Post Fire Restoration in Hawai‘i Volcanoes National Park Active

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Overview:

A challenge for National Parks Service is restoring post-fire habitats to native states that are resilient to further fire. Especially in areas with a history of grazing, exotic grasses cause ‘grass-fire’ cycles by acting as fire carriers, re-establishing rapidly after fire, and preventing native plant growth.  Improved understanding of grass-fire interactions and how to restore plant communities that resist grass invasion, helps post-fire forest resilience in these landscapes. 

In Hawaiʻi Volcanoes National Park -HVNP-, discontinued grazing in formerly forested montane areas, produced a novel forest of native Acacia koa. Resulting in Acacia koa tree canopy with a non-native grass understory. Similar forests in Hawaiʻi have been purposely created by establishing Acacia koa through large-scale planting in former pastureland; this approach can facilitate grass growth. Acacia koa allows more light through its canopy than other native trees, and adds nitrogen, increasing soil nutrients available for grass.  

The Keauhou Ranch fire recently burned 2,978 acres in HVNP, much of which was koa forest. Post-fire restoration in this area allows us to test ways to break the grass-fire cycle and help to improve strategic restoration in former pasturelands in Hawaiʻi. 

Objectives: 

1. Identify differences in persistence of exotic grasses in plots with and without existing plant diversity. Ecological theory suggests that more diverse species mixtures will attain greater plant volume, achieve closed canopy cover, and take up more resources - light, water, nutrients. Based on this, we predict that non-native grass cover will diminish more quickly in a diverse plot vs. monoculture or low diversity plots.  

2. Determine how native woody planting/seeding density affects native plant survival and growth, as well as non-native grass volume. In addition to species diversity, it is possible that varying the density of plantings will affect the ability of the sites to resist grass invasion. 

3. Determine how grass cover is related to burn severity and native plant recovery to better inform future restoration goals. Quantifying relationships between grass cover and plant community recovery is important for management strategy. For example, if we knew that more than 40 percent non-native grass cover before fire drives post-fire type conversion to 100 percent grass, we could target areas with more than 40 percent grass for restoration and set restoration goals to have less than 40 percent grass.