Multiplicación vegetativa

Es la producción de un nuevo organismo a partir de un fragmento del propio organismo, que pueden ser porciones de tallo y hojas (unidad reproductora). Este potencial de regeneración se ha explotado históricamente por el hombre de forma natural en correspondencia con a la multiplicación vegetativa. A partir de los principios de la mitosis y la totipotencia de la célula vegetal se sustentó la multiplicación vegetativa artificial.

Formas de la multiplicación vegetativa:

Natural

Producción de un nuevo organismo a partir de un fragmento del propio organismo, que pueden ser porciones de tallo y hoja. Este potencial de regeneración se ha explotado históricamente por el hombre de forma natural en correspondencia con a la multiplicación vegetativa natural, a partir de los órganos metamorfoseados utilizando la presencia de las yemas, que son; tuberculosis, bulbos,estolones,rizomas.

Artificial

A partir de los principios de la mitosis y la totipotencia de la célula vegetal se sustentó la multiplicación vegetativa artificial, que recurre a tallos no metamorfoseados en este tipo de técnica; se utilizan las yemas de los nudos y se aplican diferentes artificios, por medio de los cuales se propagan las plantas por multiplicación vegetativa artificial.

Entre las que podemos citar: estacas, acodo, margullo, injertos  y que es un caso especial. También se incluyen las técnicas de cultivo de tejidos invitro. Es de destacar que siempre que se utilicen estos tipos de propagaciones vegetativas, los individuos obtenidos serán idénticos a la planta madre. Los individuos obtenidos de semillas producto del proceso de fecundación como resultado de la reproducción sexual, están sujeto a las leyes de la herencia como consecuencia de la variabilidad genética.

Partes utilizadas en la propagación vegetativa natural

Tubérculo

Es un tallo subterráneo de tipo geófito, se caracteriza por su crecimiento anómalo, ya que forma las yemas; gran cantidad de tejido parénquima de reserva y un fino tejido suberoso. Se mantienen como huellas de los tallos, sin presencia de raíces. Pasado un tiempo de manera espontánea y condiciones adecuadas, se pueden originar nuevas plantas. En la actualidad se cosechan los tubérculos; unos se comercializan y otros se utilizan en la propagación vegetativa, para mantener la variedad deseada de papa.

Bulbo

El bulbo consta de un disco o platillo, donde se localizan las yemas cubiertas por catáfilos de hojas. Esto le permite originar nuevas plantas por este tipo de reproducción. Las especies son ajo, gladiolo.

Estolón

Es una rama lateral de crecimiento horizontal, con nudos que forman raíces en la parte ventral y hojas en el dorso, se cortan de tramo en tramo donde aparecen las raíces, se eliminan las hojas y se siembran. Se utilizan en la fresa, pangola, violeta.

Retoño, hijo o vástagos

Este tipo de multiplicación vegetativa natural, se aprovecha en la agricultura, a partir de los rizomas, que producen en sus yemas, vástagos, retoños e hijos. Este tipo de propagación se aplica mucho en especies tales como; plátano, mariposa y piña . A esta variante de propagación se le llama retoños o hijos, entre productores.

Partes utilizadas en la multiplicación vegetativa artificial

Otros tallos no metamorfoseados se utilizan en la multiplicación vegetativa artificial, se recurre a las yemas de los tallos, se elaboran estacas y acodos. En los injertos se utiliza el cambio vascular para lograr el efecto deseado.

Estacas

El ingenio del hombre permitió, utilizar la capacidad de muchas plantas de regenerarse y poder formar un punto vegetativo caulinar o radical en las zonas de cicatrización. Así, logran unidades reproductoras a partir de las estaca, tanto de pedazos de tallos como de hojas, que colocadas en condiciones favorables son capaces de formar un nuevo individuo con caracteres iguales a la planta madre. Las estacas se usan ampliamente en horticultura y jardinería. Se utilizan soluciones de fitohormonas, que aceleran el enraizamiento de las mismas.

Entre las especies de plantas que se propagan por trozos de tallos provistos de yemas cuya configuración responde a los patrones generales de los tallos aéreos estudiados, se pueden citar; la caña de azúcar, yuca, cacao, rosales, marpacífico y croton.

Las hojas de muchas especies pueden desarrollar también puntos de crecimientos por la actuación de los meristemos, como son: las begonias , violeta africana y siempreviva.

