POLLINATION
We all know that pollen comes from the flowers and that's how plants spread. But there's a bit more to it than that. All pollen is male and is produced by Stamens. It's goal is to reach a Stigma which is the female part of the flower. Assuming this goes well fertilisation will occur and lead to the production of seeds. Below are some photos which may surprise you.
Nope - these are not germs but different grains of pollen under a microscope. A single flower head of an average grass can produce ten million pollen grains!
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A close up of a lily. The six dusty looking sausages are the Anther which are part of the Stamen (male bits).
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A close up of a Stigma which is part of the pistil (female bits). The Stigma is usually hairy or sticky to help trap the pollen.
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There are several ways that our trees and shrubs pollinate, but quite often these goes unnoticed. Trees such as Sycamore have lovely green flowers, but from a distance they will often be mistaken for the leaves. Although there are up to 100,000 species of trees across the globe they will fall into one of two groups:
- Angiosperm (Angiospermae / Magnoliophyta)
- Gymnosperms
Basically these means flowering plants and non-flowering plants. So the Angiosperm are the flowering plants and the Gymnosperms are the non-flowering plants. Both of these fall under the general group of Spermatophytes which means plants that bears seeds. Angiosperms are considered more evolved than the Gymnosperms as flowers are more effective for pollination than compared to cones. To help make this a little easier nearly all trees that shed their leaves (Deciduous) are Angiosperms and most of the trees that retain their leaves (Evergreens) are Gymnosperms. Just to give you a rough idea of numbers there around 50 different species of Native tree in the UK and only 5 of these are Evergreens. Below are two videos I have uploaded to YouTube to help out:
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Norway Maple flowers in March 2017. These are typically pollinated by insects.
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Montery Pine flowers in March 2017. As you can see these are wind pollinated.
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All Gymnosperms are wind pollinated which limits their reproduction quite a bit. It means that a single tree has to make billions of grains of pollen in any hope of it landing on a female part of a suitable tree. As you can see this process is very hit and miss and lot of pollen is wasted this way. That is why the Angiosperms are considered to be more evolved as they can pollinate in more ways. This means less pollen is needed and the new seedlings can be carried further away from the parent tree(s). These include:
- Wind pollination
- Insect pollination
- Animal pollination
- Water pollination
The reason I have already included Wind pollination is with some Angiosperm trees they will use two or more methods of pollination rather than just one. Wind pollination is quite random as you can imagine so some years may allow for better pollen spread than others. With insect pollination the tree can attract insects which then do all of the hard work of getting the male pollen grains to the female parts of the tree(s). We all know how hard our honey bees work but there are all sorts of other pollinating insects such as beetles, butterflies, moths and flies. In some cases the flowers smell of rotting meat to attract flies rather than bees. Animal pollination is not as common as insect or wind pollination but as some animals can travel quite far it can have huge benefits. Bats are one of the main animal pollinators and then others such as humming birds, sun birds, mice, shrews and other small rodents. We don't have the stunning humming birds in the UK, but we do have 18 species of bat and a small selection of rodents to help pollinate our flowers. Below are two videos I've uploaded to YouTube showing a Honeybee nest in a Scots Pine tree and a Humming Bird Hawk Moth on a Buddleia bush. Both of which are excellent insect pollinators.
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During my tree recording in 2016 I stumbled upon this Honeybee nest within a Black Pine.
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A very busy (and fast) Humming Bird Hawk Moth feeding on a Buddleia bush.
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I have yet to record any solid videos of our various animal pollinators, but I did stumble upon a very adventurous mole back in 2013 and a baby House Mouse also in 2013. As they were rummaging amongst the grass they may well of been brushing against some flowers and and acting as animal pollinators. Please note that with animal pollination in almost all cases the animal will feed off the nectar off the flowers which leads to the pollen being stuck to their fur. In some cases flowers have developed to be specifically pollinated by rodents.
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An adventurous mole found during a walk along the canal to Double Locks in 2013.
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A baby House Mouse found near a rockery in 2013.
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So now that we have a better understanding of how pollen is spread we can look at the two main types of pollination. These are:
- Self-Pollination (Autogamy / Geitonogamy)
- Cross-Pollination (Allogamy)
There is a little more to it than just Self-Pollination and Cross-Pollination. Here is a breakdown of what else is involved:
- Autogamy (Self-Pollination) is where the pollen is transferred to the stigma of the same flower
- Geitonogamy (Self-Pollination) is where the pollen is transferred to another flower on the same plant.
