DISTRIBUSI HUTAN BAKAU DI LAGUNA PANTAI SELATAN YOGYAKARTA (Mangrove Distribution at the Lagoons in the Southern Coast of Yogyakarta) - Tjut Sugandawaty Djohan (Pusat Studi Lingkungan Hidup Universitas Gadjah Mada, 2007)
ABSTRAK Kehadiran sisa hutan bakau di laguna Bogowonto, pantai selatan Yogyakarta menunjukkan bahwa pada masa lalu laguna tersebut didominasi oleh hutan bakau, sehingga penelitian ini bertujuan mempelajari kehadiran vegetasi bakau di laguna-laguna dan muara sungai di pantai selatan tersebut. Ada empat laguna di pantai Selatan Yogyakarta, laguna Bogowonto, Serang, Progo, Opak, dan satu muara sungai, Kali Baron. Laguna tersebut merupakan laguna internitten, artinya pada musim kemarau, mulut sungainya tertutup gumuk pasir dan laguna didominasi oleh perairan tawar dan merupakan ekosistem tergenang. Sebaliknya di musim hujan mulut sungai terbuka, laguna bersifat sebagai ekosistem pasang surut. Data vegetasi dicuplik dengan menggunakan kuadrat plot berukuran 10m x 20m dengan ulangan dua kali. Kuadrat plot ditempatkan pada pusat distribusi mangrovenya, yang dipilih mulai dari rawa burit ke arah muara sungai. Tekstur tanah, hara tanah, salinitas air dan hara air juga dikaji. Kehadiran hutan bakau di laguna dibatasi oleh tekstur tanah. Tekstur pasir, 60-99 %, mendominasi laguna Serang, Progo, Opak dan muara kali Baron. Komunitas bakau hanya ditemukan di laguna Bogowonto, yang tersusun atas 5 jenis bakau, Sonneratia alba, Nypa fruticans, Acanthus ilicifolius, Acrosticum sp., dan Derris heterophylla, dan dua jenis spesies peralihan, Pandanus sp. dan Cynodon dactylon. Pola distribusi komunitasnya mengelompok (clump), mempunyai tipe riverine mangrove,dan tidak membentuk zonasi. Sonneratia hadir mulai dari muara sungai sampai di rawa burit. Ketika air surut salinitas berkisar antara 0-6,5 %. Nypa hanya ditemukan satu kelompok di kaki gumuk. Distribusi Sonneratia tidak ditentukan oleh tinggi genangan, akan tetapi tinggi pneumatophor mengikuti pola tinggi genangan air. Di laguna Bogowonto, spesies bakau tidak mempunyai zonasi dan beradaptasi pada sistem ekologinya. ABSTRACT The presence of mangrove remnant at the lagoon of Bogowonto River in the southern coast of Yogyakarta indicated that in the past this lagoon was dominated by mangroves. Therefore, this study focused on the presence of mangrove vegetation in the lagoons and river mouth of the southern coast of Yogyakarta. There are four lagoons in the southern coast of Yogyakarta, Bogowonto, Serang, Progo, and Opak, and one river mouth, Kali Baron. During the dry season, these lagoons were inundated by freshwater and became stagnant waters, and during the wet season they experienced of intertidal conditions. Vegetation data were collected using quadrate plots of 10m x 20m, which were placed at the center of distribution in selected areas of the lagoon and the mouth of the river. Water levels, soil textures, soil nutrients, water nutrients and water salinity were also measured. The presence of mangrove in the lagoons and river mouth was dictated by soil texture. Substrate of sand, 60-99%, dominated the lagoons of Serang, Progo, and the river mouth of Kali Baron. The mangrove community only occurred at the Bogowonto lagoon. This mangrove vegetation was composed into five mangrove species, Sonneratia alba, Nypa fruticans, Acanthus ilicifolius, Acrosticum sp., and Derris heterophylla, and two transition species, Pandanus sp. and Cynodon dactylon. The distribution pattern was clump, had riverine type, and had no zonation. Sonneratia was occured from the mouth of the river to the back swamp. Nypa clump dominated at the foot of the sand dune. The salinity during low tide was around 0 to 6.5 ‰. The distribution of Sonneratia was not depended on the water level, but the height of pneumatophors followed the pattern of the inundation water. The mangrove species was adapted to system ecology of the Bogowonto lagoon.