Mongol Empire rode wave of mild climate, but warming now may be tipping region into unparalleled drought

Researchers studying the rings of ancient trees in mountainous central Mongolia think they may have gotten at the mystery of how small bands of nomadic Mongol horsemen united to conquer much of the world within a span of decades, 800 years ago. The rise of the great leader Genghis Khan and the start of the largest contiguous empire in human history was propelled by a temporary run of nice weather.The rings show that exactly when the empire rose, the normally cold, arid steppes of central Asia saw their mildest, wettest weather in more than 1,000 years. Grass production must have boomed, as did vast numbers of war horses and other livestock that gave the Mongols their power. But the tree rings, spanning 1,112 years from 900 to 2011, also exhibit an ominous modern trend. Since the mid-20th century, the region has warmed rapidly, and the rings show that recent drought years were the most extreme in the record — possibly a side effect of global warming. In a region already pressed for water, the droughts have already helped spark a new migration in a vast region where people until now have lived the same way for centuries, moving herds from place to place and living in tents. Now, those herders are being driven rapidly into cities, and there could be greater future upheavals. The study appears in this week’s early online edition of the Proceedings of the National Academy of Sciences.”Before fossil fuels, grass and ingenuity were the fuels for the Mongols and the cultures around them,” said lead author Neil Pederson, a tree-ring scientist at Columbia University’s Lamont-Doherty Earth Observatory. “Energy flows from the bottom of an ecosystem, up the ladder to human society. Even today, many people in Mongolia live just like their ancestors did. …

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Coral fish biodiversity loss: Humankind could be responsible

Literal biodiversity reservoirs, coral reefs and associated ecosystems are in grave danger from natural and human-made disturbances. The latest World Resources Institute assessment is alarming with 75% of coral reefs reported as endangered worldwide, a figure that may reach 100% by 2050. The numbers are concerning, particularly as coral reefs provide sustenance and economic benefits for many developing countries and fish biodiversity on coral reefs partly determines the biomass available for human consumption.A Multi-Facetted BiodiversityWhile phylogenetic diversity in communities is acknowledged for its vital heritage value, illustrating, as it does, a “part” of the tree of life, ecosystem functional diversity has long been overlooked in impact studies. An ecosystem’s richness is also measured both in taxonomic biodiversity terms (number of different species) as well as by the number of lineages or functions performed by many ecosystem goods and services.*There have not as yet been any studies into the impact of human activity on coral fish community taxonomic, functional and phylogenetic taxonomic diversity loss.Functional and Phylogenetic Diversity Loss RevealedAfter sampling 1553 fish communities through underwater surveys in 17 Pacific countries, researchers assessed the taxonomic, functional and phylogenetic diversity levels of a group of species fished along a human density gradient ranging from 1.3 to 1705 persons per sq. km of reef.The social and environmental data were collected under the PROCFish and CoFish projects co-ordinated by the Secretariat of the Pacific Community and funded by the European Union.The results showed a sharp drop in functional and phylogenetic diversity levels, particularly above 20 people per sq. km of reef, while species richness was barely affected along the gradient.When human population density reached 1700 persons per sq. km of reef, the impact on functional and phylogenetic diversity levels (-46 % and -36 %, respectively) was greater than on species richness (-12 %).A Tree of Life that Needs ProtectingThe research shows that species numbers are a poor indicator of anthropogenic pressure, while two other biodiversity components are far more heavily affected by human density. These components make up the tree of life, i.e. the diversity of biological traits and phylogenetic lineages that are essential for coral systems to function.The researchers emphasised how important it was to conserve all the components of biodiversity. They also recommended using trait and lineage diversity as reliable and sensitive indicators of damage to species communities.*Some reef fish species play key roles in ecosystem functions: regulating competition between algae and coral colonies; and creating areas that are conducive to recruiting coral larvae by bio-erosion, etc.Story Source:The above story is based on materials provided by Institut de Recherche pour le Dveloppement (IRD). …

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How evolution shapes the geometries of life

