Tree of the Week for July 31st-August 7th, 2011: Picea engelmannii
I have recently returned to Maine from a long trip across the nation, visiting my family in Illinois and escorting my best friend to school in Colorado. I'll be spending the next few Tree of the Week entries discussing some characteristic Midwestern and Rocky Mountain trees. I begin this week with one from the West, a tree whose montane habitat is far from the daily experiences of most of us. It grows high on the chill slopes of the western mountains, looking down on the hot and droughty plains below. This noble tree, no stranger to snows that lie still on the ground in July, is the...
Engelmann Spruce, Picea engelmannii
Synonyms: Columbian spruce, mountain spruce, silver spruce, pino real (in Spanish), white spruce (a name normally saved for the related species P. glauca),
Native? Y, but in the west of the United States, not the east.
Range and Habitat: Engelmann spruce grows all along the major western mountain chains, from central British Columbia down to Arizona and New Mexico. The heart of its range is in the northern Rockies, in the cool valleys of eastern British Columbia, Idaho, and Montana. There it grows at comparatively low elevation, mostly from 5000 to 7500 feet, but occasionally as low as 2000 feet. As one moves further and further south it becomes restricted to higher and higher elevations, as high as 12,000 feet in the mountains that overlook the deserts of Arizona. Farther west, it may be found on the Cascades of Washington, Oregon, and British Columbia, but not on the mild Pacific-facing side. Instead, Engelmann spruce grows on the east side, on lower slopes (about 4000-6000 feet). It just barely crosses the border into far northern California, where it may be found less than a hundred miles from where the mighty coast redwoods grow serene and primal.
The narrow band that Engelmann spruce grows in is an area with specifics of summer heat, winter cold, and available moisture defined by its elevation and topography. It is the region that the great 19th-century naturalist C. Hart Merriam named the "Hudsonian Zone", in reference to the similarity between the climate here and that of the Hudson Bay region of Canada. The average annual temperature is just above freezing, and frost can occur during any month of the year. The zone receives ample precipitation - just 24 inches per year, but when you consider how little of that evaporates in such a cold climate, it seems ample enough. Within this zone it grows in the choicest locales, where the soil is relatively deep1 and moisture-filled. Engelmann spruce continues right on up to the treeline, though - about 11,500 feet in the Colorado Rockies - where it and subalpine fir (Abies lasciocarpa) grow as krummholz2.
Plant ID: It can be difficult for the newcomer to distinguish between the many and varied conifer species of the American west. The true pines and the larches are easy enough to pick out, but the various spruces, firs, junipers, false cedars, hemlocks, and Douglas-firs that grow dark and ominous across the mountain-slope are sure to confuse. But you may know the spruces at once from the true firs by the way that their cones depend from their branches, not ascending like the true firs3; and by their scaly bark, rather than the smooth but resin blister-encrusted bark of the true firs. And spruces may be told apart from all other western conifers by the way that their needles stand out on small woody pegs4. Telling the various spruce species apart, though, is a trickier matter. Fortunately, there are only 3 other spruces that grow near enough to P. engelmannii that they might be confused: P. pungens, the blue spruce, in the south; P. sitchensis, the Sitka spruce, in the far west; and P. glauca, the white spruce, in the north. The chief way that botanists distinguish these species are by obscure characteristics that frankly I cannot work myself up to bother looking at in the field, and so cannot expect my readers to do the same. But between environmental tells and some general characteristics a person can expect to ID the various spruces correctly more often than not.
Now, blue spruce shares the southern Rockies with Engelmann spruce, but they grow in different habitats. Blue spruce grows at lower altitudes than Engelmann spruce, and tends to be found on shallower slopes, as well. It loves the old filled-in beaver pond and the edges of winding streams, whereas Engelmann spruce prefers plummeting white water and subalpine meadows. Also, blue spruce has slightly longer cones (6-11 cm instead of 4-8 cm5), grayer bark, and needles that are not merely stiff and pointed, but are actually spiked at the tip! Lastly, blue spruce tends to be wider than the narrow-crowned exclamatory Engelmann spruce, but this is not a reliable difference.
