Bark

Bark is the outermost layer of stems and roots of woody plants, such as trees and shrubs. The tissues included depend on how broadly the term is defined and the age of the plant (whether considering primary tissues or secondary growth). Broadly defined, bark refers to all those tissues outside the vascular cambium, or all tissues from the living phloem outward. However, in popular use, the term bark is often used in reference to only the cork or only to the periderm (cork, cork cambium, and phellederm) in plants with secondary growth. Some definitions include the vascular cambium in the definition.

The outer bark of dead cork cells gives the pattern seen in trees, adding to the diversity in nature and enhancing human aesthetic pleasure. But bark also provides many other values to human beings. Bark is the source of the anti-malarial drug quinine, the commonly used salicylic acid (aspirin), and numerous cancer drugs, as well as adding a wide variety of other benefits, such as cork, teas, cinnamon, fiber, tannic acid, and so forth.

Tissues included in bark

For many plants, the dividing point between bark and the rest of the organism usually is considered the vascular cambium. The vascular cambium is a part of a woody stem where cell division occurs. It contains undifferentiated cells that divide rapidly to produce secondary xylem to the inside and secondary phloem to the outside. The vascular cambium lies between these two layers. Vascular cambium is usually found on dicots and gymnosperms but not monocots, which lack secondary growth.

Along with the xylem, the phloem is one of the two tissues inside a plant that are involved with fluid transport. The phloem transports organic molecules (particularly sugars) to wherever they are needed. Xylem is the primary water-conducting tissue. Xylem is not part of the bark, whereas phloem is included.

Cork, sometimes confused with bark in colloquial speech, is the outermost layer of a woody stem, derived from the cork cambium. Cork is an external, secondary tissue impermeable to water and gases. It serves as protection against damage, parasites, and diseases, as well as dehydration and extreme temperatures. Some cork is substantially thicker, providing further insulation and giving the bark a characteristic structure; in some cases thick enough to be harvestable as cork product without killing the tree.

Epidermis is the outer, single-layered group of cells that covers the leaf and young tissues of a vascular plant, including primary tissues of stems and roots. The epidermis serves several functions—protection against water loss, regulation of gas exchange, secretion of metabolic compounds, and (especially in roots) absorption of water and mineral nutrients.

In young stems of woody plants (trees, shrubs, and some perennial vines), the bark is made up of the following tissues arranged from the outside surface to the inside:

• Cork – an external, secondary tissue impermeable to water and gases.
• Cork cambium – A layer of cells, normally one or two cell layers thick that is in a persistent meristematic state that produces cork.
• Phelloderm – (not always present) A layer of cells formed in some plants from the inner cells of the cork cambium (Cork is produced from the outer layer).
• Cortex – The primary tissue of stems and roots. In stems, the cortex is between the epidermis layer and the phloem, in roots the inner layer is not phloem but the pericycle.
• Phloem – nutrient conducting tissue composed of sieve tub or sieve cells mixed with parenchym and fibers.

In primary tissues, the bark of stems (broadly defined) includes the phloem, cortex, and epidermis, and the bark of roots would be the cortex and epidermis. The cork cambium subsequently is responsible for secondary growth that replaces the epidermis in roots and stems..

In roots with secondary growth, the cortex and epidermis may be sloughed off as cork is formed, and in these cases the bark includes the phloem, cork cambrium, cork, and phelloderm.

In old stems, the epidermal layer, cortex, and primary phloem become separated from the inner tissues by thicker formations of cork. Due to the thickening cork layer, these cells die because they do not receive water and nutrients. This dead layer is the rough corky bark that forms around tree trunks and other stems. In smaller stems and on typically non-woody plants, sometimes a secondary covering form called the periderm, which is made up of cork cambian, cork, and phelloderm. It replaces the dermal layer and acts as a covering much like the corky bark—it too is made up of mostly dead tissue. The skin on the potato is a periderm.

Uses

The bark of some trees is edible, and native American Indians used to feed on the inner bark of various trees, such as ceder, slippery elm, and white birch, when other sources of food were scarce. Diverse teas are produced from bark, such as using the inner bark of slippery elm (Ulmus rubra), and the bark from different species of trees historically has been used for such treatments as toothaches, fever, low blood pressure, asthma, inflammation, and so forth.

Many important medicinal products are obtained from bark. These include the alkaloid quinine, which is extracted from the root and trunk bark of Cinchona, native to the South American Andes. Quinine is an effective remedy against malaria, and indeed the plant was named after the Countess of Chinchon who was cured of malaria in 1623 using the bark, the Spanish having been introduced to its use in 1633 by the native Indians in Peru. Salicylic acid (aspirin) is derived from the bark of willow trees. Cancer drugs, among others, are also derived from barks, including treatments for colon, ovarian, lung, and breast cancer.

