Editing Conifer (section)

==Description==

{{refimprove section|date=April 2025}}

[[File: 00 29 0496 Waipoua Forest NZ - Kauri Baum Tane Mahuta.jpg|thumb|right|[[Tāne Mahuta]], the biggest [[kauri]] (''Agathis australis'') tree alive, in the [[Waipoua Forest]] of the Northland Region of [[New Zealand]].]]

All living conifers are woody plants, and most are trees, the majority having a monopodial growth form (a single, straight trunk with side branches) with strong [[apical dominance]]. Many conifers have distinctly scented [[resin]], secreted to protect the tree against [[insect]] infestation and [[fungus|fungal]] infection of wounds. Fossilized resin hardens into [[amber]], which has been commercially exploited historically (for example, in New Zealand's 19th-century [[kauri gum]] industry).

The size of mature conifers varies from less than one metre to over 100 metres in height.<ref>{{cite book |last1=Enright |first1=Neal J. |last2=Hill |first2=Robert S. |title=Ecology of the Southern Conifers |date=1995 |publisher=Melbourne University Press |isbn=978-0-522-84566-2 }}{{pn|date=January 2025}}</ref> The world's tallest, thickest, largest, and oldest living trees are all conifers. The tallest is a [[Sequoia sempervirens|coast redwood]] (''Sequoia sempervirens''), with a height of 115.55 metres (although one mountain ash, ''[[Eucalyptus regnans]]'', allegedly grew to a height of 140 metres,<ref>{{Cite news |date=1872-02-22 |title=STATE FOREST OF THE WATTS RIVER. |url=http://nla.gov.au/nla.news-article197448140 |access-date=2024-04-06 |work=Age}}</ref> the tallest living [[Flowering plant|angiosperms]] are significantly smaller at around 100 metres.<ref>{{Cite journal |last1=Shenkin |first1=Alexander |last2=Chandler |first2=Chris J. |last3=Boyd |first3=Doreen S. |last4=Jackson |first4=Toby |last5=Disney |first5=Mathias |last6=Majalap |first6=Noreen |last7=Nilus |first7=Reuben |last8=Foody |first8=Giles |last9=bin Jami |first9=Jamiluddin |last10=Reynolds |first10=Glen |last11=Wilkes |first11=Phil |last12=Cutler |first12=Mark E. J. |last13=van der Heijden |first13=Geertje M. F. |last14=Burslem |first14=David F. R. P. |last15=Coomes |first15=David A. |date=2019 |title=The World's Tallest Tropical Tree in Three Dimensions |journal=Frontiers in Forests and Global Change |volume=2 |page=32 |doi=10.3389/ffgc.2019.00032 |doi-access=free |bibcode=2019FrFGC...2...32S |hdl=2164/12435 |hdl-access=free }}</ref><ref>{{Cite news |date=2018-12-11 |title=100 metres and growing: Australia's tallest tree leaves all others in the shade |url=https://www.abc.net.au/news/2018-12-12/new-milestone-for-australias-tallest-tree-centurion/10604588 |access-date=2024-04-06 |work=ABC News |language=en-AU}}</ref>) The thickest (that is, the [[Árbol del Tule|tree with the greatest trunk diameter]]) is a [[Taxodium mucronatum|Montezuma cypress]] (''Taxodium mucronatum''), 11.42 metres in diameter. The largest tree by three-dimensional volume is a giant sequoia (''[[Sequoiadendron giganteum]]''), with a volume 1486.9 cubic metres.<ref>{{cite book |last=Vidaković |first=Mirko |title=Conifers: Morphology and Variation |date=1991 |publisher=CAB International |isbn=978-86-399-0279-7 }}{{pn|date=January 2025}}</ref> The smallest is the [[Lepidothamnus laxifolius|pygmy pine]] (''Lepidothamnus laxifolius'') of New Zealand, which is seldom taller than 30&nbsp;cm when mature.<ref>{{cite web |last=Wassilieff |first=Maggy |title=Conifers |publisher=Te Ara&nbsp;– the Encyclopedia of New Zealand updated 1-Mar-09 |url=http://www.teara.govt.nz/en/conifers/6/5 |access-date=17 December 2012 |archive-date=1 March 2010 |archive-url=https://web.archive.org/web/20100301031106/http://www.teara.govt.nz/en/conifers/6/5 |url-status=live }}</ref> The oldest non-clonal living tree is a Great Basin bristlecone pine (''[[Pinus longaeva]]''), 4,700 years old.<ref>{{cite book|last1=Dallimore|first1=W.|first2=A.B.|last2=Jackson|first3=S.G.|last3=Harrison|year=1967|title=A handbook of Coniferae and Ginkgoaceae|edition=4th|location=New York|publisher=St. Martin's Press|page=xix}}</ref>

