Ten-Year Results of Fertilizing 

 Grand Fir, Western Hemlock, 

 Western Larcli, and Douglas-fir 

 with Nitrogen in Northern Idaho 



Russell T. Graham 

 Jonalea R. Tonn 



INTRODUCTION 



Forest fertilization has become an accepted manage- 

 ment tool for increasing merchantable volumes of forest 

 stands in many areas of the country. However, there is 

 reluctance to apply fertilizers operationally because of 

 inconsistent growth responses and because of a paucity 

 of information on the response of forest stands to fertili- 

 zation, particularly in the Northern Rocky Mountains. 



Nitrogen, usually the most growth-limiting nutrient of 

 forest soils, is the most commonly applied fertilizer. The 

 addition of other elements, such as phosphorus, potas- 

 sium, and sulfur, seldom improves gains achieved from 

 applying nitrogen alone (Gessel and others 1965; Heil- 

 man 1971; Miller and Reukema 1974). Nitrogen is 

 usually applied in the form of urea that contains 46 per- 

 cent nitrogen, or in the form of ammonium nitrate that 

 contains 34 percent nitrogen. 



The site on which fertilizer experiments are located 

 can influence results. Usually, better growth responses 

 to fertilizer occur on poor sites (Miller and Fight 1979). 

 But often, as Miller and Reukema (1974) found, good 

 sites also have excellent response to application of fer- 

 tilizer. They reported ammonium nitrate applied at 

 300 lb per acre significantly increased growth of 75-year- 

 old Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco 

 var. menziesii) on a highly productive site in western 

 Washington. In contrast, Graham and Tonn (1979) 

 reported no increase in growth attributable to the appli- 

 cation of nitrogen fertiUzer on western white pine (Pinus 

 monticola Dougl.) on a good site in northern Idaho. 

 Webster and others (1976) reported poor growth 

 responses to the application of nitrogen fertilizer on 

 western hemlock {Tsuga heterophylla [Raf.] Sarg.) along 

 the Pacific coast. On inland sites, they reported a good 

 response. 



How an individual species reacts to the application of 

 fertilizer can also be highly variable. As noted earlier, 

 western white pine in one study in northern Idaho did 

 not respond to nitrogen fertilizer, while in another 

 (Ryker and Pfister 1967) there was a 39 percent increase 

 in the diameter growth of nitrogen-fertilized western 

 white pine over unfertilized pine. Similarly, Loewenstein 

 and Pitkin's study in northern Idaho (1963) reported 

 nitrogen-fertilized western white pine with a 187 percent 

 increase in height growth, as compared to unfertilized 

 pine. Scanlin and others (1976) reported a 61 percent 



growth increase of grand fir (Abies grandis [Dougl. ex D. 

 Don] Lindl.) due to nitrogen fertilizer application in 

 northern Idaho. Loewenstein and Pitkin (1963) also 

 reported a 286 percent response to the application of 

 nitrogen fertilizer on grand fir in northern Idaho. 



As these examples show, the results of fertilizer trials 

 are highly variable. They also show how uncertain the 

 results from the application of fertilizers can be. There- 

 fore, the surest way to select areas for operational fertili- 

 zation is to match stand and soil characteristics of suc- 

 cessful, experimental field trials (Miller and Fight 1979). 



This study was undertaken to document the results of 

 nitrogen fertilization in two stands on experimental 

 forests chosen as representative of good sites in north- 

 ern Idaho. We reasoned that stands of proper age, grow- 

 ing on sites with no Ukely moisture or other nutrient 

 hmitations to growth, might respond well to the applica- 

 tion of readily available nitrogen. 



STUDY DESIGN 



Two fertilization studies were established in young, 

 natural stands of mixed conifers in the Tsuga 

 heterophylla/Pachystima myrsinites habitat type 

 (Daubenmire and Daubenmire 1968). One was located at 

 the Deception Creek Experimental Forest (DCEF), and 

 the other was at the Priest River Experimental Forest 

 (PREF). Both represent excellent forest sites in northern 

 Idaho. 



The DCEF study, on a north aspect, in lower Snyder 

 Creek was 4.5 acres in size. Slope angles ranged from 

 gentle to 50 percent. The soils of the area are inceptisols 

 overlaying gneiss parent material. The stand developed 

 under seed trees from a 1952 cutting. The seed trees 

 were removed in 1965, and in 1971 the stand was 

 cleaned to a 10-foot-square spacing. A uniform stand of 

 dominant and codominant trees remained. Species 

 represented in the stand included: 



western white pine 



western larch (Larix occidentalis Nutt.) 

 Douglas-fir 

 grand fir 

 western hemlock 



Engelmann spruce (Picea engelmannii Parry ex 

 Engelm.) 



subalpine fir [Abies lasiocarpa [Hook.] Nutt. var. 

 lasiocarpa) 



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