Why does a mouse’s heart beat about the same number of times in its lifetime as an elephant’s, although the mouse lives about a year, while an elephant sees 70 winters come and go? Why do small plants and animals mature faster than large ones? Why has nature chosen such radically different forms as the loose-limbed beauty of a flowering tree and the fearful symmetry of a tiger?These questions have puzzled life scientists since ancient times. Now an interdisciplinary team of researchers from the University of Maryland and the University of Padua in Italy propose a thought-provoking answer based on a famous mathematical formula that has been accepted as true for generations, but never fully understood. In a paper published the week of Feb. 17, 2014 in the Proceedings of the National Academy of Sciences, the team offers a re-thinking of the formula known as Kleiber’s Law. Seeing this formula as a mathematical expression of an evolutionary fact, the team suggests that plants’ and animals’ widely different forms evolved in parallel, as ideal ways to solve the problem of how to use energy efficiently.If you studied biology in high school or college, odds are you memorized Kleiber’s Law: metabolism equals mass to the three-quarter power. This formula, one of the few widely held tenets in biology, shows that as living things get larger, their metabolisms and their life spans increase at predictable rates. Named after the Swiss biologist Max Kleiber who formulated it in the 1930s, the law fits observations on everything from animals’ energy intake to the number of young they bear. It’s used to calculate the correct human dosage of a medicine tested on mice, among many other things.But why does Kleiber’s Law hold true? …

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Crocodilians can climb trees and bask in the tree crowns

When most people envision crocodiles and alligators, they think of them waddling on the ground or wading in water — not climbing trees. However, a University of Tennessee, Knoxville, study has found that the reptiles can climb trees as far as the crowns.Vladimir Dinets, a research assistant professor in the Department of Psychology, is the first to thoroughly study the tree-climbing and -basking behavior. The research is published in the journal Herpetology.Dinets and his colleagues observed crocodilian species on three continents — Australia, Africa and North America — and examined previous studies and anecdotal observations. They found that four species climbed trees — usually above water — but how far they ventured upward and outward varied by their sizes. The smaller crocodilians were able to climb higher and further than the larger ones. Some species were observed climbing as far as four meters high in a tree and five meters down a branch.”Climbing a steep hill or steep branch is mechanically similar, assuming the branch is wide enough to walk on,” the authors wrote. “Still, the ability to climb vertically is a measure of crocodiles’ spectacular agility on land.”The crocodilians seen climbing trees, whether at night or during the day, were skittish of being approached, jumping or falling into the water when an approaching observer was as far as 10 meters away. This response led the researchers to believe that the tree climbing and basking are driven by two conditions: thermoregulation and surveillance of habitat.”The most frequent observations of tree-basking were in areas where there were few places to bask on the ground, implying that the individuals needed alternatives for regulating their body temperature,” the authors wrote. “Likewise, their wary nature suggests that climbing leads to improved site surveillance of potential threats and prey.”The data suggests that at least some crocodilian species are able to climb trees despite lacking any obvious morphological adaptations to do so.”These results should be taken into account by paleontologists who look at changes in fossils to shed light on behavior,” said Dinets. “This is especially true for those studying extinct crocodiles or other Archosaurian taxa.”Dinets collaborated with Adam Britton from Charles Darwin University in Australia and Matthew Shirley from the University of Florida.Research by Dinets published in 2013 found another surprising crocodilian characteristic — the use of lures such as sticks to hunt prey. …

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An unprecedented threat to Peru’s cloud forests

Sep. 11, 2013 — Peru’s cloud forests are some of the most biologically diverse ecosystems in the world. A profusion of tree and plant species as well as one third of Peru’s mammal, bird and frog species make their home in these perennially wet regions, located along the eastern slopes of the Andes Mountains. The high elevation (6,500-11,000 feet), and remote location of these areas makes them some of the hardest to reach and therefore hardest to study ecosystems in the world. To date, scientists only believe a fraction of cloud forest tree and plant species have been discovered.This massive array of underexplored biodiversity will face an unprecedented threat before the end of the century.Now, researchers at Wake Forest University in Winston-Salem, N.C. have pieced together startling new evidence that shows rapid 21st century warming may spell doom for tree species in Peruvian cloud forests, with species losing 53-96 percent of their populations.Stuck in a Hot PlaceThe habitats of most Andean plants-and therefore the habitats of the organisms that use them for food and shelter- are determined largely by temperature. Temperatures change quickly on the slopes of the Andes due to the region’s steep terrain. This means the vast majority of trees and plants only can live in a range that extends a few hundred meters.”I could be standing among a group of one tree species and throw a rock completely across their ranges,” says David Lutz, the paper’s lead author and a former postdoctoral associate at Wake Forest University. Lutz, who is now a post-doctoral research associate at Dartmouth College in New Hampshire, says this means cloud forest trees are particularly sensitive to climate change.Historically, Andean cloud forest seedlings sprout higher in elevation during periods of global warming. However, an unprecedented rate of projected temperature gain in the region over the next century, 5 degrees Celsius, will have them going upslope faster than ever before, says Miles Silman, professor of Biology at Wake Forest University. …