===Foliage===
[[File:Pseudotsuga menziesii 06280.JPG|left|thumb|upright|[[Pinaceae]]: needle-like leaves and vegetative buds of Coast Douglas fir ([[Pseudotsuga menziesii var. menziesii|''Pseudotsuga menziesii'' var. ''menziesii'']])]]
[[File:Araucaria Leaves.JPG|thumb|[[Araucariaceae]]: awl-like leaves of Cook pine (''[[Araucaria columnaris]]'')]]
[[File:Abies grandis 5359.JPG|left|thumb|upright|In ''[[Abies grandis]]'' (''grand fir''), and many other species with spirally arranged leaves, leaf bases are twisted to flatten their arrangement and maximize light capture.]]
[[File:C lawsoniana Lge.jpg|thumb|[[Cupressaceae]]: scale leaves of [[Chamaecyparis lawsoniana|Lawson's cypress]] (''Chamaecyparis lawsoniana''); scale in mm]]

Since most conifers are evergreens,<ref name="Campbell-2005" /> the [[leaf|leaves]] of many conifers are long, thin and have a needle-like appearance, but others, including most of the [[Cupressaceae]] and some of the [[Podocarpaceae]], have flat, triangular scale-like leaves. Some, notably ''[[Agathis]]'' in Araucariaceae and ''[[Nageia]]'' in Podocarpaceae, have broad, flat strap-shaped leaves. Others such as ''[[Araucaria columnaris]]'' have leaves that are awl-shaped. In the majority of conifers, the leaves are arranged spirally, the exceptions being most of Cupressaceae and one genus in Podocarpaceae, where they are arranged in decussate opposite pairs or whorls of 3 (−4).

In many species with spirally arranged leaves, such as ''[[Abies grandis]]'' (pictured), the leaf bases are twisted to present the leaves in a very flat plane for maximum light capture. Leaf size varies from 2&nbsp;mm in many scale-leaved species, up to 400&nbsp;mm long in the needles of some pines (e.g. Apache pine, ''[[Pinus engelmannii]]''). The [[stoma]]ta are in lines or patches on the leaves and can be closed when it is very dry or cold. The leaves are often dark green in colour, which may help absorb a maximum of energy from weak sunshine at high [[latitude]]s or under forest canopy shade.

Conifers from lower latitudes with high sunlight levels (e.g. Turkish pine ''[[Pinus brutia]]'') often have yellower-green leaves, while others (e.g. [[blue spruce]], ''Picea pungens'') may develop blue or silvery leaves to reflect [[ultraviolet]] light. In the great majority of genera the leaves are [[evergreen]], usually remaining on the plant for several (2–40) years before falling, but five genera (''[[larch|Larix]]'', ''[[Pseudolarix]]'', ''[[Glyptostrobus]]'', ''[[Metasequoia]]'' and ''[[Taxodium]]'') are [[deciduous]], shedding their leaves in autumn.<ref name="Campbell-2005" /> The seedlings of many conifers, including most of the Cupressaceae, and ''Pinus'' in Pinaceae, have a distinct juvenile foliage period where the leaves are different, often markedly so, from the typical adult leaves.

===Tree ring structure===
[[File:Report on the relation of railroads to forest supplies and forestry - together with appendices on the structure of some timber ties, their behavior, and the cause of their decay in the road bed, on (14755970324).jpg|thumb|A thin transverse section showing the internal structure of conifer wood]]

[[Dendrochronology#Growth rings|Tree rings]] are records of the [[wikt:influence|influence]] of [[Ecology#Physical environments|environmental]] conditions, their anatomical characteristics record growth rate changes produced by these changing conditions. The microscopic [[structure]] of conifer wood consists of two types of [[cell (biology)|cells]]: '''parenchyma''', which have an oval or polyhedral shape with approximately identical dimensions in three directions, and strongly elongated tracheids. '''Tracheids''' make up more than 90% of timber volume. The tracheids of earlywood formed at the beginning of a [[growing season]] have large radial sizes and smaller, thinner [[cell wall]]s. Then, the first tracheids of the transition zone are formed, where the radial size of cells and the thickness of their cell walls changes considerably. Finally, latewood tracheids are formed, with small radial sizes and greater cell wall thickness. This is the basic pattern of the internal cell structure of conifer tree rings.<ref name="Ledig-1982">{{cite journal |last1=Ledig |first1=F. Thomas |last2=Porterfield |first2=Richard L. |date=1982 |title=Tree Improvement in Western Conifers: Economic Aspects |journal=Journal of Forestry |volume=80 |issue=10 |pages=653–657 |doi=10.1093/jof/80.10.653 |osti=5675533 }}</ref>

===Reproduction===

{{Main|Conifer cone}}

Most conifers are [[Plant reproductive morphology#Terminology|monoecious]], but some are [[Plant reproductive morphology#Terminology|subdioecious]] or [[Plant reproductive morphology#Terminology|dioecious]]; all are [[Anemophily|wind-pollinated]]. Conifer seeds develop inside a protective cone called a [[strobilus]]. The cones take from four months to three years to reach maturity, and vary in size from {{Convert|2 to 600|mm|frac=8}} long.

