Town Indexes 

At 11:25 AM 6/2/03 -0400, you wrote:

Jess, Colby, Will, Dale, Lee, Tom, et al:

I would expect southern towns to commonly exceed their northern counterparts with respect to the Rucker Index. I just don t have a feel for how much. For Massachusetts the following tall tree relationships currently exist.

Entity                  Rucker Index            % of Mass Index Location

State                        137.2                           100

site                          133.95                            98


township                    117.5                             86


Typical Tall tree site      110                               80

Average mature site       92                                 67

         The above table shows the relationships between the state as a whole and the maximum index for a town, max for a single site, a typical site with tall trees, and a typical mature forest site. The last number is a little shaky. It may be high. I m curious how a state like South Carolina compares. I suspect that sites like Congaree and Station Cove will score above 95% of the state maximum. The ratio of site index to the state index could be used to identify sites worthy of special protection.


From: Lee E. Frelich

Sent: Monday, June 02, 2003 4:38 PM
Subject: Re: Town Indexes


I expect a latitudinal gradient in urban Rucker index. I wouldn't be surprised if it varied by 30-40 feet from South to North.

We can probably break 90 feet for the Rucker Index in the Minneapolis Metro area, although that's higher than it would have been 10 or 20 years ago. It seems that trees are growing taller now than in the past. Maybe that's an early sign of global warming.


From: Robert Leverett 
Sent: Monday, June 02, 2003 8:49 PM


         The plan I've established for myself is to sample spots along the Massachusetts river systems, using the top down approach in selecting trees. I think I can cover the region from 41 to 43 degrees latitude north and 71 to 74 degrees longitude west. That's about as big of a slice as I can hope to cover with any degree of thoroughness. Hopefully Howard Stoner can pick up and extend westward toward Dale's territory, and Dale to Tom's territory, which would give us a pretty good picture of the species from New England to Ohio. If you and Paul pick up from there (with a zigzag northward), we can take the species quite a bit farther west.

        Since stream corridors are almost certain to give us long swaths of good cottonwood habitat, we never have to worry about where to look.  In addition, since the species isn't used for lumber and does fit in with wetland conservation, we have plenty of mature trees to sample. I'm simply amazed at what I've been overlooking. Talk about having blinders on. I could never fairly point the finger at anyone else for tuning something out.


From: Gary A. Beluzo
Sent: Monday, June 02, 2003 10:24 PM
Subject: RE: Town Indexes

Bob and Lee:

Exciting! Are there other species you can think of that would fit in the same category as the cottonwoods (i.e. large mature trees that have been left because they have little commercial value and their habitat is for the most part protected)? I am thinking that many of the riparian trees might fit into that category and hence be good measures of the Rucker Index and portend the effects of global warming?


At 06:54 AM 6/3/03 -0400, you wrote


       Silver maple fits the requirement. Maybe green ash and sycamore to a degree. I can't believe how blind I've been to the riparian habitat.  The large cottonwoods near the Connecticut River that I measured on Sunday are spectacular trees. If we encountered maples or oaks of the size of the cottonwoods in our mountain forests, we would be hooting and hollering for days. We've got lots of great territory to cover, partner.


From:   Lee E. Frelich 
Sent:   Tuesday, June 03, 2003 9:13 AM
Subject:        Re: Town Indexes

Bob and Gary:

We also have green ash and silver maple in riparian habitats, as well as bur oak, swamp white oak, black willow, and basswood. The southern part of MN and WI also have honey locust, Kentucky coffee tree, and sycamore, especially along the Mississippi, Wisconsin, and Rock Rivers.

The upper Mississippi in MN, WI, IA and IL probably has an area of riparian habitat the size of one of those little states out east. The bottomland is several miles in width by 400 miles long and lined with 500 foot bluffs on either side.

There are also interesting seepages in the coulees (valleys that are perpendicular to the river with small streams that empty into it). The coulees have forests of sugar maple, white oak, red oak, walnut, black ash and yellow birch in coves enclosed by steep rocky walls. Great potential for unusually tall trees there. They are a lot like Ice Glen, and there are dozens of them. The best of them are in state parks.

The final odd feature are algific slopes. They have caves that fill with ice from seepage during the winter, and they take all summer to melt, so the caves give off cold air, which percolates out through talus slopes, which support really bizarre features like a balsam fir stand in Iowa a few hundred feet from bur oak savanna, and 250 miles south of the southern edge of the main range of balsam fir.


At 10:48 AM 6/3/03 -0400, you wrote:


Very interesting descriptions. I'm amazed at the habitat diversity of the upper Mid-west. So many jewels that hardly get noticed.

