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Trees' diminished resistance to tropical cyclone winds attributed to insect invasions

Date:
January 31, 2014
Source:
American Society for Horticultural Science
Summary:
Researchers compared the impact of two tropical cyclones that occurred in Guam in 1997 and 2004 on the resilience and health of the native tree species Cycas micronesica. Findings revealed that 100 percent recovery followed the 1997 typhoon, but infestations of two invasive insects were responsible for 100 percent mortality of the trees during the 5 years after the 2004 typhoon. The invasive pests eliminated the species' resilience to tropical cyclone damage in less than 10 years between the two typhoons.

The 300+ species of cycads comprise the most threatened group of plants studied to date. Guam's Cycas micronesica is being endangered by recent alien insect invasions.
Credit: Thomas Marler

Guam experiences more tropical cyclones than any other state or territory in the United States. These cyclones--called typhoons in the western Pacific Ocean--can be devastating to Guam's dense native forests. The impact of large-scale tropical cyclones affects the health of managed and unmanaged forests, urban landscapes, and perennial horticulture plantings for many years after the actual storm. In fact, the island's forests are often called 'typhoon forests' because their health and appearance is inextricably defined by the most recent typhoons.

As recently as 2002, Cycas micronesica was the most abundant tree species in Guam. The species is recognized for its innate ability to recover from damage after a tropical cyclone. Resprouting on snapped tree trunks, or "direct regeneration," enabled C. micronesica to sustain its status as the most abundant tree in Guam through 2002. Although native tree species like C. micronesica possess traits that enable them to recover from tropical cyclone damage, invasive pests and other environmental challenges are compromising the species' resiliency.

Thomas Marler from the College of Natural and Applied Sciences at the University of Guam, and John Lawrence from the U.S. Department of Agriculture, Natural Resources Conservation Service reported on a large-scale study of Cycas micronesica in HortScience. The team compared the impact of two tropical cyclones--Typhoon Chaba in 2004, and Typhoon Paka in 1997--on the resilience and health of Cycas micronesica. They noticed that the proportion of trees exhibiting "mechanical failure" during Typhoon Chaba--in which peak wind speeds were less than half of those in Typhoon Paka--surpassed the damage documented during the more powerful Typhoon Paka. "We set out to determine how a tropical cyclone with moderate wind speeds could impose greater mechanical damage to a highly resistant tree species than a more powerful event only 7 years earlier," explained Marler.

Marler and Lawrence discovered that although Typhoon Paka compromised the ability of the C. micronesica canopy to avoid wind drag, it was alien invasions following Typhoon Paka that virtually eliminated C. micronesica's resilience to tropical cyclone damage. The data showed that stem decay caused by earlier damage from a native stem borer reduced the species' tolerance to external forces, resulting in stem failure in Typhoon Chaba. Invasions of two invasive insects (Aulacaspis yasumatsui in 2003 and Chilades pandava in 2005) were found to be responsible for the 100% mortality of the intact portions of the trees' snapped stems during the 5 years after Typhoon Chaba.

"A span of less than one decade allowed two alien invasions to eliminate the incipient resilience of a native tree species to tropical cyclone damage," the authors wrote. "This study underscores the fact that many years of observations after tropical cyclones are required to accurately determine [trees'] resilience."

The complete study and abstract are available on the ASHS HortScience electronic journal web site: http://hortsci.ashspublications.org/content/48/10/1224.full


Story Source:

The above story is based on materials provided by American Society for Horticultural Science. Note: Materials may be edited for content and length.


Journal Reference:

  1. Thomas E. Marler And John H. Lawrence. Phytophagous Insects Reduce Cycad Resistance to Tropical Cyclone Winds and Impair Storm Recovery. HortScience, October 2013

Cite This Page:

American Society for Horticultural Science. "Trees' diminished resistance to tropical cyclone winds attributed to insect invasions." ScienceDaily. ScienceDaily, 31 January 2014. <www.sciencedaily.com/releases/2014/01/140131130753.htm>.
American Society for Horticultural Science. (2014, January 31). Trees' diminished resistance to tropical cyclone winds attributed to insect invasions. ScienceDaily. Retrieved July 27, 2014 from www.sciencedaily.com/releases/2014/01/140131130753.htm
American Society for Horticultural Science. "Trees' diminished resistance to tropical cyclone winds attributed to insect invasions." ScienceDaily. www.sciencedaily.com/releases/2014/01/140131130753.htm (accessed July 27, 2014).

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