Chad's Garden: Weather, Climate & the Mystery of the Critchfield's Spruce

The story of a highly-unique tree that became extinct at the end of the last Ice Age.

Posted: Jul 30, 2020 11:31 PM
Updated: Aug 11, 2020 5:36 PM

Overall:

An extinct species of spruce was found in the late 1990s in old lake beds & floodplain deposits (pollen, old fossilized cones, needles, twigs) dating back tens of thousands of years in the Southeast U.S.  It was found to be abundant & even in pure stands with other temperature & even southern tree species.  Even there & then, the climate was still rather warm for spruce species that we find now in North America.  However, spruce species in China are cold-sensitive.  This extinct species represents a single member of that Asiatic family of more temperaturate weather spruces.  Some of these cold-sensitive spruces are quite rare & seem to represent a dying branch of spruce species.  This shows that even abundant species can alarmingly become rare & extinct with climate change &/or disease & competition pressures.  This serves as a warning for future native species that may be abundant now, but may have pressures in the future as climate changes & disease & pests may increase.

Discussion:

When paleoclimatologists & paleobotanists (Stephen T. Jackson and Chengyu Weng) were analyzing lake core deposits in southwestern Georgia, South Carolina, Mississippi & Tennessee & wind-blown loess (silt) deposits in northwestern Mississippi to western Tennessee, they kept finding an abundance of spruce pollen during Ice Ages & varying amounts even between Ice Ages, called interglacials. 

They then found spruce cones, seeds, needles & twigs that somewhat resembled modern-day Red Spruce (Picea ).  Well, it was colder during Ice Ages, but what explained some pollen & spruce material in interglacials?  What can explain a spruce species near the Florida state line in such a warm environment for a spruce? 

The cold-weather species like Red, Black & White Spruce were found farther northward during the Wisconsin Ice Age (the last glaciation 22,000-12,000 years ago).

Cold climate spruce species map (as far south as Tennessee & far northern Georgia.  This map does not show the far southern mystery spruce species.

Sites cored with an abundance of this mystery spruce pollen & spruce parts (but this also include southern South Carolina & in northwestern Mississippi near Tunica where this species pollen was abundant):

The pollen of this enigmatic spruce was not accompanied of boreal species (northern species) like Jack, Red, Eastern White Pine, etc or White Spruce, but of likely Shortleaf Pine, oak species, American Beech, American Elm, American Hornbeam, maples, Tuliptree & other more temperate species apparently.  One site analyzed with this spruce in Tennessee was mostly oak species.  The only site that had any boreal or more-northerly species with it was in far northwestern Georgia where it was found with Red, Jack & Eastern White Pine. 

Close examination of the cones & seeds revealed that this was no modern-day spruce species, but a newly-discovered one that shared company with more Indiana to Kentucky, Tennessee & Alabama natives.  This tree, named Picea critchfieldii, appears to have been abundant across the Southeast, especially during Ice Ages, but these periods were known also for being drier (so much water locked up in ice & much lower CO2 levels).  Given the tendency for the pollen to show up with mesic species, it must have competed well with beech, tuliptrees, basswood, etc. & been confined to more moist areas where it formed near pure stands in many places.  It reminds me of the rather uncommon modern-day southern Spruce Pine, which tends to mingle with more mesic species in the Deep South & into Florida like Southern Magnolia, beech, Sweetgum, Tuliptree, etc. 

During the last Ice Age Sea levels were much lower during this time & the more traditional southern forests we find today with Longleaf, Slash, Loblolly Pine & various oaks, hollies, magnolias shifted southward onto the Continental Shelf, deep in Florida & over the Caribbean.  These species were cut-off in the Caribbean to as far south as Mexico & Hondoras & branched off into the Longleaf Pine look-a-like of Caribbean & Honduran Pine.  Genetic analysis shows that the long-needled southern pines like Slash, Longleaf to even Loblolly (which all are rather sensitive to colder weather) came from Central American & southern Mexico & Caribbean ancestors.

