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Oak decline is a chronic problem in Missouri Ozark forests. Red oak group species are most susceptible and decline is reportedly more severe on droughty, nutrient-poor sites. However, it was not clear whether greater decline severity was caused by poor site conditions or is simply due to the greater abundance of red oak group species found on poorer sites. We conducted this study to determine whether oak decline severity in oakdominated Missouri Ozark forests is related to factors strongly influencing site quality including soil, landform position, and slope-aspect. We monitored the survival of 6606 dominant or co-dominant oak trees for 10 years and surveyed crown dieback on more than 1995 oak trees during a single year to determine if mortality and the presence of decline symptoms were related to site factors. Analysis confirmed that red oak group species had more crown dieback and greater mortality than did white oak group species. We also found greater red oak mortality on upper slope positions and where soils were gravelly and low in base cations. However, the abundance of red oaks was also greater in these same locations. Further analysis showed that if the initial abundance of red oaks was included as a covariate in the model, the site factors no longer were significant effects related to oak mortality. Moreover, we found that frequency of oaks exhibiting crown dieback was the same or sometimes greater on high quality sites. These findings show that red oak mortality is more prevalent on droughty and nutrient-deficient sites because red oak group species are more abundant there. Rather than simply predisposing oaks to decline, droughty and nutrient-deficient site conditions most likely favored the establishment and growth of red oaks following the extensive logging during the early 1900s. The extensive oak decline occurring on droughty and nutrient-deficient soils today appears to due to the high abundance of mature red oak group species on these sites. Published by Elsevier B.V.

The effects of silvicultural treatments (e.g., even-aged management, EAM, and unevenaged, UAM) on 4 microclimatic variables (air temperature, incoming solar radiation, humidity, and soil temperature) were examined in oak forests of southeastern Missouri Ozarks, USA. Nine mobile climatic stations were used to collect field data during the summers of 1995 (pre-harvest), and 1997 and 1998 (post-harvest). Spatial variation of air temperature at 2 m height increased 96 and 35% (2-year average) after harvest in UAM and EAM sites, respectively, as quantified by 95% confidence intervals (CI). UAM increased the variability of air temperature at the lower end of the daily range in the CI more than at the upper end, while EAM had a stronger effect on raising spatial variation at the upper end of the CI than at the lower end. Spatial variation of soil temperature within an 80 × 80 m grid increased significantly during daytime after harvest, especially at the surface, but did not change much during nighttime. EAM resulted in a larger increase of soil temperature variation than did UAM. Greater amplitudes of diurnal soil temperatures (especially at the surface) were observed at depths of 0, 5, and 10 cm and were more evident at the EAM site after harvest. The duration of variation in post-harvest soil surface temperature during daytime was about 3 times longer than pre-harvest at the EAM site. Spatial variation in radiation increased 56 and 128% in UAM and EAM sites after harvest, respectively. Except for radiation, significance levels of differences in means of microclimatic variables were reduced after harvest among the 3 Ecological Land Types (ELTs); the spatial variation of microclimate was smaller among ELTs within the same treatment than between treatments. Our results suggested that, usually, EAM affected the microclimate more than UAM did, especially in raising soil temperatures on northeast slopes (ELT 18 ).

The effects of management on soil carbon efflux in different ecosystems are still largely unknown yet crucial to both our understanding and management of global carbon flux. To compare the effects of common forest management practices on soil carbon cycling, we measured soil respiration rate (SRR) in a mixed-conifer and hardwood forest that had undergone various treatments from June to August 2003. The mixed-conifer forest, located in the Sierra Nevada Mountains of California, had been treated with thinning and burning manipulations in 2001, and the hardwood forest, located in the southeastern Missouri Ozarks, had been treated with harvesting manipulations in 1996 and 1997. Litter depth, soil temperature, and soil moisture were also measured. We found that selective thinning produced a similar effect on both forests by elevating SRR, soil moisture, and soil temperature, although the magnitude of response was greater in the mixed-conifer forest. Selective harvest increased SRR by 43% (from 3.38 to 4.82 µmol·m -2 ·s -1 ) in the mixed-conifer forest and by 14% (from 4.25 to 4.84 µmol·m -2 ·s -1 ) in the hardwood forest. Burning at the conifer site and even-aged harvesting at the mixed-hardwood site did not produce significantly different SRR from controls. Mean SRR were 3.24, 3.42, and 4.52 µmol·m -2 ·s -1 , respectively. At both sites, manipulations did significantly alter SRR by changing litter depth, soil structure, and forest microclimate. SRR response varied by vegetation patch type, the scale at which treatments altered these biotic factors. Our findings provide forest managers first-hand information on the response of soil carbon efflux to various management strategies in different forests.Résumé : Bien que cruciaux pour comprendre et gérer le flux global de carbone, les effets de l'aménagement sur les émissions de carbone du sol dans différents écosystèmes sont encore largement inconnus. Afin de comparer les effets des pratiques courantes d'aménagement forestier sur le recyclage du carbone du sol, les auteurs ont mesuré le taux de respiration du sol (TRS) dans une forêt mélangée de conifères et une forêt feuillue qui avaient subi différents traitements de juin à août 2003. La forêt mélangée de conifères, située dans la Sierra Nevada en Californie, avait subi des traitements d'éclaircie et de brûlage en 2001. La forêt feuillue, située dans les monts Ozarks au sud-est du Missouri, avait subi différents traitements de récolte en 1996 et 1997. L'épaisseur de la litière, la température du sol et la teneur en eau du sol ont aussi été mesurées. Ils ont observé que l'éclaircie jardinatoire a produit un effet semblable dans les deux forêts en élevant le TRS, la teneur en eau du sol et la température du sol quoique l'ampleur de la réaction ait été plus forte dans la forêt mélangée de conifères. La coupe de jardinage a augmenté le TRS de 43 % (de 3,38 à 4,82 µmol·m -2 ·s -1 ) dans la forêt mélangée de conifères et de 14 % (de 4,25 à 4,84 µmol·m -2 ·s -1 ) dans la forêt feuillue. Le brûlage dans le cas des conifères et ...

Managers are often concerned about oak mortality in maturing mixed-oak forests, but they often lack explicit information about mortality risk for oaks that differ in species, size, crown class, competitive status, and growth rate. In eastern North America, tree species in the red oak group (Quercus Section Lobatae) are typically shorter lived than those in the white oak group (Section Quercus), and red oak group mortality can be greatly exacerbated during episodes of oak decline. We analyzed factors associated with red oak group mortality for two large data sets from the Ozark Highlands and identified groups of trees that differed significantly in mortality risk. One data set was from a large, upland Ozark forest with more than four decades of uneven-aged management, and the other was representative of relatively undisturbed upland oak forests in the same ecoregion. Neither location experienced significant episodes of oak decline during the period of observation, and our results represent endemic mortality for mature (sawtimber size) forests in the region. We found that mortality rates for trees in the red oak group were four to six times greater than mortality rates for associated trees in the white oak group. We also found that red oak group mortality was significantly related to tree crown class, tree diameter, and basal area of larger competitors. When recent tree dbh growth was known, it significantly increased the ability to predict future mortality for some classes of trees. Annual mortality rates for different classes of trees in the red oak group ranged from 0.4 to 10.7%. Classes of trees in the red oak group that were most likely to die (in rank) were as follows: trees with dbh growth <0. /ha; and trees with annual dbh growth greater than 0.6 cm (assuming recent dbh growth is known). This information can be used when preparing silvicultural prescriptions and/or forest management plans to identify and treat classes of trees that are at high risk of mortality. Published by Elsevier B.V.

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