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The objective of the study was to characterize annual ryegrass seed population dynamics, managed for natural re-sowing, in no til systems in rotation with soybean, in different chronosequences An area was cultivated for two years with soybean, left as fallow land for the next two years and then cultivated again with soybean for the next two years. The four chronosequences represented different management periods, two with soybean (6 and 8 years old) and the other two resting (3 and 9 years old). Soil samples were taken every month during one year and divided into two depths (0-5 and 5-10 cm). Vegetation dynamics were also evaluated (number of plants, inflorescences and seedlings). Soil seed bank (SSB) dynamics showed structural patterns in time, with a "storage period" in summer, an "exhausting period" during autumn and a "transition period" in winter and spring. Pasture establishment by natural re-sowing was totally dependent on the annual recruitment of seeds from the soil. The influence of the management practices on the SSB was more important than the number of years that these practices had been implemented. Places where soybean was sown showed the largest SSBs. Most of the seeds overcame dormancy and germinated at the end of the summer and beginning of the autumn, showing a typically transitory SSB, but with a small proportion of persistent seeds O estudo objetivou a caracterização da dinâmica de populações de sementes de azevem anual em manejo de revegetação, em um sistema de plantio direto em rotação com soja, em diferentes seqüências. A soja foi cultivada por dois anos e cultivada novamente depois de dois anos de pousio. As quatro seqüências representaram diferentes períodos de manejo, dois deles com soja (6 e 8 anos) e os outros dois restantes (3 e 9 anos). Amostras de solos foram tomadas a cada mês, durante um ano, em duas profundidades (0-5 e 5-10 cm). A dinâmica de vegetação foi também avaliada (numero de plantas, inflorescências e plântulas). A dinâmica do banco de sementes do solo (SSB) mostrou padrão estrutural no tempo, com um período de armazenamento no verão, um período de exaustão durante o outono e um período de transição no inverno e primavera. O estabelecimento de pastagem por revegetação natural 'e' totalmente dependente do banco de sementes do solo. A influência das praticas de manejo no SSB e mais importante do que o numero de anos que estas praticas tem sido implementadas. Locais onde a soja foi cultivada mostraram maior SSB. A maior parte das sementes teve sua dormência quebrada e germinaram no final do período de verão e começo do outono, mostrando um típico SSB transitório, mas com pequena proporção de sementes persistentes.

Summary Digitaria sanguinalis, Eleusine indica, Setaria glauca and S. viridis are troublesome summer annual weeds in turf. For taking rational decisions on the necessity for the level and type of weed management, it is important to know when weeds are ready to emerge (dormancy status) and also how long weed seeds can survive in the soil. Seeds of these four species were buried 4.0–4.5 cm deep in steel mesh net bags placed under permanent turf and periodically exhumed for 3 years to evaluate viability and determine the dormancy/non-dormancy cycle. D. sanguinalis, S. glauca and S. viridis showed the typical dormancy cycle of summer annual species, and their seed viability declined completely after 3 years of burial. In contrast, E. indica demonstrated unusual behaviour, with long persistence and no dormancy.

The seed germination characteristics of three threatened Festuca sp. [F. punctoria Sm., F. cyllenica Boiss. et Heldr. subsp. uluana Markgr.-Dannenb., F. paphlagonica (St.-Yves) Markgr.-Dannenb. subsp. paphlagonica] were investigated. These species are endemic and spread on alpine belt. The study was carried out with wet-cold and dry-cold stratification throughout 15 days, different doses of GA3 (50, 100 and 150 ppm) and hormone-stratification combined treatments, and non-treatment series. We found that the germination rates of three fescue seeds for various treatment series were different. The mean germination percentage of F. cyllenica was higher (80%) than that of F. punctoria and F. paphlagonica which were fairly low (50-60%). Germination rates increased by wet-stratification treatment in F. punctoria and also increased with 100 ppm GA3 application to the seeds of F. paphlagonica. When taken into consideration the germination percentages of all fescue species, the seeds of F. punctoria and F. paphlagonica can be dormant, but the seeds of F. cyllenica are non-dormant.

Church forests are sanctuaries for different organisms, ranging from microbes to large animals, which have almost disappeared in most parts of northern Ethiopia. Despite the actual and potential significance of these forests, studies and documented information on their bio-physical features and socio-economic setting are either scanty or totally lacking. A study was, therefore, carried out in seven of these church forests, namely Hiruy, Zahara, Gibtsawit, Gelawdiwos, Dengolt, Debresena and Ascha with the objective of assessing the composition, densities and spatial heterogeneity of soil seed banks. The number of viable seeds in the soil samples, from both germination and sieving, corresponded to a seed bank density down to 9 cm in the soil of 7594 seeds m −2 at Ascha, 2064 seeds m −2 at Debresena, 4208 seeds m −2 at Dengolt, 3158 seeds m −2 at Gelawdiwos, 2754 seeds m −2 at Gibtsawit, 2759 seeds m −2 at Hiruy, and 1909 seeds m −2 at Zahra. The total number of species recorded was 50, representing at least 22 plant families, in the seven church forests, of which 13 were recorded from Ascha, 29 from Debresena, 26 from Dengolt, 19 from Gibtsawit, 22 from Gelawdiwos, 20 from Hiruy and 21 from Zahra. There was a significant difference in seed densities and number of species recovered from the soil seed banks of the seven church forests. Ascha had a significantly higher seed bank density than all other church forests. Dengolt exhibited a significantly higher number of species compared with other church forests. Of the identified species recorded from the seven church forests, 83% were herbs, 11% trees and 6% shrubs. Our results revealed that church forests accumulate large quantities of persistent seeds of herbaceous species in the soil while only five (6%) of the 91 woody species recorded in the standing vegetation of the seven church forests were represented in the soil seed banks. The fact that most of the dominant tree species do not accumulate seeds in the soil suggests that their regeneration from seeds would be prevented by removal of mature individuals in the standing vegetation. The results also provided further evidences that consolidate the conclusions of previous studies, i.e. the future existence of the woody flora characteristic of dry Afromontane areas in Ethiopia depends on the conservation and sustainable utilization of the few remnant natural forests.