Rucker Height Index (RI)

One of the primary goals of ENTS is to to document tall trees on these sites using our accurate measurement methodologies. A stalwart measure we try to compile for a site is a Rucker Index (RI). This is the average height of the tallest individual of each of the ten tallest species found on the site. Measurement of additional trees allows us to look in greater detail at each of these sites.

The Rucker Site index is essentially a foreshortened version of a complete species/height 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:

http://www.nativetreesociety.org/measure/rucker_site_index.htm

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."  Another summary of the merits of the Rucker Index and discussions can be found on these pages:

http://www.nativetreesociety.org/measure/rucker/trip_reports_rucker.htm

http://www.nativetreesociety.org/measure/rucker/rucker_index2.htm

Dale Luthringer recently published a list of the top ten sites in Pennsylvania based upon the ten species Rucker Index:

Top 10 Pennsylvania Rucker Index Sites

Site                                          Rucker Index

Cook Forest State Park           137.15

Fairmont Park                         132.27

McConnells Mill State Park    130.85

Clarion River                           129.72

Wintergreen Gorge                 127.53

Ricketts Glen State Park         126.29

Walnut Creek Gorge               123.66

Anders Run Natural Area       121.59

Ohiopyle State Park                120.36

Little Elk Creek Gorge           119.45

There are two variants of the Rucker Index that bear some consideration.  The first is a five species Rucker height Index (RI5).  This is particularly useful when there is a limited number of tall species found on a site.  Dr. 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!”  It also is useful for comparing sites for which there has only been a limited amount of measurement.  Obviously with more measurements, taller specimens of many of the species reported may be found and certainly specimens of other species are likely to be found that could raise the Rucker Index of the site.  But lacking that information as an initial glimpse of the height of species at a site can be represented by a five species Rucker Index (RI5). Below is a recalculation of the top five standard ten species Rucker Index sites in Pennsylvania as they would appear using a RI5:

The third Rucker Index worth considering is one in which the maximum heights of the twenty tallest species are averaged.  This RI20 can only be calculated for sites that have been extensively measured, and therefore a comparison can be made among only a few sites.  But if the Rucker Index is designed t be a foreshortened version of the complete species/height profile, then the more species included in the index the more representative it will be of the site as a whole.  A major goal of describing a site that should be included, but is often left wanting, is a listing of all the woody species present, and a height measurement of as many of those species as possible.  In Pennsylvania there are only a handful of sites for which a valid RI20 can be calculated:

Summary Table

Site                                          RI10                 RI5                   RI20

Cook Forest State Park             137.15              147.2                118.26

Fairmont Park                           132.27              140.54             

McConnells Mill State Park        130.85              137.26              116.92

Clarion River                             129.72              136.5

Wintergreen Gorge                    127.53              132.2                114.86

Ricketts Glen State Park            126.29                                     

Walnut Creek Gorge                  123.66              128.3                114.83

Anders Run Natural Area            121.59              129.18              111.43

Ohiopyle State Park                  120.36              130.06              105.45

Little Elk Creek Gorge                119.45

Allegheny River Islands              (119.2)              125.46              110.24

Erie Bluffs State Park                (116.3)              125.48              105.44

ARI – without Hemlock I.            (111.34)            120                   93.08

It would be a major step forward for the ENTS organization to try and compile RI20 Indexes for all of our sites that have extensive measurement, and to try to obtain RI20 Indexes for new sites and sites that currently just fall short of that number.

General Comments

There are several things that can be seen from this initial data set.  Overall the trends of what sites have the highest Rucker Index is very similar for RI10, RI5, and RI20 calculations. 

The exceptions are those sites with only a limited number of species.  At these sites the RI quickly falls off to include very small trees, if there are enough species present at all to do a RI20.  Some examples in the temperate east might include smaller sites on areas frequently flooded.  The species present on these sites are limited to flood tolerant species.  In the Allegheny River Islands there were only a handful of tall species present on the flooded islands.  These included sycamore, silver maple, basswood, black locust, and pignut hickory.  Other species present occurred on areas flooded less often include species such as red oak and black walnut.  The values presented for the RI’s for the Allegheny River Islands also include those species from Hemlock Island, a portion of which is high and dry except perhaps for a several hundred year flood event.  These included white pine and hemlock.  Above is listed the Rucker Indexes for the Allegheny River Islands both with and without Hemlock Island:

