Of course, experiments that fail at their intended goals do have
a way of succeeding otherwise, sometimes.
It had been a dark mud pit, devoid of
tallgrass life, made gloomy by dense shade of invading green ash trees. Decades ago
we girdled them, planted seed from nearby healthier savanna and oak woods ponds
(some of them now gone) – and waited with Great Anticipation. Instead we were at first greeted with Bitter Disappointment. None of our
planted species showed up. The pond developed a rank, dense thatch made up of such weeds as tickseed,
barnyard grass, and knotweed. But that turned out to be a passing phase and
within a few short decades, Oak Pond was gorgeous, diverse, and flowery. For
more detail, see Endnote 1.
Then apparently, it sprang a leak.
Generations of blue-spotted salamanders, spring peepers, and
chorus frogs had gone through their larval stages here and marched forth to
populate our trees (peepers), grasses (chorus), and sub-surface tunnels
(salamanders). The pond had been their nursery, because these larvae need water
to breathe and to feed. Salamander babies are ferocious predators of mosquito
larvae and other tiny water animals. Tadpoles eat soggy decaying plant matter,
even though they too will be predators as adults.
Back when it was still a pond, it also supported the Sommes’
only population of the threatened plant, marsh speedwell (Veronica scutallata). Fortunately seed was gathered here and spread
to other Somme ponds, where this speedwell still thrives.
We did not at first quite notice when Oak Pond ceased to be.
Perhaps we have many kinds of records, filed away somewhere, that would help us
understand what happened and when.
Frog monitoring data tell us that as recently as April 21, 2011
– frog monitor Tim Wilson reported great numbers of chorus frogs calling in Oak
Pond. Later that same year, on June 1, there must have still been water in the
pond, as Wilson reported calling chorus frog and eastern gray treefrog. (See
Endnote 2).
But in recent years, the pond has been bone dry all spring
and summer. This year, I happily noticed winter water filling the pond on
February 20.
But when I walked by on March 12th, although all
our other Somme Ponds were filled to the brim, the late Oak Pond was already bone
dry.
But on March 12, with all Somme's other ponds filled to the brim, where did the pond go? |
What happened? Perhaps in mid February the recent water was being held in the pond by many inches of solid frozen soil, but when the ice melted (counter-intuitively from the bottom of the pond), there was no impermeable layer to hold the water in?
We expected, indeed, most people expected that when you cut
invading trees away from a natural prairie pond, it would hold water longer. The leaves of trees transpire a lot of water - after the roots suck it out of the ground.
Clearly, something different is happening here.
This pond is at the
crest of a moraine (the Deerfield Lobe of the Lake Border Moraine). Morainal
crests can have porous, gravelly soils, that send water promptly down to the aquifer. But
moraines can also have “clay lenses” and patches of claypan soils – that restrict
the passage of water. Could it be that green ash roots gradually penetrated a claypan and then slowly rotted away? Might the rotting of those roots be
like removing plugs from the holes those roots made?
Alternatively, is it possible that the luxuriant vegetation
that grew in the pond itself changed the soil in some way that destroyed the
functioning of the claypan?
How do claypans form? And will those processes in time close the putative holes that could have been created by rotting stumps? Does any expert on soils or hydrology read this blog? Or does anyone know a generous expert they might appeal to – who might be willing to weigh in? (Sadly, we have no research funds to offer.)
How do claypans form? And will those processes in time close the putative holes that could have been created by rotting stumps? Does any expert on soils or hydrology read this blog? Or does anyone know a generous expert they might appeal to – who might be willing to weigh in? (Sadly, we have no research funds to offer.)
And – what is a steward to do?
Ah hah! For that we finally have a clear answer. In the absence
of better knowledge and expertise, all is going well enough already. Oak Pond
may become Oak Meadow. That’s great, if that’s what it wants to do, absent more
beneficial ideas and proposals. If this acre is not habitat for frogs, they can
move to our many other ponds, and the former Oak Pond can become habitat for
voles, meadow plants, snakes, and bumble bees. It’s too bad that we invested
rare wetland seed there, but we’ve learned a lot from that seed already, and we
now have at least four populations of the threatened speedwell that we wouldn’t
otherwise have, and those came from the population that for a while thrived in Oak
Pond. We do not expect all of our restored rare species populations to survive.
We just give them a chance. Many of them may die out at Somme. Many others – as
the soils, amounts of shade, species abundances, and global climate all change –
may surprise us by moving to other niches, as they find opportunities for
themselves, as they always have.
Thanks to all who work, study, and advocate to advance this
great experiment in conservation.
