It sounds like you have a good bit of land. If you don't want to go removing any of the existing trees, one way you can sort of cover your bases to ensure there will always be a decent screen there is to add more trees to it. What I suggested earlier only rather than remove anything just add another 30-40 or so feet of planting. With a solid row of trees, you're in trouble if something happens to just one tree. With multiple rows of mixed species, your bases are covered. In my opinion leyland cypress looks 10 times better than green giant, especially in the winter time. They hold their color 100%. But that isn't to say you shouldn't plant some. Mix up the planting. But don't think you're going to patch up the gap in the row with a green giant and expect it to blend in because it wont. Nor will a bald cypress for that matter. Then again you may not be as concerned with how it looks as you are about patching the hole. In that case go for it.

These trees often suffer from disease and insect attack. You appear to have ok soil drainage. Assume you have good sun exposure? The existing trees look to be too close to the Leyland (or any other tree for that matter). I would recommend 12' minimum clearance to other trees. Leyland does not have good drought resistance here in central Texas with 32" annual rainfall. Here it should be watered during periods of hot dry weather and it may still fail. Trim off the dead parts and throw the dead limbs away.

hey ... they are conifers ... but also trees .... in case you need to know in the future .. where are you.. what is your soil... any other info that you might think important that might help ... are they zone appropriate for your area???? though lack of sun WILL impact vigor on a conifer that needs full sun .... it usually will not cause suspended animation for 9 years ... ergo.. i suspect there might be other issues besides the sun ... there is no reason not to move a plant if it is within your physical ability .... but why bother moving it.. if there are other problems which will allow them to continue to lack vigor .... make sense?? good luck ken

I'm not sure why we make such a fuss about zone maps - they are only guidelines afterall and individual microclimates due to topography, elevation and proximity to bodies of water do come into play. If you get a good sized detailed map of WA state, there ARE pockets of zone 7 in western Washington, most notably in the Olympia area at the southern most point of Hood Canal. And comments from forum participants living in that area certainly seem to confirm this. And FWIW, all hardiness zone maps are based on the same data, that being the initial climate information compiled and zoned by Henry Skinner of the National Arboretum with the AHS in the early 60's and published as the USDA zone map in 1965. It was revised in 1990 and is currently undergoing another revision based on more recent climatic averages. And yes, that zone map and all subsequent revisions do show the Olympic Peninsula as zone 8 - obviously that may not apply to the top of Mt. Olympus but not too many folks garden up there :-)) And most of the OP is very temperate.....witness the Olympic rainforest and the banana belt of the east side of the Olympics. Here's what the National Arboretum says about the zone maps: "The USDA Hardiness Zone map divides North America into eleven zones based on temperature and each is referred to by the zone number, i.e. Zone 5. Additionally, each zone is subdivided into two sections, A and B to further delineate temperature ranges, i.e. Zone 5a. The zones can be thought of as a general guidance as there is no clear-cut delineation between zones. Any location may be warmer or colder based on topography, drainage or wind exposure." (emphasis mine)