Edward J. Rykiel

A model comparison for daylength as a function of latitude and day of year

A model that calculates the length of the day for a flat surface for a given latitude and day of the year is described. Calculated daylengths are within 1 minute of values published in Smithsonian Meteorological Tables and the Astronomical Almanac for latitudes between 40 ° North and South with a maximum error of 7 minutes occurring at 60 ° latitude. The model allows the use of different definitions of sunrise/sunset and the incorporation of twilight. Comparisons with other daylength models indicate that this model is more accurate and that variation in accumulated hours of daylight of up to one week over the course of the growing season can be accounted for by how sunrise/sunset are defined.

Ozone alters carbon allocation in loblolly pine: assessment with carbon-11 labeling.

Loblolly pine (Pinus taeda L.) seedlings were exposed to 0.120 micromol mol(-1) (ppm) ozone for 7 h per day, 5 days per week for 12 weeks. No visible damage resulted from this regime. A short-lived radioisotope of carbon ((11)C) was used to characterize changes in plant physiology caused by ozone, the first time this technique has been used for ozone exposure studies. In comparison to plants kept in charcoal-filtered air, pines exposed to ozone exhibited reductions in photosynthesis (16%), speed of phloem transport (11%), phloem photosynthate concentration (40%) and total carbon transport toward roots (45%). Photosynthate not transported to the roots appeared to accumulate in the stems. Primary branches of pines exposed to ozone were some 50-60% heavier than those of control pines. Ozone was thus shown to have a significant short-term impact on phloem transport processes that results in a shift in allocation of photosynthate favoring stems.

An integrated rate methodology (IRM) for multi-factor growth rate modelling

Abstract The integrated rate methodology (IRM) is a method for calculating a plant growth index to estimate the effective relative growth rate from a potential relative growth rate. IRM is a procedure for constructing a single growth multiplier equation that integrates multiple environmental factors affecting plant growth into a number between zero and one. The method can be used to simulate growth dynamically. The IRM framework can be used for both qualitative and quantitative modelling where the growth rate of a given entity or quantity is relevant. There are many applications in biological, economic and engineering areas. Here we develop the methodology in the context of plant growth modelling. We show how to treat multiple factors and how to include interactions. The methodology strikes a compromise between simplicity and complexity for the problem and data at hand, and can easily be used as a component of larger models.

Comparison of Markovian matrix models of a primary successional plant community

Abstract Markov matrix models have been used to simulate a variety of dynamic ecological systems such as communities and landscapes. An important question is whether time-homogeneous Markov models are adequate for successional dynamics or whether non-homogeneous models are needed to reflect changes in species composition over time. We evaluate some alternative Markov model formulations, ranging from homogeneous to semi-homogeneous, to see which might be useful in replicating observed vegetation dynamics in a primary successional plant community at Mount St. Helens, Washington. We used a two-step multivariate process to classify vegetation in 1×1 m quadrats in a 12×14 m study plot which was surveyed annually from 1983 to 1994. Four different Markov models were derived to simulate successional dynamics at the quadrat level, ranging from a completely time-homogeneous model based on quadrat class transitions pooled across all survey years, to one with annual constraints on classes allowed and with annually-adjusted transition probabilities based on these allowed classes. Although none of these models were particularly successful in replicating the observed number of vegetation classes or the number of quadrats in each class across all the survey years, the models with more annual constraints produced better results than the completely homogeneous model. The generally poor showing of these models relates primarily to annual variations in species dynamics in this community. The substantial turnover in species each year results in rapid turnover of vegetation classes, so that transitions among classes vary greatly from year to year. It appears that annual influences, both biotic and abiotic, must be implemented in the models for accurate simulations in this and probably most other primary successional communities.

A Knowledge System Environment for Ecosystem Management

Ecosystem management is a collective term used to embrace a philosophy and set of methodologies associated with land-use manipulation or modification (Grumbine 1994; Kaufmann et al. 1995; Sedjo 1995; Lackey 1996). Broad-based issues dealt with under the umbrella of ecosystem management include biodiversity (Wilson 1992; Groombridge 1995; Heywood and Watson 1995), sustainability of ecological systems (Lubchenco et al. 1991; Risser et al. 1991; Covington and DeBano 1993; Levin 1993; Bormann et al. 1994a), maintenance of ecosystem health (Costanza et al. 1993; USDA Forest Service 1996), preservation of ecosystem integrity (Monnig and Byler 1992; Woodley et al. 1993). conservation and stewardship (Sample 1991; Callicott 1994; Alpert 1995), public participation (Wondolleck 1988; Knopp and Caldbeck 1990; Loikkanen 1995), and landscape management (Lucas 1991; Diaz and Apostol 1993; Urban 1993; Boyce 1995; Forman 1995a, 1995b).