Patterns of postglacial vegetation establishment clarified by lacustrine sedaDNA from Baffin Island, Arctic Canada

<p>The colonization of recently deglaciated landscapes by tundra vegetation during the early Holocene is an important case study for understanding possible rates and patterns of plant migration in a rapidly warming world. Fossil pollen in lake sediment has traditionally served as the primary tool for reconstructing paleovegetation and understanding postglacial biogeography. However, because pollen can be wind-transported long distances and, in some cases, reworked from older deposits on the landscape, pollen-based vegetation histories can sometimes obscure the true history of plant colonization. In contrast, lacustrine sedimentary ancient DNA (sedaDNA) is sourced locally and is less likely to be adequately preserved through reworking events, thus making it a more reliable proxy for determining the precise timing of plant colonization. Here, we present three sedaDNA records from Holocene lake sediment across southern Baffin Island, Arctic Canada, that clarify the timing of postglacial vegetation changes. In particular, DNA from the subarctic shrub <em>Betula</em> (dwarf birch) first appears thousands of years after deglaciation in all three lake catchments, suggesting delayed colonization despite its strong pollen signal in early postglacial sediments. While moderate levels of <em>Alnus</em> (alder) pollen characterize early to mid-Holocene lake sediments from the region, sedaDNA suggests that <em>Alnus</em> was likely not present in any of the three lake catchments during the Holocene. In addition, aquatic plant community changes indicated by sedaDNA faithfully reflect the timing of early Holocene warmth in the region, highlighting the potential utility of aquatic plant DNA as a qualitative temperature proxy. We suggest that ancient plant DNA in lake sediment provides key paleoecological information that is distinct from traditional proxy records, particularly during periods of relatively rapid ecological change like the early Holocene. </p>

Patrolling the Scottish Border – plant migration history

There have been successive waves of plant migration north across the Scottish Border since the end of the Ice Age. For those species that never penetrated far into Scotland and which lack specialised means of long-distance dispersal, the distinctive distribution patterns shown by BSBI’s tetrad mapping provide evidence of the likely dates and dispersal mechanisms of the migrations, separating out migration relating to man’s activities. Twelve distribution maps have been prepared for native or archaeophyte species that illustrate contrasting histories. Conclusions are drawn as to whether or not species which lack specialised means of long-distance dispersal are able to migrate north over fragmented natural habitats in response to climate change.

New and Repeating Tipping Points: The Interplay of Fire, Climate Change, and Deforestation in Neotropical Ecosystems

A 370,000-year paleoecological history of fire spanning four glacial cycles provides evidence of plant migration in response to Andean climate change. Charcoal, an indicator of fire, is only occasionally observed in this record, whereas it is ubiquitous in Holocene-aged Andean records. Fire is a transformative agent in Amazonian and Andean vegetation but is shown to be rare in nature. As humans promote fire, fire-free areas become microrefugia for fire-sensitive species. A distinction is drawn between microrefugia resulting from fire-free zones and those caused by unusual climatic conditions. The importance of this distinction lies in the lack of warmer-than-modern microrefugia aiding upslope migration in response to warming, whereas fire-free microrefugia support tree species above modern tree line or in areas of Amazonia least used by humans. The synergy between fire, deforestation, and climate change could promote a state-change in the ecosystem, one where new microrefugia would be needed to maintain biodiversity. Past tipping points are identified to have occurred within ca. 1°C–1.5°C of modern conditions. The recent climatic instability in both Amazonia and the Andes is viewed in the context of ecological flickering, while the drought-induced and fire-induced tree mortality are aspects of critical slowing down; both possibly portending an imminent tipping point.

