Elizabeth A. Jones

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.

Models of potential height and diameter for Eucalyptus globulus in Portugal

When modeling tree dimensions, it is common in many forest growth models to first predict the potential diameter or height in the absence of resource limitation, and then to modify this downward using functions reflecting the impact of various limiting resources on growth. Most of these models, however, were not parameterized using observations of true potential growth. This study utilizes data from a field trial of Eucalyptus globulus in central Portugal to parameterize models of potential height and diameter of E. globulus in the absence of growth reduction due to moisture or nutrient limitation. The resulting models represent tree height and diameter as functions of a single variable, the growing degree days (5 °C basis) accumulated since the date of planting.

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.

Nitrogenase activity associated with decayed wood of living northern Idaho conifers

Nitrogen fixation, as determined by the acetylene reduction technique, was demonstrated in decay columns of western larch and western white pine caused by Phellinus pini, western red cedar caused by Postia sericeomollis, and western hemlock and grand fir caused by Echinodontium tinctorium. Nitrogenase activity varied with tree species, fungal pathogen, wood decay stage, and seasonal moisturetemperature regimes within decaying stems. Nitrogen fixation potential in the productive forest eco? systems of northern Idaho was calculated between 0.06 kg/ha/yr and 4.91 kg/ha/yr and was primarily dependent on volume of decay in live standing trees on site.

Ecological implications of projected climate change scenarios in forest ecosystems of central North America

Climate change scenarios in central North America were projected for selected weather stations using a stochastic daily weather simulation model. The projections were conditioned on changes in seasonal temperature and precipitation as predicted by several global climate models. The impacts of these projected changes on temperate forest ecosystems were evaluated through projected changes in such variables as average annual temperature, average growing season temperature, and the ratio of potential evaporation to precipitation during July and August. Even the mildest climate change scenario examined indicated that ecologically significant changes could occur in the composition and productivity of these forests. The possibility also exists that climatically induced regional decline episodes for a number of important commercial species could occur in the northern temperate forests of central North America.

Evaluating forest stress factors using various forest growth modeling approaches

Abstract This paper examines in detail the relative merits of several modeling approaches to evaluating forest site, physical, chemical and climatic stresses. The modeling approaches considered are (i) empirical growth and yield (management) models (STEMS and FOREST); (ii) successional models (JABOWA/FORET gap-phase simulation models and FORSKA); (iii) forest process models (FOREST-BGC). The models were analyzed in terms of their assumptions, formulation, and predictive ability. The analysis incorporated intensive measurements of tree growth and weather conditions taken over 7 years in two stands of northern hardwoods located in Upper Michigan (USA). The process model was very detailed and required many input variables. All models performed poorly when pridictions were compared with the observed data making accurate site-specific predictions impossible without local calibrations.

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.

Modeling diameter growth in local populations: a case study involving four North American deciduous species

Abstract Many existing models representing the growth of forest overstory species as a function of environmental conditions make a number of assumptions which are inappropriate when applied to local populations. For example, maximum tree diameter and height are often assumed to be constant limiting factors for a given species even though growth functions can often be localized by utilizing information in the forest growth and yield literature to make site-specific estimates of these values. Most existing models also use an annual timestep which may be inappropriate when attempting to model the growth response of individual trees to environmental conditions. In this study, a model utilizing a weekly timestep is described and applied to four widespread North American deciduous tree species. Because response to environmental conditions can vary regionally as a result of genetic heterogeneity, the resulting model should not be considered as universally appropriate for these species. This study illustrates methods which can be utilized to develop models for application to local populations.