KAJIAN STRUKTUR VEGETASI DAN DINAMIKA HARA DI HUTAN HUJAN TROPIKA BASAH DAS KAHAYAN PROPINSI KALIMANTAN TENGAH
Sosilawaty, Ir.,MP., Prof. Dr. Ir. Djoko Marsono, M.Sc.
2012 | Disertasi | S3 Ilmu LingkunganHutan hujan tropika mempunyai ekosistem yang spesifik, dan bisa terjaga dengan baik karena adanya keterkaitan antar komponen penyusun didalamnya sebagai suatu kesatuan yang utuh. Ekosistem hutan dapat dipertahankan apabila mekanisme siklus hara dan keanekaragaman jenis yang tinggi tetap terpelihara. Kawasan hutan hujan tropika dilokasi penelitian sebelumnya merupakan areal yang pernah dieksploitasi oleh Hak Pengusahaan Hutan (HPH) dan pengolahan kayu bansaw yang sebagian masih beroperasi secara illegal, sehingga dimungkinkan adanya perubahan komposisi dan struktur didalamnya serta proses siklus hara yang berlangsung dalam ekosistem hutan mengalami gangguan dengan meningkatnya kehilangan atau lepasnya unsur-unsur hara kedalam ekosistem DAS. Penelitian ini bertujuan untuk : 1). Mengkaji Komposisi, struktur dan keanekaragaman jenis vegetasi penyusun hutan, 2). Mengkaji pola komunitas tegakan hutan, 3). Mengkaji masukan hara yang terdapat didalam tanah hutan, Throughfall, Stemflow, dan keluaran hara kedalam sungai melalui sedimen suspensi dan sedimen dasar, 4). Mengkaji keseimbangan hara pada ekosistem hutan dan ekosistem DAS. Penelitian dilakukan dengan menentukan blok pengamatan berdasarkan overlay peta topografi/ kelerengan, hasil overlay pada masing-masing Sub DAS dibagi menjadi jalur-jalur pengamatan/releve. Jalur-jalur/ releve penelitian dibagi berdasarkan tingkat kelerengan yaitu 0-2 %, >2-8 % dan >8-15 %. Setiap releve dibuat petak-petak ukur dengan luas yang berbeda berdasarkan tingkat pertumbuhan yaitu : semai, pancang, tiang dan pohon. Struktur vegetasi diamati dengan membuat jalur segi empat berukuran 200 ft (61 meter) x 25 ft (7,6 meter), dipetakan dan dicatat diameter, tinggi tajuk, tinggi sampai cabang dan lebar tajuk tiap pohon, kemudian dibuat proyeksi vertikal dari pohon-pohon dalam jalur pengamatan dan hasilnya merupakan suatu diagram profil. Pola Komunitas diketahui dengan analisis ordinansi dua dimensi, kemudian dari data vegetasi pada setiap jalur pengamatan dihitung nilai Indeks Keanekaragaman Jenis. Hasil penelitian vegetasi menunjukan komposisi jenis vegetasi pada masingmasing Sub DAS pada semua tingkat pertumbuhan didominasi oleh jenis-jenis dari famili Dipterocarpaceae. Pola komunitas vegetasi pada semua tingkat pertumbuhan memiliki pola komunitas yang hampir sama, tetapi berbeda pada pola pengelompokan tingkat tiang pada Sub DAS Rungan. Tingkat pertumbuhan semai dan pancang memiliki nilai keanekaragaman jenis yang lebih kecil pada empat Sub DAS. Struktur vegetasi memiliki 3 (tiga) lapisan tajuk yang didominansi oleh jenis-jenis dari famili Dipterocarpaceae. Unsur hara yang keluar melalui sedimen dasar cukup tinggi, ini menunjukkan adanya kebocoran hara, Sub DAS : Kahayan P total (-140.2433), P tsd (-59.1233), K total (-409.1667), K tsd (-33.2933), Ca (-6.7633) ; Miri P total (-187.033), P tsd (-46.763), K total (-387.8667), K tsd (-38.57), Ca (-10.21), Mg (-3.7267) ; Rungan P total (-201.1833), P tsd (-30.5967), K total (-275.2367), K tsd (-27.61), Ca (-3.3167), Mg (-2.927) ; Manuhing P total (-211.1033), P tsd (-42.82), K total (-261.3333), K tsd (-38.0367), Ca (-3.32), Mg (-2.363) dari ekosistem hutan kedalam ekosistem DAS.
Tropical rain forest has a specific ecosystem, and it can be well preserved caused by to the linkage amongs the constituent components inside as a whole unity. The forest ecosystem can be preserved if it could maintain the mechanism of nutrient cycling and its high diversity. Then, this closed nutrient cycling become dynamics of nutrient in the forest system and it runs well due to an appropriate output of nutrient. The area of tropical rain forest in the study location was the area that ever logging by Forest Management Right (HPH: Hak Penguasaan Hutan) and wood of bansaw processing that operated illegally in some, thus it is possibly for changing of composition and structure inside and the nutrient cycling process that will be occured in the forest ecosystem and it will be disturbed by the increasement of lost or the loose nutrient substances to the watersheds ecosystems. This study was conducted to : 1) Study the composition, structure and diversity of kind of forest vegetation composition, 2) Study the community path of forest stand, 3) Study nutrient input contain in the soil of the throughfall, stemflow, and nutrient output through the river by suspensition soluble and basic sediments, 4) Study the balance of nutrient the forest and watersheds ecosystem. This study was performed by determining the observation blocks based on the overlay of topographic or slope map. Then, the overlay results of each sub watersheds were divided into some observation or releve tracks. The study tracks were divided based on the level of slope of 0-2%, >2-8%, and >8-15%. Each releve was made by measurement cabins with different wide based on the level of growth: seedling, sapling, pole, and tree. The structur of vegetation was observed by making the quadrilateral lane of 200 ft (61 metres) x 25 ft (7.6 metres), they was mapped and noted the diameter, high of crown, high of branch, and width of crown of tree. It was noted the species which the highmore than 4.5 metre, and then it was made the vertical projection from trees lied in the observation track and the results would be a profile diagram. The community path was known by conducting ordinance analyses of two dimensions, then it counted the value of Variety Index of Diversity using the data of vegetation in each observation track. The result of the study on vegetation showed that the composition of vegetation kind in each watersheds in all level of growth was dominated by the kinds of Dipterocarpaceae family. The community path of vegetation in all levels of growth had the similar paths of community, it was only different in the grouping path of pole level in sub watersheds of Rungan. Level of growth of seedling and pole had the lower value of diversity in all sub watersheds ecosystem. The structure of vegetation had 3 (three) layers of crown, that were dominated by the kinds of Dipterocarpaceae family. It was quite high the output of nutrient substance through the basic sediment, and this showed that there was leakage of nutrient, Subs Watersheds : Kahayan P total (-140.2433), P tsd (-59.1233), K total (-409.1667), K tsd (-33.2933), Ca (-6.7633) ; Miri P total (-187.033), P tsd (-46.7633), K total (-387.8667), K tsd (-38.57), Ca (-3.7267) ; Rungan P total (-201.1833), P tsd (-30.5967), K total (-275.2367), K tsd (-27.61), Ca (-3.3167), Mg (-2.927) ; Manuhing P total (-211.1033), P tsd (-42.82), K total (-261.3333), K tsd (-38.0367), Ca (-3.32), Mg (-2.363) from forest ecosystem into the watersheds ecosystem.
Kata Kunci : Daerah Aliran Sungai, Siklus hara, Struktur vegetasi
