Animals & Aspen

Biodiversity

"The aspen ecosystem is rich in number and species of animals, especially in comparison to associated coniferous forest types.

The aspen forest type produces an abundance of forage, as much as many grasslands and more than 10 times that produced under associated conifers. ..." - USDA: Forest Service

Birds

"... Aspen trees produce long fruit capsules filled with small seeds, which are attractive to birds. Some birds will also eat Aspen leaf buds. The Aspen plays host to a large number of insects and caterpillars (which will in turn attract insectivorous birds). The Yellow-Bellied Sapsucker is known to frequent Aspen trees due to its sap content and for nesting purposes. Aspen trees are also commonly used by other cavity and branch-nesting birds." - Exploring Birds: Birds Attracted to Aspen 

"Many birds eat its twigs and buds. ... Grouse rely on its winter buds.  In the scarcity of winter, many animals will eat its bark. Cavities develop in these trees due to its susceptibility to fungus.  This provides homes and shelter to woodpeckers, owls, squirrels and other wildlife." - Precious Prairie Plants: Aspen

Insects

"... Aspen trees attract a wide variety of insects, including two species of gall midge and the aspen hoverfly which feeds on microorganisms in dead aspen wood." - Woodland Trust: Aspen

Aspen Hoverfly

This endangered species is reliant on aspens. It ranges across Alaska, Canada, and some northern states of the USA.

"The Aspen hoverfly (Hammerschmidtia ferruginea) is a red-listed species which is represented by a UK BAP (Biodiversity Action Plan). This type of hoverfly is defined as a  ‘flagship’ species , which means that by conserving them, other species will also benefit. The Aspen Hoverflys stronghold within the UK is Strathspey in Scotland. Populations of Hammerschmidtia ferruginea can be found along the Spey Valley between Kingussie, Easterness and Grantown; with a stronghold on Insh Marshes RSPB reserve site (opposite side of the Spey River from Kingussie). Their breeding habitat is Aspen (Populus tremula) woodland, including birch or pine woods with an aspen component." - FSC Biodiversity Projects: Conserving Aspen Hoverfly

Aspens & Fire

"Fire is a natural feature in much of the aspen ecosystem of western North America. It is responsible for the abundance of aspen in the West and for the even-aged structure of most stands. In some areas, many aspen stands are the same age, dating from a single great fire or a year of widespread fires. Fire appears to be necessary for the continued well-being of aspen on most sites. Many aspen stands are replaced by grass, forbs, shrubs, or conifers in the absence of fire.

Aspen is considered a fire-induced successional species that will dominate a site until it is replaced by less fire-enduring and more shade-tolerant species, such as conifers; provided a coniferous seed source is present. Fire reduces the overstory, stimulates shoots to sprout, and kills invading conifers growing in the aspen clone. Since aspen can sprout from existing roots and these suckers grow faster than the new slowing growing conifers, aspen can dominate in a grove for many years after a fire. Otherwise, aspen can be replaced relatively quickly by conifers, within 100-200 years, or the replacement may be slower taking more than 1,000 years.

Aspen forest does not readily burn. Aspen trees have moist green leaves and thick twigs that do not burn easily, unlike conifers, which have dry needles and twigs. Crown fires running through coniferous forest drop to the ground when they come to an aspen stand and may even extinguish after burning into the aspen only a few yards. Fires sometimes bypass stands of aspen enclosed within coniferous forest.

Although aspen forests do not burn readily, aspen trees are extremely sensitive to fire. A fire intense enough to kill the aspen overstory will stimulate abundant suckering, though some suckers arise after any fire. As many as 50,000 to 100,000 suckers can sprout and grow on a single acre after a fire.

Over time, the aspen suckers in a grove that emerge following a fire will slowly thin themselves. After 20 or 30 years, the aspen grove will have just about as many aspen trees as it did before the fire. As the aspen grove returns to the burned area, so do the plants and animals that depend upon them for their habitat. 

