Long-term dynamics of vegetation and disturbance of a southern boreal spruce swamp forest

Abstract. Analysis of pollen, charcoal and loss-on-ignition in peat cores from a Picea aèies-dominated swamp forest in central Sweden show the vegetation changes and disturbance patterns over 9500 yr. Six major sequences of local vegetation development are identified: (A) Pinus period, ca. 9500–7000 cal. BP; (B) Open mire period (ca. 7000–4500 cal. BP; (C) Betula period, ca. 4500–2300 cal. BP; (D) Picea period (ca. 2300–1000 cal. BP; (E) Human impact period (ca. 1000–100 cal. BP); and (F) Period of human abandonment during the last ca. 100 yr. The swamp forest has been highly dynamic in response to various natural and anthropogenic disturbance agencies. Several fires have heavily influenced the vegetation development. During the last ca. 900 yr human influence has been important, initially from grazing and trampling by domesticated animals (ca. 1000–500 cal. BP), and subsequently small-scale cereal growing (ca. 400–100 BP). Cutting, burning and animal browsing influenced the structure and dynamics of the swamp forest by creating a more open stand and suppressing tree regeneration. Recent cessation of human impact has led to increased tree regeneration and a denser swamp forest stand. The present high biodiversity, and subsequent conservation interest does not result from long-term stability or absence of fire and human impact. However, in spite of repeated disturbances, a continuity of old and senescent trees produced a forest type with abundant dead wood. With the relatively minor importance of fire over long periods of time, the swamp forest developed a structure maintaining a high biological diversity. An important issue for maintaining long-term biodiversity in the boreal landscape must be to create a mosaic where different forest types are present, with a variety of structures, substrates and processes, to provide a certain degree of freedom for species to move around in the landscape.     

Late‐Holocene fire history in a forest‐grassland mosaic in southern Brasil: Implications for conservation

Question: Is the diverse mosaic of forest/grassland (Campos) vegetation on the hills in the Porto Alegre region natural or of anthropogenic origin? What are the best approaches to management and conservation of forest/grassland mosaics in southern Brazil? Location: 280 m a.s.l., Rio Grande do Sul State (30°04′32″S; 51°06′05″W, southern Brazil. Methods: A 50-cm long radiocarbon dated sediment core from a swamp on Morro Santana was analysed for pollen and charcoal, and multivariate data analysis was used to reconstruct past vegetation and fire dynamics. Results: The formation of swamp deposits is related to a change to wetter climatic conditions since 1230 cal yr BP. The diverse forest/grassland mosaic existed already at that time and can be seen as natural in origin as it has been also shown from other studies in southern Brazil. Since 580 cal yr BP, forests expanded continuously. The marked higher occurrence of the pioneer Myrsine during the last 70 years, indicates a change in the disturbance regime. In the past, vegetation has been influenced by mostly anthropogenic fire, set first by Amerindians and later by European settlers. Conclusions: Management for conservation of forest/grassland mosaics should take into account, first, that grasslands are remnants of earlier drier Holocene periods and not a result of deforestation and, second, the history of disturbance by grazing and fire. Suppression of grazing and burning has likely resulted in a trend towards more woody vegetation under modern wet climatic conditions. If management for conservation excludes fire, the present grassland patches will tend to disappear due to forest expansion under the modern humid climate. Maintaining or reintroducing cattle grazing in conservation areas could be an alternative to fire.     

Holocene vegetational and coastal environmental changes from the Lago Crispim record in northeastern Pará State, eastern Amazonia

