Glenn D. Mroz

Microclimate in Forest Ecosystem and Landscape Ecology

Microclimate is the suite of climatic conditions measured in localized areas near the earths surface (Geiger 1965). These environmental variables, which include temperature, light, windspeed, and moisture, have been critical throughout human history, providing meaningful indicators for habitat selection and other activities. For example, for 2600 years the Chinese have used localized seasonal changes in temperature and precipitation to schedule their agricultural activities. In seminal studies, Shirley (1929, 1945) emphasized microclimate as a determinant of ecological patterns in both plant and animal communities and a driver of such processes as the growth and mortality of organisms. The importance of microclimate in influencing ecological processes such as plant regeneration and growth, soil resperation and growth, soil repiration, nutrient cycling, and wildlife habitat selection has became an essential component of current ecological research (Perry 1994). plant regeneration and growth, soil respiration, nutrient cycling, and

Changes in microclimate after stand conversion in two northern hardwood stands

Abstract Changes in air temperature, soil temperature, and soil moisture were monitored for 5 years in two northern hardwood stands after whole-tree harvesting and conversion to red pine ( Pinus resinosa Ait.) plantations. Soil temperatures at a depth of 5 cm and maximum air temperatures 2 m above the soil surface were increased 5–25% after stand conversion. Soil moisture content at a depth of 5 cm was increased by 10–20% in one stand but not in the other. Differences in stand, soil, and topographical characteristics between the two stands did not have any apparent effect on the magnitude of air or soil temperature changes after stand conversion. However, higher initial stand density and soil water holding capacity appeared to be related to increased soil moisture content at one of the sites. The increased soil temperatures after conversion were not only a result of the removal of the northern hardwood canopy but also the removal and redistribution of the forest floor caused by whole-tree harvesting. Five years after stand conversion air temperature, soil temperature, and soil moisture showed no evidence of recovering from initial post-harvest levels.

A process-based growth model for young red pine

Abstract A carbon-balance, process-based growth model was developed to simulate the growth of young red pine ( Pinus resinosa Ait.). The dry weights of current, 1-year-old, 3-year-old needless, stems and branches, and roots of individual trees were considered as state variables. The hourly rate of photosynthesis was calculated with solar radiation, air temperature, leaf water potential, and leaf age as driving variables by assuming that the needles experience the same incident light density. Maintenance respiration rate was assumed to be a function of surrounding temperature. The seasonal allocation of assimilates to each compartment was determined by the activity of each compartment and was regulated by soilwater potential. The translocation of carbohydrate reserves, litter fall, and root turnover were incorporated in the model. The simulated results fit well with observed values from three plantations in the central Upper Peninsula of Michigan.

Seasonal shoot growth of planted red pine predicted from air temperature degree days and soil water potential

Abstract On-site climatic measurements were used to model red pine (Pinus resinosa Ait.) shoot elongation. Three study sites each consisting of three 0.2-ha plots were cleared and planted with red pine. Shoot growth was measured weekly for 2 years. Incremental seasonal growth of the leading shoot was estimated using a difference form of a modified Chapman-Richards growth function. Weekly growth was estimated as a function of air temperature degree days (4.4°C basis), soil water potential, and total expected seasonal growth. An example using the model compares varying site and climatic conditions and their effect on the pattern of seedling height growth during the growing season as well as their effect on the total amount of height growth realized at the end of the growing season.

Productivity and growth efficiency in sugar maple forests

Abstract Sugar maple ( Acer saccharum Marsh.)-dominated northern hardwood forests were examined at four locations along an acid deposition and climatic gradient in the Great Lakes region of the USA. The study sites were matched in terms of physiography, soils, stand history, and vegetative characteristics. Measurements of basal area and biomass growth were made for the 1988–1991 growing seasons. There were no significant differences in either basal area of biomass increment among the four sites over the 4 year period. There was a great deal of year-to-year variability with relative basal area growth rates ranging from as low as 0.2% to as high as 2.4% on a single site in successive years. Growth efficiency measures reflected this variability with as much as an 800% difference between successive years on a single site. When coupled with year-to-year variability of up to 34% in leaf area related to heavy seed years and defoliation, this indicates that growth efficiency and leaf area measures are not consistent indicators of aboveground productivity for tolerant deciduous species, especially if derived from short-term measurements or temporary plots.

Nutrient status of bracken (Pteridium aquilinum) following whole-tree harvesting in Upper Michigan

Abstract Mineral nutrient status and biomass production of bracken, Pteridium aquilinum (L.) Kuhn, fronds and rhizomes were quantified immediately following a whole-tree harvest in Upper Michigan. Multiple sampling occurred between full leaf expansion and senescence to monitor mineral translocation from the fronds to the rhizomes, as well as differences in bracken mineral content between harvested and unharvested control sites. Bracken rhizomes on the harvested site had significantly higher concentrations of phosphorus, potassium and magnesium than the control site. Frond biomass production was lower on the harvested site, while rhizome biomass production showed no differences between sites. Rhizome P contents were significantly higher on the harvested site. Translocation of mineral elements from the fronds to the rhizomes during senescence was monitored. Nitrogen, P, and K were readily translocated, while Mg and calcium were not. The larger amounts of nutrients present in the rhizomes on the harvested site suggest increased nutrient uptake and, therefore, nutrient conservation by bracken may occur on a harvested site.

