Olle Tenow

Effects on growth of simulated and induced shoot pruning by Tomicus piniperda as related to carbohydrate and nitrogen dynamics in Scots pine.

With the combination of field survey and EPIC modeling,this paper simulated the restoration effect of soil moisture in different alfalfa (Medicago sativa)-grain rotation systems in semi-arid and drought-prone regions of Loess Plateau. In perennial alfalfa field and in grain crop field after alfalfa,the correlation coefficients between the simulated and observed values of soil moisture content in 0-10 m layer were larger than 0.9 (P0.01),and their relative root mean square errors were between 0.05 and 0.16,with the relative errors less than 10%. The dynamic changes of the simulated soil moisture contents in different soil layers were consistent with those of the observed values. In the study regions,it was difficult for the restoration of soil moisture in the deep soil layers of alfalfa field. During the cultivation of alfalfa,the soil moisture content in the layers at 8-10 m depth should not be less than 5.7%. Considering the sustainable development of agricultural production,the appropriate cultivation duration of alfalfa should be 4-6 years and no more than 8 years. For the restoration of soil moisture after alfalfa cultivation in the study regions,the rotation system potato (Solanum tuberosum) → potato → spring wheat (Triticum aestivum) could be adopted,and alfalfa could be cultivated again after 32-33 years.

Diapause, embryo growth and supercooling capacity of Epirrita autumnata eggs from northern Fennoscandia

The supercooling point (SCP) of individual Epirrita autumnata eggs (approx. 60 eggs batch−1) was tested each month from September (eggs newly laid) to April under laboratory conditions simulating winter temperatures in the field (from + 4 to −30 °C). Parallel to each test, one batch of eggs was transferred from the acclimation treatment to room temperature (∼22 °C) and the incubation duration to the first 50% hatch was recorded, giving a measure of embryo growth at the time of the SCP test. Data also give information on egg mortality, which generally was low.

Recovery of a Betula pubescens forest in northern Sweden after severe defoliation by Epirrita autumnata

. Mountain birch (Betula pubescens ssp. czerepanovii) forest in the Abisko valley of northern Sweden was completely defoliated by Epirrita autumnata caterpillars during an outbreak in 1954–1955. The defoliation resulted in an 80–90% mortality of the leaf-carrying shoots of birches in 1956 and triggered a rejuvenation of stands. The subsequent regrowth of foliage was studied in two damaged birch stands and in one unattacked stand. The number of leaves approximately doubled in the damaged stands between 1961 and 1987, while the number on the reference plot fluctuated without significant increase. Regrowth started with increased production of long shoots from surviving shoots and basal sprouts. Basal sprouts were a substantial source of new shoots in the recovery of the foliage, especially on the most damaged plot. Trees of seed origin constituted a minor fraction of the regrowth. Initial rapid growth of foliage reduced gradually and the annual leaf production in 1986/1987 was 75% of that of the reference plot. Comparison between the recovery curve and data from the reference plot indicates that the shoot population of the damaged forest will, after more than 30 years, need many more years to reach the assumed size of a mature forest. The degree of rejuvenation varied between stands, with different consequences for future dynamics of E. autumnata populations.

Geometrid outbreak waves travel across Europe

We show that the population ecology of the 9- to 10-year cyclic, broadleaf-defoliating winter moth (Operophtera brumata) and other early-season geometrids cannot be fully understood on a local scale unless population behaviour is known on a European scale. Qualitative and quantitative data on O. brumata outbreaks were obtained from published sources and previously unpublished material provided by authors of this article. Data cover six decades from the 1950s to the first decade of twenty-first century and most European countries, giving new information fundamental for the understanding of the population ecology of O. brumata. Analyses on epicentral, regional and continental scales show that in each decade, a wave of O. brumata outbreaks travelled across Europe. On average, the waves moved unidirectionally ESE-WNW, that is, toward the Scandes and the Atlantic. When one wave reached the Atlantic coast after 9-10 years, the next one started in East Europe to travel the same c. 3000 km distance. The average wave speed and wavelength was 330 km year(-1) and 3135 km, respectively, the high speed being incongruous with sedentary geometrid populations. A mapping of the wave of the 1990s revealed that this wave travelled in a straight E-W direction. It therefore passed the Scandes diagonally first in the north on its way westward. Within the frame of the Scandes, this caused the illusion that the wave moved N-S. In analogy, outbreaks described previously as moving S-N or occurring contemporaneously along the Scandes were probably the result of continental-scale waves meeting the Scandes obliquely from the south or in parallel. In the steppe zone of eastern-most and south-east Europe, outbreaks of the winter moth did not participate in the waves. Here, broadleaved stands are small and widely separated. This makes the zone hostile to short-distance dispersal between O. brumata subpopulations and prevents synchronization within meta-populations. We hypothesize that hostile boundary models, involving reciprocal host-herbivore-enemy reactions at the transition between the steppe and the broadleaved forest zones, offer the best explanation to the origin of outbreak waves. These results have theoretical and practical implications and indicate that multidisciplinary, continentally coordinated studies are essential for an understanding of the spatio-temporal behaviour of cyclic animal populations.