Bark is used for basketry making, clothing, and cloth (from beaten bark, principally in Pacific Islands, southeast Asia, parts of Africa and South America). Among the commercial products made from bark are cork, cinnamon, fiber, roofing material, tannic acid (used in tanning, most notably from the bark of oak, Quercus robur), and antiseptics, like tannins. Historically, shelters, belts, headdresses, coffins, and ornaments were made with bark, and canoes made from bark have been in use for over 3,000 years.

 

Alder

Alder is the common name for any of the various deciduous trees and shrubs comprising the flowering plant genus Alnus of the birch family (family Betulaceae), characterized by alternate, simple leaves, scaly bark, and flowers as male and female catkins that appear on the same plant, with the woody, cone-like female catkins opening to release the seeds in a similar manner to many conifer cones. The term alder also is used for the wood of these trees.

Alders exhibit bi-level functionality meeting not only their own needs for survival, growth, and reproduction, but also meeting needs within the ecosystem and for humans.

Ecologically, alders are important for fixing atmospheric nitrogen into a usable form for plants, as an early source of pollen for bees, and for erosion control on river banks. Humans use alder wood for making furniture and electric guitar bodies and as the preferred wood for making charcoal. Alder also is commonly used for cooking, being traditionally used for smoking fish and meat, with alder smoking especially common in the Pacific salmon industry in the Pacific Northwest. Humans also gain nutritional, medicinal, and aesthetic benefits from alders.

 

Description

The Betulaceae, to which alders belong, is known as the “birch family,” and includes six genera of deciduous nut-bearing trees and shrubs, including the birches, hazels, hornbeams, and hop-hornbeams. In the past, the family was often divided into two families, Betulaceae (Alnus, Betula) and Corylaceae (the rest); however, recent treatments have renamed these two groups as subfamilies within the Betulaceae—Betuloideae and Coryloideae. Betulaceae is closely related to the beech/oak family, Fagaceae.

Within the Betulaceae family, the genus Alnus, which comprises the alders, includes about thirty species of monoecious trees and shrubs, few reaching large size. They are distributed throughout the north temperate zone, and in the New World also along the Andes southwards to Chile.

Alder leaves are deciduous (not evergreen), alternate, simple, and serrated. The leaves during autumn leaf-fall lack the bright colors characteristic of many deciduous trees in the north temperate zone. The flowers are catkins with elongate male catkins on the same plant as shorter female catkins, often before leaves appear. The flowers mainly are wind-pollinated, but also visited by bees to a small extent. They differ from the birches (genus Betula) in that the female, dry, cone-like catkins are woody and do not disintegrate at maturity, opening to release the seeds in a similar manner to many conifer cones.

The common name alder is derived from an old Germanic root, and also is found to be the translation of the Old French “verne” for alder or copse of alders. The botanic name Alnus is the equivalent Latin name. Both the Latin and the Germanic words derive from the Proto-Indo-European root el-, meaning “red” or “brown,” which is also a root for the English words elk and another tree elm, a tree distantly related to the alders.

Species

The best-known species in Europe is the common or black alder (A. glutinosa), native to most of Europe and widely introduced elsewhere. The largest species is red alder (A. rubra), reaching 35 meters on the west coast of North America, with black alder and Italian alder (A. cordata) both reaching about 30 meters. By contrast, the widespread green alder (A. viridis) is rarely more than a 5 meter shrub.

Uses

Alder wood, which is fine-textured and durable, is commercially valuable for making furniture, guitars, and charcoal. The red alder, A. rubra, is an important timber hardwood on the North American Pacific coast. Alder is a preferred wood for charcoal making, and is popular as a material for electric guitar bodies. It is used by many guitar makers, notably the Fender Guitar Company, which uses it on top quality instruments, such as the Stratocaster and Jaguar. Alder provides a brighter tone than other woods (such as mahogany), and as alder is not a particularly dense wood it provides a resonant, well-rounded tone with excellent sustain.

Alder is commonly used for cooking. The wood is also traditionally used for smoking fish and meat, though this usage has often been replaced by other woods such as oak and hickory. An exception is the smoked Pacific salmon industry in the Pacific Northwest, where alder smoking is essentially universal. This is partly due to indigenous traditions of food preservation in the area, and partly because oak, hickory, mesquite and other woods favored for smoking elsewhere are not locally available in any large quantities. Species used for Pacific salmon smoking are red alder (A. rubra) and to a lesser extent Sitka alder (A. viridis ssp. sinuata).

