Alistair D Headley

Modular growth and function in the vascular cryptogam Lycopodium annotinum

Lycopodium annotinum L. is a long-lived plant that consists of a series of annually produced segments, which can be aged; a 20-year life cycle can be synthesized from historical records of the plant’s past growth. Detailed analyses of the modular construction of the plant show elements of deterministic and opportunistic growth which provide a framework in which physiological processes can be interpreted. A balance between deterministic and opportunistic growth is achieved by the relationships in terms of structure, function and longevity, between a series of horizontally growing modules and a series of more ephemeral vertically oriented modules. Each annual horizontal segment has an increasing probability of mortality as it ages, yet the segments are organized into units with indefinite apical growth and proximal senescence. In contrast, each vertical module has the inverse relationship between age and the probability of mortality : the youngest segments always die first. The result is a plant with fixed structures for photosynthesis, spore production and nutrient and water uptake, but with a highly organized and mobile transport system.

Changes versus homeostasis in alpine and sub-alpine vegetation over three decades in the sub-arctic.

Plant species distributions are expected to shift and diversity is expected to decline as a result of global climate change, particularly in the Arctic where climate warming is amplified. We have recorded the changes in richness and abundance of vascular plants at Abisko, sub-Arctic Sweden, by re-sampling five studies consisting of seven datasets; one in the mountain birch forest and six at open sites. The oldest study was initiated in 1977–1979 and the latest in 1992. Total species number increased at all sites except for the birch forest site where richness decreased. We found no general pattern in how composition of vascular plants has changed over time. Three species, Calamagrostis lapponica, Carex vaginata and Salix reticulata, showed an overall increase in cover/frequency, while two Equisetum taxa decreased. Instead, we showed that the magnitude and direction of changes in species richness and composition differ among sites.