In the far northwest of Engelmann's range, there are a few locales where its range overlaps with the Sitka spruce, that bizarre titan of the Pacific rainforest. Again, habitat is the best distinguisher, for Sitka spruce sticks mostly to the rain-soaked, ocean-facing lowlands, while the Engelmanns stick to the drier and colder mountains, particularly those peaks and valleys facing inland. Also, Sitka spruce's needles are distinctly flat in cross-section, whereas Engelmann sruce's needles are 4-sided. Although finding distinct needles to diagnose on a mature Sitka spruce, whose lowest branches might be 40 meters above the ground, may well be a challenge!
Finally, in much of Engelmann spruce's Canadian range, it overlaps with Picea glauca, familiar to my Maine readers as white spruce. This presents a more difficult case, for where the two trees overlap they hybridize freely. In general, once again, the higher up a mountain you are, the more pure-sapped of an Engelmann any given spruce will be, whereas the lower you are the more pure-sapped of a white spruce each tree will be. Looking at fine details, white spruce is slightly smaller in all parts of it anatomy, and the twigs of Engelmann spruce have more fine hairs than the often naked twigs of white spruce.
Ecology: Engelmann spruce's near-constant companion is the subalpine fir, Abies lasciocarpa. The two of them march up and down the Rockies together, forming a spruce-fir forest type similar to the balsam fir/red spruce type of northern New England and eastern Canada. Their chief enemy in the extreme elevations they grow is wind, especially the winter wind that can shred a tree to bits with blown ice dust. It is these wicked winds that cause the trees at the timberline to grow prostrate and crooked. Of the two species, Engelmann spruce is slightly less shade-tolerant and cold-tolerant than subalpine fir6, but I believe that the spruce is slightly faster-growing and longer-lived7. Certainly Engelmann spruce can achieve some tremendous ages - the above mentioned Forest Service publication claims that "dominant trees are often 350 to 450 years old, and 500- to 600-year-old trees are not uncommon".
The Rocky Mountain forests have been plagued in recent years by various problems traceable in large part to global warming. Rain comes more erratically, and long droughts are becoming more common. High in its mountain fastnesses, Engelmann spruce need not concern itself with these for the moment. The titan peaks it clusters around still reliably wring abundant rains from the atmosphere. But the summers do grow ever warmer, and this causes a different problem - insects. Insects are, in general, ectotherms, and so the longer and warmer summers allow them to be more active. The two species which are the most problematic are the spruce beetle, Dendroctonus rufipennis, and the western spruce budworm, Choristoneura occidentalis. The former is a beetle that burrows under the skin of the tree to lay its eggs in the inner bark. It has been absolutely devastating in Alaska in recent years, completely eliminating spruces from some areas8. The latter insect is a kind of moth, and a close relative to the eastern spruce budworm, C. fumiferana, that gives such nightmares to Maine foresters and loggers. Its principal food is the needles of the true firs, but during heavy infestations it will go after the needles of spruces as well. P. engelmannii is less resistant to budworm attacks than are some of our eastern spruces, like the red spruce, and so it suffers heavily in large outbreaks.
Uses and Silviculture: Like almost all spruces, the wood of P. engelmannii is of very high quality. Lightweight but strong, it is used frequently in construction, and select grades will go to make airplane parts and musical instruments9. However, its exploitation is limited by inaccessibility, and though it is still a major commercial species in the U.S., it is cut in rather smaller quantities than one would expect from its wide range. But those trees not cut are still of immense value. Though their needles are nigh-inedible for vertebrates, the trees themselves provide homes for many species. The caverns in the trunks of superannuated individuals are nests for a variety of birds and small mammals; their shade provides respite from summer heat and deep winter snows alike; the damp, dark environment beneath their boughs is an excellent environment for many wildflowers and berry plants; and their seed cones are devoured by migrating birds and cached for winter by hungry and far-sighted squirrels.
Of more obvious importance than this is its help protecting the watersheds of the rivers that feed the droughty plains below. While on the one hand the Engelmann spruce decreases the total amount of water reaching the lowlands by transpiring much of it back into the atmosphere, it also helps to regulate the water's flow. By preserving millions of tons of high-altitude soil, the spruce prevents great floods from sweeping down from the mountain immediately after the snows melt and ensures that there is still water to be found in the riverbeds even when the August heat and drought are at their worst. Without this regulatory function, cities such as Denver would be, at best, much more expensive for their citizens to maintain, and at worst impossible.
