Arboreal Cover Research Articles

Modern surface pollen assemblages from the Middle and High Atlas, Morocco: insights into pollen representation and transport

Thirty-three modern surface samples were collected in the environmentally and climatologically contrasting regions of the Middle and High Atlas Mountains, Morocco. Samples representing forest and steppe montane environments (1935–2760 m above sea level) are clustered around study sites at Lake Tislit (High Atlas, semi-arid oro-Mediterranean bioclime) and Lake Sidi Ali and Michliffen (Middle Atlas, sub-humid montane Mediterranean bioclime). Good discrimination between regional pollen spectra is evident, with Middle Atlas samples reflecting higher arboreal cover (Cedrus and evergreen Quercus) and High Atlas samples with high abundances of non-arboreal taxa, including Artemisia and Fabaceae. These four taxa (Cedrus, evergreen Quercus, Artemisia and Fabaceae) are furthermore shown to be reliable indicators of local source vegetation within a 100 m2 quadrat, taking into account threshold abundances of 7%, 20%, 4% and 10%, respectively. Deciduous Quercus, Olea and Phillyrea show long-distance pollen dispersal across both regions, contributing to non-trivial arboreal pollen (AP) values of up to 35% (typically 20–30%) in the High Atlas spectra. In the Middle Atlas, AP values of 40 to 50% occur in open sampling locations and > 60% under forest canopy cover. These insights should be taken into account when interpreting ancient pollen spectra from regional lakes and bogs for palaeoenvironmental reconstruction.

Arboreal Cover Boards: Using Artificial Bark to Sample Cryptic Arboreal Lizards

Abstract: Arboreal reptiles are often difficult to capture because of their cryptic nature and propensity to flee out of reach when approached. In addition, arboreal lizards often seek refuge under loose or peeling tree bark; therefore researchers often remove it to catch them, thereby potentially damaging habitat. Using arboreal cover boards, or “artificial bark,” might reduce damage to natural shelter sites, allowing repeated surveys. We compared capture success and population structure of samples obtained by two capture methods—active searches (visual encounter surveys [VES]) and arboreal cover boards used as artificial bark—on two species of arboreal lizards, Inland Snake-eyed Skinks (Cryptoblepharus australis) and Dubious Dtellas (Gehyra dubia). Two types of arboreal cover boards (cardboard and closed-cell foam) were strapped around the main trunks of trees with elastic straps. Systematic VES during the day (for Cryptoblepharus) and at night (for Gehyra) were conducted in conjunction with monitoring...

Análisis de dos áreas naturales protegidas en relación con el crecimiento del Área Metropolitana de Xalapa, Veracruz

The establishment of natural protected areas and the urban growth are two inseparable processes as they are functionally connected, but their dynamics tend to be troublesome and turn into the epitome of the wicked relationship between humans and nature. The urban natural protected areas are usually agricultural fields remains or woods saved from their destruction caused by the constant expansion of the urban spot. However, if this rescue is not clear and definitive, either because the governmental actions are incomplete, unsuitable or corrupt, or because people do not get to use these areas (difficult access, dangerous places, or inappropriate facilities), the threats for these territories will then reappear as the urban extension will tend to surround, invade and take up the natural protected areas.With the aim of analyzing the spatio-temporal dynamics of the human and nature relationship in an urban context, the natural protected areas “Molino de San Roque” and “Cerro de la Galaxia” were studied in correlation with the urban growth of Xalapa, Veracruz, Mexico. Both areas look deserted and defenseless. The interpretation of aerial photographs from 1993 to 2009 revealed that 41.8% of the Molino de San Roque's area and 50.7% of the Cerro de la Galaxia's area showed no alteration in the density and expansion of their vegetation; 12.2% and 26.7%, respectively, showed some vegetation growth, meanwhile 46% and 22.6%, again respectively, reflected a decrease in the bushy and arboreal cover. Micro historic-geographical analysis proved that in the inner parts of these areas, being the lower trafficked ones, we could notice some vegetation recovery, whereas in the periphery segments, deforestation was observed. The progressive human invasion was the biggest threat for these areas, but the abandonment by authorities constitutes another one. The greatest loss was not so much about the natural protected areas shrinkage, but rather about the quality of the landscape. An effective protection of the natural areas will never be reached if these areas keep remaining as deserted places. Indeed, this desertion leads to a separation between society and nature as citizens have no opportunity of using these natural areas in a practical or recreational way.

