Editing Tree line (section)

===Arctic tree lines===
[[File:Canada tree line map.png|thumb|right|Map of tree line in Canada]]
Like the alpine tree lines shown above, polar tree lines are heavily influenced by local variables such as [[aspect (geography)|aspect]] of slope and degree of shelter. In addition, [[permafrost]] has a major impact on the ability of trees to place roots into the ground. When roots are too shallow, trees are susceptible to [[windthrow]] and erosion. Trees can often grow in river [[valleys]] at latitudes where they could not grow on a more exposed site. Maritime influences such as [[ocean currents]] also play a major role in determining how far from the equator trees can grow as well as the warm summers experienced in extreme continental climates.{{cn|date=July 2023}} In northern inland [[Scandinavia]] there is substantial maritime influence on high parallels that keep winters relatively mild, but enough inland effect to have summers well above the threshold for the tree line. Here are some typical polar treelines:
{{Clear}}
{| class="wikitable sortable"
|-
!align="left" class="unsortable"|Location
!align="left"|Approx. longitude
!Approx. latitude of tree line
!class="unsortable"|Notes
|-
|Norway
|{{sort|024|24°E}}
| style="text-align:center;"|70°N
|The [[North Atlantic current]] makes Arctic climates in this region warmer than other coastal locations at comparable latitude. In particular the mildness of winters prevents [[permafrost]].
|-
|[[West Siberian Plain]]
|{{sort|075|75°E}}
| style="text-align:center;"|66°N
|
|-
|[[Central Siberian Plateau]]
|{{sort|102|102°E}}
| style="text-align:center;"|72°N
|Extreme [[continental climate]] means the summer is warm enough to allow tree growth at higher latitudes, extending to northernmost forests of the world at 72°28'N at [[Ary-Mas]] (102° 15' E) in the [[Novaya River]] valley, a tributary of the [[Khatanga River]] and the more northern [[Lukunsky grove]] at 72°31'N, 105° 03' E east from Khatanga River.
|-
|[[Russian Far East]] ([[Kamchatka Peninsula|Kamchatka]] and [[Chukchi Peninsula|Chukotka]])
|{{sort|160|160°E}}
| style="text-align:center;"|60°N
|The [[Oyashio Current]] and strong winds affect summer temperatures to prevent tree growth. The [[Aleutian Islands]] are almost completely treeless.
|-
|[[Alaska]], United States
|{{sort|208|152°W}}
| style="text-align:center;"|68°N
|Trees grow north to the south-facing slopes of the Brooks Range. The mountains block cold air coming off of the Arctic Ocean.
|-
|[[Northwest Territories]], Canada
|{{sort|228|132°W}}
| style="text-align:center;"|69°N
|Reaches north of the Arctic Circle because of the continental nature of the climate and warmer summer temperatures.
|-
|[[Nunavut]]
|{{sort|265|95°W}}
| style="text-align:center;"|61°N
|Influence of the very cold [[Hudson Bay]] moves the treeline southwards.
|-
|[[Labrador Peninsula]]
|{{sort|293|72°W}}
| style="text-align:center;"|56°N
|Very strong influence of the Labrador Current on summer temperatures as well as altitude effects (much of Labrador is a plateau). In parts of [[Labrador]], the treeline extends as far south as 53°N. Along the coast the northernmost trees are at 58°N in [[Napartok Bay]].
|-
|[[Greenland]]
|{{sort|315|50°W}}
| style="text-align:center;"|69°N
|Determined by experimental tree planting in the absence of native trees because of isolation from natural seed sources; a very few trees are surviving, but growing slowly, at [[Kangerlussuaq Fjord|Søndre Strømfjord]], 67°N. There is one natural forest in the [[Qinngua Valley]].
|}