Quoted from vid1900:

Because Europe does not have the ideal climate for mass syrup production, Maple wood is more of a North American product.
Maple is a short lived tree (usually less than 100 years), so when a stand of trees becomes too old to be useful to the syrup industry, it is cut down for lumber. It then becomes Baseball Bats, Guitar Necks, Bowling Ally Lanes and of course pinball playfields. Most syrup farms rotate between 4 stands of trees, so they always have the proper age trees available.
Of course, you can't buy good Maple plywood at Home Depot. The "Maple Ply" at Depot has a core of soft pine with a paper thin veneer of maple applied on the faces.
Pinball playfields are made of "Lumber Core" Maple plywood. That means that the outer and inner plys are all made of Maple. The outer face plys are thick Maple, allowing the inserts to be sanded flush with the surface of the plywood; without the worry of sanding through to the next ply.
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In Europe, the Baltic region has an abundance of Birch trees, so you often hear the terms Russian Birch or Baltic Birch.
Baltic Birch is made up of many thin layers of Birch. That is why you can always tell which kind of plywood was used by looking at the shooter lane layers. If the shooter lane has many thin layers, you know it was made from Baltic Birch plywood.
Because the face plys of Baltic Birch are thin, the gluing and sanding of the playfield inserts must be much more precise; or you can sand right through to the underlying layer.
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Maple is a little bit harder than Birch, but either wood can be used to make a quality playfield.