From:    "Colby Rucker" 
Subject: Habitat
Date:    Mon, 8 Sep 2003 21:20:17 -0400

Bob,

When you began your cottonwood quest, I sort of yawned because I've only seen
cottonwoods that were kidnapped and stuck in some inhospitable piece of soil
where they retaliated by growing rapidly just so they could become a stag-headed
menace as soon as possible.

Of course, I wasn't being fair, because cottonwoods are rather picky, preferring
to luxuriate in soils built or replenished by the seasonal floods. And I, being
a child of the coastal plain, think of rivers as being languid estuaries amid
the often exhausted sands of a flat landscape inhabited by scrub pine, Spanish
oak, post oak, blackjack oak and beetle-infested locusts.

No wonder I retreat to the cool green haunts of Chase Creek Woods, in the
Highlands of the Severn, Maryland's "Hudson in Miniature." Chase Creek, once
called Timberneck Creek, lies at the narrowest, and therefore, most precipitous
part of the Severn watershed. It coincides with the great Aquia Deposit, with
its glauconite-laden greensands rich in potassium. Belt Woods is also on the
greensands, but lacks the dramatic topography.

The east-running ravines are sheltered from the prevailing westerly winds, and
the deepest escape the summer droughts that kill the oaks and maples before
their time, and turn the tops of the tuliptrees once eager to reach new heights.
In the deepest ravines, unweathered greensands still yield circumneutral soils
from ancient deposits where Late Cretaceous shells are but occasional
impressions. And so, starting with the entire Chesapeake environment, we come
down to a few small low slopes where the the afternoon suns never turn the
corner, and we find ideal habitat.

Well, I don't know if it's ideal habitat, so I just say it mimicks ideal
habitat. The indicator species speak to that. There's glade fern, maidenhair
fern, silvery spleenwort, broad beech fern, pawpaw, spicebush, showy orchis,
mayapple, richweed, wild hydrangea and hercules club. Here is Maryland's
largest white oak, spicebush, northern red oak and perhaps seven other native
species. Many of the indicator species also occur at Belt Woods, and both sites
have tuliptrees, white oaks, black oaks, northern red oaks and other trees of
exceptional height in close proximity to the indicator species.

So, what do indicator species indicate? Obviously, there's the matter of
fertile soils, especially those that are circumneutral. Tuliptree, pawpaw and
bitternut are associates of the rare glade fern, but those trees aren't rare, so
what's special about these tall-tree sites? In large measure, it's the
comparative freedom from drought stress. Of course, in the mountains, where
rainfall is greater, temperatures lower, and sheltering topography more
extensive, trees do grow taller.

That said, are the mentioned indicator species a relevant guide to exceptional
tree sites off the coastal plain? Are there others in those habitats? If so,
do they indicate factors beyond freedom from drought stress? It appears many
are still relevant; after all, glade fern isn't common anywhere.

So, how do we break down habitat in an entire county or state, by the best of
the best, until we come down to a few acres of exemplary habitat? If a pawpaw
is an uncommon find at Baxter Creek, does that suggest it's not exceptional
habitat, but only mimicks such? If so, are there sites with better habitat?
What indicators would lead us in that direction? Do we need to pay more
attention to shell marl as at Carters Grove, or Chapman's Landing, or limestone,
as at the Brevard Fault line?

Yes, your cottonwoods are a picky lot, but impressive with the right habitat.
We've measured a lot of tall trees all over, and it's probably time to associate
numbers with habitat. Good habitat isn't self-evident; many sites just mimick
exceptional conditions, sort of like actors masquerading as the real thing.
Still, the numbers are there, are we need to ask what roles these sites play on
the larger stage.

Colby