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

Mineral deficiency and the presence of Pinus sylvestris on mires during the mid- to late Holocene: Palaeoecological data from Cadogan's Bog, Mizen Peninsula, Co. Cork, southwest Ireland

Pollen records across parts of Ireland, England and northern Scotland show a dramatic collapse in Pinus pollen percentages at approximately 4000 radiocarbon years BP. This phenomenon has attracted much palaeoecological interest and several hypotheses have been put forward to account for this often synchronous and rapid reduction in pine from mid-Holocene woodland. Explanations for the 'pine decline' include prehistoric human activity, climatic change, in particular a substantial increase in precipitation resulting in increased mire wetness, and airborne pollution associated with the deposition of tephra. Hitherto, one largely untested hypothesis is that mineral deficiency could adversely affect pine growth and regeneration on mire surfaces. The discovery of pine-tree remains (wood pieces, stumps and trunks) within a peat located at Cadogan's Bog on the Mizen Peninsula, southwest Ireland, provided an opportunity to investigate the history of Pinus sylvestris and also to assess the importance of mineral nutrition in maintaining pine growth on mires. Pollen, plant macrofossils, microscopic charcoal and geochemical data are presented from a radiocarbon dated monolith extracted from this peat together with tree ring-width data and radiocarbon dated age estimates from subfossil wood. Analyses of these data suggest that peat accumulation commenced at the site around 6000 years BP when pine was the dominant local tree. Thereafter Pinus pollen percentages diminish in two stages, with the second decline taking place around 4160 ± 50 years BP. Concomitant with this decline in Pinus pollen, there is a noticeable, short-lived increase in wet-loving mire taxa and a decrease in the concentration of phosphorus, potassium, magnesium, calcium, sodium, iron and zinc. These results suggest that increased mire surface wetness, possibly the result of a change in climate, created conditions unsuitable for pine growth c. 4000 years BP. Mire surface wetness, coupled with a period of associated nutrient deficiency, appears to be a possible explanation for a lack of subsequent pine-seedling establishment for most of the later Holocene

Eleocharis obtusa

Angiosperm

Phytosociological analysis of Aspen communities on three site classes for Populus grandidentatain western Cheboygan County, Michigan

Ten 20×20 m plots were surveyed in each of three site classes (poor, medium, and good) for Populus grandidentata growth on three different podzolized soils in western Cheboygan County, Michigan, 14 miles south of the Straits of Mackinac. A phytosociological table shows that exclusive differential species distinguish communities of the poor sites from those of the good sites. In both groups some species are persistent from earlier stages of succession and others are invading species responsible for more recent succes sional change. The medium site class lacks differential species. Poor-site stands are developing toward Pinus resinosa-P. strobus forest and Quercus rubra-Pinus forest. Good-site stands are developing toward Acer-Fagus forest, a mesophytic community characteristic of the “northern hardwoods” regional climax. Medium-site stands have potentialities for development toward either the Pinus communities or the Acer-Fagus community, but predominantly in the direction of the latter. Zehn Aufnahmen von jeder Standortsklasse (arm, mittel, gut) hinsichtlich des Wachstums von Populus grandidentata auf drei verschiedenen podsolierten Böden in West Cheboygan County, Michigan, 14 Meilen südlich der Mackinacstrasse werden vorgelegt. Eine phytosoziologische Tabelle erweist, dass die ausschliesslichen Differentialarten die Pflanzengesellschaften der armen Standorte von jenen der guten unterscheiden. Einige Arten der beiden Gruppen haben sich aus früheren Sukzessionsstufen erhalten, während einige andere als Eindringlinge aufzufassen sind. Der Mittelstandortsklasse fehlen die Differentialarten. Die Pflanzengesellschaften der armen Standortsklasse entwickeln sich zum Pinus resinosa-P. strobus -Wald und zum Quercus rubra -Wald, Gesellschaften der guten Standortsklasse zum Acer-Fagus -Wald einer mesophytischen Gesellschaft, die für den „nördlichen Laubwald” den Regionalklimax darstellt. Mediumstandortsbestände können sich entweder zu den Pinus -Gesellschaften oder aber zu der Acer-Fagus -Gesellschaft (meistens zu letzterer) entwickeln. Dix relevés de 20 x 20 m. ont été faits dans chacune des trois catégories (pauvre, moyenne et bonne) de sites de rapportant à la croissance de Populus grandidentata sur trois soils podsolizés dans la partie occidentale du Comté de Cheboygan (Michigan), 14 miles au Sud du Détroit de Mackinac.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43879/1/11258_2004_Article_BF00303792.pd