On the importance of leaves

As promised last week I've done some looking into leaves, why they are different across diferent types of trees and plants, and what makes our Baobab and Neem leaves specially adapted to the hot dry conditions of countries like Burkina Faso and Ghana.

It would seem that something sticks in the mind from school days biology, as most of us know that the most important thing a leaf does is produce food for the rest of the tree through the process of photosynthesis. Importantly for us, in this they also produce oxygen and use up carbon dioxide. For plants like Neems, their leaves shown below, it's also important to know that because leaves have a large surface area for maximum reciept of carbon dioxide and sunlight, they also lose water through a process called transpiration.

For trees growing in drylands Africa, water is hard to come by and much of the year is spent with very little rainfall, whereas there is plenty of sunlight. This means that the leaves can generate lots of food, but also risk losing a lot of water. One thing that trees in such areas can do is lose their leaves during the dry season, which means that trees such as the Baobab can avoid losing too much precious water through transpiration. The leaves can also be shaped in a way to take advantage of all that sunshine, and so are flat and thin, unlike say pine needles.

Leaves are the food factories for our Baobab and Neem seedlings, but they can be used as food for people too. As we say at TREE AID, 'not just a tree'. I've got lots of fascinating facts on the things that people in Africa use our Baobabs and Neems for when they grow to full size in the wild, and will blog about them soon!

Neems!

Having been away for about a week I've come back to lots of fresh growth on the Baobabs and, more excitingly, two Neem germinations! This is really good stuff, as we hadn't seen any signs of life amongst so much Baobab activity, and I had been beginning to loose hope that any might germinate.

The two Neem seedlings have germinated in pots marked 1 and 3, which would suggest that they are equally happy being soaked for 24 hours, or 15 minutes prior to sowing, or in fact anything in between. They've also gone from seeds to seedlings with a full set of 'true' leaves and another one on the way in what feels like quite a short space of time, certainly relative to the Baobabs anyway.

As you can see, the Neems have very different leaves to the Baobabs. Rather than having large, oval leaves with their pointed tips and smooth edges, they have three or four smaller, serrated leaves branching from a central point to make up a more feathery looking leaf. Also, whereas the cotyledon and 'true' leaves of the Baobab looked quite similar in the end, the difference between the two on the Neem could hardly be greater. The cotyledon leaves look very much like half a green peanut; small, thick, and with none of the serration or featheriness that you can see in their 'true' leaves.

I'm intrigued as to why the leaves of the two plants are so different. Tony Hill, our Programmes Director and general tree knowledge man, says that even young leaves that aren't cotyledons can look quite different to adult leaves, and so the Neem leaves will end up being larger and a bit more sturdy. It will be interesting to see if I can find out how these leaves are best adapted and suited to the conditions of drylands Africa.

More space for Baobab roots

The four Baobabs in the one pot that had been most successful so far have been looking a bit crowded as of late, and so it seemed about time that they got their own homes.

Using the same winning combination of paper on the kitchen floor and sharp sand/compost mix I set about taking the seedlings out of the one pot and repotting them in their own pots; a process known in the gardening trade as pricking out.

I upturned their pot, making sure I could support the compost from beneath without squashing or damaging the seedlings, and gently squeezed the sides of the pot to loosen the soil from the pot. The seedlings and their compost slid out onto the paper, and with the compost being such a gritty, loose mix there was no need for prising it apart to separate the seedlings.


As you might expect, the roots were already quite deep, being about the same length down as the leaves are high. Interestingly there were no side roots at all, but they were sturdy seedlings, and not as fragile or delicate as I was expecting. In Africa these characteristics would serve them well in reducing the likelihood of damage, and in giving each seedling the best chance of being the one that survived amongst competition from other seedlings that might have germinated nearby; all fighting for water, nutrients and space.

Now each of the four seedlings has more room, with two having their own individual pots of a similar size to the one they've just been moved out of, and the other two sharing a slightly larger and notably deeper pot. I thought it wise, given how deep the roots are already, to have a go at seeing what that extra roots space will do for them. It will be interesting to watch their progression over the next few weeks to see if any problems arise, and at what rate the new leaves develop.