Seed collection

Seed Collection

Seed Collection (1)

Seed dispersal in forests

The success of a forest is directly linked to the ability of the vegetation—trees and other plants—to reproduce. Healthy reproduction enables the forest to be perpetuated over time. Nature has devised several ways for the seeds of plants to be dispersed. The success of a plant depends not only on the production of seed but also on the dispersal of that seed. Dispersal is the process by which plant species move into a new area. In order to survive, plants cannot just drop their seeds. If they did, the new seedlings would have to compete with the parent plant and with each other. Plants have developed a number of ways to increase the chances of their seeds being spread far enough away from the parent. There are different types of seed dispersal mechanisms. The different mechanisms include wind, water, animals, and fire. The mechanism used depends on the habitat the plant is located in. Following table lists the different dispersal mechanisms and common seeds that are dispersed by that mechanism.

Wind dispersal

Some seeds are carried to a new location by wind. Seeds travel the wind currents and gentle breezes with the potential of colonizing a distant mountain slope or valley. These seeds are very lightweight so that they can travel great distances. Many plants have developed ingenious adaptations for wind dispersal. They can resemble parachutes, helicopters, and gliders. There are several major types of wind dispersal that operate in forests:

  • Gliders
  • Parachutes
  • Helicopters (whirlybirds)
  • Flutterer/spinners
  • Cottony seeds

Gliders include seeds with two wings that resemble the wings of an airplane. Parachutes have an umbrella-like crown of tiny hairs above a slender one-seeded fruit. These fragile seeds can become airborne with the slightest gust of wind. Milkweed and dandelion fluff are well-known examples of this type of wind dispersal.

Helicopters—also called whirlybirds—are seeds that have a single wing attached to the seed. Like a fan blade or propeller blade, the wing has a slight pitch to it, enabling the seed to spin as it falls. Depending on the wind velocity and distance above the ground, helicopter seeds can be carried long distances. Flutterer/spinners have papery wings that flutter and spin in the air and can be carried short distances by the wind.

Cottony seeds include seeds and tiny seed capsules with a tuft of cottony hairs at one end or seeds embedded in a cottony mass. Many plant families have this type of seed: the willow family, cottonwoods, cattail family, kapok tree, floss silk tree, and the sycamore family.

Water dispersal

Fruits, such as the water lily and the coconut palm, are carried by water. Coconuts can travel for thousands of miles (km) across oceans. Biologists believe the original coconut palms on the South Sea islands (such as Tahiti, Samoa, Tonga, and Fiji) grew from fruits that were carried there from the main continents (such as South America) by ocean currents.

Animal dispersal

Squirrels collect nuts, like acorns, and bury them for their winter food supply. If they forget about the seeds and do not eat them, the seeds have the potential to germinate and grow into oak trees. Other seeds can catch on the fur of animals and the feathers of birds and can be transported great distances—such as burs.

Fire

In order to survive wildfires, some plants have adaptive traits that allow them to reproduce (an adaptive trait is a characteristic that helps a plant survive and make the most of its habitat). Some plants have developed fire-adaptive traits that enable them to survive in areas prone to wild-fires. The intensity of the fire is crucial to the seed’s dispersal—the fire must reach a certain temperature. The frequency of the fire is also important. Many species of pine trees have cones that only open after a fire. These pines are called serotinous.

The lodgepole pine—common in the western parts of the United States—is both serotinous and free-opening, which means that when the pine grows in an area where there are frequent fires, the cones are serotinous, but when it grows in an area where fires are less frequent, the cones open and release the seeds without the need for fire.

Seed Collection

Quality of the nursery and plantation project greatly depends on the quality of seeds collected. The seeds should be collected from locally available selected trees (plus trees). If the desired trees are not locally available, one can obtain seeds from different organizations. Collection of seeds from suitable trees require knowledge of the time of seed ripening and dispersal. Seeds collected before ripening or maturity may either give poor germination or may not germinate at all as it may quite infertile. 

A slight error in judging the maturity of the seeds at the time of collection may result in failure of nursery. The change in color and softening of tissues of fruit may give some indication about approach of maturity of seeds. In the case of pulpy fruits, the pulp softens and skin starts developing wrinkles. During the period of seed collection, the seed which ripen very early or very late are generally found to be poor and often infertile. The seed is collected by various methods as described below. 

1, Collection of fallen seeds from the ground: 

This method can be applicable to the species which produce large quantity of seeds or fruits which fall unbroken below the mother trees. Care should be taken to see that only freshly fallen seeds are collected. Seeds or fruits which are not fully ripen and insect attacked should be avoided. The floor under the selected mother trees should be cleared of weeds, leaf litter, other under growth and seeds of previous years during the period coinciding with the onset of seed fall. This method is followed in the species like Tectona grandis, Shorea robusta, Acrocarpus fraxinifolius, Trewia nudiflora, Gmelina arborea, Atrocarpus hirsute, Anthocephalus cadamba etc. 

2, Collection of seeds by lopping the branches: 

The seeds or fruits which are either too small or to be economically picked from the ground after falling or likely to be dispersed widely by wind can be collected by this method. Normally this type of seed collection is done by lopping the branches of seed trees and lopping should be confined to smaller twigs and thin branches, otherwise it will affect the growth of the tree. When the time of felling in an area (coupe) corresponds with the time of seed collection, this method is considered as the cheapest and easiest method. This method is followed in the species like Terminallia myriocarpa, Betula species, Dalbergia sissoo, Acacia catechu, Albizzia species, Holoptelia integrifolia, Hymenodicton excelsum, Ailanthus species etc. 

3, Collection of seeds from standing trees: 

Seeds of some species are likely to get damaged by falling with branches, or get easily dispersed by natural agencies like wind. This type of seeds is collected by climbing on the trees. Sometimes, a sickle tied to a bamboo with a small bag attached to it is used for this purpose. Examples for the seeds collected by this method are Morus alba, Bombax ceiba, Ceiba pentandra etc.

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