Re: Allelochemicals, Echinodorus

> krandall at world_std.com (Karen A Randall)  wrote:
> First of all, thank you for a very interesting post!

We aim to please!

> I think we are not all imagining the same thing when we use the 
> terms "light", moderate" and "heavy" planting.  

I think you are right--terminology is a big issue to me, and I
don't know that everyone on this list has uniform understanding
of these categories (I know I don't)  :^>.  I keep dropping back 
to my metrics in forest mensuration (because I know what that is), 
and I'm really trying hard not to use terms like "co-dominant" 
and "intermediate", but I keep thinking some scale or "rules of 
thumb" would allow more consistent relation of experience.

For my tanks, (the frugal, penny-pinching tightwad that I am), I
get enough plants so that each competes closely with another plant
on at least two out of four sides.  Thus, all of my plants have
an "out" where they can grow into a space relatively free from
competition, or can compete directly with their immediate neighbors.
As in my previous post, I think this competition is important.  I
do not have problems with "deformed" vegetation from lopsided
competition, but can simply uproot those plants that may have
problems and turn them around.  Of course, larger plants don't get
lopsided from competition with neigbors, so I don't need to uproot
them.  :^>

After some period of growth, the plants eventually "fill in" those
open spaces, and I may end up with 3 out of 4 sides or 4 out of
4 sides with competition (various levels of competition).  Then
I know I must prune.  My schedule is rather hectic at present,
and I must admit that I do prune back heavily, to a very minimal
amount of competition.  I do not have significant problems with
algae, (that may partially due to low light, 1-2 watts/gallon),
but I am getting "good" growth (real quantifiable, huh?).  :^>

> Certainly, a tank 
> can get so crowded that the growth rate drops off.  I would not 
> term that "densely planted", I'd term it "over crowded".<g>  

Agree again.  Of course, the rate is dropping off (with increasing
severity) as competition is introduced.  While some plants do grow
better in the presence of other plants of the same or different
species (usually a result of micro-climate modification), any plant
"aware" of another plant is fundamentally in direct competition
with its neighbor.  From studies on terrestrial plants, the "first
day" after pruning is absolutely the most productive day for
growth (given a constant nutrient sufficient environment).  That
"first day" may last a long time (like a year or two for woody
trees), as competition is slowly introduced.  The productivity drop 
is rather stark and significant thereafter as neighbors 
"rub elbows" with neighbors.  Productivity decreases on a sigmoidal 
curve, with a severe drop in Net Primary Productivity (NPP) 
(along the sigmoidal curve vertical) long before the plant begins 
to show signs of stress.  The NPP can stagnate at zero for decades 
for many trees (I can show you a zillion 60 year old Pinus contorta 
[lodgepole pine] that have 1" diameter stems, or a zillion 90 
year-old Picea engelmanii [Engelman's spruce] that are only 8" 
tall.)  Since non-woody plants operate on a completely different 
time-scale, I would suppose most aquatic perrenials should have 
no problem with a NPP of zero for a few months.  (It begings dying 
with a negative NPP).  I'm convinced that many of my plants that
have heavy competition on 4 out of 4 sides have an NPP of zero, but
seem to exist fine for a while until I get around to pruning
everything back (this is more easily demonstrated for rosette-type 
plants than for stem plants that merely extend upwards.).

One more thought on competition:  for many terrestrial systems, the
actual competition is almost *entirely* below soil.  Many fields
don't have trees simply because the competition for root space is
so complete that nothing can get a foothold (even though the
established plant species does not appear to exude allelochemicals).  
In these fields, trees simply cannot grow because root competition 
is so severe, even though sufficient light and water may be 
available.  I am absolutely convinced that this also takes place 
in aquaria around mature species with strongly developed root 
systems.  (I was over at George's house, and he told be to stick 
my finger into his substrate at one spot;  I couldn't;  the root 
mass was so well-developed, it was like trying to stick your 
finger through plywood).

> George and I have what I would consider "densely planted" tanks, 
> and I know from what I've seen of his tanks and what I've read 
> from him that both of us aim for optimum growth.  

I am very impressed with George's tanks.  His growth is excellent.
(Sorry, I haven't seen yours!  :^>  )  However, I know "optimum"
must be somewhat arbitrary.  The farmer must decide if he wants
the biggest ears of corn (space those plants far apart), or the
most possible corn (pack them in there, more plants "more-than-
compensate" for the decreased productivity of individual plants).

That, I suppose, is the art;  are we gardener (the population) or 
horticulturist (the individual)?  Some of both, I should think.

> I may stress the term "densely planted" because I am so often 
> faced with helping a planted tank beginner who is having problems 
> balancing a 55G tank with two anaemic Swords, a bunch of failing 
> Cabomba and two bunches of "Princess Pine".  To too many people, 
> that's what a planted tank is.  At the same time I tend to stress 
> light fish stocking, again, because beginners tend to overdo it in 
> that area.

Yes--that I understand.  :^>  I guess we would both agree that almost
"no competition" exists there?  :^>

> So maybe in your terms, my tanks are "moderately" planted, since I 
> do whack away at them with a machete fairly frequently.  

That has statistically proven to be the most efficient method (most 
productive in terms of given resources and resulting biomass) for
a total resource investment over a given period of time.  I should 
do that, but I don't (I will use time constraints as an excuse).  :^>

Sorry for the long post.  

--charley                            Fort Collins, Colorado USA
charleyb at gr_hp.com	or	charley at agrostis_nrel.colostate.edu