PINE
A pine is any conifer in
the genus Pinus of the family Pinaceae. Pinus is the sole
genus in the subfamily Pinoideae. The Plant
List compiled by the Royal Botanic Gardens, Kew, and Missouri
Botanical Garden accepts 126 species names of pines as current, together
with 35 unresolved species and many more synonyms. Pine may also refer to
the lumber derived from pine trees; pine is one of the more
extensively used types of wood used as lumber.
Etymology
The modern English name "pine" derives
from Latin pinus, which some have traced to the Indo-European
base pīt- ‘resin’ (source of English pituitary). Before the 19th century, pines were often
referred to as firs (from Old Norse fura, by way
of Middle English firre). In some European languages, Germanic
cognates of the Old Norse name are still in use for pines—in Danish for,
in Norwegian fura/fure/furu, Swedish fura/furu, Dutch vuren,
and German Föhre—but in modern English, fir is
now restricted to fir (Abies) and Douglas fir (Pseudotsuga).
Description
Pine trees are evergreen, coniferous resinous trees (or,
rarely, shrubs) growing 3–80 m (10–260 ft) tall, with the
majority of species reaching 15–45 m (50–150 ft) tall. The
smallest are Siberian dwarf pine and Potosi pinyon, and the tallest
is an 81.79 m (268.35 ft) tall ponderosa pine located in
southern Oregon's Rogue River-Siskiyou National Forest.
Pines are long-lived and typically reach ages of
100–1,000 years, some even more. The longest-lived is the Great Basin
bristlecone pine, Pinus longaeva. One individual of this species,
dubbed "Methuselah", is one of the world's oldest living
organisms at around 4,600 years old. This tree can be found in
the White Mountains of California. An older tree, now cut down,
was dated at 4,900 years old. It was discovered in a grove
beneath Wheeler Peak and it is now known as "Prometheus"
after the Greek immortal.
The spiral growth of branches, needles, and cone
scales may be arranged in Fibonacci number ratios. The new
spring shoots are sometimes called "candles"; they are covered in
brown or whitish bud scales and point upward at first, then later turn green
and spread outward. These "candles" offer foresters a means
to evaluate the fertility of the soil and the vigor of the trees.
Bark
The bark of most pines is thick and
scaly, but some species have thin, flaky bark. The branches are produced
in regular "pseudo whorls", actually a very tight spiral but
appearing like a ring of branches arising from the same point. Many pines are
unimodal, producing just one such whorl of branches each year, from buds at
the tip of the year's new shoot, but others are multinodal, producing two
or more whorls of branches per year.
Foliage
Pines have four types of leaf:
- Seed leaves (cotyledons) on seedlings are borne in a whorl of 4–24.
- Juvenile leaves, which follow immediately on seedlings and young plants, are 2–6 cm long, single, green, or often blue-green, and arranged spirally on the shoot. These are produced for six months to five years, rarely longer.
- Scale leaves, similar to bud scales, are small, brown, and not photosynthetic, and arranged spirally like the juvenile leaves.
- Needles, the adult leaves, are green (photosynthetic) and bundled in clusters called fascicles. The needles can number from one to seven per fascicle but generally number from two to five. Each fascicle is produced from a small bud on a dwarf shoot in the axil of a scale leaf. These bud scales often remain on the fascicle as a basal sheath. The needles persist for 1.5–40 years, depending on species. If a shoot is damaged (e.g. eaten by an animal), the needle fascicles just below the damage will generate a bud which can then replace the lost leaves.
Cones
Pines are mostly monoecious, having the male
and female cones on the same tree, though a few species
are sub-dioecious, with individuals predominantly, but not wholly,
single-sex. The male cones are small, typically 1–5 cm long, and only present
for a short period (usually in spring, though autumn in a few pines), falling
as soon as they have shed their pollen. The female cones take 1.5–3 years
(depending on species) to mature after pollination, with actual
fertilization delayed one year. At maturity, the female cones are 3–60 cm long.
Each cone has numerous spirally arranged scales, with two seeds on each fertile
scale; the scales at the base and tip of the cone are small and sterile,
without seeds.
