Lack of latitudinal trends in wood anatomy of Dodonaea viscosa (Sapindaceae), a species with a worldwide distribution

Latitudinal or altitudinal variation in several anatomical characters of wood is common for woody dicotyledonous genera with a wide distribution, but whether such variation exists at the species level is disputed. Latitudinal and altitudinal trends in wood anatomy of Dodonaea viscosa were studied, using 102 samples collected between 41.2degrees S and 33.3degrees N latitude and 7-2750 in altitude. We studied variation in four quantitative features: vessel element length, fiber length, vessel frequency, and tangential vessel diameter. Ontogenetic trends were minimal with a slight decrease or increase in the innermost stem and were negligible among the studied specimens. Throughout the distributional range of the species, no latitudinal trends were detected in either the Northern or Southern Hemispheres, Altitudinal trends were also nonexistent, except for two features in specimens from China and Japan. Absence of latitudinal or altitudinal trends in this widely distributed species suggests that in some species the species-level variation in wood anatomy is not controlled by ecological gradients.

Influência do tempo de armazenamento na emergência de Dodonaea viscosa Jacq. (Sapindaceae).

Dodonaea viscosa Jacq. (vassoura-vermelha; Sapindaceae) é uma arvoreta comportamento agressivo, pioneira, de dispersão anemocórica, com grande produção de sementes ortodoxas e distribuição cosmopolita. Com base na necessidade de se conhecer o período adequado de armazenamento de D. viscosa, foi realizado experimento de emergência de plântulas em sistema floating, com substrato comercial.

不同环境紫茎泽兰幼苗动态和特征

紫茎泽兰（Eupatorium adenophorum Spreng.）入侵我国已有70余年的时间，目前已经对我国西南地区造成了严重危害，却缺少有效的防治方法加以控制。本研究着眼于紫茎泽兰治理效果，在两片大面积综合防治样地的基础上，针对综合防治后样地紫茎泽兰再生长情况展开调查研究，并在野外观测的基础上设计两项置于样地附近的盆栽实验，研究紫茎泽兰在不同环境条件下的存活情况，以及与不同物种混播的种间竞争情况。 对综合治理1年后的样地中4个紫茎泽兰种群调查、分析结果表明，在不同的生境，采取不同的方法治理紫茎泽兰会导致紫茎泽兰采取不同的生长和繁殖对策进行再生长。紫茎泽兰生长速度为：水分充足的环境大于水分不充足的环境，萌生植株大于实生植株。种植替代物种绞股蓝（Gynostmma pentaphyllum）能够抑制紫茎泽兰的高生长，但在绞股蓝的压迫下紫茎泽兰长成L型，反而增加了冠幅、分蘖数目和单位株高的分枝数。在繁殖方式方面：采用拔除方法治理的区域紫茎泽兰以克隆繁殖为主，而采用喷洒化学除草剂治理的区域则以有性繁殖为主。 固定样方调查显示，紫茎泽兰再生长的1年当中，群落随季节变化而变。群落的盖度、密度和物种丰富度均随着旱季的深入而达到最低，第二年雨季到来后上升，紫茎泽兰在群落中处于绝对优势，尤其是在旱季优势更为明显。一年生紫茎泽兰在旱季部分植株死亡（死亡率为53.38±1.55%），少部分（5.66±0.45%）开花，产生种子的密度约为50 000ind∙m-2。与本地优势灌木物种车桑子（Dodonaea viscosa）、台湾相思（Acacia confuse）和马桑（Coriaria nepalensis）相比，紫茎泽兰具有更快的生长速度，更大的高度、密度和盖度。 紫茎泽兰种子的萌发需要充足的水分和遮荫条件。在盆栽实验当中，浇水或遮荫条件下足量紫茎泽兰的种子能够萌发更多的幼苗，而且幼苗的死亡率也比无浇水或无遮荫的处理低。在遮荫或去除其它物种竞争的条件下，紫茎泽兰幼苗生长速度更快。只要水分充足紫茎泽兰幼苗不会因拥挤而死亡，但是个体平均生物量会因拥挤而减小。 紫茎泽兰幼苗与本地3种草本植物比较结果，在未遮荫条件下，紫茎泽兰幼苗数量极少，且个体也非常小，而相同条件下荩草（Arthraxon hispidus）和含羞草决明（Cassia mimosoides）生长良好;在遮荫条件下荩草、含羞草决明和戟叶酸模（Rumex haxtatus ）与紫茎泽兰相比则几乎没有优势。 成株紫茎泽兰生命力强，难以控制，幼苗时期是采用替代控制方法治理紫茎泽兰的最佳时期。在替代控制物种选择方面，可以在根除后播种本地灌木和草本植物，因为草本植物在早期可以抑制紫茎泽兰幼苗的萌发和生长，而同时播种的灌木种类则可以在植被恢复的后期起到控制紫茎泽兰再生长的重要作用。

