Exotic Pollen Research Articles

Tropical Islands as Paleoecological Laboratories: Gauging the Consequences of Human Arrival

Inter-island paleoecological comparisons have provided useful information concerning the role of humans vs. background-level disturbance in tropical ecosystems. Major ecological changes have occurred since human arrival in Madagascar, the West Indies, the Hawaiian Islands, and elsewhere. Prehuman vegetation changes and disturbances have also been documented for many islands. Instructive inter-island similarities and differences have been detected in the chronology, distribution, and extent of human activities, vegetation changes, and biotic extinctions. The earliest stratigraphic proxy evidence for initial human impacts (including increased charcoal particle influx to sediments, first appearance of exotic pollen, increase in ruderal pollen, and paleolimnological evidence for cultural eutrophication of lake waters) generally confirm but sometimes predate the earliest conventional archaeological evidence for human activity. Carefully chosen sites permitting the close integration of palynological, paleontological, and archaeological data from a variety of island settings with differing geographic and historical contingencies can enable investigators to more fully evaluate the importance of a range of human and ecological variables in determining the overall character and dynamics of ecosystems.

Implications of recent long-distance pollen transport events for the interpretation of fossil pollen records in Fennoscandia

Under favourable conditions, a considerable amount of long-distance transported pollen can be deposited far from its place of origin. In Fennoscandia, in most cases, such situations occur when there is a strong southerly air circulation from South-Europe and/or North-Africa. Soil particles and pollen grains associated with the top soil or the present vegetation, can be lifted up by strong surface winds and brought up to higher levels, where further transportation takes place. During the last few years several of these events have been reported.The pollen analysis of three events with coloured precipitation from different parts of Fennoscandia provides information about such exotic pollen rain and its extent. The quantity of exotic pollen in the snow samples analysed is high, generally in the range of 500–2000 pollen grains cm−2 per episode. However, the amount of transported pollen can even be as great as that deposited during local anthesis in the same year, and influx values can exceed 30, 000 pollen grains cm−2 per few hours of snowfall. The results are analysed in relation to trajectory calculations, the actual phenological data, and pollen concentrations monitored by volumetric sampling from the air. Since the long-distance transport of pollen grains depends mainly on climatological factors, the hypothesis that exotic pollen deposition was common throughout the whole of the Holocene in Fennoscandia is presented. Long-distance transport of pollen grains can, therefore, be regarded as a potential source of error in the interpretation of Holocene pollen diagrams from Fennoscandia.

The abundance of exotic western hemlock pollen at Waterdevil lake, white pass, northern British Columbia: a preliminary analysis

The abundance of exotic western hemlock pollen was studied at Waterdevil Lake, northern British Columbia, in order to determine whether or not its depositional history was independent of change s in pollen productivity in the likely source area, coastal forests of western hemlock-Sitka spruce, about 30 km to the southwest. A comparison with the abundance of western hemlock pollen at Lily Lake, Alaska, which lies within the coastal source area, supports this notion. The one major vegetational change during the late Holocene at Waterdevil Lake, the transition from subalpine fir forest to lodgepole pine-subalpine fir forest, coincides with an increased abundance of exotic western hemlock pollen. These preliminary results suggest that a study of exotic pollen in this region may be useful for interpreting past changes in circulation patterns.

Tracing Black Cutworm and Armyworm (Lepidoptera: Noctuidae) Northward Migration Using Pithecellobium and Calliandra Pollen

Identifying the pollen attached to black cutworm, Agrotis ipsilon (Hufnagel), and armyworm, Pseudaletia unipuncta (Haworth), moths provided a powerful tool for recognizing food plants used by these noctuids before initiation of long-range movement. Pollen was found primarily on the proboscis and in decreasing frequency on the eyes, legs, and antennae. Fourteen moths collected in Iowa and Missouri were marked with the exotic pollens Pithecellobium spp. or Calliandra spp, or both. These plants are indigenous to southern climes, and the closest site of origin to the capture points is in southern Texas. From the closest plant location in Texas, these moths traveled 1,300km to central Missouri, 1,450 km to northern Missouri, and 1,600 km to central Iowa. Moths captured in March probably originated ≥600 km farther to the south than those captured in late April and May. Known exotic pollen was discovered on moths captured during May in Iowa, but these same pollens were found on moths captured earlier in Missouri. These results provided evidence of moth immigration into Missouri from within Mexico, possibly from the state of Tamaulipas.