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400-year study finds Northeast forests resilient, changing

Sep. 5, 2013 — A joint Harvard-Smithsonian study released today in the journal PLOS ONE reveals how much — and how little — Northeastern forests have changed after centuries of intensive land use.A hike through today’s woods will reveal the same types of trees that a colonial settler would have encountered 400 years ago. But the similarities end there. Jonathan Thompson, research associate at the Smithsonian Conservation Biology Institute and lead author of the new study, explains, “If you only looked at a tree species list, you’d have the impression that Northeast forests haven’t changed. But once you start mapping the trees, and counting them up, a different picture emerges.” Thompson adds, “In some ways the forest is completely transformed.”To draw these conclusions, Thompson and his colleagues compared colonial-era tree records to modern US Forest Service data across a 9-state area stretching from Pennsylvania to Maine.Their results show stark contrasts between pre-colonial forests and today. Maples have exploded across the Northeast, their numbers increasing by more than 20 percent in most towns. Other tree types have declined sharply. Beeches, oaks, and chestnuts show the most pronounced loss — big trouble, Thompson notes, for wildlife that depend on tree nuts for winter survival.Pine numbers have shifted more than any other tree type, increasing in some places, decreasing elsewhere. Thompson pins this variability to ecology and economy: “Pine is valuable for timber, but quick to return after cutting. It has a social and environmental dynamism to it.”The nine states in the study share a similar — and notable — forest history: during the 18th and 19th centuries, more than half the forestland was cleared for agriculture and cut for timber. …

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Woodland salamanders indicators of forest ecosystem recovery

Aug. 28, 2013 — Woodland salamanders are a viable indicator of forest ecosystem recovery, according to researchers from the U.S. Forest Service’s Pacific Southwest Research Station.PSW Research Wildlife Biologist Dr. Hartwell Welsh and Garth Hodgson examined two species of woodland salamanders across four stages of tree development at Mill Creek — a disturbed old-growth redwood forest in northern California. They found that the numbers and body condition of two common species of salamander tracked closely with forest stand growth, development, and structural changes. Using salamander population numbers and physiological condition on adjacent, never harvested old-growth parkland to reference advancements along this developmental pathway, they demonstrated relationships between salamander counts and body condition and aspects of forest advancement including stand age, tree size, ambient moisture, canopy closure, and litter depth.The case study established that when woodland salamanders are found in high abundance, it indicates a healthy forest, having undergone ecological advancement and ecosystem recovery.There have been concerns about using indicator species as metrics of ecosystem conditions; however, amphibians are increasingly becoming accepted as researchers verify their applicability and usefulness. The woodland salamanders evaluated in Mill Creek were deemed credible due to their conservatism, trophic role, and high site fidelity, which tie them closely to conditions of place.The findings of this case study are important because old-growth forests are quickly diminishing, but they provide crucial environmental services to society. According to the researchers, this type of forest is a unique carbon sink containing the most abundant land carbon stocks on the planet. Old-growth forests sequester carbon pollution and support the world’s most diverse ecosystems.Mill Creek is an old-growth forest located in Del Norte, Calif. in a geographically limited coastal redwood forest bioregion, which has seen extensive commercial logging for more than 100 years. …

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Woodland salamanders indicators of forest ecosystem recovery

