Editing Dune (section)

===Coastal dunes===
[[File:LIVER AAS UDLOEB I JULI 2012 (ubt)-002.JPG|thumb|Coastal dunes covered in grasses around the mouth of the Liver Å river in Denmark]]
[[File:Newborough Dune Rejuvenation.webm|thumb|Newborough Dune Rejuvenation, Wales; video of work done by [[Natural Resources Wales]]; 2015]]

Coastal dunes<ref name="sloss-etal-2012">{{Cite journal |url=https://www.nature.com/scitable/knowledge/library/coastal-dunes-geomorphology-25822000/ |last1=Sloss |first1=C. R. |last2=Shepherd |first2=M. |last3=Hesp |first3=P |year=2012 |title=Coastal Dunes: Geomorphology |journal=Nature Education Knowledge |volume=3 |number=10 |page=2  |access-date=15 January 2021}}</ref> form when wet sand is deposited along the coast and dries out and is blown along the beach.<ref>{{cite book |last1=Bird |first1=ECF |title=Coasts: an introduction to systematic geomorphology |date=1976 |publisher=Australian National University Press |location=Canberra, Australia |asin=B004750SVK}}</ref> Dunes form where the beach is wide enough to allow for the accumulation of wind-blown sand, and where prevailing '''onshore winds''' tend to blow sand inland. The three key ingredients for coastal dune formation are a large sand supply, winds to move said sand supply, and a place for the sand supply to accumulate.<ref>{{cite book |last1=Goldsmith |first1=Victor |title=Coastal Sedimentary Environments |chapter=Coastal Dunes |date=1978 |doi=10.1007/978-1-4684-0056-4_5 |pages=171–235|isbn=978-1-4684-0058-8 }}</ref> Obstacles—for example, vegetation, pebbles and so on—tend to slow down the wind and lead to the deposition of sand grains.<ref name=Hesp1989>{{Cite journal| last = Hesp | first = P.| year = 1989| title = A review of biological and geomorphological processes involved in the initiation and development of incipient foredunes| journal = Proceedings of the Royal Society of Edinburgh, Section B: Biological Sciences| volume = 96| pages = 181–201| doi =  10.1017/S0269727000010927 }}</ref> These small "incipient dunes or "shadow dunes" tend to grow in the vertical direction if the obstacle slowing the wind can also grow vertically (i.e., vegetation). Coastal dunes expand laterally as a result of lateral growth of coastal plants via seed or [[rhizome]].<ref>{{Cite journal|last=Godfrey|first=P. J.|date=1 September 1977|title=Climate, plant response and development of dunes on barrier beaches along the U.S. east coast|journal=International Journal of Biometeorology|volume=21|issue=3|pages=203–216|doi=10.1007/BF01552874|issn=0020-7128|bibcode=1977IJBm...21..203G|s2cid=85391018}}</ref><ref>{{Cite journal|last1=Goldstein|first1=Evan B.|last2=Moore|first2=Laura J.|last3=Vinent|first3=Orencio Durán|date=8 August 2017|title=Lateral vegetation growth rates exert control on coastal foredune "hummockiness" and coalescing time|journal=Earth Surface Dynamics|volume=5|issue=3|pages=417–427|doi=10.5194/esurf-5-417-2017|issn=2196-6311|doi-access=free}}{{open access}}</ref> Models of coastal dunes suggest that their final equilibrium height is related to the distance between the water line and where vegetation can grow.<ref name=DuranMoore2013>{{Cite journal| last1 = Durán | first1 = O.| last2=Moore|first2= L. J. |year = 2013| title = Vegetation controls on the maximum size of coastal dunes| journal = Proceedings of the National Academy of Sciences| volume = 110 | issue = 43 |  pages = 17217–17222| doi =  10.1073/pnas.1307580110 | pmid=24101481 | pmc=3808624| bibcode = 2013PNAS..11017217D| doi-access = free}}</ref> Coastal dunes can be classified by where they develop, or begin to take shape. Dunes are commonly grouped into either the Primary Dune Group or the Secondary Dune Group.<ref name="sloss-etal-2012"/> Primary dunes gain most of their sand from the beach itself, while secondary dunes gain their sand from the primary dune. Along the Florida Panhandle, most dunes are considered to be foredunes or hummocks.<ref>{{cite journal |last1=Houser |first1=C |last2=Hapke |first2=C |last3=Hamilton |first3=S |title=Controls on coastal dune morphology, shoreline erosion and barrier island response to extreme storms |journal=Geomorphology |date=15 August 2008 |volume=100 |issue=3–4 |pages=223–40|doi=10.1016/j.geomorph.2007.12.007 |bibcode=2008Geomo.100..223H }}</ref><ref>{{cite journal |last1=Claudino-Sales |first1=V |last2=Wang |first2=P |last3=Horwitz |first3=MH |title=Factors controlling the survival of coastal dunes during multiple hurricane impacts in 2004 and 2005: Santa Rosa Barrier Island, Florida |journal=Geomorphology |date=15 March 2008 |volume=95 |issue=3–4 |pages=295–315|doi=10.1016/j.geomorph.2007.06.004 |bibcode=2008Geomo..95..295C }}</ref> Different locations around the globe have dune formations unique to their given coastal profile.

