An Analysis of the Environmental Disturbances in the United States by the Ice Storms
Throughout the United States there are many major environmental disturbances that effect the way trees maintain their ability to live. One major disturbance that effects the way trees grow are ice storms. Ice storms can be deadly for many trees but trees also can not be damaged at all because they become resistant to the ice. Almost every year there has been an ice storm that effects part of the northern and eastern United States effecting not only the people that live in that county but also the population of tree species within a forest community. Throughout the years scientists have been studying the effects that ice has on trees. The position of the stand, thickness of the ice, crown structure, and thickness of the wood on the trees are only some of the reasons why certain tree species can withstand the intensity of an ice storm. An ice storm can produce up to 2cm of ice on power lines, telephone poles, and tree limbs.
Many different scientific journals have been written explaining the effects of ice on different tree species. Alan Rebertus and fellow scientists studied storm damage at an old growth hickory forest called dark hollow, following an ice storm that occurred in Northern Missouri on December 6 and 7 of 1994, which produce 4.62 cm of frozen rain coating the trees. 27% of 1386 live trees were damages, 7% severe (Rebertus et al 1997). In 1993 the scientists conducted a pre-storm survey where 30 0.1 ha plots were established, spaced 80 meters apart (Rebertus et al 1997). They recorded the status of the trees whether the tree was dead or alive and crown classes, whether a species was dominant, co-dominate, intermediate, or suppressed. After two years in 1995 a post-storm survey was conducted to see the trees susceptibility following such an intense storm. The trees were put into groups 0,undamaged; 1, light; which was the breakage of small limbs, 2, moderate; which was breakage of small limbs approximately 15 cm thick, 3, servere; which was snapping of major limbs (Rebertus et al 1997).
ANOVA was used to compare percent damage of all trees among topographic position, and linear regression analysis was used to examine how damage varied with the topographic site coefficient (Rebertus et al 1997). In the scientist research they had come to the conclusion that Basswood, American Elm, Sugar Maple, and Northern Red Oak were most susceptible. The least susceptible were Shagbark Hickory, Black Walnut, Easter Hophornbean and White Oak. Northern Red Oak and White Oak were almost resistant to the ice. It was more likely that trees in crown position would be undamaged. Trees that were on the lower slope were more likely to be damaged rather than trees in the upper slopes due to the position in the forest.
John Bernard and his fellow researchers also studied the effects of an ice storm that happened in Western New York during March 3-4 of 1991, which deposited 2 cm or more of ice on 19,740 km squared radius (Bernard et al 1993). The researchers agreed with Rebertus and his fellow researchers that the effect of the storm deals with the angle of which the slope stands. Bernard and his researchers also gathered information that it also has to do with the elevation of the forest community, and the wind to determine the hardest hit counties.
They compared Monroe and Ontario counties to determine the severity of the storm from upland and a lowland point of view. The researchers sampled three 10 x 50m plots in wooded hedgerow and one 10 x 50m plot on the edge of one of the mature forest stands ( Bernard et al 1993). Bernard and his fellow researchers determined that a tree that was tipped over would be classified 100% damaged (Bernard et al 1993). Finally they gathered information on 31 different tree species in 31 different quadrants, and measured diameters of approximately 940 standing trees and 1285 downed trees and limbs (Bernard et al 1993).
Throughout their research they determined that the average percent damage to trees was 20%, the forests edge site along the forest field ecotone was the greatest damaged at 50% (Bernard et al 1993). The bottomland forest of Silver Maple, Elm-Ash and Red Maple-Ash communities had below average crown damage at 15% and 13% (Bernard et al 1993). When the tree species were compared, the percent of tree thrown was correlated to slope angle, as was the percent crown damage (Bernard et al 1993). Finally after all the research they came to the conclusion that almost 60-70% of the trees were severely damaged. The south- facing slope was more likely to be damaged do to its position. The north-facing slope had been facing the sun, which melted some of the ice.
Lemon had also studied the effects of a glaze storm in New York, but he mainly focused on forest ecology of ice storms. He studied how glaze storms effected not only tree limbs but also the composition of the tree, such as where it is located, exposure to the sun, crown position and stands. Lemon defined glaze as a clear layer of ice formed by under cooled water freezing on the surface of objects (Lemon 1961). In his research the Northern and eastern United Stated were affected the most. New York has suffered the most over the years having over 12 glaze storms. Lemon estimated the damage of the glaze storm. He estimated that the glaze breakage is not simply a function of its weight but the arrangement of the branches and the strength of live wood also have to do with the amount of breakage (Lemon et al 1961). Lemon chooses trees relatively close in size and age to determine the tree resistance to the glaze. He categorizes the trees ranging from very susceptible to damage, Moderate to damage, and resistance to damage. American Elm, American Basswood, Butternut, Eastern cottonwood, Silver Maple, and Black Cherry were very susceptible to damage. White Ash, Shagbark, Red Spruce, and Yellow Birch were resistance to damage (Lemon 1961).
Croxton another scientist who researched the effects of ice storms conducted a survey to establish the damage that had occurred to 979 trees of 52 different species during a January 1937 storm that occurred in Missouri and Illinois. Like Lemon the damages were categorized ranging from severe, moderate, and little damage. The main factors that effected the trees the most were age, gravity of the wood, thickness of the ice, and crown symmetry. Throughout his survey salis babylonica, betula alba, and betula lutea were 100% damaged. Although breaking is not necessarily fatal to trees if the wounds are properly taken care of, the effect, in some cases is similar to heavy pruning (Croxton 1939). Many of the tree species recovered well. Croxton was not able to study the damages more closely but the findings were enough to conduct a survey to establish the total damage that were done to many species of a forest community.
Craig Lorimer studied and compared the characteristics of stands within a steady state-northern hardwood and existing old growth forest in northern Michigan. Lorimer focused mainly on gap formation of small and large disturbances. The occurrence of large-scale disturbance also appears to reduce subsequent frequency of small gap by removing most of the older, susceptible individuals (Lorimer 1989). Even aged secondary growth stand make up most of North America ranging from 60-80 years old (Lorimer 1989). Gap are not created when trees die and if they do create gaps that are immediately filled in by crowns from trees on the opposite side(Lorimer 1989). Although no comparison of gap dynamics in young and old temperate hardwood have not yet been made available but evidence suggests that old growth forest may have higher rates of gap formation (Lorimer 1989). Lorimer characterized uneven aged hardwood stands, which is a series of small patches in different growth phase. Cutting of trees or groups of trees periodically created small gaps to maintain the look of an old growth forest. The future wooded landscape in many rural areas is likely to be more diverse in terms of species and structure than either the pre-settled forest or the present forest (Lorimer 1989).
Throughout the research I have come to the conclusion that species of trees vary in many ways, depending on the structure of the tree, placement of the tree on a slope or stand, gravity of the trees wood, and most of all the intensity of the storm. There are many different ways to study the effect of a storm on trees, ranging from pre-storm survey, post-storm survey, studying the gap formation, or crown position. All these forms of research can determine if a tree species is susceptible, or resistance to an ice storm that may produce up to or more the 2cm of ice on tree limb.
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