Floral Composition of the Kayan-Sembakung Delta in North Kalimantan (Indonesia) in Different Disturbance Regimes

Abstract

This paper presents the results of a preliminary study that identify the floral composition of the Kayan-Sembakung Delta in North Kalimantan under different disturbance regimes. The landforms described in the Regional Physical Planning Project for Transmigration in Indonesia land-system map were evaluated to define the mangrove ecosystem boundary. The mangrove ecosystem disturbance levels distinguished by reclassifying the land-cover map of the mangrove ecosystem into four categories, i.e. heavily disturbed mangrove (represented by shrimp ponds abandoned five years ago or less), moderately disturbed mangrove (represented by shrimp ponds abandoned more than five years ago), regrown (secondary) mangrove forest (that may have been logged for wood but did not experience terrain alteration for fishpond development), and relatively undisturbed (primary) mangrove forest. A vegetation survey was conducted in several transects for each of these categories. Basal area, density, species diversity, and abundance of species in each location were calculated to understand the floral composition of the mangrove ecosystem. The study reveals that the mangrove forest in the Simanggaris River has the highest total basal area of 44.50 m2/ha, as well as the highest tree density of 1635 individual/ha, which indicates the most dense and mature remaining mangrove forest followed by the Sikang River near Liago Village with 85.75% of canopy cover. The heavily degraded mangrove ecosystem in Ibus Island has the highest importance value index of 278.89%, with Sonneratia sp. as the dominant species. The Kayan-Sembakung Delta hosts at least six original mangrove species, i.e. Rhizophora apiculata, Osbornia octodonta, Lumnitzera littorea, Avicennia sp, Rhizophora sp, and Sonneratia sp. In addition to the six original mangrove species listed, the inner part of the Kayan Delta also has several forest patches dominated by Nypa fruticans, whereas some parts of the Delta host a mixed vegetation composition between freshwater and brackish water ecosystems.