Multitrunk Trees and Other Forms -  Edward Frank, December 2007

Multitrunk Trees, Woody Vines, and Other Forms

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Multitrunk Trees, Woody Vines, and Other Forms

by Edward Forrest Frank, December 2007


Most trees fall into the simple category of single trunk trees.  Through the years guidelines for measuring trees have focused on this basic form.  However, this is not the only growth form that trees may have.  A second form that is commonly found are trees with multiple stems. these multitrunk trees can be considered in many ways to be a cluster of individuals trees that happen to be close together.  However since they share a common central root system, and canopy space, in other ways they are not fully two or more individual trees, and not something that cannot be considered just a single large organism. Considering how to define and differentiate trees with this form form led to the creation of several more categories of tree forms, some of which are infrequent, but not unusual, and some that are simply odd.  Clonal coppices and groves are an example of an infrequent form.  This growth form is exhibited by only a limited number of tree species, but examples of these forms can cover hundreds of acres of land.  These tree forms  grow by send out subterranean roots which sprout new trunks.  The individual trunks can be considered as individual single trunk trees, but the group because of the way they have grown, and the interconnectivity of the root systems, past and present can in some ways be considered a group organism.  So I have offered some suggestions on characterizing these colonies.  The odd forms include those forms that grew because of unusual circumstances that affected the tree, or those trees that simply have an unusual growth form not seen in most other tree species.  The breakdowns I have proposed is presented in more detail below.  I don't expect people to suddenly change their focus from big and tall trees to multitrunk tree and other forms, but I feel it is important to have a framework in place for consideration of these forms.  It is often difficult to distinguish a tree with two or more fused trunks with a single trunk tree.  The investigator should use their best judgment about whether a tree has a single trunk or is a multitrunk tree, and not try to be liberal or conservative in their interpretation as this would introduce subjective bias in the data set.

Edward Frank

Categories of  Tree Forms

Single Trunk American Elm

Scarlet Oak, MI

Category 1:  Single Trunk Tree:  This is the standard growth form of most trees consisting of a single large trunk growing from a simple root mass below ground.  A single trunk tree is defined as one that has a single pith at ground level.  Measurements for this form are defined by the Tree Measuring Guidelines of the Eastern Native Tree Society by Will Blozan. It should be noted that if the tree branches below 4.5 feet, then the girth is measured at the narrowest point below the lower branching.  It has been common practice among foresters to define a forked tree as one that branches below 4.5’ above root collar, and to take measurement of both forks above swelling.  This is not part of the standard ENTS and American Forests protocol, but is a reasonable alternative measurement standard that I would encourage people to adopt.  Sometimes, especially in open areas, small sucker shoots may grow around the base of larger trees.  These are not considered as multiple stems as they tend to be very small and short lived.

Stunted pines atop Mt. Everett, MA

Stunted pine atop Mt. Everett, MA

Hickory Rune State park, PA

  • Small sized trees and shrubs:  Shrubs have been described by some definitions as smaller woody plants with multiple stems at ground level.  Many shrubs however, when they are of larger size, will have a single stem at ground level that can be measured using the criteria for trees in general.  I think there needs to be standards for measuring trees overall so that different measurements from different areas can be compared.  What I am looking at in this regard is that if you use the measurement standard of the narrowest point on the trunk below the first branching, and you are looking at a forest of stunted trees, such as are shown growing atop Mt. Greylock, then each tree will be measured at a different height, because they all surely branch below 4.5 feet.  Establishing a standard low measurement point  for short or stunted specimens smaller than some value  would allow better comparisons of these small dwarfed trees or other trees and shrubs of smaller size between each other.  They could also be measured at 4.5 feet, but what does that really tell us about the tree?  The scale of measurement needs to be appropriate to whatever it is you are trying to measure.  I am all for standardization, but not in favor of blindly following an inappropriate standard.   I am proposing measurements at 9" and 15" for trees and shrubs less than 20 feet tall as the initial low measurement points for these small specimens.
  • Low Branching or Forking Trees When you propose a classification system there often may be revisions needed upon further reflection and input from others. I recently proposed an organizing structure for measuring multitrunk trees and odd growth forms. One item that needs to be revisited is the idea of low branching trees. Pines and hemlocks typically do not stump sprout, but in areas that have been cut they are often represented by low forking trees that split just above ground level. As they grow these two stems grow into a single massive trunk. Dale Luthringer in his Cook Forest dataset refers to these as "doubles", meaning low forking trees, not multiple trunks that have grown together. Don Bertolette commented that it has been common practice among foresters to define a "forked tree" as one that branches below 4.5' above root collar, and to take measurement of both forks above swelling. When the tree is small it is easy to differentiate the branches from the main trunk. These can be measured using the standard single stem protocol in which the girth is measured at the narrowest point below the branching or forking and the height noted. However when these branches or forks grow larger they merge into a larger mass in which the individual branches and forks can not be measured or separated. Theoretically these trees should be measured at the narrowest point below 4.5 feet and the height noted, as they are by definition a single stem tree with a single pith at ground level. However as this measurement incorporates not only the main trunk, but the girth of the branches/forks as well these girths are exaggerated with respect to simple single trunk trees. For that reason they are generally put aside in a separate no-mans-land category in which they are neither multitrunk or single trunk trees. I propose these be considered a special sub-class of single trunk trees. Their girth should be measured at the narrowest point below the fork or branching with the height of measurement noted, at 4.5 feet, and if possible at any point 4.5 feet or above at which the individual stems or branches can be separately measured and that height noted. This should be the new protocol whether or not the individual branches can be separated or not. In other words this should apply to both smaller and larger examples of low branching trees. For listing purposes, these can be considered as a separate category or included in the multitrunk listings for size comparisons. For American Forest listings, their criteria requires simple the narrowest measurement below 4.5 feet as the girth of the tree.I would strongly encourage that digital photos of any of the odd tree forms be taken to accompany the measurements to better illustrate exactly waht was measured. For low branching trees we should also add 1) height of the lowest branch, 2) list whether the lower girth measurement is made on a single discrete stem, or whether it is a girth that includes merged branch, fork and trunk wood.  See:  Low Branching or Forking Trees

