It looks like the kind of a rigid support or anchoring against the wind blows. Here the another Bf 109G-14 of the 16./JG5 with the same stick under the wing.
View attachment 779459
the pic: the net.
Yes, I am not sure about these wood props, also seen on # 2992 . Note neither aircraft has chocks. I don't know, but I wonder if this could have been a field method to allow start without chocks and then, when started, they could just power "over" the wood props to taxy away?
They are not control locks, the Bf 109 F/G has a integral stick-lock in the cockpit. Rudder is locked with external clamp on the upper mass-balance.
Eng
Eng