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Notes: Summary. Similar chlorthal (dimethyl 2,3,.5,6-tetrachloroterephthalate) degradation patterns were found in pot cultures of white pine and Monterey pine grown in a sandy soil and in fallow cultures of the same soil. After 120 days, the content of chlorthal plus its degradation products (as measured by 14C-activity) had decreased to 37% in the fallow and white pine cultures. A somewhat slower rate of degradation in soil (average 45%*C-activity remaining) was observed for the Monterey pine cultures. Thus in 120 days, 55–63% of the added chlorthal had been lost from the soil system. A negligible amount of this could be accounted for by plant uptake. After 60 days of growth the rate of degradation in soil was greatly curtailed suggesting that the accumulated degradation produces were able to inhibit the further degradation of the herbicide.Analysis of *C-labelled extracts from the pine tissue showed that uptake of chlorthal varied from 0–25 to 1–2% of the total amount of the chemical added to the soil. Degraded, as well as intact chlorthal, were found in both Monterey and white pine tissue. Very limited mobility of chlorthal in the plant was observed and the concentration in the shoots was less than 10 pm. About 80% of the absorbed chlorthal remained in the root systems. Plant growth led to a rapid dilution of absorbed chlorthal. The growth of both species of pine was rapid and apparently healthy in chlorthal-treated soil and comparable to that of the control plants.

Notes: Summary. The consumption of water by weeds was determined on the basis of the loss in yield of timber suffered by 28–32–year-old plantations of red pine (Pinus resinosa Ait.). Soil and biomass analyses included several pairs of closely located stands established simultaneously on either cultivated or weed-supporting soils. The water supply of 1050 metric tons/ac, available during the growing season, was estimated as the algebraic sum of precipitation, winter storage, condensed vapour, evaporation of intercepted rainfall and gravitational discharge. The biomass of plantations on soils of satisfactory nutrient content and aeration consumed about 500 kg water for production of 1 kg dry matter. The diversion of available water by weed cover on soils of high potential site indices approached 100 kg per kg oven-dry tissues. Blueberries, sweet fern and other heath plants, with initial weight of about 10 metric tons/ac, caused more than 50% loss in the expected volume of merchantable timber. The established relations facilitate an estimate of the productive potential of weed-supporting soils and the choice of an appropriate tree spacing of forest plantations. Les mauvaises herbes, facteur inhibant de la croissance des essences forestières 〈section xml:id="abs1-1"〉〈title type="main"〉Résumé.La consommation d'eau par les mauvaises herbes a étéévaluée en rapport avec la perte de rendement en bois éprouvée par des plantations de pins rouges (Pinus resinosa Ait.) âgés de 28 à 32 ans. Des analyses du sol et de l'ensemble de la végétation ont été effectuées simultanément par paires dans des stations voisines sur des aires maintenues propres par des facons culturales ou infestées de mauvaises herbes. L'apport d'eau, de 2625 tonnes a l'hectare durant la pdriode de croissance, fut considéré comme la somme alg6– brique des precipitations, du stockage hivernal, de la condensation de la vapeur, de l'éva-poration de la pluie interceptée et de l'e'coulement par gravité. L'ensemble de la masse végétale des plantations, sur des sols d'un niveau de fertilité satisfaisant et convenablement aérés, consomme environ 500 kg d'eau pour la production de 1 kg de matiére séche. Le détournement d'eau disponible par la couverture des mauvaises herbes sur des sols à haut potentiel de fertilité approcha de 100 kg par kg de tissu dessé chéà l'étuve. Les myrtilles, les Myrica ('sweet fern’) et autres plantes de landes, avec un poids initial d'environ 25 tonnes a l'hectare provoquerent une perte de plus de 50% du volume attendu de bois commercialisable. Les relations établies facilitent l'estimation du potentiel de production des sols infestéd de mauvaises herbes et le choix d'un espacement approprié entre les arbres dans les plantations forestières.