Aug. 28, 2013 — Woodland salamanders are a viable indicator of forest ecosystem recovery, according to researchers from the U.S. Forest Service’s Pacific Southwest Research Station.PSW Research Wildlife Biologist Dr. Hartwell Welsh and Garth Hodgson examined two species of woodland salamanders across four stages of tree development at Mill Creek — a disturbed old-growth redwood forest in northern California. They found that the numbers and body condition of two common species of salamander tracked closely with forest stand growth, development, and structural changes. Using salamander population numbers and physiological condition on adjacent, never harvested old-growth parkland to reference advancements along this developmental pathway, they demonstrated relationships between salamander counts and body condition and aspects of forest advancement including stand age, tree size, ambient moisture, canopy closure, and litter depth.The case study established that when woodland salamanders are found in high abundance, it indicates a healthy forest, having undergone ecological advancement and ecosystem recovery.There have been concerns about using indicator species as metrics of ecosystem conditions; however, amphibians are increasingly becoming accepted as researchers verify their applicability and usefulness. The woodland salamanders evaluated in Mill Creek were deemed credible due to their conservatism, trophic role, and high site fidelity, which tie them closely to conditions of place.The findings of this case study are important because old-growth forests are quickly diminishing, but they provide crucial environmental services to society. According to the researchers, this type of forest is a unique carbon sink containing the most abundant land carbon stocks on the planet. Old-growth forests sequester carbon pollution and support the world’s most diverse ecosystems.Mill Creek is an old-growth forest located in Del Norte, Calif. in a geographically limited coastal redwood forest bioregion, which has seen extensive commercial logging for more than 100 years. …

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One tree’s architecture reveals secrets of a forest

Aug. 6, 2013 — Behind the dazzling variety of shapes and forms found in trees hides a remarkably similar architecture based on fundamental, shared principles, UA ecologists have discovered.Researchers in the University of Arizona’s department of ecology and evolutionary biology have found that despite differences in appearance, trees across species share remarkably similar architecture and can tell scientists a lot about an entire forest.Just by looking at a tree’s branching pattern, it turns out, scientists can gather clues about how it functions — for example how much carbon dioxide it exchanges with the atmosphere or how much water transpires through its leaves — regardless of the tree’s shape or species.The researchers’ results, published in the August issue of the scientific journal Ecology Letters, have important implications for models used by scientists to assess how trees influence ecosystems across the globe.Studies like this enable scientists to refine models used to assess and predict functions that cannot be directly measured for an entire forest, for example how much carbon dioxide and oxygen the forest exchanges with the atmosphere and how much water the trees lose through evaporation.According to the authors, their study is the first empirical test of a theory UA ecology professor Brian Enquist helped develop in 1998. That theory holds that a tree’s branching structure — specifically, the width and length of its branches — predicts how much carbon and water a tree exchanges with the environment in relation to its overall size, independently of the species.”This theory can be used to scale the size of plants to their function, such as amount of photosynthesis, water loss and respiration, especially in light of climate change,” said Lisa Patrick Bentley, who led the research, funded by the National Science Foundation, as part of a postdoctoral fellowship in Enquist’s lab. “If you were to look at an entire forest and wanted to know how much carbon this forest puts out, our study supports the idea that you might only have to look at the properties of a few trees, representing the smallest and the largest, to figure this out.””All of the tree species we studied have very similar branching patterns regardless of their difference in appearance,” she said. “For example, even though a piñon pine tree looks very different from a maple tree, there are similar general ecological, biological and physical principles that have resulted in a similar branching architecture across those species over the course of evolution.”Bentley and her team tested this prediction in five different species of trees: maple, oak, balsa, Ponderosa pine and piñon pine. They found the theory to be correct in that it allows for predictions about a tree’s function depending on its size, and also in that the theory’s principles apply across species, despite their differences in appearance.”There is a relationship between the size and shape of branches,” Bentley said. “They grow within proportion. Take a pine tree, for example: It has the general shape of a cone, while an oak tree looks like more like an inverted cone. When you think about the many different shapes of trees, I think it’s pretty amazing that you get this correlation between such different looking trees.”For their study, the researchers harvested a total of nine specimens from forest areas set aside for research purposes. A team of undergraduate and graduate student researchers dissected the trees down to the last twig, counting the number of branches, the number of branching points, or nodes, and measuring the length and diameter of each branch.The work also confirmed an idea first proposed by Renaissance polymath Leonardo da Vinci.”If you imagine collapsing all of a tree’s outermost branches into one cylinder, that cylinder would be the size of the trunk,” Bentley said. …