Compound specific stable isotopes, BIT, pollen and spores of Miocene to Pliocene sediments of ODP Hole 175-1085A

Pollen and stable carbon (d13C) and hydrogen (dD) isotope ratios of terrestrial plant wax from the South Atlantic sediment core, ODP Site 1085, is used to reconstruct Miocene to Pliocene changes of vegetation and rainfall regime of western southern Africa. Our results reveal changes in the relative amount of precipitation and indicate a shift of the main moisture source from the Atlantic to the Indian Ocean during the onset of a major aridification 8 Ma ago. We emphasise the importance of declining precipitation during the expansion of C4 and CAM (mainly succulent) vegetation in South Africa. We suggest that the C4 plant expansion resulted from an increased equator-pole temperature gradient caused by the initiation of strong Atlantic Meridional Overturning Circulation following the shoaling of the Central American Seaway during the Late Miocene.

Pollen abundance in ODP Site 123-765 (Table 1)

Middle Miocene to Holocene pollen assemblages reveal a history of environmental change in northern Australia. Grass pollen appeared, but was rare, in the late Miocene and was consistently present throughout the Pliocene, but did not become abundant until the Pleistocene. Myrtaceae pollen, characteristic of late Cenozoic assemblages in eastern Australia, is poorly represented, and no unequivocal evidence of rain forest was found.

Palynological record and radiocarbon dates for sediment core T89-16, Congo River mouth

We present a high-resolution reconstruction of tropical palaeoenvironmental changes for the last deglacial transition (18 to 9 cal. kyr BP) based on integrated oceanic and terrestrial proxies from a Congo fan core. Pollen, grass cuticle, Pediastrum and dinoflagellate cyst fluxes, sedimentation rates and planktonic foraminiferal d18O ratios, uK37 sea-surface temperature and alkane/alkenone ratio data highlight a series of abrupt changes in Congo River palaeodischarge. A major discharge pulse is registered at around 13.0 cal. kyr BP which we attribute to latitudinal migration of the Intertropical Convergence Zone (ITCZ) during deglaciation. The data indicate abrupt and short-lived changes in the equatorial precipitation regime within a system of monsoonal dynamics forced by precessional cycles. The phases of enhanced Congo discharge stimulated river-induced upwelling and enhanced productivity in the adjacent ocean.

AMS radiocarbon dates and pollen analysis of ODP Hole 175-1078C

ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1, a northward excursion of the Angola Benguela Front and the Congo Air Boundary resulted in cool sea surface temperatures but rain forest remained present in the northern lowlands of Angola. Rain forest and dry forest area increase 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant.

XRF scanning, pollen and spores of ODP Site 108-659

Pliocene vegetation dynamics and climate variability in West Africa have been investigated through pollen and XRF-scanning records obtained from sediment cores of ODP Site 659 (18°N, 21°W). The comparison between total pollen accumulation rates and Ti/Ca ratios, which is strongly correlated with the dust input at the site, showed elevated aeolian transport of pollen during dusty periods. Comparison of the pollen records of ODP Site 659 and the nearby Site 658 resulted in a robust reconstruction of West African vegetation change since the Late Pliocene. Between 3.6 and 3.0 Ma the savannah in West Africa differed in composition from its modern counterpart and was richer in Asteraceae, in particular of the Tribus Cichorieae. Between 3.24 and 3.20 Ma a stable wet period is inferred from the Fe/K ratios, which could stand for a narrower and better specified mid-Pliocene (mid-Piacenzian) warm time slice. The northward extension of woodland and savannah, albeit fluctuating, was generally greater in the Pliocene. NE trade wind vigour increased intermittently around 2.7 and 2.6 Ma, and more or less permanently since 2.5 Ma, as inferred from increased pollen concentrations of trade wind indicators (Ephedra, Artemisia, Pinus). Our findings link the NE trade wind development with the intensification of the Northern Hemisphere glaciations (iNHG). Prior to the iNHG, little or no systematic relation could be found between sea surface temperatures of the North Atlantic with aridity and dust in West Africa.

