Photo by M. Hamilton
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Deborah and I went out to Colorado a few weeks ago to visit our daughter and her husband in Greeley. Our son and his girlfriend also joined us, and we all had a great time complete with a day trip to some mountain hiking trails that we had explored 18 years ago on a family vacation. I kept my eyes open for some good blog topics, but other than a lake full of white, American pelicans and some unbelievable hail storms (3 or 4 inches of hail-ice on the road! Miles of sublimating ice-fog making roads almost impassable! Massive defoliation of trees (including a poor, indoor fig tree unintentionally left out on an uncovered patio during the storm!) ), everything was pretty “normal.” So, when in doubt, talk about trees!
Our home in Pennsylvania is a place of trees, the translation of the state’s name to “Penn’s Woods” tells you that. Flying over Pennsylvania or driving along its Interstate highways or country roads emphasizes the abundance and ubiquity of trees! Forests are everywhere! The original forests of the state represented the first in a long line of natural resources that the various colonial and then state governments of Pennsylvania gave away to economic interests. Only 5% of the state’s original forests escaped repeated logging over the past two hundred-plus years, and most of that 5% is in small, acre sized patches scattered across the commonwealth. The abundance of rainfall in Pennsylvania (average 41 inches/year) and the deep, fertile soils, and an abundance of hearty tree species have helped the state’s forests repeatedly recover from the destruction of clearcutting and mismanagement.
Photo by Colorado State Forest Service
Colorado, in contrast, does not seem to be a place extremely conducive to trees. Colorado is arid (15 inches of rain a year on average) with very uneven rainfall. The entire eastern half of the state gets 10 to 12 inches of rain per year while places in the mountains may get 35 to 40 inches of precipitation per year. You find trees in the places where water is available: along rivers and lakes, in sheltered valleys, and up on mountain slopes. Colorado cities also have lots of trees but only because of direct human intervention. The rest of the state is brush and rangeland (except where they are growing wheat, corn, hay, beans or sugar beets, and there irrigation is typically required to sustain the annual abundance of the biomass of the crop plants).
So the trees of Colorado must be trees of the mountains and trees of riversides.
Photo by M. Pixel
The state tree of Colorado is the Colorado blue spruce (Picea pungens). We saw some impressive blue spruces when we were up in Rocky Mountain National Park. Most of these trees were scattered out among some stately Ponderosa pines or bordered by dense stands of lodgepole pines or quaking aspens. The blue spruces thrive in the dry, short summers and cold, long winters of the Rockies. Colorado blue spruce has a very limited natural range, but because of its ability to grow in a wide range of environmental variables it has been planted as an ornamental tree far outside of its natural distribution! You can find blue spruces in urban and suburban landscapes all across North America and Europe. This past summer, for example, I was amazed to see blue spruces all over Prague, Czech Republic! The blue spruce is also one of the most commonly planted trees in Pennsylvania! Unfortunately, the long term health of many of these planted blue spruces is not very good. The long, hot, wet summers and short winters of these non-mountain climate zones have allowed all sorts of fungal diseases to take down many of the blue spruces (See Signs of Summer 12, August 3, 2017).
Blue spruces are not a terribly important timber tree. Its wood is light and full of knots. It also does not generate a great abundance of food for either seed eaters or browsers. It does provide, however, good cover for birds and many small mammal species. This tree is dominantly valued for its appearance and regularly makes top five or top ten lists of importance primarily because of its pleasing color and overall shape.
Photo by J. Westfall, NPS
Quaking aspens (Populous tremuloides) are the definitive hardwood tree of the mountains of the Middle Rockies. Quaking aspens have the broadest natural distribution of any tree in North America. Northern Pennsylvania is even included in the vast, continent-wide distribution of this species! It is a quick growing and relatively short-lived tree (100 to 150 years) that becomes quickly established after a fire. Quaking aspens reproduce by root sprouting and often form dense, clonal groves. They also produce air-transported, fluffy seeds that blanket the downwind areas from the mature aspen groves, although seed reproduction is not nearly as important to the species as root sprouting. When you see a stand of aspens it is possible that you are really looking at a single organism! The trees are not only genetic clones but are also highly interconnected via their roots. In southern Utah there is a 100 acre grove of quaking aspens that are one highly interconnected entity. This multi-tree organism weighs 14 million pounds and is estimated to be 80,000 years old!
Aspen groves are usually generated by fires. The quick growing aspens send up root suckers after a fire and assume a pioneering role for the successional forest sequence. It is interesting that aspen forests themselves are somewhat resistant to fires: the trees’ moist, green leaves and thick twigs resist burning, but if a fire does get established in an aspen grove the above ground trees are likely to be destroyed.
Under the aspens the slower growing pines and spruces are sheltered and protected. The deciduous nature of the aspens means that its forest floor receives more sunlight than a coniferous forest floor especially in the early spring. This allows a very vigorous growth of wildflowers and herbaceous plants in the aspen groves. Aspens forests are great places to look for wildflowers! Eventually, unless there is another fire (an increasingly likely event in our dry western ecosystems!) the conifers will grow up through the crowns of the aspens and shade them out
Public Domain
Along every river or creek and flanking every lake or reservoir are plains cottonwood trees (Populus deltoides). These cottonwoods are great, lumpy gray-barked trees of sometimes substantial girth that often rise up to 100 feet in height. Cottonwoods have thick, spreading branches that generate much needed shade and cover for a wide range of birds and mammals in the sun drenched plains of Colorado. The cottonwood trees release their eponymous “cotton” seeds in June generating snowdrifts of tumbling cotton fuzz for many miles around a stand of trees. The thick, deeply furrowed bark is resistant to fire and drought and the trees, which only live 80 to 100 years, can grow six feet in height a year in their early years of their lives. Cottonwoods often mark the edges of the scattered rivers and creeks that cross the dry high plains and were a welcome sight to early settlers announcing the presence of much needed water.
There are fifty native tree species in Colorado. I plan to be visiting the state rather frequently over the coming years. Watch for more posts, I’m just getting started!