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Chronic harvesting threatens tropical tree

Aug. 5, 2013 — Chronic harvesting of a tropical tree that many local communities in Western Africa depend on can alter the tree’s reproduction and drastically curtail fruit and seed yields over the tree’s lifetime, according to a new study.The study, which appears today in the Journal of Ecology, is the first of its kind to use what’s called “age-from-stage” mathematical modeling, a way of estimating plant age from its size, to investigate how harvesting affects a plant’s life expectancy and other life history traits, such as age at maturity.In this case, the tree Khaya senegalensis, commonly known as African mahogany, is found in many habitats in Western Africa, from forests to savanna woodland, and is considered a vulnerable species due to drought and logging. The tree is heavily harvested for its leaves, to feed cattle, and for its bark, which is used medicinally to treat many ailments, from stomachaches to reducing malaria fevers.Specifically analyzing harvesting effects on the tree in both dry and moist regions in Benin, the study found that plant harvesting affects life history in different ways depending on the climatic conditions. In the moist region, chronic harvest delayed reproduction and the trees lived longer, whereas in the dry region, chronic harvesting hastened reproduction and shortened the tree’s life span.”For indigenous people who are harvesting these plants, knowing how long a particular species is going to persist or how soon it is going to reproduce is valuable information for planning and management, especially for plants for which fruits are harvested,” said Orou Gaoue, the study’s lead author and assistant professor of ecology, evolution and conservation biology at the University of Hawaii at Manoa.”As we consider how global warming may affect human livelihood and the resources we use, it is important to understand and account for the ways in which variation in climate and human behavior can change the traits or productivity of harvested wild plants,” Gaoue added. “Here we found that if you fail to account for that variability, even in harvesters’ behavior, you may underestimate the effect of harvesting on population life history traits.”

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Climate change threatens forest survival on drier, low-elevation sites

June 28, 2013 — Predicted increases in temperature and drought in the coming century may make it more difficult for conifers such as ponderosa pine to regenerate after major forest fires on dry, low-elevation sites, in some cases leading to conversion of forests to grass or shrub lands, a report suggests.Researchers from Oregon State University concluded that moisture stress is a key limitation for conifer regeneration following stand-replacing wildfire, which will likely increase with climate change. This will make post-fire recovery on dry sites slow and uncertain. If forests are desired in these locations, more aggressive attempts at reforestation may be needed, they said.The study, published in Forest Ecology and Management, was done in a portion of the Metolius River watershed in the eastern Cascade Range of Oregon, which prior to a 2002 fire was mostly ponderosa pine with some Douglas-fir and other tree species. The research area was not salvage-logged or replanted following the severe, stand-replacing fire.”A decade after this fire, there was almost no tree regeneration at lower, drier sites,” said Erich Dodson, a researcher with the OSU Department of Forest Ecosystems and Society. “There was some regeneration at higher sites with more moisture. But at the low elevations, it will be a long time before a forest comes back, if it ever does.”Similar situations may be found in many areas of the American West in coming decades, the researchers say, and recruitment of new forests may be delayed or prevented — even in climate conditions that might have been able to maintain an existing forest. While mature trees can use their roots to tap water deeper in the soil, competition with dense understory vegetation can make it difficult for seedlings to survive.Openings in ponderosa pine forests created by wildfire have persisted for more than a century on harsh, south-facing slopes in Colorado, the researchers noted in their report. And fire severity is already increasing in many forests due to climate change — what is now thought of as a drought in some locations may be considered average by the end of the next century.If trees do fail to regenerate, it could further reduce ecosystem carbon storage and amplify the greenhouse effect, the study said.Restoration treatment including thinning and prescribed burning may help reduce fire severity and increase tree survival after wildfire, as well as provide a seed source for future trees, Dodson said. These dry sites with less resilience to stand-replacing fire should be priorities for treatment, if maintaining a forest is a management objective, the study concluded.Higher-elevation, mixed conifer forests in less moisture-limited sites may be able to recover from stand-replacing wildfire without treatment, the researchers said.

