Penetrable canopy

Flowering of S. divinorum, as in many forest understory species, is promoted by sunlight, and the extent of flowering of a given population is dictated by the amount of sunlight that penetrates the canopy. We saw... 

My Guide then seized my hand and bade me follow him to the next Chamber. When I had penetrated through the veil which closed the entrance, again I saw a throne upon which a Woman was seated, clothed in Majesty, and wearing the Crown of Authority. By her side was an Eagle, and above her was a canopy which seemed to be formed of the Wings of Angels. 

Large droplets will not penetrate the canopy (Figure 2). 

To estimate amount of spray penetrating the canopy and depositing on the ground, we collected spray on Kromekote paper cards. Tables I-IV provide deposit data from several aerial application projects. As expected more spray was recovered on the ground in the open forest than was recovered beneath trees. 

Researchers (Armstrong and Yule (6), and Snowden (2)) provided information on distribution of spray in the crown however, data often has been lacking on quantifying the pesticide spray immediately before it penetrates the canopy. 

In 1980 the FS conducted an aerial spray test in a Florida seed orchard to obtain data on penetration of spray into the canopy (16). As part of the test design, spray was sampled on... 

The data sets reviewed, document our knowledge on the deposition of aerial sprays released over coniferous forests. Conifers are relatively efficient collectors of spray drops as more drops are consistently observed on the ground in open areas than beneath trees. Spray which penetrates the upper canopy, and is unaccounted for on samplers in the lower canopy, probably was filtered out by foliage. More deposits are observed in the upper crown than in the lower crown. Data are lacking, however, on the fate of drops which do not penetrate the canopy. There is a potential for these drops to penetrate the canopy downwind or to drift off target. 

Modeling of Aerial Spray Drift and Canopy Penetration... 

The FSCBG aerial spray computer program is the result of more than a decade of refinement and verification of spray dispersion models used by the USDA Forest Service and the U. S. Army for predicting the drift, deposition and canopy penetration of particles and drops downwind from aircraft releases. This paper describes the mathematical framework of the models and selected applications of the models to military and Forest Service projects. 

The FSCBG aerial spray models and computer program are a result of more than a decades effort in the development, refinement and application of models for use by the U. S. Army and USDA Forest Service in predicting drift, deposition and canopy penetration from aerial releases. During the 1960 s, the U. S. 

Grim, B. S. J. W. Barry "A canopy penetration model for aerially disseminated Insecticide spray released above coniferous forests." Final Report MEDC Project No. 2425, USDA Forest Service Equipment Development Center, Missoula, MT, 1975. 

To illustrate this distribution, Figure 1 shows the result of an actual aerial application of a typical pesticide spray to a broadleafed tree species (3). The "application level" (A) simply assumes that all the spray leaving the aircraft becomes uniformly distributed over the target area (1.12 kg/ha), and the curve shows the parathion levels analytically detected on a statistical sampling of leaves. A major part of the applied pesticide (B) fails to reach the canopy, as corroborated by Barry (2) with conifers, and is assumed to represent airborne drift, volatilization, and, to a lesser extent, penetration to the ground. Once on the... 

Penetration of this UV radiation to ground level depends upon the type of forest stand and canopy ( 6). A clumped stand and erectophile canopy admit the greatest proportion (about 35% of the UV incident at the top), as expected. However, in either normal or planophile canopies in any type of stand, penetration always is less than 15% and often is on the order of only 2%. Almost all photodegradation will be expected to occur at or above the top contour of the sprayed foliage. 

Figure 9-7. Variation in leaf angle and hence foliar absorption coefficient with distance above the ground for (a) various idealized plants and (b) sugar beet measured at various canopy positions (Hodariova, 1979). Hie greater erectness of the uppermost leaves leads to a lower k for them and hence to better penetration of PPF down to the lower leaves.

The daytime temperature profiles were easy to interpret, as done above, but the nighttime profiles did not have a simple interpretation. Sunlight impinges on the forest as a directed beam, some of it penetrates the canopy, especially with almost overhead sun. Day and night, heat radiation is emitted by all surfaces and in all directions, and radiatively cooled leaves chilled adjacent air, which sank toward the groimd. The net effect in our examples was that there was a minor temperature inversion throughout the forest... 

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