rucker index   Darian Copiz
  May 11, 2005 10:07 PDT 

What is the purpose of the Rucker Index?

Re: rucker index   Edward Frank
  May 11, 2005 11:37 PDT 


The Rucker Site index is essentially a foreshortened version of a complete
profile of all the species found on a particular site. The best overview
on the Rucker Index, both strengths and weaknesses is provided on the ENTS
website at:

Colby Rucker wrote in 1993 :
"...the average height of the tallest examples of the ten tallest species
found at each site.   This index, often called the “Rucker index,” provides
a numerical evaluation of both maximum height and diversity of the dominant
species. High index values are the result of many factors,
including climate, topography, soils, and a lack of disturbance. While the
most extensive sites benefit from a greater variety of habitat and more
individual trees, some exceptional sites are quite small."

The Rucker Site Index or Rucker Index has a numerous merits that make it a
useful measurement when comparing various tall tree sites.

1) The formula is straight forward, unambiguous, and easy to apply. The
measurement is simply the average height of the tallest examples of the ten
tallest species found at each site. Anyone who can add ten numbers and then
divide by ten can calculate the figure.

2) The index can be applied to forests in any area with any make-up of
trees. One of the biggest problems faced when comparing different areas is
that the same tree species are not found in all areas to be compared. The
index is not species dependent. It does reflect to some degree the species
included, because all tree species do not reach the same height, but
none-the-less the formula will produce a useful concrete number.

3) The index requires a fairly diverse mix of trees in order to generate a
high index value. This means in order to achieve a high index rating that
the forest patch being evaluated must not be primarily dominated by a
single species, but be reflective of a more complete and by inference
a more intact forest ecosystem. This has some drawbacks however. Robert Van
Pelt, author of "Forest Giants of the Pacific Coast" writes in a post
dated October 29, 2002, “The low diversity of trees in some Western forests
quickly reduces the Index to below 200. Humboldt Redwoods SP,
for example, has the world's tallest tree, and 86 trees over 350'. Due to
the overwhelming dominance by redwood, the Index drops below 200 after only
six species are included!”

4) To get a sufficient diversity of trees of great height requires a fairly
large plot of forest. This limits sites with a very small area and few
trees generally from having a high index. The value in this, as I see it,
is small sites with only a couple of spectacular trees, or only a single
big tree do not falsely appear from the index value alone to be the equal
of larger sites with larger numbers of trees.   

Ed Frank
RE: rucker index   Darian Copiz
  May 11, 2005 13:25 PDT 


The attached link was a good read. My understanding of the index is that it can be used to compare the "tallness" of sites while factoring in diversity. Is this for the purpose of defining champion tree tallness sites or is there a larger goal?

Re: rucker index   Edward Frank
  May 11, 2005 17:20 PDT 


If you want to make comparisons between different sites with regard to the
maximum tree size on the sites, you need to develop some criteria to do it.
The Rucker index was developed to serve that purpose. It allows
comparisons to be made between sites of different sizes, different
tree compositions, in different locations. In addition it promote
measuring trees beyond just the very tallest to a species depth of at least
ten species or more. Much of the interest in RI is purely competitive, but
the Rucker Index does serve a real purpose. It seems well suited to making
these types of comparisons.

Re: rucker index   Will Blozan
  May 11, 2005 17:27 PDT 

Furthermore, multiple iterations of the RI can indicate the depth of the
tree resources of the site.

Will B
RE: rucker index   Gary A. Beluzo
  May 12, 2005 05:21 PDT 


What about using tree height measurements to discover canopy complexity? In
other words use a variation of the Rucker Index to compute sites that have
the most "vertical depth" in the canopy. Also, a variation could be used to
determine species richness? I am interested in developing other indices that
evaluate forests in other ways besides "tallness". Any ideas?

RE: rucker index   Gary A. Beluzo
  May 12, 2005 06:20 PDT 


I understand how the index provides a sense of the "depth of the tallness"
but I am not seeing how it provides an evaluation of dominant species
diversity, since a given index could be reflective of the 10 tallest of 30
species or the 10 tallest of 100 species.

The Rucker Index is a good means of comparing different sites of the same
forest type within a certain latitude. Beyond that, I think there needs to
be some way of "weighting" heights according to species and factoring in
environmental and latitudinal differences IF the index is to be of value
ecologically. Of course comparing the Rucker Index of sites to see where
the tallest forest is can be just plain fun. I enjoy the playful
competitiveness of our list members!

