Treelines are ecotones between alpine forest and tundra ecosystems and have different typologies including diffuse and abrupt. Treelines can advance in response to climate change if tree growth becomes accelerated and seedling recruitment and survival occurred regularly and quickly enough to allow the treeline to move upward. Abrupt treeline advancement is controlled by seedling recruitment and survival which are typically both controlled by precipitation, especially snow. Tree growth at abrupt treelines responds to the same limiting factors as seedling survivorship; if the precipitation is low enough to kill seedlings, it is likely low enough to reduce growth of adult trees. Treeline advancement at a diffuse treeline is typically limited by tree growth which in turn is typically limited by temperature. Treelines can change typology from abrupt to diffuse and hence change the factors that limit their advancement and limit tree growth. There are several spatial dynamics that can occur between trees at the treeline. Trees growing on the upper edge of the treeline should face a harsher environment than trees within the forest below. Some trees form clusters, which increase resource competition but be beneficial for tree growth through facilitation. The present study analyzes tree growth at an advancing treeline that had recently switched typology from abrupt to diffuse. Based on the reasoning above it is hypothesized that the abrupt to diffuse switch in typology should coincide with a change from precipitation to temperature control of tree growth. Moreover, the study investigates how trees above and below the treeline as well as singletons versus clusters are affected differently by precipitation and temperature. Under abrupt typology, trees above the treeline would be more affected by snow than trees below the treeline. Under diffuse typology, trees above and below the treeline will mainly be affected by temperature. Lastly, it is predicted that, during the abrupt phase, singletons will be more affected by precipitation than clusters because they lack facilitation benefits. Both chronologies showed high variability from 1935 to 1970, with two large peaks of high growth, and low variability of growth after 1970. The chronology detrended only for age showed a gradual increase in tree ring width index from 1970 to 2009, coinciding with an increasing temperature caused by climate change. Tree growth had a statistically significant positive correlation with previous year June and current year March temperatures. Current year May and June temperatures were close to having a statistically significant positive correlation. Precipitation in the form of snow in winter and early spring had a negative effect. During the treeline’s abrupt phase, tree growth was mainly limited by spring and winter snow. As the treeline typology changed to diffuse, growth limitation by growing season temperature became more important than growth limitations fluctuations in growth compared to trees below treeline. However, higher sensitivity to climatic variables for trees above treeline was not found. Clustered trees are more sensitive to temperature changes as is supported by the abundance of fluctuation in the master chronology. The groupings of clustered, singletons, above treeline and below treeline did not show differences in their response to temperature and precipitation. Springs and falls with high precipitation were correlated with high tree growth and vice versa. An increase in temperature during the months of March, May and June was correlated to an increase in tree growth. Moreover, analysis of 35 years long segments lagged by five years shows that up until the 1960s, precipitation had a major effect on tree growth. More precipitation in April led to a decrease in growth. Since 1980s, temperature was the factor causing the major effect. These changes coincided with the change in treeline typology from abrupt treeline to diffuse treeline.