Editing Deciduous (section)

== Botany ==<!-- This section is linked from [[Autumn leaf color]]. See [[WP:MOS#Section management]] -->
In [[botany]] and [[horticulture]], '''deciduous [[plant]]s''', including [[tree]]s, [[shrub]]s and [[herbaceous]] perennials, are those that lose all of their [[Leaf|leaves]] for part of the year.<ref>{{cite web |url= http://www.botany.uwc.ac.za/ecotree/leaves/decidu.htm |title= Trees that lose their leaves |author= University of the Western Cape |author-link= University of the Western Cape |publisher= botany.uwc.ac.za |url-status= dead |archive-url= https://web.archive.org/web/20130325032527/http://www.botany.uwc.ac.za/ecotree/leaves/decidu.htm |archive-date= 25 March 2013 }}</ref> This process is called [[abscission]].<ref>{{cite web|url=http://warnell.forestry.uga.edu/service/library/for99-025/for99-025.pdf |title=Falling Tree Leaves: Leaf Abscission |author= Dr. Kim D. Coder |author2=University of Georgia |author2-link=University of Georgia |publisher= forestry.uga.edu |year= 1999 |url-status= dead |archive-url= https://web.archive.org/web/20130518095724/http://warnell.forestry.uga.edu/service/library/for99-025/for99-025.pdf |archive-date= 18 May 2013 }}</ref> In some cases leaf loss coincides with winter—namely in [[temperate]] or [[polar climate]]s.<ref>{{cite web |url= https://www.sciencedaily.com/articles/d/deciduous.htm |title= Reference article : "Deciduous" in Wikipedia |author= Science Daily |author-link= Science Daily |publisher= sciencedaily.com |access-date= 2020-03-23 |archive-url= https://web.archive.org/web/20150425050857/http://www.sciencedaily.com/articles/d/deciduous.htm |archive-date= 25 April 2015 |url-status= dead }}</ref> In other parts of the world, including tropical, subtropical, and arid regions, plants lose their leaves during the [[dry season]] or other seasons, depending on variations in [[rain]]fall.{{cn|date=June 2023}}

The converse of deciduous is [[evergreen]], where foliage is shed on a different schedule from deciduous plants, therefore appearing to remain green year round because not all the leaves are shed at the same time.<ref>{{cite web |url= http://pubs.cas.psu.edu/freepubs/pdfs/sc229.pdf |title= Evergreen Shrubs and Trees for Pennsylvania |author= J. Robert Nuss |author2= Pennsylvania State University |author2-link= Pennsylvania State University |publisher= psu.edu |year= 2007 |access-date= 2020-03-23 |archive-date= 6 September 2006 |archive-url= https://web.archive.org/web/20060906083235/http://pubs.cas.psu.edu/freepubs/pdfs/sc229.pdf |url-status= dead }}</ref> Plants that are intermediate may be called [[semi-deciduous]]; they lose old foliage as new growth begins.<ref>{{cite web |url= http://www.ibiblio.org/openkey/intkey/web/glossary.pdf |title= Glossary of Botanical Terms |publisher= The Illinois - North Carolina Collaborative Environment for Botanical Resources: Openkey Project |page= 22 |access-date= 2020-03-23 }}</ref> Other plants are semi-evergreen and lose their leaves before the next growing season, retaining some during winter or dry periods.<ref>{{Cite book |first1= William |last1= Weber |author2= Lee J. T. White |author3= Amy Vedder |author4= Lisa Naughton-Treves |title= African rain forest ecology and conservation an interdisciplinary perspective |place= New Haven |publisher= Yale University Press |date= 2001 |page= 15 }}.</ref>

[[File:Forsythia turin.JPG|thumb|right|alt=Flowering branch of forsythia amid bare trees|Like a number of other deciduous plants, ''[[Forsythia]]'' flowers during the leafless season.]]

