Disturbances and structural development of natural forest ecosystems with silvicultural implications, using Douglas-fir forests as an example

Forest managers need a comprehensive scientific understanding of natural stand development processes when designing silvicultural systems that integrate ecological and economic objectives, including a better appreciation of the nature of disturbance regimes and the biological legacies, such as live trees, snags, and logs, that they leave behind. Most conceptual forest development models do not incorporate current knowledge of the: (1) complexity of structures (including spatial patterns) and developmental processes; (2) duration of development in long-lived forests; (3) complex spatial patterns of stands that develop in later stages of seres; and particularly (4) the role of disturbances in creating structural legacies that become key elements of the post-disturbance stands. We elaborate on existing models for stand structural development using natural stand development of the Douglas-fir - western hemlock sere in the Pacific Northwest as our primary example; most of the principles are broadly applicable while some processes (e.g. role of epicormic branches) are related to specific species. We discuss the use of principles from disturbance ecology and natural stand development to create silvicultural approaches that are more aligned with natural processes. Such approaches provide for a greater abundance of standing dead and down wood and large old trees, perhaps reducing short-term commercial productivity but ultimately enhancing wildlife habitat, biodiversity, and ecosystem function, including soil protection and nutrient retention. © 2002 Elsevier Science B.V. All rights reserved

Moderate to high levels of exercise are associated with higher resting energy expenditure in community-dwelling postmenopausal women

Postmenopausal women experience an age-related decline in resting energy expenditure (REE), which is a risk factor for energy imbalance and metabolic disease. Exercise, by association with greater lean tissue mass and other factors, has the potential to mediate REE decline, but the relationship between exercise and REE in postmenopausal women is not well characterized. This study tests the hypothesis that exercise energy expenditure (EEE) is positively associated with REE, opposing the effects of age and menopause. The study tests this hypothesis in a cross-sectional sample of healthy postmenopausal women (N = 31, aged 49 - 72 years) with habitual exercise volumes at or above levels consistent with current clinical recommendations. Subjects kept four weeks of exercise diaries quantifying exercise activity, and were measured for body composition, maximal oxygen uptake, and REE. Multiple regression analysis was used to test for relationships between EEE, age, body composition, and REE. EEE and lean tissue mass (fat-free mass: FFM; and fat-free mass index: FFMI) exhibited significant, positive relationships with REE. The relationship between REE and EEE remained significant even after controlling for lean tissue mass. These results support the hypothesis that exercise is positively associated with REE, counter to the negative effects of age and menopause, and indicate a continuous relationship between exercise and REE across the moderate-to-high exercise range. Exercise at levels at and above current clinical guidelines may, in part, ameliorate risk for energy imbalance and metabolic disease through a positive relationship with REE

Avaliação da suplementação de vitamina A nas características seminais em reprodutores suínos Assessment of vitamin A supplementation on boar semen characteristics

Avaliou-se o efeito da suplementação de vitamina A na dieta sobre as características seminais (volume, motilidade, pH, vigor e concentração espermática, número total de espermatozoides, percentual de espermatozoides vivos e anormalidades morfológicas) de reprodutores suínos no período de um ano (junho de 2004 a junho de 2005). Utilizaram-se dez reprodutores híbridos com 328,5 ± 2,12 dias de idade e 191,0 ± 12,0 kg distribuídos em duas rações, uma controle, com 10.000 UI de vit. A por kg de ração por dia, e outra com 16.000 UI de vit. A, fornecidas na quantidade de 2,5 kg/dia. O delineamento foi inteiramente casualizado com medidas repetidas no tempo. Não houve efeito significativo da suplementação de vitamina A na dieta nem de interação com o tempo nas características seminais estudadas. O tempo teve efeito significativo no pH, na concentração espermática, no número total de espermatozoides, no percentual de espermatozoides vivos, nas anormalidades morfológicas, na motilidade e no vigor espermático. Apesar da não-significância da suplementação de vitamina A, foi possível detectar diferenças numéricas no aumento da motilidade e de espermatozoides vivos, bem como na diminuição das anormalidades morfológicas, resultados que indicam ação da vitamina A.<br>The objective of this study was to evaluate the effect of vitamin A feed supplementation on the following boar semen characteristics: volume, motility, vigor, seminal pH, spermatic concentration, total number of spermatozoa, percentage of living sperm cells and morphologic abnormalities. The experiment was carried out with 10 hybrid boars (328.5 ± 2.12 days of age and 191.0 ± 12.0 kg live weight). The boars were separated into two treatments and fed with two vitamin A levels: control, 10.000 UI/kg feed daily; and vitamin A, 16.000 UI. The boars received 2.5 kg feed daily. A randomized complete design was used with replication measurements in time. There was no significant effect of vitamin A supplementation on the characteristics studied, and nor on the time and treatment interaction. The was significant effect of time on pH, spermatic concentration, total number of spermatozoa, percentage of living sperm cells, morphologic abnormalities, motility and vigor. Although detect significant differences were not detected between both treatments, numerical differences were detected indicating that vitamin A influenced the average increase in motility and the percentage of living sperm cells and the reduction in the percentage of morphologic abnormalities. Data showed support the idea that vitamin A is intimately associated with spermatogenesis