Alder formerly was used in the manufacture of gunpowder, or for smelting metal ores. The bark was historically used for dyes and tanning, and remains in use for these purposes.

Alders offer some nutritional and medicinal value. Alder catkins are edible and high in protein. Although they are reported to have a bitter and unpleasant taste, they are best remembered for survival purposes. Native Americans used red alder bark (Alnus rubra) to treat poison oak, insect bites, and skin irritations. Blackfeet Native Americans used an infusion made from the bark of red alder to treat lymphatic disorders and tuberculosis. Recent clinical studies have verified that red alder contains betulin and lupeol, compounds shown to be effective against a variety of tumors (Tilford 1997).

Alders also are grown in gardens and are sometimes made into bonsai. Alders are exceptionally good windbreakers and are planted on the west coast of Scotland to shelter gardens (TFL 2008).

Ecological benefits

Ecologically, alders provide many benefits, including nitrogen fixation, an early source of pollen for bees, and erosion control on river banks because of their spreading root system.

Their ability to fix atmospheric nitrogen is a result of a symbiotic relationship with the filamentous, nitrogen-fixing actinobacteria Frankiella alni. The bacteria are contained in light brown root nodules, which may be as large as a human fist, with many small lobes. This bacteria converts atmospheric nitrogen into soil-soluble nitrates, which can be utilized by the alder, and favorably enhances the soil fertility generally. Alders benefit other plants growing near them by taking nitrogen out of the air and depositing it in the soil in usable form; fallen alder leaves make very rich compost.

Alder catkins are one of the first sources of pollen for bee species, especially honeybees, which use it for spring buildup. Alders are also used as a food plant by some Lepidoptera (butterfly and moth) species.

Alders can help in pioneering sites that are difficult for growing trees. Alders are sturdy and fast-growing, even in acidic and damaged sites such as burned areas and mining sites. Italian alder is particularly useful on dry, infertile sites. Alders can be used as a producer of simple biomass, growing quickly in harsh environments.

 

Dragon Blood Tree

Dracaena cinnabari, the Socotra Dragon Tree or Dragon Blood Tree, is a Dragon Tree native to the Socotra archipelago in the Indian Ocean. It is so called due to the red sap that the trees produce.

Taxonomy

The first description of D. cinnabari was made during a survey of Socotra led by Lieutenant Wellsted of the East India Company in 1835. It was first named Pterocarpus draco, but in 1880, the Scottish botanist Isaac Bayley Balfour made a formal description of the species and renamed it as Dracaena cinnabari. Of between 60 and 100 Dracaena species, D. cinnabari is one of only 6 species which grows as a tree.

Description

The Dragon blood tree is arguably the most famous and distinctive plant of the island of Socotra. It has a unique and strange appearance, described as “upturned, densely -packed crown having the shape of an upside-down umbrella”. This evergreen species is named after its dark red resin, that is known as “dragon’s blood”.

Unlike most monocot plants, the Dracaenaceae display secondary growth, D. cinnabari even has growth zones resembling tree rings found in dicot tree species. Along with other arborescent Dracaena species it has a distinctive growth habit called ‘Dracoid habitus’. Its leaves are only found at the end of its youngest branches, their leaves are all shed every 3 or 4 years before new leaves simultaneously mature. Branching tends to occur when the growth of the terminal bud is stopped, either due to flowering or traumatic events (e.g. herbivory).

Its fruits are small fleshy berries containing between 1 and 3 seeds. As they develop they turn from green to black and then become orange once they are ripe. The berries are eaten by birds (e.g. Onychognatus species) and thereby dispersed. The seeds are between 4mm and 5mm in diameter and weigh on average 68 mg. The berries exude a deep red resin, known as dragon’s blood.

Like other monocotyledons, such as palms, the dragon’s blood tree grows from the tip of the stem, with the long, stiff leaves borne in dense rosettes at the end (4, 5, 7). It branches at maturity to produce an umbrella shaped crown, with leaves that measure up to 60 centimeters long and 3 centimeters wide. The trunk and the branches of the Dragon blood are thick and stout and display dichotomous branching, where each of the branches repeatedly divide in two sections.

Biology

The dragon’s blood tree usually produces its flowers around February, though flowering does vary with location. The flowers tend to grow at the end of the branches. The flowers have inflorescences, and they bear small clusters of fragrant, white or green flowers. The fruits take five months to completely mature. The fruits are described as a fleshy berry, which changes from green to black as it gradually ripens. The fleshy berry fruit ends up being an orange-red color that contains one to three seeds (is only one seed). The berries are usually eaten and dispersed by birds and other animals.

