Funding for this research was provided by the National Science Foundation (DEB-1457675). We thank the many participants in the Ice Storm Experiment (ISE) who helped with the ice application and associated field and laboratory work, especially Geoff Schwaner, Gabe Winant, and Brendan Leonardi. This manuscript is a contribution of the Hubbard Brook Ecosystem Study. Hubbard Brook is part of the Long-Term Ecological Research (LTER) network, which is supported by the National Science Foundation (DEB-1633026). The Hubbard Brook Experimental Forest is operated and maintained by the USDA Forest Service, Northern Research Station, Madison, WI.&#160;Video and images are by Jim Surette and Joe Klementovich, courtesy of the Hubbard Brook Research Foundation.

1. Develop the experimental design
<ol>
	<li>Determine the intensity and frequency of icing based on realistic values.</li>
	<li>Determine the size and shape of the plots.
	<ol>
		<li>If the goal is to evaluate tree responses, select a plot size that is large enough to include multiple trees and most of their root systems, which varies depending on factors such as tree species and age.</li>
		<li>For safety purposes, design the plots so that the entire plot area can be sprayed from outside the boundary.</li>
		<li>Spac...

<ol>
	<li>Zhou, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Great+2008+Chinese+Ice+Storm:+Its+socioeconomic&#8211;ecological+impact+and+sustainability+lessons+learned.">The Great 2008 Chinese Ice Storm: Its socioeconomic&#8211;ecological impact and sustainability lessons learned.</a> Bulletin of the American Meteorological Society. 92 (1), 47-60 (2011).</li><li>Call, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Changes+in+ice+storm+impacts+over+time:+1886-2000.">Changes in ice storm impacts over time: 1886-2000.</a> Weather, Climate, and Society. 2 (1), 23-35 (2010).</li><li>Zarnani, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Learning+to+predict+ice+accretion+on+electric+power+lines.">Learning to predict ice accretion on electric power lines.</a> Engineering Applications of Artificial Intelligence. 25 (3), 609-617 (2012).</li><li>Smith, A. B., Katz, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=US+billion-dollar+weather+and+climate+disasters:+data+sources,+trends,+accuracy+and+biases.">US billion-dollar weather and climate disasters: data sources, trends, accuracy and biases.</a> Natural Hazards. 67 (2), 387-410 (2013).</li><li>Lafon, C. W., Speer, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+dendrochronology+to+identify+major+ice+storm+events+in+oak+forests+of+southwestern+Virginia.">Using dendrochronology to identify major ice storm events in oak forests of southwestern Virginia.</a> Climate Research. 20 (1), 41-54 (2002).</li><li>Smith, K. T., Shortle, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Radial+growth+of+hardwoods+following+the+1998+ice+storm+in+New+Hampshire+and+Maine.">Radial growth of hardwoods following the 1998 ice storm in New Hampshire and Maine.</a> Canadian Journal of Forest Research. 33 (2), 325-329 (2003).</li><li>Duguay, S. M., Arii, K., Hooper, M., Lechowicz, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ice+storm+damage+and+early+recovery+in+an+old-growth+forest.">Ice storm damage and early recovery in an old-growth forest.</a> Environmental Monitoring and Assessment. 67 (1), 97-108 (2001).</li><li>Irland, L. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ice+storms+and+forest+impacts.">Ice storms and forest impacts.</a> The Science of the Total Environment. 262 (3), 231-242 (2000).</li><li>Dale, V. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Climate+change+and+forest+disturbances.">Climate change and forest disturbances.</a> BioScience. 51 (9), 723-734 (2001).</li><li>de Groot, M., Ogris, N., Kobler, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effects+of+a+large-scale+ice+storm+event+on+the+drivers+of+bark+beetle+outbreaks+and+associated+management+practices.">The effects of a large-scale ice storm event on the drivers of bark beetle outbreaks and associated management practices.</a> Forest Ecology and Management. 408, 195-201 (2018).</li><li>Faccio, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+ice+storm-created+gaps+on+forest+breeding+bird+communities+in+central+Vermont.">Effects of ice storm-created gaps on forest breeding bird communities in central Vermont.</a> Forest Ecology and Management. 186 (1), 133-145 (2003).</li><li>Degelia, S. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+overview+of+ice+storms+and+their+impact+in+the+United+States.">An overview of ice storms and their impact in the United States.</a> International Journal of Climatology. 36 (8), 2811-2822 (2016).</li><li>Rauber, R. M., Olthoff, L. S., Ramamurthy, M. K., Miller, D., Kunkel, K. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+synoptic+weather+pattern+and+sounding-based+climatology+of+freezing+precipitation+in+the+United+States+east+of+the+Rocky+Mountains.">A synoptic weather pattern and sounding-based climatology of freezing precipitation in the United States east of the Rocky Mountains.</a> Journal of Applied Meteorology. 40 (10), 1724-1747 (2001).</li><li>Bell, G. D., Bosart, L. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Appalachian+cold-air+damming.">Appalachian cold-air damming.</a> Monthly Weather Review. 116 (1), 137-161 (1988).</li><li>Rackley, J. A., Knox, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+climatology+of+southern+Appalachian+cold-air+damming.">A climatology of southern Appalachian cold-air damming.</a> Weather and Forecasting. 31 (2), 419-432 (2015).