Assessment of Chloride Deicing Impacts to Roadside Vegetation in the Black Hills

Complaints have been received recently concerning the discolored and dead trees along the edges of highways in the Black Hills. Chloride deicers have long been known to cause damage to roadside vegetation, primarily due to the chloride ions building up in plant tissues, either from root absorption or from roadside spray or aerosol collecting on foliage. Unfortunately, one of the most susceptible plant families to chlorides is the Pinaceae, which means that the predominant tree species found in the Black Hills, ponderosa pine, is extremely susceptible to chloride-induced damage. A memo recently sent to State Foresters by Dr. John Ball, South Dakota State University (SDSU) Department of Horticulture, Forestry, Landscape & Parks described the results of chloride analyses on ponderosa pine samples collected from along the roadside and reads in part, “…the samples we collected from browning ponderosa pines along the roads have been analyzed and here are the results. Regardless of the de-icing salts used, and there are many on the market, the primary toxicity issue is with the chloride component. Chloride, typically brought to the canopy by drift from salt-laden spray, is carried to the tips and margins of needles where it accumulates to lethal concentrations. Typical symptoms of chloride injury are browning needles and suppressed growth. Other ions in the de-icing salt, sodium and magnesium for example, can also injure plants but they enter and accumulate in tissue much slower so rarely are involved in tree decline and death. The normal value of chloride in foliar tissue is about 0.05% (dry weight basis). Symptoms appear when the internal chloride content is about 0.3%. The needles we collected along the road in various locations in the Black Hills ranged from 0.47 to 0.63%. The situation is complicated by an existing infestation of pine beetles throughout the Black Hills. The Mountain Pine Beetle (Dendroctonus ponderosae) and Pine Engraver Beetle (Ips pini) are the two species primarily responsible for the damage. A 2003 Forest Health Highlight-South Dakota, produced jointly by the U.S. Forest Service and South Dakota Division of Resource Conservation and Forestry, listed 270,200 trees damaged by the Mountain Pine Beetle covering 189,700 acres as well as 120,700 trees damaged by Pine Engraver Beetles involving 45,200 acres. The bulk of this damage occurred within the Black Hills. Add to this the intermittent drought conditions throughout the Black Hills over the past several years and the likelihood of tree mortality becomes even greater due to combined stress. Research is needed to clearly delineate the effects of deicing in the Black Hills on pine trees adjacent to the roadside as well as the extent of any damages with respect to the surrounding forest. This project would provide the information necessary to modify current procedures to minimize impact, if necessary. The objectives of this research project are to: (1) define the extent, distribution, sources and contributing factors involved in roadside tree damage and injury adjacent to highways in the Black Hills; and (2) develop recommendations and guidelines for modifying current deicing and roadside maintenance practices to minimize impact to roadside trees. Research tasks include: (1) Review current literature with respect to deicer impacts to roadside vegetation, including effects of deicer form and composition. (2) Meet with the technical panel to review project scope and work plan. (3) Conduct interviews with appropriate SDDOT staff to acquire knowledge of current South Dakota Department of Transportation (SDDOT) deicing procedures and usage use and collect information on the highway network in the Black Hills such as ADT (average daily traffic), maintenance priority and geometry on the highway network in the Black Hills. (4) Perform a limited survey of other states, provinces and researchers involved with assessing deicer impacts to various pine species. (5) Develop a statistically-derived matrix, including provisions for quality control/ and assurance, for sampling, testing and data analysis taking into consideration highway segment type, deicing practices, timeframe and environmental control. (6) Execute the approved sampling and testing work plan while providing photodocumentation of sampling sites. (7) Conduct a field trip with panel members near the end of the first year’s sampling program to illustrate initial findings. (8) Provide an interim report twelve months after beginning the research and meet with the technical panel to discuss the status of the project, the rationale for sampling and testing during the second year and any needs for task modification. (9) Complete additional sampling and testing, focusing on critical information necessary to refine any tentative results. (10) Provide an assessment of the impact of deicing materials and practices in the Black Hills including discussion of effects of highway segment types, traffic, clear zones and terrain. (11) Formulate recommendations and guidelines, including a decision matrix, for optimizing deicing practices to minimize phytotoxic impacts while maintaining safety, with a discussion of any potential economic impacts. (12) Prepare a final report and executive summary of the research methodology, findings, conclusions, and recommendations. (13) Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.


    • English


    • Status: Active
    • Funding: $150610.00
    • Contract Numbers:


    • Sponsor Organizations:

      South Dakota Department of Transportation

      Transportation Building, 700 E Broadway
      Pierre, SD  United States  57501
    • Project Managers:

      Foster, John

      Huft, David

    • Performing Organizations:

      South Dakota State University, Brookings

      Department of Civil and Environmental Engineering
      Brookings, SD  United States  57007
    • Principal Investigators:

      Ball, John

    • Start Date: 20060401
    • Expected Completion Date: 0
    • Actual Completion Date: 20100430
    • Source Data: RiP Project 26321

    Subject/Index Terms

    Filing Info

    • Accession Number: 01461466
    • Record Type: Research project
    • Source Agency: South Dakota Department of Transportation
    • Contract Numbers: SD2006-01
    • Files: RIP, STATEDOT
    • Created Date: Jan 3 2013 1:46PM