Distribution of pollen and spores in sediments of ODP Hole 175-1078C

The distribution of pollen in marine sediments is used to record vegetation change on the continent. Generally, a good latitudinal correspondence exists between the distribution patterns of pollen in the marine surface sediments and the occurrence of the source plants on the adjacent continent. To investigate land-sea interactions during deglaciation, we compare proxies for continental (pollen assemblages) and marine conditions (alkenone-derived sea surface temperatures) of two high-resolution, radiocarbon-dated sedimentary records from the tropical southeast Atlantic. The southern site is located West of the Cunene River mouth; the northern site is located West of the Angolan Huambe Mountains. It is inferred that the vegetation in Angola developed from Afroalpine and open savannah during the last Glacial maximum (LGM) via Afromontane Podocarpus forest during Heinrich Event 1 (H1), to an early increase of lowland forest after 14.5 ka. The vegetation record indicates dry and cold conditions during the LGM, cool and wet conditions during H1 and a gradual rise in temperature starting well before the Younger Dryas (YD) period. Terrestrial and oceanic climate developments seem largely running parallel, in contrast to the situation ca. 5° further South, where marine and terrestrial developments diverge during the YD. The cool and wet conditions in tropical West Africa, South of the equator, during H1 suggest that low-latitude insolation variation is more important than the slowdown of the thermohaline circulation for the climate in tropical Africa.

Palynology of the Middle to Late Miocene from ODP Hole 175-1085A off the west coast of South Africa

Aim To test whether the radiation of the extremely rich Cape flora is correlated with marine-driven climate change. Location Middle to Late Miocene in the south-east Atlantic and the Benguela Upwelling System (BUS) off the west coast of South Africa. Methods We studied the palynology of the thoroughly dated Middle to Late Miocene sediments of Ocean Drilling Program (ODP) Site 1085 retrieved from the Atlantic off the mouth of the Orange River. Both marine upwelling and terrestrial input are recorded at this site, which allows a direct correlation between changes in the terrestrial flora and the marine BUS in the south-east Atlantic. Results Pollen types from plants of tropical affinity disappeared, and those from the Cape flora gradually increased, between 10 and 6 Ma. Our data corroborate the inferred dating of the diversification in Aizoaceae c. 8 Ma. Main conclusions Inferred vegetation changes for the Late Miocene south-western African coast are the disappearance of Podocarpus-dominated Afromontane forests, and a change in the vegetation of the coastal plain from tropical grassland and thicket to semi-arid succulent vegetation. These changes are indicative of an increased summer drought, and are in step with the development of the southern BUS. They pre-date the Pliocene uplift of the East African escarpment, suggesting that this did not play a role in stimulating vegetation change. Some Fynbos elements were present throughout the recorded period (from 11 Ma), suggesting that at least some elements of this vegetation were already in place during the onset of the BUS. This is consistent with a marine-driven climate change in south-western Africa triggering substantial radiation in the terrestrial flora, especially in the Aizoaceae.

Pollen distribution in marine sediment samples along the south-western African coast

The distribution of pollen in marine sediments is used to reconstruct pathways of terrigenous input to the oceans and provides a record of vegetation change on adjacent continents. The wind transport routes of aeolian pollen is comprehensively illustrated by clusters of trajectories. Isobaric, 4-day backward trajectories are calculated using the modelled wind-field of ECHAM3, and are clustered on a seasonal basis to estimate the main pathways of aeolian particles to sites of marine cores in the south-eastern Atlantic. Trajectories and clusters based on the modelled wind-field of the Last Glacial Maximum hardly differ from those of the present-day. Trajectory clusters show three regional, and two seasonal patterns, determining the pathways of aeolian pollen transport into the south-eastern Atlantic ocean. Mainly, transport out of the continent occurs during austral fall and winter, when easterly and south-easterly winds prevail. South of 25°S, winds blow mostly from the west and southwest, and aeolian terrestrial input is very low. Generally, a good latitudinal correspondence exists between the distribution patterns of pollen in marine surface sediments and the occurrence of the source plants on the adjacent continent. The northern Angola Basin receives pollen and spores from the Congolian and Zambezian forests mainly through river discharge. The Zambezian vegetation zone is the main source area for wind-blown pollen in sediments of the Angola Basin, while the semi-desert and desert areas are the main sources for pollen in sediments of the Walvis Basin and on the Walvis Ridge. A transect of six marine pollen records along the south-western African coast indicates considerable changes in the vegetation of southern Africa between glacial and interglacial periods. Important changes in the vegetation are the decline of forests in equatorial Africa and the north of southern Africa and a northward shift of winter rain vegetation along the western escarpment.