Multitrunk Silver maple, King Island, ARIW, PA

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158'+ triple-stemmed sycamore, Baxter Creek, GSMNP

Seven Sisters Live Oak, LA

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Pith of the trunks forming the Seven Sisters - diagram by Will Blozan

Category 2:  Multitrunk Trees  This is the second largest category of tree forms.  These are trees and shrubs that have more than one stem growing from a single root mass. these trees have a fused base area that consist of multiple piths at ground level, These generally form when the original stem of the tree was damaged, broken, or browsed by animals, damaged  from falling (natural or man-caused)  This results in new stem sprouting from the root mass.  In general these stems are all of similar age and size, but will often reduce to developing one, or a few dominant stems.    Trees commonly growing in flood plains, such as Silver Maple and Willow, are often are damaged during floods and this may be the most common growth form of the species.  Trees growing as second growth forest after timbering operations also  have a higher than normal incidence of multiple trunk trees due to damage of small trees during the operation and from stump sprouts.  The different stems of these multi-trunked trees often flair outward.  The fused base should be measured at a height of 4.5 feet, if it extends that high, or measured at the narrowest point below 4.5 feet when it does not extend that high.   The number of individual stems making up the measured girth should be noted, in addition any stems not included in the girth measurement should also be noted.  Where possible the girth of the largest single stem should be measured at 4.5 feet or at whatever height it becomes separate from the multi-trunk mass for comparison with single trunk trees. Optionally the girth and height  of each individual stem making up the multitrunk tree can be measured.  The height of the tallest stem, and the crown spread of the multi-trunk mass  should also be measured.  A website from Great Britain is the first site I have found that tries to define how to measure multi-trunk trees, although I am not following their protocol.  It should be noted that stems developing from a very large stump, will have a very large hollow in the center that will falsely inflate a 4.5’ height girth measurement.  This situation should be noted.

Silver maple multitrunk clump on King Island, ARIW, PA

Mountain laurel multitrunk clump, PA

  • Multitrunk Clump:  This is a number of individual trunks growing from a central root mass. It may incorporate a multitrunk tree as well as individual stems that have not been incorporated into the multitrunk tree.  Over time a series of closely packed individual stem may fuse into a multitrunk tree, while other stems will be lost through stem exclusion.  These differ from a clonal coppice in that the trunks in a coppice tend to sprout from lateral roots extending from the central mass rather than from the central root mass itself. A closely packed series of trunks can be considered a multitrunk clump, if they are not one of the limited number of  species that sprout stems from lateral roots.  The trunks in the multitrunk clump tend to be similar in age and size.  Shrubs often grow in this form with a series of stems/trunks growing from the central root mass.  To characterize these forms, at a minimum the girth and height of the largest stem, the canopy spread of the entire clump, and the number of significant stems, in the judgment of the investigator, in the clump should be noted.  If these shrubs or trees are short or dwarfed specimens, the lower measurement points suggested above, at 9" and 15", should be used in addition to the standard girth measurement at 4.5 feet.

