Stemflow leaching from the above-ground vegetative surfaces of broadleaved deciduous canopy trees has been well documented during the growing season. Winter stemflow leaching from the leafless crowns ...of deciduous trees is less well understood, especially in the context of global climate change. Boreal and northern temperate forests are forecast to have a lower incidence of snow events and an increased frequency of rain and mixed precipitation events. A change in the seasonal precipitation regime may be significant due to linkages among global change, stemflow leaching, and biogeochemical processes. The aim of this paper is to (1) demonstrate the extent of winter stemflow nutrient leaching from deciduous trees; (2) explore how winter stemflow leachate quantity may vary as a function of the type of precipitation event; and (3) quantify the extent to which an increase in the incidence of snow-to-rain events would enhance stemflow leaching. Measuring meteorological conditions, stemflow volumes, and stemflow chemistry over two successive winter seasons in New England demonstrated that winter stemflow drainage was significantly enriched compared to the incident bulk precipitation: 162 times greater for K+, 44 times greater for Ca2+, and 29 times greater for Mg2+. Snow-to-rain events leached considerably greater quantities of base cations from the deciduous trees than all other types of precipitation events. An increased frequency of snow-to-rain events from 13.8% to 25% of winter precipitation events would substantially increase mean stemflow nutrient inputs to the bases of forest trees during winter. Implications for significantly increased winter stemflow leachate inputs, corresponding to an increased incidence of snow-to-rain events, include a shift in the biogeographic range of species, delayed leaf emergence, and increased soil respiration.
Physical geographers are often confronted with the decision of whether to publish in geography or nongeography journals. The present study seeks to quantify the number of articles with a significant ...hydrology content published in geography versus hydrology journals by physical geographers from 1997 to 2002 using the ISI Web of Knowledge electronic database. Of 690 articles published in the 10 selected geography and hydrology journals during the period of study, over four-fifths were published in hydrology journals. Based on our interpretation of the data, the comparatively smaller audience in geography and the risk of acquiring fewer citations compels physical geographers to publish in hydrology journals for increased visibility. A critical mass of physical geographers should consider publishing some of their work in physical geography journals to elevate the status of geography in the academy.
Stemflow leachate chemistry from a deciduous canopy tree species monitored during late winter and early spring precipitation events demonstrated significant chemical enrichment. By considering ...stemflow volume and chemical concentration in relation to the quantity that would be expected in a rain gage occupying an area equivalent to the trunk basal area, manganese was found to be enriched by a mean factor of 1450 and potassium by a mean factor of 580. The most pronounced enrichment was documented during a late winter rain-on-snow event characterized by temperature oscillations near the freezing point. During this event, manganese was enriched by a factor of 4400 and potassium by 1715. We conclude that mixed precipitation events with multiple freeze-melt cycles can generate significantly more leachate than spring rainfall events because of lower air temperatures and increased kinematic viscosity and surface tension of stemflow drainage. These physical properties lengthen the residence time of intercepted precipitation on the woody frame of the tree and promote its funneling from inclined branches. Stemflow represents a spatially localized and enriched point input that may affect tree vigor in early spring. The influence of localized aqueous chemical fluxes to the forest floor on forest biogeochemistry and ecophysiological functioning are discussed.
Leaf transpiration rates of
Impatiens capensis were measured beneath a broadleaved deciduous forest canopy over successive growing seasons using a steady-state porometer. The transpiration ...measurements, which continued into early autumn, provided a framework for assessing whether
I. capensis exhibits stomatal opening in response to the autumnal increase in available direct-beam radiation reaching the forest floor. The deciduous canopy LAI (leaf area index) decreased from a growing season maximum of 3.94 m
2 m
−2, while the understory
I. capensis population located along a stream channel maintained LAI values ranging from 0.58 to 1.05 m
2 m
−2 late into the growing season. Late morning and early afternoon leaf transpiration rates during the months of June and July averaged about 8 μg cm
−2 s
−1, with a mean stomatal conductance of 0.5 cm s
−1. In August, leaf transpiration averaged almost 12 μg cm
−2 s
−1, with stomatal conductance exceeding 1.5 cm s
−1. However, beginning in early to mid-September, before canopy leaf-fall, the persistent green leaves of
I. capensis exhibited a sharp decline in transpiration, possibly a result of decreasing vapor pressure deficits or non-lethal physiological damage induced by cold stress. This physiological decline offsets any advantage that could have been gained by the increased exposure to direct-beam radiation after canopy leaf-fall in mid-October. Although green leaf area and seed-bearing capsules may persist until the first frost in October or early November, there is no evidence of stomatal opening suggestive of carbon assimilation for enhanced seed development during this early autumn period. We conclude that the persistent green leaf area of
