Tree Growth as Affected by Soil Moisture Availability

Bassett, J.

doi:10.2136/sssaj1964.03615995002800030040x

Cited by 45 publications

(18 citation statements)

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“…(1) Two light response curves for shadeintolerant and shade-tolerant species are distinguished (Botkin et al 1972), and the response curve to be used is interpolated between these two extremes by taking into account the relative shade-tolerance class of the species (Ellenberg 1986), yielding the light growth factor gALGF c • (2) For the effect of the growing season temperature on tree growth, a parabolic relationship between the annual sum of degree-days (uDD) and tree growth (gDDGF s ) is assumed (Botkin et al 1972). (3) A square-root function (Bassett 1964) is used to relate drought stress (uDrStr) to tree growth (gSMGF s ) based on the species-specific drought tolerance, kDrT s • (4) Three asymptotic response curves (Aber et al 1979, Pastor andPost 1985) are used to modify maximum tree growth as a function of nitrogen availability (gSNGF s ), and each species is assigned one of these response curves. This formulation does not rely on the definition of an absolute site-specific, climate-dependent maximum biomass as required in earlier models such as FORECE (cf.…”

Section: Model Formulationmentioning

confidence: 99%

A Simplified Forest Model to Study Species Composition Along Climate Gradients

Bugmann¹

1996

Ecology

277

276

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Forest models based on the gap dynamics hypothesis (gap models) have gained an important role in forest ecology and have grown rather complex in the last 20 yr. They have been applied extensively to study the impacts of climatic change on ecosystems although they originally were not built for this purpose. The objectives of this study were (1) to develop a new forest gap model, ForClim, that includes only a minimum number of ecological assumptions but robust parameterizations of the effects of climate on plant population dynamics; (2) to test the realism of ForClim as compared to its predecessor model, FORECE; and (3) to examine the behavior of FORECE and ForClim systematically along climate gradients in Europe. ForClim is composed of three modular submodels: ForClim—P for plant population dynamics, ForClim—S for soil carbon/nitrogen turnover, and ForClim—E for providing reliable parameterizations of the abiotic environment. For the core model, ForClim—P, it was found that only four factors are sufficient to model tree growth, another four factors are required to model tree establishment, and only two factors are required to model tree mortality. The behavior of ForClim was tested at a large number of sites in the European Alps. The model yields tree species compositions that conform to field data and are very similar to those of the predecessor model. Based on this evaluation alone, it would not be possible to favor one of the models over the other. The behavior of both models then was examined systematically in a parameter space spanned by the annual mean temperature and the annual precipitation sum. From this exercise it became evident that both the pattern of aboveground biomass and the realized niches of the dominating tree species are simulated realistically by ForClim. Extremely steep gradients are characteristic of FORECE, and many ecotones are simulated to occur in the wrong places in FORECE. Thus, some of the current forest gap models can be simplified without reducing the realism of their behavior, and models other than FORECE should be scrutinized in this respect as well. The present study also suggests that the evaluation of model behavior at scattered sites is insufficient to show their validity for simulating forest dynamics along climate gradients. Further rigorous model comparisons and validation studies are required to increase the reliability of this promising class of models.

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Section: Model Formulationmentioning

confidence: 99%

A Simplified Forest Model to Study Species Composition Along Climate Gradients

Bugmann¹

1996

Ecology

277

276

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“…Water was applied when 40% of the available soil water was depleted from the upper 50 cm of the soil profile. The threshold of 40% was chosen because tree diameter growth is limited when soil water drops below this level (Bassett 1964). Irrigation was not applied from November 1993 to March 1994 because available soil water was above this threshold level.…”

Section: Study Site Characteristics and Study Designmentioning

confidence: 99%

Seasonal trends of light‐saturated net photosynthesis and stomatal conductance of loblolly pine trees grown in contrasting environments of nutrition, water and carbon dioxide

Murthy

Zarnoch

Dougherty³

1997

Plant Cell & Environment

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Repeated measures analysis was used to evaluate the effect of long-term COj enhancement on seasonal trends of lightsaturated rates of net photosynthesis (A^at) and stomatal conductance to water vapour {g^^^) of 9-year-old lohloUy pine {Pinus taeda L.) trees grown in a 2 x 2 factorial experimental design of nutrition and water. A significant interaction effect of CO2 and nutrition on mean Ag^t was observed for juvenile foliage. Also, juvenile foliage exposed to +350 /imol mor' CO2 had a higher rate of increase of A^at between late summer and early autumn. This would lead to a greater potential for recharging carbohydrate reserves for winter. Mature foliage was affected by CO2, water and nutrient treatments in two ways. First, A^^t was significantly increased as a result of elevated CO2 in January, a period when stomatal conductance was only 47% of the maximum observed rate. Secondly, the rate of increase of A^^t from winter to early spring was accelerated as a result of both nutrient + water and + 350 ^mol mol"' CO2 treatments. This accelerated response resulted in a greater potential for photosynthate production during the period when growth initiation occurred. Nutrient, water or carbon dioxide treatments did not significantly alter trends \ng^._^^ for mature or juvenile foliage. A significant nutrition x CO2 interaction was observed for the mature foliage, suggesting that g^.^î ncreased with increasing CO2 and nutrition. These results may have important consequences for the determination of the water use efficiency of loblolly pine. In spite of lowg^^^j in the winter to early spring period, there was a substantial gain in A^at attributable to elevated CO2 concentrations.

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“…Finally, based on experimental evidence by BASSETT (1964), the drought day growth factor gDS y,l,s used in FORCLIM-P is calculated by FORCLIM-W1 according to Eq. 18.…”

Section: Thornthwaite and Mather (1957)mentioning

confidence: 99%