Airborne pollen and spores on the Arctic island of Jan Mayen

Abstract A survey of airspora collected on Jan Mayen, an isolated North Atlantic island (71°N, 8°30′W), using a Burkard seven-day volumetric trap from 24th April to 31th August, 1988, revealed only very small concentrations. A total of 10 different pollen types were recorded, constituting a seasonal sum of 29 pollen grains. The local pollen season was confined to July, with Oxyria digna and Salix as the most numerous pollen types recorded. Exotic pollen grains, namely Betula, Pinus and Castanea type, were recorded in three periods during June and July. Studies of back trajectories indicate North America and/or Iceland and Greenland as possible source areas for the Betula pollen. There were more diatoms than pollen in the local airspora. Fungal spores mainly occurred in late July and August. Cladosporium constituted less than 5% of the total seasonal sum of fungal spores, while basidiospores contributed nearly 12%. The highest diurnal average of Cladosporium was 27 spores m−3 air. The seasonal maximum of unidentified fungal spores reached a diurnal average of 639 spores m−1 air on 27th August.

Seasonal and annual variation of pollen content in the snow of a Canadian high Arctic ice cap

Seasonal and annual pollen deposition over an eight‐year period (1981‐89) in the snow layers of the Agassiz Ice Cap, Ellesmere Island, was investigated. The annual and seasonal layers were determined from the snow stratigraphy. Thirteen to thirty‐five kg were sampled for each layer. Most of the pollen grains deposited on the ice cap originate either from the high Arctic regional tundra, or from the boreal forest and low Arctic tundra over 1,000 km to the south. The regional pollen types show large variations throughout the year and the maximum concentration is normally found in the late summer‐early autumn snow. The exotic types usually show less seasonal variation, although with slight maximum in the spring or summer layers. The annual regional and exotic pollen influx to the ice cap can be highly variable. These variations are tentatively related to climatic parameters.

Where has all the pollen gone?

Problems encountered in preparation of samples for fine resolution pollen analysis highlighted a need to better understand the effects of pollen processing methods in determining the composition of pollen spectra at the final stage of analysis. We carried out some experiments which focussed on the physical rather than chemical aspect of preparation and concentrated on differences in pollen buoyancy and geometry, sample type and tube substrate. Results of these experiments showed differential losses of exotic compared to fossil pollen and a lack of consistency in results between parallel samples. Although considerable attention has been given to the “exotic pollen addition” method for quantitative pollen analysis, little work has previously been published on potential weaknesses of this technique. Our findings underline the importance of understanding the behaviour of both exotic and fossil pollen in different preparation regimes to properly interpret pollen assemblages and caution against strict adherence to a preparation “recipe” without monitoring possible pollen losses at different stages.

Modern and late Quaternary pollen spectra of fiord sediments, eastern Baffin Island, Arctic Canada

Pollen spectra of thirty surface samples from Baffin Island fiords are dominated by a Betula/Filicales/Cyperaceae/Gramineae association that is somewhat representative of local or regional vegetation. However, Betula and Filicales are over-represented and Salix, Cyperaceae and Ericales are under-represented compared to their importance in the present vegetation. Two possible causes for this disparity, related to the fluvial processes that furnish most pollen to fiords, are: (1) fluvial reworking of older sediment that contains abundant Betula and Filicales; and (2) greater resistance of these taxa to corrosion and degradation during fluvial transport. The pollen stratigraphy of five piston cores from fiords contains two types of pollen assemblages. In the lower portions of the cores, exotic pollen types and pre-Quaternary palynomorphs are abundant. The upper portions of the cores contain an assemblage roughly representative of the present vegetation, in which Cyperaceae and Gramineae are abundant and exotic and pre-Quaternary types are reduced or absent. The lower assemblage was deposited during the late glacial/deglacial transition and deglaciation ca. 12,000 to 6000 B.P., when eastern Baffin Island had little vegetation cover and long-distance transport and reworking were virtually the only pollen sources. A feature of several cores is a major peak in Dinoflagellates about 5000 B.P. This event may be related to the postglacial marine climatic optimum in the eastern Canadian Arctic between 5000 and 3000 B.P.

