Stacey Robbins - June 2018

Through June, my time has been focused on preparing for fieldwork while the sites I have selected from satellite images are becoming available after snowmelt.  After selecting a couple potential sites around Red Lodge, I spent a few days hiking and scouting out which areas would be best to survey.  Each location needs to have an abrupt tree line, plus 300 m above it with terrain at which a tree could potentially establish.  This turned out to be more rare than expected, as many of the areas in my preliminary search turned into rocky, uninhabitable terrain.  It is essential to my study to choose an appropriate site where the variable of mycorrhiza could be measured and interpreted as a potential factor affecting growth, rather than a site where obvious factors like lack of soil and rock are the major governing variables.  One of the difficult aspects of the study is that there is generally always more than a single variable to consider when understanding what causes a tree line to move or change. 

Through the end of June, I was able to hike and begin data collection.  The process for this involved identifying and collecting a data point where the tree line ends on a GPS, then measuring 30 m and 300 m in walking distance above and below that tree line.  At each of these locations, I then placed a flag every 10 m over a 100 m transect.  At each flag, I used a 1x1 m quadrat to access ground cover in terms of percent bare ground (rock or soil), litter, forbs, shrubs, grass and lichen.  I used a densitometer to record the canopy cover at each location.  Any trees present at each of the forty sites (4mx10m) were counted and identified as less than breast height, or greater than breast height.  Those in the greater than breast height groups were then classified by species, and the diameter of each was recorded.  A core subsample was collected from 5 trees from each species (when available) to access age.  The common tree species at the sites included lodgpole pine (Pinus contorta) , subalpine fir (Abies lasiocarpa) and whitebark pine (Pinus albicaulis) with few engelmann spruce (Picea engelmannii).  Finally, a soil sample of 50 g was collected within each plot. 

As far as unexpected obstacles go, there have been many.  I had planned to collect seeds from each site to grow in the greenhouse with the soil sample, but seeds are not yet fertilized or mature until late August at this elevation.  I was able to order seeds collected in the same forest from the forest service, but they are Engelmann spruce, rather than pine or fir, which are more prominent at my sites.  I decided to revise my plan as follows; I will start a group of seedlings with the soil samples and spruce seeds, and start a second group of seedlings with new soil samples from the same sites in August after I successfully collect fresh seeds from my sites.  Obstacles aside, I continue to enjoy the opportunity to do research.  I have a new appreciation and understanding of all the hard work and continuous revisions and adjustments required to collect useful information!

Image 1: Example of ground cover at 30 m above tree line at one site

Image 2: Example of ground cover at 300 m above treeline at one site

Image 3: One of the three final sites for assessment

Image 4: Another of the three final sites for assessment (looking at the upper area)


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