Many deciduous plants [[flower]] during the period when they are leafless, as this increases the effectiveness of [[pollination]]. The absence of [[leaf|leaves]] improves wind transmission of pollen for wind-pollinated plants and increases the visibility of the flowers to [[insect]]s in insect-pollinated plants. This strategy is not without risks, as the flowers can be damaged by frost or, in dry season regions, result in water stress on the plant.{{cn|date=June 2023}}

[[Spring (season)|Spring]] {{Not a typo|leafout}} and [[fall]] leaf drop are triggered by a combination of daylight and air temperatures. The exact conditions required will vary with the species, but generally more cold-tolerant genera such as ''Salix'' will leaf-out earlier and lose their leaves later, while genera such as ''Fraxinus'' and ''Juglans'' can only grow in warm, frost-free conditions so they need at least 13 hours of daylight and air temperatures of around 70&nbsp;°F (21&nbsp;°C) to leaf out. They will be among the earliest trees to lose their leaves in the fall. In sub-Arctic climates such as [[Alaska]], leaves begin turning colors as early as August. However, for most temperate regions it takes place in late September through early November and in subtropical climates such as the southern United States, it may be November into December.{{cn|date=June 2023}}

Leaf drop or [[abscission]] involves complex physiological signals and changes within plants. When {{Not a typo|leafout}} is completed (marked by the transition from bright green spring leaves to dark green summer ones) the chlorophyll level in the leaves remains stable until cool temperatures arrive in autumn. When [[autumn]] arrives and the days are shorter or when plants are drought-stressed,<ref name="Pessarakli2005">{{cite book |author= Mohammad Pessarakli |title= Handbook of photosynthesis |url=https://books.google.com/books?id=0_3XqlcKPpwC&pg=PA725 |access-date= 9 October 2010 |year= 2005 |publisher= CRC Press |isbn= 978-0-8247-5839-4 |page=725 }}</ref> the chlorophyll steadily breaks down, allowing other pigments present in the leaf to become apparent and resulting in non-green colored foliage. The brightest leaf colors are produced when days grow short and nights are cool, but remain above freezing.<ref name="Linzey2008">{{cite book |author= Donald W. Linzey |title= A natural history guide to Great Smoky Mountains National Park |url= https://books.google.com/books?id=UcGn0f7LiJsC&pg=PA27 |access-date= 9 October 2010 |date= 1 April 2008 |publisher= Univ. of Tennessee Press |isbn= 978-1-57233-612-4 |page=27 }}</ref> These other pigments include [[carotenoid]]s that are yellow, brown, and orange. [[Anthocyanin]] pigments produce red and purple colors, though they are not always present in the leaves. Rather, they are produced in the foliage in late summer, when sugars are trapped in the leaves after the process of abscission begins. Parts of the world that have showy displays of bright autumn colors are limited to locations where days become short and nights are cool. The New England region of the United States and southeastern Canada tend to produce particularly good autumn colors for this reason, with Europe producing generally poorer colors due to the humid maritime climate and lower overall species diversity {{citation needed|date=January 2023}}. It is also a factor that the continental United States and southern Canada are at a lower latitude than northern Europe, so the sun during the fall months is higher and stronger. This combination of strong sun and cool temperatures leads to more intense fall colors. The Southern United States also has poor fall colors due to warm temperatures during the fall months and the Western United States as it has more evergreen and fewer deciduous plants, combined with the West Coast and its maritime climate. (''See also'': [[Autumn leaf color]]) Most of the Southern Hemisphere lacks deciduous plants due to its milder winters and smaller landmass, most of which is nearer the equator with only southern South America, the South island of [[New Zealand]], and southern Australia, particularly [[Tasmania]] and [[Victoria (state)|Victoria]], producing distinct fall colors.

The beginnings of leaf drop starts when an abscission layer is formed between the leaf [[petiole (botany)|petiole]] and the stem. This layer is formed in the spring during active new growth of the leaf; it consists of layers of cells that can separate from each other. The cells are sensitive to a [[plant hormone]] called [[auxin]] that is produced by the leaf and other parts of the plant. When auxin coming from the leaf is produced at a rate consistent with that from the body of the plant, the cells of the abscission layer remain connected; in autumn, or when under stress, the auxin flow from the leaf decreases or stops, triggering cellular elongation within the abscission layer. The elongation of these cells breaks the connection between the different cell layers, allowing the leaf to break away from the plant. It also forms a layer that seals the break, so the plant does not lose sap.{{cn|date=June 2023}}

Some trees, particularly oaks and beeches, exhibit a behavior known as "[[marcescence]]" whereby dead leaves are not shed in the fall and remain on the tree until being blown off by the weather. This is caused by incomplete development of the abscission layer. It is mainly seen in the seedling and sapling stage, although mature trees may have marcescence of leaves on the lower branches.

