Are naturalistic explanations the default assumption?

1. Some Christian philosophers take the position that naturalistic explanations are the default assumption, so that extra evidence is required to acknowledge a miracle. Hume and his followers take that a step further to say the presumption of a naturalistic explanation is so strong that there will never be enough evidence to overcome that presumption. But let's go back to the weaker claim. Certainly it's easy to come up with examples where Christians regard a naturalistic explanation as the first explanation to reach for. So does that concede that there is, indeed, a standing presumption against recognition of a miracle? 

2. I'll make the preliminary point that drawing a firm line between naturalistic and supernatural explanations is more important to atheists that Christians. Atheists require that dichotomy to eliminate the supernatural side of the dichotomy while Christians don't require the same distinction since they don't eliminate the natural side. So these are asymmetrical concerns. 

3. Let's take a comparison. Suppose I'm walking on a trail, and up ahead I see a fallen tree. In principle, there are basically two possible causes for the fallen tree. 

i) A natural cause made it fall. Perhaps it was blown over in a wind storm because it had a shallow root system; or rain eroded the topsoil–exposing the root system; or it was hollowed out by Ambrosia beetles or heart rot.  

ii) It was cut down. Felled by logger with a chainsaw.

In the debate over miracles, (i) illustrates a naturalistic explanation while (ii) is a nonnatural explanation–akin to a supernatural explanation. The result of intervention by an agent outside the normal lifecycle of trees using "artificial" means.  

Now, viewing the tree at a distance, where all I see is the effect, before I'm in a position to see the tree up close, is there a default explanation? Is it antecedently more likely that it was felled by natural processes rather than a logger? At that stage, we don't have enough information to justify a default explanation. Whether it was felled by natural or artificial means is a contextual question whose answer crucially relies on specific evidence one way or the other. There is no explanatory presumption in a vacuum.