If a modern-day Critchfield Spruce was to exist it would most likely be found in the "lost world" of sorts for interesting, nearly extinct species in a small area of northwest Florida (deep bluffs & canyons along & near the Appalachicola River) that hosts the extremely rare to nearly extinct Florida Torreya & Florida Yew (Yews are more northerly plants of shady, deep coniferous forests in the U.S. & Canada).  The rare Ashe Magnolia is also found in this wet, cool, dark world of Ice refugia along the Appalachicola River.  It features the hilliest terrain in Florida & many northern species reach their southernmost ranges here. 

Critchfield's Spruce cones that were found in one particular deposit (this image courtesy of Stephen T. Jackson and Chengyu Weng & their groundbreaking 1999 paper on this newly-discovered native former member of our U.S. flora):

There are other small, isolated population of very rare trees that were likely more common in long pre-glacial times like:

Virginia Roundleaf Birch (nearly extinct in the wild), Frankliniana (now extinct in the wild), Durand Oak, Nutmeg Hickory & Pyramid Magnolia. 

In 2016 two new, extremely rare species of primitive magnolia were found in a remote area of northeastern Mexico:

Magnolia rzedowskiana & Magnolia dealbata

One is similar to the rare Bigleaf Magnolia & the other, the Pyramid Magnolia, both in the southern U.S.

In researching the Critchfield Spruce, we find that several other more temperate spruce species are nearing extinction & represent a lost lineage of spruces dating back hundreds of thousands to millions of years favoring warmer, more muggy areas.  This branch of spruces seems to be only represented in eastern Asia.  They all seem to have resemblance to Critchfield Spruce fossils & handle more consistent heat & humidity better than other spruces. 

This represents a group of endemics that a relics of more widespread Tertiary flora in the U.S. & Asia.

In Cindy Tang's book The Subtropical Vegetation of Southwestern China, she writes:

"Within the warm, humid evergreen broad-leaved forest zone and the transitional zone between the evergreen and the deciduous broad-leaved forests, where there is also an admixture of species of gymnosperms, some extant Tertiary relict plant species thrive today, in particular in unstable habitats where natural disturbances occur frequently, such as steep or scree slopes, rocks crevices, cliffs, limestone areas with outcrops, or stream banks. Most of the Tertiary relict plants are light-demanding and appear to be stress-tolerant. In general, their regeneration depends on natural disturbances where there is little competition from other species."

The Cold-Sensitive Spruces:

Here is a USDA zone map for reference once again:

The Martinez Spruce (Picea martinezii) is only found in two lingering populations in moister areas in northeastern Mexico near the Gulf of Mexico at low to moderate elevations.  It is found near the rare Mexican Beech, Mexican Shagbark Hickory (Mexican subspecies of this hickory) & Mexican Magnolia.  Known for tolerating a warmer climate better than any modern-day spruce it is classified as Critically Endangered. 

Hardy to USDA Zone 8: cold hardiness limit between 10° and 20°F

Image below is courtesy of American Conifer Society & was taken by Carlos Gerardo Velazco Macias in the trees native habitat of Nuevo Leon (northeastern Mexico).

Chihuahua Spruce (Picea chihuahuana), tolerates heat & humidity very well & is only represented by 25 small, isolated populations in Mexico.  It is considered endangered.  It resembles Colorado Blue Spruce, but its genome suggests it closest relatives are in East Asia (other than the other spruce species mentioned here).

Trees in native habitat in image below (courtesy of Daniel Acosta & De Heraldo De Chihuahua newspaper)

Another image of the species in native habitat (photo by Jeff Bisbee & the Royal Botantical Garden Edinburgh):

Two other ultra-rare conifers:

Brewer's Spruce (Picea breweriana) is one of the rarest trees in North America & only represented by small, isolated populations in five counties on the California-Oregon state line.  Very beautiful species with its weeping branches, it grows typically at around 4000' & prefers a wet environment & will not germinate in open sunlight or soil that has moisture fluctuation of very dry to very moist.  It looks like a weeping Norway Spruce, but with silvery-bluish green needs. 

