The Death and Life of Ash: Landscape Tactics to Adapt to Invasive Species

This project was developed in response to the impacts of the Agrilus planipennis (Emerald Ash Borer, hereafter EAB), an invasive species threatening North American forests. The emerald ash borer is a wood-boring beetle indigenous to Asia. Since its accidental introduction, EAB has spread and devastated Fraxinus spp. (ash) populations across the United States. Changing human behaviors have created new anthropogenic pathways for pest dispersal. For example, EAB spreads through human-assisted movement of material like firewood. EAB lays eggs in ash crevices, which hatch into larva that tunnel through the tree's bark and feed on the vascular tissue of the tree, cutting off nutrient transport (USDA 2009).

In Massachusetts, the spread of EAB may cause the regional elimination of Fraxinus americana (white ash), which anchors the forest ecosystem through multi-species interaction. Ash is a critical food source and component of habitats for threatened amphibians, like Scaphiopus holbrookii (eastern spadefoot) and Ambystoma laterale (blue-spotted salamander) and provides critical ecological services like leaf litter accumulation (Stephens et al. 2013). Anthropogenic changes to leaf litter input affect the fitness of a larval amphibian. An infested ash will die in 3–5 years, indicating the necessity of early intervention (USDA APHIS 2011). Culturally, ash has been used as a replacement tree for Ulmus spp. (elm) killed by Ophiostoma sp. (fungi known to cause Dutch elm disease) in urban areas, revealing a recent history of invasion, species loss, and ecological change that embodies the Anthropocene. This project envisions a hybrid management of EAB to live with the insect's inevitable threats.

Since 2012, EAB has steadily spread via the road system and urban expansion, causing enormous canopy loss in ash-abundant areas (BenDor et al. 2006). On a territorial scale, a gradient of vulnerability emerges within a visual analysis of Massachusetts, through the overlay of confirmed

Figure 1.

Research mapping of the vulnerability of forests and scale of EAB impact at the territorial scale. (Source: Bureau of Geographic Information [MassGIS], Commonwealth of Massachusetts, Executive Office of Technology and Security Services).

Figure 2a.

Design Proposal: An ash-free buffer zone is proposed to slow EAB spread from existing infested areas and road systems, protecting the existing white ash within the core habitat of a state forest.

Figure 2b.

Design Proposal: A combination of design strategies including reforestation and vernal pond construction are proposed within the buffer zone. (Source for basemap: Bureau of Geographic Information [MassGIS], Commonwealth of Massachusetts, Executive Office of Technology and Security Services).

infestation, threatened habitats, human influence, and the presence of ash (Figure 1). My project focuses on the ash-concentrated habitat in the Berkshire transition area of Massachusetts where ash-dependent amphibian habitat is present (Figure 2a). My proposed restoration design aims to slow the spread of EAB in the vicinity of this habitat and dedicate an area of core habitat to attempt to protect from the impacts of EAB. This project accepts the larger ecosystem impacts of EAB but proposes that strategically preserved pockets of ash forest throughout Massachusetts could be beneficial for sensitive species, future research, and public engagement.

Design Proposal

My design proposes a regional buffer ring strategy for preemptive ash removal and management to protect the EAB-free core habitat zone in the Berkshire transition area (Figure 2a, 2b). Research has shown that it is effective to offset an ash-free zone from adjacent infestation as a quarantine area based on the fly range of EAB (Herms and McCullough 2014). The forest within the regional buffer ring today is composed of less than 30% ash canopy, therefore the proposed selective removal of the ash over time will not remove the entire forest. My proposal combines two hybrid operations to complete selective removal in the buffer ring. One is to combine ash removal with

Figure 3.

Human Experience: A proposed renovation of the existing trail system in the local state forest, located in the transition...