Vegetational and coastal environmental changes have been interpreted from a 600cm long and 764014C yr B.P. old sediment core from Lago Crispim located in the northeastern Pará State in northern Brazil. The radiocarbon dated sediment core was studied by multi-element geochemistry, pollen and charcoal analysis.Holocene Atlantic sea-level rise caused an elevation of local water table, which allowed the formation of organic deposits in a probably former inter-dune valley. Dense, diverse and tall Amazon rain forest, and some restinga (coastal vegetation) covered the study area at the beginning of the record at 764014C yr B.P. Mangrove vegetation developed along rivers close to the core site at that time. Subsequent decrease in less mangrove vegetation near the study site indicates a sea-level regression, beginning since around 700014C yr B.P. Lower sea-levels probably favoured the formation of a local Mauritia/Mauritiella palm swamp at 662014C yr B.P. Oscillations of higher and lower sea-level stands probably changed the size of the local palm swamp area several times between 6620 and 363014C yr B.P. Sea-level transgression at around 363014C yr B.P., caused marked coastal environmental changes: the development of mangroves near the site, the replacement of the local palm swamp by a Cyperaceae swamp, the substitution of the surrounding former Amazon rain forest and some restinga vegetation mainly by salt marshes. High amount carbonised particles suggest a strong human impact by burning on the coastal ecosystems during this late Holocene period.Highest concentrations of NaCl and also Ca, Mg and K in the upper sediment core indicate that the Atlantic was close during the late Holocene period. The core site, which is today 500m from the coastline and only 1-2m above modern sea-level, was apparently never reached by marine excursions during the Holocene.Less representation of mangrove since ca. 184014C yr B.P., may be related due to a slightly lower sea-level or to human impact in the study region. The modern shallow lake seems to be formed recently by road construction, forming an artificial dam.     

Holocene vegetation and water level history in two bogs of the Cordillera de Talamanca, Costa Rica

Pollen records of Holocene sediment cores from the Costa Rican Cordillera de Talamanca (La Chonta bog, 2310 m and La Trinidad bog, 2700 m) show the postglacial development of the montane oak forest zone from ca. 9500 to 1500 yr BP. During the early Holocene (ca. 9500–700 yr BP), alder vegetation covered the La Chonta and La Trinidad bogs and their adjacent hills. The upper forest line is inferred to be at 2800–3000 m elevation. A Podocarpus-Quercus forest characterised the middle Holocene (ca. 7000–4500 yr BP). The upper forest line is located at >3000 m reaching the present-day altitudinal distribution. A Quercus forest characterised the late Holocene (ca. 4500–1500 yr BP). Compared to modern conditions, the early Holocene has similar average temperatures, but the moisture level was probably higher. Pollen evidence for the late Holocene indicates drier environmental conditions than today. In order to improve the paleoecological interpretation, we described the local vegetation and used moss samples as pollen traps at both montane bogs along strong soil moisture gradients.The Netherlands Centre for Geo-ecological Research, ICG     

Methodological and practical aspects of the presentation and interpretation of microscopic charcoal data from lake sediments

Analysis of microscopic charcoal particles is a useful part of palaeoecological research and is mostly used in conjunction with pollen analysis. However, there is considerable variation in the methodology of charcoal analyses. This paper considers various methods for the analysis of microscopic charcoal and the presentation of charcoal data in the context of a study of the upper sediments of two lakes Estonia. The results are evaluated by comparing both the pollen and charcoal data with documentary evidence of forest fires over the past 60 years. Indications of fires both varying in extent and at different distances from the lakes are evaluated in both the pollen and charcoal diagrams. The results suggest that the total area curve for charcoal particles per unit mass of sediment dry matter (cm² g⁻¹) provides the best indicator of forest fires. Fires in the study area are reflected differently in the charcoal and pollen curves. It is suggested that the charcoal data have the potential to indicate disturbance at a greater distance from the coring site than indicated by the pollen data. Received February 5, 2002 / Accepted August 14, 2002     

Late quaternary vegetation dynamics and human impact on Alexander Selkirk Island, Chile