</li><li>Cortinas, J. V., Bernstein, B. C., Robbins, C. C., Strapp, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+analysis+of+freezing+rain,+freezing+drizzle,+and+ice+pellets+across+the+United+States+and+Canada:+1976-90.">An analysis of freezing rain, freezing drizzle, and ice pellets across the United States and Canada: 1976-90.</a> Weather and Forecasting. 19 (2), 377-390 (2004).</li><li>Changnon, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characteristics+of+ice+storms+in+the+United+States.">Characteristics of ice storms in the United States.</a> Journal of Applied Meteorology. 42 (5), 630-639 (2003).</li><li>Jones, K., Thorkildson, R., Lott, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+development+of+a+U.S.+climatology+of+extreme+ice+loads.+Technical+Report+2002-01.">The development of a U.S. climatology of extreme ice loads. Technical Report 2002-01.</a> National Climatic Data Center. , 23 (2002).</li><li>Groisman, P. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+changes+in+the+frequency+of+freezing+precipitation+in+North+America+and+Northern+Eurasia.">Recent changes in the frequency of freezing precipitation in North America and Northern Eurasia.</a> Environmental Research Letters. 11 (4), 045007 (2016).</li><li>Klima, K., Morgan, M. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ice+storm+frequencies+in+a+warmer+climate.">Ice storm frequencies in a warmer climate.</a> Climatic Change. 133 (2), 209-222 (2015).</li><li>Cheng, C., Auld, H., Li, G., Klaassen, J., Li, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Possible+impacts+of+climate+change+on+freezing+rain+in+south-central+Canada+using+downscaled+future+climate+scenarios.">Possible impacts of climate change on freezing rain in south-central Canada using downscaled future climate scenarios.</a> Natural Hazards and Earth Systems Sciences. 7 (1), 71-87 (2007).</li><li>Cheng, C. S., Li, G., Auld, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Possible+impacts+of+climate+change+on+freezing+rain+using+downscaled+future+climate+ccenarios:+Updated+for+eastern+Canada.">Possible impacts of climate change on freezing rain using downscaled future climate ccenarios: Updated for eastern Canada.</a> Atmosphere-Ocean. 49 (1), 8-21 (2011).</li><li>Kunkel, K. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Monitoring+and+understanding+trends+in+extreme+storms:+State+of+knowledge.">Monitoring and understanding trends in extreme storms: State of knowledge.</a> Bulletin of the American Meteorological Society. 94 (4), 499-514 (2013).</li><li>Dipesh, K. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+simulated+ice+storm+damage+on+midrotation+loblolly+pine+stands.">Effects of simulated ice storm damage on midrotation loblolly pine stands.</a> Forest Science. 61 (4), 774-779 (2015).</li><li>Collins, B. S., Pickett, S. T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Demographic+responses+of+herb+layer+species+to+experimental+canopy+gaps+in+a+northern+hardwoods+forest.">Demographic responses of herb layer species to experimental canopy gaps in a northern hardwoods forest.</a> Journal of Ecology. 76 (2), 437-450 (1988).</li><li>Yorks, T. E., Leopold, D. J., Raynal, D. 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R., Carlton, G., Lezberg, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Forest+response+to+catastrophic+wind:+Rusults+from+an+experimental+hurricane.">Forest response to catastrophic wind: Rusults from an experimental hurricane.</a> Ecology. 80 (8), 2683-2696 (1999).</li><li>Rustad, L. E., Campbell, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+ice+storm+manipulation+experiment+in+a+northern+hardwood+forest.">A novel ice storm manipulation experiment in a northern hardwood forest.</a> Canadian Journal of Forest Research. 42 (10), 1810-1818 (2012).</li><li>Jones, K. F., Mulherin, N. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+evaluation+of+the+severity+of+the+January+1998+ice+storm+in+northern+New+England.">An evaluation of the severity of the January 1998 ice storm in northern New England.</a> U.S. Army Cold Regions Research and Engineering Laboratory, Snow and Ice Division. , 66 (1998).</li><li>Rhoads, A. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+an+intense+ice+storm+on+the+structure+of+a+northern+hardwood+forest.">Effects of an intense ice storm on the structure of a northern hardwood forest.</a> Canadian Journal of Forest Research. 32 (10), 1763-1775 (2002).</li><li>James, F. C., Shugart, H. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+quantitative+method+of+habitat+description.">A quantitative method of habitat description.</a> Audubon Field Notes. 24 (6), 727-736 (1970).</li><li>Lemmon, P. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+spherical+densiometer+for+estimating+forest+overstory+density.">A spherical densiometer for estimating forest overstory density.</a> Forest Science. 2 (4), 314-320 (1956).</li><li>Korhonen, L., Korhonen, K., Rautiainen, M., Stenberg, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Estimation+of+forest+canopy+cover:+a+comparison+of+field+measurement+techniques.">Estimation of forest canopy cover: a comparison of field measurement techniques.</a> Silva Fennica. 40 (4), 577-588 (2006).</li><li>Fiala, A. C. S., Garman, S. L., Gray, A. 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It is critical to perform experimental simulations of ice storms under appropriate weather conditions to ensure their success. In a previous study30, we found that the optimal conditions for spraying are when air temperatures are below -4 &#176;C and wind speeds are less than 5 m/s. Natural ice storms most commonly occur when air temperatures are slightly less than freezing (-1 to 0 &#176;C), and although the ideal temperatures for ice storm simulations are colder, they are still within the temper...

