Deep-planting influence on the development and growth of Eucalyptus globulus (Labill.)

Deep-planting influence on the development and growth of Eucalyptus globulus (Labill.)
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   _________________________________________________________________________________________ In Borralho, N. et al. (2004). Eucalyptus in a Changing World. Proc. of IUFRO Conf., Aveiro 11-15 October 2004   DEEP-PLANTING INFLUENCE ON THE DEVELOPMENT AND GROWTH OF EUCALYPTUS GLOBULUS   (LABILL.) CLONAL CUTTINGS F. Ruiz 1 ; G . López 1   and G. Toval 2 1   Centro de Investigación y Tecnología de ENCE (CIT). Apdo.223. 21080-Huelva, SPAIN.   ( 2   Dirección de Investigación y Tecnología de ENCE (DIT). Crta.Campañó s/n.Vao-Ribeiro. 36157-Pontevedra, SPAIN   ( ABSTRACT The planting method is one of the factors that affect most plant performance in the field. This study analyses and describes the results obtained in two trials of deep-planting with a clonal stock of Eucalyptus globulus . Three deep-planting treatments, were established in a experimental design of randomised complete blocks. Trials were located in two representative forest areas in the province of Huelva (SW Spain): Coastal Sand Plains and Shale Soils in Andévalo . The analysis of height and diameter growth during 6 years following the plantation showed that the deep-planting treatments presented a significantly lower shoot growth than root collar planted at surface. No significant differences in survival were seen between treatments in all cases. Analysis of current growth shows that plants planted with the root collar at ground level growth better than those planted below surface, particularly in dry years. The global results indicate that planting the root collar below the surface declines growth of E. globulus  clonal stock and after 6 years causes a significant reduction in wood volume production. IntroductionThe Research and Development Direction of ENCE group has been undertaking a plan of forest innovation and improvement of Eucalyptus globulus since 1982. This plan defined zones of improvement according to climate and weather conditions, and involves a program of genetic improvement and another of silviculture to maximise tree growth (Toval & Vega 1982). Specifically in silviculture, the objective is to develop a strategy of forest management for each zone within each area of interest for ENCE (Northern-, Southwest-Iberian peninsula and Uruguay). Silviculture includes four lines of research: (i) soil preparation and techniques for planting, (ii) intermediate intervention, (iii) fertilisation, and (iv) insect and disease controls. The first of these lines, aims to optimise machinery and mechanisation of soil preparation, nursery production, stocking per hectare, season of planting, planting and establishment techniques. The establishment of E. globulus  planting in the Iberian Peninsula has been developed according to the inclusion of new techniques, i.e.: in mechanisation, changes in labour cost, new genetic material. First reports for planting mentioned about the use of dig holes manually for planting of seedling in some cases bare-rooted and also directly sown (Villegas de la Vega 1953). In the Southwest, bare-rooted seedling were planted just keeping local weed control but survival was low (Martín 1946). Then, better practices of soil cultivation, weed control and better root in seedling containers were adopted. Now, the generalised soil preparations practices include cross ripping and insert the plant into each crossing lines. These practices give better anchorage of the rooting system as defence against wind damage (Ruiz et al.  2001). The planting hole is made with a tool of similar size of the container. This rod planting is press vertically in the surface and plants are inserted into the hole. This system gives a good level of survival and improves markedly tree development at early ages (Toval 1999). Regardless the adoption of better practices in the Iberian Peninsula, particularly in areas of dry climate, plant seedling deeper than the root collar is a strong habit of foresters independently of the tree