Timo Vuorisalo

MOOSE BROWSING ON SCOTS PINE ALONG A GRADIENT OF PLANT PRODUCTIVITY

Pines growing in unproductive habitats experience more damage by moose than those growing in more productive habitats. This suggests that trees in unproductive habitats are qualitatively different, e.g., more palatable to moose, and/or less able to recover from browsing. Moose browsing was compared on four phenotypes of Scots pine taken from a gradient of forest productivity. The trees were exposed, side by side, at test stations during winter. Consumption of twig biomass was highest on pines from the most productive habitat and lowest on those from the moderately productive habitat with an overstory of mature pines. Consumption was intermediate on pines from the least productive habitat and from the moderately productive habitat without an overstory. Pines from the- highly productive habitat had greater nitrogen, potassium, and phosphorus content and more readily de- gradable dry matter (when incubated in the rumen of a cow) than did pines from the less productive habitats. Even though they provided a lower quality food for moose, pines in the less productive habitats generally suffered most from moose browsing. The slender twigs and the slow growth rate of these pines allow the moose to browse the main part of the needle-bearing twigs, in contrast to pines from more productive habitats. We also recorded the mortality response to simulated winter browsing in living pines on this same forest productivity gradient. Pine mortality was greater in the less productive habitats than in the more productive ones. These findings largely explain why pines growing in habitats of low and medium productivity suffer more than pines in highly productive habitats, where the possibility for growth is better. Severe damage to stands growing on poor soils most probably arises where moose density is high and where moose have already harvested most of the available twigs from pines growing in the more productive habitats. The moose are then forced to utilize the suboptimal food resources available in less productive habitats.

Interactive effects of pollination and heavy metals on resource allocation in Potentilla anserina L.

We studied resource allocation between sexual reproduction and clonal prop- agation in a perennial stoloniferous clonal plant, Potentilla anserina, an obligate outcrosser. We manipulated reproductive effort of Potentilla anserine either by hand-pollinating all flowers or by preventing pollination. To test the effect of resource-limiting conditions on resource allocation and reproductive output, we used a control and two levels of heavy metals (copper and nickel) to limit plant growth. The experiment was conducted as a 2 X 3 factorial design to reveal possible interactions between reproductive manipulation and resource limitation. Heavy metals decreased the total biomass of the plants and number of flowers and ramets produced. Only 50% of the plants grown with the higher level of heavy metals produced flowers. Pollination treatment interacted significantly with the heavy-metal treatment. In the metal control (no metals added) and lower heavy-metal treatment, there were no significant differences in total vegetative biomass between the two pollination treatments. Costs of reproduction in terms of subsequent flowering in the later season appeared to be clear, because the number of flowers per whole plant was lower if the plants were hand-pollinated and because the proportion of flowering ramets decreased due to hand- pollination. However, flowering may also be partly hormonally controlled. In contrast, hand- pollinated plants exposed to high concentrations of heavy metals tended to have greater biomass of vegetative plant structures and higher number of flowers compared to nonpol- linated plants. Together, these results suggest that environmental factors may alter costs of reproduction but do not support the idea that these costs are more acute in resource (pho- tosynthate)-limiting conditions.

Urban development from an avian perspective: causes of hooded crow (Corvus corone cornix) urbanisation in two Finnish cities

The hooded crow (Corvus corone cornix) colonised Turku and Helsinki, two cities in southern Finland, in the first half of the 20th century as a breeding species. Their urban population densities, however, remained low for decades, in spite of considerable changes in the urban environment. Since the 1960s, the breeding populations have increased very rapidly in both cities. The possible causes of the early colonisation of cities, the long period of low population density, and the recent rapid population increases are discussed based on environmental history data. The establishment of city parks in the 19th century was probably a prerequisite for initial colonisation, although it cannot alone explain the timing of colonisation. Hooded crow populations did not increase before the 1960s, although biological waste production increased considerably and large landfills were continuously available near both cities. In Turku, the rapid increase of the crow population took place after the availability of biological waste in the main landfill had decreased due to opening of a municipal waste incinerator. Suitable habitats created by urban expansion and a lack of predators in cities during the breeding season may have promoted urbanisation. The main factor promoting urban population growth has probably been decreased persecution in cities since the 1960s. Low levels of persecution in urban areas have facilitated the habituation of crows to humans and traffic, and probably explain the recent colonisation of city centres as breeding habitats.

Nutritional quality as a defense against herbivores

The generally low nutritional quality of plants may result from its being adefense against herbivores, an adaptation to abiotic factors, or an incidental by-product. To demonstrate the defensive nature, we should be able to show that there is variation, fitness differences and a hereditary basis. We demonstrate that, in the mountain birch (Betula pubescens ssp. tortuosa), the low nutritional quality is a potential active defense against herbivorous insects, especially if it correlates with repellency caused by allelochemicals. However, it is almost impossible to show this conclusively.

Life history evolution in plants.

List of Contributors. Preface. 1. Modularity and Plant Life Histories T. Vuorisalo, P. Mutikainen. 2. Modelling and Measuring Plant Life Histories J. Ehrlen. 3. Fitness Interactions among Plants: Optimal Defence and Evolutionary Game Theory J. Tuomi, et al. 4. Genetic Variation in Life-History Traits: Heritability Estimates within and Genetic Differentiation among Populations S.J. Mazer, G. LeBuhn. 5. Resource Allocation, Trade-Offs, and Reproductive Effort in Plants E.G. Reekie. 6. Phenological and Developmental Costs of Male Sex Function in Hermaphroditic Plants V.M. Eckhart, J. Seger. 7. Evolution of Plant Dispersal O. Eriksson, K. Kiviniemi. 8. Senescence in Plants B. Pedersen. 9. Pathogens and Plant Life Histories K. Clay, W. van der Putten. 10. Impact of Herbivore Tolerance and Resistance on Plant Life Histories K. Lehtila. Glossary. Index.

