168 Moffat et al.: Experimental Tree Planting on U.K. Containment Landfill Sites Growth Tree growth was evaluated by means of annual measurements of height from 1994 to 1999 and on a 2-year basis from 2000 onward, except at Beech Farm where annual observations were continued until 2001 as a result of replanting of the experiment. Table 3 contains the predicted means of log tree height at age 8 years (9 years). The species by site interaction was again sig- nificant (P < 0.001) and, similar to the survival analysis, the year of planting was not. Figure 2 shows the mean annual increment and height for each of the species at each site. It shows that Shaw Tip produced the fastest height growth rates for most species and that the slowest tree growth occurred at Grunty Fen. Across all sites, height growth rates were greatest in the poplar, alder, cherry, whitebeam, and ash species. Species with slow absolute growth rates included beech, sycamore, and oak, although care must be exercised in making comparisons among species with different growth habits. Growth increments did not show steady annual increases and the performance of individual species planted at different sites was also markedly variable. This probably reflects different climatic or site conditions such as soil moisture or nutrient status in different years. However, annual increments of most species at Grunty Fen appeared to be suppressed compared with the other sites, especially between 1994 and 1999, and tree growth rate has showed little tendency to accelerate in more recent years at this site. Most species reached their maximum annual increment in 2000 to 2001 or in 2002 to 2003 (Table 4), which may reflect, in part, the fertilizer applications in 1999 and 2002. Annual rainfall data from three meteorological stations within reasonable prox- imity to Yanley (Long Ashton), Shaw Tip (Oxford), and Pimbo (Bradford) indicate that 1995 to 1996 were relatively dry years, which may help to explain the small increments in annual growth rate during this period. It is also possible that tree growth re- sponded to the upturn in annual rainfall between 1997 and 2000. Summer drought in 1995 was very pronounced at all sites, which probably explains why such poor height increments were expe- rienced in the subsequent growth period. Nutrition Taylor (1991) gives foliar nitrogen (N), phosphorus (P), and potassium (K) concentrations that are regarded as representing deficient and optimal conditions for the more common species in British forestry. For the remaining species, information from Auchmoody and Smith (1977), Callan and Westcott (1996), and Ystaas and Frøynes (1997) was used to estimate deficient and optimal values. The appropriate values for optimum and defi- cient N, P, and K status are presented in Table 5 together with an assessment of the status of each of the tree species at each of the five sites. The results demonstrate that N deficiency was wide- spread with most species demonstrating severe deficiency at two or more sites. Only white poplar and Italian alder demonstrated optimal N status at some sites. These results generally agree with the growth data discussed previously and may explain the re- duced growth rate in some species in 2000 to 2001. Italian alder might be expected to show less of a N deficiency than other species because of its N-fixing capability when infected with the actinomycete Frankia. However, it is possible that at some sites, trees were poorly nodulated, impairing their ability to fix N. When reapplication of N fertilizer was made in Spring 2002, the maximum annual increment in 2002 to 2003 was identified in some species (Table 4), which might be attributed to this addition. Phosphorus and K were generally optimal in whitebeam, syc- amore, poplar, cherry, and ash but showed some deficiency in other species. Corsican pine was deficient in P and K at most sites. Oak and beech also exhibited slight or moderate deficien- cies in K. The foliar data confirm that K supply is generally not a problem for woodland establishment on brownfield land (Mof- fat and McNeill 1994). In 1998, of the 37 combinations of species and site investi- gated, only three, alder at Shaw Tip and poplar at Pimbo and Beech Farm, were considered to have optimal nutrient supply (Kennedy and Moffat 1999). In 2001, only four had optimal supply of all three nutrients despite a N application in Spring 1999; species include poplar at Pimbo, Shaw Tip, and Yanley and Italian alder at Yanley. The deficiencies identified in the 2001 foliar analysis demonstrate the lack of impact longevity of the applied N fertilizer. It is possible that considerable leaching of N occurred in the soil materials used, most of which contained little organic matter. Reclamation using these materials in 1993 to 1994 predated guidance on soil-forming materials (Bending et al. 1999), which strongly advocated the use of organic wastes to build up fertility and nutrient-holding capacity of the substrates. Experience from this study would appear to confirm the appli- cability of this guidance, because supplementary fertilizer appli- cation was required only 3 years after the first application. Re- Table 4. The year species achieved their maximum annual height increment during the 10-year monitoring period (1993 to 2003). Ash Beech Farm 2001 2002–2003 2001 Grunty Fen 2002–2003 Beech —— Corsican pine English oak Leyland cypress —— Silver maple Sycamore Whitebeam White poplar Wild cherry 2001 2001 2000 ©2008 International Society of Arboriculture 2002–2003 2002–2003 Pimbo 1999 — 2002–2003 2002–2003 Shaw Tip 1997 1999 — — 2000 —— 1997 — 2002–2003 1999 1999 1998 2002–2003 1998 1996 1997 — 1997 2002–2003 —— 1999 — 2000–2001 1997 1997 Yanley 1997 — 2002–2003 1997 Hybrid larch —— 2002–2003 —— Italian alder 1999 — — 1997 2002–2003 1997 2000–2001
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