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Large trees with hollows are an important component of stand structural complexity worldwide. Understanding their population dynamics is needed to manage cavity-dependent biota. We quantified long-term rates of collapse of 302 measured trees with hollows in 1939-aged regrowth mountain ash (Eucalyptus regnans F. Muell.) forest in southeastern Australia. We identified time-dependent dynamics in which the collapse rates of trees slowed from ~4% annually between 1983 and 1993 to ~2.2% between 1993 and 2007. Transitions of trees between different decay states (forms) also slowed over time. Nevertheless, during the 24-year period of our study, over half of our marked and measured trees had fallen, but there was no recruitment of new trees with hollows. Under current projections, few trees with hollows will occur on our field sites by ~2050, although more had been forecast in earlier investigations. Such a paucity of trees with hollows in extensive areas of regrowth mountain ash forests will lead to a shortage of nesting and sheltering sites for cavity-dependent biota. We suggest a short-medium (10- to 100-year) focus on the conservation of old growth and multi-aged stands will be needed to maintain populations of those species strongly associated with trees with hollows in mountain ash forests. Resume: Les gros arbres creux sont une composante importante de la complexite structurale des peuplements partout dans le monde. II est necessaire de comprendre la dynamique de leur population pour gerer le biote qui depend des cavi-tes. Nous avons quantifie le taux a long terme d'effondrement de 302 arbres creux mesures dans une foret de recru composed d'eucalyptus geants (Eucalyptus regnans F. Muell.). Nous avons identifie une dynamique dependante du temps selon laquelle le taux d'effondrement des arbres a ralenti, passant de ~4 % par annee entre 1983 et 1993 a ~2,2 % entre 1993 et 2007. Le passage des arbres d'un stade (forme) de decomposition a un autre a egalement ralenti avec le temps. Malgre tout, durant la periode de 24 ans visee par notre etude, plus de la moitie des arbres marques et mesures sont tombes, mais il n'y a eu aucun recrutement de nouveaux arbres creux. Selon les projections actuelles, il y aura peu d'arbres creux dans nos sites d'etude vers ~2050 bien que les recherches precedentes en aient predit un plus grand nombre. Une telle rarete d'arbres creux dans une vaste zone de foret de recru composee d'eucalyptus geants entrainera une penurie de sites pouvant servir d'abris et de lieux de nidification pour le biote qui depend des cavites. Nous concluons que. pendant une periode de 10 a 100 ans, il faudra mettre I'accent sur la conservation des vieux peuplements inequiennes pour maintenir les populations des especes etroitement associees aux arbres creux dans les forets d'eucalyptus geant. [Traduit par la Redaction], Introduction Large trees, particularly those with cavities or hollows, are a key component of forest structure around the world (Linder and Ostlund 1998; Rose et al. 2001). They play many [...]

The distribution of marsupial folivores in Australian eucalypt forests is extremely patchy and, although distribution patterns are known to be partly determined by nutritional factors, the role of plant secondary metabolites (PSMs) has been little studied. We investigated variation in the foliar concentrations of five constituents: total phenolics (TP); the foliar component bound by polyethylene glycol (PEGBC); the formylphloroglucinol compound, sideroxylonal (a strong deterrent of mammalian herbivory); the terpene, cineole; and nitrogen (N). These constituents were analyzed using near infrared spectroscopy in 501 individual tallowwood (Eucalyptus microcorys) trees at 42 sites across a broad geographic range in eastern Australia. We tested three hypotheses: (1) trees with lower foliar N produce higher PSM concentrations; (2) PSM concentrations are greater at colder sites; and (3) PSM concentrations are higher at sites with low resource availability. Hypothesis 1 was true for all PSMs considered and was the result of variation that occurred within sites. This is consistent with the carbon/nutrient balance hypothesis and with the hypothesis that PSMs protect leaves from photodamage. Hypothesis 2 was upheld for all constituents. This was consistent with both the growth--differentiation balance hypothesis, and with the hypothesis that PSMs represent an evolutionary adaptation to greater risks of photodamage and frost damage in cold environments, Hypothesis 3 was rejected, with one PSM, sideroxylonal, being affected by resource availability in a manner opposite to that predicted. The optimal defense hypothesis offers an explanation for this result (as sideroxylonal concentrations increased along with the apparent nutritional quality of the foliage, possibly to provide defense against higher rates of herbivory). We found that trees associated with koala fecal pellets had lower concentrations of sideroxylonal and cineole. We discuss this finding and further implications for the herbivores of Eucalyptus of the patterns of plant defense that we detected. Key words: Australia; carbon-nutrient balance; Eucalyptus; formylphloroglucinol compounds; graphical vector analysis; herbivory; koala; LMA; near infrared spectroscopy; phenolic; plant defense; sideroxylonal.

In mice heterozygous for p53 (Trp53(+/-)), the incidence of mammary tumors varies among strains, with C57BL/6 being resistant and BALB/c being susceptible. Mammary tumor phenotypes were examined in female Trp53(+/-) F1 mice (C57BL/6 x BALB/c;n = 19) and N2 backcross mice [(C57BL/6 x BALB/c) x BALB/c] (n = 224). Susceptibility to mammary tumors segregated as a dominant phenotype in F1 females, but a higher frequency and shorter latency in N2 mice indicated a contribution from recessive-acting modifiers. Segregation of the hypomorphic BALB/c alleles for DNA-dependent protein kinase catalytic subunit (Prkdc) and p16(INK4A) (Cdkn2a) was analyzed in the N2 mice. The time to first tumor (considering all tumor types) was significantly different among the four genotype combinations (P = 0.01). Cdkn2a had a strong effect (P = 0.008) but was restricted to Prkdc(B/B) mice (P = 0.001), indicating a strong interaction between the loci. Differences in mammary tumor occurrence among genotypes for Prkdc and Cdkn2a in N2 mice were not statistically significant. This study indicates that BALB/c Prkdc and Cdkn2a alleles do modify tumor incidence in Trp53(+/-) mice and highlights the complexity of gene interaction effects in determining cancer phenotypes but discounts these alleles as major recessive loci contributing to spontaneous mammary tumor susceptibility.