Indexing hybrids and varieties   Jess Riddle
  Mar 19, 2007 19:50 PST 


For measurement purposes, how should we treat hybrids and named
varieties? I'm sure some people would just ignore hybrids and not
divide taxa below the species level, but I just can't see this group
doing that. I'm sure we'll track the maximum dimensions of hybrids
and named varieties whenever we recognize them, but what about species
in a Rucker Index or other indexes? Should a hybrid and a parent
species both be allowed to count in a Rucker Index thus, in a sense,
allowing the parent species to be counted one-and-a-half times?
Should multiple varieties of the same species be allowed to count in a
Rucker Index?

These questions are not just hypothetical. The RHI 10 for Groundhog
Creek, NC includes Saul's Oak, the white-chestnut hybrid. If the
index is expanded to 11 or more "species", white oak would also
qualify based on height. This post was precipitated by Will Blozan's
question about Biltmore ash in the Oconaluftee watershed. The
standard form of white (Fraxinus americana var. americana) and
Biltmore ash (Fraxinus americana var. biltmoreana) have each been
measured to 148.6' tall in the watershed. I have initially simply
listed white ash in the Rucker Index. If both varieties were included
separately, the index would rise 0.78'.

Any thoughts?

RE: Indexing hybrids and varieties   Steve Galehouse
  Mar 19, 2007 20:17 PST 

Jess, ENTS-

I think it all boils down to "lumpers" and "splitters" in a taxonomic
sense; if a tree type is currently accepted as a variety or race of a
species, it should count as the species as far as maximum size--if it is
currently accepted as a hybrid, it should count apart and in addition to
its presumed parents. Lots of room to waffle, especially with oaks that
freely hybridize.

Steve Galehouse

RE: Indexing hybrids and varieties   Joshua Kelly
  Mar 20, 2007 06:06 PST 


On the subject of including varieties and hybrids in Rucker Indeces, I
propose an ecological definition:

If varieties and their sister taxa occur in the same conditions, I propose
listing only one in the Rucker Index. If they tend to be fairly
ecologically discrete, as in Fraxinus americana var. americana and F.
americana var. biltmoreana (they seem to seperate by elevation and soil
quaility), I think including both in the Rucker Index of a watershed,
mountain range, state, or region is tenable.

In the opposite case, I would be less entusiastic about including taxa that
had a large ecological overlap.

The case of hybrids is actually a bit more complex, because they are quite
genetically distinct, yet they may share the exact same habitat as both of
their parents. I don't haven't formulated a clear opinion about including

Re: Indexing hybrids and varieties   Edward Frank
  Mar 20, 2007 08:09 PST 


I am a splitter. If there is a defined, named, naturally occurring, hybrid
or named variety, I would count each as a separate type in terms of Rucker