Acodo

Esta técnica tiene dos variantes acodo de tierra y acodo aéreo se realizan sobre las ramas de las plantas. El acodo de tierra, se toma una rama de la planta madre deseada, se hacen cortaduras de forma tal que llegue a los meristemos, se dobla la rama y obligándola a tocar suelo y acto seguido, se cubre con tierra, al enraizar el área, se obtienen una unidad reproductora, se siembran y se obtiene una nueva planta igual a la progenitora.

Para el acodo aéreo, se realizan cortaduras en distintas ramas, terminadas las cortaduras, se rodean las zonas con tierra y material adecuado y se sujeta con polietileno, yute u otro material idóneo para logar el enraizamiento, cuando surge el enraizamiento, se corta de la rama y se siembra la unidad reproductora.

Injerto

Se entiende por injerto, al traslado de una yema a la rama de una planta (patrón), donde ésta se inserta y se ata para fijarla y asegurar la concrescencia de los tejido que deben quedar unidos al prender el injerto hecho. Para lograr los injertos, se debe tener en cuenta:

• Las especies deben ser afines por lo general no es posible injertar individuos de especies distintas, no obstante, existen excepciones como los géneros: Citrus y Rosa.
• Hay que colocar el injerto en posición normal, de acuerdo a las leyes de la polaridad. Sí se invierten, no desarrollará el brote de la yema injertada.
• El injerto solo puede realizarse en plantas que posean cambio vascular, para que sea posible la adherencia de los tejidos.
• Existe una influencia reciproca entre el patrón y el injerto, pero no es tema a debatir.
• Las especies de rosales y muchos frutales no producen semilla cuando se propagan por este medio.
• Son variados los tipos de injertos que se practican: aproximación,escudete, de corona y púa. Esto será tema medular en Fitotecnia.

 

 

 

 

Seasonal evergreen forest

 

Seasonal tropical forest: also known as moist deciduous, semi-evergreen seasonal, tropical mixed or monsoon forests, typically contain a range of tree species: only some of which drop some or all of their leaves during the dry season. This tropical forest is classified under the Walter system as (ii) tropical climate with high overall rainfall (typically in the 1000–2500 mm range) concentrated in the summer wet season and cooler “winter” dry season: representing a range of habitats influenced by monsoon (Am) or tropical wet savannah (Aw) climates (as in the Köppen climate classification). Drier forests in the Aw climate zone are typically deciduous and placed in the Tropical dry forest biome: with further transitional zones (ecotones) of savannah woodland then tropical and subtropical grasslands, savannas, and shrublands.

Climate

 

The climate of seasonal forests is typically controlled by a system called the Intertropical Convergence Zone (ITCZ) located near the equator and created by the convergence of the trade winds from the Northern and Southern Hemispheres. The position of these bands vary seasonally, moving north in the northern summer and south in the northern winter, and ultimately controlling the wet and dry seasons in the tropics. These regions appear to have experienced strong warming, at a mean rate of 0.26 degrees Celsius per decade, which coincides with a global rise in temperature resulting from the anthropocentric inputs of greenhouse gases into the atmosphere. Studies have also found that precipitation has declined and tropical Asia has experienced an increase in dry season intensity whereas Amazonian has no significant pattern change in precipitation or dry season. Additionally, El Niño-Southern Oscillation (ENSO) events drive the inter-annual climatic variability in temperature and precipitation and result in drought and increased intensity of the dry season. As anthropogenic warming increases the intensity and frequency of ENSO will increase, rendering tropical rainforest regions susceptible to stress and increased mortality of trees and other plants.

Structure

As with tropical rainforests there are different canopy layers, but these may be less pronounced in mixed forests, which are often characterised by numerous lianas due to their growth advantage during the dry season. The colloquial term jungle, originally derived from Sanskrit, has no specific ecological meaning but originally referred to this type of primary and especially secondary forest in the Indian subcontinent. Determining which stands of mixed forest are primary and secondary can be problematic, since the species mixture is influenced by factors such as soil depth and climate, as well as human interference.

Mangrove

A mangrove is a shrub or small tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves occur worldwide in the tropics and subtropics, mainly between latitudes 25° N and 25° S. The total mangrove forest area of the world in 2000 was 137,800 square kilometres (53,200 sq mi), spanning 118 countries and territories.

Mangroves are salt-tolerant trees, also called halophytes, and are adapted to life in harsh coastal conditions. They contain a complex salt filtration system and complex root system to cope with salt water immersion and wave action. They are adapted to the low oxygen (anoxic) conditions of waterlogged mud.

The word is used in at least three senses: (1) most broadly to refer to the habitat and entire plant assemblage or mangal, for which the terms mangrove forest biome, and mangrove swamp are also used, (2) to refer to all trees and large shrubs in the mangrove swamp, and (3) narrowly to refer to the mangrove family of plants, the Rhizophoraceae, or even more specifically just to mangrove trees of the genus Rhizophora.