Big Tree: The Gymnosperm Database lists the largest living Engelmann to be one growing in British Columbia that is 220 cm (7 ft 2 in) in diameter and 41 m (134 1/2 ft) tall. Though this one wins the overall contest, taller spruces are relatively easy to find, and one growing in Washington towers a full 67 m (220 ft) from toe to top - taller than any living tree east of the Mississippi! As mentioned in a previous section, Engelmann spruces can reach quite impressive ages, especially in the high mountains, and the Gymnosperm Database (again) lists the oldest being a 911-year old tree found in Colorado in 1995. Imagine - when this tree germinated, William the Conqueror's servants had just finished compiling the Domesday Book; nearer to the tree's home, the Anasazi were still dwelling in their great stone cities amidst piñon and corn.
Taxonomy: Reading around on the Gymnosperm Database, I find that the current theory is that the spruces evolved somewhere in western North America just after the end of the Cretaceous period. Rather amusingly, despite the near-universal association of spruces and firs (here in Maine, the pairing comes almost automatically - I hear "spruce" and mentally fill in the "/fir"), it is believed that the closest relatives of the spruces are actually the true pines of the genus Pinus. All of these mentioned conifers are members of that most prolific of northern conifer families, the Pinaceæ or Pine family. It is one which needs no introduction, I feel, so complete is its domination of the cold forests of the north. Pine, spruce, fir, larch, hemlock, douglas-fir...just to name them is to evoke the vanillic whiff of pine sap and the sound of a cold brook babbling towards some clear-watered lake.
Evoking the vanillic whiff of pine sap since 1986,
--mark
1Not that the soil is anywhere very deep in the high mountains!
2Literally, "crooked wood". Image courtesy of the good people over at The Gymnosperm Database.
3Image courtesy of the Trees of Wisconsin: Abies balsamea page at the University of Wisconsin - Green Bay.
4Image courtesy of Jeffrey S. Pippen of Duke University.
5Information again from the Gymnosperm Database.
6At least according to the Forest Service's Fire Ecology publication.
7This is really more of an educated guess than anything I've read in a published source I can remember, so take it with a grain of salt!
8According to Wikipedia, anyway.
9This information taken from the Forest Service again.
Engelmann Spruce, Picea engelmannii
Synonyms: Columbian spruce, mountain spruce, silver spruce, pino real (in Spanish), white spruce (a name normally saved for the related species P. glauca),
Native? Y, but in the west of the United States, not the east.
Range and Habitat: Engelmann spruce grows all along the major western mountain chains, from central British Columbia down to Arizona and New Mexico. The heart of its range is in the northern Rockies, in the cool valleys of eastern British Columbia, Idaho, and Montana. There it grows at comparatively low elevation, mostly from 5000 to 7500 feet, but occasionally as low as 2000 feet. As one moves further and further south it becomes restricted to higher and higher elevations, as high as 12,000 feet in the mountains that overlook the deserts of Arizona. Farther west, it may be found on the Cascades of Washington, Oregon, and British Columbia, but not on the mild Pacific-facing side. Instead, Engelmann spruce grows on the east side, on lower slopes (about 4000-6000 feet). It just barely crosses the border into far northern California, where it may be found less than a hundred miles from where the mighty coast redwoods grow serene and primal.
The narrow band that Engelmann spruce grows in is an area with specifics of summer heat, winter cold, and available moisture defined by its elevation and topography. It is the region that the great 19th-century naturalist C. Hart Merriam named the "Hudsonian Zone", in reference to the similarity between the climate here and that of the Hudson Bay region of Canada. The average annual temperature is just above freezing, and frost can occur during any month of the year. The zone receives ample precipitation - just 24 inches per year, but when you consider how little of that evaporates in such a cold climate, it seems ample enough. Within this zone it grows in the choicest locales, where the soil is relatively deep1 and moisture-filled. Engelmann spruce continues right on up to the treeline, though - about 11,500 feet in the Colorado Rockies - where it and subalpine fir (Abies lasciocarpa) grow as krummholz2.
