Last Glacial Maximum refugia were places ( refugia ) in which humans and other species survived during the Last Glacial Period, around 25,000 to 18,000 years ago. [1] Glacial refugia are areas that climate changes were not as severe, and where species could recolonize after deglaciation . [2]
Globally, the temperatures during the Last Glacial Maximum (LGM) were 4.0 ± 0.8 °C cooler than present day. [3] The colder climate contributed to ice sheet growth in North America, Europe, and Antarctica. At this time there were major climate shifts around the world. Some areas became too dry to support life, and others housed more vegetation and mammals.
The northern hemisphere was heavily impacted by ice sheets during the LGM. Some recent archaeological evidence suggests the possibility that human arrival in the Americas may have occurred prior to the Last Glacial Maximum more than 30,000 years ago. This evidence was found adjacent to ice sheets, [4] but research is still in an early stage. The best attested shelters are therefore mainly those in Eurasia. Aside from human habitation in the north, other animals and vegetation thrived in refugium south of ice sheets.
The southern hemisphere saw much less extensive glaciation, and outside Antarctica lacked continental ice sheet growth. Vast areas of Australia and Africa were too dry for human habitation of any sort, [5] even by the most specialized and well-adapted foragers. However, Sub-Saharan Africa was a refuge for many humans. [6] South America was not inhabited by humans during the LGM, but many other animals existed and thrived there.
The Laurentide and Cordilleran ice sheets overtook the majority of Canada and parts of the United States during the last glaciation. South of the glaciers, the major biomes on the continent were tropical semi-desert, subalpine parkland, temperate steppe grassland, and main taiga. [7] In the present day climate, the biomes in North America are tundra, boreal forest, temperate forest, grassland, desert and several more. [8] As the ice sheets retreated, biomes moved northward.
During the LGM, beech and maple trees were found in temperate deciduous forests in the southeast United States. These areas were a refuge to many species. [9] As the glacier retreated, trees and other vegetation would have migrated north to follow the climatic conditions they required. [9]
The first humans were thought to have arrived in North America around 30,000 years ago from Beringia. Homo sapiens were discovered in the high latitude northern hemisphere 30,000 years ago, however they did not migrate south until almost 15,000 years ago. [10]
The majority of the regions north of 40° N were overtaken by glaciers during the LGM. In these areas the climate was 10-25 °C lower than the current temperatures. [11] South of the glaciers housed a steppe-tundra climate, along with small sections of forest steppe and open boreal woodlands. [7] In these lowland areas the temperature was more mild, 2-5 °C less than the present day. [11] In the present, Europe has several biomes such as the Mediterranean, temperate forests, boreal forests and several steppes.
Due to the harsh conditions in Europe during the LGM, humans remained in certain regions. West of the Alps housed the Solutrean and Proto Solutrean cultures. The Solutrean people lived in between a forest steppe and a steppe tundra. This area had the highest probability of containing human refugia during the LGM. [12] Parts of Italy and extending into Romania contained the Epi-Gravettian cultures. [13]
Most trees in Europe lived in select refugium. Several requirements of these refugium include: soil moisture, relatively warm temperatures, shelter from wind, and no permafrost. There are two proposed hypotheses for tree refugia during the LGM in Europe. The first pertains to trees thriving in high-altitude locations in southern Europe. The second hypothesis suggests that forest trees existed only in small scattered refugia where there was adequate moisture. [11]
In Asia the main biomes during the LGM were forest steppes, semi-arid temperate woodlands, scrub woodlands, and tropical woodlands. There were some deserts in the region as well; 75% of the area consisted of dry steppes, semi-deserts, and deserts. [7] [14] The remaining areas in Asia were covered with tropical rainforests.
There were several factors that controlled where plants and animals thrived in Asia during the LGM. In the south, precipitation was the major factor that contributed to species refugia. Contrastingly, the higher latitude's main limiting factor was temperature. [15] Climate conditions in central Asia were too harsh to allow human habitation. However, several hominin sites have been discovered in Uzbekistan. This implies that during unfavorable glacial conditions, hominin did not move. [16]
The climate was drastically different between Northern Africa and Southern Africa. In the north, Africa was mainly a tropical extreme desert, but also housed small sections of tropical semi-desert, tropical grassland and tropical woodland. [7]
The Sahara desert falls in Northern Africa, and during the LGM it moved slightly south due to the ice sheets in the north. When that occurred, the northern tip of Africa became a haven for humid and moist mixed forests. These climatic conditions were similar to southern Europe, now called the Mediterranean. [17] During the LGM, winter global temperatures were 10-20 °C cooler. Even with the cold, the Mediterranean housed a mosaic of suitable micro climates for temperate and thermophilic animals. [18] Many animals that moved to this area would have died from the cold tundra during the LGM. [17]
The Congo tropical rainforest resides in the southern region of Africa. During the Last Glacial Maximum, the rainforest was not as large as it is today. This was because the Earth was drier. With less humidity, the Congo shrank by 54%. [19] In addition, the LGM allowed for savannas, tropical grasslands, tropical thorn scrub, tropical semi-desert, tropical extreme desert, and semi-arid temperate woodland. [20] Today, Southern Africa consists mainly of savannas, deciduous woodlands, tropical rainforests, and deserts.