- Abiotic (Cross-Pollination) is where the pollination is carried out without the use of insects or animals. So wind or water only. About 10% of plants are pollinated this way.
- Anemophily (Cross-Pollination) is where the pollination is carried out by the wind. This is the most common form of abiotic pollination
- Hyrdophily (Cross-Pollination) - Basically water pollination. Note that some water plants still bear flowers and are pollinated by other means
- Biotic (Cross-Pollination) - is where the pollination is carried out by organisms. This means without the use of wind or water. So insects and animals. About 90% of plants are pollinated this way
- Entimophily (Cross-Pollination) - A fancy name for insect pollination
- Zoophily (Cross-Pollination) - Is the pollination performed by vertebrates like birds, bats and mice. This may also include invertebrates (insects) according to research
- Ornithophily (Cross-Pollination) - As the name suggests this is the pollination by use of birds
- Chiroperophily (Cross-Pollination) - Not so likely here in the UK. This is pollination by bats
- Anthropophily (Cross-Pollination) - This is pollination performed by people. Usually for hybridization techniques
One last thing to cover about the Angiosperm (flowering plants) are the three main type of flowers. Below are some examples:
Horse Chestnut flowers are hermaphrodite which means each flower contains both male and female parts. Hermaphrodite flowers are also known as perfect flowers.
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Aspen is dioecious which means the male and female flowers are on different trees. Top photo is Female and Male are below.
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Common Hazel is monoecious meaning that both male and female flowers are on the same tree but different parts. The tiny red flower is the female one. The long dangly green one (catkin) are the male flowers.
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As you can see our trees and shrubs have many clever ways of pollinating, but there is also the timing of it all. Trees tend to shed pollen during the Spring (Jan - April) and our grasses during the summer (May - Sept). Even in the Autumn time pollen is being shed by weeds. Basically pollen is shed all year round. Below is a rough guide of when our most common trees shed pollen:
- Alder (Alnus) – pollen released between January and late April, peaking between mid-February and early April
- Ash (Fraxinus) – pollen released between early March and late May, peaking between early April and early May
- Birch (Betula) – pollen released between early March and mid-June, peaking between late March and mid-May
- Elm (Ulmus) – pollen released between early February and late April, peaking between early March and early April
- Hazel (Corylus) – pollen released between early January and late April, peaking between mid-February and mid-March
- Lime (Tilia) – pollen released between early June and early August, peaking between mid-June and mid-July
- Oak (Quercus) – pollen released between late March and mid-June, peaking between late April and early June
- Pine (Pinus) – pollen released between early April and late July, peaking between early May and late June
- Plane (Plantanus) – pollen released between early March and late May, peaking between mid-April and mid-May
- Poplar (Populus) – pollen released between mid-March and early May, peaking between mid-March and early April
- Yew (Taxus) – pollen released between early January and late April, peaking between late February and late March
- Willow (Salix) – pollen released between early February and early May, peaking between early March and early April
The last thing to cover is things that can affect the success of pollination. Some examples are below:
Severe weather conditions such as heavy rain / flooding.
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Pesticides / Weed killers.
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Climate change.
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Although a fair amount of plants are wind pollinated around 75% of crops require pollination by insects or other means. In the UK about one third of pollination is done by Honey bees so you can see how important these little critters are. Don't forget our cute and fluffy bumblebees who are also excellent pollinators and can withstand the rain better. Sadly we've lost three species of native Bumblebees over the years and six more are now listed as endangered. This is mainly down to modern farming and the use of various pesticides. In some countries the situation is so bad that farmers have to pollinate the flowers by hand. If we want to help our trees to spread and grow we need to look after our insect pollinators. If you have a garden try and grow plants that flower at different times of the year. Other ways we can help is by trying to eat more local / organic foods. Below are two more examples of our important insect pollinators.
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A Honey Bee pollinating Holly flowers.
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A Tawny Mining Bee emerging to pollinate nearby flowers.
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If there is anything out of place or wrong please contact me. Equally if there is anything you wish to add please let me know.