Survival analysis of declining black and scarlet oaks in the Ozark Highlands, Missouri
Zhaofei Fan, Department of Forestry, Mississippi State University
Xiuli Fan, Department of Forestry, University of Missouri
Stephen R. Shifley and John M. Kabrick, U. S. Forest Service Northern Research Station, Columbia, MO
Martin A. Spetich, U.S. Forest Service Southern Research Station, Hot Spring, AR
Randy G. Jensen, Missouri Department of Conservation, Ellington, MO
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Introduction
Black oak
Predisposing factors
site condition
stand density
tree species/age
oak decline
and mortality
1. Dominant and codominant trees with dbh ≤ 27cm and bal ≤ 13 m2/ha
2. Dominant trees with dbh ≤ 23 cm and bal > 13 m2/ha
3. Dominant and codominant treeswith dbh ≤ 27cm and bal ≤ 13 m2/ha
4. Codominant trees with dbh > 27cm and bal ≤ 13 m2/ha
5. Dominant and codominant treeswith dbh > 23cm and bal > 13 m2/ha
6. Intemediate and suppressed trees withbal ≤ 14 m2/ha
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Survival (100%)
Among oaks, black oak (Quercus velutina Lam.) and
scarlet oak (Quercus coccinea Muenchh.) are the two major
species that have suffered “oak decline syndrome” in
Missouri forests (Dwyer et al. 1995). Oak decline results from
the interaction of predisposing stress factors (e.g., poor site
quality, unfavorable stand condition, advanced tree age) and
secondary disease and insect pests (e.g., root fungi, insect
borers) (Figure 1). It has been a top priority in forest health
management to identify potential oak decline risk factors and
predict declining tree’s survival time. According to a set of
published study results, the major predisposing factors of oak
decline include tree species, crown class, dbh, and bal
(basal area in larger trees). Survival analyses of declining
oak trees by these risk factors will help stand level decline
evaluation and prescription of silvicultural treatments to
mitigate oak decline and mortality.
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7. Intemediate and suppressed trees with bal ≤ 14 m2/ha
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Inciting factors
drought
frost
tree damage
Contributing factors
armillaria root disease
red oak borer
canker fungi
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Figure 1. The process and causal factors of oak decline
and mortality (adapted from Starkey et al. 2004).
Scarlet oak
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1. Dominant and codominant trees with dbh ≤ 30cm and bal ≤ 12 m2/ha
2. Dominant and codominant trees with 30 cm <dbh ≤ 42 cm and bal ≤ 7 m2/ha
3. Dominant and codominant trees with dbh ≤ 24 cm and bal > 12 m2/ha
4. Dominant and codominant trees with 30 cm < dbh ≤ 42 cm and bal > 7 m2/ha
5. Intermediate trees with bal ≤ 14 m2/ha
6. Dominant and codominant trees with 24 cm < dbh ≤ 30 cm and bal > 12 m2/ha
7. Dominant and codominant trees with dbh > 42 cm
8. Intemediate trees with bal > 14 m2/ha
Data and Methods
• We used crown class, dbh and bal to classify black and scarlet oaks into 7 and 9 risk groups based on the 1999-2006
Missouri Ozark Forest Ecosystem Project (MOFEP) data (Shifley et al. 2006).
• We used the product-limit method to evaluate the survival rate of black and scarlet oaks within each risk group (Fan et
al. 2006).
Compared to white oak (92% of survival), only 65 and 73 % of black oak and scarlet oak, respectively, survived after
sixteen years (Fig. 2). The difference in survival time between black and scarlet oaks was statistically significant
(p<0.0001). As shown by the estimated survival curves, there was no evident difference between black and scarlet oaks
for the first eight years (1990-1998). But after then black oak mortality escalated quickly so that only about 65% of black
oak trees tagged in 1990 were alive by year 2006.
Black and scarlet oaks were classified into seven and nine risk groups, respectively (Figure 3). Crown class was the
most significant factor to survival for both species. Sixteen-year survival rates of dominant and codominant black oak
varied from 50 to 85 percent depending on tree size (dbh) and competition condition (bal). While less than half of
intermediate and suppressed trees survived. Competition condition (bal) was more important than tree size (dbh) to the
survival of black oaks (Figure 3).
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black oak
Survival (100%)
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9. Suppressed trees
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Figure 3. Survival of black and scarlet oaks by survival groups from 1990 - 2006.
There was a wide discrepancy in survival (from 64 to 91%) among the six risk groups of dominant and
codominant scarlet oaks. Unlike black oak, tree size (dbh) had more influence than competition (bal) on scarlet oak
survival. With same or similar competition condition, for example, trees ≤30 cm dbh had nearly 15% higher survival
than trees > 30 cm. Survival of suppressed scarlet oaks was very low (37%), but intermediate scarlet oak survival
changed significantly. Compared to trees with bal> 14 sq meters/ha (50% of survival), intermediate scarlet oak with
bal < 14 sq meters/ha had a survival rate of 70% which was even higher than certain dominant and codominant
tree groups (survival of 66%).
Conclusion
scarlet oak
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Results and Discussion
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Survival (100%)
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In the Ozark Highlands, large-scale oak decline has caused precipitous mortality, reaching 2.3% annually among
red oak species. Black and scarlet oaks can be classified into different risk groups based on the well known
predisposing factors including crown class, dbh and bal (basal area in larger trees, a measure of competition from
above). Survival of each risk group can be estimated based on monitoring data like MOFEP or FIA and be used to
prescribe treatments to mitigate oak decline and mortality.
white oak
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Major references
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Dwyer, J. P., B. E. Cutter, and J. J. Wetteroff. 1995. A dendrochronological study of black and scarlet oak
decline in the Missouri Ozarks. For. Eco. Manag. 75:69-75.
Fan, Z., J. M. Kabrick, and S. R. Shifley. 2006. Classification and regression tree based survival analysis in oakdominated forests of Missouri’s Ozark highlands. Can. J. For. Res. 36: 1740-1748.
Shifley, S. R., Z. Fan, J. M. Kabrick, and R. G. Jensen. 2006. Oak mortality risk factors and mortality estimation.
For. Eco. Manag. 229:16-26.
Starkey, D. A., F. Oliveria, A. Mangini, and M. Mielke. 2004. Oak decline and red oak borer in the interior highlands of Arkansas and Missouri: natural phenomena, severe occurrences. In: Spetich, M. (Ed.), U.S.
Department of Agriculture, Forest Service, General Technical Report SR-73, pp. 217-222.
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Figure 2. Survival of black and scarlet oaks versus white oak (reference) in unmanaged mature forest from 1990 to 2006.