Mechanical injury and fungal infection induce acquired resistance in Norway spruce.

Norway spruce trees (Picea abies (L.) Karst.) pretreated by wounding and fungal infection showed highly enhanced resistance to a subsequent challenge inoculation with the pathogenic bluestain fungus Ceratocystis polonica (Siem.) C. Moreau. This is the first time the effectiveness of the constitutive and inducible defenses has been shown to depend on prior wounding and infection in conifers, although such acquired resistance has previously been found in several angiosperms. Trees that were pretreated with a combination of 12 bark wounds (1.6 x 10 cm), four fungal inoculations and four sterile inoculations 1-15 days before mass inoculation with C. polonica at 400 inoculations per square meter over a 0.8 m stem section had significantly shorter necroses in the phloem, less bluestained sapwood, and less dead cambium than untreated control trees. Pretreatment with four fungal or sterile inoculations alone did not lead to enhanced resistance. Pretreatment by bark wounding alone seemed to provide an intermediate degree of resistance compared to bark wounding, fungal inoculations and sterile inoculations combined. All trees had a marked increase in the number of resin ducts in the year of inoculation compared with previous years, suggesting that formation of traumatic resin ducts play an important role in the development and maintainance of enhanced resistance.

What causes population cycles of forest Lepidoptera?

Hypotheses for the causes of regular cycles in populations of forest Lepidoptera have invoked pathogen-insect or foliage-insect interactions. However, the available data suggest that forest caterpillar cycles are more likely to be the result of interactions with insect parasitoids, an old argument that seems to have been neglected in recent years.

Induced Responses in Phenolic Metabolism in Two Norway Spruce Clones after Wounding and Inoculations with Ophiostoma polonicum, a Bark Beetle-Associated Fungus.

Two Norway spruce (Picea abies Karst.) clones, one resistant and the other susceptible to mass inoculation with Ophiostoma polonicum Siem., were compared with regard to their phenolic compositions and chalcone synthase (CHS) and stilbene synthase activities of their phloem before and at 6 and 12 d after artificial inoculation with sterile malt agar or O. polonicum. In unwounded phloem, the resistant clone differed from the susceptible clone by the presence of taxifolin glycoside, lower concentrations of stilbene glycosides, and higher CHS activity. After inoculation, (+)-catechin concentration and CHS activity dramatically increased around the wound, particularly in the resistant clone. Stilbene synthase activity also increased, but more slowly and to a lower level, whereas the concentrations of stilbenes remained stable. Tanning ability decreased in the susceptible clone, whereas it remained stable in the resistant one. It is proposed that the induced phenolic response of Norway spruce phloem consists of an activation of the phenolic pathway, finally leading to tannins and insoluble polymers. It is suggested that resistance to O. polonicum depends on the ability of the tree to easily activate the flavonoid pathway.

Ecological engineering - An idea whose time has come?

The era of cheap fossil fuels is nearing its end. industrial, agricultural and human pollutants have reached alarming levels in water, soil, air and stratosphere. Consumers no longer tolerate poisons in their food and water, are now concerned with global warming and ozone depletion, and value fields and forests for their scenery and wildlife as well as food and fibre. We are at the crossroads, searching for answers to these and many other pressing ecological problems. On one side sit 'deep ecologists' who patiently await the reactions of global Gaia. On the other sit 'biotechnologists' who would design and build new organisms and new ecosystems. The first approach is defeatist, for it awaits the decimation of the human population. The otheris activist, but will it work? Here we examine the idea of 'ecological engineering', which offers some promise of solutions to our problems if it can integrate the practical sides of ecosystem, landscape, community and population ecology with relevant formal concepts from the engineering sciences.

Are ecological systems chaotic - And if not, why not?

Chaotic dynamics emerge when positive/negative feedback systems are dominated much of the time by positive feedback growth processes. Although all ecological systems contain the seeds of chaos (positive feedback), empirical evidence and evolutionary/ecological reasoning support the view that ecosystems do not normally behave chaotically. They may, however, be driven to chaos by human actions that increase growth rates or induce delays in the regulatory (negative feedback) processes.

Natural regulation of herbivorous forest insect populations.

From basic principles of positive/negative feedback control and classical density-dependent/independent population theory we outline a general explanation for the regulation of herbivore populations in forested ecosystems. We identify three fundamental patterns of behavior; (i) populations regulated close to equilibrium ("tight" regulation) by fast-acting negative feedback processes, (ii) populations regulated by delayed negative feedback processes ("loose" regulation) which often exhibit wide-amplitude density cycles, and (iii) populations characterized by positive feedback processes over certain density ranges that may exhibit divergent (metastable) behavior. We then discuss the effects of these different kinds of herbivore population behavior on the dynamics of forest ecosystems and explore some elemental models of herbivore/forest interactions. Finally, using the spruce bark beetle, Ips typographus, as an example, we demonstrate how the theory can be used to explain the dynamics of specific herbivore populations and to develop general strategies for managing destructive herbivore outbreaks.