It depends on many things: what are the objects used for ecosystems? Native vue plants? Or imported objects? If the latter, do these objects have large texture maps applied to,them? generally ,big textures can cause OOM ( bear in mind that a 4096x4096 single map uses 64 megs of ram)

If imported geometry, did you resave the objects first in vob format? It would be a good idea.

Do you use shadow maps? They can be very ram hungry too, depending on their size and bias.