Aim To reconstruct the history of vegetation and environments using pollen, charcoal and sediment analysis, and to identify the timing and nature of climate change and human impact on the vegetation of a remote Pacific island. Location Cerro de Los Inocentes, 1000 m above sea level, Alexander Selkirk Island (33°45′S, 80°45′W), Chile. The westernmost island of the Juan Fernandez Archipelago, south‐east Pacific Ocean. Methods A 150‐cm long sediment core comprising 87 cm dark brown peat overlying 63 cm of yellow grey clay was extracted from a shallow depression on the southern slopes of Cerro de Los Inocentes. Pollen, charcoal, sediment and accelerator mass spectrometry radiocarbon analyses were used to construct a record of vegetation change through time. Numerical analysis of multispecies data allowed the classification of fossil assemblages into distinct pollen zones. Results Pollen and spores are preserved throughout the sediment with high concentrations coinciding with the beginning of organic sediment accumulation at around 8000 ¹⁴C yr BP. Prior to 8000 ¹⁴C yr BP, the deposition of clays, presumably from upslope erosion, occurred in a landscape sparsely vegetated by grasses, ferns and Pernettya rigida heath, including several plants that are only found 100–200 m above the site today (Zone CI‐1). After 8000 ¹⁴C yr BP, a P. rigida heath was the dominant vegetation (Zone CI‐2). A shift to a wet heath–shrubland (Zone CI‐3) occurred at 6000 ¹⁴C yr BP and was followed by a transition to a treefern–shrubland mosaic accompanied by periodic burning (Zone CI‐4) after 4500 ¹⁴C yr BP. The impact of human occupation is evident in Zone CI‐5 at 450 ¹⁴C yr BP with the loss of forest species, increased burning and invasion of the exotic plant Rumex. Main conclusions The pollen and charcoal record provides the first evidence of vegetation changes spanning at least the last 8000 ¹⁴C yr BP from the high altitude environment of Alexander Selkirk Island. Prior to 8000 ¹⁴C yr BP, the altitudinal ranges of different plant species may have been suppressed by a cooler and drier climate. Increasing precipitation and temperatures at the end of the last glacial period may have mobilized exposed sediments in a sparsely vegetated upland environment, altering local drainage patterns, eventually leading to slope stabilization and deposition of organic detritus under an increasing density of heath and shrub vegetation. The subalpine heath–shrubland persisted until 4500 ¹⁴C yr BP when first evidence for sustained burning is found in association with the establishment of a more open treefern–shrubland vegetation pattern. In the absence of human occupation at this time, the influence of increased climatic variability associated with more frequent El Niño‐Southern Oscillation events during the mid to late Holocene is considered one of the main driving forces behind increased vegetation disturbance during this period. The record provides evidence that island vegetation patterns have been highly dynamic over millennial to decadal time‐scales and that the flora has persisted through periods of rapid and major climate change. This changed with the discovery of the island by European explorers in the late sixteenth century and the subsequent introduction of goats and exploitation and burning of forests, which resulted in the progressive destruction of native vegetation and the invasion of introduced plants. There is evidence that reduced burning and control of the goat population within the last 50 years has resulted in marginal recovery of some high altitude native plant species.     

A short pollen diagram from rainforest in highland eastern Victoria

Pollen data from the Rooty Breaks swamp – a Sphagnum bog surrounded by Atherosperma-Elaeocarpus rainforest – in the eastern Victorian highlands appears to reflect changes in the mode of pollen and spore deposition at the study site, from the time sediments began accumulating at about 5500 BP until the present day. In the lower half of the deposit, pollen of rainforest taxa is more common than it is in the top half, while Eucalyptus pollen reflects the reverse situation. Although the pollen changes may reflect climatic change it is suggested that most of the pollen and spores in the lower sediment were stream-borne. Later the stream moved away from the site and the records became more representative of atmospheric pollenrain. Throughout the period covered by the pollen diagram the Rooty Breaks swamp itself was dominated by Leptospermum grandifolium. The pollen record shows that the association of important taxa in rainforests of the highlands of eastern Victoria was established by at least 5500 BP. The presence of sparse old eucalypts throughout the area dominated by rainforest suggests that sclerophyll forest was replaced by rainforest in the recent past. However, this change is not evidenced in the pollen diagram.     