RE: rucker index   Darian Copiz
  May 12, 2005 06:23 PDT 

Part of the reason I ask is because to me it seems that it is primarily
a competitive tool. That doesn't mean I think it's wrong. Personally, I
would love to see the Mid-Atlantic beat both the Northeast and
Southeast. Even though the likelihood of the Southeast being beaten
seems impossible, I'm sure others would agree it's fun to route for the

RE: rucker index   Darian Copiz
  May 12, 2005 06:56 PDT 

This is much of what I was getting at. I think the southeast mountains are dominant primarily because of three factors: highest annual rainfall in the East, longer days, and steep ravines. However, these are things that the Rucker Index does not factor in. I think excellent site descriptions are what can give ecological value to the index - the site descriptions help answer why the site has a high RI. One thing I have been a little confused about is whether the RI is trying to tell us about the site or about the trees.

RE: rucker index   Edward Frank
  May 12, 2005 07:36 PDT 


I don't say anywhere that it provides an evaluation of dominant species
diversity. I believe that 10 species is a better characterization of the
forest than one or two species. I would like to see RI including more
species or all of the species present if possible. Any type of combination
measurement is a compromise between a variety of factors. You can compare
sites at different latitudes, it is when you interpret the information that
you need to consider climatic variations. You can measure temperature at
different latitudes and understand that it will be warmer in the tropics.
The Rucker index could be considered a "temperature" reading of forest
sites. The weighting of various parameters is in the evaluation of the
results, not in the measurement itself.

RE: rucker index   Gary A. Beluzo
  May 12, 2005 07:52 PDT 


Well considering the RI is looking at the mean value of the 10 trees (each
representing the tallest measured specimen for each of 10 species), I
suspect it is telling us something about both the trees and the site.
Obviously stand age (up to a certain point because the age versus height
curve is logarithmic?) as well as all of the other variables already
mentioned is going to have an influence on the RI of one site versus another
so I agree that there is no substitute for complete site descriptions when
interpreting or comparing RI values between sites.

RE: rucker index   Ernie Ostuno
  May 12, 2005 10:40 PDT 

Well now I am curious about what type of index would have the best
chance of being a good indicator of old growth forest. What about one
that includes the volume of moss, lichens and dead woody debris? Is
there an equivalent of a laser rangefinder that can measure that?

RE: rucker index   Gary A. Beluzo
  May 12, 2005 10:56 PDT 


Funny you should mention that because all along I have believed that to get
at the degree of naturalness or what I call the "autopoietic forest" we may
need to evaluate COMPLEXITY because as humans MANage systems they become
simplified in many structural and functional ways. Perhaps for a given
forest type digital analysis from 360 degree camera views would help to
define the degree of structural complexity. Of course this would still
leave functional complexity.. how would we approach that problem? Ecological
modeling (and systems ecology) still has a long way to go.

Responding to Darian's question   Robert Leverett
  May 12, 2005 12:22 PDT 


   I'll take this opportunity to clarify (I hope) Rucker indexing for
our new members. We have 114 now.

   In the way of background, three Ents are basically responsible for
launching the Rucker index. First and foremost is the late Colby Rucker.
Secondly, there is Will Blozan, and thirdly and most humbly, yours
truly. Colby conceived the index primarily to evaluate the growth
potential of various habitats. He never used the concept without a
concurrent evaluation of the site conditions in terms of soil, aspect,
climate, etc. and he was always cautious in making comparisons among
sites. He wanted to insure apples to apples comparisons. By contrast, I
was inclined to throw caution to the wind.

    Since its inception, the Rucker index has come to serve several
divergent purposes. One purpose of the index is promotional. We use the
Rucker index to bring attention to sites we believe are important or
exceptional. Of course the Rucker index is but one of several means by
which we can call attention to a site. However, those of us who freely
use the Rucker index for promotional purposes need to provide the
caveats needed to issue that we don't trivialize the Rucker analysis

    A lighter use of the Rucker index is obviously for sporting
competition - as in "my Rucker index is higher than yours." And those of
us who regularly use Rucker indexing freely admit that we can't resist
the competitive aspect. It's fun. Nudging MTSF's index upward has
provided the Massachusetts contingent with loads of fun. Similarly, Dale
over in PA is the image of pure competitiveness. Down in the Smokies,
Will is on another level. He has no competition, except from Jess. But,
it's all fun.

    At a more scientific level, the most obvious purpose of the index is
to depict (more or less) what is happening at a site in terms of maximum
tree heights and circumferences. In this regard, Rucker indexing has a
descriptive purpose partly born of the lack of specific and accurate
site descriptions done in the past by others. Beyond simple description,
the index provides us with a still picture, if a highly simplified one,
of what the forest is doing in achieving height and/or circumference
growth at a specific point in time. But computing an index is just the
first cut at the determination. Because, in mulling over an index for a
site, we obviously need to be aware of the span of tree ages that
contribute to the index and site conditions. Those of us who use Rucker
indexing are aware of site conditions and the age structure of the trees
whether or not we discuss the details in our e-mails. Computing an index
is in actuality the initiation of a process.