Modern humans evolved from Africa, with their first known appearance being ~195,000 years ago. [21] The earliest dated fossils outside of Africa are between 90,000 to 120,000 years ago. [21] During the LGM, 27-66% of Africa was a refugium for humans. Humans thrived here because of the abundance of humidity, accessibility of woodlands, and lastly precipitation/access to water. The Zambezi, Omo river, and the Great Rift Valley lakes were major sources of water in southern Africa. [22]
South America contained several biomes during the LGM. First, the Andes mountains held glaciers which created a tundra in surrounding areas. Secondly, the Amazon rainforest contained tropical rainforests, grasslands, deserts, and savannas. [20] The ITCZ, trade winds, and insolation created an environment that allowed high precipitation rates in the Amazon. [23] South of the Amazon rainforest was significantly drier. For example, precipitation east of the Andes was ~20-30% lower than present day values. Additionally, the southern tip of the continent had ~40-50% lower precipitation. [24]
Humans arrived in South America approximately 15,000 years ago. [25] Due to the timing, humans arrived after the LGM.
The South American deer, Hippocamelus, was known to live in high altitude locations and cold valleys. Historically, they lived anywhere between 36.5° S and 54° S. Presently, they live between 40° S and 51° S. The habitat of Hippocamelus shrank as the LGM came to an end. The change in location is theorized to be caused by a lack of cold tundra areas, as well as higher sea level. [26]
During the Last Glacial Maximum, Australia was cooled and became arid. The annual temperatures decreased approximately 10 °C, and rainfall decreased 60%. [27] Australian biomes during the LGM include tropical extreme desert, tropical semi-desert, tropical thorn scrub and scrub woodland, tropical grassland, and tropical woodland. [20] The largest biome was the tropical extreme desert. This region was considered a "barrier", meaning devoid of human activity. Australia housed refugia such as the Gulf Plans/Einasleigh Uplands, Brigalow Belt South, Murray Darling Depression, Tasmanian Central Highlands, and many others. [27]
The majority of refugia existed along the coast where woodlands and grasslands were found. The Australian Wet Tropics are a region in the northeast that contain rainforests. The rain forest expanded and contracted throughout the glacial cycles. During the LGM, it withdrew to a refugia near the coast. A majority of the wet tropics were replaced with woodlands and grasslands after the LGM. [28]
A biome is a distinct geographical region with specific climate, vegetation, and animal life. It consists of a biological community that has formed in response to its physical environment and regional climate. Biomes may span more than one continent. A biome encompasses multiple ecosystems within its boundaries. It can also comprise a variety of habitats.
The Global 200 is the list of ecoregions identified by the World Wide Fund for Nature (WWF), the global conservation organization, as priorities for conservation. According to WWF, an ecoregion is defined as a "relatively large unit of land or water containing a characteristic set of natural communities that share a large majority of their species dynamics, and environmental conditions". For example, based on their levels of endemism, Madagascar gets multiple listings, ancient Lake Baikal gets one, and the North American Great Lakes get none.
A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur naturally on all continents except Antarctica and are found in most ecoregions of the Earth. Furthermore, grasslands are one of the largest biomes on Earth and dominate the landscape worldwide. There are different types of grasslands: natural grasslands, semi-natural grasslands, and agricultural grasslands. They cover 31–69% of the Earth's land area.
A savanna or savannah is a mixed woodland-grassland ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of grasses. According to Britannica, there exists four savanna forms; savanna woodland where trees and shrubs form a light canopy, tree savanna with scattered trees and shrubs, shrub savanna with distributed shrubs, and grass savanna where trees and shrubs are mostly nonexistent.
Rangelands are grasslands, shrublands, woodlands, wetlands, and deserts that are grazed by domestic livestock or wild animals. Types of rangelands include tallgrass and shortgrass prairies, desert grasslands and shrublands, woodlands, savannas, chaparrals, steppes, and tundras. Rangelands do not include forests lacking grazable understory vegetation, barren desert, farmland, or land covered by solid rock, concrete and/or glaciers.
The Last Glacial Maximum (LGM), also referred to as the Last Glacial Coldest Period, was the most recent time during the Last Glacial Period where ice sheets were at their greatest extent 26,000 and 20,000 years ago. Ice sheets covered much of Northern North America, Northern Europe, and Asia and profoundly affected Earth's climate by causing a major expansion of deserts, along with a large drop in sea levels.
The Holarctic realm is a biogeographic realm that comprises the majority of habitats found throughout the continents in the Northern Hemisphere. It corresponds to the floristic Boreal Kingdom. It includes both the Nearctic zoogeographical region, and Alfred Wallace's Palearctic zoogeographical region.