A 2800-year multi-proxy sedimentary record of climate change from Lake Çubuk (Göynük, Bolu, NW Anatolia)

The sediment of Lake Çubuk in NW Anatolia, which is situated very close to the climate boundary between the dry Central Anatolia and the wet Marmara region, is regarded as a suitable climate archive to test inward and outward movements of this boundary in accordance with past climate variations. Herein, we study the stratigraphic record of the last 2800 years of this landslide-dammed lake at 1030 m elevation, using multi-proxy tools (sedimentology, major and trace element geochemistry, stable isotopes, pollen, diatoms and ostracods) and compare the results with other contemporaneous Anatolian climatic records. Our findings indicate that Lake Çubuk recorded seven distinct climatic periods in the last 2800 years that have been previously revealed elsewhere in Anatolia. The most arid period occurred at the end of the Near-East Aridification Phase at approximately 200 BC when the δ18O shifted to very negative values, and the planktonic diatom ratio considerably decreased. The Dark Ages and the late Byzantine periods between AD 670 and 1070 are characterized by more positive δ18O values, increasingly higher lake levels and the most extensive arboreal cover of the entire record. The ‘Little Ice Age’ appeared suddenly, within 40 years, at AD 1350 and is reflected in all of the proxies, including a positive shift in δ18O, a sharp decrease in pollen of shrub and herb to the benefit of pine trees and a rapid increase in benthic diatom abundance indicating a lake level shallowing. In many parts of the record, a close match between the stable isotopes and the pollen assemblage zones in the last 2800 years demonstrates that climate rather than human activity was the primary driver of vegetation cover in this mid-altitude mountain of NW Anatolia.

English

Fifty-eight modern pollen surface samples from different Scots pine forest communities ( Pinus sylvestris var. iberica Svoboda) in the Iberian Central System (central Spain) were palynologically and statistically analyzed (using hierarchical cluster analysis and principal component analysis) to derive correlations between pollen assemblages and environmental gradients at the sampled points. Numerical classification and ordination were performed on pollen data to assess similarities among (central Iberian)-Scots pine forest phytosociological associations. The results show a strong relationship between altitude, temperature, rainfall, arboreal cover and variations in pollen taxa percentages. The statistic discrimination of some of these forest communities has allowed us to propose three new associations.

A 2000‐year lipid biomarker record preserved in a stalagmite from north‐west Scotland

AbstractPrevious studies on lipid biomarkers preserved in Chinese stalagmites have indicated that ratios of low‐molecular‐weight (LMW) to high‐molecular‐weight (HMW) n‐alkanes, n‐alkan‐2‐ones, n‐alkanols and n‐alkanoic acids can be used as an index of vegetation versus microbial organic matter input to the system and, by extension, a marker of climatic changes, with increases in the proportion of LMW compounds coinciding with colder periods. Here we test whether this hypothesis is equally applicable to a different geographical region (north‐west Scotland), by examining a stalagmite record of the past 200 years, and a wider range of lipid markers. We also test the applicability of other lipid proxies in this context, including the use of n‐alkane ratios, to interpret vegetation changes, and unsaturated alkanoic acid ratios as climatic indicators. The results show that lipid proxies preserved in stalagmites, and especially those related to vegetation, are potentially extremely useful in palaeoenvironmental research. Of particular value is the use of C27/C31 n‐alkane ratios as a proxy for vegetation change, clearly indicating variations between herbaceous and arboreal cover. This proxy has now been successfully applied to samples from diverse environments, and can be considered sufficiently robust to be of use in analysing future stalagmite records. It will be of particular value in areas where reliable pollen records are not available, as is often the case with deeper cave deposits. However, the division between LMW and HMW aliphatic compounds is not a clear‐cut case of microbial versus plant activity, with the changes in LMW compounds relating more closely to those in their HMW analogues than in specific bacterial biomarkers. The use of unsaturated alkanoic acid ratios here gives conflicting results, with the observed variation through time depending on the isomer measured. The discrepancies between the findings of this study and previous work are likely to be due to the varying controls on the lipids (original organic matter input, and compound degradation), which in turn will be affected by whether the main climatic limiting factor on the soil is temperature or precipitation. This suggests that lipid proxies preserved in stalagmites must be interpreted with care, particularly in the case of bacterial compounds which may be derived from within the cave or from the soil. However, many of these issues can be resolved by the use of multi‐proxy studies. Copyright © 2011 John Wiley & Sons, Ltd.