species. Whether deep planting is a favourable practice to tree growth or not, remains as a controversial issue. There are reports in both side of the opinion. Some authors agree about the advantages of insert the plant root collar below the ground (i.e.: Shipman 1960; Stroempl 1990; Paterson 1993). Specifically for E. globulus , Goes (1977) recommended planting in Portugal 15 cm below the root collar. Also FAO (1981) recommended planting the root collar a little below the surface of the soil. This book cited APPM practice of planting 2.5 cm below or deeper if soil moisture declines. A deeper exploration of root system supposed advantages for proximity to get more underground water reserves. In disagree with previous reports, others showed negative impacts of planting extremely deeper pines (i.e.: Wakeley 1954; Domínguez-Lerena et al.  2001) and others species (i.e.: Hartley 1935; Toumey & Korstian 1942). This report presents results of a study designed to evaluate deep planting effects on growth of E. globulus  clones at two sites representatives of the Huelva province. MATERIAL AND METHODS Plant material was the operational clone 334-1- AR of ENCE produced at Silvasur nursery in Superleach containers (M-21 model. Industrias    Bardi S.A.L. Navarra, Spain). This type of container has 35 and 20 mm in diameter (upper and lower respectively), 220 mm in long, 123 cm3 of volume and occupies 440 holes/m2. The substrate used to fill the containers was composed pine bark. Clones used were classified before going to the field, to homogenise size (height about 60 cm). Soil preparation involved cross ripping labours of 3 rip feet and at 70 cm deep. Marking of the land for planting was done with a ripper at a 40 cm deep and perpendicular to the last line of deeper ripper done. Three treatments were tested: (T 1 ) root collar planted at surface level, (T 2 ) root collar planted 13 cm below surface, and (T 3 ) root collar planted at 23 cm below surface. Treatments were arranged in five randomised complete blocks which included 10 plants per plots. Planting holes were practiced with a rod planting made of iron. This tool has a part at the end with the container shape and size which is used to penetrate into the soil and put the plant into it. Normally, this tool has a depth limit but it was removed for the experience. Two trials were established to evaluate deep planting impacts on growth of E. globulus  clones at two sites representatives of the Huelva province. The trial called Las Arrayadas stands for the group of shale soils from Andévalo Region and trial called Coto San Isidro represent the coastal sandy plains. A common Mediterranean climate dominate the province with a long dry season (5 months) but differences amongst trials are summarised in table 1. Table 1. Details of each trial Las Arrayadas Coto San Isidro Date of planting 27/03/96 13/04/98 Tree/ha. 711 879 Spacing (m. x m.) 3.75 x 3.75 3.50 x 3.25 Latitude (N) 37º 29’ 01’’ 37º 27’ 07’’ Longitude (W) 06º 28’ 55’’ 06º 27’ 28’’  Altitude (m.a.s.l.) 175 162  Annual average temperature (ºC) 18.1 18.9  Annual rainfall (mm) 496.9 669.5 Slope (%) 18 1 Exposure 240º SW 200º S Type of soil (FAO, 1998) Cromic Luvisol Verti-Profondic Luvisol Soil depth (cm) 90 135  A layer Loam 30 Sandy loam 3 B layer Clay loam 50 Loam / Clay loam 3 Soil texture and % of coarse fraction C layer Loam 90 Clay loam 3 pH 5.7 6.0 Organic matter (%) in A layer 2.4 1.9  Annual assessments of all surviving trees height were undertaken after the first year of planting and diameter at breast height (DBH) since 4 years age up to the age of 6. The calendars of assessment for each site are presented in tables 2 and 3. Percentage of survival at 6 years age was estimated with the presence of live trees. Individual tree volume (VOL) was derived from: VOL=height x (DBH 2 ) x k  ; assuming k=0.29. These data were used to calculate volume per hectare (VOL/HA) as a ratio of the sum of all individual tree volumes per plot divided the total area corresponding to dead and alive trees per plot and referred to the hectare. A Duncan test was used a posteriori   for comparison of treatment means. Table 2. Assessments at