The mangrove biome, or mangal, is a distinct saline woodland or shrubland habitat characterized by depositional coastal environments, where fine sediments (often with high organic content) collect in areas protected from high-energy wave action. The saline conditions tolerated by various mangrove species range from brackish water, through pureseawater (3 to 4%), to water concentrated by evaporation to over twice the salinity of ocean seawater (up to 9%).

Etymology

The term “mangrove” comes to English from Spanish (perhaps by way of Portuguese), and is likely to originate from Guarani. It was earlier “mangrow” (from Portuguese mangueor Spanish mangle), but this word was corrupted via folk etymology influence of the word “grove”.

Ecology

Mangrove swamps are found in tropical and subtropical tidal areas. Areas where mangal occurs include estuaries and marine shorelines.

The intertidal existence to which these trees are adapted represents the major limitation to the number of species able to thrive in their habitat. High tide brings in salt water, and when the tide recedes, solar evaporation of the seawater in the soil leads to further increases in salinity. The return of tide can flush out these soils, bringing them back to salinity levels comparable to that of seawater.

At low tide, organisms are also exposed to increases in temperature and desiccation, and are then cooled and flooded by the tide. Thus, for a plant to survive in this environment, it must tolerate broad ranges of salinity, temperature, and moisture, as well as a number of other key environmental factors—thus only a select few species make up the mangrove tree community.

About 110 species are considered “mangroves”, in the sense of being a tree that grows in such a saline swamp, though only a few are from the mangrove plant genus,Rhizophora. However, a given mangrove swamp typically features only a small number of tree species. It is not uncommon for a mangrove forest in the Caribbean to feature only three or four tree species. For comparison, the tropical rainforest biome contains thousands of tree species, but this is not to say mangrove forests lack diversity. Though the trees themselves are few in species, the ecosystem that these trees create provides a home (habitat) for a great variety of other species.

Mangrove plants require a number of physiological adaptations to overcome the problems of anoxia, high salinity and frequent tidal inundation. Each species has its own solutions to these problems; this may be the primary reason why, on some shorelines, mangrove tree species show distinct zonation. Small environmental variations within a mangal may lead to greatly differing methods for coping with the environment. Therefore, the mix of species is partly determined by the tolerances of individual species to physical conditions, such as tidal inundation and salinity, but may also be influenced by other factors, such as predation of plant seedlings by crabs.

Once established, mangrove roots provide an oyster habitat and slow water flow, thereby enhancing sediment deposition in areas where it is already occurring. The fine, anoxic sediments under mangroves act as sinks for a variety of heavy (trace) metals which colloidal particles in the sediments have scavenged from the water. Mangrove removal disturbs these underlying sediments, often creating problems of trace metal contamination of seawater and biota.

Mangrove swamps protect coastal areas from erosion, storm surge (especially during hurricanes), and tsunamis. The mangroves’ massive root systems are efficient at dissipating wave energy. Likewise, they slow down tidal water enough so its sediment is deposited as the tide comes in, leaving all except fine particles when the tide ebbs. In this way, mangroves build their own environments. Because of the uniqueness of mangrove ecosystems and the protection against erosion they provide, they are often the object of conservation programs, including national biodiversity action plans.

Mangrove swamps’ effectiveness in terms of erosion control can sometimes be overstated. Wave energy is typically low in areas where mangroves grow, so their effect on erosion is measured over long periods. Their capacity to limit high-energy wave erosion is in relation to events such as storm surges and tsunamis.

The unique ecosystem found in the intricate mesh of mangrove roots offers a quiet marine region for young organisms. In areas where roots are permanently submerged, the organisms they host include algae, barnacles, oysters, sponges, and bryozoans, which all require a hard surface for anchoring while they filter feed. Shrimps and mud lobstersuse the muddy bottoms as their home. Mangrove crabs munch on the mangrove leaves, adding nutrients to the mangal muds for other bottom feeders. In at least some cases, export of carbon fixed in mangroves is important in coastal food webs.

Biology

Of the recognized 110 mangrove species, only about 54 species in 20 genera from 16 families constitute the “true mangroves”, species that occur almost exclusively in mangrove habitats. Demonstrating convergent evolution, many of these species found similar solutions to the tropical conditions of variable salinity, tidal range (inundation), anaerobicsoils and intense sunlight. Plant biodiversity is generally low in a given mangal. The greatest biodiversity occurs in the mangal of New Guinea, Indonesia and Malaysia.

