The dark mark is hard to diagnose, but it looks like mechanical (physical) damage that blackened as the tissues died off from the wound, not a pathogen infection. What caused the damage, we can't tell, but it's not a concerning phenomenon. As to why the shrub is largely bare in the interior, that's hard to say. If it's not getting at least several hours of direct summer sun, that could be playing a role. You mention a western exposure, and usually they are quite sunny, but we aren't certain since sometimes larger plants or trees (or a nearby building) might be shading the site for part of the day.

Some holly groups, like "blue" holly hybrids, can be vulnerable to certain infections or pests. (Botanically, they fall under Ilex x meserveae, which this shrub appears to belong to based on growth habit and leaf traits. Commonly-grown varieties include 'Blue Princess', 'Blue Girl', 'China Girl', and others.) One potential infection is web blight, which can cause a blackening (of the whole leaf at once) of foliage and dieback of branches, especially in wet conditions or situations where plants are sheared into dense, manicured shapes (though that doesn't appear to be the case here). A particular type of root rot in wet soils that aren't acidic enough for the preferences of holly is another common culprit of dieback, but here too, it might not be the best match since that tends to cause the dieback (and retained leaves, at least for a while) of entire sections of a shrub at one time, not limited to the interior only.

Is the shrub in an area that tends to stay wet or get dry (such as from nearby tree roots)? If wet or poorly-drained, root decline can cause leaf shedding, and the plant's oldest leaves on its interior or lower branches would be those that shed first, from any source of stress. If too dry, premature leaf shedding can also occur, and new growth might also be limited and not as prolific as it used to be since leaf expansion requires sufficient moisture.

Leaves being more yellow-green than the darker green they should be could imply either root stress from wet or dry periods, or that the soil acidity (pH) is outside the range preferred by hollies, which like acidic conditions. When the soil is too alkaline, for example, even soil rich in nutrients can't provide the plant with what it needs as the roots don't function well enough to absorb them. In that event, adjusting the pH lower with a sulfur application might be all that's needed, but that is best determined by having a laboratory soil test performed. (Such testing cannot assess for root pathogens, just the soil nutrient content and acidity level.) We can help to interpret test results if desired.

To improve the appearance and fullness of the holly, if you want to keep it (and setting aside any soil adjustments, if applicable), you could try cutting it back drastically to force regrowth from the center regions that will fill in gradually to regenerate the shrub. It might take a few years of growth to regain its former size; growth rate will depend in part of what variety of holly it is, since some naturally grow faster than others. This type of pruning will interrupt flowering and thus berry production for a year or more, but in its current state, we suspect it's not fruiting well currently anyway.

If you prefer to replace it instead, we can suggest some ideas once we have more information, such as:

• how much direct summer sun the area receives
• if the plant will be browsed by deer
• soil characteristics (good drainage, skews wet, gets dry)
• what rough mature size you prefer (without relying on pruning to restrain plant size)
• if you prefer the plant be evergreen, or if it could be something deciduous

Miri

Dear Miri, 

You're welcome! Feel free to reach back out again once you're ready for any follow-up questions.

Miri