In [[Pinaceae]], [[Araucariaceae]], [[Sciadopityaceae]] and most [[Cupressaceae]], the cones are [[wood]]y, and when mature the scales usually spread open allowing the seeds to fall out and be dispersed by the [[wind]]. In some (e.g. [[fir]]s and [[Cedrus|cedar]]s), the cones disintegrate to release the seeds, and in others (e.g. the [[pine]]s that produce [[pine nut]]s) the nut-like seeds are dispersed by [[bird]]s (mainly [[Nutcracker (bird)|nutcracker]]s, and [[jay]]s), which break up the specially adapted softer cones. Ripe cones may remain on the plant for a varied amount of time before falling to the ground; in some fire-adapted pines, the seeds may be stored in closed cones for up to 60–80 years, being released only when a fire kills the parent tree.

In the families [[Podocarpaceae]], [[Cephalotaxaceae]], [[Taxaceae]], and one [[Cupressaceae]] genus (''[[Juniper]]us''), the scales are soft, fleshy, sweet, and brightly colored, and are eaten by fruit-eating birds, which then pass the seeds in their droppings. These fleshy scales are (except in ''Juniperus'') known as [[aril]]s. In some of these conifers (e.g. most Podocarpaceae), the cone consists of several fused scales, while in others (e.g. Taxaceae), the cone is reduced to just one seed scale or (e.g. Cephalotaxaceae) the several scales of a cone develop into individual arils, giving the appearance of a cluster of berries.

The male cones have structures called [[sporangium|microsporangia]] that produce yellowish pollen through meiosis. Pollen is released and carried by the wind to female cones. Pollen grains from living pinophyte species produce pollen tubes, much like those of angiosperms. The [[gymnosperm]] male gametophytes (pollen grains) are carried by wind to a female cone and are drawn into a tiny opening on the ovule called the [[wikt:micropyle|micropyle]]. It is within the ovule that pollen-germination occurs. From here, a pollen tube seeks out the female gametophyte, which contains archegonia each with an egg, and if successful, fertilization occurs. The resulting [[zygote]] develops into an [[embryo]], which along with the female gametophyte (nutritional material for the growing embryo) and its surrounding integument, becomes a [[seed]]. Eventually, the seed may fall to the ground and, if conditions permit, grow into a new plant.

In [[forestry]], the terminology of [[flowering plant]]s has commonly though inaccurately been applied to cone-bearing trees as well. The male cone and unfertilized female cone are called ''male flower'' and ''female flower'', respectively. After fertilization, the female cone is termed ''fruit'', which undergoes ''ripening'' (maturation).

It was found recently that the [[pollen]] of conifers transfers the [[mitochondria]]l [[organelle]]s to the [[embryo]],{{citation needed|date=June 2021}} a sort of [[meiosis|meiotic]] drive that perhaps explains why ''[[Pinus]]'' and other conifers are so productive, and perhaps also has bearing on observed sex-ratio bias.{{citation needed|date=August 2021}}

<gallery class="center">
File:Abies lasiocarpa 6972.JPG|Pinaceae: unopened female cones of [[Abies lasiocarpa|subalpine fir]] (''Abies lasiocarpa'')
Taxus baccata MHNT.jpg|Taxaceae: the fleshy aril that surrounds each seed in the [[Taxus baccata|European yew]] (''Taxus baccata'') is a highly modified seed cone scale
Japanese Larch pollen cone, Cardiff, Wales.jpg|Pinaceae: pollen cone of a [[Japanese larch]] (''Larix kaempferi'')
</gallery>

