David Greenland Douglas G Goodin

The timescale structure of this book has served well to keep the attention of investigators focused on specific aspects of climate variability and ecosystem response. Indeed, judging by the responses received by the editors of this volume, when given a choice between focusing on one timescale or several timescales, the LTER community was far more comfortable dealing with just one scale. There are obvious reasons for this, not the least of which is that focusing on a single scale greatly simplifies things. The real world, however, does not focus on one timescale. Climatic events and ecosystem responses occur simultaneously at a variety of scales. We wished to explore the climatic variability and ecosystem responses at LTER sites across several different timescales, and the two chapters in this part attempt such an exploration. The chapters consider the temperate rainforest of the H. J. Andrews LTER site in Oregon and the tallgrass ecosystem of the Konza Prairie LTER in Kansas.

For the Andrews rainforest, and to some extent the Pacific Northwest (PNW) in general, Greenland et al. (chapter 19) discuss climate variability and ecosystem response at the daily, multidecadal, and century to millennial scales. This discussion for the PNW is supplemented in chapters 6 and 13 of this volume by a consideration of the quasi-quintennial scale and an additional ecosystem response at the decadal scale. The forest ecosystem is more complex than the grassland ecosystem. Greenland et al. cover a wide variety of potential ecosystem responses for the PNW Forest, ranging from severe weather events, to pine cone production, to century- and millennial-scale forest fire frequency regimes and their variation. The focus of chapter 19 is on some of the framework questions of this volume. The questions specifically addressed include the following: What preexisting conditions affect the impact of the climatic event or episode? Is the climatic effect on the ecosystems di rect or cascading? Does the system return to its original state? The authors also consider potential future climate change and its possible ecosystem effects. They found that timescale becomes important in addressing some of these questions. For example, at century to millennial timescales, it is suggested that there are likely to be no identical past analogs to the ecosystem at any point in time. It is unlikely that an ecosystem will return to its "original" state at this longer timescale, and the concept of "original" state itself has little meaning.

In chapter 20, Goodin et al. examine how interannual, quasi-quintennial, and in-terdecadal variation in annual precipitation and mean annual temperature at a tall-grass prairie site (Konza Prairie Biological Station) may be related to various climatic indexes and phenomena. They examine solar activity, the El Nino-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the North Pacific Index (NP), as well as how these indexes may be related to aboveground net primary productivity (ANPP). The authors present (1) period-spectrum analyses to characterize the predominant timescales of temperature and precipitation variability at Konza Prairie; (2) correlation analyses between quantitative indices of the major atmospheric processes and Konza temperature and precipitation values; and (3) the implications of variation in major atmospheric processes for seasonal and interannual patterns of ANPP. The key finding of this analysis is that the historic temperature and precipitation record at Konza Prairie displays periodicities similar to those for ENSO, NAO, and NP. Periods of stronger NAO (i.e., larger positive index values) are associated with warmer winters, periods of stronger ENSO with wetter winters, and periods of stronger NP with warmer summers. The course of the growing season as represented by aboveground biomass accumulation appears to be limited initially by temperature, then later by soil moisture.

Goodin et al. find that the effects of variation in some climatic indexes are indirect, whereas others are direct, and this relates to the type of cascade of ecosystem responses that come into play. Their analysis shows that different periodicities of varying importance make up the total temporal variation in the values of the climate indexes. The different periodicities form part of a hierarchy of climate variation. Focusing on the degree to which these hierarchical periods of temperature and precipitation variability reinforce (or oppose) each other may shed more light on the regulation of variability of ANPP or other ecosystem characteristics than considering a single periodicity or time scale separately. In addition, although, grasslands are the simpler system (compared to forests), Goodin et al. suggest the grasslands are poised in a dynamic equilibrium that makes them especially sensitive to both biotic and abiotic disturbances, including climate variability.

Both of these chapters hint, in their different ways, at the multidisciplinary, mul-titimescale, and multidimensional considerations that will have to be confronted in future stages of LTER studies.

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