Chad's Garden: Colorado Blue Spruce & the Weather

Blue Spruce is a Rocky Mountain species that is a popular ornamental in our area & beyond. Recent story ran regarding how we are losing them & that you should not plant them anymore. Is this correct? What is behind this?

Posted: Jul 24, 2020 5:59 PM
Updated: Jul 24, 2020 11:29 PM

We had run a story out of a station in South Bend several weeks back regarding disease outbreak underway with Blue Spruce right now.  One nurseryman recommended not planting Blue Spruce anymore due to this factor & its seemingly inability to adapt to our climate.  A host of pathogens are causing decline at the moment (as it has been in the past) tied to our wet springs & summer with very high dew points.

We have long known that Blue Spruce is susceptible to disease outbreaks, this is nothing new. 

Disease outbreaks occur in many species, native to our area, or not.  For example, native Tuliptrees are susceptable to drought from just lack of water, but also a fungal infection in such years.  In fact, not only does it defoliate when topsoils dry, it also is subject to outbreak of fungal disease during drought that cases substantial dieback of the foliage & may kill the tree.

Outbreak occurred in the 2012 drought (especially in southern Indiana), in 2011 & in 2007, recently.

Also, I remember a large amount of pole-sized Red Pine my grandfather had planted back in the 1960s died out in the 1988 drought when the trees were susceptible to blister disease.  85% were lost, but only one or two have been lost since 1988 & the current ones still look good.

The factor behind outbreaks of disease in Blue Spruce right now has to do with the weather that we had last year & the two years prior.  They were very wet in the spring & summer with very high humidity with many instances of dew points in the mid to upper 70s.  Those are the conditions that Blue Spruce does not do well.  It is not adapted to our climate due to its native range being in the Rockies.

However....................disease susceptibility seems to also be tied to Blue Spruce genetics & does not affect all the trees the same way.

Where did the seed come from of the Blue Spruce in your yard?  Where did the genetics come from?

When we look at a Blue Spruce native range map (below), we can see that it is native in the counties from mountains of southern New Mexico to Idaho & Wyoming.

Where it is most common in range (Colorado & Wyoming), it is a co-dominant species at 5,000-9,000' with native stands of Concolor Fir, Corkbark Fir, Engleman Spruce, Rocky Mountain Douglas-fir, as well as Narrowleaf Cottonwood, Gambel Oak, Rocky Mountain Maple, willow species & Mountain Alder.  It like deeper colluvial & alluvial, loose soils sandy-loam soils on lower, northerly slopes of canyons & ravines, often near & along mountain streams.  Seedlings must have a good water supply for the first several years of life. 

It is likely limited away from southerly & other slopes & other areas of the Rockies by fire frequency that is more conducive to Ponderosa & Lodgepole Pine.  Blue Spruce is highly fire-sensitive.

Overall, all of the native populations have been found to occur anywhere from 5,000-12,000' in elevation over its range.

Not only that, but its distribution covers a large geographic area with varying soil types, growing season length, magnitude of heat & cold & rock/parent material types.  There are also remote pockets of populations separated from each other by mountains & wildfire frequency across the Blue Spruce's range.

Specimens may be very tall, lush forest trees or may be short, fatter & more shrubby & squatty at the highest elevations in more northerly latitudes in the Rockies.

As a result, considerable genetic variability exists.  An example is Douglas-fir in the Rockies & Sierras.  It is split into three subspecies (now considered separate species of D-F) due to many of these same factors.

Growing seasons & conditions vary from the chimney of Idaho to nearly the Mexican border.  

With such variability different genotypes have evolved to be adapted to their environment.  Whether be the reaction to competition, or its reaction to heat, cold, drought, Blue Spruce is not like a species that is completely uniform over a level plain.  

As a result, the trees in a nursery will vary in their performance at your home.  It is unclear where the seed & genes originate.  Are they from high mountains of Wyoming originally?  Are they from lower terrain along a moist stream with cottonwoods in New Mexico?  Are they on a highly-calcareous soil in Utah?  Are they from the pocket populations that have evolved in northern Idaho?  Or, do they come from 7,000' in a spruce-fir forest in a central Colorado canyon nestled between 10,000' peaks?

Most Blue Spruce likes slightly acidic soil, but a couple populations of Blue Spruce in Utah grow & thrive on calcareous limestone.  

Not only that, but now nurseries offer 38 horticultural varieties from natural adaptions & mutations that have occurred in their natural environment & different genotypes have been pollinated.

Colorado Blue Spruce will continue to be a favorite landscape tree & has been for decades & decades.  How long it survives in your yard or if it is supremely adapted to your home is dependent on the genetics (outside of your soil type, care, chemical use, etc.).

In this study:

Bongarten, B. C.; Hanover, J. W. 1986. Provenance variation in blue spruce (Picea pungens) at eight locations in the northern United States and Canada. Silvae Genetica. 35(2-3): 67-74.

It was found that Colorado Blue Spruce growth rate decreased the farther north the tree was grown away from its latitude of parent range.  However, it is not clear the elevation at which the seed was collected, which is likely a big factor.

Colorado Blue Spruce forest near Telluride, Colorado on a slope toward stream & canyon with some Narrowleaf Cottonwoods (photo courtesy of the American Conifer Society):

Colorado Blue Spruce in New Mexico (image courtesy of Western New Mexico State University):

Colorado Blue Spruce in southwestern New Mexico's Mogollan Mountains (image courtesy of Western New Mexico State University):

Tree near Salt Lake City, Utah (photo courtesy of W. Mark and J. Reimer & Urban Forest Ecosystems Institute):

 Tree in Colorado (image courtesy of Colorado State University):

Tree at Ramsey Canyon Preserve in southeastern Arizona near U.S.-Mexican border.  This preserve is very interesting in its shorter, bright, bright blue Blue Spruce genotype (due to much more wax on the needles).  Area is at an "ecological crossroads", where the Sierra Madre of Mexico, the Rocky Mountains, and the Sonoran and Chihuahuan desert ecosystems all merge (image courtesy of rwstorm & hikearizona.com)

Bright blue, narrow, conical tree southwest of Flagstaff, Arizona in the Mogollan Rim (image courtesy of hikearizona.com & Brad Shaw):

Colorado Blue Spruce in its habitat in Colorado (image courtesy of uncovercolorado.com & Kristen Bobb):

Old-growth Colorado Blue Spruce in Colorado (courtesy of American Forests organization):

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