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This study presents a meta-analysis of a collective dataset describing the succession from abandoned fields to semi-natural
grassland and heathland vegetation over the past century. The study objectives were to develop a method for statistical discrimination
between abandoned fields and semi-natural habitats and to analyze the probability that an abandoned field had developed into
a semi-natural habitat. A statistical classification model was developed, based on lists of vascular plants from 2059 plots
from Danish semi-natural grasslands and heathlands, and abandoned fields of varying age. This model was shown to discriminate
effectively between abandoned fields and semi-natural habitats, and it was found to be potentially useful for the detection
of abandoned fields approaching semi-natural vegetation. We suggest that the model may help clarify restoration targets and
assess biological condition in formerly cultivated areas. Statistical modeling revealed that succession age, period of abandonment
and succession trajectory had significant effects on the probability that abandoned fields reached the semi-natural phase.
Our study indicates that restoration projects targeting grassland and heathland should take local species pools and soil fertility
into account.
Nomenclature: Species names follow Flora Europaea (Tutin and others 1964–1993). 相似文献
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Water, ash, C, H, N, lipid, carbohydrate, chitin and protein contents were determined for 28 species of midwater crustaceans. Variation of these components as a function of depth of occurrence, relative buouancy and respiratory rate of these species was examined. Vertical distribution data for 10 of the species based on discrete depth crawls is provided. The relative bouyancies of 16 of these species were measured. The caloric contents of 21 species were calculated. Lipid content (percent wet weight) and caloric density increased at intermediate depths, but apparently decreased at the greatest depths; it is suggested that this decrease is related to the relatively large size of these organisms and the energy limiting conditions in the deep-sea. Protein content (percent wet weight) decreases with increasing depth of occurrence, and is apparently related to a substantial fraction of the decrease in respiratory rate with increasing depth of occurrence in these species. Within the range of values examined, relative buoyancy appeas to be independent of metabolic rate. It is, therefore, suggested that the energy involved in maintaining an animal in the water column is generally insignificant compared to its overall activity. Furthermory, advantages of neutral buoyancy other than energy conservation may be more important selective factors for this characteristic. 相似文献
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De Wit Helene A. Mulder Jan Nygaard Per H. Aamlid Dan Huse Magne Kortnes Egil Wollebæk Gro Brean Roald 《Water, Air, & Soil Pollution: Focus》2001,1(1-2):103-118
Aluminium (Al) is a key element in critical loadcalculations for forest. Here, we argue for re-evaluating theimportance of Al. Effects of two levels of enhanced Alconcentrations and lowered Ca:Al ratios in the soil solutionin a field manipulation experiment in a mature spruce stand(1996–1999) on tree vitality parameters were tested. Inaddition, Al solubility controls were tested. Various loads ofAl were added to forest plots by means of an irrigationsystem. Potentially toxic Al concentrations and criticalratios of Ca to inorganic Al were established. The ratio of Cato total Al was not a suitable indicator for unfavourableconditions for plant growth. No significant effects on crowncondition, tree growth and fine root production were observedafter three years of treatment. In 1999, foliar Mg content inthe highest Al addition treatment had declined significantly.This agreed with the known response to Al stress of seedlingsin nutrient solution experiments. No support was found forusing the chemical criterion Ca:Al ratio in soil solution,foliar and root tissue as an indicator for forest damage dueto acidification. Al solubility was considerably lower thanimplied by the assumption of equilibrium with gibbsite,particularly in the root zone. The gibbsite equilibrium iscommonly used in critical load models. Substitution of thegibbsite equilibrium with an Al-organic matter complexationmodel to describe Al solubility in soil water may have largeconsequences for calculation of critical loads. The resultsindicate that critical load maps for forests should bereconsidered. 相似文献
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A new species has recently invaded coastal dune ecosystems in North West Europe. The native and expansive inland grass, Deschampsia flexuosa, progressively dominating inland heaths, has recently invaded coastal dunes in Denmark, occasionally even as a dominant species.
A total of 222 coastal locations with 5,000 random sample plots have been investigated. These findings are in contrast to
historical records, and D. flexuosa has never been considered belonging to coastal dune ecosystems. The occurrence of the typical inland grass in the coastal
dunes is a strong indication of increase in nutrient level and that human influences may cause a native species to be invasive
in new ecosystems. This could be a radical example of change in species composition due to a long lasting exceedance of critical
load of nitrogen. The investigation also showed a general increase in cover of the most dominant species. 相似文献
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