information on the effects of brick making on plant diversity. This study was undertaken to assess the plant community structure following the rise in brick-making activities within Sironga wetland.
The total area is approximately 899.4 km 2 [8]. The study area has two rainy seasons that is well distributed throughout the year with the long rainy season occurring in December to June and short rain seasons from July to November.
Annual rainfall ranges between 1200 mm -2100 mm per annum. Daily temperatures range between 28.7˚C and 10.1˚C respectively. The average normal temperature is 19.4˚C which is favorable for both agricultural and livestock production [9]. Sironga wetland is an area where most activities of brick making take place and the volume of bricks produced in this area is the highest compared to other wetlands in the County including the neighbouring Nyabomite, Nyabioto and Charachani wetlands.

Sampling and Data Analysis
An ecological survey study design was adopted in this study. Vegetation foliar cover was determined using the quadrat method. The centre of the study area  The Shannon entropy index analysis revealed that species diversity for herbs in Sironga Wetland was 0.987, 0.899 and 1.144 for herbs, sedges and grasses respectively. The diversity of all the plant species showed that grasses had the highest diversity followed by herbs and reeds respectively. The dominance of the grasses is assumed to be high because it is fast growing aquatic species of the wetland and therefore when trees/shrubs are cut, the grasses take over fast.

Results and Discussion
Sedges and grasses are also the main peat formers in wetland environments [