The Paleoclimate of Blackhawk, Colorado (CU's Science Discovery Program)

The research site simulated in this activity is the Eiven Jacobson farm outside the town of Blackhawk, Colorado. It is located on the Peak to Peak Highway at an elevation of 9002 feet.

In a valley on the farm, a peat bog developed over the centuries. Through carbon-14 dating of the sediment layer and pollen samples, the paleoclimate of this area of Colorado has been established. The peat bog and soils underneath it have been in existence for eons and have accumulated sediments over time. Trapped in these sediments are pollen grains from a variety of plants that grew in the area at the time the sediments were deposited. By examining the sediments from the bottom to top (oldest to youngest), we can reconstruct the vegetation changes that occurred in the farm's area during the last several thousand years. Because we know something of the climatic conditions that these plants need to survive, we can use the vegetation data to reconstruct the past climate in this area for the last 10,000 years. As climate changes with time, so do the plant communities. Plant communities will migrate up the mountains during the warming periods and fall back down again as the climate cools. The tree line changes in conjunction with this shift, perhaps helping us understand why there are ancient bristlecone pines on Mt. Evans (elevation 14,000+ feet).

Layer

Time Period

Description

#1

150 Years Before Present (ybp) - Present

As our temperatures warm from the Little Ice Age, the plants change as well, back to those that thrive in warmer climates. Today at approximately 9000 feet, we find ponderosa pines, meadow grasses, wildflowers, and aspens, which are all indicative of the milder climate we are experiencing.

#2

650 - 150 ybp

The term "Little Ice Age" gives us an idea of a change that began to happen climatically at this time. Gone were the warm days of the Medieval Warming Period and the big chill set in; cooler temperatures were the norm. Once again the Engelmann spruce and limber, lodgepole, and bristlecone pines dotted the landscape.

#3

1,500 - 650 ybp

This period is termed the "Medieval Warming Period." No longer do the spruces and cold-tolerant plants dominate the landscapes. The vegetation is also shifting with the change in temperatures. Now the landscapes primarily consist of ponderosa pines, Douglas fir, meadow grasses, and wildflowers.

#4

3,500 - 1,500 ybp

A cooler and moister period succeeds the past warmer climate. The predominant vegetation species are Engelmann spruces, limber, lodgepole, and bristlecone pines, aspen, and wet peat plants, such as sedges, willows, and mosses. At about 2,000 ybp, the peat from the Jacobson's peat bog began to develop and grow in this cooler, wetter climate.

#5

8,000 - 3,500 ybp

This was a warmer era, with the vegetation dominated by Douglas fir, ponderosa pine, aspen, meadow grasses, and wildflowers, similar to what we see now on the Jacobson farm. These species tend to grow best under temperate, somewhat moist conditions. Forest fires were also quite prevalent during this time.

#6

10,000 - 8,000 ybp

The period right after the last glacier was a very cold time with gradual warming. The cold temperatures at the end of the Pleistocene period were giving way to the warming trends of the Holocene. The era was characterized by a very short growing season. The landscape resembled an arctic/alpine tundra, with the meadows dominated by alpine grasses, daisies, alpine sage, and sedges. Scatter trees, the cold-tolerant Engelmann spruce, some willows, and aspens began to appear toward the end of this period in scattered tree islands.

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