Ice storms are an important natural disturbance that can have both short- and long-term impacts on the environment and society. Intense ice storms are problematic because they damage trees and crops, disrupt utilities, and impair roads and other infrastructure1,2. The hazardous conditions that ice storms create can cause accidents resulting in injuries and fatalities2. Ice storms are costly; financial losses average $313 million per year in the United States (US)3, with some individual storms exceeding $1 billion4. In forest ecosystems, ice storms can have negative consequences including reduced growth and tree mortality5,6,7, increased risk of fire, and proliferation of pests and pathogens8,9,10. They can also have positive effects on forests, such as enhanced growth of surviving trees5 and increased biodiversity11. Improving our ability to predict impacts from ice storms will enable us to better prepare for and respond to these events.
Ice storms occur when a layer of moist air, that is above freezing, overrides a layer of subfreezing air closer to the ground. Rain falling from the warmer layer of air supercools as it passes through the cold layer, forming glaze ice when deposited on sub-freezing surfaces. In the US, this thermal stratification can result from synoptic weather patterns that are characteristic of specific regions12,13. Freezing rain is most commonly caused by Arctic fronts that move southeastward across the US ahead of strong anticyclones13. In some regions, topography contributes to the atmospheric conditions necessary for ice storms through cold air damming, a meteorological phenomenon that occurs when warm air from an incoming storm overrides cold air that becomes entrenched alongside a mountain range14,15.
In the US, ice storms are most common in the &#8220;ice belt&#8221; that extends from Maine to western Texas16,17. Ice storms also occur in a relatively small region of the Pacific Northwest, especially around the Columbia River Basin of Washington and Oregon. Much of the US experiences at least some freezing rain, with the greatest amounts in the Northeast where the most ice prone areas have a median of seven or more freezing rain days (days during which at least one hourly observation of freezing rain occurred) annually16. Many of these storms are relatively minor, although more intense ice storms do occur, albeit with much longer recurrence intervals. For example, in New England, the range in radial ice thickness is 19 to 32 mm for storms with a 50-year recurrence interval18. Empirical evidence indicates that ice storms are becoming more frequent at northern latitudes and less frequent to the south19,20,21. This trend is expected to continue based on computer simulations using future climate change projections22,23. However, the lack of data and physical understanding make it more difficult to detect and project trends in ice storms than other types of extreme events24.
Since major ice storms are relatively rare, they are challenging to study. It is difficult to predict when and where they will occur, and it is generally impractical to &#8220;chase&#8221; storms for research purposes. Consequently, most ice storm studies have been unplanned post hoc assessments occurring in the wake of major storms. This research approach is not ideal because of the inability to collect baseline data before a storm. Additionally, it can be difficult to find unaffected areas for comparison with damaged areas when ice storms cover a large geographic extent. Rather than waiting for natural storms to occur, experimental approaches may offer advantages because they enable close control over the timing and intensity of icing events and allow for appropriate reference conditions to clearly evaluate effects.
Experimental approaches also pose challenges, especially in forested ecosystems. The height and width of trees and the canopy makes them difficult to experimentally manipulate, as compared to lower-stature grasslands or shrublands. Additionally, disturbance from ice storms is diffuse, both vertically through the forest canopy and across the landscape, which is difficult to simulate. We know of only one other study that attempted to simulate ice storm impacts in a forest ecosystem25. In this case, a rifle was used to remove up to 52% of the crown in a loblolly pine stand in Oklahoma. Although this method produced results that are characteristic of ice storms, it is not effective at removing larger branches and does not cause the trees to bend over, which is common with natural ice storms. While no other experimental methods have been used to study ice storms specifically, there are some parallels between our approach and other types of forest disturbance manipulations. For example, gap dynamics have been studied by felling individual trees26, forest pest invasions by girdling trees27, and hurricanes by pruning28 or pulling down whole trees with a winch and cable29. Of these approaches, pruning most closely imitates ice storm impacts but is labor intensive and costly. The other approaches cause mortality of whole trees, rather than the partial breakage of limbs and branches that is typical of natural ice storms.
The protocol described in this paper is useful for closely mimicking natural ice storms and involves spraying water over the forest canopy during sub-freezing conditions to simulate glaze ice events. The method offers advantages over other means because the damage can be distributed relatively evenly throughout forests over a large area with less effort than pruning or downing whole trees. Additionally, the amount of ice accretion can be regulated through the volume of water applied and by selecting a time to spray when weather conditions are conducive for optimal ice formation. This novel and relatively inexpensive experimental approach enables control over the intensity and frequency of icing, which is essential for identifying critical ecological thresholds in forest ecosystems.