===Life cycle===

Conifers are [[heterosporous]], generating two different types of spores: male [[microspore]]s and female [[megaspore]]s. These spores develop on separate male and female [[sporophylls]] on separate male and female cones. In the male cones, microspores are produced from microsporocytes by [[meiosis]]. The microspores develop into pollen grains, which contain the male gametophytes. Large amounts of pollen are released and carried by the wind. Some pollen grains will land on a female cone for pollination. The generative cell in the pollen grain divides into two [[haploid]] sperm cells by [[mitosis]] leading to the development of the pollen tube. At fertilization, one of the sperm cells unites its haploid nucleus with the haploid nucleus of an egg cell. The female cone develops two ovules, each of which contains haploid megaspores. A megasporocyte is divided by meiosis in each ovule. Each winged pollen grain is a four celled male [[gametophyte]]. Three of the four cells break down leaving only a single surviving cell which develop into a female [[multicellular]] gametophyte. The female gametophytes grow to produce two or more [[archegonia]], each of which contains an egg. Upon fertilization, the [[diploid]] egg gives rise to the embryo, and a seed is produced. The female cone then opens, releasing the seeds which grow to a young [[seedling]].

# To fertilize the ovum, the male cone releases [[pollen]] that is carried in the wind to the female cone. This is [[pollination]]. (Male and female cones usually occur on the same plant.)
# The pollen fertilizes the female gamete (located in the female cone). Fertilization in some species does not occur until 15 months after pollination.<ref>{{Cite web |url=http://bioserv.fiu.edu/~biolab/labs/1011/Spring%202009/TA%20notes%20and%20pictures/Week%205%20-%20Seed%20Plants.htm |title=Gymnosperms |access-date=2014-05-11 |archive-date=2015-05-27 |archive-url=https://web.archive.org/web/20150527001621/http://bioserv.fiu.edu/~biolab/labs/1011/Spring%202009/TA%20notes%20and%20pictures/Week%205%20-%20Seed%20Plants.htm |url-status=dead }}</ref>
# A fertilized female gamete (called a [[zygote]]) develops into an [[embryo]].
# A [[seed]] develops which contains the embryo. The seed also contains the integument cells surrounding the embryo. This is an evolutionary characteristic of the [[Spermatophyta]].
# Mature seed drops out of cone onto the ground.
# Seed germinates and seedling grows into a mature plant.
# When the plant is mature, it produces cones and the cycle continues.

==== Female reproductive cycles ====
Conifer reproduction is synchronous with seasonal changes in temperate zones. Reproductive development slows to a halt during each winter season and then resumes each spring. The male [[strobilus]] development is completed in a single year. Conifers are classified by three reproductive cycles that refer to the completion of female strobilus development from initiation to seed maturation. All three types of reproductive cycle have a long gap between [[pollination]] and [[fertilization]].

'''One year reproductive cycle''': The genera include ''[[Abies]]'', ''[[Picea]]'', ''[[Cedrus]]'', ''[[Pseudotsuga]],'' ''[[Tsuga]]'', ''[[Keteleeria]]'' ''([[Pinaceae]])'' and ''[[Cupressus]], [[Thuja]], [[Cryptomeria]], [[Cunninghamia]]'' and ''[[Sequoia (genus)|Sequoia]] ([[Cupressaceae]])''. Female strobili are initiated in late summer or fall of a year, then they overwinter. Female strobili emerge followed by pollination in the following spring. Fertilization takes place in summer of the following year, only 3–4 months after pollination. Cones mature and seeds are then shed by the end of that same year. Pollination and fertilization occur in a single growing season.<ref name="Singh-1978">{{cite book |last=Singh |first=Hardev |title=Embryology of Gymnosperms |date=1978 |publisher=Gerbrüder Borntraeger |isbn=978-3-443-14011-3 }}{{pn|date=January 2025}}</ref>

'''Two-year reproductive cycle''': The genera includes ''[[Widdringtonia]]'', ''[[Sequoiadendron]]'' (''[[Cupressaceae]]'') and most species of ''Pinus''. Female [[strobilus]] initials are formed in late summer or fall then overwinter. Female strobili emerge and receive pollen in the first year spring and become conelets. The conelet goes through another winter rest and, in the spring of the second year [[archegonia]] form in the conelet. Fertilization of the archegonia occurs by early summer of the second year, so the pollination-fertilization interval exceeds a year. After fertilization, the conelet is considered an immature cone. Maturation occurs by autumn of the second year, at which time seeds are shed. In summary, the one-year and the two-year cycles differ mainly in the duration of the pollination-fertilization interval.<ref name="Singh-1978"/>

'''Three-year reproductive cycle''': Three of the conifer species are [[pine]] species (''[[Pinus pinea]]'', ''[[Pinus leiophylla]]'', ''[[Pinus torreyana]]'') which have pollination and fertilization events separated by a two-year interval. Female strobili initiated during late summer or autumn of a year, then overwinter until the following spring. Female [[strobili]] emerge then pollination occurs in spring of the second year then the pollinated strobili become conelets in the same year (i.e. the second year). The female [[gametophytes]] in the conelet develop so slowly that the [[megaspore]] does not go through free-nuclear divisions until autumn of the third year. The conelet then overwinters again in the free-nuclear female gametophyte stage. Fertilization takes place by early summer of the fourth year and seeds mature in the cones by autumn of the fourth year.<ref name="Singh-1978"/>

