Editing American chestnut (section)

===Chestnut blight===
{{main|Cryphonectria parasitica}}
Prior to the chestnut blight, the American chestnut was a dominant tree in the ecosystem of the eastern deciduous forest. It was said that a squirrel could walk from New England to Georgia solely on the branches of American chestnuts.<ref>{{cite web |title=The Resurrection Of The American Chestnut |url=https://www.sciencefriday.com/segments/the-american-chestnut/ |website=Science Friday}}</ref> Once an important hardwood timber tree, the American chestnut suffered a catastrophic population collapse due to the chestnut blight, a disease caused by an Asian bark fungus (''[[Cryphonectria parasitica]]'', formerly ''Endothia parasitica''). The fungus was introduced when infected [[Castanea crenata|Japanese chestnut tree]]s were brought to North America in the late 19th century.<ref>{{cite journal |last=Ronsheim |first=Margaret L. |date=Feb 2022 |title=Invasive species |journal=AccessScience |publisher=McGraw-Hill Education |doi=10.1036/1097-8542.350480}}</ref> Chestnut blight was first noticed on American chestnut trees in what was then the New York Zoological Park, now known as the [[Bronx Zoo]], in the borough of [[The Bronx]], [[New York City]], in 1904, by chief forester Hermann Merkel. Merkel estimated that by 1906 blight had infected 98 percent of the chestnut trees in the borough.<ref name="merkel">{{cite book |last=Merkel |first=Hermann W. |url=https://books.google.com/books?id=xsdLAAAAYAAJ&dq=Hermann+Merkel+chestnuts&pg=PA97 |title=A Deadly Fungus on the American Chestnut |publisher=[[BiblioBazaar|Nabu Press]] |year=2011 |isbn=978-1-245-32858-6 |series=Annual Report of the New York Zoological Society |volume=10 |location=[[Charleston, South Carolina]] |access-date=October 25, 2015 |via=[[Google Books]] |orig-date=1906}}</ref> While Asian chestnut species evolved with the blight and developed a strong resistance, the American chestnut and Allegheny chinquapin have little resistance.<ref>{{cite journal |last1=Newhouse |first1=Andrew E. |last2=Spitzer |first2=Jesse E. |last3=Maynard |first3=Charles A. |last4=Powell |first4=William A. |title=Chestnut Leaf Inoculation Assay as a Rapid Predictor of Blight Susceptibility |journal=Plant Disease |date=January 2014 |volume=98 |issue=1 |pages=4–9 |doi=10.1094/PDIS-01-13-0047-RE|pmid=30708571 |doi-access=free |bibcode=2014PlDis..98....4N }}</ref><ref name="Wang-2015">{{cite book |author1-link=Kan Wang |last=Wang |first=Kan |title=''Agrobacterium'' Protocols |series=Methods in Molecular Biology |publisher=[[Humana Press]] |publication-place=New York, NY |year=2015 |volume=1224 |isbn=978-1-4939-1657-3 |oclc=898898245 |pages=vii-viii |doi=10.1007/978-1-4939-1658-0 |pmid=25568905 |s2cid=3705500}} {{ISBN|978-1-4939-1657-3}}.</ref>{{rp|145}}<ref name="Barnes-Delborne-2021">{{cite journal | last1=Barnes | first1=Jessica C | last2=Delborne | first2=Jason A | title=The politics of genetic technoscience for conservation: The case of blight-resistant American chestnut | journal=[[Environment and Planning E: Nature and Space]] | publisher=[[SAGE Publishing|Sage]] | date=2021-06-24 | volume=5 | issue=3 | issn=2514-8486 | doi=10.1177/25148486211024910 | page=251484862110249 | s2cid=236783237| doi-access=free }}</ref> The airborne bark fungus spread {{convert|50|mi|km|abbr=on}} per year and in a few decades girdled and killed more than three&nbsp;billion American chestnut trees. [[Salvage logging]] during the early years of the blight may have unwittingly destroyed trees that had high levels of resistance to the disease and thus aggravated the calamity.<ref name=sam>{{cite journal |last=Detwiler |first=Samuel |url=https://books.google.com/books?id=UFQyAQAAMAAJ&dq=Samuel+Detwiler+1915+american+chestnut&pg=PA953 |title=The American Chestnut Tree: Identification and Characteristics |journal=American Forestry |volume=21 |issue=362 |date=October 1915 |page=957-959 |location=[[Washington D.C.]] |publisher=[[American Forestry Association]] |via=[[Google Books]] |access-date=October 25, 2015 }}</ref> New shoots often sprout from the roots when the main stem dies, so the species has not yet become extinct. However, the stump sprouts rarely reach more than {{convert|6|m|ft|0|abbr=on}} in height before blight infection returns, so the species is classified as functionally extinct<ref name="History of the American Chestnut">{{Cite web|url=https://www.tacf.org/the-american-chestnut/history-american-chestnut/|title=History of the American Chestnut|website=The American Chestnut Foundation|language=en-US|access-date=2020-02-28}}</ref> since the chestnut blight only actively kills the above ground portion of the American chestnut tree, leaving behind the below-ground components such as the root systems. It was recorded in the 1900s that the chestnut blight would commonly reinfect any novel stems that grew from the stumps, therefore maintaining a cycle that would prevent the American chestnut tree from re-establishing.<ref>{{Cite web |url=http://www.arnoldia.arboretum.harvard.edu/pdf/articles/1992-52-2-evolution-of-the-chestnut-tree-and-its-blight.pdf|title=Evolution of the Chestnut Tree and its Blight|last=Anagnostakis|first=Sandra|archive-url=https://web.archive.org/web/20170505133607/http://arnoldia.arboretum.harvard.edu/pdf/articles/1992-52-2-evolution-of-the-chestnut-tree-and-its-blight.pdf|archive-date=May 5, 2017}}</ref> However, some American chestnut trees have survived because of a small natural resistance to the chestnut blight.<ref>{{Cite journal |last1=Dierauf|first1=Tom |first2=Joel |last2=Artman |first3=John R. |last3=Elkins |first4=S. Lucille |last4=Griffin |first5=Gary J. |last5=Griffin |s2cid=83066643 |title=High Level of Chestnut Blight Control on Grafted American Chestnut Trees Inoculated with Hypovirulent Strains |journal=Journal of Arboriculture |volume=23 |issue=2 |date=March 1997 |pages=87–88 |doi=10.48044/jauf.1997.013 |url=https://joa.isa-arbor.com/articles.asp?JournalID=1&VolumeID=23&IssueID=2|doi-access=free }}</ref>