The seeds are mostly small and winged and
are anemophilous (wind-dispersed), but some are larger and have only
a vestigial wing, and are bird-dispersed (see below). Female cones are
woody and sometimes armed to protect developing seeds from foragers. At
maturity, the cones usually open to release the seeds. In some of the
bird-dispersed species, for example, whitebark pine,), the seeds are only
released by the bird breaking the cones open. In others, the seeds are stored
in closed cones for many years until an environmental cue triggers the cones to
open, releasing the seeds. This is called serotiny. The most common form
of serotiny is presence, in which a resin binds the cones shut until melted
by a forest fire, for example in Pinus rigida.
Evolutionary history
Conifers evolved about 300 million years ago,
and pines perhaps around 153 million years ago. The genus Pinus is
thought to have diverged from other pines about 95 million years ago.
Pinus is the largest genus of the Pinaceae,
the pine family, which is the oldest and largest conifer family. It dates back
to 206 million years ago. Based on
recent transcriptome analysis, Pinus is most closely
related to the genus Cathaya, which in turn is closely related
to spruces. These genera, with firs and larches, form the
pinoid clade of the Pinaceae.
The evolutionary history of the genus Pinus has
been complicated by hybridization. Pines are prone to inter-specific
breeding. Wind pollination, long life spans, overlapping generations, large
population size, and weak reproductive isolation make breeding across
species more likely. As the pines have diversified, gene transfer between
different species has created a complex history of genetic relatedness.
Taxonomy, nomenclature, and codification
Pines are gymnosperms. The genus is divided
into two subgenera based on the number of fibrovascular bundles in
the needle. The subgenera can be distinguished by cone, seed, and leaf
characters:
·Pinus subg. Pinus,
the yellow, or hard pine group, generally with harder wood and two or three
needles per fascicle. The subgenus is also named diploxylon,
on account of its two fibrovascular bundles.
· Pinus subg. Strobus,
the white, or soft pine group. Its members usually have softer wood and five
needles per fascicle. The subgenus is also named haloxyfop,
on account of its one fibrovascular bundle.
Each subgenus is further divided into sections and
subsections.
Many of the smaller groups of Pinus are
composed of closely related species with recent divergence and a history of
hybridization. This results in low morphological and genetic differences. This,
coupled with low sampling and underdeveloped genetic techniques, has made
taxonomy difficult to determine. Recent research using large genetic datasets
has clarified these relationships into the groupings we recognize today.
Distribution
Pines are native to the Northern Hemisphere,
and in a few parts of the tropics in the Southern Hemisphere. Most regions
of the Northern Hemisphere (see List of pines by region) host
some native species of pines. One species (Sumatran pine) crosses the
equator in Sumatra to 2°S. In North America, various species occur in regions
at latitudes from as far north as 66°N to as far south as 12°N.
Pines may be found in a very large variety of
environments, ranging from semi-arid desert to rainforests, from sea level up
to 5,200 meters (17,100 ft), from the coldest to the hottest environments
on Earth. They often occur in mountainous areas with favorable soils and at least
some water.
Ecology
Pines grow well in acid soils, some also
on calcareous soils; most require good soil drainage, preferring
sandy soils, but a few (e.g. lodgepole pine) can tolerate poorly drained
wet soils. A few are able to sprout after forest fires (e.g. Canary Island
pine). Some species of pines (e.g. bishop pine) need fire to regenerate,
and their populations slowly decline under fire suppression regimes.
Several species are adapted to extreme conditions
imposed by elevation and latitude (e.g. Siberian dwarf pine, mountain
pine, whitebark pine, and the bristlecone pines). The pinyon pines and a
number of others, notably Turkish pine and gray pine, are
particularly well adapted to growth in hot, dry semi-desert climates.
The seeds are commonly eaten by birds, such as
grouse, crossbills, jays, nuthatches, siskins, and woodpeckers, and
by squirrels. Some birds, notably the spotted
nutcracker, Clark's nutcracker, and pinyon jay, are of importance in
distributing pine seeds to new areas. Pine needles are sometimes eaten by
some Lepidoptera (butterfly and moth) species
(see list of Lepidoptera that feed on pines), the Symphytan species pine
sawfly, and goats.
Pine pollen may play an important role in
the functioning of detrital food webs. Nutrients from pollen aid
detritivores in development, growth, and maturation, and may enable fungi to
decompose nutritionally scarce litter. Pine pollen is also involved in
moving plant matter between terrestrial and aquatic ecosystems.
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