In this monthly feature, we span the globe to examine Our Changing Landscape with time series of medium resolution RapidEye satellite imagery. The RapidEye archive dates back to late 2008 and already contains more than 5 billion square kilometers of data. This month, we check back on the mountain pine bark beetle outbreak that scourged the Rocky Mountain landscape.
The RapidEye ConstellationA 5-meter color RapidEye image collected on June 20, 2014 over the section of Roosevelt National Forest, Colorado that is in the animation below. (Images Courtesy: RapidEye)
RapidEye is a constellation of five 5-meter medium resolution satellites each offering five spectral bands of information. The RapidEye constellation offers daily revisits to every location on the planet with a huge footprint that is 77-km wide. The data is priced competitively with a starting cost of $1.28 per square kilometer for all five spectral bands – academics do receive discounts. RapidEye adds a fifth band, the red edge, to the ‘traditional’ multispectral set of blue, green, red and near-infrared (NIR). The additional spectral data in the red edge band allows users to extract more useful land ‘information’ than can be from traditional 4-band imagery sources. When RapidEye imagery is ordered as a Level 3A Orthorectified product, images from multiple dates are extremely well registered, making it the ideal data source for Our Changing Landscape.
A Look-In on the Mountain Pine Bark Beetle Outbreak in ColoradoClick on the image above to see an animation of the Mountain Pine Bark Beetle outbreak from 2011 to 2014 over the area seen in color above. The images used in this animation where created using a similar NDVI calculation as used in our original piece. We have used three images in this animation from June 28, 2011, June 2, 2013 and then June 20, 2014. The June 28, 2011 is the last image used in our original piece; we have also chosen an area that is as close to the original extents selected. In this animation, you can see significant deadening of the forests (dead vegetation is in red; live vegetation is in green) from 2011 to 2013 as might be expected. However, in the 2014 image, the forest looks to recover significantly. We can offer two possible explanations of this rapid green-up. First, we could be seeing understory vegetation significantly increase in vigor as the dead pines fall to the ground only to be replaced by shorter emergent grasses and bushes. A more likely explanation is that there is a thin layer of haze in the imagery which could cause our assumption of the live-dead NDVI break at 0.15 to be wrong for this date. An atmospheric correction on all three datasets could help to eliminate these differences but is beyond the scope of this article.
The first part of this piece on the mountain pine bark beetle outbreak ran in our March 2013 edition of The Geospatial Times. In this article, we introduced the epidemiology of the outbreak and also provided some statistics on its geographic extent. In this second part of the story, we will take a look back in on Roosevelt National Forest in Colorado to see how the forest’s trees may have recovered or continued to be degraded by the outbreak. But before that, a quick update on the mountain pine bark beetle outbreak seems to be in order.
- It appears that our March 2013 story may have caught the outbreak at its height as new incidents are on the decline. This makes sense as any outbreak be it a disease or insect blight, will eventually fade back as the number of healthy hosts to infect declines, in this case lodgepole, limber and ponderosa pine.
- But as one beetle outbreak fades, another one is on the rise in Colorado, a spruce beetle outbreak this time that is also in Wyoming and the Black Hills. While this outbreak will not be as significant as the mountain pine bark beetle given that its target are less common in the Rocky Mountain region (i.e. Engelmann spruce and blue spruce), it infested 338 square miles of Colorado forests in 2013. Similar to mountain pine bark, this spruce beetle outbreak is tied in part to extended periods of drought in the West.
- One interesting study about the mountain pine bark beetle outbreak suggests that the addition of the dead trees to the fire fuel load does not increase the chance for large forest fires as conventional wisdom often suggests. But even if the dead trees are not increasing fire risk, they can significantly impact the local water cycle with detrimental effects on mountain streams.
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