The first link that I posted above shows a diagram with a mountain leading down to a sea. Across the picture from left to right shows how temperature (and associated biomes) shift as the latitude increases. The same image shows the temperature decrease with altitude and the same corresponding march of biomes. The Wikipedia page for tree line has a nice table that shows how it varies from just a few hundred meters in extreme latitudes up to more than 5000 meters at near-equatorial areas. Similarly, the arctic tree line tends to hit around 60-70 degrees of latitude, depending on local conditions. Tree line also varies by species and you likely will encounter a succession of tree lines as you head up a mountainside. The 5200 meter treeline, for example, is for a local species that is very drought tolerant.

And the obligatory mapping wisdom: people don't go near the tree line without very good reason. Road paths tend to minimize the total energy required to traverse them. Rivers and cog railways cross contour lines at right angles; roads and animal paths rarely do.