A multidisciplinary approach to reveal the Sicily Climate and Environment over the last 20 000 years

Abstract We present a thorough review of the knowledge on the climate and environment in Sicily over the last 20 000 years, taking into account results of several studies carried using terrestrial and marine records. We obtain a coherent framework of the most important changes succeeded in the island, even if some points need further investigation. All the reconstructions of surface temperatures of the seas and the air surrounding Sicily point out severe climatic conditions during the last glacial period. The steppe- and semisteppe-like vegetation pattern testifies, together with additional evidence from geochemical data of lacustrine evidence, markedly arid conditions. Fi-nally, significant episodes of sea level drop connected Sicily to the Italian Peninsula and favoured the dispersion of faunal elements from southern Italy. The transition between the last glacial and the Holocene was not characterized by a gradual warming but was punctuated by two abrupt suborbital climatic fluctuations: Bølling-Allerød (warm) and Younger Dryas (cold), as recognized in the sediments recovered close to the northern and southern coast of Sicily. A denser arboreal cover is possibly indicated by the occurrence of dormouse and Arvicola remains. Finally the sensitivity of Sicily to climate perturbations is demonstrated by the occurrence of repeated subtle climatic anomalies during the Holocene, including the Little Ice Age, also known from historical chronicles. Forests, woods and Mediterranean maquis developed in the early-middle Holocene. Thereafter was a general decline of arboreal vegetation, following a general aridification trend that seems to be a common feature in southern Europe and North Africa. Science Greek colonization (7th century before Christ), the landscape was intensively modelled for agriculture and breeding, leading to a significant loss of vegetation cover.

Formation processes through archaeobotanical remains: The case of the Bronze Age levels in El Mirador cave, Sierra de Atapuerca, Spain

El Mirador site has a sequence formed by burnt dung resulting from pastoral activities during the Bronze Age and the Neolithic period. Because there is a high sediment variation in the profile, facies descriptions were used to guide the archaeologists in their work. Paleobotanical and mineralogical analyses were used to describe and understand the formation of the facies from the MIR 4 level. Furthermore, the paleobotanical results serve to reconstruct the landscape in Atapuerca during the Bronze Age. Most seeds recovered are from Triticum aestivum/durum, but other cereals and also Leguminoseae and fruits have been identified. Charcoal analysis has yielded mainly deciduous and evergreen Quercus. Pollen analysis has revealed a low arboreal cover, with Pinus, Quercus and riverside trees. Most of the pollen record corresponds to herbs, such as Poaceae and Asteraceae. All these results indicate a mosaic of different biota with forest, pastureland and cultivated fields near the site. Most of the phytoliths come from the leaves and stems of festucoid grasses. However, there are some differences in the phytolith type and number, the amount of faecal spherulites, the mineralogical composition and the percentage of multicellular structures that indicate that not all the facies in the site have been formed in the same way. Thus, the work carried out has demonstrated that some facies are related more to agricultural activities than to pastoralism activities, and that other facies have been affected by incipient diagenetic processes.

A 23,000 yr pollen record from Lake Rukwa (8°S, SW Tanzania): New data on vegetation dynamics and climate in Central Eastern Africa

Pollen analysis of a 12.8-m-long core (R96-I) from the southern basin of Lake Rukwa (Tanzania, 8°S, 33°E, 793 m a.s.l.) provides new information on the vegetation history of central eastern Africa and on lake level fluctuations in response to climate changes during the last 23,000 cal yr BP. Between 23,000 and 20,000 cal yr BP (the Last Glacial Maximum), the occurrence of open and poorly diversified local woodland and bushland around the lake, and the significant presence of modern regional afromontane forest components close to Lake Rukwa, indicate cooler and probably drier climatic conditions than today. The deglacial period, between 16,500 and 12,300 cal yr BP, characterised by a retreat of montane elements at higher altitudes on the plateau, under warmer conditions, synchronous with a progressive expansion of local more wooded formations, appears to be climatically transitional, but the permanence of swampy environments near the core site indicates that the lake remained low. From 12,100 cal yr BP, the maximum development and diversity of local woodland and bushland implies an increase in rainfall that persisted until 5500 cal yr BP. More humid conditions are confirmed by the lowest representation of aquatics registered in our pollen sequence, indicating that, during this period, Lake Rukwa was high. After 5500 cal yr BP, a deterioration of the regional and local arboreal cover, the large extension of grasses and of swampy environments near the core site, indicate the progressive establishment of drier conditions in the basin. The aridification trend intensified ca. 3500 cal yr BP toward modern conditions. These palaeobotanical reconstructions in the Lake Rukwa basin for the last 23,000 cal yr BP supplement those previously proposed in central eastern Africa between 4° and 13°S from more incomplete or less well age-constrained pollen sequences.

