Direct and Environmental Uses of Mangrove Resources on Kilwa Island, Southern Swahili Coast, Tanzania
Total Page:16
File Type:pdf, Size:1020Kb
Special Issue (Article)/特集(論文) Exploitation and Conservation of Middle East Tree Resources in the Oil Era Direct and Environmental Uses of Mangrove Resources on Kilwa Island, Southern Swahili Coast, Tanzania NAKAMURA Ryo Ⅰ . Introduction Ⅱ . Maritime Environments and Life on Kilwa Island Ⅲ . Three Ecological Sea Zones of Kilwa Island Ⅳ . The Mangrove Inland Sea and the Kilwa Kingdom Ⅴ . Direct and Environmental Uses of Mangroves Ⅵ . Conclusions: The Importance of Mangroves in Past, Present, and Future Maritime Life スワヒリ海 岸南 部タンザニア・キルワ島 に お ける マング ローブ 資 源 の直 接 利 用と環 境 利 用 中村 亮 東アフリカのスワヒリ海岸はアフリカでも有数のマングローブ面積を保有する地域で ある。ここのマングローブは、紀元前よりのインド洋交易をつうじて、木材資源が少ない 215 Direct and Environmental Uses of Mangrove Resources on Kilwa Island, Southern Swahili Coast, Tanzania (Nakamura) アラブ・ペルシャ地域へ建築材として輸出されてきた歴史背景をもつ。スワヒリ海岸のな かでも、タンザニア南部のルフィジ川流域とキルワ沿岸部は、国内のマングローブ面積の 64%(69,785ha)を保有する海資源の豊かな地域である[Wang et al. 2002]。 本論文の目的は、タンザニア南部のキルワ島を事例に、住民によるマングローブ資源利 用の現状について、「直接利用」と「環境利用」にわけてその多面的利用法を解明すること と、居住空間と資源が限定されている海村社会(とくに島嶼部)におけるマングローブ資 源の重要性を提示することである。キルワ島は中世のインド洋交易において金交易を独占 することにより興隆した海洋イスラーム王国であったが、現在は 1000 人弱の住民が、マ ングローブとサンゴ礁に囲まれた海で主に半漁半農の生業形態でくらす小海村である。 キルワ島は、島と大陸との間のマングローブに囲まれた内海と、インド洋に面してサン ゴ礁が発達した外海という、自然環境が対照的な二つの海をもつ。その海環境は、生態海 域1:マングローブ内海、生態海域2:サンゴ礁をもつ外海、生態海域1と2の自然条件を 兼ね備えた生態海域3(境海)、の三生態海域に分かれる。 生態海域1に面する場所に、キルワ王国時代(10C半)から居住空間が歴史的に形成さ れてきた。ここは北モンスーンの影響を受けて、暑気に涼しくマラリア蚊の少ないことよ り居住空間として適しているばかりではなく、キルワ王国にとっては、外海から奥まった 遠浅の海に面しているので、外敵からの防衛という点でも適していた。また、キルワ島の 半数近くの漁場が生態海域1に集中しており(30/66)、かつ、全漁法の半数以上が生態海 域1でおこなわれることより(23/41)、マングローブ環境が生業空間としても適している ことがわかる。 キルワ島には8種類のマングローブが自生している。その利用は、マングローブを建築 材や燃料などとして使用する「直接利用」と、マングローブが作り出す環境を漁場や塩田と して使用する「環境利用」に大別される。七通りの直接利用(建築材、船材、漁具材、燃料、 薬、飼料、玩具)と五通りの環境利用(漁場、航路、塩田、養蜂、防波風林)が確認された。 この二つの利用法の関係は、微妙なバランスの上に成り立っているといえる。マングロー ブの過度な伐採はマングローブ環境を壊してしまうし、マングローブ環境の保全のために 伐採を禁止してしまうと、マングローブの直接利用に依拠した住民生活に支障をきたして しまうからである。しかし現在までのところ、人びとがマングローブの重要性を伝統的な 知識をつうじて理解しており、また、この地域の人口密度が少ないこともあって、キルワ 島周辺のマングローブ資源は良く保全されているといえる。 キルワ島におけるマングローブは、材料や生業空間としの重要性だけではなく、キルワ 沿岸部の地域社会を形成する媒介の場所としての重要性ももっている。マングローブ内海 には住民が日常的に移動する航路が網の目のように張り巡らされており、このマングロー ブ内海を媒介としてキルワ島周辺地域には、親族関係、友人関係、近距離交易などをつう AJAMES no.26-1 2010 216 じた親密な地域関係が存在している。 マングローブ資源が歴史的に果たしてきた役割、同時に、現在の住民によるマングロー ブ利用法をしっかりと認識することが、近年の沿岸部開発や観光化によって海環境への人 的圧力が高まってきたタンザニア南部沿岸地域における、人と自然との持続可能な関係を 模索するために必要不可欠である。 I. Introduction 1. Objectives The objectives of this paper are (1) to show how the people on Kilwa Island, located just off the southern Swahili Coast, Tanzania, make use of mangrove resources by analyzing the two ways in which they use them: directly as a material resource (direct use) and indirectly as an environment that sustains life (environmental use); and (2) to consider how harmonious coexistence between humans and the natural environment may be achieved and sustained in this maritime society with otherwise limited living space and resources. The multiple roles of the mangrove resources as materials, occupational spaces, and a medium for the formation of a regional society on Kilwa Island are clarified from the perspectives of direct and environmental uses. Kilwa Island