Toolik ITEX site NDVI values continue to decrease with cold and snow

Dry heath sites are near NDVI values similar to the beginning of the season, moist acidic NDVI has decreased to mid June levels

Imnavait ITEX wet acidic and dry heath site NDVI values continued to decrease with snow and cold

Control plots at both sites are senescing at a faster rate compared to the OTCs

Utqiaġvik dry heath OTC and control NDVI values have leveled off with slight decrease

Utqiaġvik wet meadow OTC and control NDVI values continue to slowly increase

Snow early in the week halted tram runs, but helped NDVI to decline to June levels

We met our season goal of 60 tram runs, just 1 short of the record

Like the Toolik transect, NDVI at the Imnavait transect decreased to June levels with snow and cold

We ended the season with a total of 56 tram runs, just 2 short of the record

Whole transect NDVI values leveled off, while dry heath values continue to decrease and wet meadow continue to increase

26 Utqiaġvik runs for the 2021 season

Dry heath plots are approaching NDVI values similar to the beginning of the season, driven by early senescence of A. alpina.

Dry heath OTC and controls continue to decrease, albeit at a slower rate after A. alpina senesced.

Utqiaġvik dry heath OTC and control NDVI values have leveled off, with no senescence decrease yet.

Utqiaġvik wet meadow OTC and control NDVI values appear to be leveling off.

Cold temps in the 30-40s and snow on 8/11 have senescence finally underway!

Like at the Toolik transect, NDVI at the Imnavait transect is decreasing with snow and cold temps

NDVI values at the Utqiaġvik transect have leveled off and even decreased, indicating a possible start to senescence.

Toolik ITEX site NDVI values are starting to decrease, especially following our first freeze on 8/6.

Imnavait ITEX wet acidic OTC and control plot NDVI values have begun to decrease, indicative of the early stages of senescence.

Dry heath OTC and controls have begun to precipitously decrease, as driven by A. alpina.

Utqiagvik Dry Heath OTC and control NDVI values have leveled off.

Utqiagvik Wet Meadow OTC and control NDVI values continue to increase slightly.

NDVI is just starting to drop at the Toolik Transect following our first freeze on 8/6.

Like at the Toolik transect, NDVI at the Imnavait transect is beginning to drop following the freeze on 8/6.

NDVI values are just leveling off at the Barrow transect, indicating peak season!

Toolik Plots

Toolik ITEX dry heath OTC and control NDVI have started to trend downward with A. alpina senescence.

Toolik ITEX moist acidic OTC and control NDVI have leveled off and remain steady with warm weather. 

We expect to see site-wide declines soon with decreasing temperatures. 

Imnavait Plots

Imnavait ITEX wet acidic OTC and control plots all continue to increase, as they are dominated by shrubs and graminoids.

Dry heath OTC and controls have leveled off and remain steady with warm weather.

Again, we expect to see declines in NDVI as temperatures cool. 

Utqiaġvik Plots

Utqiagvik Dry Heath OTC and control NDVI values appear to have leveled off.

Utqiagvik Wet Meadow OTC and control NDVI values continue to increase.

Toolik Transect

NDVI continues to hold steady at the Toolik transect, as temps remain at ~55-65 F. We expect temperature decreases in the next week, which will accelerate NDVI decline.

Imnavait Transect

NDVI at the Imnavait transect continues to increase. In similar fashion to the Toolik transect, we expect to see a decline as temperatures from from 55-65 F in the coming week. 

Utqiaġvik Transect

NDVI at both the dry heath and wet meadow portions of the Utqiaġvik transect is increasing. 

Toolik Plots

NDVI for the Arctous alpina-dominated ITEX dry heath OTC and control plots has started to trend downward with A. alpina senescence. 

NDVI for the graminoid-dominated ITEX moist acidic OTC and control has leveled off. 

Imnavait Plots

NDVI in the graminoid dominated wet acidic OTC and control plots at Imnavait Creek continues to increase. 

NDVI in the dry heath OTC and controls have leveled off and slightly started to trend down due to A. alpina senescence.