Madonna dell'Arma (San Remo, Italie) : expression locale de la végétation ligure au cours du Paléolithique moyen

Pollen analysis of Madonna dell’Arma cave inside part (Liguria, Italy) allowed us to reconstitute, at local scale, the Ligurian coastal vegetation between the end of the last interglacial period and the beginning of the pleniglacial. This transition period shows an important representation of arboreal cover and a persistence of thermophilous elements that allowed us to considerate the western Liguria as a periglacial refuge. During the end of the last interglacial, xerophytic, halophytic herbs and shrubs taken over from a Mediterranean pre-forest unit in the first slopes constituted the coastal zone. The nearness of Argentina torrent and the Armea influenced, in the coast, the existence of marshy zones colonized by hygrophilous trees. In the Ligurian lowlands spread out sclerophyllous and mesophilous forests according to altitude. The beginning of the pleniglacial is indicated in the sequence by increases of Pinus, Cupressaceae and Artemisia in the context of a decline in the thermophilous components. This picture of vegetation has become integrated into the multidisciplinary studies of the site and contributed to the elaboration of palaeoclimatic hypothesis similar as those revealed by the fauna.

Pollen-based vegetation changes in southern Tanzania during the last 4200 years: climate change and/or human impact

The age-constrained pollen data of a sedimentary sequence from the crater Lake Masoko, southern Tanzania (9°20′S, 33°45′E, 770 m), display a continuous record of vegetation for the past 4200 years. This record provides evidence that wetter Zambezian woodlands always occupied this area during the late Holocene, reaching a maximum extent between 2800 and 1650 cal yr BP related to increase in summer monsoon intensity. However, three main episodes of decline have been detected, between 3450 and 2800 cal yr BP, between 1650 and 1450 cal yr BP and from 1200 to 500 cal yr BP, for which a climatic interpretation, decrease in the summer monsoon strength, was preferentially advanced. The first is synchronous with lowstand of many tropical African lakes and, so, mainly induced by increased aridity. In contrast, the abrupt change in the pollen record at 1650–1550 cal yr BP is marked by a large extension of grasslands at the expense of arboreal cover, further by an increase in Ricinus communis and an intensification of burning. It could thus indicate local clearance of vegetation by man. However, at the same time, the decline of montane forest suggests the impact of a more regional change. During the last episode, between 1200 and 500 cal yr BP, dry climatic conditions are inferred from a combination of pollen, diatom and magnetic proxies, although the occurrence of Late Iron Age settlements in the region means that local human interference cannot be excluded. This study illustrates the difficulties in deciphering ecological and anthropological changes from pollen data in African tropical regions.

Palynological investigation at Bilancino dam (Mugello, Central Italy)

Summary Palynological analyses were carried out in a Gravettian settlement; the settlement is situated on a natural terrace that faces the Sieve valley (Tuscany—Italy). Samples were collected from various levels that reflected the chronological periods that preceded, were contemporary with and followed the interval of inhabitation of the site. The aim of the study was to contribute to the reconstruction of the local floral context before, during and after human presence. The most ancient layers seemed to belong to the early Pleistocene. The level that coincided with human settlement were datable to Würm III. During that period, the arboreal cover at the site was very scarce. The only abundant trees were pines, particularly Pinus sylvestris L. In the spectra, many hygrophytes were present. After the site had been abandoned by its human occupants, a decrease in the amount of hygrophytes was noted. This may indicate a local trend towards dryness. The most recent spectra show that there is an increasing arboreal cover.

