So why is the topic of glacial refugia so important?

The winners and losers in the gamble of life - from a climate change perspective

Since late 20th century with scientific recognition of glacial-interglacial shifts during the Pleistocene, there has been a revolution in understanding of the impermanence of vegetation patterns. Today it is known that until mid-latitude cooling and reduced CO2 levels during the Pliocene, tropical flora flourished at high latitudes from the time of the dinosaurs. 

Oxygen isotope analysis of foraminafera in ocean sediment cores revealed the connection between rapid changes in ice volume and sea surface temperatures Shackleton (1967), later confirmed by Greenland ice core records Dansgaard (1993), and still later by Antarctic ice cores Barnola (1987).  With this historic sequencing established, pollen analysis from anaerobic lake sediment cores continues to contribute vital information regarding prehistoric vegetation patterns.

Northern Hemisphere Glaciation

The transient nature of vegetation is impacted by earth-sun orbital cycles Milankovic (1941).  Seasonality is a major control of vegetation - the axial tilt of the earth or obliquity as it called in astronomical terms, between 21.8 - 24.4 degrees over a period of 41,000 years affects the strength of seasonality affecting the amount of insolation received in summer and winter.  A 2nd astronomical orbital forcing called Precession with a 27,000 year cycle - akin to the gyrations of a spinning top - alters the distance between the earth and the sun - modifying the dates of perihelion and aphelion, earth-sun distances between December and June. Together, enhanced by earth system feedbacks, these orbital forcings have a subtle yet profound impact on vegetation patterns. 

Naturalists such as F. E. Clements (1874-1945)  believed dynamic vegetation patterns were based on succession to a mature state of vegetation best suited to local conditions, an idea that at best is only partly correct. Today there is heated debate over the extent of prehistoric burning by early hunter gathers that may have altered the prehistoric landscape worldwide. 

By the time Europeans arrived in the Americas, there had been extensive alteration of the landscape by fire: the Central Valley grasslands may have been oak forests that were burned by native American groups in order to facilitate hunting and clear forests of decaying matter.  Only since the late 20th century has there been recognition by the U.S. National Park Service of the contribution of fire to reinvigorate decaying and diseased vegetation.  When the Spanish arrived in California, they banned Native Americans from setting fires, although  burning through the late 19th century was recorded by missionaries and explorers.    

Unraveling prehistoric vegetation patterns today is aided by genetic analysis which can pinpoint movements down to the subspecies.  Pollen analysis is restricted to taxa.

Plant Succession during Deglaciation at Glacier Bay, Alaska which was ice covered until  around 300 years ago Chapin (1994)

Map of Glacier Bay, Alaska 

The remarkable Rosebay Willow Herb that covered London bomb sites and was a pioneer species during the deglaciation of Glacier Bay, Alaska 

1st came Rosebay Willow Herb, with Alder trees next and with Dryas Octapetalus 
growing in ring formation (asexually). Then Spruce and Hemlock (that prefers a shadier site – came later in the sequence after 250 years). In process succession – how important is the soil? Interestingly, alders are well-known as nitrogen-fixing plants that  enrich the soil and as the amount of nitrogen in the soil increases through time, then other plants could come in.


Today we live in the Holocene Interglacial.  Due to human industry, global warming will bring unprecedented changes and the onset of the next NH glaciation will be delayed.   

Current vegetation patterns are expected to shift, particularly within areas of the subtropics such as SW North America, India and Africa where increased aridification is predicted in future decades.  Clearly there will  be some winners - plants  enjoy enhanced CO2 and more warm, humid weather - so many heat-loving plants may thrive.

The Pallid Bat

In a world of climate change, there will no doubt be some losers -  bat populations already being driven to extinction by White Nose Syndrome (WNS)  Lorch (2011) will be further threatened by climate change impacts on echolation - (echo - location) to identify prey by emitting a high frequency ultrasonic squeak, listening for the echo back of the location of a juicy insect for dinner.  Unfortunately increased humidity and warmth attenuates the high frequency sound, lessening the range of echolation effectiveness of bats attuned to high frequencies to locate food sources Luo (2013).  

Coast redwoods (Sequoia sempervirens) distributed along a narrow band of California's northern coast could possibly turn out to be winners as the climate warms (Professor A. Roger Byrne, U.C. Berkeley personal communication).  During the Northern California summer, these red giants take advantage of the coastal fog to capture water out of the air— summer is the critical growing season for the trees, despite being California's dry season.  Future warming temperatures may possibly bring the fog belt further inland extending the habitat of the world's tallest trees, the Coastal redwoods, Sequoia sempervirens.

Sequoia Sempervirens bathed in its life-giving fog