Dag-Inge Øien

Climate warming alters effects of management on population viability of threatened species: results from a 30-year experimental study on a rare orchid

Climate change is expected to influence the viability of populations both directly and indirectly, via species interactions. The effects of large-scale climate change are also likely to interact with local habitat conditions. Management actions designed to preserve threatened species therefore need to adapt both to the prevailing climate and local conditions. Yet, few studies have separated the direct and indirect effects of climatic variables on the viability of local populations and discussed the implications for optimal management. We used 30 years of demographic data to estimate the simultaneous effects of management practice and among-year variation in four climatic variables on individual survival, growth and fecundity in one coastal and one inland population of the perennial orchid Dactylorhiza lapponica in Norway. Current management, mowing, is expected to reduce competitive interactions. Statistical models of how climate and management practice influenced vital rates were incorporated into matrix population models to quantify effects on population growth rate. Effects of climate differed between mown and control plots in both populations. In particular, population growth rate increased more strongly with summer temperature in mown plots than in control plots. Population growth rate declined with spring temperature in the inland population, and with precipitation in the coastal population, and the decline was stronger in control plots in both populations. These results illustrate that both direct and indirect effects of climate change are important for population viability and that net effects depend both on local abiotic conditions and on biotic conditions in terms of management practice and intensity of competition. The results also show that effects of management practices influencing competitive interactions can strongly depend on climatic factors. We conclude that interactions between climate and management should be considered to reliably predict future population viability and optimize conservation actions.

Germination ecology of the boreal-alpine terrestrial orchid Dactylorhiza lapponica (Orchidaceae)

In order to reveal some of the germination requirements of The boreal-alpine terrestrial orchid Dactylorhiza lapponica, several experiments were carried out on seeds collected from the Sølendet, nature reserve, central Norway. Seeds were sown in seed packets made of nylon cloth and deployed in situ vertically in the peat in order to study the temporal pattern of seed germination and determine if the seeds became part of the soil seed bank. In vitro germination experiments were carried out varying the growth media, fungal partner and chilling treatment, in order to study the effect of a fungal symbiont on germination and early protocorm development, and the possibility of a physiological seed dormancy. A high rate of germination a short time after sowing in the in vitro experiments together with a very low survival after deployment in the in situ experiments (0.2% after three years) indicate that D. lapponica seeds are not part of a long-lived soil seed bank. In vitro experiments also demonstrated that a fungal symbiont was not required for germination. Seeds sown in situ had very low germination rate (11%–12%) and lack of available nutrients is suggested as a possible explanation. Presence of a fungal symbiont clearly enhanced the early development of protocorms in vitro, and is probably necessary for the seedling to grow beyond the earliest protocorm stages under natural conditions. The results indicate that recruitment is highly variable and very low relative to population size, indicating that survival of established plants is crucial to the fate of a population.

Outlying haymaking lands at S lendet, central Norway: effects of scything and grazing

Solendet Nature Reserve, situated 700-800 m a.s.l., covers 306 ha. Solendet mainly consists of calcareous fens and wooded grasslands that were mown for hay for several centuries; the hay was vital for keeping the livestock through the winter. A vegetational succession commenced as soon as haymaking ceased (c. 1950), the most obvious change being the formation of scrub and a heavy litter layer in the tall fen and swamp communities. Mowing recommenced in the nature reserve in 1974, and the vegetation and landscape is being restored. Permanent plot methods have been applied to follow the effects of scything and cattle grazing on the flora and vegetation, with emphasis on the rich fen vegetation.

Nutrient limitation in boreal rich-fen vegetation: A fertilization experiment

Abstract Rich-fen vegetation influenced by hay-making in the Sølendet Nature Reserve, Central Norway, was fertilized with N, P and K in a full-factorial fertilization experiment to investigate the nutrient limitation of plant growth at both community and species levels. Above-ground biomass, shoot density and nutrient concentration were measured in several species and groups of species at three sites after two years of fertilization. At the community level, the results indicate multiple limitation by N and P in the two least productive rich-fen communities: one characterized by small sedges and herbs, and the other by high abundance of Menyanthes trifoliata and tall sedges. Increased nutrient availability had no effect on a more highly productive, tall-growing, spring-influenced community, indicating no nutrient limitation. The results at the species level correspond well with those at the community level, indicating multiple limitation by N and P in most of the dominant and sub-dominant species. However, P seems to limit growth more than N in Succisa pratensis, and N seems to limit growth more than P in Carex panicea. Furthermore, Eriophorum angustifolium seems to be limited by K. The results did not show which nutrient limits the growth of Carex dioica, C. lasiocarpa and Trichophorum cespitosum. Indications that growth in low-productive, boreal rich-fen communities is generally limited by P was not confirmed. Nomenclature: Lid & Lid (1994) for vascular plants and Frisvoll et al. (1995) for bryophytes. The terminology concerning mire ecology follows the Scandinavian tradition (Sjörs 1983; Moen 1990).

