Storende elementen in het landschap: welke, waar en voor wie?

Dit onderzoek bouwt voort op twee publicatie van de WOT Natuur & Milieu: Verrommelt het platteland onder stedelijke druk? (Veeneklaas et al., 2004, Planbureaurapport 22) en Verrommeling in Nederland (Veeneklaas et al., 2006, WOt-rapport 6). Daar is gekeken welke elementen in het landschap potentieel storend zijn. Op basis van oordelen van deskundigen van Alterra werd geconcludeerd dat de storendheid van een element afhangt van het landschap waarin het staat. Het huidige onderzoek gaat verder: deelt de Nederlandse bevolking het oordeel van de deskundigen? Welke kenmerken van de landschappen zijn hierbij belangrijk? En verschillen elementen in de mate waarin ze storend worden gevonden? Kortom: Welke elementen, waar en voor wie zijn deze storend? Een element wordt als storend beschouwd, als het landschap zonder het element aantrekkelijker wordt gevonden dan hetzelfde landschap met dat element. Het gaat hierbij om empirisch onderbouwde uitspraken

Krassen op het landschap : over de beleving van storende elementen

Het onderzoek naar verrommeling is tot nu toe vooral gebaseerd op oordelen van deskundigen. Maar vinden gewone burgers ook dat Nederland een steeds rommeliger landschap krijgt? WOt-paper 1 doet verslag van een onderzoek waarin door middel van foto’s en interviews aan burgers is gevraagd of ook zij vinden dat het landschap verrommelt, en zo ja welke elementen zij dan als meest storend ervaren. Het blijkt onder andere dat mensen zich vooral ergeren aan de verstoring naarmate het landschap er om heen nog gaaf is. En ook: hoe verder weg de verstoring is, hoe minder storend deze is

Distance-independent individual tree diameter-increment model for Thya (Tetraclinis articulata (VAHL.) MAST.) stands in Tunisia

Aim of study: The aim of the work was to develop an individual tree diameter-increment model for Thuya (Tetraclinis articulata) in Tunisia. Area of study: The natural Tetraclinis articulata stands at Jbel Lattrech in north-eastern of Tunisia. Material and methods: Data came from 200 trees located in 50 sample plots. The diameter at age t and the diameter increment for the last five years obtained from cores taken at breast height were measured for each tree. Four difference equations derived from the base functions of Richards, Lundqvist, Hossfeld IV and Weibull were tested using the ageindependent formulations of the growth functions. Both numerical and graphical analyses were used to evaluate the performance of the candidate models. Main results: Based on the analysis, the age-independent difference equation derived from the base function Richards model was selected. Two of the three parameters (growth rate and shape parameter) of the retained model were related to site quality, represented by a Growth Index, stand density and the basal area in larger trees divided by diameter of the subject tree expressing the inter-tree competition. Research highlights: The proposed model can be useful for predicting the diameter growth of Tetraclinis articulata in Tunisia when age is not available or for trees growing in uneven-aged stands

Naar een steekproef landschap; ontwerp van een methode en pilotstudie

Kwantitatieve gegevens over de veranderingen in het landschap ontbreken vrijwel op nationaal niveau. Dit rapport beschrijft een methode om veranderingen in de graadmeter landschapswaarde te volgen. Het geeft inventarisatieprotocollen voor de variabelen ruimtegebruik, groen-blauwe dooradering, beheerstoestand kleine landschapselementen, informatiewaarde van terreinvormen en ontginningsgeschiedenis, en maat van de ruimte. De methode is ontwikkeld en getest in vier gebiedjes (Tilburg-Zuidwest, Zieuwent,Abcoude, Nisse)

A new classification and linear sequence of extant gymnosperms

A new classification and linear sequence of the gymnosperms based on previous molecular and morphological phylogenetic and other studies is presented. Currently accepted genera are listed for each family and arranged according to their (probable) phylogenetic position. A full synonymy is provided, and types are listed for accepted genera. An index to genera assists in easy access to synonymy and family placement of genera.Peer reviewe

Hydrophobia of gymnosperms: myth or reality? A global analysis

According to the classical textbooks, the gymnosperms are the only seed plants without aquatic species. Recently, however, a set of virtually complete compilations on gymnosperms has been published, enabling a new evaluation of the putative hydrophobia of gymnosperms. This synthesis aims at portraying the relation of all extant gymnosperm species to aquatic and wetland habitats. We present a database of all 986 extant gymnosperm species with their ecological characteristics including 291 cycads, 80 gnetophytes, one ginkgophyte and 614 conifers. We define four categories reflecting the level of hydrophobia and hydrophily of all species and their possible adaptation to wetlands and/or aquatic habitats. Eighty-two percent (805) of the extant species of gymnosperms are clearly hydrophobic, but 18% (180) are classified as hydrophilic. The podocarp Retrophyllum minus is the only obligate inhabitant of aquatic habitats. This contribution classifies gymnosperms into four categories in reference to their physiological and morphological adaptation to a moisture gradient. It relativizes the putative hydrophobia of gymnosperms and provides new perspectives for research on gymnosperms

