While we’re re-visiting bristlecones and foxtails, the Here are three interesting online articles, each of which discusses areas in the Sierra Nevada CA, which are now submerged, but where forests grew in the Medieval Warm Period. Many readers of this blog will have read articles about trees being disgorged from receding glaciers and it’s hard not to wonder about comparisons.Scott Stine, who has published in Nature about the phenomenon, has on line article here from 2001. Here is an interesting picture showing submerged medieval trees from Tenaya Lake, Yosemite National Park.



Picture from Stine article: Tenaya Lake, Yosemite National Park (elev. 8,150 ft). 1,000 years ago, trees grew in then-dry Tenaya Lake. Today only their tops show: still rooted in as much as 70 feet of water. Stine also discusses other well-dated medieval (G-1 AD1100) trees from Walker Lake, Mono Lake, the West Walked River, Owens Lake (desiccated in the MWP), Osgood Swamp near Lake Tahoe, Independence Lake north of Tahoe and Fallen Leaf Lake south of Lake Tahoe. Stine observed:

Indeed, increasing evidence indicates that there is little that is climatically “normal” about the past century – and- a-half; it appears, in fact, to be California’s third- or fourth-wettest century-scale period of the past four or more millennia. Since statehood, Californians have been living in the best of climatic times.

Philip Catarino, one of the divers cited by Stine, has a 2000 article online here. He observed:

During the last 500 years, a wet climate, punctuated by intermittent but substantial droughts, began to dominate the region, and lake levels again rose and cirques glaciers reformed in the Sierra. A series of substantial droughts are documented during this period, however. Dozens of submerged tree stumps are located up to 300 feet below the present day level of Donner Lake a tributary of the Truckee River; carbon –14 samples from one stump date from AD 1433 (Lindstrom and Bloomer 1994). Another warm period, documented by tree-ring studies and Truckee River run-off, dated between AD 1579-1585, and again around AD 1630 (Hardman and Reil 1936). It is possible that Lake Tahoe contributed relatively little water to the Truckee River during the last 200 years. During the century between the mid 1700s to mid 1800s, the level of Lake Tahoe may have been below its rim, with no water flow into the Truckee River. This is documented by a submerged stump in the Upper Truckee River Delta dating from AD 1720 (Lindstrom 1996a), one from Donner Lake dating from AD 1800 (Lindstrom and Bloomer 1994) and one in Emerald Bay dating to AD 1840 (Lindstrom 1992). The 40 years between AD 1875-1915 were the longest period during which the flow of the Truckee River was above the average. During the AD 1930s drought, Lake Tahoe ceased to flow from its outlet for six consecutive years. Drought within the last decade (late 1980s to 1990s) either stopped Tahoe’s flow into the Truckee or reduced it to almost nothing.

While there have only recently been rooted trees found in Fallen Leaf Lake, there is a considerable amount of avalanche debris located beneath the waters of the lake. The current trees have recently been sampled and the dating available in the fall of 1998. The size and scope of the tree discovered dwarfs all other trees that have been discovered in the Sierra. It appears to be a Jeffery Pine that is over 27.5 m tall and a diameter at breast height (dbh) of over 244 cm. It raises many questions on how severe a drought was that lowered the lake level by a 30.5 m and remained there long enough for a tree to root and grow this size before being submerged by a more wet climate regime.

Kleppe, 2005 here reported:

The author of this paper has discovered large trees rooted at a depth of 36.5 m (120′) below the existing surface level of Fallen Leaf Lake. Fallen Leaf is one of the major watershed areas for Lake Tahoe. Some of these trees measure over 30 m (98′) tall with a circumference of over 4.5 m (15′), which is an indication that they were over two hundred years in age when they died. The significance of this discovery is the fact that for these trees to be rooted below the surface of the lake, the lake must have been down at least 36.5 m for over two hundred years. ….The carbon dating of the raised tree samples indicated that the tree died in A.D. 1215 ± 40 years….

Evidence of these medieval droughts appears at many sites in and adjacent to the central Sierra, i.e., Mono Lake, Tenaya Lake, the West Walker River, Osgood Swamp (Stine, 1994), Fallen Leaf Lake (Kleppe and Norris, 1999; Kleppe, 2004), Lake Tahoe (Lindstrom, 1990), and Pyramid Lake (Benson and others, 2002). These recent studies of selected tree stumps rooted in present day lakes, marshes and streams, suggest that California’s Sierra Nevada experienced severe drought conditions for more than two centuries before 1112 A.D. and for more than 140 years before 1350 A.D. During these periods runoff from the Sierra was significantly lower than during any of the persistent “dry spells” that have occurred in the region over the past 150 years.

Here is a picture of a medieval tree recovered from Fallen Leaf Lake:



NAS panelist Franco Biondi, together with Kleppe and Scotty Strachan , has a 2005 poster entitled Underwater Dendrochronology of Sierra Nevada Lakes with the following nice picture of divers in 1990

They state:

The master chronology was formed by a total of 22 series from 16 different trees, and spanned the period AD 543-2003, or 1461 years, with sample depth à⣃¢’¬°à⣠3 series from AD 654.. For dendrochronological dating, we developed a western juniper (Juniperus occidentalis) reference chronology that spans the period from AD 543 to 2003. One underwater sample, i.e. a branch cross section cut from a standing tree, was crossdated with the master chronology for the period AD 1085-1153.

Obviously there have been a lot of hydrological changes in the Sierra Nevadas since the MWP.

References:

JOHN A. KLEPPE, ,2005. A study of ancient trees rooted 36.5 m (120′) below the surface level of Fallen Leaf Lake, California Journal of the Nevada Water Resources Association http://www.ee.unr.edu/downloads/nwra2005No3.pdf

P.R.Caterino, 2000. RECONSTRUCTING ANCIENT AVALANCHES OF THE SIERRA NEVADA RANGE. http://www.avalanche.org/~moonstone/ISSW%2098/caterino.htmLindstrom, Susan G. 1985. Archaeological investigations at Tallac Point (CA-ELD-184). U.S.F.S, LTBMU, South Lake Tahoe.

Lindstrom, Susan G. 1990. Submerged Tree Stumps as Indicators of Mid-Holocene Aridity in the Lake Tahoe Region. Journal of California and Great Basin Anthropology. 12(2):146-157. Malki Museum. Banning

Franco Biondi, John A. Kleppe, and Scotty Strachan 2005 Underwater Dendrochronology of Sierra Nevada Lakes http://woods.geography.unr.edu/Posters/FallenLeafLakePoster.pdf

Ccott Stine, 2001. The Great Droughts of Y1K, Sierra Nature Notes 1 http://www.yosemite.org/naturenotes/paleodrought1.htm



