Impact of Southern Pine Beetle Outbreaks on Wildlife Habitat Suitability

 Maria D. Tchakerian1, Jaehyung Yu1, Robert N. Coulson1, and Forest Oliveria2

1. Knowledge Engineering Laboratory, Texas A&M University, College Station, Texas

2. USDA Forest Service, Forest Health Protect, Pineville, Louisiana

Introduction

The southern pine beetle (SPB) (Dendroctonus frontalis Zimmermann (Coleoptera Scolytidae)) is the most destructive pest of pine forest in the southeastern United States. This insect infests yellow pines and is a significant mortality agent affecting softwood production. The economic, social, and ecological impact of SPB is catastrophic across the South. From 1960 to 2003, timber losses have been estimated to exceed $2.5 billion (Coulson et al. 2004). Few studies have evaluated the impact of SPB on wildlife habitat. Maine et al. (1980) used a qualitative model to estimate the impact on amount and kind of food due to changing overstory and understory vegetation for several wildlife species. However, the approach did not consider the spatial arrangement of the SPB-infested stands within the forest. Wildlife habitat requirements are related both to the structure of the habitat and to the landscape surrounding the habitat (Store and Jokimaki 2003). Therefore, quantifying the impacts of SPB on wildlife habitat at the meso-scale landscape requires consideration of infested stand adjacency and configuration within the pine forest. In this study our goal was to evaluate how changes in forest composition and configuration resulting from SPB herbivory impact the quality of wildlife habitats in a meso-scale southern forest landscape. The objectives of the study were as follows: (i) to estimate the changes of forest structure and composition as a result of SPB outbreaks using an adaptation of FIAD, FVS, SPB data, and GIS and (ii) to assess the consequences of these changes for wildlife habitat suitability through accepted habitat models.

Methods

The steps in the methodology for this study are illustrated in Figure 2. Stand inventory data was assembled from FIAD (Forest Inventory and Analysis Database). The Southern Variant of FVS (Forest Vegetation Simulator) was used to project stand conditions prior to and following infestation by SPB. Representative wildlife species from a variety of taxa were selected (Figure 3) and the habitat suitability for each stand was assessed using Habitat Suitability Index (HSI) models published by the U.S. Fish and Wildlife Service. Landscape habitat suitability was defined by preparing a mosaic of HSI values for the stands forming the forest.

Figure 1.Steps in assessing the impact of SPB on southern forest landscapes.

FRAGSTATS was utilized for landscape pattern analysis.  Once the habitat suitability index for the landscape was defined for each species, we evaluated the change in landscape structure expected to result from herbivory by SPB and assessed the impact on wildlife habitat suitability.

 

Study Area

Figure 2. Location of the Bankhead (Alabama) National Forests (USDA Forest Service, 2003).

 

Selected Management Indicator Species

Figure 3. Selected species used for quantifying SPB impacts on wildlife habitat quality. These species are important because they are Management Indicator Species which population changes reflect the effects of management activities.

 
Results

Southern Pine Beetle Impact on Pine Warbler Habitat

Variables used for the evaluation (Shroeder, 1982):

      V1 =  Percent tree canopy closure of overstory pines
      V2 =  Successional stage of stand
      V3 =  Percent of dominant canopy pines with deciduous understory in the upper one third layer

Metrics Class 3
Without SPB
With SPB
Class Area (Ha)
22,822
14,464
# of Patches
606
794
Patch density
1.47
2.56
Mean Patch Size
37.66
18.21
Mean Core Area
6.92
2.50
 
 

Southern Pine Beetle Impact on Gray Squirrel Habitat

To evaluate winter food and cover/reproduction habitat (Allen, 1982):

  Winter food
    V1 = Percent canopy closure of trees that produce mast  > 10 inches dbh
    V2 = Diversity of hard mast producer trees
  Cover and reproduction
    V3 = Percent tree canopy closure
    V4 = Average dbh of overstory trees
    V5 = Percent shrub crown cover

I

Southern Pine Beetle impact on Eastern Wild Turkey Fall/Winter/Spring Food Habitat

Variables used for the evaluation (Schroeder, 1985a):

   V1 = Number of hard mast producing trees/ha > 10 inches dbh
   V2= Percent of canopy closure of soft mast producing tress
   V3= Percent of shrub crown cover (food production, behavioral, and soft mast producing shrubs)

Metrics Class 3
Without SPB
With SPB
Class Area (Ha)
824
12,559
# of Patches
65
450
Patch density
0.17
1.20
Mean Patch Size
12.68
60.12
Mean Core Area
0.94
13.8

Southern Pine Beetle impact on Northern Bob White Winter Food Habitat

 Variables used for the evaluation (Shroeder, 1985b):

   V1 = Percent of canopy cover of herbaceous food plants
   V2= Percent of ground that is bare or covered with a light litter
   V3= Number of pine or oak trees/ha > 10 inches

Metrics Class 3

Without SPB

With SPB

Class Area (Ha)
18,550
28,924
# of Patches
419
626
Patch density
0.59
1.88
Mean Patch Size
44.27
46.20
Mean Core Area
9.29
15.15

Conclusion

1. Using stand data, the FVS, and the HSI we created maps that defined classes of habitat suitability in a meso-scale forest landscape for 4 wildlife species.

2. Using data from SPBIS we evaluated the effects of an outbreak of the southern pine beetle on habitat suitability for the 4 species.

3. Impact varied in predictable ways by species:

    Pine Warbler habitat was destroyed.

    Grey Squirrel habitat was not affected.

    Wild Turkey habitat was affected both negatively and positively.

    Northern Bobwhite Quail habitat was enhanced.

4. The effect of the insect outbreak was to perforate the forest landscape which generally decreased habitat patch size, increased habitat patch density, increased habitat patch number, and reduced core area of habitat patches.

5. Habitat for each species was always present within the national forests.  Another dimension to the study will be an investigation of species movements in relation to dispersion patterns of habitat patches.