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Control of Forest Invasives

ForestInvasivesMap 512This map indicates historic locations of forest invaders at the Lanphere Dunes.

 

Introduction 
Invasive plant species have been managed in the dune forests of Humboldt Bay National Wildlife Refuge since 1998.  English ivy (Hedera helix), the most prolific invader, reduces diversity, alters successional patterns, and negatively impact the natural regeneration of understory forest plants.  Fruits of forest invasives are spread by birds, and English ivy can also spread vegetatively.  Vines become established on trees and lead to mortality by increasing susceptibility to storm damage and reducing available light for photosynthesis.  While English ivy poses the worst threat with its ability to cover large areas, other invasive species also compete for available habitat and are targeted for management, including; contoneaster (Contoneaster franchettii), English holly (Ilex aquifolium), tawhiwhi (Pittosporum tenuifolium), New Zealand nightshade (Solanum aviculare), bull thistle (Cirsium vulgare), and periwinkle (Vinca major).
 
The coastal dune forest 
Coniferous dune forests are uncommon in California and are at the southern limit of their range on our refuge.  Some unique cold-acclimated species have found refuge in the forest, including the reindeer lichen (Cladonia portentosa ssp. pacifica) and kinnikinnick (Arctostaphylos uva-ursi).   In 2011 an uncommon wintergreen species was discovered in the dune forest, the little prince’s pine (Chimaphila menziesii). Thought to be a montane to subalpine species, the little prince’s pine in the dune forest represents a coastal, disjunct population, able to survive in the cool fog belt.  The only other known coastal population, other than an isolated site on the Big River estuary in Mendocino County, lies 1,000 miles to our north on Haida Gwaii, British Columbia (Queen Charlotte Islands).  This discovery of Chimaphila menziesii on the Humboldt coast illustrates the role of the dunes forest as a refugium  Preserving the authentic forest character through invasive species control helps to sustain this refugium role, which may become even more valuable under climate change and as invasive plants increase their dominance outside refuge lands.
 
How is English ivy detected and control work prioritized? 
At first, English ivy infestations were mapped on air photos, but by 2002 staff had begun mapping all forest invasives using global positioning systems (GPS).  In 2010 an intensive forest-wide mapping effort lead to the creation of a Geodatabase, which is a computerized mapping system that ties spatial data (where species occur) to monitoring data (extent of infestation, progress on eradication).   The geodatabase aids in the prioritization of sites, and is updated regularly to reflect any newly detected infestations and all control efforts.  
 
How is English ivy removed and controlled? 
While many experiments have tested different methods of removing English ivy, hand pulling of stems and vines (and to the extent possible, rhizomes) has proven the most effective in the dune forest.  Grazing by goats was attempted, but only the leaves were consumed and the root nubs quickly resprouted. Flaming was tested and wilted but did not kill the leaves, which are covered with a waxy cuticle. Due to the close proximity of the forest to shell fish resources in the Mad River Slough, as well as the lack of community support, herbicides have not been a preferred treatment method.  
 
Work crews of many types have been employed to hand pull English ivy.  The California Conservation Corps (CCC), Calfire (CDF), and volunteer groups have completed the bulk of the large scale ivy sites.  The forest invasives geodatabase allows the appropriate site and labor needs to be matched with the right work crew.  Meticulous hand pulling of roots and rhizomes is necessary to prevent resprouting.  Piles of pulled ivy will compost in less than five years.   Ivy sites need to be revisited after the initial treatment to pull any resprouts several times before eradication occurs.    
 
Our Progress 
Although funding has not been continuously available over the past 14 years, management has proven to be effective in both eliminating the historic coverage of 19 acres of English ivy, and preventing further establishment into uninfested forest. The development of the Geodatabase has allowed for easier detection and monitoring. We are approaching the level of control referred to as “maintenance,” in which periodic checks and removal of any persisting plants or newly dispersed individuals is all that is required to keep our forest invasives-free.
 
Last Updated: Feb 12, 2013
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