A pollen record from the Agassiz Ice Cap, northern Ellesmere Island, Canada

A continuous pollen record from the last glacial period to 100 B.P. was obtained from an ice core drilled in 1977 near the top of the Agassiz Ice Cap. Pollen concentrations are low (c. 15–173 grains/100 I) through‐out the core and exotic pollen grains (from distant sources) dominate over regional pollen grains (from Ellesmere Island). The very low concentrations during the Wisconsinan glacial period and the early Holocene are attributed to the increased distance of potential sources as most of northern North America was ice‐covered or supported tundra vegetation. An increase of exotic grains (mainly birch and alder) at c. 7,600 B.P. corresponds to the period of alder migration into the Low Arctic regions. The subsequent fluctuations of exotic pollen, especially the increase at c. 3,100 B.P., are unexplained at present. Regional pollen concentrations start to increase at c. 6,100 B.P. and a maximum concentration is reached at c. 3,100 B.P. The pollen record suggests that plant migration into northern Ellesmere was limited until 6,100 B.P., then increased gradually and continued to do so for about 1,000 years after the climate had started to deteriorate at about 4,000 B.P.

A method of introducing exotic pollen for paleoecological analysis of sediments

A detailed account is given of the procedure required to estimate the number of grains in one milligram of pollen. This enables the addition by weight of an accurate number of exotic pollen to sediments for the estimation of absolute pollen counting, concentration and influx. It avoids the use of pollen tablets and the time-consuming pollen suspensions, and minimizes the error resulting from the addition of exotic pollen.

Palynological Indications of the Quaternary Vegetation History of Marion Island (Sub-Antarctic)

The pollen assemblages of a number of surface samples, Quaternary peat profiles and a moraine at Marion Island were analysed. The results, as well as those of previous investigations, were used to reconstruct the vegetation history of the island. Pollen spectra in interglacial deposits suggest that the vegetation at that time probably consisted of a slightly different species assemblage, but was comparable to that of present-day lowland communities along the island's shore. At the end of the Pleistocene and during the Holocene after the glaciers had receded, certain areas supported fjaeldmark vegetation and then were over- grown by mire vegetation. The process, comprising a succession of barren fjaeldmark through Azorella selago peats to mire communities, was probably in- fluenced by local changes in the drainage patterns and moisture availability and was not necessarily the direct result of temperature amelioration. The develop- ment of peat at three near-shore sites between approx. 7000 and 6000 yr BP was possibly related to increasing proximity of the shore lines due to rising sea-levels in the early Holocene. The influence of fauna associated with marine life can be detected in the profiles situated at relatively low altitudes near the shore. The pollen spectra in present-day surface samples from the high altitude region (approx. 200-800 m above sea level) and the fossil spectra in an undated moraine sample were taken to indicate cooler conditions. These spectra are characterized by high counts of Azorella pollen together with relatively high proportions of exotic pollen, indicating poor vegetation cover and low local palynomorph produc- tion. As in earlier studies (Schalke & van Zinderen Bakker, 197 1) the composi- tion of studied Holocene pollen spectra is not indicative of small temperature changes which may have occurred. The oceanic climate possibly helped to dampen such effects.

Exotic Pollen and Long-Distance wind Dispersal at a Sub-Antarctic Island

Abstract Exotic pollen grains on Marion Island (southern Indian Ocean) make up ±1.2% of the spectra recorded in samples of various surface soils, peat profiles and a moraine matrix. They consist mainly of elements transported over long distances across the circum-Antarctic ocean by the prevailing westerly winds. The majority of forms originate from the southern tip of Africa while others come mainly from the more distant South-American region. The results imply that there is a regular transport of small particles to Marion Island by wind but that wind dispersal has probably not played a major role in the establishment of the present biota on the island.

