A glacial refugium (''plural refugia'') is a geographic region which made possible the survival of

flora Flora is all the plant life present in a particular region or time, generally the naturally occurring ( indigenous) native plants. Sometimes bacteria and fungi are also referred to as flora, as in the terms '' gut flora'' or '' skin flora''. ...

and

fauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is '' flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. ...

in times of

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gre ...

s and allowed for post-glacial re-colonization. Different types of glacial refugia can be distinguished, namely

nunatak A nunatak (from Inuit language, Inuit ''nunataq'') is the summit or ridge of a mountain that protrudes from an ice field or glacier that otherwise covers most of the mountain or ridge. They are also called glacial islands. Examples are natural p ...

, peripheral and lowland refugia.Holderegger, R., Thiel-Egenter, C. (2009): A discussion of different types of glacial refugia used in mountain biogeography and phytogeography. Journal of Biogeography 36, 476-480. Glacial refugia have been suggested as a major cause of the patterns of distributions of flora and fauna in both temperate and tropical latitudes. With respect to disjunct populations of modern-day species distributions, 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 (regarded as paleoendemics or glacial relicts) are generally uncontested as bona fide glacial refugia.

Identification of glacial refugia

Traditionally, the identification of glacial refugia have occurred through the assessment of palaeoecological evidence, to determine the origins of modern taxa. For example, paleoecological approaches, which focus on the study of fossil organisms and their remains, have been used to reconstruct the distributions of pollen in Europe, for the 13,000 years since the last glaciation. Researchers in this case ultimately established the spread of forest trees from the mountainous southern fringe of Europe, which suggests that this area served as a glacial refugia during this time.

Different types of glacial refugia

In studies exploring the extent of glacial refugia in mountain species, three distinct types of glacial refugia have been identified.

Nunatak glacial refugia

A nunatak is a type of glacial refugia that is located on the snow-free, exposed peaks of mountains, which lie above the ice sheet during glaciations. The identification of ‘diversity hotspots’ in areas, which should have been migration regions during major glacial episodes, is evidence for nunatak glacial refugia. For example, the

Monte Rosa : , other_name = Monte Rosa massif , translation = Mount Rose , photo = Dufourspitze (Monte Rosa) and Monte Rosa Glacier as seen from Gornergrat, Wallis, Switzerland, 2012 August.jpg , photo_caption = Central Mon ...

mountain ranges, the

Avers Avers ( rm, Avras; wae, Òòver(s), , ) is a high Alpine valley region and a municipality in the Viamala Region in the Swiss canton of Graubünden. It includes Juf, the highest-altitude year-round settlement in Europe. History Avers is first ...

, and the

Engadin The Engadin or Engadine ( rm, ;This is the name in the two Romansh idioms that are spoken in the Engadin, Vallader and Puter, as well as in Sursilvan and Rumantsch Grischun. In Surmiran, the name is ''Nagiadegna'', and in Sutsilvan, it is ...

e and the Bernina are all floristically rich proposed nunatak regions, which are indicative nunatak glacial survival.

Peripheral glacial refugia

Peripheral glacial refugia still exists within the mountain system but contrary to nunataks, which exist on the peaks, this type of refugia is located along the borders of mountain systems. Evidence for this type of mountain refugia can be found along the borders of the

Carpathian Mountains The Carpathian Mountains or Carpathians () are a range of mountains forming an arc across Central Europe. Roughly long, it is the third-longest European mountain range after the Urals at and the Scandinavian Mountains at . The range stretche ...

Pyrenees The Pyrenees (; es, Pirineos ; french: Pyrénées ; ca, Pirineu ; eu, Pirinioak ; oc, Pirenèus ; an, Pirineus) is a mountain range straddling the border of France and Spain. It extends nearly from its union with the Cantabrian Mountains to ...

or European Alps, all of which were formally glaciated mountain systems. For example, using the

amplified fragment length polymorphism AFLP-PCR or just AFLP is a PCR-based tool used in genetics research, DNA fingerprinting, and in the practice of genetic engineering. Developed in the early 1990s by KeyGene, AFLP uses restriction enzymes to digest genomic DNA, followed by liga ...

(AFLP) technique, researchers have been able to infer the survival of ''Phyteuma globulariifolium'' in peripheral refugia in the European Alps.

Lowland glacial refugia

Peak glacial refuges eastern North America

Lowland glacial refugia, unlike nunatak and peripheral glacial refugia, is a type of refugia that exists outside of the mountain system in the lowlands. Situated beyond the limits of ice shields, lowland refugia has been identified for a number of plant and animal species. In Europe, for example, through allozyme analysis, researchers have been able to confirm the continuous distribution of '' Zygaena exulans'' in between the foothills of the Pyrenees and the Alps during the last ice age. In eastern North America, lowland glacial refuges along the Atlantic and Gulf Coasts host

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

plants — some of which are rare, even endangered, and others entail the most southerly disjunct populations of plants that commonly appear only hundreds of miles to the north. Major rivers draining southward from the

Appalachian Mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. The ...

are associated with a gradation of

paleoendemic Paleoendemism along with neoendemism is a possible subcategory of endemism. Paleoendemism refers to species that were formerly widespread but are now restricted to a smaller area. Neoendemism refers to species that have recently arisen, such as thro ...

tree species. These range from the extinct Critchfield spruce near the outlet of the

Mississippi River The Mississippi River is the List of longest rivers of the United States (by main stem), second-longest river and chief river of the second-largest Drainage system (geomorphology), drainage system in North America, second only to the Hudson B ...

, to extinct-in-the-wild ''Franklinia'' along the

Altamaha River The Altamaha River is a major river in the U.S. state of Georgia. It flows generally eastward for 137 miles (220 km) from its origin at the confluence of the Oconee River and Ocmulgee River towards the Atlantic Ocean, where it empties ...

, to the critically endangered

Florida torreya ''Torreya taxifolia'', commonly known as Florida torreya or stinking-cedar, but also sometimes as Florida nutmeg or gopher wood, is an endangered canopy (biology), subcanopy tree of the yew Family (biology), family, Taxaceae. It is native to only ...

and Florida yew at the downstream end of the

Chattahoochee River The Chattahoochee River forms the southern half of the Alabama and Georgia border, as well as a portion of the Florida - Georgia border. It is a tributary of the Apalachicola River, a relatively short river formed by the confluence of the Chatt ...

system. (See illustration at right.)

References