Adaptations to low oxygen

Red mangroves, which can survive in the most inundated areas, prop themselves above the water level with stilt roots and can then absorb air through pores in their bark (lenticels). Black mangroves live on higher ground and make many pneumatophores (specialised root-like structures which stick up out of the soil like straws for breathing) which are also covered in lenticels.

These “breathing tubes” typically reach heights of up to 30 cm, and in some species, over 3 m. The four types of pneumatophores are stilt or prop type, snorkel or peg type, knee type, and ribbon or plank type. Knee and ribbon types may be combined with buttress roots at the base of the tree. The roots also contain wide aerenchyma to facilitate transport within the plants.

Limiting salt intake

Red mangroves exclude salt by having significantly impermeable roots which are highly suberised (impregnated with suberin), acting as an ultra-filtration mechanism to exclude sodium salts from the rest of the plant. Analysis of water inside mangroves has shown 90% to 97% of salt has been excluded at the roots. In a frequently cited concept that has become known as the “sacrificial leaf”, salt which does accumulate in the shoot (sprout) then concentrates in old leaves, which the plant then sheds. However, recent research suggests the older, yellowing leaves have no more measurable salt content than the other, greener leaves. Red mangroves can also store salt in cell vacuoles. As seen in the photograph on the right, white or grey mangroves can secrete salts directly; they have two salt glands at each leaf base (correlating with their name—they are covered in white salt crystals).

Limiting water loss

Because of the limited fresh water available in salty intertidal soils, mangroves limit the amount of water they lose through their leaves. They can restrict the opening of their stomata (pores on the leaf surfaces, which exchange carbon dioxide gas and water vapour during photosynthesis). They also vary the orientation of their leaves to avoid the harsh midday sun and so reduce evaporation from the leaves. Anthony Calfo, a noted aquarium author, observed anecdotally a red mangrove in captivity only grows if its leaves are misted with fresh water several times a week, simulating frequent tropical rainstorms.

Nutrient uptake

Because the soil is perpetually waterlogged, little free oxygen is available. Anaerobic bacteria liberate nitrogen gas, soluble ferrum (iron), inorganic phosphates, sulfides and methane, which make the soil much less nutritious. Pneumatophores (aerial roots) allow mangroves to absorb gases directly from the atmosphere, and other nutrients such as iron, from the inhospitable soil. Mangroves store gases directly inside the roots, processing them even when the roots are submerged during high tide.

Increasing survival of offspring 

Red mangrove seeds germinate while still on the parent tree.

In this harsh environment, mangroves have evolved a special mechanism to help their offspring survive. Mangrove seeds are buoyant and are therefore suited to water dispersal. Unlike most plants, whose seeds germinate in soil, many mangroves (e.g. red mangrove) are viviparous, whose seeds germinate while still attached to the parent tree. Once germinated, the seedling grows either within the fruit (e.g.Aegialitis, Avicennia and Aegiceras), or out through the fruit (e.g. Rhizophora, Ceriops, Bruguiera and Nypa) to form a propagule (a ready-to-go seedling) which can produce its own food via photosynthesis.

The mature propagule then drops into the water, which can transport it great distances. Propagules can survive desiccation and remain dormant for over a year before arriving in a suitable environment. Once a propagule is ready to root, its density changes so the elongated shape now floats vertically rather than horizontally. In this position, it is more likely to lodge in the mud and root. If it does not root, it can alter its density and drift again in search of more favorable conditions.

Taxonomy and evolution

The following listing (modified from Tomlinson, 1986) gives the number of species of mangroves in each listed plant genus and family. Mangrove environments in the Eastern Hemisphere harbor six times as many species of trees and shrubs as do mangroves in the New World. Genetic divergence of mangrove lineages from terrestrial relatives, in combination with fossil evidence, suggests mangrove diversity is limited by evolutionary transition into the stressful marine environment, and the number of mangrove lineages has increased steadily over the Tertiary with little global extinction.

A red mangrove, Rhizophora mangle.

Above and below water view at the edge of the mangal.

Salt crystals formed on grey mangrove leaf.

Red mangrove seeds germinate while still on the parent tree.

PINE-OAK FOREST

Establishing secure tenure is widely recognized as a fundamental component of sustainable forest management. Policy-makers generally prefer privatization to achieve these ends, although common property institutions may also be appropriate. But if common property tenure is insecure and fails to control exploitation, theory predicts that private tenure should lead to better forest conditions. In this case study of a western Honduras community, forest mensuration data were collected from four private forests and two relatively open access common property forests. Statistical analyses failed to find consistent, significant differences in vegetation structure or soils related to tenure. Notable contrasts between forests reflected historical conditions and owner preferences. Neither form of tenure appeared to emphasize concerns for sustainable management, and ongoing processes of change constrained the possibility for limiting common property forest exploitation. The study adds to others which show that the outcomes of private or common property tenure relate substantially to the socioeconomic, political, and ecological context.