Utqiaġvik Plots

Barrow NDVI continues to increase. Dry heath and wet meadow NDVI values between OTC and control plots closely mirror one another, possibly due to late snowmelt or poor weather. 

Toolik Transect

NDVI still steady at the Toolik transect. The first sunset occurred on 7/20, so senescence will follow shortly. 

Imnavait Transect

NDVI at the Imnavait transect is leveling off, just in time for the beginning of senescence following the first sunset!

Utqiaġvik Transect

NDVI in the wet meadow portion of the Utqiaġvik transect has begun to level off, while NDVI in the dry heath is still increasing slowly. 

Toolik Plots

Dry heath OTC and control NDVI have continued to level off. We expect to see an NDVI decline in the coming weeks as peak season draws to a close. 

Moist acidic OTC NDVI has leveled off as those plots are shrub-dominated and approaching senescence. The moist acidic control NDVI continues to increase, as those plots are shrub AND graminoid dominated.

Imnavait Plots

Dry and wet acidic OTC and control plots all continue to increase, as those plots are dominated by both shrubs and graminoids.

Dry heath NDVI is slightly higher than wet acidic NDVI due to higher prevalence of shrubs (Arctous alpina) at the dry heath sites.

Utqiaġvik Plots

Utqiaġvik NDVI continues to increase, and will likely not level off/decrease for several weeks. 

Control and OTC dry heath sites have slight NDVI differences, with wet meadow control and OTC closely tracking each other. This difference may be due to late snowmelt.

Toolik Transect

Toolik NDVI continues on a level path.

Imnavait Transect

Imnavait NDVI has finally begun to level off.

Utqiaġvik Transect

Barrow NDVI continues to increase. 

Toolik Plots

The Normalized Difference Vegetation Index (NDVI) in experimental (OTC) and control plots is similar at the Toolik moist acidic tundra (MAT) site, however the NDVI in the experimental plots is significantly higher. This is to be expected - higher temperatures in chambered plots mean larger, more quickly growing plants with a higher "greenness" index.

NDVI in experimental (OTC) and control plots is also similar at the Toolik dry site. The NDVI values more closely mirror eachother here because lichens are the primary cover, and can only get so green. 

NDVI is generally lower overall at the Toolik dry site because lichens are the primary cover, as opposed to the Imnavait dry site where the primary cover is Arctous alpina and Vaccinium vitis-idaea and NDVI is higher.

Imnavait Plots

The Normalized Difference Vegetation Index (NDVI) in experimental (OTC) and control plots is similar at the Imnavait dry site, however the NDVI in the experimental plots is slightly higher. Again, this is to be expected - higher temperatures in chambered plots mean larger, more quickly growing plants with a higher "greenness" index.

NDVI in experimental (OTC) and control plots is also similar at the Imnavait wet acidic tundra (WAT) dry site. The NDVI values closely mirror each other here because graminoids are the primary cover, and at this point in the season, even with the use of an open top chamber, they haven't quite grown to their full potential yet. 

Again, NDVI is generally higher overall at the Imnavait dry site because the primary cover is Arctous alpina and Vaccinium vitis-idaea as opposed to the Toolik dry site which is predominately lichens.

Toolik Transect

NDVI at the Toolik transect began to level off in late June (JD 175) following a large increase in mid June (JD 165). In the early season, the MAT portion of the transect showed higher NDVI than the dry or shrub portions of the transect, but that relationship soon flipped, with the dry and shrub portions of the transect outpacing the MAT portion. This switch happens because of shrub leaf-out in mid June (JD 165).

Imnavait Transect

NDVI at the Imnavait Creek transect does not show a dramatic change like NDVI at the Toolik Lake Transect. This is because the Imnavait transect is dominated by graminoids (Eriophorum spp., etc.) that experience full green-up later in the season. 

Utqiaġvik Transect

The NDVI at the Barrow transect has remained relatively static through the duration of the season. Plants in Barrow never truly "green-up" like those at the Toolik and Imnavait transects.