 Allegheny River Islands        125.46             (119.2)             110.24

ARI – without Hemlock I.     120                  (111.34)           93.08

As can be seen from the numbers the Rucker Index drops much faster when considering only those islands which flood more frequently and which have a more limited species diversity.  The recent exploration of the Millstone Creek area along the Clarion River resulted in only 14 native species measured, with another 4 species noted including choke cherry and staghorn sumac.  These two species are not very tall. So it is unlikely, unless the survey area was increased significantly and perhaps beyond the immediate flood plain, it will be difficult to even locate 20 native tree species within the area, let alone 20 species with a good height.

Overall I feel the compilation of twenty species Rucker Indexes for sites where we have enough measurement data is a worthwhile project.  It provides a look at the sites in greater detail, and will encourage the measurement of species beyond the tallest ten.  If there is use for the data for trees of the eleventh to twentieth tallest species on the site, more of that data will be collected.  The more data collected. The better understanding there is of the forest it represents.  Five species Rucker Indexes should be calculated for existing sites.  I have been working toward that slowly as I go back and compile Rucker Indexes from various sites, but it is a slow process.  It would be much more efficient if they were calculated when the sites are described.  There are limitations for the five species Rucker Index in that it represents only a small portion of the species present, but it does allow us to roughly compare sites with only limited measurement data with those with more measurement data.  It also may be appropriate for characterizing sites with only a very limited number of tall species.

Edward Frank and Dale Luthringer

==============================================================================
TOPIC: Rucker Index Thoughts
http://groups.google.com/group/entstrees/browse_thread/thread/2ab23939bb66f780?hl=en
==============================================================================

== 1 of 17 ==
Date: Fri, Sep 26 2008 5:59 am
From: dbhguru@comcast.net


Ed and Don,

I present MTSF's RI20 below. DUDES, IT RULES! I'm psyched.

Bob

Rucker Height Index Report

== 4 of 17 ==
Date: Fri, Sep 26 2008 9:27 am
From: "Will Blozan"

Ed,

Great thoughts. I support the reasoning for the R5 and R20 indices. If only
there was some way to incorporate the area needed to obtain a certain Rucker
Value. An R5 acre, R10 acre, R20 acre index?

Smokies R5 is 176.5

Smokies R20 is 156.6 (Jess, correct if I am missing something)

Species	Height
Pinstr	188.8
Liritul	181.9
Tsugcan	173.1
Robipsu	171.8
Fraxame	167.1
Platocc	162.2
Carygla	159.7
Aescfla	157.3
Carycor	156.3
Picerub	155.3
Magnacc	151.9
Querrub	151.4
Tilihet	150.4
Queralb	147.1
Juglnig	144.3
Acersac	144.2
Fagugra	142.6
Acerrub	142.4
Quermon	142.3
Liqusty	142.3
R20=	156.62

Will F. Blozan

President, Eastern Native Tree Society
President, Appalachian Arborists, Inc.

== 6 of 17 ==
Date: Fri, Sep 26 2008 10:49 am
From: dbhguru@comcast.net


Will, Ed

The Great Smokies are off the charts - simply off the charts. There is no other forest in eastern North America that can touch that range of mountains for tall trees: not other mountain sites in North Carolina, not even the high index mountain forests of South Carolina that Jess has explored, not Savage Gulf or Fall Creek Falls in Tennessee, and not Congaree NP in South Carolina, unless our upcoming February trip uncovers high canopy forests with new record holders that have thus far not been discovered. To make such a discovery would be just as exciting a proposition as finding ever taller trees in the Smokies. I look forward to Congaree in February. I'm just praying for a low mosquito population at that time of year. God, I hate those little blooksuckers!