Rodent Diversity and Land Use in Montebello, Chiapas, Mexico

We analyzed the abundance and diversity of Heteromyid and Murid rodents in the Lagos de Montebello National Park and adjacent areas, Chiapas, Mexico. We sampled three habitat types with different degrees of disturbance: pine-oak-liquidambar forest, ecotone and crop farming lands. Habitat types were defined considering characteristics such as heterogeneity, structural complexity and arboreal cover. We obtained ancillary habitat data considered important for small mammal requirements. Data on rodent communities were obtained by capture-mark-recapture between February and October 1996. We made 410 captures in 3820 trap-nights effort. Ten species were recorded, including one endemic with restricted distribution in Chiapas. Mouse diversity in the forest was significantly higher than within the farm lands. A Kendall correlation analysis showed positive relationship between rodent community species richness and habitat heterogeneity. Diversity of rodents was associated with the habitat complexity and structural elements, and negatively correlated with farming intensity. We found a high beta diversity and low similarity of the rodent communities in the three different habitats. Community composition strongly changed from the forest through the ecotone into the farm lands, with five species gained and seven species lost. The highest species richness was found in the ecotone; however, it showed a strong dominance of a single species that can convert into a plague of crops, and relatively low abundance of the other species. The pine-oak-liquidambar forest had the highest diversity indices, sheltering a particular rodent community within the study area, it therefore probably has the most important role in the conservation of the local biodiversity.

Nouvelle séquence pollinique du lac Tanganyika: 30,000 ans d'histoire botanique et climatique du bassin Nord

This paper presents the pollen analysis of a new core from the Northern basin of Lake Tanganyika (4°30′S, 29°20′E, 773 m) which documents for the first time the uninterrupted botanical and climatic history of this region from 32,000 yr BP until today. Rich and well diversified pollen spectra give evidence of important changes in the vegetational communities of this basin. Before 15,000 yr BP, poorly diversified Zambezian woodlands occurred while numerous swampy ericaceous shrublands developed along the shoreline indicating cooler and drier climatic conditions than today. Between 15,000 and 10,000 yr BP, a great change occurred marked by the retreat of the Ericaceae. However, the continuation of open woodlands, the occurrence of cold and dry tolerant elements on the plateaus suggest that climate was still cool and dry. From 10,000 yr BP, the development (in extension and diversity) of wetter Zambezian communities including Guinean components, the dissppearance of many cold high altitude taxa imply an increase in rainfall and temperature, well documented until 2600 yr BP. This optimum climatic phase is interrupted by a distinct hydrological episode dated between 6800 and 6700 yr BP, by palynology and sedimentology previously interpreted as a sudden and temporary overflow of Lake Kivu via the Rusizi river into North Lake Tanganyika. After 2600 yr BP, a deterioration of the arboreal cover and the extension of grasses indicate the progressive establishment of the modern climatic conditions in the basin. The occurrence of pollen grains of Ricinus communis and Elaeis guineensis could indicate a recent human impact on the local vegetation. These reconstructions confirm those previously proposed for the Holocene period in the Northern Tanganyika basin, but also complete those proposed for the Last Glacial period in the Mpulungu basin, 400 km southward.

Paleoenvironnements du bassin Nord-Tanganyika (Zaire, Burundi, Tanzanie) au cours des 13 derniers mille ans: Apport de la palynologie

Detailed palynological data recorded from two cores of lake Tanganyika (Rumonge and Nyanza-Lac basins) document the botanical, climatic and hydrological history of this basin from 13,000 B.P. Rich and well diversified microflora show an important climatic change during the Late Pleistocene-Holocene transition. Prior to 12,000 B.P., the extension of montane communities at lower altitude than their modern range, suggests cool climatic conditions. Between 12,000 and 10,000 B.P., soudano-zambezian and zambezian woodlands (Miombo) expand around the lake, reaching their maximum of development and diversity between 10,000 and ca. 2500 B.P. This change is related both to an increase in temperatures and to a higher rainfall than before. The humid phase between 10,000 and 2500 B.P. is interrupted by a distinct episode interpreted as a local hydrological event concerning the North-Tanganyika basin. Indeed, the composition of the microflora would suggest a sudden and temporary overflow of Lake Kivu via the Rusizi river, later than 6000 B.P. and prior to 2500 B.P. After 2500 B.P., a deterioration of the arboreal cover is detected, related to the progressive establishment of the modern climatic conditions.