Long-Term Influence of Herbivores on Northern Birch Forests

Species of many insects, some mammals and birds feed on buds and leaves of mountain birch, Betula pubescens ssp czerepanovii (Haukioja and Heino 1974; Brittas 1988; Neuvonen et al. 2001). Of these species, two geometrid moths, Epirrita autumnata (autumnal moth) and Operophtera brumata (winter moth), are the most important because of their large-scale and long-term influence on mountain birch ecosystems. The earliest report on an outbreak is by Ruge in the 1700s from Nord-Valdres in southern Norway (see references in Tenow 1972), and the next is of a mass occurrence in 1852 at Alta in northern Norway. Since then, 15 outbreak periods have been documented and a sixteenth is currently (2004) going on (Tenow 1972; Ruohomaki et al. 2000; Helena Bylund, pers. observ). Conclusively, these outbreaks are indigenous and ancient phenomena in the mountain birch/insect system. The population fluctuations are more or less synchronized, the caterpillars causing defoliating outbreaks about every 9–11 years (Tenow 1972; Haukioja et al. 1988; but cf. Chap. 9). The consequences of an outbreak depend on several circumstances, primarily what type of birch forest is attacked, i.e. heath forests mainly with polycormic (multi-stemmed) trees which propagate in particular by basal sprouts (cf. Chap. 1), or meadow forests on richer sites with monocormic (single-stemmed) trees propagating mainly by seeds (Sandberg 1963; cf. Holm 1994). Circumstances influencing the severity of an outbreak are age of the forest and previous abiotic and biotic stresses. In the case of severe defoliations, many monocormic trees die, as do many stems of polycormic trees. In surviving stems the mortality of shoots is heavy. Stems and trees that survive benefit from reduced competition and will soon produce new leaves. However, more important is the long time it takes for basal sprouts and seedlings to grow and replace the leaf-carrying canopy that was lost with stems and tree individuals that died (Tenow and Bylund 2000; Tenow et

Long‐term dynamics of leaf miners, Eriocrania spp., on mountain birch: alternate year fluctuations and interaction with Epirrita autumnata

Abstract. 1 Abundance of leaf‐mining larvae of the outbreak species Eriocrania spp. was monitored in northern Sweden in 1955–67 and 1984–92 in a mountain birch forest rejuvenated by an Epirrita autumnata outbreak in 1954–55. 2 Eriocrania mine density fluctuated in a regular biennial pattern, probably due to a semivoltine life cycle. The alternate year fluctuations had shifted phase between the two study periods. 3 The density fluctuated at a significantly higher mean level and with a lower amplitude in the c. 10‐year‐old forest in the 1960s than in the 30‐year‐old forest in the 1980s. However, no difference was found in mine density between c. 30‐ and >60‐year‐old stands in the 1980s. 4 Significant correlations between the density of mines in high‐density years and date of budburst, and between rate of change between high‐density years and the time between snow‐melt and budburst indicate effects of weather. No correlation was found between yearly average mine density and date of budburst, precipitation or temperatures in May or June. 5 No correlation was found between the mean densities of Eriocrania mines and E.autumnata caterpillars in the same and the two preceding years. However, in the first (1955) and highest of three studied E.autumnata peaks a negative effect on population density of Eriocrania was indicated. 6 A significant, negative correlation between the number of Eriocrania mines and E.autumnata caterpillars on single branches was found in three out of eighteen years. The separation of caterpillars and mines at branch level indicates an effect of avoidance at intermediate population densities.

Growth in Scots pine (Pinus silvestris L.): A hypothesis on response to Blastophagus piniperda L. (Col., Scolytidae) attacks

Abstract The purpose of this paper is to suggest an explanation of the long-lasting and drastic growth rate reduction in stands of Scots pine, caused by a common pine shoot beetle attack. Based on an evaluation of nitrogen economy and canopy growth it is hypothesized that the growth reduction is primarily an effect of removal of needle biomass and secondarily an effect of decreased rate of nitrogen uptake. Consequences of this hypothesis are discussed and experiments aimed at testing it are suggested.

Discovery of continental-scale travelling waves and lagged synchrony in geometrid moth outbreaks prompt a re-evaluation of mountain birch/geometrid studies.

The spatio-temporal dynamics of populations of two 9-10 year cyclic-outbreaking geometrids, Operophtera brumata and Epirrita autumnata in mountain birch forests in northern Fennoscandia, have been studied since the 1970´s by a Swedish-Norwegian research team and, during the last decade, by Norwegian and Finnish research teams. Some of the early results have been challenged by the Norwegian team. To examine the base for disagreements, five of the papers published by the Norwegian team (2004-2011) are reviewed. It is found that conclusions in these papers are questionable or data could not be interpreted fully because two decisive traits in the spatio-temporal behaviour of outbreaks of the two species were not considered.

Estimation of leaf number and leaf biomass of hazel (Corylus avellana L.) by two methods

Two methods for estimating the number and biomass of hazel leaves were compared within the framework of an IBP/PT project. The first method estimates the number and biomass of leaves when the leaves are fully developed. The second method involves collecting falling leaves in litter traps during summer and autumn. Simple random sampling was used in both methods to estimate the number of leaves, two-stage sampling to estimate the dry weight. A condition for comparison of the two methods was that they could be assumed to estimate the same population value. This assumption was made as regards the number of leaves in three of four plots. The second method was found to be more effective, i.e. gave the least variance in relation to the time input.

A response to Jepsen et al. (2016)

Important findings, e.g. in ecology, should be questioned and debated. Our findings that defoliating looper outbreaks travel as waves across Europe and the response here to such a questioning could be a start of a debate (photo: winter moth carterpillar).