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Whitebark pine trees: Is their future at risk?

June 10, 2013 — There’s trouble ahead for the whitebark pine, a mountain tree that’s integral to wildlife and water resources in the western United States and Canada.Over the last decade, some populations of whitebark pines have declined by more than 90 percent. But these declines may be just the beginning.New research results, supported by the National Science Foundation (NSF) and published today in the Journal of Ecology, suggest that as pine stands are increasingly fragmented by widespread tree death, surviving trees may be hindered in their ability to produce their usually abundant seeds.”With fewer seeds, you get less regeneration,” says ecologist Joshua Rapp, affiliated with NSF’s Harvard Forest Long-Term Ecological Research (LTER) site and lead author of the paper.Whitebark pine populations vary between producing a high number of seed cones some years, and a low number of seed cones other years.This variation depends on four factors: male pollen cones, female seed cones, wind and proximity.Each year, pollen from male cones is carried on the air to fertilize female seed cones perched atop nearby trees.”In low-cone years, less pollen is released, reaching extremely few female cones,” says Elizabeth Crone, senior ecologist at the NSF Harvard Forest LTER site and co-author of the paper.”But as more and more whitebark pines die, every year becomes a low-cone year.”In isolated pockets of trees, the gene pool is also diminished, meaning the seeds produced may be less viable over time.”For decades, researchers have struggled to understand why many different organisms–trees, fish, corals, insects–from various habitats reproduce synchronously and at certain intervals,” says Saran Twombly, program director in NSF’s Division of Environmental Biology, which funded the research.”By combining field data on seed and pollen production for whitebark pines with models that simulate mature cone production, this study helps to answer that question for these pines.”To reach their conclusions, the scientists had to look back in time.They inspected branches from seven whitebark pine sites in western Montana, counting the scars left by pollen cones and seed cones.”All the years with a high number of seed cones had one thing in common: a high number of pollen cones,” says Rapp. “The success of the seeds seems to depend on the amount of pollen produced.”Whitebark pine seeds are an essential food source for many animals in mountain habitats.The Clark’s Nutcracker, a mountain bird, can store up to 100,000 seeds in underground caches each year. Squirrels also store thousands of seeds underground.A diminished number of seed cones has an effect on grizzly bears, the scientists say; the bears regularly raid squirrel seed caches to prepare for winter hibernation.”In the past, low years for whitebark pine cones have led to six times more conflicts between grizzlies and humans, as hungry bears look for food in campgrounds,” says Crone.”Now, concerns about viability of whitebark pine populations are one of the main reasons grizzly bears in Yellowstone National Park are still listed as threatened under the Endangered Species Act.”Birds, squirrels and bears are not the only species that depend on whitebark pine.Vast stands of whitebark pine help to maintain the mountain snowpacks that provide water to more than 30 million people in 16 U.S. states each year.Whitebark pines are often the only trees at the highest elevations. Their branches retain snow as it blows across gusty mountaintops. Their shade moderates snow-melt in the spring, keeping flows down the mountain in check.A small percentage of whitebark pine trees have outlived the ongoing destruction by pests and disease. These trees are the next area of focus for Crone’s team.”We want to find out whether the surviving trees are still producing cones,” Crone says. “They represent the future of whitebark pines.”

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Sahara olive tree: Genetic heritage to be preserved

May 3, 2013 — The Saharan cousin of Mediterranean olive trees remains largely unknown. However, this subspecies (called the Laperinne’s olive tree) is of great interest for several reasons. IRD researchers and their partners showed that its longevity is ensured by its original vegetative reproduction. Extremely drought-resistant, this “relict” tree could act as a genetic resource to improve its domestic counterparts, provided conservation actions are implemented to prevent its disappearance.


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The most resistant of all olive trees

Contrary to its cultivated counterpart, the Laperrine’s olive tree did not choose the mildness of the Mediterranean climate. It grows in the middle of the Sahara desert at an altitude of between 1400 and 2800m, spanning southern Algeria, Niger and northern Sudan. In order to survive in this inhospitable environment over the past several million years, it had to adapt to extremely arid conditions. In order to preserve this exceptional genetic heritage over the course of time, it developed an unusual reproductive strategy. As researchers have demonstrated in a recent synthetic study, it reproduces through vegetative or clonal growth.