Long-term land-use and landscape dynamics in Budalen, central Norway

Humans have used resources in mountain landscapes for thousands of years, but the intensity and continuity of different land uses and the corresponding landscape changes are not well understood. This study examined long-term interactions between land use and landscapes in Budalen, central Norway, by using a multidisciplinary approach. Palaeoecological investigations at three sites in a north-south transect along the length of the valley indicate mowing and livestock grazing from AD 1500 to 1600. No clear signs of human-induced vegetation shifts are indicated at earlier time stages at the two southern sites. No archaeological findings support land use prior to AD 1500. Written sources give evidence for haymaking at AD 1600 and a more intense land use with summer farming followed in the eighteenth century. Land-use impact had a longer continuity at the northernmost site where furnaces for iron production and other human artefacts are dated as early as 180 BC–AD 25. These archaeological findings closely correspond to an opening of the woodland. We conclude that the intensity, diversity and continuity of land use decreased with increasing distance from permanent settlements in the lowland. The wooded grasslands probably dominated the Budalen valley also before humans started to use the land.

Hay crop of boreal rich fen communities traditionally used for haymaking

The traditional use of fen areas for hay production had been extensive in boreal Europe, but few studies have investigated the hay crop of different fen plant communities. We studied the hay crop from upper boreal (sub-alpine) rich fens using data from 81 permanent plots over more than 30 years in one coastal (oceanic) area and one inland (continental) area in central Norway. Permanent 12.5 m2 plots were mown with a scythe every year, every 2nd year or every 4th year. A large majority of the plots under study were lawn and open margin communities classified within or related to the phytogeographical order Caricetalia davallianae. There was no difference in the hay crop between the study areas in these communities, indicating that biomass production is about the same in ecologically similar rich fens that share the same dominant species. The first hay crop (including litter) from lawn communities was about 160 g/m2 after 20–30 years of abandonment. Regular mowing every second year reduced the hay crop by more than 30 %, and stabilized it after three mowings. The hay crop decreased with increasing mowing frequency; in lawn and open margin communities, mowing every 4th, every 2nd and every year yielded on average 140, 113 and 65 g/m2, respectively. In earlier times, it used to take farmers about 10 days’ work to harvest one hectare. Thus, the traditional practice of mowing every 2nd year was efficient in terms of the hay crop and labour input, and the quality of the hay was improved due to a lower litter fraction.

Actuarial senescence in a long-lived orchid challenges our current understanding of ageing

The dominant evolutionary theory of actuarial senescence—an increase in death rate with advancing age—is based on the concept of a germ cell line that is separated from the somatic cells early in life. However, such a separation is not clear in all organisms. This has been suggested to explain the paucity of evidence for actuarial senescence in plants. We used a 32 year study of Dactylorhiza lapponica that replaces its organs each growing season, to test whether individuals of this tuberous orchid senesce. We performed a Bayesian survival trajectory analysis accounting for reproductive investment, for individuals under two types of land use, in two climatic regions. The mortality trajectory was best approximated by a Weibull model, showing clear actuarial senescence. Rates of senescence in this model declined with advancing age, but were slightly higher in mown plots and in the more benign climatic region. At older ages, senescence was evident only when accounting for a positive effect of reproductive investment on mortality. Our results demonstrate actuarial senescence as well as a survival–reproduction trade-off in plants, and indicate that environmental context may influence senescence rates. This knowledge is crucial for understanding the evolution of demographic senescence and for models of plant population dynamics.

Long‐term effects of nutrient enrichment controlling plant species and functional composition in a boreal rich fen

Co-ordinating Editor: Sabine Güsewell Abstract Questions: How does longterm increase in nutrient availability affect species composition, species diversity and functional composition in boreal rich fens, and how does this differ from shortterm effects? What are the possible mechanisms behind the observed changes, and how does nutrient limitation influence species diversity in these communities? Location: Sølendet Nature Reserve, central Norway. Methods: A fullfactorial field experiment. Plots in two localities received one of following treatments (n = 3): no nutrient addition (control), N, P, K, NP, NK, PK and NPK addition. Cover of plant species was recorded before treatment, and after two and 15 years of treatment. Results: Two years of nutrient addition caused small changes in species composition, but addition of NP led to large increase in abundance of species with high ability to exploit the added nutrients—a direct result of the elimination of nutrient limitation in the communities. After 15 years of nutrient addition there were significant changes following three different pathways, one for each of N, P and NP addition. The addition of NP led to large community shifts, considerable species turnover and reduced species and functional richness, mainly caused by increase in cover of highly competitive and tussockforming grasses like Deschampsia cespitosa, Festuca ovina and Molinia caerulea, outcompeting other species, especially bryophytes. Addition of N led to smaller changes in species turnover, and without clear dominant species. Addition of P led to considerable species turnover, but no reduction in species or functional richness, and the bryophyte diversity increased. This is explained by the bryophytes’ association with Nfixing cyanobacteria, suggesting less N limitation and a greater ability to utilize the added P when vascular plants suffer from N shortage. In addition, bryophytes are more sensitive to low P availability, due to larger P requirements compared to vascular plants. There was no effect of K addition. Conclusions: Both N and P limitation is essential for the maintenance of high species diversity in boreal rich fens, and P limitation controls bryophyte diversity. From a management perspective, N and P limitation is vital in the conservation of boreal rich fens or when a functional fen system is reestablished through restoration measures.