it seems like a contradictory thing to do. If you are focusing on natives for woodlands in your local, you won't need irrigation. If not, it doesn't seem like you are doing a woodland garden. I guess a woodland garden can be different from a native woods. In general, yes I would be concerned about where you are doing that irrigation with regard to the treees. It depends on the tree how much moisture it will tolerate on a constant basis. I think you might need real professional help on that one.

I'd try to place the irrigated area away from the trees I most want to save. I think you will also be digging up or smothering tree roots, native plants etc in the process.

I have an irrigation system in my woodland and it is primarily to insure that the trees are irrigated during periods of drought. It requires a lifetime to replace a mature tree!
I didn't bury the distribution pipes. Too many roots and too much work. I just laid them on top of the ground and after the first leaf fall, they were hidden. After a number of years, you can't find them, without digging.
All of the pipes slope downward toward the water source and are fed from a manifold, with a valve for each zone, so they can be watered individually. A single valve feeds the manifold and a drainage valve is provided. In the fall before first freeze, the water is shut off, the drain valve opened and all of the manifold valves are opened. Gravity then drains all of the pipes and sprinklers.
For my system, I use impulse sprinkler heads elevated on vertical pipes, 4, 5 or 6 ft. tall to clear surrounding shrubs and plants. They can be adjusted to cover specific areas, from a few degrees, up to 360° and up to a 50ft. distance.
It has served well for about 20 years, with very little maintenance effort required. It is a manual system, requiring timing on my part, but after purchasing an electic timer and valves, I haven't installed them.
Rb

I ended up setting up stationary sprinklers every 10 yards or so with a hose that leads from the sprinkler out to the rock border that divides my garden from my lawn. I still haul the main hose to each of the nozzles, one after the other, but I don't' have to risk smashing plants moving the sprinkler in and out....

What part of the country do you live in? Where I live a mature tree would never need irrigation. Irrigation is only used for golf courses and intense planting of ornamentals (but never trees with established roots). I am in western PA.

I live in central Indiana. My intention of installing irrigation is not to water the mature trees, but all of the perennials I've planted over the past 5 years. No, not every plant would be considered a native plant. I've got about 60 different varieties of hostas, in addition to turtlehead, toad lillies, candleabra primrose, native azaleas, kirengshoma, epimedium, ferns, lungwort, woodland phlox, daffodils, etc., etc....quite a variety of shade lovers. The trees soak up every bit of water in the summer, and with the past several summers being incredibly hot, installing irrigation seems to be one way to save my garden. I've got oak, ash, beech, redbud, dogwood, hickory and a few maple trees. In the past I've watered with a sprinkler but it's a hassle getting it out to the woods and moving it around. I've got the longest hose in the state of Indiana! Further thoughts?

Yep, your garden sounds a lot like mine. I water an inch a week and hope some rain supplements. In dry years the trees will win in a fight for water. I have a well, so water is a lot cheaper than losing all the plants I put in. I will compare hose length anytime. It is the storing it when done for the week I hate most.

I'm on a well also. And razorback, thanks for the info. I appreciate it.

myrtle....
This section of the country, among others, are experiencing unprecedented drought conditions, that has existed for a number of years. Not every year is extremely dry, but the dry years far outnumber the ones with normal rainfall. Consequently, there are some areas experiencing near desert conditions. Outdoor watering restrictions, including limited water draws from streams, wells and reservoirs, have existed for many years and last year we had a total ban on outdoor watering for 6 months.
Last year we were in the exceptional drought category(the worst scenario). That was recently upgraded to severe for some areas. (See map on this link and note SE).
Drought Monitor

There are many reports of mature trees, especially Oaks, that are dying and inspections indicate it is not due to any widespread disease.
All of the trees in my woodland were planted by me, as I purchased a bare canvas more than 40 years ago. I do not wish to lose any of them.
Hope you or anyone else, never have to experience what we are desperately trying to cope with. Cisterns and rain barrels aren't the ultimate answer, as you must have rainfall to fill them!
Rb

Some trees the small roots close to the surface of the ground are just as important as the thick roots.

I feel for ya, drought conditions make having a garden stressful.

Since there is a drought you want to make sure your not draining your well. It can happen. I would use a soaker hose.you can lay them out and cover them with mulch so they arent seen. they use a lot less water then a sprinkler type.

Any system with water going into the air,loses a large percentage due to evaporation. The soaker hose you hook up to a regular hose where there is no garden and turn it on when you want the garden watered.

You dont have to stand around holding a hose, I like that and its much more thorough.

cyn

I have a mature woodland and I do not irrigate my established plants - trees, shrubs, perennials, ferns, grass. If I have a dry summer, the wildflowers and ferns may go into a premature dormancy. If we had a drought and I had an irrigation system and irrigated one inch a week for four weeks I would use 75,000 gallons of water.