    We begin the process by looking for the height superlatives for the
represented species. We select the tallest member (that we can find) of
the ten tallest species and average the heights. We call this average
the site's Rucker index. We typically report the result on the ENTS list
as an average tree height. By definition, no species can enter a
calculation of the index more than once. Although we commonly use 10
species, the Rucker index concept can be applied to any number of
species at a site and can be computed a single time or iteratively.
Incidentally, Colby always felt self-conscious at seeing his name in
print or tied to these site averages. He was always modest.

    If we can't get 10 species at a site, we drop down in number, but we
must always convey the number of species used in the average that we
incorporate in the index, if other than 10, if we don't list the
individual trees. We don't compare a 10-species index to a 5-species
index. In terms of iterations, if we want to apply the index again, we
first remove the trees included in the first iteration and then proceed
as though we were making the calculation for the first time. All
subsequent iterations after the first are blind to what came before.
Although for list purposes we commonly report one index for a site, in
fact we compute many.

    For important sites, we apply the index iteratively to gain greater
understanding of what each species is doing ecologically. But before
going deeper into the ecological use of the index, I'd like to return to
the competitive use of the index. We obviously do use the Rucker index
to superficially compare sites to one another based on one iteration and
that smacks of competition. For instance, we proudly banter about Zoar
Valley's index at 136.2, Cook Forest's at 136.0, and MTSF's at 135.4. If
we stopped there, Rucker indexing would be little more than sport.
However, applying the Rucker index iteratively shows us what each
species is doing at a site. We come to know where the growth hot spots
are and we gain insight into each species' potential for the
environmental and climatic variables we think shape growth potential.
Much of this knowledge is acquired in the searching process. So, Rucker
indexing on important sites evolves into a process that produces a
stream of numbers that we can examine for many patterns and toward
answering many questions. This is the real meaning of Rucker indexing.

    Perhaps an example will help others on the list to understand where
we take the indexing process. Suppose we want to profile MTSF in terms
of Rucker indexing. We would begin by computing a simple index and
display the results. The Rucker Index for the 10 tallest species in
MTSF follows.

Height Species Circumference
166.4 WP 10.2
151.5 WA 6.2
133.8 SM 5.0
133.5 NRO 9.3
131.0 HM 10.7
130.0 AB 7.8
128.4 BNH 4.1
127.7 BTA 3.5

126.1 RM 6.2
125.4 ABW 5.9

135.4 Rucker Index               6.9

      Stating the obvious, from the 10-species index, we see that there
is one native species over 160 feet, 2 over 150, and 6 that reach 130
feet. We would continue with additional species and find that 12 reach
120 feet and 20 reach 100 feet. This would allow us to see the trend of
the index as we add species as shown below.

     # Species            Rucker Index
           5                   143.2
         10                   135.4
         15                   129.8
         20                   124.4
         25                   116.2

    To this point, we'd be measuring, if crudely, site growing
potential. What isn't revealed in the above indices is the distribution
and relative abundance of each species. So we would investigate
individual species height distributions. We would examine the dependency
of the index on one or more species. For instance, if we run Mohawk's
index iteratively for 10 species, we find that the index remains above
120 for 16 iterations. We would notice that the white pine, white ash,
sugar maple, northern red oak, and hemlock are represented in every
iteration and that white pine is the first member in each iteration and
that white ash is the second. This speaks to the behavior of those
species and to also to their abundance.
       Let's examine the behavior of white pine. In Mohawk, in terms of
height, clearly white pine is by far the most dominant. The top ten
pines average 160.6 feet in height and 9.7 feet in circumference. The 33
tallest trees in MTSF are all white pines. Then comes a lone white ash
followed by the white pine again resuming its dominance. There are 72
pines in Mohawk above 150 feet in height and presently we've confirmed
207 above 140 feet. The dominance of the great whites in Mohawk is
indisputable. How does white pine affect the index? Is Mohawk so
dominated by this one species, that if we remove it, Mohawk shrinks to
considerably lesser insignificance? Not quite. The indexing process
shows that other species play the major role. If we remove white pine
and recompute a 10-species Rucker index for Mohawk, we still get 131.3.
This is well above the next highest Massachusetts site. In addition, the
pines grow mostly in isolated second-growth stands. So what is Mohawk
without the great whites? There is a second forest of highly significant
hemlocks and hardwoods

       Currently, our database lists 1 white ash over 150 feet in
height, 16 over 140 feet in height, 52, and over 130 feet in height. A
small number may be remeasurements of the same trees, but we haven't
measured all the 130s by a long shot. so for now, 52 130's is a good
determination. Ash trees over 120 are common in Mohawk. If we eliminate
the super performing white ash from the indexing, and recalculate a 10
species index, we get 128.2 - still significantly above the next site in
Massachusetts. Given the number of species that exceed 120 feet and the
above analysis, Mohawk begins to emerge as a truly remarkable site for
its latitude.

