First: Take a deep breath and relax!!! Did you mean that the tree was in front of the sun or in other words, the tree was between you and the sun? If so, the tree would likely be a siloette or a "black" shape as you discribe. It sounds like you were using the Matrix meter. If the surrounding scene is brighter or darker than your subject the matrix meter can under expose or over expose the image. If the tree fills the circle in the center of the viewfinder you could try using center weighted metering. If not use Spot metering with the active AF point somewhere over the tree trunk. You could also dial in some negitive exposure compensation in any metering mode. Good Luck and Enjoy your Nikons!