Paavo Närhi

Orchids do not pay costs at emergence for prolonged dormancy.

In plants, prolonged dormancy is often considered a response to resource depletion or environmental stress that comes at a fitness cost. However, apparent costs of dormancy could reflect the state in which plants entered dormancy, rather than effects of dormancy per se. We tested this hypothesis for a terrestrial orchid, Epipactis atrorubens, by analyzing differences in vital rates of dormant and emergent plants using generalized linear mixed models, applied to eight years of demographic data. Dormant E. atrorubens plants did not form one homogeneous stage class. Instead, the vital rates of dormant plants mirrored performance of plants in their life stage before dormancy. Plants emerging from dormancy were slightly (albeit only marginally statistically significantly) larger than plants transitioning from the matching aboveground stage class, especially for smaller and younger stage classes. Because small plants were most likely to go dormant, plants emerging from dormancy were also smaller than average, if one were to compare all previously dormant plants to all previously emergent plants. Therefore, misclassifying all dormant plants into a single stage class changes whether we view dormancy as intrinsically costly, in terms of future performance upon emergence. We suggest that prolonged dormancy may be a form of phenotypic plasticity in which plants distribute their performance and reproductive effort through time, rather than a simple stress response.

Central boreal mire plant communities along soil nutrient potential and water content gradients

Peatlands have traditionally been exploited in forestry and agriculture over the boreal region, yet they also provide substantial source of fuel production. The large-scale exploitation of peatlands has raised a concern about the diversity of mire plant communities. We studied composition of mire plant communities along soil nutrient potential and water content gradients, to recognize the areas with the high plant diversity. Soil electrical conductivity (ECb) was measured to characterise soil nutrient regimes and soil dielectric permittivity (DP) the soil (volumetric) water regimes. A total of 115 mire sites were studied in the central boreal region of south-western Finnish Lapland. We found that Ward’s hierarchical cluster analysis produced eight stable ECb and DP clusters with discrete vegetation compositions. On the basis of a locally weighted regression analysis (Loess), Carex dioica L., Comarum palustre L., Equisetum fluviatile L., Menyanthes trifoliata L., and Scorpidium scorpioides (Hedw.) Limpr. were found as indicator species for nutrient-rich regimes as designated by high soil ECb. The soil ECb is a diagnostic measure of plant diversity as ECb > 7 mSm−1 resulted in a considerable increase in species richness. Our classification method, based on electrical measurements, provides a simple way to classify mires and focus detailed research to areas with potentially high conservation value.

Tree species distribution on mafic and felsic fells in Finnish Lapland

Abstract Physical–chemical properties of glacial tills, derived from felsic or mafic lithologies, were studied in the forest, treeline, and on tundra in western Finnish Lapland. Scots pine [Pinus sylvestris L.] dominated on felsic fells, but excess soil water content was found edaphically constraining for pine. Low soil electrical conductivity (ECa) and low Ca to Al ratios was found to constrain Norway spruce [Picea abies (L.) Karst.]. The soil ECa positively correlated with soil Mg, Na, and Ca, but negatively with Al signifying the distribution of spruce to be associated with mafic lithologies. The limit of mountain birch [Betula pubescens ssp. Czerepanovi Hämet-Ahti] was below the conifer krummholz-zone. In winter, the treeline soil was unfrozen beneath the snowpack, whereas subzero temperatures applied to forest and tundra. In spring, soil water became available weeks before final melting of snowpack, while soil temperature (ST) increased notably above 0oC three weeks after the disappearance of snow. Early season ST was not attributed to elevation or aspect. Mid-season ST was highest on tundra. We contend that, instead of ST, water or N availability, winter winds, and spatial distribution of snow are crucial with regard to spreading of tree species on the studied fells.