<table>
	<tbody>
		<tr>
			<td>Booster pump</td>
			<td>Waterax</td>
			<td>BB-4-23P</td>
			<td>401 L min-1 maximum flow; 30.3 bar maximum pressure</td>
		</tr>
		<tr>
			<td>Firefighting hose</td>
			<td>ATI Forest Products</td>
			<td>Forest-Lite G55H1F50N</td>
			<td>3.8 cm diameter, polyester, single jacket</td>
		</tr>
		<tr>
			<td>Monitor (ground placement)</td>
			<td>Task Force Tips</td>
			<td>Blitzfire XX111A</td>
			<td>2000 L min-1 maximum flow; fits 3.8 cm hose</td>
		</tr>
		<tr>
			<td>Monitor (UTV mount)</td>
			<td>Potter Roemer</td>
			<td>Fire Pro FP1S-125</td>
			<td>1325 L min-1 maximum flow; fits 3.8 cm hose</td>
		</tr>
		<tr>
			<td>Nozzle</td>
			<td>Crestar</td>
			<td>ST2675</td>
			<td>Smooth bore; double stacked; 3.8 cm intake; 1.3 cm orifice</td>
		</tr>
		<tr>
			<td>Strainer</td>
			<td>Northern Tool</td>
			<td>107902</td>
			<td>7.6 cm hose fitting, 17.6 cm outside diameter</td>
		</tr>
		<tr>
			<td>Suction hose</td>
			<td>JGB Enterprises</td>
			<td>A007-0489-1615</td>
			<td>7.6 cm diameter; 4.6 m long</td>
		</tr>
		<tr>
			<td>Water pump</td>
			<td>NorthStar</td>
			<td>106471E</td>
			<td>665 L min-1; fits 7.6 cm hose</td>
		</tr>
	</tbody>
</table>

