Editing Tree line (section)

==Causes==

Due to their vertical structure, trees are more susceptible to cold than more ground-hugging forms of plants.<ref name=coldtreeline/> Summer warmth generally sets the limit to which tree growth can occur: while tree line [[Pinophyta|conifers]] are very frost-hardy during most of the year, they become sensitive to just 1 or 2 degrees of frost in mid-summer.<ref name="tran">{{Cite book |last=Tranquillini |first=W. |title=Physiological Ecology of the Alpine Timberline: tree existence at high altitudes with special reference to the European Alps |publisher=Springer-Verlag |year=1979 |isbn=978-3-642-67107-4 |location=New York, NY}}</ref><ref>{{Cite book |last1=Coates |first1=K.D. |title=Ecology and silviculture of interior spruce in British Columbia |last2=Haeussler |first2=S. |last3=Lindeburgh |first3=S |last4=Pojar |first4=R. |last5=Stock |first5=A.J. |year=1994 |oclc=66824523}}</ref> A series of warm summers in the 1940s seems to have permitted the establishment of "significant numbers" of spruce seedlings above the previous treeline in the hills near [[Fairbanks, Alaska]].<ref name="vier4">{{Cite journal |last=Viereck |first=L.A. |year=1979 |title=Characteristics of treeline plant communities in Alaska |journal=[[Ecography|Holarctic Ecology]] |volume=2 |issue=4 |pages=228–238 |doi=10.1111/j.1600-0587.1979.tb01294.x |jstor=3682417|bibcode=1979Ecogr...2..228V }}</ref><ref name="vier8">{{Cite book |last1=Viereck |first1=L.A. |title=Forest Ecosystems in the Alaskan Taiga |last2=Van Cleve |first2=K. |last3=Dyrness |first3=C. T. |publisher=Springer-Verlag |year=1986 |isbn=978-1-4612-4902-3 |editor-last=Van Cleve |editor-first=K. |location=New York, NY |pages=22–43 |chapter=Forest ecosystem distribution in the taiga environment |doi=10.1007/978-1-4612-4902-3_3 |editor-last2=Chapin |editor-first2=F.S. |editor-last3=Flanagan |editor-first3=P.W. |editor-last4=Viereck |editor-first4=L.A. |editor-last5=Dyrness |editor-first5=C.T.}}</ref> Survival depends on a sufficiency of new growth to support the tree. Wind can [[flag tree|mechanically damage tree tissues directly]], including blasting with windborne particles, and may also contribute to the desiccation of [[leaf|foliage]], especially of shoots that project above the snow cover.{{cn|date=July 2023}}

The actual tree line is set by the mean temperature, while the realized tree line may be affected by disturbances, such as [[logging]],<ref name="coldtreeline">{{Cite journal |last=Körner |first=Christian |date=November 1, 2021 |title=The cold range limit of trees |journal=Trends in Ecology & Evolution |volume=36 |issue=11 |pages=979–989 |doi=10.1016/j.tree.2021.06.011 |pmid=34272073 |bibcode=2021TEcoE..36..979K |s2cid=235999977}}</ref> or grazing<ref>{{cite journal |last1=Wang |first1=Xiaoyi |last2=Wang |first2=Tao|title=Enhanced habitat loss of the Himalayan endemic flora driven by warming-forced upslope tree expansion |journal=Nature Ecology & Evolution |date=2022 |volume=6 |issue=7|pages=890–899 |doi=10.1038/s41559-022-01774-3|pmid=35654898 |bibcode=2022NatEE...6..890W }}</ref> Most human activities cannot change the actual tree line, unless they affect the climate.<ref name=coldtreeline/> The tree line follows the line where the seasonal mean temperature is approximately {{convert|6|C|F|disp=or}}.<ref>{{Cite journal |last1=Körner |first1=Christian |last2=Paulsen |first2=Jens |date=May 2004 |title=A World-Wide Study of High Altitude Treeline Temperatures |journal=J. Biogeogr. |volume=31 |pages=713–732 |doi=10.1111/j.1365-2699.2003.01043.x |jstor=3554841 |s2cid=59025355 |number=5|bibcode=2004JBiog..31..713K }}</ref><ref name=coldtreeline/> The seasonal mean temperature is taken over all days whose mean temperature is above {{convert|0.9|C|F}}. A growing season of 94 days above that temperature is required for tree growth.<ref>{{Cite journal |last1=Paulsen |first1=Jens |last2=Körner |first2=Christian |year=2014 |title=A climate-based model to predict potential treeline position around the globe |url=http://doc.rero.ch/record/324784/files/35_2014_Article_124.pdf |journal=Alpine Botany |volume=124 |issue=1 |pages=1–12 |doi=10.1007/s00035-014-0124-0 |bibcode=2014AlBot.124....1P |s2cid=8752987}}</ref>

Because of [[climate change]], which leads to earlier snow melt and favorable conditions for tree establishment, the tree line in [[North Cascades National Park]] has risen more than {{convert|400|ft}} in 50 years.<ref>{{cite web |author=<!-- not stated --> |title=Climate Change Resource Brief - North Cascades National Park |url=https://www.nps.gov/noca/learn/nature/climate-change-resource-brief.htm#:~:text=Forest%20line%20has%20moved%20up,pack%2C%20and%20earlier%20snow%20melt. |date=January 30, 2018 |website=U.S. National Park Service |language=en |access-date=May 13, 2025}}</ref>