Long-distance pollen transport over the southern Tasman Sea: evidence from Macquarie Island

Abstract Numerous exotic pollen and spore types occur in Holocene lake deposits on Macquarie Island. Most are con~idered to be derived from sources in the south-east Australian region. Myrtaceae pollen, which probably includes both Eucalyptus and Metrosideros, accounts for over 40% of the total exotic counts for 2 cores. Podocarpaceae, Phyllocladus, Casuarina, and Pomaderris are also present in significant proportions. Single records for Dacrydium cupressinum and Ascarina lucida, and the absence of Nothofagus “fusca” suggest that New Zealand pollen sources are relatively poorly represented. This find emphasises the need for caution when assessing the nature of the exotic pollen rain at sites on mainland New Zealand and surrounding islands.

The paleoclimatic interpretation of exotic pollen peaks in holocene records from the eastern Canadian Arctic: A discussion

Processes involved in the transport of “exotic” tree pollen and its deposition in eastern Arctic Canada are reviewed. Synoptic meteorological situations favoring transport northward from the boreal forest are analyzed via boundary-layer trajectory computations. To account for reported exotic pollen peaks in Holocene peat deposits on Baffin Island, the necessary increase in frequency of southerly wind components may be as much as an order of magnitude, which could not be accomodated in the available time interval of pollen release, if sources from all of the Canadian boreal forest are considered. If only Labrador sources are involved, the absolute increase in southerly airflow may be unexceptional. It is also shown that changing airflow direction cannot be directly linked with longitudinal displacements of the 700 mbar trough at 75°W. Other possible factors that could have produced peaks in exotic pollen include variable sedimentation rates, variable pollen production, or a non-linear relationship between airflow frequency and pollen deposition.

A late holocene pollen diagram from pangnirtung pass, Baffin Island, N.W.T., Canada

A 1.2 m section of organic-rich sediment from near Windy Lake, Pangnirtung Pass, Baffin Island, Canada, is dated by twelve radiocarbon assays which indicate that the sediment accumulated at an average rate of 6.5 cm 100 yr −1. The base of the studied exposure is about 2500 years old, whereas the sediment at a depth of 4 to 9 cm is dated about 650 years old. The sampling interval for pollen averages one sample every 39 years. The section is described in terms of the lithology of the inorganic matrix, in the plant growth form and moisture preference of the pollen taxa, and in the variations in the influx of exotic pollen ( Alnus, Picea, and Pinus). Principal Components Analysis and clustering of pollen levels were used to zone five different groupings of the pollen taxa “objectively”. Both relative and “absolute” pollen values were used in these various steps. Pollen accumulation varied between 24 and 14,300 grains cm −2 yr −1 with a median value of 501. Thirteen biozones are recognized primarily from changes in the rates of pollen accumulation and diversity. The broad climatic interpretation of the pollen stratigraphy has similarities and differences from nearby glacial moraine chronologies. Sharp increases in exotic pollen (especially Alnus) are provisionally associated with major advection of southerly air toward Cumberland Peninsula, southeastern Baffin Island.

Holocene palaeo-wind evidence from palynology in Baffin Island

TRACE amounts of wind-blown tree pollen from the highly productive boreal coniferous forests are a characteristic component of arctic tundra sediments1,2. These exotic pollen are generally regarded as mere contamination or distractions in tundra pollen diagrams3. We report here that traces of exotic pollen in late Holocene sediments from Baffin Island can be used as palaeo-wind indicators, and may be associated with periodic shifts of a trough in the atmosphere.

Exotic pollen rain on the Chatham Islands during the late pleistocene

Abtract Exotic pollen and spores have been found in two drillholes and in a vertical face cut in Quaternary peats in the Chatham Islands. They form an average of 4.5% of the total palynoflora at Te Pukaha and in a drillhole near Mt Dieffenbach, and 10% of the total palynoflora in a drillhole in the southern uplands. The nearest source for this pollen is New Zealand, approximately 725 km to the west. These palynomorphs aid in the pollen zonation of the peats. Similar percentages of pollen, especially of beech and podocarp, in New Zealand peats cannot be used to imply a local presence. A new radiocarbon date (NZ3103A) of 20100 ± 400 years B.P. is given for the Rekohu Ash.