A genetic resource for cultivated plants

A symbol of Saharan mountain ecosystems, the Laperrine’s olive tree is a source of wood for local populations. Its leaves are also a valued resource to feed animals and are used as a traditional pharmacopoeia. Scientists also underline its agronomic benefits. Indeed, it can be crossed with cultivated olive trees to improve various properties, such as the drought-resistance of the latter. Thanks to molecular analyses, biologists discovered that such crossing has already been carried out previously, confirming the possibility of hybridizing the two subspecies.

An endangered tree

Developing a conservation niche like the Laperrine’s olive tree is not a risk-free process. Today it pays the price of its isolation and genetic protectionism. The limited gene flow among populations and its vegetative reproduction method resulted in less genetic mixing over long periods of time. Under current climatic conditions, the number of trees also tends to decrease. This combination of factors leads to the gradual erosion of the genetic diversity, which lowers the ability of the Laperrine’s olive tree to adapt to environmental changes and means this subspecies is potentially endangered in the long term.

This research into the ecology and evolutionary history of the Laperrine’s olive tree helps to better identify the danger facing this tree — endemic to the Sahara desert — and to establish the priorities for conservation programmes.

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The above story is reprinted from materials provided by Institut de Recherche pour le Développement (IRD).

Note: Materials may be edited for content and length. For further information, please contact the source cited above.


Journal Reference:

  1. G. Besnard, F. Anthelme, D. Baali-Cherif. The Laperrine’s olive tree (Oleaceae): a wild genetic resource of the cultivated olive and a model-species for studying the biogeography of the Saharan Mountains. Acta Botanica Gallica, 2012; 159 (3): 319 DOI: 10.1080/12538078.2012.724281

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Invasive species: ‘Away-field advantage’ weaker than ecologists thought

May 17, 2013 — For decades, ecologists have assumed the worst invasive species — such as brown tree snakes and kudzu — have an “away-field advantage.” They succeed because they do better in their new territories than they do at home. A new study led by the Smithsonian Environmental Research Center reveals that this fundamental assumption is not nearly as common as people might think.

The away-field advantage hypothesis hinges on this idea: Successful invaders do better in a new place because the environment is more hospitable to them. They escape their natural enemies, use novel weapons on unsuspecting natives and generally outcompete natives on their own turf by disrupting the balance of nature in their new ecosystems.

“They’ve been presumed to be good citizens at home and bad citizens away,” said ecologist John Parker, lead author of the paper published in the May issue of the journal Ecology. But when researchers investigated it on a large scale, they discovered the assumption was not true for all, or even most, of the species they looked at.

The research team, which included 24 invasion biologists from the National Science Foundation-funded Global Invasions Network, compiled data on 53 different plant and animal invaders. They pulled 37 from the list of “100 of the World’s Worst Invasive Alien Species,” and 16 from an exhaustive search of the published literature. They ended up with a list that included European green crabs, Asian kelp, nutria, brown tree snakes, garlic mustard and other common suspects. After combing through hundreds to thousands of papers to find published demographic data, they were able to do a statistical analysis of whether invaders were bigger, more reproductively successful and thus more abundant in their introduced ranges.

On the surface the assumption seemed to hold true. Across all 53 species, there was a 96 percent probability invaders would do better in their adopted ecosystems. But closer inspection revealed some surprising weaknesses within the paradigm. When they looked at individual species, they discovered a handful of extremely successful invaders were driving up the average. In reality, more than half of the species performed roughly the same at home versus abroad, and a few were even likely to perform worse in foreign territory.

This suggests that the key to a successful invasion depends less on the environment and more on the individual species doing the invading. Plants, for example, were more likely than animals to thrive abroad in this study. But even the plants showed a wide range of variability, with many (like garlic mustard) performing equally well in both their introduced and home ranges.

“The general notion that invasive species are doing something fundamentally different in their new versus their old ranges may be a fair starting point overall, but there is a lot of grey area even for the worst-case invaders,” Parker said. “These findings might also have applications for management. Some species might be invasive regardless of novel conditions, whereas others thrive only because of their new environment. If this ‘newfound’ success is reversible, it’s these latter

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