Satellite-Based Assessment of Grassland Conversion and Related Fire Disturbance in the Kenai Peninsula, Alaska.

Katherine Hess,Dawn Magness,Joseph Spruce,Jeanette Cobian-Iñiguez,Victor Lenske,Jacob Ramthun,Cheila Cullen,John Bolten,Adrianna Foster

doi:10.3390/rs11030283

Abstract

Spruce beetle-induced (Dendroctonus rufipennis (Kirby)) mortality on the Kenai Peninsula has heightened local wildfire risk as canopy loss facilitates the conversion from bare to fire-prone grassland. We collected images from NASA satellite-based Earth observations to visualize land cover succession at roughly five-year intervals following a severe, mid-1990’s beetle infestation to the present. We classified these data by vegetation cover type to quantify grassland encroachment patterns over time. Raster band math provided a change detection analysis on the land cover classifications. Results indicate the highest wildfire risk is linked to herbaceous and black spruce land cover types, The resulting land cover change image will give the Kenai National Wildlife Refuge (KENWR) ecologists a better understanding of where forests have converted to grassland since the 1990s. These classifications provided a foundation for us to integrate digital elevation models (DEMs), temperature, and historical fire data into a model using Python for assessing and mapping changes in wildfire risk. Spatial representations of this risk will contribute to a better understanding of ecological trajectories of beetle-affected landscapes, thereby informing management decisions at KENWR.

Highlights

In the mid-1990s, North America’s largest recorded outbreak of spruce beetles (Dendroctonus rufipennis Kirby) killed nearly 5 million acres of forest on and around south-central Alaska’s Kenai Peninsula [1]
While our analysis focuses on the transition from forest to shrubland and herbaceous land cover types, forest growth occurred over the course of the study period (Figure 4)
Our project generated Landsat Normalized Difference Vegetation Index (NDVI) change maps and Landsat multispectral data classified into land cover maps to help corroborate in situ observations made by landscape ecologists at the Kenai National Wildlife Refuge

Summary

Introduction

In the mid-1990s, North America’s largest recorded outbreak of spruce beetles (Dendroctonus rufipennis Kirby) killed nearly 5 million acres of forest on and around south-central Alaska’s Kenai Peninsula [1]. Spruce beetle-induced mortality results in foliar desiccation (“red phase”) before an eventual needledrop (“gray phase”), opening the canopy and often permitting ecological succession towards more grass-dominant types [8]. Such infestations, in addition to causing habitat loss, harm the timber economy, detract from regional tourism, increase risk of property damage due to treefall, and cause potential shifts in the fire regime [9] Decaying trees at any stage may exhibit loose or weakened bark, cones, or branch materials that can be carried aloft during fires and create increased risk of spotting [10] Both beetle outbreaks and fires are of serious concern to wildlife, vegetation, and other natural and urban resource managers in the region. Because the Kenai Peninsula is one of Alaska’s most densely populated boroughs and is a cornerstone of the state’s tourism economy, the ability to forecast and mitigate these disturbances is of high value to a variety of local stakeholders

Objectives

Results

Discussion

Conclusion