The response of terrestrial vegetation to a globally changing environment is central to predictions of future levels of atmospheric carbon dioxide. The role of tropical forests is critical because they are carbon-dense and highly productive. Inventory plots across Amazonia show that old-growth forests have increased in carbon storage over recent decades, but the response of one-third of the world's tropical forests in Africa is largely unknown owing to an absence of spatially extensive observation networks. Here we report data from a ten-country network of long-term monitoring plots in African tropical forests. We find that across 79 plots (163 ha) above-ground carbon storage in live trees increased by 0.63 Mg C ha(-1) yr(-1) between 1968 and 2007 (95% confidence interval (CI), 0.22-0.94; mean interval, 1987-96). Extrapolation to unmeasured forest components (live roots, small trees, necromass) and scaling to the continent implies a total increase in carbon storage in African tropical forest trees of 0.34 Pg C yr(-1) (CI, 0.15-0.43). These reported changes in carbon storage are similar to those reported for Amazonian forests per unit area, providing evidence that increasing carbon storage in old-growth forests is a pan-tropical phenomenon. Indeed, combining all standardized inventory data from this study and from tropical America and Asia together yields a comparable figure of 0.49 Mg C ha(-1) yr(-1) (n = 156; 562 ha; CI, 0.29-0.66; mean interval, 1987-97). This indicates a carbon sink of 1.3 Pg C yr(-1) (CI, 0.8-1.6) across all tropical forests during recent decades. Taxon-specific analyses of African inventory and other data suggest that widespread changes in resource availability, such as increasing atmospheric carbon dioxide concentrations, may be the cause of the increase in carbon stocks, as some theory and models predict.

Three new naphthylisoquinoline alkaloids, the 7,3'-coupled ancistrotanzanine C (6), the 5,1'-coupled O-methylancistrocladinine (7), and the likewise 5,1'-coupled O,N-dimethylancistrocladine (8, previously known only as a partial-synthetic compound), have been isolated from the highland liana Ancistrocladus tanzaniensis, along with the two known 7,3'-coupled naphthylisoquinoline alkaloids ancistrocladidine (4) and ancistrotectorine (5). All of the compounds are S-configured at C-3 and bear an oxygen at C-6, and thus belong to the so-called Ancistrocladaceae type, similar to 1-3 previously isolated from this newly discovered plant species. The structural elucidation was achieved by chemical, spectroscopic, and chiroptical methods. The biological activities of the alkaloids against the pathogens causing malaria tropica, leishmaniasis, Chagas' disease, and African sleeping sickness were evaluated.

Forest fragmentation may have positive or negative effects on tropical tree populations. Our earlier study of an endemic African tree, Leptonychia usambarensis (Sterculiaceae), in the East Usambara Mountains of Tanzania, found poorer recruitment of seedlings and juveniles in small fragments compared to continuous forest, and concomitant reduction of seed-dispersal agents and seed dispersal. However, the possibility that other biotic or abiotic consequences of the fragmentation process contribute to diminished recruitment in fragments was left open. Here we test whether excessive seed predation, diminished fecundity, low seed quality, or adverse abiotic effects acted independently or in concert with reduced seed dispersal to limit seedling and juvenile recruitment in fragments. Extended observations of disperser activity, a seed placement experiment, seed predator censuses, and reciprocal seedling transplants from forest and fragment sources failed to support the alternative hypotheses for poorer seedling and juvenile recruitment in fragments, leaving reduced seed dispersal as the most plausible mechanism. Poorer recruitment of this species in forest fragments, where high edge-to-area ratios admit more light than in continuous forest, is particularly striking because the tree is an early successional species that might be expected to thrive in disturbed microhabitats.

The first phytochemical investigation of the recently discovered East African liana Ancistrocladus tanzaniensis is described, resulting in the isolation and structural elucidation of two new naphthylisoquinoline alkaloids, ancistrotanzanines A (5) and B (6), and the known compound ancistrotectoriline A (7). Ancistrotazanine A (5) represents a hitherto unprecedented 5,3'-coupling type between the naphthalene and isoquinoline portions, while 6 and 7 are 5,8'-coupled. The structures of the compounds were determined by spectroscopic, chemical, and chiroptical methods. Compounds 5 and 6 showed good activities against the pathogens of leishmaniasis and Chagas' disease, Leishmania donovani and Trypanosoma cruzi, while 5-7 displayed moderately potent antiplasmodial activities against Plasmodium falciparum parasites.