Endnote 2
ENDNOTES
Endnote 1.
If you’d like to know more of what, for a time, thrived in Oak
Pond, we can start with a list of plants. The first “breakthrough” was rice cutgrass (Leersia oryzoides); after a few years of dense annual and biennial weeds, this wetland grass started popping up in
many places. Next we started to find expanding populations of blue flag
iris (Iris virginica), hop sedge (Carex lupulina), crow’s-foot sedge (Carex crus-corvi), great bulrush (Scirpus validus), false dragon’s-head (Physostegia virginana), and in time many more. (See more in Endnote 3.)
Seed of many of these, including the endangered speedwell, came from ponds about ten miles away
that are now so dark with invasives that neither the speedwell nor most of the
other species we gathered there can still be found.
For a while the endangered American slough grass
(Beckmannia syzigachne) bloomed in this pond. But no longer. This grass proliferated for a while
in a shallow section of another Somme pond for perhaps 20 years, then vanished
there – only to show up in a distant, deeper section of the pond, with entirely
different associated plant species. (We don’t try to figure out too much.
We give seeds a chance. Then, it’s up to them and nature, except for species that need caging from the deer.)
One of our favorite memories of Oak Pond occurred when it
finally dried up, as ephemeral ponds must do, usually in mid-summer for this
pond. By drying time, larval chorus frogs and peepers had functioning lungs and left the
pond. These species cannot reproduce in permanent ponds, as those ponds support
fish and bullfrogs, both of which eat the young of the ephemeral pond species,
which are not adapted to those predators.
But one of the most dramatic predator displays offered by
Oak Pond starred cedar waxwings. They like to eat backswimmers. The backswimmers
are ferocious predators themselves, consuming a great many tadpoles, when they get
a chance. But as the pond dries down to just a square yard or so of
water, the backswimmers pop out of the water and fly off to find another pond.
Cedar waxwings would sit in the trees that circle the pond, and as soon as a
backswimmer took off, the waxwings would flit out and grab it. We never saw one
get away.
Cedar waxwings once ringed this pond in summer to hunt backswimmers. Photo by Lisa Culp Musgrave |
In late March and early April, there are often so many
peepers and chorus frogs calling from some Somme ponds that their joyful uproar blots out highway and
airplane noise. They rock! On the other hand, we stewards have never heard a
gray treefrog call. It came as something of a shock to see that rare species
mentioned in the frog monitoring record.
We had never seen leopard frogs at Somme and thus were taken aback one year to find dozens of their tadpoles in one Somme Prairie Grove pond as it dried down to nothing. We’d never heard
them either. That’s a bit more understandable, as leopard frogs call early in
the season and easily get drowned out by the peepers. Now that we’ve trained
our ears, we do sometimes hear them in the deepest of the Somme Woods ponds. They
need longer times to mature than do the little peepers, and, although the
Prairie Grove has better adult habitat for them, the Prairie Grove ponds dry sooner. But that year, somehow, at least one male and one female managed to
cross Waukegan Road and reproduce. We’ve never found them there again. We
imagine that their numbers may start to increase at Somme Woods, as the habitat there
becomes more of a grassy open woods than its former mostly-buckthorn-and-dirt condition. An alternate name for the leopard frog is “the
meadow frog.”
We can’t resist wondering whether there may also be tree
frogs surviving somewhere in or near Somme. In a Northbrook park some years
back, we recorded a frog identified (from the cell-phone recording of its call) as Cope’s gray tree frog
(by U. S. Fish & Wildlife staff). Tree frogs need ponds where water remains even later in the summer than is needed by leopard frogs. The deepest
ponds in Somme Woods probably dry sooner than they once did, because their
centers are clogged (unnaturally, some experts think) by peat-like
accumulations of cat-tail roots. Does the tree frog deserve any kind of conservation
initiative at Somme?
Endnote 3
After I finished this post, I found the following list of plants identified in Oak Pond by Robbie Sliwiinski in July 2009. I believe that most of these species are now gone.
I just hadn't much paid attention to this pond - except for an odd subliminal feeling that it had become weird. My focus was jogged back to it only by seeing it strangely once again filled with water this February. Although I hadn't paid careful attention to the vegetation, I do remember that the dominant plant was the weedy tall boneset (Eupatorium altissimum). Apparently a whole plant association died out when the pond lost its water, and the weeds blew in.
Acknowledgment
Thanks for proofing to Kathy Garness and Eriko Kojima.
Endnote 3
After I finished this post, I found the following list of plants identified in Oak Pond by Robbie Sliwiinski in July 2009. I believe that most of these species are now gone.
