[chris (OP)]

Leaves don't weigh much individually, but how much weight do they collectively add to a tree when it is in full leaf?

[iko]

Hi Chris,

I think they add quite a lot
especially under pouring rain!
...strong winds are probably
applying major forces too.
Talking about plant EXPERTS!

funkod  [] (900postlets)

[DoctorBeaver]

Surely it would depend on the type & size of the tree.

[dentstudent]

a mature healthy tree can have anything between 100 and 200,000 leaves, with the weight of each leaf being approximately 5g (but with huge internal variability). So if we take 150,000 as a mean, then that means 750,000 g or 0.75 tons (for a deciduous tree. There is far less weight fluctuation for needle mass in a conifer).

However, there is the factor of stored carbohydrates going towards the growth of the leaves which already are included in the weight of the tree, as well as the fact that many trees have already developed the next years leaves and flowers within the bud, so in actuality, the weight increase to the tree may not be all that great. The real weight increase in the tree is firstly the water used within these new leaves, and secondly the annual growth in the stem and branches. In a mature spruce forest in Britain, this can be up to 24 cubic metres per hectare (about 20 tonnes), whereas an oak stand can be as low as 3 or 4 (just under 4 tons). So per spruce tree, this would be a net weight assimilation of about 30KG per year on average.

There are other masses to include - rainfall (and this causes a high degree of weight fluctuation within the whole tree - the stems measurably grow and shrink depending on the water availability), pollution depositions, insect mass etc etc...

[chris (OP)]

Good answer Stuart. The statistic I had was for 177,000 leaves on a 50ft maple. But are you sure a leaf weighs 5g, that sounds like a lot?
 

[dentstudent]

Information I have found suggests that 1 leaf with surface area of 30 cm2 weighs about 1g.  An English oak leaf (Quercus robur) has a leaf of perhaps 20 cm2 and therefore a weight of about 0.67 g per (stalk-less)leaf. A horse chestnut (Aesculus hippocastanum) has a leaf area of (conservatively) 600 cm2, hence about 20g. This doesn't include the stalk, which may add a further few g. But, of course, the number of leaves changes for each tree. A mature Horse chestnut will have less leaves than an English oak. I'm estimating, but say a chestnut has the lower boundary of leaves, therefore about 80,000 (it's possibly even less). This gives (including the stalk) roughly 2 tons of leaf weight. An oak will have towards the upper boundary of leaf numbers, so say 200,000 at 1g each (to include stalk), giving 200 kg. So, there is enormous variability in both the crown leaf weight, and the weight of the individual leaf. If you look at the branch ends, ie the recent growth, you'll see that for the oak, the branches have a very much smaller cross section than the chestnut, which is correlated to the weight bearing requirements. This also applies to other trees, for example, large leaved species (walnut, ash, sycamore) tend to have rather large branches, whereas small leaved species (birch, aspen) tend to have smaller branches. Like so many things in nature, it's very difficult to provide a figure which encompasses everything!

[DoctorBeaver]

He knows his stuff, that Stuart bloke!  []

Very informative answer.

[chris (OP)]

Thanks Stuart, very helpful. I was on the verge of getting out my balance and weighing some leaves before you came along with your stats!

Chris

[dentstudent]

Thanks Chris, glad to help! Anything tree oriented, let me know!