Bob

== 7 of 17 ==
Date: Fri, Sep 26 2008 11:04 am
From: "Edward Forrest Frank"


Will,

I have thought and thought about the acreage issue. That is one reason I encouraged you and Jess to look at subdivisions of GSMNP to reduce the size of the block that is considered a site. Thus you can have RI for subsites more comparable in size with other locations and still have a combined RI for the entire park. Even within a defined site, you would need to know where all the trees were located because if the site was looked at in terms of acreage, you would want to define the least amount of acreage that would include the greatest Rucker Index - sort of a balance. Then there is the question of shape. In an ideal forest the area could be defined by a circle as a minimum edge, maximum area shape, but in practice, the boundaries we consider are irregular. They may follow a narrow valley, or a drainage basin, or a square patch of remnant forest. If people have ideas of how to do it, it certainly is worth talking about. As it is, I would suggest that the "site" be defined as a discrete area whose boundaries are established by the person or group involved in the measurement (The boundaries should be described as best possible). This would include both productive and less productive areas. More productive areas could be defined as a subsite, or a separate site. Then along with the Rucker Index an acreage for the "site" could be listed to provide a good context for the size of the area versus the rucker index numbers. It is information that can added and is useful, but on the other hand some of the best locations may have a high Rucker Index in a relatively small area - I am not really convinced that a Rucker Index per size of an area would be informative.

Ed

== 9 of 17 ==
Date: Fri, Sep 26 2008 11:17 am
From: "Will Blozan"

Bob,

To significantly raise the Rucker of the Smokies or Congaree will be a
monumental and likely impossible effort. Like Mohawk, the sites have been
sampled many, many times and the maximum index has been largely identified.
I need to calculate the R20 for Congaree.

Will F. Blozan

President, Eastern Native Tree Society
President, Appalachian Arborists, Inc.

== 11 of 17 ==
Date: Fri, Sep 26 2008 11:47 am
From: "Edward Forrest Frank"


ENTS,

I might suggest that the best way to keep up with the Rucker Indexes for all of the sites would first to have a listing of all the trees from the site, ordered however you want. Then a second listing for the site would include only the tallest tree of each species, and every species measured at the site should be included, and have this list sorted tallest to shortest. Whenever a new taller specimen is found for a species, the old would be deleted from this tall list and the the new one inserted at the proper place in the hierarchy. Calculating a Rucker Index would then just consist of copying the contents of the top 5, 10, or 20 cells to an adjacent column, summing those, and dividing by the number of cells. That is what I did with Dales RI20 listings and our composite listings for the Allegheny River Islands. It worked very well.

Ed

== 12 of 17 ==
Date: Fri, Sep 26 2008 11:48 am
From: dbhguru@comcast.net


Will,

I read you clearly and understand. I do realize just how much time has been spent in both locations. Just want to keep the mental door open to the possibility of a new discovery. I'm also hyping up the upcoming excursion. Being bitten by swarms of poor, half-starved mosquitos is good. Gotta think positive. I'm also thinking about that big black rat snake (I think) I almost put my hand on crawling up that big cherrybark oak as we waded hip-deep along what was supposed to be a trail.

Bob

== 14 of 17 ==
Date: Fri, Sep 26 2008 12:12 pm
From: dbhguru@comcast.net


Ed,

You're doing a great job as usual. I appreciate your bringing the topic of Rucker Indices back to life and digging out the Pennsylvania numbers. I'm anxious to get back to Mohawk and continue the update of that extraordinary site. What follows is a side by side comparison of the best site in New England (Mohawk, of course) compared to the best site in the Northeast (Cook, of course), compared to the best site in the East (the Smokies, of course). I've been a little lazy by just taking the lists from you and Will as presented along with Mohawk without switching to a common format. We know that the spread from New England to the Smokies would drop some by taking an area in the Smokies comparable to Mohawk or Cook instead of all the NP. I'm guessing that the spread from south to north is between 25 and 30 feet at the very most for comparablly-sized areas. Will and I have seen a consistent spread of 20 to 30 feet for most tree species. However, a few species like black birch seem
to maintain an almost constant maximum height from south to north. Interesting.
BTW, I list Jake's height at 169.1 feet, although my best determination favors 168.6. I could have gone as high as 169.6. It remains to be determined what Jake's precise height is. Weather permitting, we'll know on November 1st.

Bob

== 16 of 17 ==
Date: Fri, Sep 26 2008 12:44 pm
From: "Edward Forrest Frank"


ENTS,

A listing of this sort also has other advantages. It is what Colby described as a complete species profile for the site. It allows easy calculations of various Rucker Indexes. But also by having this list, you can look at it and it will jump out at you that "Oh, I saw a taller Sassafras just the other day than the one listed here." You can see at a glance if there are taller trees you just haven't measured. Most people really into it know how tall the tallest species are, but the heights of the shorter species may not be as completely at the tip of your tongue. A listing of all the species measured tells you at a glance what species you haven't measured. This is often just an oversight, or they have not been measured because they are not that tall, but a listing such as this begs for missing data and measurements to be taken.