Recovery of Introduced Pollen from a Mountain Glacier Stream

Abstract Pollen of seven genera was introduced into a stream originating from a mountain glacier in Yosemite National Park, California, USA. Cold nights and warm days produced a daily cycle of low and relatively still water followed by vigorous flow. During the ensuing 16 days repeated samples were taken of bottom sediments in stream pools and ponds from 25 sites ranging from control sites above the release point to 23 km downstream. Introduced grains were recovered from experimental and control sites within 3 km of the release point; data from these sites are presented in detail. Within the limits of the experiment there was no evidence for the segregation of pollen and spore types either in space or with time. Several days after its introduction in the stream the exotic pollen could be recovered from ponds having no water connection with the stream and also higher in elevation than the point of release of foreign pollen. Apparently the pollen became airborne, perhaps after being stranded at the water's edge or, more directly, released from the film of water surrounding air bubbles. If this should be a common phenomenon, then the entry of long-distance pollen into sediments by local air transport of grains released from rivers offers interpretive possibilities, since the direction of pollen transport in the stream would be independent of wind direction.

The Relative Pollen Productivity and Pollen Representation of North European Trees, and Correction Factors for Tree Pollen Spectra. Determined by Surface Pollen Analyses from Forests

The present work deals primarily with a determination of the relative pollen productivity of various trees from North Europe by means of their representation in pollen analyses of surface samples from forests, with the aim to calculate correction factors for pollen diagrams.Surface samples from 2 forests in Denmark were examined. The forest composition was determined by tree crown areas and tree basal areas in small sample plots. The relation of the tree crown areas to the tree basal areas was determined for the various tree species, and the data for crown area composition, basal area composition and tree frequency were compared.The pollen preservation in the various surface samples was examined.Data on wind conditions are mentioned in the chapter about pollen dispersal in the forest, and the various modes of pollen transfer are discussed. The amount of exotic pollen in the samples is used as a calculation basis for the tree pollen frequencies, and the occurrence and composition of the exotic pollen is discussed.The relationship of the forest composition to the tree pollen deposition is discussed. Pollen deposition and pollen productivity is expressed by a regression equation. The relative pollen productivity of the tree species is expressed in relation to a reference species, in the present case Fagus silvatica. Pollen representation and relative pollen representation are determined by a comparison of pollen percentages with percentages for areal frequency.Pollen productivity factors, pollen representation and correction factors were determined for Danish species of Quercus, Betula, Alnus, Carpinus, Ulmus, Fagus, Tilia and Fraxinus by means of the pollen frequencies in the surface samples. Corrected pollen percentages were compared with the tree areal percentages in the sample plots. Data for the pollen frequencies of forest plants other than the trees are presented. The data on trees from Denmark are compared with other data from Northern Europe, and correction factors were calculated for species of Pinus, Picea and Abies.Tree pollen spectra from outside the forest are discussed and the relative pollen representation is calculated. The present calculations of the relative pollen productivity of the trees are compared with previous estimates, and the application of the correction factors to pollen diagrams is discussed.

THE ASSESSMENT OF A METHOD FOR THE DETERMINATION OF ABSOLUTE POLLEN FREQUENCIES

SummaryOne method for the estimation of absolute pollen frequencies involves the addition of a known amount of an exotic pollen to a known quantity of sediment. From the observed ratio of indigenous to exotic pollen, the absolute quantity of indigenous per unit volume of sediment can be calculated.The pollen of Nyssa sylvatica was considered to be a suitable exotic for addition to northwestern European Post‐glacial sediments to be measured by this method. A series of experiments was made to estimate the settling rate of fresh N. sylvatica pollen in pure glycerine, to determine the period of agitation required to produce an even suspension of N. sylvatica pollen in pure glycerine, to observe the effects of KOH treatment and acetolysis on a mixture of fresh N. sylvatica and Ailanthus eligantissima pollen and to estimate the experimental error of the method by using it to determine the quantity of pollen in a series of homogenized samples of gyttja.The value of the method for the estimation of absolute pollen frequencies is assessed.