Tyler, There is definitely a need to go beyond the basic Rucker Index. But in many cases of tree heights, it is more of a gradational change between the canopy species and the midstory species, and the midstory species and understory species. So the results of those separate indexes would not really be as dependant on the heights themselves, but on where the person doing the reporting put the boundary between the categories when analyzing and presenting the data.. These breaks can not be some specific number, because different forests have different canopy hieghts, ad thus would have different distributions of these categories. There are two ways I think to approach this question and both can be implemented. First would be to create a Rucker Index for the 10 tallest trees, then for the twenty tallest trees. This would generate numbers that could be compared to other sites. The next thing to do would be to prepare a plot of the maximum height of every species in the site ordered from tallest to shortest. This is a complete species profile. These can be used for a more detailed comparison between sites. With this type of a plot you can see if there is any distinct break in the plot that would indicate niche occupation by different species. Can you distinguish between the canopy and midstory based simply upon the maximum plots? In the field you can measure the height you believe to be the break height between these categories and see how it matches up with what is shown on the species profile.
Often what you see as midstory trees may simply be smaller or younger specimens of the canopy species. If a species is part of both the canopy and of the midstory, where do you make the boundary between the two? Would this species be listed in both Rucker Indexes with the midstory specimen simply listed at the maximum height of where you defined the boundary to be? Ideally no, but what about canopy species that do not make the top 10? Are they to be ignored? Sometimes a tree that occupies the midstory will have a single specimen that reaches canopy height. Based upon Rucker indexes alone this species would then be part of the canopy species and not the midstory, where it could perhaps be the dominant member of the midstory. I don't think the Rucker Index is an appropriate measure to use to generate numbers for these categories because of the reasons above, among others. If a mathematical process used to generate a number value for these breaks, it gives the impression of greater validity or is given greater weight than a judgment call, even if the numbers are also based simply upon a persons estimate. This tendency is often used to misrepresent the worth of data presented. I think we should be straight forward in presenting a judgment value as a judgment value. I would recommend doing a ten species RI. ad twenty species RI, then a complete species profile. This could then be augmented with descriptive listings of what tree species you see in the canopy, in the midstory, and in the understory, and if possible field measurements of a what height do these breaks between categories occur. This height would of course be an estimate of the break and subject to judgment of the person reporting, but is still a useful number to collect so long as presented in the proper context. Ed Frank ----- Original Message ----- From: "Tyler" <[email protected]> To: "ENTSTrees" <[email protected]> Sent: Wednesday, March 04, 2009 5:07 PM Subject: [ENTS] Rucker Index > > ENTS, > > Over the last few days with the posts about Holly trees and others has > got me thinking about expanding the Rucker Index to include the entire > forest. We could have a canopy rucker index for all species above > 120', a midstory rucker index for 80-120', and an understory rucker > index for below 80'. These numbers could be adjusted for different > areas. What does anybody else think? > > > > --~--~---------~--~----~------------~-------~--~----~ Eastern Native Tree Society http://www.nativetreesociety.org Send email to [email protected] Visit this group at http://groups.google.com/group/entstrees?hl=en -~----------~----~----~----~------~----~------~--~---