If fire occurs at infrequent intervals (e.g., 50 years) and is moderately intense enough to kill most or all of the aspen and competing conifers, most aspen sites in the West will retain viable stands of aspen. More frequent fires may adversely affect site quality for aspen. Complete fire protection, however, will permit coniferous species to take over the majority of sites." - USDA: Forest Service

Logging

"Between logging for fuel, building, and pulp, and clearing for agriculture, the area of aspens declined dramatically in the nineteenth, twentieth and twenty-first centuries." - Precious Prairie Plants: Aspen

Health Issues

Fungi

"Poplar species such as aspen can be prone to a variety of fungal diseases, including cankers, leaf rusts and poplar scab." - Woodland Trust: Aspen

SAD "Sudden Aspen Decline" 

"Something seems to be happening to the aspens that paint the hills gold every autumn, leaving bald patches across the Rocky Mountain West. Some aspen stands are not recovering from disturbance and naturally regenerating the way they have in the past. The mystery of the aspen decline deepens as it seems to be occurring only in some stands and in some Western states and is not affecting any neighboring trees, though many of these have been affected by mountain pine beetle attacks. Forest scientists are working to figure out what is happening to the aspen groves.

The aspen decline has been most noticeable in southwestern Colorado, northern Arizona, and parts of Utah and Canada, but is also in Idaho, Nevada, Montana, and southern Wyoming. However, different processes or causes may be leading to the various aspen declines across the West.

For decades, forest managers have called attention to "aspen decline," a long-term reduction in area of aspen forests.  It was considered to be the result of reduced fire frequency, which allowed succession to conifer forests; and heavy browsing by large ungulates, which prevented the regeneration of aspen in burned or harvested forests.  Other researchers, however, say there is no conclusive evidence of a long-term aspen decline when presettlement conditions are considered. For example, some make the case that the number of aspen in Colorado actually has increased in the past century. They point to historical data that indicates widespread disturbance caused by timber harvesting and fires in the late 1800s and early 1900s may have enabled aspen to become abundant in the Rocky Mountains. Natural processes of succession should result in a reduction of aspen as that cohort matures and dies. Other studies have suggested that aspen decline occurs at local scales, but readily persists at larger landscape scales.

More recently, however, "sudden aspen decline" (SAD) has been reported.  As of 2007, widespread, severe, rapid dieback and mortality had affected about 13 percent of the aspen in Colorado. SAD is different from what is traditionally referred to as aspen decline. It is occurring on a landscape scale, versus the stand-level changes that are typically noted with aspen forest related to disturbance and succession. The mortality is rapidly occurring over a few years, versus the typical changes occurring over decades. In addition, pathogens and insects associated with SAD are different from those usually associated with aspen mortality in Colorado. Evidence indicates that warm drought conditions earlier in the decade played a primary inciting role, that certain stand and site factors predisposed aspen to damage, and that the pathogens and insects are killing stressed trees.

An accelerated dieback of aspen was also observed across northern Arizona following two defoliation events and several years of drought. A secondary disease and/or insect was found to be associated with the dying trees as well, including canker fungi, wood borers, and clear wing moths. Aspen regeneration by suckering was observed after the dieback, but little of it remained after heavy ungulate browsing. The extensive dieback and ungulate browsing of the aspen suckers is expected to result in forest type conversions, from aspen to conifer, in many of these sites across the state.

Aspen reproduce primarily by sprouting from root systems, rather than spreading seeds. Each "clone" can live hundreds or even thousands of years. A stem may die, but beneath the soil, the root sends out fresh shoots, and the cycle begins again. The aspen stands with dying trees do not seem to produce shoots to replace old trees as they normally would, which may be related to years of drought that inflicted deep damage." - USDA: Forest Service: Aspen Decline

Insects

"Quaking aspen appears to be host to several insect and other invertebrate pests. Some are quite damaging and may kill otherwise healthy stands of aspen. Others feed on weakened or dying trees and still others have incidental impacts. Insect species that feed on aspen include several defoliator insects, borers, leaf miners, sawflies, leafhoppers, and aphids." - USDA: Forest Service

Apps & Tools

Europe

UK

• Woodland Trust: Tree ID App "Download our free Tree ID app for Android and iPhone to identify the UK's native and non-native trees. It's an A-Z tree guide in your pocket."

Organizations

International

• Mossy Earth "The rewilding membership that restores nature across a wide range of ecosystems"

Maps

International

• Butterfly Conservation: Wild Spaces: Put Your Wild Space on the Map "Our interactive map shows the number and types of Wild Space near you. When you sign up in the UK, your Wild Space will also appear on the map so you can show everyone that you're taking action and encourage others to get involved too."

• Global View of Aspen

Europe

UK

• Butterfly Conservation: Wild Spaces: Put Your Wild Space on the Map "Our interactive map shows the number and types of Wild Space near you. When you sign up in the UK, your Wild Space will also appear on the map so you can show everyone that you're taking action and encourage others to get involved too."