Brazilian montane rainforest expansion induced by Heinrich Stadial 1 event

The origin of modern disjunct plant distributions in the Brazilian Highlands with strong floristic affinities to distant montane rainforests of isolated mountaintops in the northeast and northern Amazonia and the Guyana Shield remains unknown. We tested the hypothesis that these unexplained biogeographical patterns reflect former ecosystem rearrangements sustained by widespread plant migrations possibly due to climatic patterns that are very dissimilar from present-day conditions. To address this issue, we mapped the presence of the montane arboreal taxa Araucaria, Podocarpus, Drimys, Hedyosmum, Ilex, Myrsine, Symplocos, and Weinmannia, and cool-adapted plants in the families Myrtaceae, Ericaceae, and Arecaceae (palms) in 29 palynological records during Heinrich Stadial 1 Event, encompassing a latitudinal range of 30°S to 0°S. In addition, Principal Component Analysis and Species Distribution Modelling were used to represent past and modern habitat suitability for Podocarpus and Araucaria. The data reveals two long-distance patterns of plant migration connecting south/southeast to northeastern Brazil and Amazonia with a third short route extending from one of them. Their paleofloristic compositions suggest a climatic scenario of abundant rainfall and relative lower continental surface temperatures, possibly intensified by the effects of polar air incursions forming cold fronts into the Brazilian Highlands. Although these taxa are sensitive to changes in temperature, the combined pollen and speleothems proxy data indicate that this montane rainforest expansion during Heinrich Stadial 1 Event was triggered mainly by a less seasonal rainfall regime from the subtropics to the equatorial region.

Grand Challenges in Understanding the Interplay of Climate and Land Changes

Half of Earth’s land surface has been altered by human activities, creating various consequences on the climate and weather systems at local to global scales, which in turn affect a myriad of land surface processes and the adaptation behaviors. This study reviews the status and major knowledge gaps in the interactions of land and atmospheric changes and present 11 grand challenge areas for the scientific research and adaptation community in the coming decade. These land-cover and land-use change (LCLUC)-related areas include 1) impacts on weather and climate, 2) carbon and other biogeochemical cycles, 3) biospheric emissions, 4) the water cycle, 5) agriculture, 6) urbanization, 7) acclimation of biogeochemical processes to climate change, 8) plant migration, 9) land-use projections, 10) model and data uncertainties, and, finally, 11) adaptation strategies. Numerous studies have demonstrated the effects of LCLUC on local to global climate and weather systems, but these putative effects vary greatly in magnitude and even sign across space, time, and scale and thus remain highly uncertain. At the same time, many challenges exist toward improved understanding of the consequences of atmospheric and climate change on land process dynamics and services. Future effort must improve the understanding of the scale-dependent, multifaceted perturbations and feedbacks between land and climate changes in both reality and models. To this end, one critical cross-disciplinary need is to systematically quantify and better understand measurement and model uncertainties. Finally, LCLUC mitigation and adaptation assessments must be strengthened to identify implementation barriers, evaluate and prioritize opportunities, and examine how decision-making processes work in specific contexts.

A “rediscovered” record of Ainsliaea brandisiana (Asteraceae) from Thailand and its biogeographic significance

Ainsliaea brandisiana was regarded as distributed only in southeastern Myanmar. Koyama once reported the occurrence of A. brandisiana in Thailand in 1983, whereas Tseng thought it was a new species and described it as A. spnocephala in 1988. This treatment was accepted by Freire in 2007. Thus, the record of A. brandisiana from Thailand reported by Koyama was not valid. However, during a field trip in Phu Soi Dao National Park of northeastern Thailand, we found a remarkable species of Ainsliaea growing in mountain forests at the elevation of 1600 m. After detailed and comprehensive examination, we determined that it was A. brandisiana. This “rediscovered” record of A. brandisiana suggested a close phytogeographical connection between the mountain forests flora of southeastern Myanmar and that of northeastern Thailand, although they were separated by the lowlands rain forests of Thailand peninsula. We proposed a new hypothesis that there might be a plant migration route connecting southeastern Myanmar, northeastern Thailand and the Hengduan Mountains. Here, we described and illustrated A. brandisiana and provided photographs of its live specimens in the field, its habitat, morphological details of its floret, its distribution map and a key to all the known species of Ainsliaea from Thailand.