simulating impacts of ice storms on forest ecosystems

Ice storms can have profound and lasting effects on the structure and function of forest ecosystems in regions that experience freezing conditions. Current models suggest that the frequency and intensity of ice storms could increase over the coming decades in response to changes in climate, heightening interest in understanding their impacts. Because of the stochastic nature of ice storms and difficulties in predicting when and where they will occur, most past investigations of the ecological effects of ice storms have been based on case studies following major storms. Since intense ice storms are exceedingly rare events it is impractical to study them by waiting for their natural occurrence. Here we present a novel alternative experimental approach, involving the simulation of glaze ice events on forest plots under field conditions. With this method, water is pumped from a stream or lake and sprayed above the forest canopy when air temperatures are below freezing. The water rains down and freezes upon contact with cold surfaces. As the ice accumulates on trees, the boles and branches bend and break; damage that can be quantified through comparisons with untreated reference stands. The experimental approach described is advantageous because it enables control over the timing and amount of ice applied. Creating ice storms of different frequency and intensity makes it possible to identify critical ecological thresholds necessary for predicting and preparing for ice storm impacts.

An ice storm simulation was performed in a 70&#8210;100 year-old northern hardwood forest at the Hubbard Brook Experimental Forest in central New Hampshire (43&#176; 56&#8242; N, 71&#176; 45&#8242; W). The stand height is approximately 20 m and the dominant tree species in the area of the ice application are American beech (Fagus grandifolia), sugar maple (Acer saccharum), red maple (Acer rubrum) and yellow birch (Betula alleghaniensis). Ten 20 m x 30 m plots were established and rando...

Watch this Scientific Journal Video about Simulating Impacts of Ice Storms on Forest Ecosystems at JoVE.com

Simulating Impacts of Ice Storms on Forest Ecosystems

Ice storms are important weather events that are challenging to study because of difficulties in predicting their occurrence. Here, we describe a novel method for simulating ice storms that involves spraying water over a forest canopy during sub-freezing conditions.

Ice storms can have profound and lasting effects on the structure and function of forest ecosystems in regions that experience freezing conditions. ...