==== Tree development ====
The growth and form of a forest tree are the result of activity in the primary and secondary [[meristem]]s, influenced by the distribution of photosynthate from its needles and the hormonal gradients controlled by the apical meristems.<ref name="Fraser-1964">{{cite journal|last1=Fraser|first1=D.A.|last2=Belanger|first2=L.|last3=McGuire|first3=D.|last4=Zdrazil|first4=Z.|year=1964|title=Total growth of the aerial parts of a white spruce tree at Chalk River, Ontario, Canada|journal=Can. J. Bot.|volume=42|issue=2 |pages=159–179|doi=10.1139/b64-017 |bibcode=1964CaJB...42..159F }}</ref> External factors also influence growth and form.

Fraser recorded the development of a single white spruce tree from 1926 to 1961. Apical growth of the stem was slow from 1926 through 1936 when the tree was competing with [[herb]]s and [[shrub]]s and probably shaded by larger trees. Lateral branches began to show reduced growth and some were no longer in evidence on the 36-year-old tree. Apical growth totaling about 340 m, 370 m, 420 m, 450 m, 500 m, 600 m, and 600 m was made by the tree in the years 1955 through 1961, respectively. The total number of needles of all ages present on the 36-year-old tree in 1961 was 5.25&nbsp;million weighing 14.25&nbsp;kg. In 1961, needles as old as 13 years remained on the tree. The ash weight of needles increased progressively with age from about 4% in first-year needles in 1961 to about 8% in needles 10 years old. In discussing the data obtained from the one 11 m tall white spruce, Fraser et al. (1964)<ref name="Fraser-1964" /> speculated that if the photosynthate used in making apical growth in 1961 was manufactured the previous year, then the 4&nbsp;million needles that were produced up to 1960 manufactured food for about 600,000&nbsp;mm of apical growth or 730 g dry weight, over 12&nbsp;million mm<sup>3</sup> of wood for the 1961 annual ring, plus 1&nbsp;million new needles, in addition to new tissue in branches, bark, and roots in 1960. Added to this would be the photosynthate to produce energy to sustain respiration over this period, an amount estimated to be about 10% of the total annual photosynthate production of a young healthy tree. On this basis, one needle produced food for about 0.19&nbsp;mg dry weight of apical growth, 3&nbsp;mm<sup>3</sup> wood, one-quarter of a new needle, plus an unknown amount of branch wood, bark and roots.

The order of priority of photosynthate distribution is probably: first to apical growth and new needle formation, then to buds for the next year's growth, with the cambium in the older parts of the branches receiving sustenance last. In the white spruce studied by Fraser et al. (1964),<ref name="Fraser-1964" /> the needles constituted 17.5% of the over-day weight. Undoubtedly, the proportions change with time.

===Seed-dispersal mechanism===

Wind and animal dispersals are two major mechanisms involved in the dispersal of conifer seeds. Wind-born seed dispersal involves two processes, namely; local neighborhood dispersal and long-distance dispersal. Long-distance dispersal distances range from {{convert|11.9|-|33.7|km}} from the source.<ref>{{cite journal|last1=Williams|first1=C.G.|last2=LaDeau|first2=S.L. |last3=Oren|first3=R. |last4=Katul|first4=G.G. |year=2006 |title=Modeling seed dispersal distances: implications for transgenic Pinus taeda |journal=Ecological Applications |volume=16|issue=1 |pages=117–124|doi=10.1890/04-1901 |pmid=16705965 |bibcode=2006EcoAp..16..117W }}</ref>
Birds of the crow family, [[Corvidae]], are the primary distributor of the conifer seeds. These birds are known to [[Hoarding (animal behavior)|cache]] 32,000 pine seeds and transport the seeds as far as {{convert|12|-|22|km|abbr=on}} from the source. The birds store the seeds in the soil at depths of {{convert|2|–|3|cm|abbr=on|frac=4}} under conditions which favor [[germination]].<ref>{{cite journal |last1=Tomback |first1=D. |author-link=Diana Tomback |first2=Y. |last2=Linhart |year=1990|title=The evolution of bird-dispersed pines |journal=Evolutionary Ecology |volume=4|issue=3|pages=185–219 |doi=10.1007/BF02214330 |bibcode=1990EvEco...4..185T }}</ref>