was once an influential Islamic kingdom; in the Middle Ages, it was an international trading port, but it is now home to a small seashore village with fewer than a thousand habitants living an almost self-sufficient life, sustained by the surrounding seas with their mangroves and coral reefs. This small island population is currently in the midst of social changes arising from development, including maintenance of traffic infrastructure, restoration of the stone ruins of the old Kilwa Kingdom, conservation of the maritime environment, coastal development (oil drilling), and tourism. With such a changeable social situation, human pressure on the natural environment is increasing. 2. Studies on the Mangroves of the Swahili Coast The Swahili Coast stretches some 2,000 km from southern Somalia to northern Mozambique, including Madagascar and the Comoro Islands, and is home to one of the richest mangrove forests in Africa (total mapped mangrove area, about 217 Direct and Environmental Uses of Mangrove Resources on Kilwa Island, Southern Swahili Coast, Tanzania (Nakamura) 1,143,200 ha) [Taylor, Ravilious and Green 2003]. Mangroves are salt-tolerant forest or swamp ecosystems that occur along tropical and subtropical coastlines [Wang et al. 2002: 36]. Small mangrove colonies are also found along arid coastlines in regions including the Red Sea and the Persian Gulf [ISME 1997]. Studies on the mangroves of the Swahili Coast have emphasized the historical use of mangroves as a trading item in the Indian Ocean trade with the Arab states. Gilbert [2004], for example, addressed the mangrove pole trade in the Indian Ocean for the case of Zanzibar Island, Tanzania. However, fewer studies have examined the current daily use of mangroves by the people live in Swahili maritime societies, although a brief explanation is given in A Field Guide to the Seashores of Eastern Africa and the Western Indian Ocean Island [Richmond 2002: 26-30]. Local mangrove use, such as the direct use for building and shipbuilding materials, firewood, and charcoal making, is often used as an example of overexploitation. However, local people also recognize the value of the mangrove environment as a fishing ground and fish-breeding forest. Do these people nevertheless continue to log mangroves to the point of environmental disruption? Using the case of Kilwa Island, this study demonstrates that the range of daily mangrove usage by the local people does not disrupt the mangrove environment. Rather, problems arise from illegal logging by outsiders and large-scale development and exploitation by salt panning and prawn farming enterprises. Before planning and carrying out conservation, we must first understand the historical significance of mangroves and how the local people sustainably use mangrove resources. Mangroves also serve a crucial purpose as they are a medium of community formation in the region. The early Swahili trading ports of Kilwa, Songo Mnara, Pate, Lamu, and Mombasa were established on islands in mangrove-covered inland seas where the calm conditions were suitable for embarkation ports. The current Swahili maritime societies formed regional societies linked through these safe sea transportation routes. 