Las Arrayadas trial Las  Arrayadas 1 st  Assessment 2 nd   Assessment 3 rd   Assessment 4 th  Assessment5 th   Assessment 6 th  AssessmentHeight 26/03/97 06/04/98 29/05/99 25/03/00 15/06/01 13/06/02 DBH --- --- --- 25/03/00 15/06/01 13/06/02 Table 3. Assessments at Coto San Isidro trial Coto San Isidro 1 st  Assessment 2 nd  Assessment3 rd  Assessment4 th  Assessment 5 th  Assessment 6 th  Assessment Height 18/05/99 29/05/00 10/07/01 14/06/02 10/07/03 17/03/04 DBH --- --- --- 14/06/02 10/07/03 17/03/04    The significances of the differences between treatments, analysed as categorical factor, were tested with an ANOVA (Statgraphics Plus 5.1) separately for each trial using this model: yijk = µ+Ti+Bj+TBij+ek(ij) Where, y is the vector of observation, µ the mean, T treatment effect, B block effect, TB the interaction of treatment by block and e the random error. Data of the oldest individual tree volume and volume per hectare from both sites were pooled in another model to evaluate site S effect and interaction treatment by site ( ST ). In this case, analyse considered treatments root collar planting depth as quantitative factor using this model: y ijkl = µ+S i +T  j +B k(i) + ST ij  +TB  jk(i) + e l(ijk) Relationship between difference of current growth amongst treatments which resulted significant and climate variables were examined by lineal regression analysis. Height was used in this analysis because it offered more pairs of points for exploring (6) than DBH (with only 3). RESULTS AND DISCUSSION Significant differences of deep planting were found for DBH at different ages and sites (p < 0.05) and heights at Las Arrayadas in early ages (Table 4). Planting the root collar deeper than the surface affect negatively diameter growth. In contrast to root collar at level surface, decreases of 7.2% and 14% on DBH were observed at Las  Arrayadas and Coto San Isidro, respectively. Height showed a similar trend to DBH but less important and decreasing with age (becoming not significant after age 5). Table 4. Height and diameter (DBH) table of means for statistical differences  p < 0.05. Different letters indicate Duncan grouping (  p  < 0.05) “Las Arrayadas” height   1 height 2 height 3 height 4 height 5 height 6   T 1   163,2 a 405,0 a 610,3 a 886,7 a 1131,9 a T 2   163,4 a 407,7 a 609,0 a 862,8 a 1114,5 a T 3   135,2 b 375,7 b 554,4 b 804,0 b 1056,6 b n.s.  DBH 4  DBH 5  DBH 6   T 1   84,2 a 110,0 a 132,0 a T 2   82,3 a 108,2 a 131,7 a T 3   74,2 b 100,9 b 122,4 b “Coto San Isidro” DBH 4  DBH 5  DBH 6   T 1   128,3 a 142,7 a 167,7 a T 2   117,9 ab 131,5 ab 152,9 ab T 3   115,9 b 128,11 b 144,0 b Growth rates were best at the highest rainfall site Coto San Isidro, which agree with a better soil characteristics for E. globulus. At this trial, the small differences in height growth related to planting depth may be because there was no limitation in soil exploring by the roots. Whereas at Las Arrayadas, a shallow soil (with a high proportion of rocks fragments, a clay loam texture and a C layer sometimes at 55 cm of depth) conditioned root exploring and then, manifested a more significant decline in height growth when varying the planting depth. These results agree with previous works (Switzer 1960; Marx et al. 1963; Koshi 1960) which concluded that the decline affect more negatively under conditions of clay and waterlogged soils. Deep planting did not affect statistically survival at any sites. This agrees with other authors (Slocum 1951; Slocum & Maki 1956; Marx et al. 1963; Shiver et al. 1990; Paterson & Maki 1994) but controversial results were showed for different authors. Where some reported that deeper planting give results of higher survival rates (Shipman 1960; Stroempl 1990; Paterson 1993 all cited by Domínguez-Lerena et al. 2001) others stand that deeper planting evolves reduction of carbohydrate on plants, more susceptibility to fungi attack and consequentially mortality (Margolis & Waring 1986). Attack of Botritis sp. was observed more frequent on E. globulus plants with root collar under soil level (Ruiz, personal observation). This suggests that the risk of attacking increases under environmental conditions