Constraining 3-PG with a new δ13C submodel: a test using the δ13C of tree rings.

A semi-mechanistic forest growth model, 3-PG (Physiological Principles Predicting Growth), was extended to calculate δ(13)C in tree rings. The δ(13)C estimates were based on the model's existing description of carbon assimilation and canopy conductance. The model was tested in two ~80-year-old natural stands of Abies grandis (grand fir) in northern Idaho. We used as many independent measurements as possible to parameterize the model. Measured parameters included quantum yield, specific leaf area, soil water content and litterfall rate. Predictions were compared with measurements of transpiration by sap flux, stem biomass, tree diameter growth, leaf area index and δ(13)C. Sensitivity analysis showed that the model's predictions of δ(13)C were sensitive to key parameters controlling carbon assimilation and canopy conductance, which would have allowed it to fail had the model been parameterized or programmed incorrectly. Instead, the simulated δ(13)C of tree rings was no different from measurements (P > 0.05). The δ(13)C submodel provides a convenient means of constraining parameter space and avoiding model artefacts. This δ(13)C test may be applied to any forest growth model that includes realistic simulations of carbon assimilation and transpiration.

Long-term hydrological response to forest harvest during seasonal low flow: Potential implications for current forest practices.

Seasonal changes in the magnitude and duration of streamflow can have important implications for aquatic species, drinking water supplies, and water quality. In many regions, including the Pacific Northwest (U.S. and Canada), seasonal low flow is declining, primarily due to a changing climate, but is also influenced by urbanization, agriculture, and forestry. We review the responses of seasonal low flow, catchment storage, and tree-water relations to forest harvest over long timescales and discuss the potential implications of these responses for current forest practices and aquatic biota. We identify three distinct periods of expected low flow responses as regrowth occurs following forest harvest: in the first period an initial increase in low flow can occur as replanted stands regenerate, in the second period low flow is characterized by mixed and variable responses as forests become established, and in the third period, which follows canopy closure, low flow declines may occur over long timescales. Of 25 small catchments with ≥10 years post-harvest data, nine catchments had no change or variable low flow and 16 catchments experienced reduced low flow years after harvest. The retention of riparian buffers, limited size of harvest units, and adherence to reforestation requirements have altered the contemporary forest landscape relative to historical forest practices, but data documenting multi-decadal hydrological responses to current harvest practices is limited. Our review suggests that the magnitude of low flow responses attenuates downstream as a broader mosaic of stand ages occurs and multiple hydrological periods are represented. Declines were not observed in the seven large catchments reviewed. The consequences of low flow declines for aquatic biota are not well understood, but where data do exist aquatic biota have not been adversely affected. We identify priorities for future research that will aid in improving predictions of low flow responses to harvest as forests regenerate.

Oxyhemoglobin-induced expression of R-type Ca2+ channels in cerebral arteries.

BACKGROUND AND PURPOSE: Cerebral vasospasm after subarachnoid hemorrhage (SAH) is a major contributor to mortality and morbidity after aneurysm rupture. Recently, R-type voltage-dependent Ca(2+) channel (VDCC) expression has been associated with increased cerebral artery constriction in a rabbit model of SAH. The goal of the present study was to examine whether the blood component oxyhemoglobin (oxyHb) can mimic the ability of SAH to cause R-type VDCC expression in the cerebral vasculature. METHODS: Rabbit cerebral arteries were organ cultured in serum-free media for up to 5 days in the presence or absence of purified oxyHb (10 micromol/L). Diameter changes in response to diltiazem, (L-type VDCC antagonist) and SNX-482 (R-type VDCC antagonist) were recorded at day 1, 3, or 5 in arteries constricted by elevated extracellular potassium. RT-PCR was performed on RNA extracted from arteries cultured for 5 days (+/-oxyHb) to assess VDCC expression. RESULTS: After 5 days, oxyHb-treated arteries were less sensitive and partially resistant to diltiazem compared to similar arteries organ cultured in the absence of oxyHb. Further, SNX-482 dilated arteries organ cultured for 5 days in the presence, but not in the absence, of oxyHb. RT-PCR revealed that oxyHb treated arteries expressed R-type VDCCs (Ca(V) 2.3) in addition to L-type VDCCs (Ca(V) 1.2), whereas untreated arteries expressed only Ca(V) 1.2. CONCLUSIONS: These results demonstrate that oxyhemoglobin exposure for 5 days induces the expression of Ca(V) 2.3 in cerebral arteries. We propose that oxyhemoglobin contributes to enhanced cerebral artery constriction after SAH via the emergence of R-type VDCCs.

Raymond M. P. Donaghy: a pioneer in microneurosurgery.

Raymond M. P. Donaghy was one of the true pioneers of modern neurosurgery. His restless dedication, innovation, and desire to humbly disseminate his knowledge facilitated the advancement of the field of microneurosurgery. Many of his trainees--most notably M. Gazi Yasargil--continued to advance the field, developing innovative microsurgical instruments and techniques. The history of microneurosurgery is incomplete without a glimpse at the life of this remarkable man.