a lot wider than I see birch trees in the wild.

Are the birch you're comparing them to open grown like yours will be or are they in stands of trees? For example, forest ash trees grow relatively tall an narrow. Plant one alone in your front yard and you'll have a wide spreading monster. Their estimate does seem a little wide but hey, with the right spot I suppose.

50 foot is enough for your dogwoods and I feel its also enough for your birch.

Arbor Day website...Never depend on just one source, and evaluate the reliability of sources (the Arbor Day site is not on the top of my list), when possible.

Adverse affect...There are many different aspects to this question, but, generally, trees in the wild (forest, etc) aren't planted at certain intervals, so plant at whatever distance meets your needs. You may want to consider things like how long it will take the trees to get to their "mature" height and spread, how much they'll grow after that, what the group of trees will look like during their earlier stages, whether you want a more individual specimen look or a tight screen, what the group will look like when one of the trees dies or has a problem, and whether the monoculture look is what you want.

Multiple trunks...You should seek multi-trunk specimens that consist of single individuals, however, some nurseries do "plant multiple trees (right) next to each other" to achieve this effect more quickly. I think there was a thread about the problems of this method a while back on here.

Water consumption...I don't see how the number of trees will make a lot of difference except in the case where you have to supply water when the natural supply is insufficient. The trees will need sufficient moisture, but the area will generally have that or it won't, independent of the number of trees you have planted.

Your well...The trees shouldn't have any negative effect on your well.

Distance from dogwoods to leech field...50 feet should be fine. I can't imagine them causing a problem at that distance.

Birch are not upland trees, and as such when we plant them in the deliberate landscape we put them in turf or other areas with adequate irrigation or rainfall to match their needs. I'd at least do cut and fill to change the grade to slow down sheet flow and get more infiltration into the soil to ensure the trees flourish.

Dan

Thanks for the responses. Sounds like I will be ok with the plan I have.

I realize that birch trees are more likely to be found in the low lands and near streams, ponds, etc. However, in the area, I have seen several birch trees on higher ground with no streams, creeks, etc nearby. They seem to be growing fine and hopefully mine will too.

Thanks!
jbreits