Welcome to the Kirtland's Warbler GeoTrail (KWGT). This trail will take you in a loop in central Northern Michigan through the Jack Pine ecosystem, breeding home of the Kirtland's Warbler. This tour takes you to a total of 25 caches with an amazing trackable geocoin as a reward. The KWGT Passport can be downloaded here: https://f81c572e-1d95-4026-befc-8c60f69cbcd9.filesusr.com/ugd/31e003_41b2f3aa918442e8b08c880e746e6946.pdf
A microclimate is a set of local atmospheric conditions that differ from those in the surrounding areas, often with a slight difference but sometimes with a substantial one. The term may refer to areas as small as a few square feet or as large as many square miles. An example most people are familiar with is temperatures being cooler near a large body of water in warm months.
The cache brings you to an area of two flat glacial outwash plains separated by a slope that drops about 30 feet over a 330-foot distance. The highly drained, acid, nutrient poor, medium sands that make up the area, named Grayling Sand, were deposited by glacial meltwater when the Laurentide ice sheet was retreating. The glacial landforms of the area were built as a sequence of outwash terraces formed over one another during the Port Huron period of the Wisconsinan glaciation, approximately 13,300 to 12,500 years ago. The high-elevation landform developed as glacial meltwater flowed west to what is now the Lake Michigan basin. As the ice sheet retreated to the northeast, new drainage outlets were opened, and the western portion of the meltwater drainage system was abandoned. As a result, the meltwater began to flow east, cutting down into the terrace and forming the low-level landform.
A study of Jack Pine growth and landforms at the site showed significantly greater tree growth on the higher plain compared to the lower. Both landforms were similar in flatness and soil testing showed the soils were nearly identical (with over 95% similarity). The only difference between the landforms to explain this is the microclimate. The slope between the two allows cold air to flow from high to low. Temperature studies showed that the low area was significantly colder than the high. The ranges of temperature in each landform throughout the growing season show the extreme microclimate conditions that occur because of the topographic position of the landforms and subsequent downward cold-air flow. Remarkably, below-freezing temperatures were recorded in the low-elevation landform even in July and August. A comparison of microclimate data to the official weather data collected at Grayling suggests more extreme temperatures in the study area with the study area being characterized by a warmer than average microclimate in the high-elevation landform and a colder than average microclimate in the low-elevation landform.
The microclimate that affects tree growth also affects other living organisms. For example, Kirtland’s Warblers occupied the higher landform first, then moved into the lower area next. The lower area is also cold enough that almost no oaks grow there.
Cache
This was originally conceived as an EarthCache but was unfortunately denied. The habitat is from the Bald Hill Fire that was started by artillery fire on 10 May 1975.
Information for this cache was taken from: Kashian, D. M. 1998. Landscape ecosystems of northern Lower Michigan and the occurrence and management of the Kirtland’s Warbler. M.Sc. thesis, University of Michigan, Ann Arbor. 266 pp.