Hardy to Lower Zone 6 to upper Zone 7 cold hardiness limit to 0°F

Image of the species in its native habitat courtesy of California Polytechnic State University:

St. Lucia Fir (Abies bracteata) is a conifer that is highly-fire sensitive & only occurs in scattered stands in mostly Monterrey County, California (St. Lucia Mountains), south of San Francisco.  It cannot germinate in the open & is sensitive to the sun when young.  It likes deep canyons & streams with more consistently moist soil & shade with frequent fogs.  Only the Concolor Fir has lighter needles than this one.  It is the rarest fir in the world.

Image of tree in its native habitat courtesy of elkhornsloughctp.org, Bill Bisbee & Leor Pantilat.

This tree has a very unique cone that looks other-wordly (image courtesy of conifer.org):

They all represent more widespread populations thousands to millions of years ago & several of these represent spruces that were found much farther south than any native spruce stands exist now.

Note these spruces native to southeast Asia & how they will not tolerate too much cold, which varies from our current native U.S. & species. 

DRAGON SPRUCE

Picea asperata

Hardy to Lower Zone 6 to upper Zone 7 cold hardiness limit to 0°F

Picea asperata var. asperata — the typical variety, fully described here, growing throughout most of the range of the species
Picea asperata var. aurantiaca — Orange spruce, found locally in western Sichuan province.
Picea asperata var. heterolepis — Notch-scale dragon spruce, found locally in western Sichuan province.
Picea asperata var ponderosa — Big-cone dragon spruce, also found locally in western Sichuan province.

Image of the tree in its native habitat from graines-du-monde.be:

SARGENT SPRUCE 

Hardy to USDA Zone 8:  cold hardiness limit between 10° and 20°F

Picea brachytyla

This species is native to China — southern Gansu, southern Shaanxi, northwestern Hubei, western Sichuan, northwestern Yunnan and southeastern Xizang provinces; as well as northern Burma; and the Assam Himal of India. This species forms a prominent forest belt in moist mountains of southwestern China wet monsoonal climate with annual precipitation of 40 to 120 inches.

Image of species in its native habitat courtesy of wenbochenphotography.com

FARRER'S SPRUCE

Hardy to USDA Zone 9:  cold hardiness limit between 20° and 30°F

Picea farreri

This species is native to China — western Yunnan (Nu Jiang valley) province; as well as northern Myanmar (Fen-Shui-Ling valley).  In Myanmar, occurs in wet limestone mountains with heavy monsoon rains.

Image courtesy of EcuRed:

LIJIANG SPRUCE

Picea likiangensis

Hardy to USDA Zone 8:  cold hardiness limit between 10° and 20°F

This species is native to Bhutan; as well as China — southern Qinghai, south and western Sichuan, eastern Xizang (Tibet), and northwestern Yunnan provinces, growing in mountains, ravines, and river basins.

Photo courtesy of the American Confier Society & Chris Earle:

TAIWAN SPRUCE (southernmost spruce in the world)

Picea morrisonicola

Hardy to USDA Zone 8:  cold hardiness limit between 10° and 20°F

This species is native to Taiwan, in the central mountain range, in the vicinity of Yushan National Parkin ravines and mountain slopes.

Image courtesy of A. Farjon at Taroko National Park, Taiwan.

So What Happened to Our Own Warmer-Climate, More Temperature Spruce Species?

What made the Critchfield's Spruce go exinct in the Southeastern U.S.?

It is hard to say.  Competition from other species, disease or perhaps increased burning by Native Americans.  There were also multiple warm, dry "prairie periods" that promoted the expansion of the grassland ecosystem much farther eastward.  Eastern Hemlock, which is a tree that likes cool, moist forests greatly shrunk in range during these periods & oak & hickory proliferated (as did prairie plants).  With peak in Native American populations, there was also an increase in burning to encourage large herbivores for grazing.

A combination of all of these factors may have led to its demise, but obviously, this class of spruce species is hanging by a thread in North America, but doing better in China.

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