Tuesday, 23 November 2010

Is Nature inefficient?

Whilst doing a bit of work in the garden recently, I noticed how many of the "Fish tree" (Sorbus) berries have fallen to the ground. The Asparagus bed is covered in them.

These berries are obviously very attractive to birds. As I write I am looking out of the window and watching some Wood-pigeons rather inelegantly gorging themselves on them. Blackbirds are also frequent customers of this tree. All the exuberant bird antics tend to result in three berries falling to the ground for every one that is eaten! (You just try swallowing an apple whole without using your hands, whilst balancing on a narrow pole 20 feet up, and without being able to hold on...). This is probably Nature's way of  "sowing" the seeds.

Each one of these berries has the potential to become another tree -- but it's a very small chance. In my garden they will not be allowed to grow, and I will dig up any that germinate, but maybe some of the seeds eaten by the pigeons, blackbirds etc will emerge in due course in the birds' droppings and fall somewhere that is not under the supervision of a gardener and therefore have a greater chance of success.

All this has got me thinking about why some plants produce huge numbers of seeds whilst others produce very few. Compare Avocado with Chilli (in the seed numbers sense I mean). Why is it that some are so much more efficient than others? And then why, come to think of it, do some plants choose to propagate themselves by sending out runners instead of relying on seeds? What is the most unusual method of propagation you know?

Have you heard of the "Egyptian Walking Onion"? Another name for it is the Tree_onion It doesn't literally walk, but it produces a clutch of bulblets at the end of each of its long leaves. These leaves get top-heavy and fall over, allowing the bulblets to touch the ground and take root, distant from the parent plant by the length of the leaf. In this way the onion patch gets bigger each year if left alone. Clever!

What about the Himalayan Balsam plant? Himalayan_Balsam Its ripe seeds are catapulted my means of a sort of spring mechanism, often travelliing up to 7 metres from the parent plant! If you have ever had one in your garden (NOT recommended because they are very invasive) you have probably heard them "firing off"; they make a loud clicking sound when they fire.

How about the Pohutukawa ("New Zealand Christmas tree")? Metrosideros_excelsa This incredibly robust and tenacious tree starts off very small, and will grow even in the tiny folds and crevices of volcanic lava rock, which tend to collect moisture and dust which eventually creates a sort of soil. As the tree grows, the dense foliage in the umbrella-like shape of the tree creates shade for its own roots, and the tangled root system itself creates more nooks and crannies for capturing water and airborne soil and dust particles, so that the cycle can be repeated. Viewed from above, a Pohutukawa grove would appear like a series of circles with the big trees in the middle and little ones on the outside.  I remember seeing this clearly demonstrated on Rangitoto island just off Auckland, a very young volcanic island.

I'd be interested to hear from my readers about any plants they have with unusual propagation methods.


  1. I don't have plants with unusual propagation methods but I'm always amazed by the way some have what seems to be a superfluity of seeds. An odd thing about this group is how the seeds from some seem almost all to grow while with others, hardly any result in new plants.


  2. In Australia we have a group of plants that ONLY germinate after fire. One that springs to mind is the Banksia family. After the fire has passed and the ash cooled the seeds are released from the cones and voila..baby banksias. Some wildflowers require smoke to germinate.
    Some of the acacias wait till a hot day and their pods audibly pop, catapulting their seeds. To grow acacia/wattle from seed it is best to soak the seeds in boiling water to increase your strike rate. Alternately you can rub them on sandpaper to weaken the casing.

  3. Obviously web addresses aren't permitted in comments. I added one following the wildflower/smoke sentence and it has been deleted. Anyway, you can always do a search yourself.

  4. I guess some produce more seeds than others because at one time the environment that they were growing in required it, same as the one that needs fire (must have been a lot of fires in that area when the plant was developing?). Perhaps some need to throw their seeds because no animal carries that type of seed anywhere so if not thrown the plant the plant would have always produced right beside itself and maybe it produces too much shade.
    I find it intersting that a lot of trees and plants can propogate vegetatively.

  5. Hehehehe it's like Darwin all over again! Pondering the apparent inefficiency of nature was how he came up with his ideas.
    You, or a plant or animal, can invest your efforts and energy and nutrients and parental care in a small number of offspring and give them lots of help, like the avocado seed which is full of nutrients, or you can invest in lots of smaller offspring that get spread all over the place like the fish tree, so you increase the odds that some might end up in a favourable environment to survive; but then you can't afford to give each one lots of nutrients or care or whatever. Plants that evolved in changing and unreliable environments are more likely to have developed the 'lots of small seeds' option because investing in just one seed might have ended in disaster if conditions suddenly changed. I guess that means the avocado evolved in a pretty reliable environment so it could put all its eggs in one basket, so to speak. In the long run if each baby plant contains half the parent plants' genes then it only needs two surviving offspring to ensure that any given gene gets passed on to the next generation.

    Aaah, the magic of evolution. That's the end of the mini biology lecture!

  6. Thanks Fiona for your erudite explanation. I just knew that all that parental care I lavished upon you would be worthwhile in the end...! Aren't you glad you didn't have hundreds of siblings?


Thank you for taking time to leave me a comment! Please note that Comment Moderation is enabled for older posts.