3. Mangroves in Tanzania The Swahili Coast and the Arabian/Persian regions, which are separated by about 4,000 km, have been connected by Indian Ocean trade for over a thousand years. As a building material, mangrove wood had, by the mid-nineteenth century, become the single most important cargo carried via the Indian Ocean trade to dry AJAMES no.26-1 2010 218 Arabian/Persian regions that lacked tree resources [Curtin 1981; Gilbert 2004]. This historical mangrove trade destroyed vast mangrove areas along the Swahili Coast. For example, Pemba Island, located off the shore of Tanzania, was once called Green Island (Al Jazeera Al Khadra) because of the richness of its mangroves, but now little of its mangrove area remains. Population growth in Tanzania has also impacted the mangroves. For example, the Michamvi area of Zanzibar had about 800 ha of mangroves in 1949, but only 43 ha in 1989; the Maruhubi area had 1,040 ha in 1949 and 76.5 ha in 1989 [Taylor, Ravilious and Green 2003: 17]. In recent years, the Tanzanian mangrove forest has been well preserved; a report titled Remote Sensing of Mangrove Change along the Tanzania Coast indicated that the area covered with mangroves in Tanzania remained nearly unchanged between 1990 and 2000, encompassing 109,593 ha in 1990 and 108,138 ha in 2000 [Wang et al. 2002: 43]. The southern coastal districts of Tanzania around Rufiji (48,030 ha), which has the largest single mangrove forest in eastern Africa, and Kilwa (21,755 ha) made up about 64% of the domestic mangrove area in 2000 [Wang et al. 2002: 43]. Based on the author’s field studies(1) , this paper describes the mangrove use in the Kilwa coastal regions, especially on Kilwa Island (Kilwa Kisiwani), Kilwa District, Lindi (Wilaya ya Kilwa, Mkoa wa Lind), Tanzania. II. Maritime Environments and Life on Kilwa Island Kilwa Island is a small lagoon island off the southern Swahili Coast of Tanzania. It is 12 km² in area and 23 km in circumference. Situated at the mouth of three rivers (the Mavuji, Msekela, and Gongo rivers), the island is surrounded by two contrasting seas: an inland sea (lagoon) covered with mangroves and the open sea fringed with coral reefs (Figure 1). Kilwa Island is located at 9 degrees south latitude and is included in the East African monsoon area, with high winds all year long. Isolated about 300 km from the nearest metropolitan areas in Tanzania (Dar es Salaam in the north and Mtwara in the south) because of bad road conditions, the island is almost completely cut off from modern economic development. According to Tanzania’s 2002 population and housing census, the population density in the Lindi region is the lowest in the 219 Direct and Environmental Uses of Mangrove Resources on Kilwa Island, Southern Swahili Coast, Tanzania (Nakamura) Figure 1 Natural Environments in the Kilwa Coastal Region Mavuji riv. S market ٨ S Kilwa Masoko mangrove tideland fringing reef ٨ harbor Luayo S salt pan S harbor ٨ village 0 1 2 3 km Kilwa Island Indian Ocean Mgongo S9°00’ Sangarungu sea Msekera riv. Sanje ya kati Nisasu sea Songo Mnara Pwani Creak Pande region N Gongo riv. (Source) Made by the author based on Nakamura [2007b: 51]. AJAMES no.26-1 2010 220 country at only 12 people/km² (cf. 1,793 people/km²