Ed

== 17 of 17 ==
Date: Fri, Sep 26 2008 1:19 pm
From: dbhguru@comcast.net

Ed,

I couple more thoughts to add to what you've said, and said well.

Sometimes it is good to go into a forest with blinders on to all but one or two species as opposed to wandering about trying to stay sensitive to all species. When I activate my stripped maple filter, the large, bright green leaves stand out in the understory and I can quickly and easily home in on stripped maples that are above 50 feet in height. So far in MTSF, I've measured three striped maples over 60 feet and have this beautiful understory species pretty well mapped out. I'll soon turn my attention onto witch hazel. I'll have to install another mental filter to be active from 20 to about 35 feet maximum - I think.

I completely agree that documenting the growth maximums for all species, short and tall can provide us with a much better understanding of the growth potential of an area. Some of the shorter species may be far more useful than personally have heretofore understood. The ones growing in southern New England forests are usually shortlived. Consequently, we can see many more of them through their entire life cycles and therefore have a better opportunity to catch more at their peak heights. That's far less likely for species that live for three or more centuries and are economiclaly valuable at 60 years of age.

Bob

== 2 of 3 ==
Date: Fri, Sep 26 2008 1:37 pm
From: "Edward Forrest Frank"


Bob.

I guess I don't look at the trees with my focus on one or two species, but am interested in finding as many as possible. I really don't understand the process of focusing on a few species. I know that in one example of hawthorns, other people were not even seeing the species at all in spite of the fact that in front of them were 40 foot high specimens representing the tallest in the state, and including a national AF Champion. I just don't get the blinders or filters- I see all of them - the tall pines, the striped maples, etc. I don't think I miss a good example of a particular tree species because I am not focused on that species alone. You have in the past suggested that early on the more commercial species are the ones you noticed first when exploring forest, then you broadened your perspective to see others. I hope I am not misrepresenting what you implied. Perhaps focusing on a particular limited number of species is part of your process. I don't know - I find the smaller species as interesting as the tallest, but I will admit I am impressed by really tall trees and really fat trees. I am interested in the interactions between the trees and other forest components, I am interested in the processes of the forest. Tall trees are just one thing to look at in the forest, and I tend to look at the forest broadly rather than focusing on a few species. However whatever works the best for you is what you should do.

Ed

== 3 of 3 ==
Date: Fri, Sep 26 2008 2:41 pm
From: dbhguru@comcast.net


Ed,

I'm speaking about on any single outing. Over time, the focus is on all the species growing at a sight. There are times when I'm multi-species focused - in fact most of the time. I'm merely presenting an alternatie way to homing in on a species say that has been under-sampled. The technique might not work for everyone.

Bob

==============================================================================
TOPIC: Rucker Index Thoughts (area)
http://groups.google.com/group/entstrees/browse_thread/thread/8e9cfae0710071bc?hl=en
==============================================================================

== 1 of 2 ==
Date: Sat, Sep 27 2008 9:10 am
From: "Jess Riddle"


Ed, Will, all;

The first solution that comes to mind for the area dependency of the
Rucker Index is to produce Rucker Index-Area curves. I'm borrowing
this idea from the ecology literature where a analogous problem occurs
with species richness, the total number of species. Species richness
for a site is dependent on the size of the site, and the number of
species found, even for a small site, is dependent on the sampling
effort, especially where species are often cryptic such as with fungi.
To address those problems, plots are constructed with species
richness on the y-axis and either area or sampling effort, which could
be number of days sampled, time spent sampling, or number of samples,
on the x-axis. A curve is then fit to the data, so the species
richness for different sized sites or different sampling intensities
can be interpolated or extrapolated. The curve usually takes a
logarithmic form, increasing rapidly at first but then appearing to
approach an asymptote.