In biology, a refugium is a location which supports an isolated or relict population of a once more widespread species. This isolation (allopatry) can be due to climatic changes, geography, or human activities such as deforestation and overhunting.
During the Last Glacial Maximum, the mammoth steppe, also known as steppe-tundra, was once the Earth's most extensive biome. It stretched east-to-west, from the Iberian Peninsula in the west of Europe, across Eurasia to North America, through Beringia and Canada; from north-to-south, the steppe reached from the arctic islands southward to China. The mammoth steppe was cold and dry, and relatively featureless, though topography and geography varied considerably throughout. Some areas featured rivers which, through erosion, naturally created gorges, gulleys, or small glens. The continual glacial recession and advancement over millennia contributed more to the formation of larger valleys and different geographical features. Overall, however, the steppe is known to be flat and expansive grassland. The vegetation was dominated by palatable, high-productivity grasses, herbs and willow shrubs.
The Late Glacial Interstadial (LGI) c. 14,670 to c. 12,890 BP, also called the Bølling–Allerød interstadial, represents the first pronounced warming since the end of the Last Glacial Maximum (LGM). Human populations, which had previously been forced into refuge areas, gradually begin to repopulate the Northern Hemisphere's Eurasian landmass.
A forest steppe is a temperate-climate ecotone and habitat type composed of grassland interspersed with areas of woodland or forest.
The Holdridge life zones system is a global bioclimatic scheme for the classification of land areas. It was first published by Leslie Holdridge in 1947, and updated in 1967. It is a relatively simple system based on few empirical data, giving objective criteria. A basic assumption of the system is that both soil and the climax vegetation can be mapped once the climate is known.
Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial factor in shaping plant community, biodiversity, metabolic processes and ecosystem dynamics for montane ecosystems. Dense montane forests are common at moderate elevations, due to moderate temperatures and high rainfall. At higher elevations, the climate is harsher, with lower temperatures and higher winds, preventing the growth of trees and causing the plant community to transition to montane grasslands and shrublands or alpine tundra. Due to the unique climate conditions of montane ecosystems, they contain increased numbers of endemic species. Montane ecosystems also exhibit variation in ecosystem services, which include carbon storage and water supply.
The northern and southern hemispheres of the earth have a dynamic history of advancing and retreating ice sheets. The glacial and interglacial periods are linked to regular eccentricities in the Earth's orbit and correspond to approximately 100 kyr cycles. The advancing, or glacial periods can cause a massive displacement of flora and fauna as it drives them away from the poles, with the most recent glacial maximum having occurred about 20,000 years ago.,
Vegetation classification is the process of classifying and mapping the vegetation over an area of the Earth's surface. Vegetation classification is often performed by state based agencies as part of land use, resource and environmental management. Many different methods of vegetation classification have been used. In general, there has been a shift from structural classification used by forestry for the mapping of timber resources, to floristic community mapping for biodiversity management. Whereas older forestry-based schemes considered factors such as height, species and density of the woody canopy, floristic community mapping shifts the emphasis onto ecological factors such as climate, soil type and floristic associations. Classification mapping is usually now done using geographic information systems (GIS) software.
A glacial refugium is a geographic region which made possible the survival of flora and fauna during ice ages and allowed for post-glacial re-colonization. Different types of glacial refugia can be distinguished, namely nunatak, peripheral, and lowland. Glacial refugia have been suggested as a major cause of floral and faunal distribution patterns in both temperate and tropical latitudes. With respect to disjunct populations of modern-day species, especially in birds, doubt has been cast on the validity of such inferences, as much of the differentiation between populations observed today may have occurred before or after their restriction to refugia. In contrast, isolated geographic locales that host one or more critically endangered species are generally uncontested as bona fide glacial refugia.
Changing climate conditions are amplified in polar regions and northern high-latitude areas are projected to warm at twice the rate of the global average. These modifications result in ecosystem interactions and feedbacks that can augment or mitigate climatic changes. These interactions may have been important through the large climate fluctuations since the glacial period. Therefore it is useful to review the past dynamics of vegetation and climate to place recent observed changes in the Arctic into context. This article focuses on northern Alaska where there has been much research on this theme.
The wood-pasture hypothesis is a scientific hypothesis positing that open and semi-open pastures and wood-pastures formed the predominant type of landscape in post-glacial temperate Europe, rather than the common belief of primeval forests. The hypothesis proposes that such a landscape would be formed and maintained by large wild herbivores. Although others, including landscape ecologist Oliver Rackham, had previously expressed similar ideas, it was the Dutch researcher Frans Vera, who, in his 2000 book Grazing Ecology and Forest History, first developed a comprehensive framework for such ideas and formulated them into a theorem. Vera's proposals, although highly controversial, came at a time when the role grazers played in woodlands was increasingly being reconsidered, and are credited for ushering in a period of increased reassessment and interdisciplinary research in European conservation theory and practice. Although Vera largely focused his research on the European situation, his findings could also be applied to other temperate ecological regions worldwide, especially the broadleaved ones.