Treelines are climatically constrained ecotones existing worldwide. With global warming and climate change, treelines are expected to advance in elevation on a global scale. Previous research has shown that abrupt treeline shapes are advancing at far slower rates than diffuse treeline structures, indicating that temperature increases are not the only factor. Smaller-scale, endogenous factors may be at play including microclimates, tree-to-tree interactions and feedbacks. Our study at an abrupt treeline on Pike’s Peak aims to understand the effects of temperature and smaller-scale factors on seedling growth, in the effort to try and understand the feedbacks involved in treeline movement and formation. Results indicate that this specific abrupt treeline is creating a microclimate that facilitates seedling growth above the historical treeline. Once this new growth of seedlings matures, another abrupt treeline will form and perpetuate the process.