A number of deciduous plants remove nitrogen and carbon from the [[foliage]] before they are shed and store them in the form of proteins in the vacuoles of [[Parenchyma (botany)|parenchyma]] cells in the roots and the inner bark. In the spring, these proteins are used as a nitrogen source during the growth of new leaves or flowers.<ref>{{cite book |last=Srivastava |first=Lalit M. |year=2002 |title=Plant growth and development. Hormones and environment |location=Amsterdam |publisher=Academic Press |isbn=0-12-660570-X |page=476}}</ref>

=== Function ===

[[File:Autumn Leaf 08Nov17.jpg|thumb|alt=Fallen leaves covering a patch of ground|Deciduous plants in mid- to high [[latitude]]s shed their leaves as temperatures drop in [[autumn]].<ref>{{cite book |last1= Bonan |first1= Gordon |title= Ecological Climatology: Concepts and Applications |date= 2015 |publisher= Cambridge University Press |isbn= 9781316425190 |page= 294 |url= https://books.google.com/books?id=kq8kDQAAQBAJ&pg=PA294 |language= en }}</ref>]]

Plants with deciduous foliage have advantages and disadvantages compared to plants with evergreen foliage.<br>
Since deciduous plants lose their leaves to conserve water or to better survive winter weather conditions, they must regrow new foliage during the next suitable growing season; this uses resources which evergreens do not need to expend.<br>
Evergreens suffer greater water loss during the winter and they also can experience greater [[predation pressure]], especially when small. Deciduous trees experience much less branch and trunk breakage from glaze ice storms when leafless, and plants can reduce water loss due to the reduction in availability of liquid water during cold winter days.<ref>{{cite journal |last= Lemon |first= P. C. |year= 1961 |title= Forest ecology of ice storms |journal= Bulletin of the Torrey Botanical Club |volume= 88 |issue= 1 |pages= 21–29 |doi= 10.2307/2482410 |jstor= 2482410 }}</ref>

Losing leaves in winter may reduce damage from insects; repairing leaves and keeping them functional may be more costly than just losing and regrowing them.<ref name=Labandeira1994>{{cite journal
 |last1= Labandeira |first1= C. C.
 |last2= Dilcher |first2= D. L.
 |last3= Davis |first3= D. R.
 |last4= Wagner |first4= D. L.
 |year= 1994
 |title= Ninety-seven million years of angiosperm-insect association: paleobiological insights into the meaning of coevolution
 |journal= Proceedings of the National Academy of Sciences of the United States of America
 |volume= 91
 |issue= 25
 |pages= 12278–12282
 |doi= 10.1073/pnas.91.25.12278
 |pmid= 11607501
 |pmc= 45420
 |bibcode= 1994PNAS...9112278L
|doi-access= free
 }}</ref> Removing leaves also reduces [[Cavitation#Vascular plants|cavitation]] which can damage [[xylem]] vessels in plants.<ref>{{Citation |last=Mayr |first=Stefan |title=Freezing Stress in Tree Xylem |date=2016 |work=Progress in Botany 77 |pages=381–414 |editor-last=Lüttge |editor-first=Ulrich |url=https://link.springer.com/chapter/10.1007/978-3-319-25688-7_13 |access-date=2024-10-31 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-25688-7_13 |isbn=978-3-319-25688-7 |last2=Améglio |first2=Thierry |editor2-last=Cánovas |editor2-first=Francisco M. |editor3-last=Matyssek |editor3-first=Rainer|url-access=subscription }}</ref> This then allows deciduous plants to have xylem vessels with larger diameters and therefore a greater rate of [[transpiration]] (and hence CO<sub>2</sub> uptake as this occurs when [[stomata]] are open) during the summer growth period.