Delayed Budbreak: A Defensive Response of Mountain Birch to Early-Season Defoliation?

Delayed budbreak has been suggested to be a potentially defensive characteristic of deciduous trees against early-feeding lepidopteran larvae. We therefore tested the effects of early (in June) and late (in August) manual defoliations on leaf development in mountain birch. Early defoliation induced a significant delay in budbreak, whereas late defoliation influenced only slightly leaf flush during the next growing season. This supports the defense hypothesis. However, the responding units were separate branches rather than entire birch trees, since leaf growth was delayed on defoliated branches relative to untreated branches on the same trees. Furthermore, as artificial defoliation induced the delay in leaf flush, the presence of larvae is not necessary for triggering these localized responses in mountain birch. The fact that both early and late defoliation reduced final leaf size may suggest that the observed defoliation effects were associated with localized resource deficiencies suppressing leaf growth. Still, a delay in budbreak on previously defoliated branches, due to resource shortage or other causes, could be expected to adversely affect immobile early-feeding larvae. Mobile larvae, on the other hand, should be generally capable of overcoming within-tree variation in the predictability of their food resources.

On plant sectoriality, or how to combine the benefits of autonomy and integration

Plant sectoriality implies physiological subdivision of physically coherent plant structures. It is largely determined by vascular structure. Sectorial transport of carbon assimilates, mineral nutrients, water or hormones may be an essential component of plant phenotype in ecological interactions. Most studies of sectoriality have focussed on its effects on plant growth, resource allocation and herbivory. Since sectoriality allows semiautonomous reactions to environmental stimuli to be displayed by different plant parts, it also needs to be considered in discussions of selfishness vs. altruism of plant parts. Future lines of research should include analysis of the genetic basis of sectoriality, investigations into root sectoriality and its effects, studies of the impacts of sectoriality on plant life histories, and analyses of intra- and interpopulation variation in traits related to sectoriality.

Localized effects of branch defoliations on weight gain of female inflorescences in Betula pubescens

Separate branches of white birch were defoliated in early summer before leaves had fully expanded. Four branches within each experimental tree were treated as follows: complete defoliation (CD), partial defoliation (PD), defoliation of generative short shoots with female catkins (GD), and control with no treatment. The treatments did not affect final catkin length, but final catkin weight was reduced in all of them. Defoliation of generative short shoots and complete defoliation of branches influenced catkin weight more (GD 13%, CD 14%) than partial defoliation (7%). Unexpectedly, the weight gain of female catkins did not negatively correlate with the severity of defoliation (5 to 95%) among PD branches. Our results thus support only a limited autonomy of short shoots and branches in white birch. The weight gain of female catkins is mainly supported by resources that are transported from other parts of trees into generative short shoots. Consequently, short shoots and branches are semi-autonomous units which are integrated parts of larger functional units involving entire birch trees or their shoot-root sub-systems.

Global patterns of arthropod herbivory on an invasive plant, the physic nut (Jatropha curcas L.).

The physic nut (Jatropha curcas L.) is a multipurpose and oil‐producing shrub of Central and South American origin. Since the 15th century, this shrub has existed across tropical regions. Despite its presumed resistance to herbivores, reports show that arthropod herbivores infest it. However, no comprehensive account of arthropod herbivores, which consume the physic nut, exists. Here, we conducted a literature review that provides a comprehensive account of arthropod herbivores of the physic nut. Based on the co‐evolutionary hypothesis, we expected to find a higher herbivore of species richness and a larger proportion of native herbivores within the native range than elsewhere. As physic nut is a well‐defended plant chemically, we expected to find evidence for highest herbivory levels in plant parts that are the least defended. By the literatures review, we compiled 78 arthropod herbivores representing nine orders and from 31 families that feed on physic nut across the globe. As expected, the highest numbers of herbivores (34 species) were documented within the native range of the J. curcas and the lowest species number (21 species) in Africa. Of the 34 species in Central and South America, 94% were of native origin. Nine species were found feeding on J. curcas on more than one continent. Origins of 49% of species were from the native range of J. curcas. The highest percentage (54%) of species belonged to Hemiptera. With regard to feeding guilds, 59% of the herbivores belonged to sucking and 41% to chewing species. Forty‐one per cent of species were flower or fruit feeders, and 36% foliage feeders. We conclude that J. curcas is, despite its toxicity, vulnerable to herbivory, mainly to foliage, flower and fruit feeders.

Density patterns of gall mites (Acarina:Eriophyidae) in a polluted area

Trends in the densities of six species of gall mites on European aspen (Populus tremula) and on two birch species (Betula pubescens and B. pendula) were compared in an air pollution gradient from the Harjavalta copper-nickel smelter, SW Finland. The densities of gall mites on both birch species decreased towards the smelter and were negatively correlated with the levels of copper and nickel in the birch leaves. In contrast, the densities of aspen mites correlated neither with distance from the pollution source nor with the content of heavy metals in aspen leaves. Both birch and aspen trees tended to produce smaller leaves near the smelter, but a significant correlation between gall mite densities and site-specific leaf areas was only found for one species of mite.