Response of North American ecosystem models to multi-annual periodicities in temperature and precipitation

Abstract

Ecosystem models typically use input temperature and precipitation data generated stochastically from weather station means and variances. Although the weather station data are based on measurements taken over a few decades, model simulations are usually on the order of centuries. Consequently, observed periodicities in temperature and precipitation at the continental scale that have been correlated with largescale forcings, such as ocean-atmosphere dynamics and lunar and sunspot cycles, are ignored. We investigated how these natural climatic fluctuations affect aboveground biomass in ecosystem models by incorporating some of the more pronounced continental-scale cycles in temperature (4, 11, 80, 180 year periods) and precipitation (11 and 19 year periods) into models of three North American forests (using LINKAGES) and one North American grassland (using STEPPE). Even without inclusion of periodicities in climate, long-term dynamics of these models were characterized by internal frequencies resulting from vegetation birth, growth and death processes. Our results indicate that long-term temperature cycles result in significantly lower predictions of forest biomass than observed in the control case for a forest on a biome transition (northern hardwoods/boreal forest). Lower-frequency, higher-amplitude temperature oscillation caused amplification of forest biomass response in forests containing hardwood species. Shortgrass prairie and boreal ecosystems, dominated by species with broad stress tolerance ranges, were relatively insensitive to climatic oscillations. Our results suggest periodicities in climate should be incorporated within long-term simulations of ecosystems with strong internal frequencies, particularly for systems on biome transitions.

Assessing potential impacts of climatic change on subalpine forests on the eastern Tibetan Plateau

“…Previous studies (Cohen and Pastor 1991;Yeakley et al 1994;Lasch et al 1998) examinated the effect on model behaviour of the measured interannual autocorrelation (serial correlation) of temperature and precipitation (i.e. climate variability on the time scale of years to decades and centuries) using a weather generator.…”

Overstory-Imposed Heterogeneity in Solar Radiation and Soil Moisture in a Semiarid Woodland

“…Semiarid ecosystems, shrublands and woodlands in particular, are highly sensitive to climate, as evident from biogeographical analyses (Stephenson 1990, Neilson et al 1992. The proportions of the two plant functional types depend not only on the magnitude of climatic inputs, but also on intraannual timing and interannual variations (Eagleson and Segarra 1985, Neilson 1986, Neilson et al 1992, Frank and Inouye 1994, Yeakley et al 1994. The sensitivity of the two plant functional types to climatic differences has been explained in terms of differing abilities to exploit vertical heterogeneity in soil moisture, which is determined largely by climate (Walter 1971).…”

Desired future conditions for pinon-juniper ecosystems

“…As a result, one finds a wide range of vegetation patterns and an accompanying large number of transitional zones between vegetation patterns. These zones (known as tension zones, or ecotones) are thought to be particularly sensitive to disturbance and to climatic fluctuations, including those resulting from an elevation in greenhouse gases (Gosz and Sharpe 1989, Yeakley et al 1994.…”