Late Quaternary pollen records from the middle Caquetá river basin in central Colombian Amazon

Three pollen records are presented from the Pantano de Monica region (0°42′S, 72°04′W, 160 m elevation) on the lower terrace of Rio Caquetá of the central Colombian Amazonas. Ten radiocarbon dates from three cores indicate that the deposits are of Holocene age, but the pollen data suggest that the record may also contain the Late Glacial. The core Pantano de Monica 1 covers the time interval from 11,150 BP (extrapolated) to 4730 BP. During the Late Glacial and early Holocene this swamp was smaller in size and waters were more shallow than today, with abundant Mauritia palm trees. This indicates that the lower terrace of the Caquetá River was better drained than today, which might be related to changes in the drainage system and/or drier conditions during that time. Late Glacial and early Holocene vegetational changes in the rain forests surrounding the swamp Pantano de Monica indicate successional stages, probably related to changes in the drainage system and/or climate changes. Presence of Podocarpus pollen grains up to 2.6% of the total sum (and influx of 78 grains cm⁻² yr⁻¹) point to the regional presence of Podocarpus at the beginning of the Holocene. Evidence of Podocarpus during glacial times in other pollen records from the Amazon basin has been taken as indicative of cooling. Core Pantano de Monica 2 was taken in a small swamp (1000 m distance to Pantano de Monica 1) and starts at 4000 BP when this location was well drained. Several changes in the composition of the rain forest are documented, such as increase in disturbance (increase of Cecropia) followed by a quick recovery (increase of Psychotria). Protium and Caryocar tree taxa were frequent, suggesting that the lower terrace area was well drained until 3080 BP, after which small swamps developed. Core Pantano de Monica 3 is from the wet forest in between the two swamps and represents the period since 3260 BP. Pollen data show a continuously increasing presence of palms, probably Euterpe, suggesting either a transition from well-drained to less drained conditions in the lower terrace during the late Holocene, and/or a more intensive human impact of the rain forest on the lower terraces of Rio Caquetá. The three records from the lower terrace of Rio Caquetá show different forest compositions in the past and indicate that the rain forest environments were not stable during Late Glacial and Holocene times. Comparison with other data from lowland records of northwestern South America suggest that climate change is a major factor for environmental change in central Colombian Amazon.     

Vegetation and Environment History for the Past 14 000 yr BP from Dingnan, Jiangxi Province, South China

A Late Pleistocene-Holocene pollen, phosphorus, and charcoal record was reconstructed from a peatland in southern Jiangxi Province in southern China. The area today has a mountainous and rolling landscape with villages, small towns, and agriculture dominated by rice paddies, vegetable, and fruit gardens, as well as areas of secondary forest and pine re-afforestation. The record opens before 14 300 yr BP, with Alnus woodland dominating the wetland areas and with an open Quercus woodland on the surrounding slopes. The forest area becomes more complex from approximately 12 800 yr BP and further from 9 000 yr BP. At approximately 6 000 yr BP, there is evidence of clearing and, by 4 500-4 000 yr BP, a complete collapse in the wetland Alnus and terrestrial forest as the low-lying areas are converted to rice production. For much of the record, the occurrence of fire around the site was low, although there is evidence of regional fires. Fire was used as a tool in clearing and then used in the annual cycles of stubble burning after rice harvest. Nutrient levels, as reflected by total phosphorus in the sediment, seem to be closely related to forest changes and high values in the surface layers probably result from land-management techniques associated with agriculture. Therefore, human impact greatly altered forest cover, fire frequency, and nutrient dynamics; this has been evident for approximately 6 000 yr BP and then intensities towards the present day.     

