Were the trees checked for watering needs regularly after planting and during the past 18 or so months? Maryland has been in a notable drought for the past two years, which is stressing many plants, especially any young plantings that are not yet established. (It generally takes trees and shrubs about 2 to 3 years after planting to establish enough to be more self-sufficient.) Products like tree-watering bags can help with watering multiple young trees, although watering by hand or with a sprinkler is also fine. The bags tend to hold around 20 or 25 gallons of water, which is a good volume to provide when watering is needed. Our Watering Trees and Shrubs page has more information.

River Birch is aptly name as it does prefer soils with consistent levels of moisture; they don't have a high tolerance for drought, and it's quite common (even for established mature trees) for them to have leaves turn yellow and shed during stressful periods in summer.

It's hard to tell from the photos why the Serviceberries are defoliating early, but it might also be due to water stress. You might not be able to tell if any of the currently-leafless branches or twigs are dead or alive until spring, when new leaves emerge. Sometimes, environmental stress (like from drought and high heat) can make trees and shrubs more vulnerable to opportunistic infections like Botryosphaeria canker, a fungal infection that can kill branches. It usually causes dying leaves to stay attached to the branches rather than fall off, but in either case, there would be no remedy for branch dieback (regardless of the cause) other than to prune off branches that don't leaf-out in spring.

Keep monitoring the trees for watering needs in the meantime by feeling the soil moisture around 6 inches deep. If it feels somewhat dry to the touch at that depth, watering would probably benefit the trees. If it's damp instead when checked, watering should be able to wait. Recent heavy rains may or may  not have soaked in enough to rehydrate roots for the short term...such deluges deliver lots of water, but don't always actually soak into the soil much before running off.

It's good that the trees are separated from the lawn by a small ring of turf-free zone (we can't tell if it's mulched because we can't zoom in enough), but it would help to enlarge those zones to keep the turfgrass further away. Not only does this reduce the risk of damage from mowers or other lawn care (although the trunk cages that presumably are for deer protection do help with that too), but it also will help reduce the root competition a bit between the trees and the lawn.

A mulched zone at least 2 feet out from each trunk in all directions would be ideal (but only to a depth of around 2 to 3 inches thick, and not mounded). To be fair, wild trees in a woodland won't have a mulch area around their trunk base, but they also won't have an expanse of grass surrounding them either, whose roots can be fairly competitive. As the trees mature and shade-out the lawn so it eventually declines, you can stop mulching if you prefer to have the tree grove have a more natural look.

Miri