thank you for the kind answer, you do not need to apologize for this
As indicated (notes on pictures in the keys),
all this material is free to use as long my name (or ©JDL) and
http://www.plantentuin.ugent.be is mentioned.
So you can use all the images to build on your 'Baumlisten'.
I think these can be useful because there are some relevant diagnostic details, often not to be seen on photo's.
Also feel free to cut out parts like a particular leaf, as long my conditions are accomplished.
If this sounds arrogant, please consider just a minute that the reason there for is that it partly helps my principals to value my work.
On the other hand I can or would not like to provide material for book writers neither to get paid for it - it is intended to be FREE.
see the oak names site
http://www.oaknames.org/whatsnew.asp
where Piers Trehane also expresses this, for the same reason (5 NOVEMBER 2009).
best regards,
Jan