Coastal sand dunes can provide privacy and/or habitats to support local flora and fauna. Animals such as sand snakes, lizards, and rodents can live in coastal sand dunes, along with insects of all types.<ref>{{cite web |last1=Ronica |first1=D |title=How sand dunes work |url=https://science.howstuffworks.com/environmental/earth/geology/sand-dune3.htm |website=HowStuffWorks |access-date=4 December 2018|date=27 October 2008 }}</ref> Often the vegetation of sand dunes is discussed without acknowledging the importance that coastal dunes have for animals. Further, some animals, such as foxes and feral pigs can use coastal dunes as hunting grounds to find food.<ref>{{cite web |last1=Hill |first1=K |title=Dune Habitats |url=https://naturalhistory2.si.edu/smsfp/IRLSpec/Dunes.htm |website=Smithsonian Marine Station |access-date=4 December 2018}}</ref> Birds are also known to utilize coastal dunes as nesting grounds. All these species find the coastal environment of the sand dune vital to their species' survival.

Over the course of time coastal dunes may be impacted by [[tropical cyclone]]s or other intense storm activity, dependent on their location. Recent work has suggested that coastal dunes tend to evolve toward a high or low morphology depending on the growth rate of dunes relative to storm frequency.<ref>{{Cite journal|last1=Durán Vinent|first1=Orencio|last2=Moore|first2=Laura|date=February 2015|title=Barrier island bistability induced by biophysical interactions|journal=Nature Climate Change|volume=5|issue=2|pages=158–162|doi=10.1038/nclimate2474|issn=1758-6798|bibcode=2015NatCC...5..158D|url=https://cdr.lib.unc.edu/downloads/1257b286c}}</ref><ref>{{Cite journal|last1=Goldstein|first1=Evan B.|last2=Moore|first2=Laura J.|date=2016|title=Stability and bistability in a one-dimensional model of coastal foredune height|journal=Journal of Geophysical Research: Earth Surface|volume=121|issue=5|pages=964–977|doi=10.1002/2015JF003783|issn=2169-9011|bibcode=2016JGRF..121..964G|doi-access=free}}</ref> During a storm event, dunes play a significant role in minimizing wave energy as it moves onshore. As a result, coastal dunes, especially those in the foredune area affected by a [[storm surge]], will retreat or erode.<ref>{{cite journal |last1=Morton |first1=RA |title=Effects of Hurricane Eloise on beach and coastal structures, Florida Panhandle |journal=Geology |date=1 May 1976 |volume=4 |issue=5 |pages=277–80|doi=10.1130/0091-7613(1976)4<277:EOHEOB>2.0.CO;2 |bibcode=1976Geo.....4..277M }}</ref> To counteract the damage from tropical activity on coastal dunes, short term post-storm efforts can be made by individual agencies through fencing to help with sand accumulation.<ref>{{cite journal |last1=Charbonneau |first1=B |last2=Wnek |first2=JP |title=Reactionary fence installation for post-Superstorm Sandy dune recovery |url=https://eartharxiv.org/ntjsc |journal=Eartharxiv ePrints |date=24 September 2018 |doi=10.31223/osf.io/ntjsc |bibcode=2018EaArX....NTJSCC |access-date=4 December 2018 |archive-date=30 July 2020 |archive-url=https://web.archive.org/web/20200730053248/https://eartharxiv.org/ntjsc |url-status=dead }}</ref>

How much a dune erodes during any storm surge is related to its location on the coastal shoreline and the profile of the beach during a particular season. In those areas with harsher winter weather, during the summer a beach tends to take on more of a convex appearance due to gentler waves, while the same beach in the winter may take on more of a concave appearance. As a result, coastal dunes can get eroded much more quickly in the winter than in the summer. The converse is true in areas with harsher summer weather.<ref>{{cite web |last1=Maine Sea Grant |title=Seasonal changes |url=https://www.seagrant.umaine.edu/coastal-hazards-guide/beaches-and-dunes/learn-more/seasonal-changes |website=Maine Sea Grant College Program |access-date=4 December 2018 |archive-url=https://web.archive.org/web/20181205003653/https://www.seagrant.umaine.edu/coastal-hazards-guide/beaches-and-dunes/learn-more/seasonal-changes |archive-date=5 December 2018 |url-status=dead }}</ref>