The high density of American chestnuts within its range and the lack of natural immunity allowed the blight to spread quickly and cause infection and die-off in nearly every tree exposed.<ref name="Barnes-Delborne-2021" /> Early attempts to treat chestnut blight were both chemical (such as the use of [[Fungicide|fungicides]]) and physical (such as removing infected limbs through [[Arboriculture|tree surgery]] and the removal of infected trees from cultivated and wild stands). Quarantine measures were also put into place, with the later support of the [[Plant Quarantine Act]], which was an attempt to prevent the importation of other potential plant pathogens. These attempts to contain the spread of chestnut blight were unsuccessful; the devastation of the species was worsened because the chestnut blight resulted in isolation of remaining specimens, resulting in asexual propagation of many isolated American chestnuts, low genetic diversity of stands of American chestnuts, and consequent vulnerability to [[extirpation]].<ref>{{cite journal |last1=Stilwell |first1=Kevin L. |last2=Wilbur |first2=Henry M. |last3=Werth |first3=Charles R. |last4=Taylor |first4=Douglas R. |title=Heterozygote advantage in the American chestnut, Castanea dentata (Fagaceae) |journal=American Journal of Botany |date=February 2003 |volume=90 |issue=2 |pages=207–213 |doi=10.3732/ajb.90.2.207|pmid=21659110 }}</ref>

Chestnut blight is not to be confused with [[sun scald]], where winter sun reflects off of snow, warming the bark on the sun-facing trunk (this is the south-facing trunk in the Northern Hemisphere). This snow-reflected sunlight repeatedly warms and thaws the trunk during the day, resulting in vulnerability of the bark and cambium to freezing cold temperatures during the subsequent night, eventually resulting in bark cankers that resemble chestnut blight. Also, sun scald makes the damaged bark vulnerable to invasion by pathogens.<ref>{{cite web |title=Diseases |url=https://www.canr.msu.edu/chestnuts/pest_management/diseases |website=Chestnuts |language=en}}</ref>