For our study purposes, how do you see the roles of the different habitats for the study of the maximum growth potential models we've been contemplating? Which habitats do you see as providing the greatest returns for us? My approach so far has been to look for the absolute richest sites and work downward from that, since the absolute species maximums will occur on the good sites. So far in Massachusetts, lower elevation mountain cove and ravine sites produce the tallest members of the representative species. The riverine habitats produce the largest trees and fastest growth rates. The larger the river system, the deeper the soil deposits.

One puzzle to me at this point is exactly what determines where the cottonwoods dominate? More to the point, where do they cease to dominate, i.e. the interface zone? Of course flood plains and river corridors are where I find the species in abundance, but as I follow a feeder stream into the uplands, cottonwood abundance and individual tree size drops dramatically. Quicker than I can presently account for. Why don't I see at least a few whoppers on the upper Deerfield? The other species there are doing just fine, but so far I haven't found a single really huge cottonwood. Perhaps cottonwoods need much deeper soils. What conditions would support silver maple dominance over cottonwood and vice versa? My belief has been that every year is a good year for cottonwood seed production. Am I wrong?

Dang it, Lee, I've gone cottonwood crazy.



Starting at the maximums and working down (which means working up in latitude and elevation) is a good strategy. It seems to be easier to characterize maximum tree height than the pattern of tree height among habitats.

Cottonwood only grows into a big tree (15' cbh) on deep soils, and also it is extremely intolerant of shade and cannot compete (especially at the seedling stage) with other species that are more shade-tolerant once you get far from the river. Cottonwood can function as an early successional species after a major disturbance (tornado, flood, fire, clearcutting), regardless of distance from the river. But it cannot grow in its own shade,
and it only dominates for long time periods in areas where there is frequent flooding, since it can better survive the period of root saturation and lack of oxygen than other species, and it is even a little better at that than silver maple. The seedlings can grow to heights of 10 or 20 feet in a year or two, thus getting above the flood levels of all but the greatest floods (we have 40 foot floods in the Midwest, but only every 10 or 20 years, a typical spring flood is only 10-15 feet). Any seedling that is totally submerged for more than a few hours will die.

I suspect that the flooding history of a site determines the difference between dominance by silver maple and cottonwood, but don't really know the details. There are always plenty of seeds for both species, so that doesn't explain the differences.

Cottonwood, silver maple, swamp white oak, green ash and other flood plain tree species do well in big cities, especially commercial areas with lots of pavement, because their roots are adapted to floods and can tolerate the lack of oxygen underneath sidewalks. We use cottonwood in Minneapolis, where they grow to about 40 feet in height in 5 years, even when planted in concrete, but then they die from ground frost. Black ash is another wetland tree that has recently gained attention as an urban tree. They can survive in sidewalk planting pits, including lack of oxygen, tons of salt which is used in commercial areas to keep sidewalks from becoming skating rinks (which is fine with me but dangerous for old fogies), and extreme ground frost to depths of 7 feet, like we had this past winter.


At 02:00 PM 6/3/03 -0400, you wrote:


There's always a reason. Thriving in paved-over areas due to the species adaptation to oxygen-deprived environments made immediate sense - once you said it. I'm now thinking of the cottonwood corridors I regularly pass that have developed adjacent to paved areas. Of course! Do you see any east to west developmental factors for the species such as appears to be the case for tuliptree?

Tulips seem to gain in stature going westward at the same latitude and elevation. Little River Gorge, just west of springfield has old tuliptrees as do a few spots in the southwestern part of Mass, but they are puny compared to Green Lakes and Zoar Valley. Going southward into Connecticut, tuliptrees quickly become abundant and start to appear taller (gotta get down there more). At first I thought the species was highly sensitive to a slight drop in average temperature, but Green Lake State Park blows that theory, as does Zoar Valley.

Understanding the adaptations of species to their environments is what fascinates me most. Your statement about cottonwoods: "since it can better survive the period of root saturation and lack of oxygen than other species, and it is even a little better at that than silver maple", was of particular interest. Who is presently studying these adaptive traits and have there been any recent revelations of which you are aware?



There is a strong east-west gradient in drought and severe storm frequency (and variability in general, with more extremes towards the west) in the Midwest. This means that trees get taller as one goes east at the same latitude from the prairie-forest border to Lake Michigan, although the coves in southwestern WI may be an exception.

The major problem with comparing trees across a large region is the variability in soils. One should only compare tree heights across lat and lon gradients on similar soils. However, I doubt that we will ever be able to describe soil adequately enough to say how similar they are over large areas. We will have to settle for getting a lot of sites where trees are measured and dividing the whole cluster into high, medium and low heights, and assume that these represent very good, good and poor soils for each region, even if very good doesn't mean the same thing in MA and GSMNP.

I know a few people who have studied floodplain forests, including Paul Harcombe at Rice University in Houston, Rebecca Sharitz at Savanna River Ecology lab, and Kurt Shulz at Southern IL University. Most of what little I know comes from seeing their presentations at meetings and reading their papers.