where part of the stem remains under the ground level. Planting the root collar below the surface of the soil aimed to get better survival under conditions of water deficit was a strong habit within foresters but this formal experience proved that it was an inaccurate practice. Differences in current height growths between root collar planted at surface level treatment and root collar planted at 23 cm below surface treatment (T 1 -T 3 ) were of different sign according to the year. Specifically at Las  Arrayadas trial, relationship of different current growth and climatic variables were explored, such as chronological annual rainfall, annual rainfall of the last 12 months before the assessment and seasonal rainfall. The best fit of the relationship was obtained with annual rainfall of the last 12 months before the assessment. The lineal model adjusted was: y = 40.745 – 0.04307 x; r  2  = -0.887; p < 0.05. The model explains that in dry years, plants planted at ground level grew better than those planted below surface (Figure 1). This may be because in dry years, the fog plays an important roll in the    tree water balance and the superficial root architecture has a better position to capture this type of water available.  Annual Rainfall (12 month before the assessment) T1-T3 mmcm34054074094011401340-20-100102030   Figure 1. Plot of fitted model of regression between differences in current height growths between root collar planted at surface level treatment and root collar planted at 23 cm below surface treatment (T1-T3) and annual rainfall of the last 12 months before the assessment. Individual tree volume at age of 6 years was mainly affected by site (p < 0.001) and treatment (p < 0.05) sources of variation. From the lineal fitted model of treatment by planting depth relationship it is assumed that a reduction of 0.6 dm 3  of tree volume took place every centimetre of deeper root collar plantation (Figure 2). This trend in the results for E. globulus are consistent with other found for Pinus halepensis (Domínguez-Lerena et al. 2001). Depth of root collar below surface    V   O   L   6   º cmdm3048121620247580859095100   Figure 2. Plot of fitted model of regression between individual tree volume at age of 6 years (dm 3 ) and depth of collar root planting (cm).   Finally, volume per hectare (VOL/HA) is the indicative of productivity for the treatment tested. The analysis showed that the planting depth is a significant effect on VOL/HA (  p  < 0.05). A decrease on growth is manifested when the root collar is planted below the surface (Figure 3). The decrease marked 0.47 m 3 /ha every centimetre of increase of planting depth (r  2  = 0.938). Depth of root collar below surface    V   O   L   /   H   A   6   º cmm3/ha0481216202430405060   Figure 3. Plot of fitted model of regression between volume per hectare at age of 6 years (m 3 /ha) and depth of collar root planting (cm). In disagreement to traditional practices, this work prove that planting the root collar below the surface declines growth of Eucalyptus globulus  clonal stock and after 6 years causes a significant reduction in wood volume production. This effect is due to individual tree volume reduction instead of survival. In addition, planting trees below the collar root was more negative under dry area conditions as tested in the trials.    ACKNOWLEDGEMENTS Thanks to Dr. Juan Domingo Santos from the Departamento de Ciencias Agroforestales, Universidad de Huelva for sample undertaking and providing soil analyses. Special thanks to D.  Anselmo Rama from ENCE, pioneer of the E. globulus  silviculture in SW Spain, for his motivation on the initial idea of this research. REFERENCES FAO (1981) “El eucalipto en la repoblación forestal ”.  Roma, Italia. Domínguez-Lerena S.; Villar Salvador P.; Fuertes L. and Peñuelas J.L. (2001). Proc. III CFE, mesa nº3, tomo II: 49-54. Goes E. 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Escuela Especial de Ingenieros de Montes. Madrid. España. Wakeley P.C. (1954). “Planting the southern pines”. Southern Forest Experiment Station. U. S. Dept. Agric. Monograph nº 28.
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