The Life Cycle of a Tree


Life Cycle The Basics

Trees grow from seeds. They develop into tall woody plants. These produce flowers with male and female parts. Pollen from the male flower fertilises the female flower and seeds are formed. These are shed from the tree and new trees grow from them.



Life Cycle The Problems

Trees are plants they cant move. So if male flowers are on one tree and female flowers on another tree as in holly- how will the pollen get to the female flowers?
Putting the male and female plants on the same tree as in Alder trees , or indeed putting the male and female parts in the same flower as in Hawthorn or mountain ash, gives rise to a new problem - that of self fertilisation. Trees breeding with themselves will have little genetic variety and this behaviour will lead to sterility and extinction.
When the seeds ARE formed a new problem arises how to spread the seeds? They cant just fall off the tree and germinate underneath it. There is not enough space in the soil or enough light for new trees to grow here.

Life Cycle The Solutions!

Employ an agent! or better - still bribe one.

Pollination Getting the male pollen to the female stigma so that that the ovary can be fertilised.

WIND as a pollinating agent.

Pollen is a very light powder carried on male parts called anthers. It can easily be blown in the wind. Trees that rely on wind to carry their pollen have special flowers called catkins. These form and ripen on trees early in year before leaves open to get in the way. The wind blows the pollen from the male catkins to the female flowers. So this is how holly trees with female flowers are fertilised with pollen from trees with male flowers a distance away.

If both male and female catkins are on the same tree as in hazel or willow, they both will not be ripe at the same time on that tree to avoid self- pollination.

Trees must produce lots of pollen as the wind blows it in every direction and much of it is wasted.

Photos of these trees or of the catkins on them.

Bribing INSECTS to do the job.

A more focussed way is to send the pollen directly to the flower to be fertilised. This can be done by getting insects to carry it. Trees that do this have very noticeable flowers with coloured petals so the insects can see them. They have a supply of sweet flavoured nectar the bribe- buried deep within the flower. To get at this the insect must suck its head and tongue right into the flower. If the pollen is ripe it will brush off on the insects head. The next flower the insect visits may have the female part ripe and ready for fertilisation and the insects will brush some pollen on to the stigma as it seeks the nectar deep in the flower. Any particular flower will have the male parts ripe before the female parts to avoid self fertilisation.

Moths, butterflies, bees, flies all seek nectar from flowers and pollinate them by accident.





Seeds - How to get rid of them

Seeds are formed as the fertilised ovary swells and develops. They will form the next generation of trees if they can be deposited far enough away from the parent tree to have enough space and light. How have trees managed to do this?

WIND as a seed dispersal agent.

Properly designed seeds can be blown far away from the parent tree. Trees such as Sycamore and Ash have seeds with wings on them which can be carried considerable distances by the wind. Conifers such as Pine and spruce have seeds with wings inside the large female cones. These open when ripe and are blown away by the wind. Tall trres that rise above the canopy of tropical rain forests such as the kapok tree have very light seeds with parachutes attached. These can blow for miles over the jungle.

Make destruction-proof seeds

This is what trees that produce berries do. They surround the hard coated seed with a luscious berry, colour the berry an obvious red or shiny black and wait for a hungry bird or mammal to come and eat it. The hard seed survives the jouney through the intestine and will be excreted far away from the parent tree and have a better chance to germinate. Elder, Hawthorn, Guelder Rose, Spindle, Cherry, Mountain ash ase this successful strategy.

Overwhelm by abundance

Trees that produce nuts are also providing food. At first glance this would seem to be suicidal as no new tree will germinate from the droppings of an animal that that feasted on hazelnuts or acorns. These trees however produce such an enormous number of nuts per tree that they will not all be eaten by hunry animals. Squirrels will store nuts and may not eat them all over the winter period. Jays and Rooks bury individual acorns and may not retrieve every one of them. Mice may not eat all the beech nuts or conkers that they collects. Only a few need to remain uneaten for new trees to grow.

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