A study into the mobility of iron in podzolized Sarawak upland soils by means of selective iron extractions.

The presence of relatively large amounts of crystalline free iron oxides gradually increasing with depth, a virtual absence of new iron accumulations in the amorphous form and a great activity of organic acids in complexing iron in surface horizons were observed. Additional field information provides evidence of large accumulations of iron oxides at great depth in cracks and joints of sedimentary rocks. These characteristics suggest that there has been a relative accumulation of crystalline iron oxides through desilication during an early stage in soil formation. This was followed by a loss of iron in varying degree from the upper horizons, which can most likely be attributed to fossil argilluviation and weathering of iron-rich clay, or possibly to fossil reduction with transport in ferrous form. The latter would presuppose the existence of poorly drained conditions prior to strong dissection resulting in the present landscape. The strong and extensive accumulation of iron oxides at great depth in cracks and joints may be attributed to the oxidation and precipitation of ferrous and ferric iron mobilized upon initial oxidation of pyrites in the weathering front of the sedimentary rocks. Lateral movements of soil water may play a role in this. (Abstract retrieved from CAB Abstracts by CABI’s permission

Long-term disturbance dynamics and resilience of tropical peat swamp forests

Summary 1.The coastal peat swamp forests of Sarawak, Malaysian Borneo, are undergoing rapid conversion, predominantly into oil palm plantations. This wetland ecosystem is assumed to have experienced insignificant disturbance in the past, persisting under a single ecologically-stable regime. However, there is limited knowledge of the past disturbance regime, long-term functioning and fundamentally the resilience of this ecosystem to changing natural and anthropogenic perturbations through time. 2. In this study, long-term ecological data sets from three degraded peatlands in Sarawak were collected to shed light on peat swamp forest dynamics. Fossil pollen and charcoal were counted in each sedimentary sequence to reconstruct vegetation and investigate responses to past environmental disturbance, both natural and anthropogenic. 3. Results demonstrate that peat swamp forest taxa have dominated these vegetation profiles throughout the last c. 2000-year period despite the presence of various drivers of disturbance. Evidence for episodes of climatic variability, predominantly linked to ENSO events, and wildfires is present throughout. However, in the last c. 500 years, burning and indicators of human disturbance have elevated beyond past levels at these sites, concurrent with a reduction in peat swamp forest pollen. 4. Two key insights have been gained through this palaeoecological analysis: (i) peat swamp forest vegetation has demonstrated resilience to disturbance caused by burning and climatic variability in Sarawak in the late Holocene, however (ii) coincident with increased fire combined with human impact c. 500 years ago, these communities started to decline. 5. Synthesis. Sarawak's coastal peat swamps have demonstrated resilience to past natural disturbances, with forest vegetation persisting through episodes of fire and climatic variability. However, palaeoecological data presented here suggest that recent, anthropogenic disturbances are of a greater magnitude, causing the observed decline in the peat swamp forest communities in the last c. 500 years and challenging the ecosystem's persistence. This study greatly extends our knowledge of the ecological functioning of these understudied ecosystems, providing baseline information on the past vegetation and its response to disturbance. This understanding is central to developing management strategies that foster resilience in the remaining peat swamp forests and ensure continued provision of services, namely carbon storage, from this globally important ecosystem.</p