Late Quaternary vegetation and climate change in the Panama Basin: Palynological evidence from marine cores ODP 677B and TR 163-38

The Late Quaternary paleoenvironmental history from Pacific slopes of the western Andes is reconstructed by pollen analysis of 32 samples from two marine sediment cores from the Panama Basin, eastern equatorial Pacific: core ODP 677B (83°44.2200′ W, 1°12.1440′ N, 3473 m water depth) is 185 cm long and spans the last 39,410 years, core TR 163-38 (81.583° W, 1.337° N, 2200 m water depth) is 103 cm long and covers the last 17,380 years. Six ecological groups were established: mangrove, brackish and fresh water swamps, terra firma lowland forests, broad range taxa, Andean forests, and open vegetation. A good correspondence was found between the changes of these ecological groups in the two cores. The records evidence the continuous presence of all vegetation types during the last 39,410 years and specially the uninterrupted occurrence of tropical rain forest. They record a development from: (1) a cold and humid phase (39,410-28,120 yr cal BP) with moderately high sea levels, (2) the coldest and driest phase in the record (28,120-14,500 yr cal BP) accompanied by the lowest sea levels, (3) a transitional phase when sea level rose and humid conditions dominated, (4) a stage (11,300-5600 yr cal BP) of the highest sea levels and moisture conditions including a drier period ∼7000 yr BP, to (5) a final period (5600 yr cal BP-Present) when sea level reached its present height, humidity persisted, and indicators of disturbance expanded. Peaks in pollen and spore concentration, associated with high river discharge periods, indicate periods of higher precipitation around 33,500, 28,000 and 12,000-9000 yr cal BP. Although main vegetation responses seem to reflect rainfall and moisture variations, a good correspondence was found between δ¹⁸O values and percentages of Andean and lowland pollen, suggesting that vegetation also responded to tempearture changes.     

Late Quaternary grassland (Campos), gallery forest,fire and climate dynamics,studied by pollen,charcoal and multivariate analysis of the São Francisco de Assis core in western Rio Grande do Sul (southern Brazil)

We present a detailed pollen and charcoal record of a 368-cm-long sediment core from the lowland Campos (grassland) region near the city of São Francisco de Assis in the western Rio Grande do Sul State in southern Brazil. Based on four AMS radiocarbon dates, the record represents the last about 22,000 cal yr BP. The region was naturally covered by Campos throughout the recorded glacial and Holocene period under cold and relatively dry and warm and dry condition, respectively. Initial expansion of gallery forest after 5170 cal yr BP indicates a change to wetter climatic conditions. Maximum extent of gallery forest after 1550 cal yr BP reflects the wettest recorded period. There is some evidence of plant migration from the eastern Atlantic coastal lowland reaching the western lowland, first after mid Holocene times by Cecropia and, possibly, species of Myrsine and Moraceae and later, after about 1000 cal yr BP, by species of Alchornea and Acalypha. Multivariate analysis revealed that the long-term pollen composition dynamics is a two-phase process, with random, chaotic changes characterizing some periods when climate conditions were likely more stable, and directional compositional changes (phase transitions) in periods coincide with major climate and/or anthropogenic changes. Natural fires were rare during full- and lateglacial periods, but became frequent at the beginning of the Holocene, suggesting the beginning of human occupation of the western lowland at that time. Highest fire frequency is found during the wet late Holocene period, suggesting an increase of indigenous populations in the São Francisco de Assis region.     

History of a Pinus strobus-dominated stand in northern New York

Abstract. Pollen, plant macrofossils and charcoal from a small forest hollow were analyzed to determine the formation and dynamics of a Pinus strobus-dominated forest stand on outwash soil in northern New York. P. strobus, Betula papyrifera and Abies balsamea colonized the upland surrounding the hollow following a major disturbance that occurred ca. 360 yr ago. Pre-disturbance vegetation consisted of shade-tolerant Tsuga canadensis, Fagus grandifolia and Picea ruhens. The size-class distribution of modern vegetation suggests continuing recruitment of A. balsamea and Acer rubrum at the site. The status of P. strobus and B. papyrifera in the stand is uncertain, but there is no evidence for recolonization of T. canadensis, F. grandifolia or P. rubens. Frequent windthrow has probably played a role in stand dynamics since ca. 310 yr BP due to the high wind-susceptibility of overstory and understory tree taxa in the modern forest patch. Vegetation change that occurred following fire(s) ca. 310 yr BP was recorded by plant macrofossils but not by pollen, indicating that the pollen assemblage was insensitive to vegetation change within at least 30 m (and potentially 60 m) of the hollow. The apparent insensitivity of this small-hollow pollen assemblage to local vegetation change may be related to the relatively large size of the hollow (75 m²) and/or to its close proximity to a 0.24 ha kettle pond.     