I just hadn't much paid attention to this pond - except for an odd subliminal feeling that it had become weird. My focus was jogged back to it only by seeing it strangely once again filled with water this February. Although I hadn't paid careful attention to the vegetation, I do remember that the dominant plant was the weedy tall boneset (Eupatorium altissimum). Apparently a whole plant association died out when the pond lost its water, and the weeds blew in.
Site: Oak
Pond
Locale: SPG
Date: July
2009
By: R.
Sliwinski
File:
c:\FQA\studies\Oak Pond.inv
FLORISTIC
QUALITY DATA Native 20
100.0% Adventive 0
0.0%
20 NATIVE SPECIES Tree 0
0.0% Tree 0
0.0%
20 Total Species Shrub 0
0.0% Shrub 0
0.0%
5.8 NATIVE
MEAN C W-Vine 0
0.0% W-Vine 0
0.0%
5.8 W/Adventives H-Vine 0
0.0% H-Vine 0
0.0%
26.2 NATIVE
FQI P-Forb 8
40.0% P-Forb 0
0.0%
26.2 W/Adventives B-Forb 0
0.0% B-Forb 0
0.0%
-4.7 NATIVE
MEAN W A-Forb 0
0.0% A-Forb 0
0.0%
-4.7 W/Adventives P-Grass 3
15.0% P-Grass 0
0.0%
AVG: Obl.
Wetland A-Grass 1
5.0% A-Grass 0
0.0%
P-Sedge 8
40.0% P-Sedge 0
0.0%
A-Sedge 0
0.0% A-Sedge 0
0.0%
Cryptogam 0
0.0%
ACRONYM C
SCIENTIFIC NAME
W WETNESS PHYSIOGNOMY COMMON
NAME
ALISUB 4
Alisma subcordatum
-5 OBL Nt P-Forb COMMON WATER PLANTAIN
BECSYZ 10
Beckmannia syzigachne
-5 OBL Nt A-Grass AMERICAN SLOUGH GRASS
BOECYC 2
Boehmeria cylindrica
-5 OBL Nt P-Forb FALSE NETTLE
CXANNA 5
Carex annectens
-3 FACW Nt P-Sedge LARGE YELLOW FOX SEDGE
CXCRUS 10
Carex crus-corvi
-5 OBL Nt P-Sedge CROWFOOT FOX SEDGE
CXLUPF 10
Carex lupuliformis -5 [OBL] Nt P-Sedge
KNOBBED HOP SEDGE
CXLUPN 7
Carex lupulina
-5 OBL Nt P-Sedge COMMON HOP SEDGE
CXPELL 4
Carex pellita
-5 OBL Nt P-Sedge BROAD-LEAVED WOOLLY SEDGE
CXTRIB 3
Carex tribuloides
-4 FACW+ Nt P-Sedge AWL-FRUITED OVAL SEDGE
CICMAC 6
Cicuta maculata
-5 OBL Nt P-Forb WATER HEMLOCK
ELEERY 2
Eleocharis erythropoda
-5 OBL Nt P-Sedge RED-ROOTED SPIKE RUSH
GLYSEP 8
Glyceria septentrionalis
-5 OBL Nt P-Grass FLOATING MANNA GRASS
GLYSTR 4
Glyceria striata
-3 [FACW] Nt P-Grass FOWL MANNA GRASS
IRIVIS 5
Iris virginica shrevei
-5 OBL Nt P-Forb BLUE FLAG
LEEORY 4
Leersia oryzoides -5 OBL Nt P-Grass RICE CUT GRASS
LOBCAR 7
Lobelia cardinalis
-5 OBL Nt P-Forb CARDINAL FLOWER
SCIATR 4
Scirpus atrovirens
-5 OBL Nt P-Sedge DARK GREEN RUSH
SCULAT 5
Scutellaria lateriflora
-5 OBL Nt P-Forb MAD-DOG SKULLCAP
SIUSUA 7
Sium suave
-5 OBL Nt P-Forb TALL WATER PARSNIP
VERSCU 10
Veronica scutellata
-5 [OBL] Nt P-Forb MARSH SPEEDWELL
Acknowledgment
Thanks for proofing to Kathy Garness and Eriko Kojima.
1 comment:
It is difficult for plant roots to penetrate clay layers. It is likely the removal of the ash trees is not what caused Oak Pond to stop holding water. I must wonder if non-native earthworms have invaded causing the change. Earthworms have trouble penetrating dense clay layers just like plant roots. However, earthworms aerate the soil. Their burrows could be storing the water that was formerly creating the pond.
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