We could apply that same strategy to Rucker Indices by first
calculating the Rucker Index for the core of the site, then expanding
the area until new trees enter the Rucker Index and recalculating, and
repeating that process until the entire site was included. The
results would be plotted with RI on the y-axis and area on the x-axis
a curve fit to that data. When comparing sites, we could then
interpolate the RI of the large site at the area of the smaller site,
or give an estimated RI for all sites at some standard area.

Jess

== 2 of 2 ==
Date: Sat, Sep 27 2008 9:38 am
From: "Edward Forrest Frank"


Jess,

This is an interesting idea that could work. For irregularly shaped sites, those bounded by topography or man-made boundaries, the area could be filled progressively from the center outward until the boundaries in any direction is met and area additions stopped there, while the rest of the site would continue to be incrementally filled. You said that the curve tended to be logarithmic in shape - the areas plotted on the x-axis would then be a linear progression. I am wondering about whether this is applied to areas of vastly different sizes in your literature research? I am thinking that some small pockets of trees may be 2 or more orders of magnitude smaller than the largest sites - say a 10 acre site vs. the Smokies or a drainage basin. If you look at area, it increases with exponentially with distance (radius) from the center. Perhaps we could look at making the x-axis, the area axis, be a logarithmic scale instead of linear. This would make true logarithmic progressions plot as straight lines rather than curves, and would allow a lot to show more detail at smaller areas, and allow the plot to progress through multiple orders of magnitude. I am just thinking out loud. I am sure you have a better grasp of the math and certainly the ecology literature than I do.

Ed

== 2 of 2 ==
Date: Sat, Oct 11 2008 1:19 pm
From: "Edward Frank"


Bob,

Congratulations on finding another tall pine over 140. I have been thinking about how to deal with Rucker Indexes along the lines Jess suggested - i.e. plotting a rucker height index on a graph versus increasing area. I am wondering if it would be appropriate when comparing rucker indexes of sites within a larger area such as the Connecticut River Valley with the area of the valley itself or whether it would be better to just compare the individual sites to the composite area of the patches included in the overall rucker index? What I am saying is that much of the area of the valley contribute nothing to the rucker index as it has been cut over and farmed again and again, so should these non-contributing areas be included in the rucker index area of valley as a whole? Since the measurements are made from a patch of sites here and there, should not the area for the valley just consider the area of those patches.

I have been talking to Dale about compiling a species profile for the Clarion River corridor (defining it to basically just include the flood plains and flats, rather than the entire drainage basin). If all of the species were listed in a single table along with the heights of the tallest ( or fattest) examples of those species, then you could more easily see what gaps there were in the information, what trees were missing, or represented by undersized specimens, etc. I should have did this before my river trip Thursday with Carl, and I know I would have grabbed some measurements of trees, which were unspectacular in terms of Cook Forest, but would have contributed to the Clarion River corridor. This is something that should be considered for other broader reaches which are initially a composite of pieces of other sites. The main problem with the Clarion River stuff is that Dale has all of the data, so any scheme I come up with, means more work for poor Dale.

Ed Frank

== 2 of 2 ==
Date: Sun, Oct 12 2008 4:29 pm
From: dbhguru@comcast.net


Ed,

I'm glad you brought up the subject. I've spent a lot of time over the years thinking about how to bring area into play to facilitate fair comparisons among our sites. However, I fear I have often erred by following political boundaries to advertize an area, more as a sporting event than the practice of science. However, if we want to do it right, we do have areas to experiment with where we could do various kinds of hypothesis testing. In particular, MTSF provides us with a wealth of data that can be sensitized to area computed in a variety of ways. In fact, Mohawk amply reveals how important it is to organize around habitat. Fortunately, most of the forests in Mohawk fall into the mature to very mature classification, so area expansions don't bring into play very young forests or buildings and sidewalks. There is very little truly young forest in Mohawk.
By contrast, the Connecticut River Valley is a patchwork of fields, towns, and forests. There are swaths of mature trees along stream corridors, in yards and parks, and in the forested zone bordering the valley. But there seems little to be gained by merely expanding an area in the valley unless the expansion incorporates big tree habitat. Expanding into areas that don't have have trees sufficiently mature to communicate species potential has limited value.
In Mohawk, concave areas on ridge sides, toe slopes, and ravines contribute most of our big/tall tree habitat. I'm inclined to add up the acreage in those areas instead of starting at a point and expanding outward.

Bob