Ice storms are challenging to study because it's difficult to predict when and where they will occur. This protocol outlines a novel method for simulating natural ice storms. The experimental approach described offers the advantage of control over the timing and amount of ice applied making it possible to create ice storms of different frequency and intensity.We tested this method in a forest ecosystem, but it can also be applied in different ways, such as to evaluate the impacts of ice loads on utility lines and other infrastructure. Select a location in an area where there is access to a water source during winter, making sure that the water supply is adequate for ice application based on the pump rate and other factors such as the diameter of the hose, length of the hose, nozzle used and water pressure. Set up a supply pump at the water source and connect a suction hose.Then connect a strainer to the end of the suction hose to keep debris out of the lines. Break through any surface ice and fully submerge the strainer. The minimum depth of the water supply should be about 20 centimeters.Place a booster pump in the bed of the utility task vehicle to improve water pressure. In some cases a booster pump may not be necessary, especially for low stature vegetation. Run a firefighting hose from the supply pump to the booster pump.Use a fire fighting monitor mounted on the back of a utility task vehicle to enable safe manual control over the high pressure hose. The monitor can also be freestanding. Take care to avoid interruptions to the flow of the water, such as kinks in the hose, water draw down at the supply source or running out of gasoline for the pumps.Create ice by spraying water vertically through gaps in the canopy. Make sure the water extends above the height of the canopy so that it deposits vertically and freezes on contact with sub-freezing surfaces. Avoid stripping branches and bark from trees while spraying.Evenly distribute spray over the forest canopy by slowly driving the utility task vehicle back and forth along the edge of the application area. If freestanding monitors are used move these manually to ensure that the coverage is even. Make ground based caliper measurements of radial ice thickness on lower level branches or twigs near the edge of the application area to monitor ice accretion and determine when the target thickness has been attained.Obtain more accurate estimates of ice accretion with passive ice collectors after the application. The passive ice collectors are constructed from 30 by 2.54 centimeter dowels joined with a six-way steel connector. To measure ice accretion use an arborist throw weight to string a parachute cord over sturdy branches that can withstand the ice load.Attach the passive ice collectors to the cord and raise them up into the canopy. Once the application is completed lower the collectors to the ground, being careful not to lose any ice from the collector. Make vertical and horizontal measurements of ice thickness with calipers at multiple locations on the collector before and immediately after ice application.To determine ice thickness with the water volume method use a reciprocating saw to cut each dowel. After bringing the dowels to a heated building and melting off the ice measure the volume of the melt water with a graduated cylinder. An ice storm simulation was performed in a 70 to 100 year old forest stand at the Hubbard Brook Experimental Forest in Central New Hampshire.Ice accretion was measured on passive ice collectors using both a caliper and water volume methods. Average ice accretion on individual collectors indicated a strong positive relationship between caliper and water volume measurement methods. Measurements using the water volume method exceeded measurements with the caliper method when there was more than about eight millimeters of ice.There was a significant positive relationship between spray time and ice accretion measured with the water volume method and the caliper method. The average rate of ice accretion ranged from 1.4 to 4.2 millimeters per hour across plots. There was a marginally significant inverse relationship between air temperature and ice accretion measured with the water volume method and no significant relationship with the caliper method.Canopy cover data showed no significant differences in pre-treatment surveys. Whereas, post-treatment surveys indicate significant decreases in canopy cover in the mid-ice treatment, the mid-ice treatment that got sprayed twice and the high-ice treatment relative to the control. The effects of the simulated ice storms on surface soil temperatures was evaluated during sampling.Soils in the treated plots where significantly warmer than the control plots at both depths where all three levels evaluated. With this method it's important that the spray reaches above the tallest trees and that the water is distributed evenly over the forest canopy. The ice storm simulation technique has made it possible to identify critical thresholds in forest ecosystems which is important for predicting and preparing for ice storm impacts.

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Research

JoVE Journal

Environment

6.8K visualizações.  U.S. Forest Service, Durham, NH. Tempestades de gelo são desafiadoras para estudar porque é difícil prever quando e onde elas ocorrerão. Este protocolo descreve um novo método para simular tempestades de gelo naturais. A abordagem experimental descrita oferece a vantagem do controle sobre o tempo e a quantidade de gelo aplicada tornando possível criar tempestades de gelo de diferentes frequências e intensidades.Testamos esse método em um ecossistema florestal, mas também pode ser aplicado de diferentes formas...