PATTERNS AND IMPACTS OF DEFORESTATION WITHIN LOWLAND RIVER VALLEYS OF BORNEO

Borneo, home to one of the oldest tropical forests, has lost half of its forest habitat to palm oil plantations, threatening the existence of a number of endangered species. Previous work highlighted that the deforestation has also changed the behaviour of lowland rivers across the island, but the scale of change seemed limited given the degree of deforestation. Along the Kinabatangan River, meander migration rates increased by roughly 1.3 times in spite of complete removal of riverbank forest cover. To further assess the seeming paradox, we investigate here rates and patterns of deforestation along 8 lowland rivers of Borneo, including the Kinabatangan, to get a better sense of the broader environmental impacts of deforestation. We utilise Landsat imagery from 1989 to 2018 to construct patterns of landcover change, with images available for roughly every 5 years of record for the Baram, Barito, Kapuas, Kahajan, Kinabatangan, Mahakam, Sugut, and York Rivers. Using a maximum likelihood classification, we found that the average amount of natural forest lost for all of the rivers from 1989-1991 to 2016-2018 was 36.60%. Deforestation steadily occurred in the 29 year interval, but times of greater deforestation corresponded with times of high demand and prices for palm oil. The river that experienced the most deforestation was the Baram River with a total loss of 69.42% of its natural forest over our study period. Despite the scale of forest loss, the geomorphological response of each river was limited. Overlapping centrelines digitised from the historical imagery allowed us to calculate rates of meander migration. In nearly every case, meander migration rates remained low and seemingly unchanging, averaging 0.003 channel-widths per year. Our results suggest that the lowland rivers of Borneo are exceptionally resilient or that we are in the midst of a lag wherein much of the river responses to deforestation remain to be seen.