Adaptations & Interactions
The Colorado Blue Spruce is a very adaptable species that can withstand quite drastic changes within its environment. The Spruce displays positive phototropism as well as negative gravitropism (or geotropism) in its stem as it reaches towards the light out of the seed. The roots of the tree on the other hand display negative phototropism (they move away from the light) and positive gravitropism (they move toward gravity). Using these stimuli the Blue Spruce tree is able to sense the environment around it and react however it deems necessary. The Colorado Spruce is found growing in mountain valleys, but chiefly found near streams, where moisture levels of the soil are high. The strong, adaptable roots of the Spruce can even withstand changes in pH and even drought (up to a certain point).
Interactions between P. pungens and other species are numerous and come in all varieties (mutualism, commensalism, etc.). As review, mutualism benefits both organisms, commensalism is a symbiotic relationship where one species benefits while the other is unaffected, and in parasitism one species benefits and the other is harmed.
It has been estimated that upwards of 70% of all land plants form mutualistic relationships with mycorrhizal fungi, one of the most important associations the plant has. In the pine family the majority of the fungi are classified as ectomycorrhizae. The relationship that takes place beneath the soil, where ectomycorrhizae surround the cells in the roots of their spruce substrate with hyphae, proves advantageous for both sides. The attached mycorrhizae increase the surface area of the roots of the plant, and also allow for transportation of nutrients and minerals from plant to fungus.
The Colorado Blue Spruce provides homes for many creatures. Spruce Grouse or Falcipennis canadensis lives strictly in conifer forests, taking refuge and nesting in spruce trees. These fowl rely on the Spruce for safety, protection, occasionally food, and reproduction (taking care of their eggs). Spruce trees get nothing in return and therefore this relationship is considered commensal.
Some of the Colorado Spruce’s main predators are man and the destruction of forests and cutting down of trees. Humans use the Blue Spruce for landscaping, and other ornamental reasons, because of its vibrant blue color! Use of the Colorado Spruce around the country as a Christmas tree is another popular application. Other relationships are parasitic among the Blue Spruce and insects, and also fungus.
Ips hunteri has recently become an important pest of drought-stressed Blue Spruce in urban and residential areas of Colorado. This insect has also killed native Colorado Spruce stands in forested regions throughout the western U.S. Several other pests, of which spider mites are the worst, contribute to the decline in new growth during mid-Summer times. P. pungens can also be infected with several diseases. Some of the more severe include Rhizosphaera Needlecast and Cytospora Canker.
Rhizosphaera Needlecast is a disease that affects P. pungens, primarily in New Mexico. This plant disease is caused by the fungus Rhizosphaera kalkhoffii which mainly targets trees not grown in their natural habitat. The fungus does not kill the tree but merely limits the spruce to carry only the needles from the current year. Rhizosphaera needlecast infects needles on the lower branches first and then works its way up to the top. Contaminated needles turn a purplish brown color as fruiting bodies of the fungus protrude out from stomatal openings.Cytospora Canker species are a couple of few cankers that affect the Blue Spruce. The others, Fusarium circinatum, Sphaeropsi sapinea and Siroccus conigenus are much less fatal. Cytospora canker is caused by the fungus Leucostona kunzei and is the number one killer of Picea pungens affecting a large number of trees over 15 years old and specifically targeting trees grown outside of their native range. Although the canker does not always kill the tree, it most always leads to significant dieback and reduces the overall aesthetic quality. First signs of Cytospora canker include browning and dying of lower leaves. As the disease develops it moves up the tree and into higher branches. Ultimately needles fall off and branches become dry and brittle. Frequently amber, purplish white or white patches form on the bark in the presence of cankers and underneath these patches are the fruiting bodies of Leucostona kunzei. For a great picture of Cytospora Canker click here