     But continuing the process, we can show that there are relatively
few 130-foot sugar maples, but a lot over 120. We also find a healthy
number of red oaks over 120. In fact, we are tempted to concentrate on
the 120s as somewhat representative of Mohawk's hardwoods and hemlocks.
But we quickly find that there are fewer 120s for northern red oak,
hemlock, and black cherry than for ash and sugar maple. There are still
fewer for red maple, basswood, bitternut hickory, and bigtooth aspen.
What this tells us is that if we remove sugar maple and white ash,
Mohawk's tall tree profile drops dramatically. Interestingly, the 120s
for red maple, basswood, and bitternut hickory are highly dependent on
proximity to two species, white ash and sugar maple. It isn't clear
about black cherry. That species seems to have an independent streak. By
contrast, northern red oak and bigtooth aspen often compete among
themselves. They produce areas of "oak space" and "aspen space".
Another point is that the red maples are generalists. Tall red maples
can also be found squeezed in among the white pines.

   Despite the dominance of white pine, white ash, and sugar maple, if
we drop them out and recalculate a 10-species Rucker index for Mohawk,
we get 125.7. This does fall below Ice Glen's 126.2, but is #2 in
Massachusetts by a wide margin. How much area is required for Mohawk to
exert such dominance? If we compare Mohawk to other sites, we need to
consider geographical area. Of the nearly 7,000 acres of MTSF, only
about 1,000 acres of forest contribute to the above statistics. In fact,
if we push to the limits of all the high growth areas, we might get to
1,500 acres in Mohawk that we would use in computing Rucker indices.
Also, these 1,500 acres are near the bottoms of two river gorges. They
are not in the uplands. So we must introduce topography into the picture
to understand Mohawk. Then comes latitude, longitude, altitude,
rainfall, soil, etc. as we apply the Rucker process to individual
species over a large geographical area.

    Concurrent with multi-species analysis, we typically select
individual species and follow them across a range of target sites in
some political-geographical area, e.g. all of Massachusetts as compared
to the primary site. For example, let's take white ash. So far we have
found white ash over 150 feet in the Northeast in only one place, and
more specifically, one tree. We've found 140-footers on 2 properties in
Massachusetts: MTSF and Ice Glen, and one in NY, Kaaterskill Falls. Two
spots in Pennsylvania are almost guaranteed to have them. We've found
white ash over 130 feet in height on 3 properties in Massachusetts, 2 in
New York, and 2 in Pennsylvania. We have found white ash over 120 feet
on at least 6 properties in Massachusetts and I'm sure there are many
around the Northeast. White ash over 100 feet are common as weeds in the
Northeast. However, Mohawk's dominance for this species continues. We
perform similar analyses for other species.

    We'll eventually be able to assign probabilities for each species,
but based on what we've already done, we can safely pronounce that MTSF
is a truly exceptional site for the Northeast. Then comes the promotion
to the state, if you see where I am going.

    I hope this puts a better face on what is actually a process that
often gets short-sheeted in our sport-oriented e-mail discussions.

Re: rucker index   Edward Frank
  May 12, 2005 19:39 PDT 

Darian, Gary, Bob, others,

When you start looking at how the Natural sciences evolved. The first
thing you see is the development of a classification system. Until some
type of classification scheme is developed there is no way to contrast and
compare between differing sets of objects.  [Most of the family structures 
for the vertebrates were pretty well worked out by biologists before we 
understood anything about DNA simply through detailed classification and 
then subdividing those larger sets.}

