17 research outputs found
Infrageneric Relationships and the Origin of the Hawaiian Endemic Genus Lipochaeta (Compositae)
Infrageneric relationships of Lipochaeta were assessed by way
of a controlled crossing program that produced 14 intrasectional and 5
intersectional hybrid combinations involving the two sections Aphanopappus
and Lipochaeta. Results from uniform culture and hybridization studies
confirm that specific differences involving many traits such as leaf shape, the
number of disk floret lobes, and achene morphology have a genetic basis.
Fertility data based on pollen stainability and achene set of some of the
hybrids revealed that members of the same section are highly interfertile,
whereas the two sections are extremely well isolated from each other reproductively.
Cytogenetic evidence suggests that this isolation is due primarily to
a difference in the ploidy level of the two sections and that section Lipochaeta,
with n = 26, has an allopolyploid origin from a IS-paired taxon similar to a
diploid Lipochaeta and an unknown II-paired taxon in the extra-Hawaiian
genus Wedelia. Chromosome counts for three diploid species and one tetraploid
variety are reported for the first time
Patterns of Loss and Regeneration of Tropical Dry Forest in Madagascar: The Social Institutional Context
Loss of tropical forests and changes in land-use/land-cover are of growing concern worldwide. Although knowledge exists about the institutional context in which tropical forest loss is embedded, little is known about the role of social institutions in influencing regeneration of tropical forests. In the present study we used Landsat images from southern Madagascar from three different years (1984, 1993 and 2000) and covering 5500 km(2), and made a time-series analysis of three distinct large-scale patterns: 1) loss of forest cover, 2) increased forest cover, and 3) stable forest cover. Institutional characteristics underlying these three patterns were analyzed, testing the hypothesis that forest cover change is a function of strength and enforcement of local social institutions. The results showed a minor decrease of 7% total forest cover in the study area during the whole period 1984â2000, but an overall net increase of 4% during the period 1993â2000. The highest loss of forest cover occurred in a low human population density area with long distances to markets, while a stable forest cover occurred in the area with highest population density and good market access. Analyses of institutions revealed that loss of forest cover occurred mainly in areas characterized by insecure property rights, while areas with well-defined property rights showed either regenerating or stable forest cover. The results thus corroborate our hypothesis. The large-scale spontaneous regeneration dominated by native endemic species appears to be a result of a combination of changes in precipitation, migration and decreased human population and livestock grazing pressure, but under conditions of maintained and well-defined property rights. Our study emphasizes the large capacity of a semi-arid system to spontaneously regenerate, triggered by decreased pressures, but where existing social institutions mitigate other drivers of deforestation and alternative land-use
Chromosome Numbers of Madagascar Plants
Volume: 74Start Page: 123End Page: 12
Conservation of Madagascarâs granite outcrop orchids: the influence of fire and moisture
Quelle est la reÌponse aux perturbations, et la limitation de lâhumiditeÌ, par des taxons similaires baseÌs sur lâheÌteÌrogeÌneÌiteÌ des micro-site de lâhabitat? Pour cette eÌtude nous avons examineÌ comment la disponibiliteÌ de feu et de lâhumiditeÌ influence la reÌpartition des orchideÌes endeÌmiques malgaches speÌcifique des affleurements de granit (inselbergs). Trois ans apreÌs le passage du feu, nous avons compare les modes de distribution et lâabondance dâorchideÌes dans un habitat dâune mosaiÌque complexe de bruÌlures, en tenant compte de la densiteÌ par rapport aÌ lâintensiteÌ des deÌgaÌts dâincendie et de la disponibiliteÌ de lâhumiditeÌ. Les espeÌces du sous- tribu Angraecinae ont eÌteÌ sensibles au feu, mais toleÌrant aÌ une disponibiliteÌ limiteÌe de lâhumiditeÌ. orchideÌes Angraecinae avait un modeÌle uniforme de la distribution influenceÌe par la taille du tapis de veÌgeÌtation. Les espeÌces de la sous-tribu Habenariae eÌtaient toleÌrants de feu, mais limiteÌe aux pentes rocheuses humides par des eÌcoulements dâeau. Habenariae ont eÌteÌ randomizes regroupeÌs en masses compactes, influenceÌe par des facteurs non encore identifieÌs. Les reÌsultats suggeÌrent lâexistence de diffeÌrentes strateÌgies de survie des espeÌces. Il serait inexact de penser que les orchideÌes voisins sur un substrat de granite aurait la meÌme reÌponse aÌ des facteurs environnementaux ou de perturbation. orchideÌes Angraecoid sur les inselbergs sont exposeÌs aÌ des menaces speÌcifiques et doivent eÌtre consideÌreÌes comme des espeÌces indicatrices de la conservation est prioritaire aÌ lâavenir. Is there a difference in response to disturbance, or resource limitation, by similar taxa based on micro-site habitat heterogeneity? For this study we examined how fire and moisture availability influences the distribution of terrestrial and lithophytic orchids specific to Madagascarâs granite outcrops (inselbergs). We compared orchid density in an area with a complex mosaic of burned and non-burned vegetation patches (three years after the event). Lithophytic species (subtribe Angraecinae) were sensitive to fire, but tolerant of limited moisture availability, and had a uniform distribution pattern associated with vegetation mat size. In contrast, most terrestrial species (subtribe Habenariinae) were not impacted by fire, but were limited to slopes with high water seepage, and had a clumped distribution pattern. The results suggest varying ecological niches between orchid subtribes, and among species, occurring on shared substrate. Within the larger area, we also compared three inselbergs with different fire disturbance history. One site with potential for lightning based fires, but absence of anthropogenic fires, had the greatest diversity (subtribes, genera, and species) of orchids and the highest occurrence of species restricted to a single site. For land management purposes it is inappropriate to assume that inselberg specific orchids will have the same response to environmental stressors. Angraecinae orchids are especially at risk from human associated fire disturbance and should be regarded as indicators for future conservation efforts.
Figure 1
<p>The Androy region is situated in the southernmost part of Madagascar between Lat 24°13âČ and 25°24âČS and Long 45°20âČ and 46°26âČ E. Four areas (IâIV) were selected for detailed field investigations. Yellow squares with numbers indicate plots used in ground truthing.</p
Figure 2
<p>Pictures from the four surveyed areas a) degraded/thinned forest (Area I), b) regenerating forest (Area II), c) stable forest (Area III), d) forest patch protected by local taboos (Area IV). Pictures taken in January 2005.</p
Figure 4
<p>In the NDVI analysis (Normalised Difference Vegetative Index), the dense mature forests show multiple peaks due to differences in species composition, the regenerating forest is separated with lower NDVI values, while degraded forest and open land has distinctly different patterns. The examples given here are subsets (1.5Ă1.5 km) from the 2000 Landsat 7ETM+image.</p