Robert N. Muller

Above- and Belowground Net Primary Production in a Temperate Mixed Deciduous Forest

Our current ability to detect and predict changes in forest ecosystem productivity is constrained by several limitations. These include a poor understanding of belowground productivity, the short duration of most analyses, and a need for greater examination of species- or community-specific variability in productivity studies. We quantified aboveground net primary productivity (ANPP) over 3 years (1999–2001), and both belowground NPP (BNPP) and total NPP over 2 years (2000–2001) in both mesic and xeric site community types of the mixed mesophytic forest of southeastern Kentucky to examine landscape variability in productivity and its relation with soil resource [water and nitrogen (N)] availability. Across sites, ANPP was significantly correlated with N availability (R2 = 0.58, P = 0.028) while BNPP was best predicted by soil moisture content (R2 = 0.72, P = 0.008). Because of these offsetting patterns, total NPP was unrelated to either soil resource. Interannual variability in growing season precipitation during the study resulted in a 50% decline in mesic site litter production, possibly due to a lag effect following a moderate drought year in 1999. As a result, ANPP in mesic sites declined 27% in 2000 compared to 1999, while xeric sites had no aboveground production differences related to precipitation variability. If global climate change produces more frequent occurrences of drought, then the response of mesic sites to prolonged moisture deficiency and the consequences of shifting carbon (C) allocation on C storage will become important questions.

Intraspecific variation in production of astringent phenolics over a vegetation-resource availability gradient

SummaryThe chemical constituency of flowering dogwood (Cornus florida L.) and red maple (Acer rubrum L.) foliage was analyzed over a species compositional gradient to test the hypothesis that over subtle gradients of moisture and nutrient availability production of phenolic compounds will be increased on sites of greatest stress. Calcium and nitrogen concentrations declined along the gradient in both species, while phosphorus showed a significant decline only in red maple. Lignin concentrations in both species were unrelated to the vegetation gradient, but astringent phenolics increased by 156% and 159% in dogwood and red maple, respectively. The correlation between production of polyphenolds and site quality supports previous observations that under conditions of environmental stress production of many secondary compounds is increased, and suggests that this relationship is significant over subtle environmental gradients.

Temporal and ecological patterns of flowering dogwood mortality in the mixed mesophytic forest of eastern Kentucky.

McEwAN, R.W., R.N. MULLER, M.A. ARTHUR, AND H.H. HOUSMAN. (University of Kentucky, Lexington, KY 40546-0073). Temporal and ecological patterns of flowering dogwood mortality in the mixed mesophytic forest of eastern Kentucky. J. Torrey Bot. Soc. 127:221-229. 2000. Since its discovery in 1977, the fungal pathogen Discula destructiva (Redlin) has depressed flowering dogwood (Cornus florida L.) populations throughout most of its native range. We examined the impacts of the Cornus florida-Discula destructiva disease complex in an old-growth forest and a second-growth forest focusing on long-term trends in flowering dogwood mortality and how those trends were manifested across a range of ecological communities. The study sites were located on the Cumberland Plateau of southeastern Kentucky and were similar in terms of climate and topography. In the second-growth forest flowering dogwood stem density declined significantly from 120 stems/ha in 1992 to 62 stems/ha in 1998 (48%, 8% per year), coincident with our expectations for dogwood anthracnose-related mortality. However, in the old-growth forest, flowering dogwood stem density declined uniformly over a much longer period: 106 stems/ha (1979), 68 stems/ha (1989), and 42 stems/ha (1998; 60%, 3.1% per year). Dogwood anthracnose was not known to be present in eastern Kentucky between 1979 and 1989; therefore, it cannot be implicated as the agent individually responsible for all of the flowering dogwood mortality in the old-growth forest. In both forests, dogwood stem density and mortality were concentrated in the xeric forest communities. This concentration of mortality in drier communities and the long-term trend in mortality contradict prevailing ideas about the impacts and site characteristics of dogwood anthracnose. Observations of the degree of anthracnose infection among mature stems, saplings and seedlings suggest that the current decline in the flowering dogwood population will continue into the next generation. This study demonstrates that seemingly clear trends in anthracnose-related mortality may be blurred by long-term mortality trends.

Fine root production of astringent phenolics

SummaryChemical quality of fine roots (<1 mm diameter) was determined over a gradient of species composition in the Mixed Mesophytic Forest Region. Ash-free nitrogen, calcium, and phosphorus concentrations of roots declined by 49, 41, and 72%, respectively, over a gradient of increasing soil acidity (pH 5.3 to 4.7). Lignin concentration was unrelated to either the vegetation gradient or any of the soil changes it encompassed; however, astringent phenolics increased by 275% over the same gradient. Trends in the chemical constituency of fine roots suggest that the production of phenolics in below-ground plant parts is increased on nutrient-poor sites. This response is best related to changes in species composition, especially increasing importancy of Quercus spp.

A simple, effective method for determining the bulk density of stony soils

Abstract A new technique of determining bulk density based upon the excavation method is especially useful in stony soils and surface mine spoils. The technique involves determining the volume of an excavated hole using an expanding urethane foam which solidifies to form a perfect cast of the hole. Volume of the cast is determined by water displacement. Comparison of this method with the sand method of volume determination in a surface mine spoil showed no difference in calculated values of bulk density. However, bulk densities determined by driving a steel core of known volume into the stony surface mine spoil were consistently 12–17% lower than those determined by excavation. The new technique may be applied to sloping soil surfaces and may be used for bulk density determinations at depth in the exposed vertical face of a soil pit.

Above-ground net primary productivity and nitrogen mineralization in a mixed mesophytic forest of eastern Kentucky

Abstract Above-ground net primary productivity (ANPP) and potential nitrogen (N) mineralization were measured in four forest types along a soil fertility gradient in eastern Kentucky to test the hypothesis that ANPP in the mixed mesophytic forest region is related to both species composition and mineralizable N. N mineralization differed significantly among the four forest types, with the lowest values occurring on sites containing oak forest and the highest rates occurring on sites containing a mixed mesophytic forest. However, ANPP did not differ among forest types, and was unrelated to mineralizable N. ANPP averaged 6306 kg ha −1 year −1 , of which 56% was woody production and 44% was above-ground litter production. The poor relationship between ANPP and site fertility may reflect differential patterns of nutrient use efficiency among the deciduous species which make up the vegetation gradients of eastern Kentucky.