One exercise I have done with intro geology classes is to give each table
of 3 -5 people a box of 30 miscellaneous rocks. I tell them their exercise
for the day is to develop a classification scheme for the rocks and break
them into groups based upon the classification system they choose. How
would you break the rocks into categories? You could break them down by
size, by color, by how pointy they are, or any of a variety of other
physical, observable characteristics. Certainly one group will try to
break there rocks down into igneous, metamorphic, and sedimentary rocks
based upon a vague remembrance of middle school earth science. It is
interesting to see what groupings they discover. They are all valid
classification systems and can be internally perfect within the parameters
they define, except for the one breaking it down into igneous, metamorphic,
and sedimentary - invariably they will have some of the rocks
misidentified and placed into the wrong category. Each of these
classification schemes are a valid way to approach the problem. They each
allow you to contrast and compare the rocks within a subset, and to
contrast and compare the subsets with each other. The other consideration
is how many subsets have they made? If you put each rock into its own
category or lump all of the rocks into a single category - both valid
options - then you have not forced yourself or allowed yourself to start to
draw conclusions about what they are interpreting. The classification
system, whether good, awful, or indifferent provides a framework that
allows these comparisons to made. Without the framework each object (rock)
is considered individually and limits the type of comparisons that can be

The Rucker Index is a form of classification system that allows sites to be
rated numerically. Rather than being a weakness, the fact that the number
is blind to every parameter but height is the strength of the index. There
is no bias built into the classification system. Each site generates a
unique number, but sites like MTSF, Zoar Valley, Cook Forest, Fairmount
Park, and GSMNP can be compared and contrasted. Each represents a high
number that is the maximum number found in their region. Therefore you are
comparing the sites with the tallest trees from each area. Then you can
start looking at why the variations of the numbers exist? What are the
different species making up the Rucker Index at each location? What
species do they have in common? What species are different? Why are there
different species in different locations? What factors could account for
the different heights of the same species at the different locations?

The Rucker index provides a framework in which these questions can be
conceived and investigated. The RI may not be a perfect classification
system, but it does not need to be perfect to be useful. There really
isn't another scheme to measure the overall tallness of a forest site, and
I personally think the RI is the best way to address that characteristic.

Another thought to consider is that we see snow. I have heard that the
Inuit have forty or so different words for snow. So instead of being one
generic white type of precipitation, it become forty distinctive types of
precipitation. This lets them consider the question of what is snow, and
how it works, and what are its characteristics on a much different level
than those of us who simple see snow. Developing a Rucker Index is one way
to increase our vocabulary on the subject of forest sites. Certainly other
parameters can be and should be considered, but it is in my opinion a
useful addition to the vocabulary of trees.

Ed Frank
RE: rucker index   Darian Copiz
  May 13, 2005 07:02 PDT 

Ed, Bob, Gary, ENTS,
I have thoroughly enjoyed reading the posts on the Rucker Index. It has
made me, and I'm sure others too, think about aspects of the subject
which I had not considered previously. I do still think that care needs
to be taken in what conclusions are reached from the use of the index,
but I don't think this is, or will be a problem. At a competitive
level, some sites do seem to have an unfair advantage due to the size of
the site. However, looking at Colby's report on Belt Woods I came up
with an RI of 131.0 which for a site of about 50 acres is truly
exceptional, when one includes that this site does not have any deep
ravines that just compounds the specialness of it. Also, looking at the
report I was once again very impressed how almost every species of tree
or even shrub was measured. It appears that Colby wanted a truly
comprehensive measurement of sites. Perhaps this is also something to
strive for, in addition to the competitive level of finding a tree in
the top 10 that's a few inches taller. It appears that I may be moving
soon to within one block of Rock Creek Park in DC, near the location
where Bob made some measurements. I look forward to contributing to
making this location another star on the Rucker Index map - and
hopefully beating as many other stars as possible. :)

RE: rucker index   Gary A. Beluzo
  May 13, 2005 08:48 PDT 


I also agree that the RI is the best current way to compare tallness between
the sites. My reason for suggesting other indices is to begin assessing
these sites more ecologically, a more systems approach. I appreciate the
comments of everyone that has contributed. Let's keep it going!

RE: rucker index   Robert Leverett
  May 13, 2005 13:19 PDT 


   Reference your caution ". I do still think that care needs
to be taken in what conclusions are reached from the use of the index,".
Yes indeed, care needs to be exercised in drawing conclusions outside
the realm of pure sport. Hopefully, from the admittedly long e-mail I
sent on the subject, you see that the common 10-species, one-iteration
Rucker index is just a step in the process of examining how all the
species behave at a site. We'll continue to develop the Rucker site
indexing methodology. Lee Frelich will have probably the most to say on
what additional we include to make the individual indexes more
meaningful. One area we'll concentrate more on in the future is height
to diameter ratios in clusters of trees. The tallest red maples we
measure in western Massachusetts are invariably driven upward by
competition with some combination of nearby white pine, white ash, sugar
maple, and hemlock.

    There are so many combinations and patterns to examine. We're just
in the infancy of this kind of analysis. It's pretty exciting.