Dynamics of temperate rainforest from fine resolution pollen analysis,Upper Ringarooma River,northeastern Tasmania

Abstract The relationship between sclerophyll forest and temperate rainforest in Tasmania is believed to be driven by climate, soils and fire regime; however, this has been tested infrequently on time frames relevant to the longevity of the major forest trees involved. This study uses sediments in four small hollows from within a rainforest stand in the Upper Ringarooma valley in northeastern Tasmania, Australia, to analyse vegetation dynamics and disturbance over the last 1000 years. Pollen-vegetation relationships were investigated by comparing pollen rain and current vegetation, and the chronology was established by radiocarbon and lead-210 dates. The lead-210 data indicate that the two Sphagnum humus profiles were not always closed systems for inorganic inwash; however, the pollen and charcoal records are generally consistent indicating that a mixed Eucalyptus-Nothofagus forest shifted to a Kothofagus dominated rainforest as fire became a less prominent component of the environment. About 400 years ago Leptospermum lanigerum invaded the community as canopy gaps developed, possibly as the older Nothofagus Cunninghamii trees died. There is no strong evidence of invasion by Atherosperma moschatum as suggested by some models of forest dynamics in these forests in Tasmania. In this stand of forest, fire and erosion following flooding have been the major causes of disturbance.     

The Potential Impact of Small-Scale Physical Disturbance on Seedlings in a Papuan Rainforest1

Physical disturbance, such as falling debris, is an important cause of mortality to rain forest seedlings. I used artificial seedlings to quantify physical disturbance in a rain forest at the Crater Mountain Biological Research Station in Papua New Guinea. Single (N= 418) and clustered artificial seedlings (N= 428) were placed on eight transects spanning varied topography to assess the area's disturbance regime, to test if ground slope affected disturbance, and to test if clustering affected the incidence of damage. Two transects showed a significant departure from random in the spatial distribution of damaged seedlings within the transect, suggesting that some areas of experience more disturbance than others. Artificial seedlings on level ground experienced damage less often than artificial seedlings on slopes; disturbance increased with ground slope. Artificial seedlings in dry washes experienced the greatest probability of damage. Artificial seedlings in clusters experienced significantly less damage than single ones, suggesting clustered seedlings might be less vulnerable to damage than lone seedlings. The disturbance rate at this site (34.7% damaged in one year) was markedly lower than that measured at the La Selva Biological Reserve in Costa Rica (82.4%).     

Nesting Success of Costa Rican Lowland Rain Forest Birds in Response to Edge and Isolation Effects

Although open-cup nesting birds generally face increased risk of nest depredation from forest edge predators and brood parasites in fragmented temperate landscapes, little information exists to assess such risks in tropical birds. We compared nesting success of real birds' nests in large and small forest fragments to a control site in Caribbean lowland wet forest of Costa Rica. Pooling across species, nesting success was significantly greater in unfragmented forest than in either small, isolated fragments or the La Selva Biological Reserve, which is at the tip of a forest 'peninsula' embedded in a largely deforested landscape. Nesting success in isolated fragments did not vary according to distance from edge, suggesting that predators in fragments act throughout these forest patches. The case for increased nest predation as a plausible mechanism to explain the documented decline of forest interior bird populations in this fragmented tropical landscape is enhanced by a simple demographic model that suggests nesting success is likely too low to maintain populations at La Selva and in the fragments. The fact that the large (> 1000 ha) La Selva forest reserve is experiencing nest predation rates similar to those in much smaller fragments is cause for concern. Our results make a strong case for additional studies to document the identities of nest predators in both fragmented and unfragmented forests in such tropical forest landscapes.     