Green Plants in the Red: A Baseline Global Assessment for the IUCN Sampled Red List Index for Plants

Plants provide fundamental support systems for life on Earth and are the basis for all terrestrial ecosystems; a decline in plant diversity will be detrimental to all other groups of organisms including humans. Decline in plant diversity has been hard to quantify, due to the huge numbers of known and yet to be discovered species and the lack of an adequate baseline assessment of extinction risk against which to track changes. The biodiversity of many remote parts of the world remains poorly known, and the rate of new assessments of extinction risk for individual plant species approximates the rate at which new plant species are described. Thus the question ‘How threatened are plants?’ is still very difficult to answer accurately. While completing assessments for each species of plant remains a distant prospect, by assessing a randomly selected sample of species the Sampled Red List Index for Plants gives, for the first time, an accurate view of how threatened plants are across the world. It represents the first key phase of ongoing efforts to monitor the status of the world’s plants. More than 20% of plant species assessed are threatened with extinction, and the habitat with the most threatened species is overwhelmingly tropical rain forest, where the greatest threat to plants is anthropogenic habitat conversion, for arable and livestock agriculture, and harvesting of natural resources. Gymnosperms (e.g. conifers and cycads) are the most threatened group, while a third of plant species included in this study have yet to receive an assessment or are so poorly known that we cannot yet ascertain whether they are threatened or not. This study provides a baseline assessment from which trends in the status of plant biodiversity can be measured and periodically reassessed

Fighting their last stand? A global analysis of the distribution and conservation status of gymnosperms

Aim: Gymnosperms are often described as a marginal and threatened group, members of which tend to be out-competed by angiosperms and which therefore preferentially persist at higher latitudes and elevations. The aim of our synthesis was to test these statements by investigating the global latitudinal and elevational distribution of gymnosperms, as well as their conservation status, using all extant gymnosperm groups (cycads, gnetophytes, ginkgophytes and conifers).Location: Worldwide.Methods: We developed a database of 1014 species of gymnosperms containing latitudinal and elevational distribution data, as well as their global conservation status, as described in the literature. The 1014 species comprised 305 cycads, 101 gnetophytes, the only living representative of ginkgophytes, and 607 conifers. Generalized additive models, frequency histograms, kernel density estimations and distribution maps based on Takhtajan's floristic regions were used.Results: Although the diversity of gymnosperms decreases at equatorial latitudes, approximately 50% of the extant species occur primarily between the tropics. More than 43% of gymnosperms can occur at very low elevations (≤ 200 m a.s.l.). Gymnosperms, considering all species together as well as their main taxonomic groups separately, do not exhibit a latitudinal diversity gradient as commonly observed for many other taxa. Gymnosperms, and especially conifers, are on average less threatened at higher and equatorial latitudes.Main conclusions: Gymnosperms display an unusual latitudinal diversity gradient, which we suggest cannot fully be accounted for by angiosperm dominance and competitive superiority. We hypothesize that other factors explain their present distribution, such as the development of centres of endemism in several regions and the adaptation of certain taxa to cold and arid climates

Bioactive Constituents of Juniperus turbinata Gussone from La Maddalena Archipelago

A comprehensive phytochemical study of Juniperus turbinata (Cupressaceae) collected from La Maddalena Archipelago (Sardinia, Italy) is reported. Both the essential oil and the ethanolic extract obtained from the aerial parts were analyzed. The essential oil appears to belong to a new chemotype compared to other Mediterranean juniper accessions, as it was favored by geographic isolation of the isles. It showed a low content of monoterpene hydrocarbons and a-terpineol, entmanoyl oxide, 1,10-di-epi-cubenol as the major constituents. The ethanolic fraction contained mainly diterpenoids. Among these, 15-formyloxyimbricatolic acid (7) is a new natural product since it has hitherto been obtained only by synthetic route. The phenolic fraction contained biflavonoids: cupressuflavone (9), followed by minor amounts of amentoflavone (10) and hinokiflavone (11). The essential oil and six purified compounds (1 – 4, 8 and 9) were assessed for biological activities, namely antioxidant (assessed by DPPH·, ABTS· + and FRAP methods) and cytotoxic effects towards selected human tumor cell lines (MDA-MB 231, A375 and HCT116 cells). Compound 3 exhibited higher radical scavenging activity against ABTS·+ radical than the reference Trolox. Noteworthy, compound 8 showed powerful effects towards tumor cell lines, with IC50 values in the range of 0.060 – 0.201 lM, which make it a promising anticancer drug candidate