RELATIONSHIPS BETWEEN SOLUBLE SUGAR CONCENTRATIONS IN ROOTS AND ECOSYSTEM STRESS FOR FIRST-YEAR SUGAR MAPLE SEEDLINGS

Accumulation of reducing sugars (i.e., glucose and fructose) in plant roots has been consistently correlated with forest dieback and decline and, therefore, has potential as a biological indicator of ecosystem stress. In this study, the relationships between acidic deposition and “natural” (temperature, mycorrhizae, and nutrition) factors with first-year sugar maple seedling root sugar concentrations and growth were assessed in two sugar maple dominated forests in Michigan. Seedlings at the southern site (Wellston) had greater root growth, phosphorus, total sugar, and sucrose concentrations in roots, but lower reducing sugar concentration in roots. In addition, percent root length colonized by vesicular-arbuscular mycorrhizal fungi was less than that found for seedlings growing at the northern site (Alberta). Throughfall deposition of nitrate, sulfate, and hydrogen ions was not significantly correlated with seedling total or reducing sugar concentration. Total sugar concentration in seedling roots was positively correlated with air and soil temperatures at the southern site, but not at the northern site. Seedling tissue phosphorus concentration was correlated with total sugars at both sites, with sucrose at the southern site, and reducing sugars at the northern site. Mycorrhizal colonization rates at the Alberta site were positively correlated with reducing sugar concentration in seedling roots and negatively correlated with sucrose concentration. The results suggest that differences in seedling root sugar concentrations in these two forests are related to seedling root growth and are most likely due to ecological variables, such as available soil phosphorus, temperature, and growing season length through some complex interaction with mycorrhizae rather than acidic deposition stress.

Effects of 76 Hz electromagnetic fields on forest ecosystems in northern Michigan: tree growth

Since 1984, the possible effects of extremely low-frequency electromagnetic (EM) fields generated by a 76 Hz communication antenna on the growth and productivity of four deciduous and one coniferous species have been studied in the Upper Peninsula of Michigan. Results from two research sites are discussed here: one site near an antenna element and a control site located 50 km from the communication system. Growth models for individual tree diameters were developed for northern red oak (Quercus rubra), paper birch (Betula papyrifera), aspen (Populus tremuloides with a few individuals ofP. grandidentata), and red maple (Acer rubrum). A growth model for individual tree height was developed for young red pine (Pinus resinosa). Average differences between the observed and predicted growth were calculated for each growing season and then compared between the study sites and across the study periods to evaluate changes in growth patterns which could be attributed to EM field effects. For aspen and red maple, the results showed a stimulation of diameter growth at magnetic flux density levels of 1 to 7 milliGauss; height growth of red pine was increased at about the same exposure levels. There are no clear indications of an EM field effect on total annual diameter growth for either of the other two species.

Impacts of annual weather conditions on forest productivity: a case study involving four North American deciduous tree species

The response of four northern deciduous tree species to annual climate variation is quantified at two intensively measured sites in northern Michigan, USA. Response to changes in temperature and moisture differ with the species and is dependent on other site conditions. Relationships identified in these field studies indicate that projected climate changes may have dramatic effects on the productivity of at least some commercially important tree species in the northern United States.

Soil Nitrogen mineralization under northern hardwood forests along a sulfate and nitrate deposition gradient in the Great Lakes region

Net N mineralization (ammonification and nitrification) in the 0–10 cm mineral soil zone of five northern hardwood forest sites along a gradient of SO42− and NO3− deposition from northeastern Minnesota to central lower Michigan was measured by anin situ buried bag technique at monthly intervals from September 1987 to April 1990. Soil nitrification rates (36.9 to 46.7 kg N · ha−1 · yr−1) increased from north to south among the five study sites and were strongly associated with soil temperature (r = 0.87,p < 0.001). The rates of soil ammonification (66.8 to 84.1 kg N · ha−1 · yr−1) and amounts of total N mineralized (103.7 to 130.6 kg N · ha−1 · yr−1) did not show a clear regional trend across the gradient sites. Significant correlations between SO42−(r = 0.82,p < 0.001), NO3−(r = 0.77,p = 0.003) deposition and the adjusted means of ammonium-N after removing the effects of soil temperature indicated that SO42− and NO3− deposition had significantly impacts on ammonification process. Soil pH did not correspond to the gradient of H+ deposition, which was not correlated with either ammonification or nitrification rates across the study sites.