University of Tennessee
Forest Resources AgResearch and Education Center
Cumberland Forest Unit

Restoration of Soil Function on Coal Mine Sites

This research project was conducted by Jennifer Franklin, University of Tennessee Department of Forestry, Wildlife and Fisheries and Jan Frouz, Institute of Soil Biology, Biology Centre of the Academy of Sciences of the Czech Republic.

The following article has been assembled from information provided by the authors and is used with their permissions. Anyone wishing to use this article should seek appropriate permission from Jennifer Franklin at jenniferfranklin@utk.edu

Introduction

Services provided by an ecosystem, such as carbon sequestration and water filtration among many, are dependant upon the level at which ecosystem processes function. A potential measure of the success of restoration is to measure the level at which various processes and structures are restored in comparison with undisturbed ecosystems. Many of these ecosystem services are related to below-ground parts of ecosystems which are often neglected. We have assessed below-ground and above-ground recovery of sites in the Cumberland mountains (Fig. 1) that were mined for coal 40-50 years ago.
Figure 1a Figure 1b

Figure 1

Materials and Methods

Three sites in Morgan county, TN, at the UT Forestry Research and Education Center and one site in Kentucky were selected on the basis of their age and known history. On each site, 3 types of cover were identified based on maps, existing cover, and the knowledge of landowners and previous researchers:

PINE - Pine plantings that were originally established as research plots. Species varied within and among sites, and all had remained undisturbed since that time. However, a heavy infestation of Southern pine beetle approximately 8 years ago reduced these to small remnants of the original stands within a hardwood forest.

HW - Naturally revegetated areas that were mined, and adjacent to the research plots. No reclamation treatment was applied, and native hardwood forest became established.

CONT - Adjacent forest that was not disturbed by mining activities.

On each site three plots were established in each cover type. In Oct. of 2006 we measured:
1. Field soil respiration rates by IRGA (LI 6400, LI-COR Biosciences, Lincoln, NE)
2. Tree species and basal area using a factor 10 prism
3. Perennial understory vegetation in a 2m diameter plot
4. Height of yellow poplar (Liriodendron tulipifera) on the Tennessee sites, and trees cores were collected to determine age for site index calculations.
5. Decomposition rate over the following 6 weeks.

Soils were collected from the top 5cm including the litter layer, 5-10cm, and 10-15cm depths for measurement of:
1. root biomass
2. soil chemistry
3. laboratory microbial soil respiration in root-free soil
4. composition of soil macrofauna

Results and Discussion

Site index is commonly used in forestry as a measure of forest productivity and is primarily related to soil factors. Average site index of a common local species, yellow poplar (Liriodendron tulipifera) was 106 ft at an index age of 50 on areas that had been mined. Site index for this species and region averages 87 ft (USDA, 1962). Basal area averaged 29.4 m2 ha-1, compared with an average of 24.7 m2 ha-1 reported for eastern Tennessee in 1999 (Schweitzer, 2000). However, tree species composition differs from that of the adjacent un-mined area, which is dominated by chestnut oak (Quercus michauxii) and scarlet oak (Quercus coccinea), and from composition within the state that is dominated by oak-hickory forest types (Table 1). Areas planted to pine have undergone succession, and pine now comprises less than 10% of the total basal area. Black locust, planted extensively on mined lands from the 1960s to 1990s, was only a minor component of woody vegetation (Table 1).

Table 1

Table 1. Composition of overstory on previously mined areas (%BA mined) in comparison with species composition in the state of Tennessee (%BA, data derived from Schweitzer 2000b), expressed as a percentage of total basal area.

Soils below the remaining pine have lower respiration rates than naturally regenerated areas or areas that were left to revegetate naturally (Fig. 2). Fine root biomass was highest in un mined area followed by areas revegetated naturally by hardwood (Fig. 3).
Figure 2 Figure 3

Fig. 2 Average field soil respiration rate in two forest types on mined land (pine and hw) and adjacent unmined forest (cont). Letters indicate significant differences at p < 0.05. Bars indicate standard error.

Fig. 3 Average root biomass in soil depths 0-5 cm (a), 5-10 cm (b) and 10-15 cm (c) on two forest types on mined land (pine and hardwood) and adjacent unmined forest (control). Bars indicate standard error.

Figure 4 Field soil respiration rate was not significantly related to root mass, and appeared to be explained mainly by differences in fine root mass (R2=0.65, p<0.001). On the other hand, soil microbial respiration in root-free soil was higher in undisturbed site and pine and lower in naturally re-grown hardwoods. Differences in microbial respiration may be related to differences in soil chemistry, as preliminary results show differences in total phosphorous between cover type (Fig. 4). Results of soil microfauna, soil chemistry, and understory vegetation are still being analyzed.

Conclusions

Our results suggest that above-ground forest productivity is greater on mined sites than in the un-mined forest, based on tree basal area and site index. However, below-ground processes are still significantly different from undisturbed sites after 50 years.

Acknowledgements

We would like to thank the University of Tennessee Agricultural Experiment Station, the staff of the UT Forest Resources Research and Education Center, Victor Davis and Patrick Angel from the Office of Surface Mining, Clark Ashby, and John Rizza.

Literature cited

Beck, Donald E.1962.Yellow-Poplar Site Index CurvesRes. Note SE-180. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station. 2 p.

Schweitzer, Callie Jo. 2000a. Forest statistics for East Tennessee, 1999. Resour. Bull. SRS51. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 60 p.

Schweitzer, Callie Jo. 2000b. Forest statistics for Tennessee, 1999. Resour. Bull. SRS52. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 78 p.

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