Staghorn Sumac Clonal Coppice, Cook Forest State Park, PA

Category 3:  Clonal Coppice Some tree species form coppices in which the initial tree sends out lateral root branches, or rhizomes, and new tree stems sprout from these lateral roots.  This process continues and the result is a clonal cluster of trees derived from a single original tree.  Common examples of these coppices include the mound-like sumac colonies and rhododendron patches.  This spreading by roots is not the only method of propagation for these colonies, as they also produce seeds.  It may be difficult or impossible to distinguish whether something is a clonal coppice, or simply a cluster of individual trees growing close to each other based upon simple observation alone. However there are some clues that can be used. In a clonal coppice the trees typically are oldest in the center and younger toward the edges.  Also if the species is sexually dimorphous, meaning that there are distinct differences between the male and female fruiting bodies and that the individual trees are either male or female, if it is a clonal coppice all of trees will be of the same sex.  If they are of different sexes, then it is a cluster of different trees.  In a clonal coppice, the largest individual tree should be measured for comparison with single trunk trees.  In addition the number of stem in the coppice should be counted, and the area of the coppice should be noted.  See:  Clonal Coppices

Aspen Clonal Colony

Aspen Clonal Colony

Category 4:  Clonal Colonies  This in many ways is the same process as described for clonal coppices, but on a far larger scale.  The primary type example of a clonal colony is the aspen.  Wikipedia says:  All the aspens (including White Poplar) typically grow in large colonies derived from a single seedling, and spreading by means of root suckers; new stems in the colony may appear at up to 30-40 m from the parent tree. Each tree only lives for 40-150 years above ground, but the root system of the colony is long-lived, in some cases for many thousands of years, sending up new trunks as the older trunks die off above ground. For this reason it is considered to be an indicator of ancient woodlands. Some aspen colonies become very large with time, spreading about a metre per year, eventually covering many hectares. They are able to survive intense forest fires as the roots are below the heat of the fire, with new sprouts growing after the fire is out.   The Pando colony in Utah contains an estimated 47,000 stems and occupies 107 acres. The shear scale of these colonies suggests to me that they are not only quantitatively different from the simple clonal coppice, but represent a fundamentally different class of growth form.  In the case of these clonal colonies, again if the species is sexually dimorphous, and most aspens and poplars are dimorphous, all of trees in the colony will be of the same sex. In addition they will typically all change colors in the fall, and sprout leaves in the spring at the same time.  For measurements purposes, the largest individual specimens should be measured for comparison with single trunk trees, the area of the colony should be mapped, and the number of individual stems in the colony estimated.  

Oddball Categories

A fusion of a chestnut oak and a white oak. These adjacent trees were not just rubbing and callused but actually fused together. The top of the white oak (smaller stem in the photos) was dead but the grafted section was alive.  Photo by Will Blozan, Winding Stair section, GSMNP.

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A striped maple, a yellow birch, and an eastern hemlock germinated out of the same rotting stump and all have survived. -Jess Riddle

These are clearly three separate trees, but their juxtaposition makes them a candidate for this category in the future should they all survive

Category 5:  Conjoined and Hugging Trees   Sometimes two trees may grow to large size adjacent to each other and grow together.  These may be of the same species or even trees of two different genera or families.  These consist of two basic forms:  a) Conjoined - two trees that have become grafted together.  Generally this grafting is between two trees of the same or closely related species or genera. (see Inosculation: ) These are also sometime called Fused Trees;  and  b) Hugging - two trees that are not grafted together, but are physically touching. rubbing, intertwined, or entangled.  These need to be considered on a case by case basis.  In general the standard height, girth, and crown spread measurements can be made for each individual of the conjoined or hugging pair.

South Manitou Island, MI One of the most amazing finds here was that of this ancient fallen cedar that was actually still alive. At first sight we thought that this was a nurse log supporting a young cedar tree. But that young cedar turned out to be a limb of the fallen tree! In fact, two of the limbs of the fallen giant were still producing foliage and growing vertically up towards the sunlight from their gnarled bases - E. Ostuno

Category 6:  Fallen Trees  There are cases where an individual tree has fallen, from wind events or other causes.  On these fallen trees the upright branches form new vertical trunks, and roots may sprout from the surface of the tree where it touches the ground.  These are unusual and should be considered on a case by case basis.  Jess Riddle wrote:  "I most often see smooth barked species in floodplains forming new trunks after falling.  In Congaree National Park, American holly and ironwood commonly produce vertical shoots after falling."  Lee frelich reports:  "Black spruce also does this. On very rare occasions white pine and balsam fir can do it, but apparently only in boreal forests with deep moss.  I have seen hemlock spread out like a carpet across the forest floor in the  snow forest in the Porcupine Mountains, MI, after saplings were knocked over by heavy snow accumulation, but am not sure if its rooted in places other than the original trunk.  The willows in MN floodplains (black willow, peach leaf willow) sometimes also turn into a row of trees after blowing over."  Don Bertolette noted:  "They very seldom attain much size, as the connection to the roots usually negates effective nutrient/moisture transport mechanisms.  Several species in the west do this, and extremes do occur, but seldom larger than normal structure."  These are unusual specimens and no standard protocol for documenting them would be workable.  They need to be considered on a case by case basis.