The unusual shape of the dragon’s blood tree is an adaptation for survival in arid conditions with low amounts of soil, such as in mountaintops. The large, packed crown provides shade and reduces evaporation. This shade also allows aids in the survival of seedlings growing beneath the adult tree, explaining why the trees tend to grow closer together.

Evolution

Along with other plants on Socotra, D. cinnabari is thought to have derived from the Tethyan flora. It is considered a remnant of the Mio-Pliocene Laurasian subtropical forests that are now almost extinct due to the extensive desertification of North Africa.

Uses

Dragon’s blood is used as a stimulant and abortifacient . The root yields a gum-resin, used in gargle water as a stimulant, astringent and in toothpaste. The root is used in rheumatism, the leaves are a carminative.

The trees can be harvested for their crimson red resin, called Dragon’s blood which was highly prized in the ancient world and is still used today. Around the Mediterranean basin it is used as a dye and as a medicine, Socotrans use it ornamentally as well as dying wool, gluing pottery, a breath freshener and lipstick. Because of the belief that it is the blood of the dragon it is also used in ritual magic and alchemy. In 1883, the Scottish botanist, Isaac Bayley Balfour identified three grades of resin; the most valuable were tear-like in appearance, then a mixture of small chips and fragments, with a mixture of fragments and debris being the cheapest. The resin of D. cinnabari is thought to have been the original source of dragons blood until during the mediaeval and renaissance periods when other plants were used instead.

The local inhabitants of the city in the Socotra Island use the Dragon’s blood resin as a cure all. They use it in general wound healing, as a coagulant, cure for diarrhea, for dysentery diseases, for lowering fevers. It is also taken for ulcers in the mouth, throat, intestines and stomach.

Dragon’s blood of Dracaena cinnabari was used as a source of varnish for 18th century Italian violin-makers. It was also used as tooth-paste in the 18th century. It is currently still used as varnish for violins and for photoengraving.

Dragon’s blood red resin is used for religious purposes in American hoodoo, African-American folk magic, and New Orleans voodoo. Widely used in mojo hands for money-drawing or love-drawing, and is used as incense to cleanse a space of negative entities or influences. It is added to red ink to make “Dragon’s Blood Ink”, which is used to inscribe magical seals and talismans.

Threats

Although most of its ecological habitats are still intact, there is an increasing population with industrial and tourism development. This is putting more pressure on the vegetation through the process of logging, overgrazing, woodcutting and infrastructure of development plans. Though the dragon’s blood tree is highly widespread, it has become fragmented due to the development that has occurred in its habitats. Many of its populations are suffering due to poor regeneration. Human activities have greatly reduced the dragon’s blood population through overgrazing, and feeding the flowers and fruits to the livestock of the island. One of the species’ greatest threats is the gradual drying out of the Socotra Archipelago, which has been an ongoing process for the last few hundred years. This has resulted in non flourishing trees, and the duration of the mist and cloud around the area seems to also be decreasing. Increasing arid environments is predicted to cause a 45 percent reduction in the available habitat for Dracaena cinnabari by the year 2080.

Additional threats to the dragon’s blood tree include harvesting of its resin and use of the leaves to make rope. Presently some of the dragon’s blood trees have been used to make beehives. This was generally prohibited; this displays how the species may be threatened by a breakdown in the traditional practices of the island.

Conservation

The unique flora and fauna of the Socotra Archipelago is considered a World Heritage Site a Global 200 Ecoregion. It is a Center of Plant Diversity and an Endemic Bird Area. It also lies within the Horn of Africa biodiversity hotspot. There are multiple efforts that are being developed to help create and support a sustainable habitat and biodiversity management programs on Socotra. The dragon’s blood tree is considered as an important species for commodity and for conservation efforts on the island. The dragon’s blood falls under an umbrella species. This is a species selected for making conservation related decisions, typically because protecting these species indirectly protects the many other species that make up the ecological community of its habitat. Species conservation can be subjective because it is difficult to determine the status of many species. Thus, the dragons blood protection efforts would also benefit many other plants and animals within the area.

The dragon’s blood tree is given some protection from international commercial trade under the listing of all Dracaena species on Appendix II of CITES, but if its populations are to be effectively preserved, a variety of measures will need to be taken. These include urgent monitoring of the species’ natural regeneration and the expansion of Skund Nature Sanctuary to cover important areas of the habitats. Also, efforts on avoiding road construction in the dragon blood’s habitat, and limit grazing need to be brought to attention. Additional conservation efforts for the tree involve fencing against livestock, watering of seedlings in open areas, and involving local communities in planting seedlings.