Presuming you're flying stock antennas, not that upgraded antennas will perform better. Anything that has leaves or needles still on the trees will be an issue, to what level is based on how many trees between you and the bird. Pine Trees and cedar are the worst about signal transmission. Live Oak, now winter, still have leaves and will cause issues. Others without leaves will be less of an issue. In my experience the density for the amount of trees causes me issues, less trees less of an issue...obviously.
Standing next to a tree-line versus 100' away can make a big difference, in distance away performance. You just have to fly and determine by experience. Besides the RTH feature will take over if all else fails, just make sure your home point is set, altitude is reading correctly and adjust your RTH altitude that's appropriate for the area you're flying...then add 20'. You can always take control when the signal is reestablished and try something else.
Good Luck!