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Syntactic characterization in Lisp of the polynomial complexity classes and hierarchy
Full text linkThe definition of a class C of functions is syntactic if membership to C can be decided from the construction of its elements. Syntactic
characterizations of PTIMEF, of PSPACEF, of the polynomial hierarchy PH, and of its subclasses Delta^p_n are presented. They are obtained by
progressive restrictions of recursion in Lisp, and may be regarded as predicative according to a foundational point raised by Leivant
A resource-free classification of the time-space complexity classes between Lintime and Expspace
No full textShort term effect of nitrogen enrichment, litter removal and cutting on a Mediterranean grassland
No full textEffetti dello sfalcio e della concimazione azotata sulle praterie secodarie: un esempio relativo all’Appennino centrale
No full textRestoration of species-rich Mediterranean calcareous grassland: the role of nitrogen enrichment, plant litter removal and cutting
No full textShort-term effects of nitrogen enrichment, litter removal and cutting on a Mediterranean grassland
No full textA B S T R A C T
Semi-natural grassland communities are of great interest in conservation because of their
high species richness. These communities are being threatened by both land abandonment and nitrogen eutrophication, and their continued existence will depend upon correct
management. However, there is a distinct lack of studies of the ecological mechanisms
that regulate species diversity and productivity in Mediterranean grasslands. We
have conducted a 3-year field experiment in a species-poor grassland in central Italy to
investigate the effects of nitrogen fertilization coupled with removal of plant litter and
artificial cutting on species diversity and community productivity. Vegetation cutting
reduced living biomass but increased species diversity. In fact, cutting had positive effects
on the cover of almost all of the annual and biennial species, while it had a negative
effect on the dominant perennial grasses Brachypodium rupestre and Dactylis glomerata. Litter
removal had similar effects to cutting, although it was far less effective in increasing
species diversity. In contrast, nitrogen enrichment strongly increased the living biomass
while maintaining very low species diversity. Our results have indicated that seminatural
Mediterranean grasslands need specific management regimes for maintenance
and restoration of species diversity. In the management of these grasslands, attention
should be paid to the potential threat from nitrogen enrichment, especially when coupled
with land abandonment
Effetti dello sfalcio e della concimazione azotata sulle praterie secondarie: un esempio relativo all'Appennino centrale
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