There are many threats to these coastal communities. Some coastal dunes, for example ones in San Francisco, have been completely altered by urbanization; reshaping the dune for human use. This puts native species at risk. Another danger, in California and places in the UK specifically, is the introduction of invasive species. Plant species, such as ''[[Carpobrotus edulis]]'', were introduced from South Africa in an attempt to stabilize the dunes and provide horticultural benefits, but instead spread taking land away from native species. ''[[Ammophila arenaria]]'', known as European beachgrass, has a similar story, though it has no horticulture benefits. It has great ground coverage and, as intended, stabilized the dunes but as an unintended side effect prevented native species from thriving in those dunes. One such example is the dune field at [[Point Reyes|Point Reyes, California]]. There are now efforts to get rid of both of these invasive species.<ref>{{Cite web|date=2018-02-06|title=Large-scale removal of beachgrass leads to new life for endangered coastal lupine {{!}} The Source {{!}} Washington University in St. Louis|url=https://source.wustl.edu/2018/02/large-scale-removal-beachgrass-leads-new-life-endangered-coastal-lupine/|access-date=2020-06-09|website=The Source|language=en-US}}</ref><ref>{{Cite web|title=Hottentot Fig Removal & Control {{!}} IWS Ltd|url=https://www.invasiveweedsolutions.co.uk/invasive-weeds/non-native/hottentot-fig/|access-date=2020-06-09|website=Invasive Weed Solutions UK|language=en-GB}}</ref>

====Ecological succession on coastal dunes====
As a dune forms, plant [[Ecological succession|succession]] occurs. The conditions on an ''embryo dune'' are harsh, with [[salt spray]] from the sea carried on strong winds. The dune is well drained and often dry, and composed of calcium carbonate from seashells. Rotting [[seaweed]], brought in by storm waves adds nutrients to allow [[pioneer species]] to colonize the dune. For example, in the [[United Kingdom]] these pioneer species are often [[Ammophila (Poaceae)|marram grass]], [[sea wort grass]] and other sea grasses. These plants are well adapted to the harsh conditions of the foredune, typically having deep roots which reach the [[water table]], [[root nodules]] that produce [[nitrogen]] compounds, and protected [[stoma]], reducing [[transpiration]]. Also, the deep roots bind the sand together, and the dune grows into a [[foredune]] as more sand is blown over the grasses. The grasses add [[nitrogen]] to the soil, meaning other, less hardy plants can then colonize the dunes. Typically these are [[Calluna|heather]], [[Heath (habitat)|heath]]s and [[gorse]]s. These too are adapted to the low [[Soil#Soil moisture|soil water]] content and have small, prickly leaves which reduce transpiration. Heather adds [[humus]] to the soil and is usually replaced by [[conifer]]ous trees, which can tolerate low [[soil pH]], caused by the accumulation and decomposition of organic matter with nitrate leaching.<ref name=Miles1985>{{Cite journal| last = Miles | first = J.| year = 1985| title = The pedogenic effects of different species and vegetation types and the implications of succession| journal = European Journal of Soil Science| volume = 36| issue = 4| pages = 571–584| doi = 10.1111/j.1365-2389.1985.tb00359.x}}</ref> Coniferous forests and [[heathland]] are common [[climax community|climax communities]] for sand dune systems.

Young dunes are called [[yellow dune]]s and dunes which have high humus content are called [[grey dune]]s. Leaching occurs on the dunes, washing humus into the slacks, and the slacks may be much more developed than the exposed tops of the dunes. It is usually in the slacks that more rare species are developed and there is a tendency for the dune slacks' soil to be waterlogged where only marsh plants can survive. In Europe these plants include: creeping willow, cotton grass, [[yellow iris]], reeds, and rushes. As for vertebrates in European dunes, [[natterjack toad]]s sometimes breed here.

==== Coastal dune floral adaptations ====
[[File:Hyypänmäki Hailuoto 2012-06-06 (1).jpg|thumb|Sand dunes of Hyypänmäki in [[Hailuoto]], Finland]]
[[File:Sea dune Erosion at Talace, Wales.webm|thumb|Sea dune erosion at [[Talacre]], [[Wales]]]]
Dune ecosystems are extremely difficult places for plants to survive. This is due to a number of pressures related to their proximity to the ocean and confinement to growth on sandy substrates. These include:
* Little available soil moisture
* Little available [[soil organic matter]]/nutrients/water
* Harsh winds
* Salt spray
* Erosion/shifting and sometimes burial or exposure (from shifting)
* Tidal influences
Plants have evolved many adaptations to cope with these pressures:
* Deep taproot to reach water table ([[Abronia umbellata|Pink Sand Verbena]])
* Shallow but extensive root systems
*[[Rhizome]]s
* Prostrate growth form to avoid wind/salt spray (''Abronia spp''., Beach Primrose)
* [[Krummholz]] growth form ([[Monterrey Cypress]]-not a dune plant but deals with similar pressures)
* Thickened cuticle/Succulence to reduce moisture loss and reduce salt uptake (''Ambrosia/Abronia spp., Calystegia soldanella'')
* Pale leaves to reduce insolation (''Artemisia/Ambrosia spp.'')
* Thorny/Spiky seeds to ensure establishment in vicinity of parent, reduces chances of being blown away or swept out to sea (''Ambrosia chamissonis'')