Hi Pat,
You shouldn't have any problems with the Alder.
I don't know if you would be interested but I have written a book on Air Layering. The following is a PDF file showing the contents of the book.
Air Layering Chinese Elms Cover.pdf
The link below shows some of what is in my book.
viewtopic.php?f=9&t=6154
This section of the book doesn't show the layer being covered up. After applying the Sphagnum moss and plastic I cover the layer in aluminium foil and put a tie around the top and bottom to prevent it from coming off. This will protect the roots from sun and also makes it easy to check the root progression. Just remove the foil, check the roots and then replace the foil.
Regards Ray
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