plant collecting

Adolf Ceska aceska at VICTORIA.TC.CA
Tue Oct 12 07:53:20 CDT 1999

David Wagner published his "Rule of thumb" in Oregon Flora On-line
Newsletter and elsewhere. This is a version from BEN (Botanical Electronic
News) # 180 (Dec. 12, 1997):

From: Dr. David H. Wagner <103132.2716 at>
    originally published in the Oregon Flora On-Line Newsletter
    Volume 1 Number 3 - Oregon State University - July 1995

There have apparently been instances in  the  past  where  well-
meaning  botanists have destroyed plant populations through over
zealous collecting. The case most familiar to me concerns one of
the world's rarest  ferns,  the  pumice  grape-fern,  Botrychium
pumicola.  A  student  searching  for  new  sites  found two in-
dividuals of this species on Oregon's Tumalo  Mountain  in  1954
which  he  collected  to  make  herbarium specimens. In the late
1970s I searched the top of Tumalo  Mountain  with  friends.  We
were  experienced  fern  hunters,  but we found no Botrychium. I
strongly suspect that the two plants removed in 1954  eliminated
the  population  at  this  location.  Today  we  would hope that
botanists finding only one or two plants at a site  would  docu-
ment   their   discovery   with   photographs  and  notes.  Good
photographs and careful field notes are increasingly  acceptable
for recording plant discoveries.

Nevertheless,  from time to time, a field worker may encounter a
small population of a plant and feel it is necessary to  collect
a  bit  of it for positive identification and documentation. The
Native Plant Society of Oregon's Guidelines  and  Ethical  Codes
for  botanists  urges  that  a  collector use good judgement and
rules of thumb when deciding whether or not to collect.  But  in
this  case,  what  is  a  good rule of thumb? During the past 10
years, I have been using what I call the "1-in-20 Rule."

The 1-in-20 Rule dictates that a  botanist  never  collect  more
than one out of twenty plants. It means NOT collecting ONE plant
UNTIL  you  have found at least TWENTY. Only if twenty are found
should you consider collecting one plant. And  forty  should  be
present  before  two  are  taken, and so on. The rule applies to
parts of plants, also: remove no more than  five  percent  (one-
twentieth) of a shrub, one fern frond from a clump of twenty, 5%
of  a patch of moss, 5% of seeds from a plant. I use the 1-in-20
Rule whether I am collecting  voucher  specimens  for  the  her-
barium,  doing  rare plant work, or gathering common species for
classroom use.

The 1-in-20 Rule does not obviate the need for  good  judgement.
Only  when  a  botanist has the knowledge to assess whether col-
lecting is both ecologically  justified  and  legally  permitted
should a specimen be taken. Any pertinent factor relating to the
survival of a population needs to be superimposed on the 1-in-20
Rule. The main value of this rule of thumb is to provide a clear
point of reference from which to begin assessing a situation. It
helps  a botanist determine how much time should be spent inven-
torying before sampling is appropriate. I  suggest  the  1-in-20
Rule  as  a  minimal  criterion to be met before any taking of a
plant be considered.

There is at least a modicum  of  scientific  logic  behind  this
rule.  Statistically,  a  population  sample  of nineteen is not
significantly different from a sample of twenty. One  population
geneticist  I consulted advised me that contemporary statistical
theory would support the  1-in-20  Rule.  Another  pointed  out,
however,  that  repeated  collecting  would tend to reduce every
population to  nineteen  individuals.  This  caution  serves  to
emphasize  that  the  1-in-20  Rule  is  a  rule of thumb, not a
license to ravage.

An interesting line of argument in support of the  1-in-20  rule
has  developed  since I first published the idea in the Bulletin
of the Native Plant Society of Oregon in 1991. First, I received
a letter from James Grimes of  the  New  York  Botanical  Garden
querying  whether or not I had picked up the idea from a similar
article he and others had published in  the  newsletter  of  the
Idaho Native Plant Society a few years before. I honestly cannot
recall  seeing  their note. Then, last year, four botanists from
Australia and New Zealand published an article in  the  interna-
tional journal, Taxon, which made essentially the same recommen-
dation. Thus, three botanists or groups of botanists, deliberat-
ing  independently,  have arrived at the same standard. I submit
that  this  concurrence  from  three  separate  sources   speaks
strongly for the sensibility of the 1-in-20 Rule.



Adolf Ceska

Adolf Ceska, P.O.Box 8546, Victoria, B.C., Canada V8W 3S2
e-mail: aceska at
Phone: 250-356-7855 (work), 250-477-1211 (home)
Fax: 250-387-2733 (work)
Visit BEN web site at

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