Big leaves are wet-tropical

[Dave-Vero]

This week's cover research item for Science magazine is a fresh look at leaf size.  It turns out that physics, especially cool and freezing conditions, favors small leaves in cool and cold places; also in arid places.  In the wet tropics, bigger is better.  So here's the paper's map of "predicted geographic trends in maximum leaf size"  

"Each grid cell is color coded according to the smaller of the two predictions for maximum leaf size (daytime or nighttime) . . .  Areas coded the deepest shade of blue are those where there may be no effective thermal constraint on maximum leaf size because sufficient water is generally available for effective transpirational cooling, and warm nighttime air temperatures prevent leaves from suffering radiative frost damage."

The map confirms what I'd noticed on the South Island of New Zealand, lots of little leaves, except for the Nikau palms and lots of New Zealand flax.

[Alberto]

Very interesting map. My region in south Brazil is blue. South America seems to be the subcontinent with the biggest leaves....

My subtropical region , that in other parts of same latitude in the southern and northern hemysphere are dry to very dry, in southern Brazil are wet because of the ''flying rivers'' [''rios voadores''in portuguese] yhat brings humidity from the Amazon blocked by the Andes to the south.

https://www.youtube.com/watch?v=teeXse6pk7k

Edited September 2, 2017 by Alberto

[PalmatierMeg]

I've noticed that the leaves of many of tropical trees, i.e. poinciana, jacaranda and the like, are made up of 1000s of tiny "leaflets". I believe that is an adaptation to tropical storm winds and hurricanes to allow airflow around them to reduce stress on branches.

[realarch]

Thanks for that bit of info Dave, interesting. 

Tim

[Dave-Vero]

Poinciana (Delonix regia) is native to parts of northern/western Madagascar with signitficant dry seasons, rather similar to Puerto Rico, Hispaniola, and Cuba, where it thrives.  Those areas seem to be in big-leaf terrain.

During hurricane Harvey, the flooded condition of southeast Texas fed further rain.  It was as if the Gulf of Mexico had moved inland.  I've seen indications that the Amazon's forests, which evaporate a great deal of water, function the same way.  In Florida, restoring marshes has locally increased rainfall.  Evidence that the Andes direct moisture, and rain, to the south is really interesting and of course important.  

On the map, the big-leaf area of northern Vietnam and southern China is interesting.  A fair number of ornamental plants come from there.