Summary-The humus forms during the life cycle of a spruce forest are described. A significant change in humus form may be attributed to plant and soil fauna changes. This phenomenon is considered to be fundamental for the renewal of the forest ecosystem. Forest dynamics is perceived as a biphasic cycle, (i) the tree growth phase with a shift from mull towards moder humus form, as a consequence of a decline in earthworm populations and (ii) a humus form improvement from moder towards earthworm mull humus, during the second half of the life of spruce trees. This results from a succession of earthworm species. The particular role of anecic species during the second phase has been highlighted, where they allow endogeic earthworm species and young spruce seedlings to install themselves in the regeneration site, the fall of parent trees not being considered as the chief factor governing humus changes.The life cycle of the spruce ecosystem can nevertheless be impaired by the development of a bilberry heath, with a mor humus form which is detrimental to the germination and growth of spruce seedlings.Earthworm populations of anecic and endogeic species are present in this case but without any burrowing activity.

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Context Studies about the impact of global health electives on host institutions are scarce and often made from the perspective of institutions that send students. The present research examined the impact of short‐term electives in global health (STEGHs) from the under‐represented perspective of host institutions in Benin. Methods The authors conducted 30 semi‐structured interviews from a convenience sample of Beninese health care professionals who had hosted Canadian medical students. Interviewees had previously supervised STEGHs in one of the five different institutions. A subsequent qualitative thematic analysis methodology was used to compilate codes and generate themes. Results Hosting STEGH students motivated respondents to increase their medical knowledge through self‐driven learning. They perceived an improvement in the quality of their care and felt a negligible impact on patient safety. They negatively commented on the lack of clear pedagogic objectives that they could rely on. Interviewees think current STEGH partnerships do not advantage them because institutions that send students offer little support during the electives. Furthermore, sending institutions do not offer the same opportunity for local medical students or professionals to take part in such electives outside of Benin. Conclusions Although host health care professionals evaluated global health electives positively overall, specific improvements could mitigate their negative impacts and help create a more balanced partnership between sending and host institutions. Sending institutions could involve host institutions in curriculum planning. They could invest in building reciprocal elective programmes to receive students from elsewhere. Meanwhile they can maximise the transfer of relevant medical knowledge, and provide expertise, resources and support during the electives.

An altitudinal transect was studied at the montane level in a spruce forest, in order to describe changes in humus form dynamics. Whatever the elevation, the periodicity of humus form changes is copied on forest dynamics. Spruce regeneration is restricted both in space and time to favourable micro-site conditions accompanying tree fall gaps. One of these conditions is a shift from moder to mull humus form. As a result, this forest ecosystem shows a space-time mosaic pattern. The recovery of mull humus form takes more time as elevation increases and thus the ratio mull:moder progressively decreases. Simultaneously, burrowing earthworms become scarce. Nevertheless mull humus form does not change basically at increased elevation. On the other hand, moder has little organic matter at the lower montane level. At the mid montane level, accumulation of holorganic faeces into OH horizon is maximum. A mor-moder (few faunal traces) is observed during tree growth phase at the upper montane level. Lack of nutrient availability was hypothesized to explain the observed shift from mull to moder or mor-moder during the phase of intense tree growth. An increased independancy between the building of a moder humus profile and the actual accumulation of organic matter was the main change occurring with elevationl The transition to the subalpine level may thus be defined as the highest elevation up to which the forest ecosystem is able to reverse the mor-building process produced by tree growth. The discoupling between primary producers, plant debris accumulation and decomposers observed in the subalpine spruce forest leads to a breaking point in the carrying capability of humus for spruce seedlings. At high elevation spruce seedlings are mainly observed on rotten wood.The influence of humus form dynamics upon forest sustainability was discussed. The lack of humus biological activity at higher elevation was found to be a reason for the weakness of the forest ecosystem faced to the bilberry heath. Forest sustainability depends both on mull and moder. It was observed that moder failed to recover after mull along the forest cycle and turned to mor in harsh climate conditions. Consequences of management practices on the issue of competition between forest and heath were also discussed.

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