Conifers are the hardest trees for many kinds of plants to grow under, I think you are making one or two assumptions here that may not be correct. It is abnormal, for instance for the area within the branches of a hemlock to be more moist - these are prone to heart rot and tend to deflect water away from within their skirts rather than have it be moister than surrounding soil.

In nature, what grows beneath what is determined by climate, soils and which species are present in the area. A particular kind of tree will have different associates on different sites.

Hhhmmm...thanks for answering, but I'm not sure what you mean by "It is abnormal, for instance for the area within the branches of a hemlock to be more moist". I didn't mean that it was more moist than the surrounding soil, that would indeed be strange. I just meant that a variety of plants under a hemlock (not directly under, but 20' from the trunk) seem to have less drought stress than plants 20' from an equivalently large maple. I can only infer from this that the tree is sucking up less moisture than the maple. So it is to say that that one [area of soil] is moister than the other, not "moist".
Somewhere in the literature there must be a comparative analysis of moisture uptake from various tree species, I just wondered if the ecological portrait of conifers corroborated my hypothesis or not. Don't many PNW gardens feature plants growing under towering douglas firs? Certainly I feel like I've seen many such images just here on gardenweb.

A lot of the best Rhododendron gardens over here have old Scots Pines as an overstorey. I'd think other pines would work as well with Rhododendrons. Other broadleaf evergreens, not necessarily at all. Hollies do best in full sun, and so do evergreen Magnolias.

Resin

Don't know if this helps, you may already be up on it.

{{gwi:771265}}

Thanks it does help! Very interesting, may I ask where that comes from?
Interesting a Morus is listed in the "low water use" #3 bucket. (no pun intended!) Because I have a mulberry tree that is surprisingly easy on the plants underneath it compared to the maple. Looks like my focus on Pinus, Abies and Larix for that area has been a wise one!

Unlike hemlocks, pines are seral. It is common for them to be overtaken and replaced by other trees and shrubs over time, where site conditions allow climax species (such as hemlocks) to do this.

is that true in every biome though? It seems there are certain permanent pine forests around the world - part of the US SE, parts of Europe like the Black Forest, the appropriately named pine barrens of NJ (which, ironically, is where Rarefind is located and what most of their overstory consists of!). But please enlighten us as to how this relates to the matter at hand? Since the chart does not classify hemlock, I assume we are to rank them along with pines as the instructions tell us to do...

from wikipedia:
In the absence of fire barrens will proceed through successional stages from pine forest to a larger climax forest, such as oak-hickory forest.

ok, but, the fire does occur, doesn't that make the pines the climax if that's all that can survive there? Still not sure what it has to do with their water uptake.

davidrt28 - ...may I ask where that comes from?

If you search under building subsidence caused by trees this information is often used as a guide to safe planting distances from property.

Here's the link to the site I grabbed the chart from.

Here is a link that might be useful: Link

I think conifers and ferns look good togeather in a
woodland setting

Surprised to see "cupressus" listed as having a high water demand. Arizona Cypress and cousins are located in some of the drier parts of the world. Italian Cypress also seems to have much more resistance to drought than the chart indicates.

That list for decidious trees is off. They must have it backwards?

Good topic.

I wonder if water demand is different than water tolerance. While a Taxodium distichum my become a dominate tree in southern swamps it is not the least drought tolerant tree by far judging by what I'm seeing in suburban landscapes this year. Does that mean it uses the most water or can just tolerate the most water?

In my experience the trees which get their leaves late and loose their leaves early - juglans nigra for example - are kinder to plant under. More of the year whatever you plant will get sun. I do not know if this applies to water or not. Am I correct in ASSUMING conifers on the whole do not go dormant until late in the year?

Juglans nigra is kind to plants that are underneath it? Surely you're joking?

I'd take the chart to read as the water demand for a tree to be healthy as opposed to how much water the tree is capable of pulling from the soil. Acer a 3?

I grow a number of things below mature Pinus nigra and Juglans nigra. Unfortunately, none are broadleaf evergreens but like water (hosta) and I have not seen a difference in water needs there

In my experience, Juglans nigra are fine for Tsuga, Chamaecyparis and most Picea. They are death to Abies and Rhododendron, so-so for Pinus. As for conifers shutting down, soil temps going below 40F is the number I keep hearing.

tj