NASA: US - Colorado - Rocky Mountains - Boulder and Fort Collins area - Tiny Beetles Take a Large Bite Out of the Forest - With bark beetle info - August 2012

Posted by ricardo marcenaro | Posted in | Posted on 13:53

Tiny Beetles Take a Large Bite Out of the Forest
acquired September 11, 2005 download large image (8 MB, JPEG, 3832x3832)
Tiny Beetles Take a Large Bite Out of the Forest
acquired September 28, 2011 download large image (8 MB, JPEG, 3832x3832)
acquired September 11, 2005 - September 28, 2011 download Google Earth file (KML)
A single pine bark beetle is about the size of a grain of rice. But when the beetle population swells, it can have a major impact on forest health. And that’s exactly what has been happening across the Rocky Mountains over the past decade.
In Colorado, severe beetle infestations showed up in lodgepole pine forests about 50 miles west of Boulder and Fort Collins around 2000. Over time, the affected area grew so that by 2011 the infestation had spread east to ponderosa pine forests that were much closer to the two cities. (A map showing the progression between 1998 and 2011 is available here).
The beetle epidemic caused so many trees to die-off that the impacts are visible from space. The Thematic Mapper on Landsat 5 acquired these images of lodgepole pine forests near Grand Lake, Colorado on September 11, 2005, and September 28, 2011—before and after a severe infestation led to die-off of the tree canopy.
Over six years, beetle activity turned entire ridges and valleys brown. Forest die-off is most visible in the center of the image and along both sides of the Kawuneeche Valley. The brownest areas in the 2011 image are generally stands of lodgepole pine, a slender tree that grows at 6,000 to 11,000 feet (1,800 to 3,300 meters) in elevation. Either spruce or aspen dominates the green areas that escaped infestation, such as the forests near Gravel Mountain and areas west of the Kawuneeche Valley.
Not all of the browning is due to beetles. In the upper central and lower right of the image, logging has also had an impact. And despite the beetle damage to the upper canopy, the forests are anything but dead. Even in the most severely affected areas, large numbers of trees survive.
It has been suggested that all the dead needles and trees trunk left after a beetle infestation must make wildfires more common and severe. It wasn’t uncommon for beetles to get the blame for exacerbating the destructive High Park fire that raged near Fort Collin in June 2012.
However, Bill Romme, a Colorado State University professor who has studied the relationship, is not convinced. “Most research indicates that there is little or no such relationship between beetle-caused tree mortality and subsequent fire occurrence and severity in lodgepole pine forests,” he noted in an email. “Fire occurrence and severity in these forests are controlled primarily by weather conditions. Variation in fuel conditions, such as that introduced by the beetles, is a secondary and generally minor influence on fire behavior.”
Researchers do think pine beetles can affect the risk of severe fires, but the impacts are not always straightforward. The most dangerous fires—crown fires—leap from treetop to treetop in an explosive wall of flame, rather than creeping along the ground surface. For the first few years after an infestation, beetle-impacted forests may have an increased risk of crown fires due to the dry needles that remain clinging to the tops of dying trees. But as these needles—and other debris—drop to the ground, the risk of crown fires drops as well. According to one study, forest die-off from pine beetles infestations can reduce the risk of crown fires for decades by thinning forests.
Thomas Veblen, the head of a biogeography research group at the University of Colorado that has also studied the link between beetles and fires, shares Romme’s skepticism. One of the telling features of the image pair above, Veblen noted, is the lack of burn scars. Beetles started attacking the area during the early 2000s; but even as trees have been dying, there has not been a significant fire.
“While dead trees from pine beetles provide a teachable moment for discussing fire hazard, the underlying factor explaining the increase in area burned across the western U.S.—which is well documented—since the 1980s is warming,” Veblen said.
NASA Earth Observatory image created by Robert Simmon, using Landsat data provided by the United States Geological Survey. Caption by Adam Voiland, with information from Thomas Veblen and Bill Romme.
Instrument: 
Landsat 5 - TM