Plant ID: It can be difficult for the newcomer to distinguish between the many and varied conifer species of the American west. The true pines and the larches are easy enough to pick out, but the various spruces, firs, junipers, false cedars, hemlocks, and Douglas-firs that grow dark and ominous across the mountain-slope are sure to confuse. But you may know the spruces at once from the true firs by the way that their cones depend from their branches, not ascending like the true firs3; and by their scaly bark, rather than the smooth but resin blister-encrusted bark of the true firs. And spruces may be told apart from all other western conifers by the way that their needles stand out on small woody pegs4. Telling the various spruce species apart, though, is a trickier matter. Fortunately, there are only 3 other spruces that grow near enough to P. engelmannii that they might be confused: P. pungens, the blue spruce, in the south; P. sitchensis, the Sitka spruce, in the far west; and P. glauca, the white spruce, in the north. The chief way that botanists distinguish these species are by obscure characteristics that frankly I cannot work myself up to bother looking at in the field, and so cannot expect my readers to do the same. But between environmental tells and some general characteristics a person can expect to ID the various spruces correctly more often than not.
Now, blue spruce shares the southern Rockies with Engelmann spruce, but they grow in different habitats. Blue spruce grows at lower altitudes than Engelmann spruce, and tends to be found on shallower slopes, as well. It loves the old filled-in beaver pond and the edges of winding streams, whereas Engelmann spruce prefers plummeting white water and subalpine meadows. Also, blue spruce has slightly longer cones (6-11 cm instead of 4-8 cm5), grayer bark, and needles that are not merely stiff and pointed, but are actually spiked at the tip! Lastly, blue spruce tends to be wider than the narrow-crowned exclamatory Engelmann spruce, but this is not a reliable difference.
In the far northwest of Engelmann's range, there are a few locales where its range overlaps with the Sitka spruce, that bizarre titan of the Pacific rainforest. Again, habitat is the best distinguisher, for Sitka spruce sticks mostly to the rain-soaked, ocean-facing lowlands, while the Engelmanns stick to the drier and colder mountains, particularly those peaks and valleys facing inland. Also, Sitka spruce's needles are distinctly flat in cross-section, whereas Engelmann sruce's needles are 4-sided. Although finding distinct needles to diagnose on a mature Sitka spruce, whose lowest branches might be 40 meters above the ground, may well be a challenge!
Finally, in much of Engelmann spruce's Canadian range, it overlaps with Picea glauca, familiar to my Maine readers as white spruce. This presents a more difficult case, for where the two trees overlap they hybridize freely. In general, once again, the higher up a mountain you are, the more pure-sapped of an Engelmann any given spruce will be, whereas the lower you are the more pure-sapped of a white spruce each tree will be. Looking at fine details, white spruce is slightly smaller in all parts of it anatomy, and the twigs of Engelmann spruce have more fine hairs than the often naked twigs of white spruce.
Ecology: Engelmann spruce's near-constant companion is the subalpine fir, Abies lasciocarpa. The two of them march up and down the Rockies together, forming a spruce-fir forest type similar to the balsam fir/red spruce type of northern New England and eastern Canada. Their chief enemy in the extreme elevations they grow is wind, especially the winter wind that can shred a tree to bits with blown ice dust. It is these wicked winds that cause the trees at the timberline to grow prostrate and crooked. Of the two species, Engelmann spruce is slightly less shade-tolerant and cold-tolerant than subalpine fir6, but I believe that the spruce is slightly faster-growing and longer-lived7. Certainly Engelmann spruce can achieve some tremendous ages - the above mentioned Forest Service publication claims that "dominant trees are often 350 to 450 years old, and 500- to 600-year-old trees are not uncommon".