No Photos Available

Category 7:  Tree Complexes  Lee Frelich described some white cedar growing in swales in the Door Peninsula of Wisconsin:  "Many ancient white cedars line the swales, and many more are fallen into the swales, but remain alive, with the individual branches turning upright to become new trees, which then blow down a few hundred years later in many directions, and their branches become trees as well, the whole tangle a historical puzzle that may be hundreds or even a thousand or more years old. I call these cedar complexes. Sometimes it isn't even clear if they (genetically) are one tree; if another tree falls across a downed cedar, it can graft to the other tree."  Situations such as this where there are a tangled mass of trees, re-sprouting, grafting, and other processes can have no better name than a complex.  They need to be documented on a case by case basis.

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Banyan tree in front of the Old Lee County Courthouse in Fort Myers, Florida.  Photo by Wknight94.

Category 8:  Banyan-Like Trees  There are several examples of this tree planted as an exotic in the United States.   It is a member of the fig family.   "(Ficus bengalensis), a remarkable tree of India and tropical Africa sends down from its branches great numbers of shoots, which take root and become new trunks. A single tree thus may spread over a large area and look like a small forest. This tree, belonging to the family Moraceae, is considered to be sacred in some places in India.  A specimen in the Calcutta botanical garden is more than 100 years old. It has a main trunk 13 feet (4 m) in diameter, 230 trunks as large as oak trees, and more than 3,000 smaller ones. The largest banyan tree known is on the island of Sri Lanka. It has 350 large trunks and over 3,000 small ones. The banyan often grows to a height of over 21 meters and lives through many ages. "  I would consider this to include any tree that produces multiple trunks through the growth of aerial roots that grow to form new trunks.

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Bald Cypress with cypress knee and Great Egret, Everglades National park, FL - photo by NPS

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Mangrove roots, Everglades National Park, FL. - photo by NPS

Category  9:  Mangroves and other trees with large aerial roots.  No protocol has yet been defined.  Options might include documenting the spread of the aerial roots and their height.  For Bald Cypress noting the distance from the trunk of the cypress knees and their size.  

"Big Cedar" along highway in Olympic National Park, WA.  This tree is described in Bob Van Pelt's book "Forest Giants of the Pacific Coast" as the Kalaloch Cedar.  It is measured at 123 feet high, and 19.6 feet in diameter.  Several large epiphytic hemlocks grow atop this tree.  One is directly above me in the photo - Photo by Ed Frank

Category 10:  Epiphytic Trees:  In general these are not unique in any way aside from their placement in the branches or canopy of other trees.

Woody Vines

Woody vines are generally considered to be a plant that contains woody material but does not stand upright on its own, They tend to climb on the branches and trunks of other plants. There are many of them in the Northeast and Eastern Untied States. Prominent in the woods around PA are Grape Vines, Virginia Creeper, and Poison Ivy. ENTS periodically measure the girth of some of these. Jess Riddle has reported Grape Vines with girths of 4 feet in the southern US.  In one report on the Ocanaluftee Basin of GSMNP,  Jess Riddle commented: "Grape vines, often over four inches in diameter, frequently tie together all of the canopy layers, and may be accompanied by Duthcman's pipe vine.
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Epworth-by-the-Sea, St. Simons Island, GA , a 4'9" cbh grape vine growing on a live oak. - photo by Jess Riddle

Virginia Creeper

How should these be measured? Where possible try to find the rooted end and measure the girth 4.5 feet from the end of the vine, and the obvious thickening at branching points should also be avoided. If the rooted end is not located a measurement anywhere along the length of the vine will suffice.  There is very little data on Grape (Vitus sp.) and other vine species. The are significant as secondary species in many of our woods. They can a a major component in may area, as most of you know who have ever tried to work their way through a grape thicket.  Will Blozan reports that "The “tallest” species I have encountered are Virginia creeper and Dutchman’s pipe, both over 120’. I recorded VA creeper at 130.5 feet in one of the Tsuga Search trees I climbed."  In one report on the Ocanaluftee Basin of GSMNP,  Jess Riddle commented: "Grape vines, often over four inches in diameter, frequently tie together all of the canopy layers, and may be accompanied by Duthcman's pipe vine.

--- Woody Vines Section  ---more----


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