A bark beetle is one of approximately 220 genera with 6,000 species of beetles in the subfamily Scolytinae. Traditionally, this was considered a distinct family Scolytidae, but now it is understood that bark beetles are in fact very specialized members of the "true weevil" family (Curculionidae). Well-known species are members of the type genus Scolytus - namely the European elm bark beetle S. multistriatus and the large elm bark beetle S. scolytus, which like the American elm bark beetle Hylurgopinus rufipes, transmit Dutch elm disease fungi (Ophiostoma). The mountain pine beetle Dendroctonus ponderosae, southern pine beetle Dendroctonus frontalis and their near relatives are major pests of conifer forests in North America. A similarly aggressive species in Europe is the spruce Ips Ips typographus. A tiny bark beetle—the coffee berry borer, Hypothenemus hampei is a major pest of coffee around the world.


Ecology

Bark beetles are so-named because the best known species reproduce in the inner bark (living and dead phloem tissues) of trees. Some species, such as the mountain pine beetle (Dendroctonus ponderosae), attack and kill live trees. Most, however, live in dead, weakened, or dying hosts. Bark beetles are ecologically and economically significant.[1] Outbreak species help to renew the forest by killing older trees. Other species aid in the decomposition of dead wood. However, several outbreak-prone species are known as notorious pests.

Bark beetles often attack trees that are already weakened by disease, drought, smog, conspecific beetles or physical damage. Healthy trees may put up defenses by producing resin or latex, which may contain a number of insecticidal and fungicidal compounds that can kill or injure attacking insects, or simply immobilize and suffocate them with the sticky fluid. Under outbreak conditions, the sheer number of beetles can, however, overwhelm the tree's defenses, and the results can be disastrous for the lumber industry.

In some places, such as the Šumava National Park in the Czech Republic's Bohemian forest, problems with bark beetles have become a heated issue with a political dimension. On one side, some experts (usually with a background in environmental sciences) demanded that nature be left alone and that natural processes be allowed to take their course, even if it meant the bark beetle would destroy most of the forest. On the other side, other experts (usually with a background in forest management[citation needed]) demanded intervention. During the 1980s and 1990s, the Šumava park management mostly favored intervention. Many outside groups became involved in the dispute, such as the lumber industry (which supported intervention because of possible profit to be made), or some local politicians, afraid that tourists would turn back from a forest decayed after a beetle invasion. The anti-intervention side got support from entomologists from the Czech Academy of Sciences and from several environmental organizations, such as Friends of the Earth. At the height of the dispute, there were cases where activists literally defended the trees with their bodies, tying themselves to the trunks, and the dispute was widely covered in the main Czech daily newspapers and on TV news.[2]

Some bark beetles form a symbiotic relationship with certain Ophiostomatales fungi, and are named "ambrosia beetles" after these "ambrosia fungi". The ambrosia beetles (such as Xyleborus) feed on fungal "gardens" and are one of only three insect groups known to farm fungi. The other two groups are ants and termites, neither of which is particularly closely related to beetles. Courtesy of the fungus, ambrosia bark beetles are able to indirectly feed from many more species of trees than their evolutionary relatives that do not feed on fungi, by having the fungi do the work of overcoming the plants' chemical defenses. The beetles carry the fungal spores in special structures, called mycangia, and inoculate the trees as they attack them.

Like many other insects, Scolytinae will emit pheromones to attract conspecifics which are thus drawn to trees already colonized by bark beetles. This can result in heavy infestations and eventually death of the tree. Many are also attracted to ethanol, one of the byproducts of microbial growth in dead woody tissues.


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NASA: US - Colorado - Rocky Mountains - Boulder and Fort Collins area - Tiny Beetles Take a Large Bite Out of the Forest - With bark beetle info - August 2012 





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