Modern pollen–vegetation relationships along transects on the Whangapoua Estuary, Great Barrier Island, northern New Zealand

Aims To quantify pollen–vegetation relationships from saline to freshwater in an estuarine gradient from surface samples of the modern pollen rain, to allow more accurate interpretations of the stratigraphic palynological record. Location Whangapoua Estuary, Great Barrier Island, northern New Zealand. Methods Six transects were laid out along a vegetation sequence running from estuarine mud to freshwater swamp. Along these transect lines, 108 plots were sampled for vegetation and surface sediments from wet sand, mud, plant litter or moss (sand and mud sites are inundated by most tides, other sites less frequently). All sediment samples were analysed for pollen. The relationships between plant species frequency and pollen representation were examined at a community scale using twinspan and ordination analyses, and for individual species using fidelity and dispersibility indices, regression and box‐plot analyses. Results The quantitative relationships between source taxon vegetation frequency and its pollen representation varied between species due to differential pollen production and dispersal. twinspan of the surface pollen samples suggests five vegetation types: (A) mangrove (Avicennia marina); (C) Leptocarpus similis salt meadow; (D) Baumea sedges; (E) Leptospermum shrubland; and (F) Typha/Cordyline swamp forest. The (B) Juncus kraussii community is not represented palynologically owing to the destruction of its delicate pollen grains during acetolysis of samples. Detrended correspondence analysis places these communities on an estuarine‐to‐freshwater gradient. However, pollen assemblages at the seaward end of the salinity gradient are less clearly representative of the associated vegetation than those at the landward end, probably because the open vegetation at the former allows the influx of wind‐ and water‐dispersed pollen from surrounding vegetation. Main conclusions The vegetation pattern (zonation) at Whangapoua is reflected in the pollen rain. When the long‐distance and over‐represented pollen types are excluded, five out of six of the broad vegetation communities can be identified by their pollen spectra. Species with high fidelity and low‐to‐moderate dispersibility indices can be used to identify the vegetation types in the sedimentary sequences. The more open vegetation types at the ‘marine end’ of the sequence tend to be ‘overwhelmed’ by regional pollen, but the nature of the sediments and the presence of discriminatory species (e.g. A. marina, Plagianthus divaricatus, Cordyline australis), even in small amounts, will allow correct identification of the local vegetation represented in sedimentary palynological sequences. A box‐plot analysis indicates that the pollen and spore types A. marina (mangroves), Sarcocornia quinqueflora (salt meadow), P. divaricatus (sedges), Gleichenia (shrubland) and C. australis (swamp forest) are highly discriminatory in relation to vegetation type. These discriminatory palynomorphs help with the interpretation of stratigraphic pollen studies. However, salt marsh vegetation communities in the sediments must be interpreted with caution as the marine sediments are easily affected by erosion, bioturbation and tidal inundation effects.     

A fine-resolution Pliocene pollen and charcoal record from Yallalie, south-western Australia

Aim This paper aims to reconstruct a high‐resolution fire and vegetation history from a period when humans were absent in Australia. This is then used to comment on the frequency of natural fire in high biodiversity heathland, and to compare this with historical fire regime in the same region. Methods A section of varved sediment covering a period of c. 84 years was taken from Palaeolake Yallalie in south‐western Australia. The sediments were separated into approximately single to small multiples of years and then analysed for charcoal, pollen and sediment analysis to reconstruct the environmental conditions at the time. Results The charcoal record indicates fire recurrence to have been roughly between 5 and 13 years, a little longer than those of the historical period. The pollen record was dominated by Casuarinaceae, Myrtaceae and a large number of Proteaceae species; these are intermixed with Araucariaceae, Nothofagus and Podocarpus. This suggests there was a mix of sclerophyll woodland and a mosaic of rain forest elements, thus conditions must have been wetter, particularly in the summers, compared with today. Conclusions We assume that fire was most likely confined to the sclerophyll vegetation, and that fire has been a significant feature of the environment long before humans entered Australia. The slightly longer fire recurrence times compared with the present result from the intermittent nature of lightning and wetter summers at the time.     