PINE FOREST

Temperate pine forest is a terrestrial biome found in temperate regions of the world with warm summers and cool winters and adequate rainfall to sustain a forest. In most temperate coniferous forests, evergreen conifers predominate, while some are a mix of conifers and broadleaf evergreen trees and/or broadleaf deciduous trees. Temperate evergreen forests are common in the United States of America, areas of regions that have mild winters and heavy rainfall, or inland in drier climates or mountain areas. Temperate coniferous forests are found mainly in the Northern Hemisphere in North America, Europe, and Asia. A separate ecoregion, the tropical coniferous forests, occurs in more tropical climates.

OAK FOREST

An oak is a tree or shrub in the genus Quercus of the beech family, Fagaceae. There are approximately 600 extant species of oaks. The common name “oak” also appears in the names of species in related genera, notably Lithocarpus (stone oaks), as well as in those of unrelated species such as Grevillea robusta (silky oaks) and the Casuarinaceae (she-oaks). The genus Quercus is native to the Northern Hemisphere, and includes deciduous and evergreen species extending from cool temperate to tropical latitudes in the Americas, Asia, Europe, and North Africa. North America contains the largest number of oak species, with approximately 90 occurring in the United States, while Mexico has 160 species of which 109 are endemic. The second greatest center of oak diversity is China, which contains approximately 100 species.

Evergreen Forests In Honduras

 

The most species-rich ecosystems in Honduras are its Evergreen forests, which are found at all altitudes, from lowland rainforests to high mountain cloud forests. A total of 15 of these evergreen ecosystems are found in the country, most of which are found in the wetter North.

The most extensive of these evergreen systems are the Lowland Evergreen forests of the Atlantic Coast, which include both moderately drained forests on the coastal plain and well-drained forests on the surrounding foothills. These forests are Honduras’ most species-rich ecosystems with as many as 115 species of tree being found per hectare (House 97). They are amply represented in the National Park System in the Río Plátano reserve, and to a lesser extent in the Tawahka reserve. Smaller areas are found in the other north coast reserves such as Pico Bonito, Texiguat, y Capiro y Calentura. These reserves are also particularly rich in amphibious species (26 species corresponding to 31% of the national number of species of amphibians).

Types Of Evergreen Forests:

1. The Submontane Evergreen forests are very similar to their lowland neighbours though there is a clear decrease in tree species diversity and an increase in epiphyte diversity. These forests are also restricted to the north coast, with a large area found in the Rio Plátano Biosphere Reserve, while additional important areas are found in Pico Bonito and Texiquat reserves. 
2. The Evergreen Swamp forest found on the north coast in all of the wetland reserves, are dynamic ecosystems, but they remain the best-conserved lowland evergreen forests along the north coast. Even though they do not have a high diversity of tree species they do support large numbers of epiphytes and a rich fauna in particular bird species.

Types Of Seasonal Evergreen Forests:

1. Seasonal Evergreen broadleaved forest are found in the East of the country in the department of Olancho, particularly in the Rio Patuca reserve. These forests are clearly seasonal in nature with over 25 % of the trees loosing their leaves for long periods of the dry season.
2. The Lowland Seasonal Evergreen Broadleaved forests on karstic soils are found in the Tawahka reserve and to a lesser extent in the Patuca. that these ecosystems  are found in the previously mentioned reserves but also in the Lake Yojoa region.
3. Seasonal Evergreen Pine forest . All of these forests have been modified by human activity, being periodically burnt and grazed.  In the Mosquitia, (Honduras and Nicaragua) were human intervention is less intensive they resemble the pine forests of the Belizean coastal plains.

the seasonal submontane pine forest,which was the dominate ecosystem throughout much of inland Honduras, unbroken areas of which today, are found only in the department of Olancho. No single viable piece of this ecosystem is found within the National Parks System.

Characteristics:

• The trees are evergreen as there is no period of drought or frost.
• The canopy tree species are mostly tall hardwoods with broad leaves that release large quantities of water through transpiration, in a cycle that is important in raising as much mineral nutrient material as possible from the soil.
• They do not shed their leaves at a time and therefore always remain green and are called evergreen forest.
• Here, the trees are 60 m in height (196 ft) and the rainfall is between 150 cm. to 300 cm.
•