==== Deciduous woody plants ====

The deciduous characteristic has developed repeatedly among woody plants. Trees include [[maple]], many [[oak]]s and [[nothofagus]], [[elm]], [[beech]], [[aspen]], and [[birch]], among others, as well as a number of [[conifer]]ous [[genus|genera]], such as [[larch]] and ''[[Metasequoia]]''. Deciduous shrubs include [[honeysuckle]], [[viburnum]], and many others. Most temperate woody vines are also deciduous, including [[Vitis|grape]]s, [[poison ivy]], [[Virginia creeper]], [[wisteria]], etc. The characteristic is useful in plant identification; for instance in parts of [[Southern California]] and the [[American Southeast]], deciduous and [[evergreen oak]] species may grow side by side.{{cn|date=November 2023}}

Periods of leaf fall often coincide with seasons: winter in the case of cool-climate plants or the dry-season in the case of tropical plants,<ref>{{cite book |last= Cundall |first= Peter |year= 2005 |title= Flora: The Gardener's Bible: Over 20,000 Plants |location= Ultimo, NSW, Australia |publisher= ABC Publishing |isbn= 0-7333-1094-X }}</ref> however there are no deciduous species among tree-like [[monocotyledonous]] plants, e.g. [[Arecaceae|palms]], [[yucca]]s, and [[Dracaena (plant)|dracaenas]]. The [[hydrangea hirta]] is a deciduous woody shrub found in [[Japan]].{{cn|date=November 2023}}

=== Regions ===
[[File:Sydney in Autumn.jpg|thumb|[[Deciduous trees]] were introduced to the [[temperate]] regions of [[Australia]] where they are used as [[ornamental plants]], as seen here at a [[urban forestry|suburban street]] in [[Sydney]].]]
Forests where a majority of the trees lose their foliage at the end of the typical growing season are called deciduous forests. These forests are found in many areas worldwide and have distinctive ecosystems, understory growth, and [[soil]] dynamics.<ref>{{cite book |editor1-last= Röhrig |editor1-first= Ernst |editor2-last= Ulrich |editor2-first= Bernhard |year= 1991 |title= Temperate deciduous forests |series= Ecosystems of the world, 7 |location= Amsterdam |publisher= Elsevier |isbn= 0-444-88599-4 }}</ref>

Two distinctive types of deciduous forests are found growing around the world.

[[Temperate deciduous forest]] biomes are plant communities distributed in North and South America, Asia, Southern slopes of the Himalayas, Europe and for cultivation purposes in Oceania. They have formed under climatic conditions which have great seasonable temperature variability. Growth occurs during warm summers, leaf drop in autumn, and dormancy during cold winters. These seasonally distinctive communities have diverse life forms that are impacted greatly by the seasonality of their climate, mainly temperature and precipitation rates. These varying and regionally different ecological conditions produce distinctive forest plant communities in different regions.{{cn|date=June 2023}}

[[Tropical and subtropical dry broadleaf forests|Tropical and subtropical deciduous forest]] biomes have developed in response not to seasonal temperature variations but to seasonal rainfall patterns. During prolonged dry periods the foliage is dropped to conserve water and prevent death from drought. Leaf drop is not seasonally dependent as it is in temperate climates.  It can occur any time of year and varies by region of the world.{{Citation needed|date=December 2021}} Even within a small local area there can be variations in the timing and duration of leaf drop; different sides of the same mountain and areas that have high water tables or areas along streams and rivers can produce a patchwork of leafy and leafless trees.<ref>{{cite journal |first= Stephen H. |last= Bullock |author2= J. Arturo Solis-Magallanes |title= Phenology of Canopy Trees of a Tropical Deciduous Forest in Mexico |journal= Biotropica |date= March 1990 |pages= 22–35 |doi= 10.2307/2388716 |volume= 22 |issue= 1 |jstor= 2388716 |bibcode= 1990Biotr..22...22B }}</ref>

<gallery widths="200" heights="160">
File:Chacachacare dry forest 3.JPG|alt=Aerial view of tropical deciduous trees|Dry-season deciduous [[tropical forest]]
File:Spring Forest Leaves in Texas Hill Country.jpg|alt=View of treetops with light spring growth scattered amid darker evergreens|Mixed tropical and subtropical deciduous forest in spring, [[Texas]], United States
File:Dry Teak Forest Theppakadu Mudumalai Mar21 A7C 00488.jpg|Tropical [[dry deciduous forest]]s in southern India in the [[Mudumalai Tiger Reserve]]
</gallery>