Increased threat of island endemic tree’s extirpation via invasion-induced decline of intrinsic resistance to recurring tropical cyclones

Abstract

Cycas micronesica populations in Guam have been threatened by the invasion of the armored scale Aulacaspis yasumatsui. I integrate four factors that illuminate an acute need for intervention to reduce an unprecedented threat caused by the invasion. First, mechanical failure of healthy C. micronesica trees during catastrophic winds is rare because of the cycad tree’s unique pachycaulis stem design. Second, tree-winching and three-point bend stress tests revealed the natural resistance to damage from tropical cyclones has been compromised by the chronic feeding of this homopteran pest. Third, no typhoon event has occurred since the arthropod’s invasion and its spread in the year 2005 to actually test extent of mechanical failure for the unhealthy remaining trees. Fourth, historical records indicate the probability that Guam will experience typhoon force winds is 0.51 in three years and 0.91 in 10 y. These four factors integrate to predict the next typhoon may eliminate the surviving C. micronesica trees and stewardship of this declining population requires intervention to counter this prediction.

<b>Adventitious rooting of mature <I>Cycas micronesica</I> K.D. Hill (Cycadales: Cycadaceae) tree stems reveals moderate success for salvage of an endangered cycad</b>

“…Perennial forest species in the Mariana Islands are equipped with traits that enable resilience to chronic pressures of tropical cyclones (Marler 2001). Experimental approaches were used to predict an increase in major structural damage of C. micronesica trees by tropical cyclones that would occur following the invasions of the exotic insect herbivores (Marler 2013). A tropical cyclone occurred in 2015, which tested this prediction, and confirmed an increase in major stem snapping or toppling occurred in exposed sites .…”

First, do no harm

“… 2 Prior to the non-native insect invasions that have endangered C. micronesica , the Guam population experienced minimal root anchorage failure during tropical cyclones 3 and rapid tree health recovery following tropical cyclones. 4 Traditional winching techniques were used to predict that sustained A. yasumatsui infestations compromise the mechanical properties of C. micronesica stems, 5 and these predictions were confirmed in May 2015 when increased stem failure occurred during Typhoon Dolphin. 6 However, the sustained pest infestations did not influence the extent of C. micronesica root failure during Typhoon Dolphin, indicating the original roots maintained their anchorage traits.…”

Tree conservation can be constrained by agents from conservation permitting and funding agencies

“…Indeed, ecosystem changes can be misunderstood in insular settings if consistent monitoring is not used [50]. This wise approach of a funding agency enabled the accumulation of the only existing long-term C. micronesica survival data set throughout three islands and has resulted in numerous peer-reviewed articles that are available to inform future C. micronesica conservation decisions [51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68].…”