A process-based model was used to estimate global patterns of net primary production and soil nitrogen cycling for contemporary climate conditions and current atmospheric CO2 concentration. Over half of the global annual net primary production was estimated to occur in the tropics, with most of the production attributable to tropical evergreen forest. The effects of CO2 doubling and associated climate changes were also explored. The responses in tropical and dry temperate ecosystems were dominated by CO2, but those in northern and moist temperate ecosystems reflected the effects of temperature on nitrogen availability.

Global climate change and terrestrial net primary production

This paper is the first global study of the extent to which fire determines global vegetation patterns by preventing ecosystems from achieving the potential height, biomass and dominant functional types expected under the ambient climate (climate potential). To determine climate potential, we simulated vegetation without fire using a dynamic global-vegetation model. Model results were tested against fire exclusion studies from different parts of the world. Simulated dominant growth forms and tree cover were compared with satellite-derived land- and tree-cover maps. Simulations were generally consistent with results of fire exclusion studies in southern Africa and elsewhere. Comparison of global 'fire off' simulations with landcover and treecover maps show that vast areas of humid C(4) grasslands and savannas, especially in South America and Africa, have the climate potential to form forests. These are the most frequently burnt ecosystems in the world. Without fire, closed forests would double from 27% to 56% of vegetated grid cells, mostly at the expense of C(4) plants but also of C(3) shrubs and grasses in cooler climates. C(4) grasses began spreading 6-8 Ma, long before human influence on fire regimes. Our results suggest that fire was a major factor in their spread into forested regions, splitting biotas into fire tolerant and intolerant taxa.

/pdf/the-global-distribution-of-ecosystems-in-a-world-without-1aq6mksi7x.pdf

The global distribution of ecosystems in a world without fire

Polyploidy is a prominent process in plants and has been significant in the evolutionary history of vertebrates and other eukaryotes. In plants, interdisciplinary approaches combining phylogenetic and molecular genetic perspectives have enhanced our awareness of the myriad genetic interactions made possible by polyploidy. Here, processes and mechanisms of gene and genome evolution in polyploids are reviewed. Genes duplicated by polyploidy may retain their original or similar function, undergo diversification in protein function or regulation, or one copy may become silenced through mutational or epigenetic means. Duplicated genes also may interact through inter-locus recombination, gene conversion, or concerted evolution. Recent experiments have illuminated important processes in polyploids that operate above the organizational level of duplicated genes. These include inter-genomic chromosomal exchanges, saltational, non-Mendelian genomic evolution in nascent polyploids, inter-genomic invasion, and cytonuclear stabilization. Notwithstanding many recent insights, much remains to be learned about many aspects of polyploid evolution, including: the role of transposable elements in structural and regulatory gene evolution; processes and significance of epigenetic silencing; underlying controls of chromosome pairing; mechanisms and functional significance of rapid genome changes; cytonuclear accommodation; and coordination of regulatory factors contributed by two, sometimes divergent progenitor genomes. Continued application of molecular genetic approaches to questions of polyploid genome evolution holds promise for producing lasting insight into processes by which novel genotypes are generated and ultimately into how polyploidy facilitates evolution and adaptation.

/pdf/genome-evolution-in-polyploids-eeag8xqgqu.pdf

Genome evolution in polyploids

Data from the advanced very-high-resolution radiometer sensor on the National Oceanic and Atmospheric Administration's operational series of meteorological satellites were used to classify land cover and monitor vegetation dynamics for Africa over a 19-month period There was a correspondence between seasonal variations in the density and extent of green-leaf vegetation and the patterns of rainfall associated with the movement of the Intertropical Convergence Zone Regional variations, such as the 1983 drought in the Sahel of westem Africa, were observed Integration of the weekly satellite data with respect to time for a 12-month period produced a remotely sensed estimate of primary production based upon the density and duration of green-leaf biomass Eight of the 21-day composited data sets covering an 11-month period were used to produce a general land-cover classification that corresponded well with those of existing maps

https://science.sciencemag.org/content/sci/227/4685/369.full.pdf

African land-cover classification using satellite data.

Handbook of LEGUMES of World Economic Importance

The Vegetation of Africa

The vegetation of Africa.

The vegetation of the highest mountains in tropical Africa is so different from that of the surrounding ‘lowlands’* that it has attracted the attention of travellers and scientists since the earliest days of botanical exploration. Even to the layman, it is familiar because of the unusual growth-forms of its giant lobelias and senecios. In recent years the flora and vegetation of these high peaks have been regarded by specialists (Hauman 1955, Hedberg 1965) as sufficiently distinct to justify the recognition of a separate phytogeographical ‘Afroalpine’ Region.

The Afromontane Region

ummary
The Afromontane floristic region is briefly described and examples of its complex biogeographical and evolutionary relationships are given. The origin of disjunctions of the Afromontane flora remains a matter of controversy but current hypotheses based on biogeographic and stratigraphic evidence are examined; the former are found to require some modification while the latter tend to be discordant with the facts. Evidence is presented which indicates a relatively recent southern migratory track between the mountains of East and West Africa, at least for forest trees. The implications for conservation and research arising from the complexity of the Afromontane flora and its outstanding scientific interest are discussed.

Resume
La region floristique d'Afromontagne est brievement decrite et des exemples de ses relations biogeographiques et evolutives sont donnees. L'origine de disjonction dans la flore d'Afromontagne reste une matiere controversee mais des hypotheeses basees sur des donnees biogeographiques et stratigraphiques sont examinees; les premieres requierent quelques modifications alors que les secondes semblent discordantes avec les faits. Certaines evidences indiquent une voie de migration vers le Sud relativement recente entre les montagnes d'Afrique de 1'Est et de I'Ouest, tout au moins pour les arbres forestiers. Les implications pour la conservation et la recherche dues e la complexite de la flore d'Afromontagne et l'interet scientifique qui en decoule sont discutes.

F. White

Papers

The Vegetation of Africa

The vegetation of Africa.

The Afromontane Region

The history of the Afromontane archipelago and the scientific need for its conservation

The evergreen forests of Malawi