Palynological study of a holocene peat and a miocene coal deposit from NW Borneo

The development of a Holocene peat near Marudi (Sarawak) and a Miocene coal near Berakas (Brunei) is studied pollen-analytically and stratigraphically by comparison with present-day swamp vegetation along the NW Bornean coast. A number of 76 pollen and spore types were recognized and are briefly diagnosed.The Marudi profile starts on mangrove sediment and shows a succession which is closely comparable to the present-day zonation of the large raised bog of which it forms part.The Berakas profile starts on fluviatile sediments and remains in the mixed swamp forest stage. This small deposit has remained close to the coast and peat growth is terminated by marine transgression.The floristic composition of the mixed swamp forest stage in both bogs, separated in age by approximately seven million years is closely comparable. Minor differences which exist can be attributed to differences in size, ecologic conditions and accessibility from mainland reservoirs.Only on spore type, Stenochlaena areolaris has become extinct in Borneo.     

A long‐term record of Quercus decline,logging and fires in a southern Swedish Fagus‐Picea forest

Abstract. We reconstructed forest development and disturbance events (fire and logging) during the last 1000 yr with tree‐ring data, pollen and charcoal analysis from a semi‐natural Fagus sylvatica‐Picea abies forest (ca. 1 km²) in the hemiboreal zone. According to pollen analysis, Quercus robur together with Pinus sylvestris was abundant in the forest until the turn of the 18th/19th centuries when these species disappeared completely (Quercus) or nearly completely (Pinus) and were replaced by Fagus and Picea. The disappearance of Quercus was corroborated by the remarkable discovery of a single Quercus stump that had been cut in the 18th century and had become overgrown and preserved by a very old Picea. In total 11 fires were dated from 1555 to 1748 from fire scars in several Pinus stumps cut 100 ‐ 200 yr ago. Since the last fire in 1748, no Quercus or Pinus have regenerated in the core of the reserve apart from single pines in neighbouring managed forest (80 yr ago). During the period of documented fires Fagus was protected from fires in a refuge made up of large boulders. Picea colonized the region at the time when the fires ceased 250 yr ago. We hypothesize that most of the fires were probably of human origin because of their patchiness and high frequency compared to the natural background levels of lightning ignitions in the region. On a 300‐yr time scale, logging and fire suppression seem to strongly overshadow the effect of climate change on forest composition and dynamics.     

LEAF DEMOGRAPHY OF A NEOTROPICAL RAIN FOREST CYCAD,ZAMIA SKINNERI (ZAMIACEAE)

Tropical rain forest understories are extremely light-limited environments. Little is known about the demography of leaves in these habitats. To determine leaf longevity and causes of mortality for a species in the understory of a neotropical rain forest, we studied 634 leaves on 173 individuals of the cycad shrub Zamia skinneri for 10 yr at the La Selva Biological Station, Costa Rica. Five different seasonal cohorts of leaves were followed. No significant differences among cohorts were found in median leaf longevity, but the cohorts did differ in the proportion of leaves dying in annual intervals from <1 to ≥6 yr. Median minimum time alive for all leaves was 4.6 yr. Epiphyll coverage increased from 0% in the first year of life to 75%-100% by year 4. Leaf mortality was well described by two separate exponential functions, approximately 10% mortality/yr until year 4, then abruptly increasing to ca. 51%/yr. Of 625 leaf deaths, 77.0% were due to unexplained causes, 16.5% to physical damage by falling litter, 4.8% to attacks by larvae of the lycaenid butterfly Eumaeus minyas, and 1.8% to other causes. Leaf longevity was positively correlated with leaf size. Individuals of Z. skinneri frequently survive more than a century in very dark understory conditions. We suggest that leaf longevity in these circumstances is determined by the inevitable deterioration in leaf carbon balance due to leaf aging and increasing epiphyll coverage, and by loss due to physical damage and attacks by the specialist herbivore.