I. capensis fails to exploit the increase in available direct-beam radiation in the final stage of its life cycle.
Key Points
Evaluated method may allow removal of multidirectional bending strains
Canopy water loading signal may be isolated using the evaluated method
Sample storms show water loading response to ...rainfall until storage capacity
To improve the water budgeting of forested catchments and inform relevant hydrologic theory regarding water cycling within forests, the scientific community has been seeking simple, inexpensive, direct methods for determining rain water storage on in situ tree canopies. This paper evaluates an installation arrangement and routine for one such method: mechanical displacement sensors placed on a tree's trunk to directly monitor compression under canopy water loading from rainfall. The evaluated installation routine aligns mechanical displacement sensors along orthogonal axes passing through the mechanical center of the trunk to reduce wind‐induced noise. The experimental attainment of neutral bending axes for a subject hardwood and softwood tree suggests the routine is precise and approximates the trunk's mechanical center well regardless of differences in cellular axial stiffness between heart and sapwood. When installed in this precise sensor arrangement, bending tests of different loading directions produced a consistent signal ratio between sensor pairs of approximately −1 (1 unit compression/1 unit elongation), allowing the identification and removal of bending strains from the raw strain signals to isolate the compression component attributable to canopy water storage loads. The same experiments performed on sensors just 5 cm off the trunk's computed mechanical center were unable to produce neutral bending axes or consistent signal ratios during bending from variable loading directions. Results from the method evaluation were translated into a data processing technique that is then applied to strain data collected through two sample rain events (one each for the hardwood and softwood trees). The processed strain data showed a clear synchronicity between rainfall and canopy loading, as well as periods of maximized canopy water loading (canopy storage capacity). Our results indicate that the evaluated arrangement and installation procedure for mechanical displacement sensors may be able to provide scientists with simple, direct canopy water storage estimates at high temporal resolution and sensitivity.
The aim of the present investigation was to assess histologically the effect of LLLT (GaAIAs, 830 nm, 40 mW, CW, (Phi) approximately 0.6 mm, 16 J/cm(2) per session) on the repair of surgical defects ...created in the femur of the Wistar Albinus rat. The defects were filled to lyophilized bovine bone (Gen-ox), organic matrix) associated or not to GTR (Gen-derm).
A major problem on modern Dentistry is the recovery of bone defects caused by trauma, surgical procedures or pathologies. Several types of biomaterials have been used in order to improve the repair of these defects. These materials are often associated to procedures of GTR. Previous studies have shown positive effects of LLLT on the repair of soft tissue wounds, but there are a few on its effects on bone healing.
Surgical bone defects were created in 42 animals divided into five groups: Group I (control, 6 animals); Group II (Gen-ox, 9 animals); Group III (Gen-ox + Laser, 9 animals); Group IV (Gen-ox + Gen-derm, 9 animals); Group V (Gen-ox + Gen-derm + Laser, 9 animals). The animals on the irradiated group received 16 J/cm(2) per session divided into four points around the defect (4 J/cm(2)) being the first irradiation immediately after surgery and repeated seven times at every 48 h. The animals were humanly killed after 15, 21, and 30 days.
The results of the present investigation showed histological evidence of improved amount of collagen fibers at early stages of the bone healing (15 days) and increased amount of well organized bone trabeculae at the end of the experimental period (30 days) on irradiated animals compared to non irradiated ones.
It is concluded that a positive biomodulative effect on the healing process of one defect associated or not to the use of organic lyophilized bone and biological bovine lyophilized membrane on the femur of the rat.
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