The Rocky Mountain forests have been plagued in recent years by various problems traceable in large part to global warming. Rain comes more erratically, and long droughts are becoming more common. High in its mountain fastnesses, Engelmann spruce need not concern itself with these for the moment. The titan peaks it clusters around still reliably wring abundant rains from the atmosphere. But the summers do grow ever warmer, and this causes a different problem - insects. Insects are, in general, ectotherms, and so the longer and warmer summers allow them to be more active. The two species which are the most problematic are the spruce beetle, Dendroctonus rufipennis, and the western spruce budworm, Choristoneura occidentalis. The former is a beetle that burrows under the skin of the tree to lay its eggs in the inner bark. It has been absolutely devastating in Alaska in recent years, completely eliminating spruces from some areas8. The latter insect is a kind of moth, and a close relative to the eastern spruce budworm, C. fumiferana, that gives such nightmares to Maine foresters and loggers. Its principal food is the needles of the true firs, but during heavy infestations it will go after the needles of spruces as well. P. engelmannii is less resistant to budworm attacks than are some of our eastern spruces, like the red spruce, and so it suffers heavily in large outbreaks.
Uses and Silviculture: Like almost all spruces, the wood of P. engelmannii is of very high quality. Lightweight but strong, it is used frequently in construction, and select grades will go to make airplane parts and musical instruments9. However, its exploitation is limited by inaccessibility, and though it is still a major commercial species in the U.S., it is cut in rather smaller quantities than one would expect from its wide range. But those trees not cut are still of immense value. Though their needles are nigh-inedible for vertebrates, the trees themselves provide homes for many species. The caverns in the trunks of superannuated individuals are nests for a variety of birds and small mammals; their shade provides respite from summer heat and deep winter snows alike; the damp, dark environment beneath their boughs is an excellent environment for many wildflowers and berry plants; and their seed cones are devoured by migrating birds and cached for winter by hungry and far-sighted squirrels.
Of more obvious importance than this is its help protecting the watersheds of the rivers that feed the droughty plains below. While on the one hand the Engelmann spruce decreases the total amount of water reaching the lowlands by transpiring much of it back into the atmosphere, it also helps to regulate the water's flow. By preserving millions of tons of high-altitude soil, the spruce prevents great floods from sweeping down from the mountain immediately after the snows melt and ensures that there is still water to be found in the riverbeds even when the August heat and drought are at their worst. Without this regulatory function, cities such as Denver would be, at best, much more expensive for their citizens to maintain, and at worst impossible.
Big Tree: The Gymnosperm Database lists the largest living Engelmann to be one growing in British Columbia that is 220 cm (7 ft 2 in) in diameter and 41 m (134 1/2 ft) tall. Though this one wins the overall contest, taller spruces are relatively easy to find, and one growing in Washington towers a full 67 m (220 ft) from toe to top - taller than any living tree east of the Mississippi! As mentioned in a previous section, Engelmann spruces can reach quite impressive ages, especially in the high mountains, and the Gymnosperm Database (again) lists the oldest being a 911-year old tree found in Colorado in 1995. Imagine - when this tree germinated, William the Conqueror's servants had just finished compiling the Domesday Book; nearer to the tree's home, the Anasazi were still dwelling in their great stone cities amidst piñon and corn.
Taxonomy: Reading around on the Gymnosperm Database, I find that the current theory is that the spruces evolved somewhere in western North America just after the end of the Cretaceous period. Rather amusingly, despite the near-universal association of spruces and firs (here in Maine, the pairing comes almost automatically - I hear "spruce" and mentally fill in the "/fir"), it is believed that the closest relatives of the spruces are actually the true pines of the genus Pinus. All of these mentioned conifers are members of that most prolific of northern conifer families, the Pinaceæ or Pine family. It is one which needs no introduction, I feel, so complete is its domination of the cold forests of the north. Pine, spruce, fir, larch, hemlock, douglas-fir...just to name them is to evoke the vanillic whiff of pine sap and the sound of a cold brook babbling towards some clear-watered lake.
Evoking the vanillic whiff of pine sap since 1986,
--mark
1Not that the soil is anywhere very deep in the high mountains!
2Literally, "crooked wood". Image courtesy of the good people over at The Gymnosperm Database.
3Image courtesy of the Trees of Wisconsin: Abies balsamea page at the University of Wisconsin - Green Bay.
4Image courtesy of Jeffrey S. Pippen of Duke University.
5Information again from the Gymnosperm Database.
6At least according to the Forest Service's Fire Ecology publication.
7This is really more of an educated guess than anything I've read in a published source I can remember, so take it with a grain of salt!
8According to Wikipedia, anyway.
9This information taken from the Forest Service again.