Báo cáo lâm nghiệp: "Effects of seedling density on the growth of Corsican pine (Pinus nigra var. maritima Melv.), Scots pine (Pinus sylvestris L.) and Douglas-fir (Pseudotsuga menziesii Franco) in containers"

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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Effects of seedling density on the growth of Corsican pine (Pinus nigra var. maritima Melv.), Scots pine (Pinus sylvestris L.) and Douglas-fir (Pseudotsuga menziesii Franco) in containers...

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Nội dung Text: Báo cáo lâm nghiệp: "Effects of seedling density on the growth of Corsican pine (Pinus nigra var. maritima Melv.), Scots pine (Pinus sylvestris L.) and Douglas-fir (Pseudotsuga menziesii Franco) in containers"

Original article Effects of seedling density on the growth of Corsican pine (Pinus nigra var. maritima Melv.), Scots pine (Pinus sylvestris L.) and Douglas-fir (Pseudotsuga menziesii Franco) in containers b Mason Richard Jinks a Bill a Commission Research Agency, Alice Holt Lodge, Wrecclesham, Forestry Farnham, Surrey, GU10 4LH, United Kingdom b Forestry Commission Research Agency, Northern Research Station, Roslin, Midlothian, EH25 9SY, United Kingdom (Received 20 May 1997; accepted 29 September 1997) Abstract - Corsican pine, Scots pine and Douglas-fir seedlings were grown in containers at a con- stant volume at densities ranging from 100 to over 1 000 plants m Both shoot and root dry . -2 weight of each species decreased with increasing density, especially at densities greater than 500 m In contrast, shoot height of Corsican and Scots pine increased at high densities, but the . -2 height of Douglas-fir was unaffected by density. Shoot height was not correlated with dry weight in Douglas-fir and Scots pine, and was negatively correlated in Corsican pine. Root collar diam- eter was positively correlated with seedling weight in all three species. Increasing the volume of tray cells only increased seedling size in Douglas-fir at densities lower than 400 m Survival . -2 of outplanted Douglas-fir seedlings was reduced in plants grown at the highest density (1 550 m ). -2 Height and diameter increments were greatest in plants raised at intermediate densities around 780 m (© Inra/Elsevier, Paris.) . -2 Pinus nigra var. maritima / Pinus sylvestris / Pseudotsuga menziesii / containers / density Résumé - Effets de la densité des semis sur la croissance du pin noir de Corse (Pinus nigra maritima Melv.), du pin sylvestre (Pinus sylvestris L.) et du sapin de Douglas (Pseudotsuga var. menziesii Franco) en conteneurs. Des semis de pin noir de Corse, pin sylvestre et sapin de Douglas ont été cultivés en conteneurs à volume constant, avec des densités variant de 100 jusqu’ à plus de1 000 plantes mLe poids sec des pousses et des racines a décru chez chaque . -2 espèce lorsque la densité se trouvait accrue, particulièrement dans le cas de densités supérieures à 500 m Par contraste, la hauteur des pousses du pin noir de Corse et du pin sylvestre s’est accrue . -2 * Correspondence and reprints E-mail: r.jinks@forestry.gov.uk
les densités élevées, mais celle du sapin de Douglas n’a pas été changée par la densité. Il n’y avec eu de corrélation entre la hauteur des pousses et le poids sec chez le sapin de Douglas et le a pas pin sylvestre, mais on a observé une corrélation négative chez le pin noir de Corse. Le diamètre du collet a montré une corrélation positive avec le poids des plantes chez les trois espèces. L’augmentation du volume des compartiments des bacs n’a pas accru la taille des semis de sapin de Douglas que dans le cas de densités inférieures à 400 m La survie des semis de . -2 de Dou- sapin glas repiqués était réduite chez les sujets cultivés à la densité la plus élevée (1 550 m). Les plus -2 grandes accroissements en hauteur et en diamètre ont été trouvés le plus élevé chez les plantes cul- tivées en utilisant des densités intermédiaires à peu près de 780 semis m (© Inra/Elsevier, . -2 Paris.) nigra var. maritima / Pinus sylvestris / Pseudotsuga menziesii / conteneurs / densité Pinus 1. INTRODUCTION in the absence of confounding effects of cell volume. Comparisons of seedling growth in different sized containers are There is a wide range of cellular or often difficult to interpret because an modular tray systems available for rais- increase in cell volume is usually accom- ing tree seedlings and these are designed panied by an increase in the distance with features that favour seedling growth between cells. In tray systems where the and are also efficient for nursery and out- cells are separated from each other, the planting operations. The size and arrange- effects of growing density are caused by ment of the cells in trays has an important competition for space and light between influence on seedling size and must be the shoots of neighbouring seedlings; com- matched to the species growth rate and petition for water and mineral nutrients the length of the production period. The only occurs in systems with permeable growth of seedlings is affected by both cell walls such as paper pots. cell volume and by the growing density imposed by the spacing of the cells in the In general, the results of the few studies trays. Generally, seedling size becomes where container volume has been held larger when cell volume is increased while constant show that seedlings grown at growing space is held constant [2, 6, 7, higher densities tend to grow taller but 15]. The greatest increase in size often have lower stem diameters and dry weight occurs in response to changes in the vol- than seedlings grown at wider spacing [1, ume of small cells since small cells restrict 14, 16]. However, species appear to differ growth earlier than larger ones [6]. The in their responsiveness to changes in con- dimensions (diameter and height) of the tainer density, particularly in terms of cells used to achieve a particular volume effects on shoot height. In Douglas-fir can also influence growth of shallow root- seedlings grown at four densities, shoot ing species like white spruce (Picea glauca height was only slightly affected by den- (Moench) Voss) where, at the same den- sity between 270 and 810 seedling m , -2 sity, seedlings grew more in wider diam- but was increased by 40 % at 1 080 m -2 eter cells [2]. [16]. Spacings between 450 and1 808 seedlings mhad little effect on the height -2 density is considered to be Container important a factor as cell volume in of loblolly pine seedlings. Longleaf pine, as governing seedling growth [9]. There are, however, showed a much larger increase in however, relatively few reports on the both height and seedling dry weight than direct effects of seedling density on growth loblolly pine when grown in a larger vol-
the effects of container density on the wider-spaced container system [1]. ume, growth and survival of Douglas-fir Shoot height of white spruce increased by seedlings after outplanting was studied in 60 % as density was increased from 100 to 1 100 m while stem diameter and root , -2 the fifth experiment. weight all decreased [14]. In British nurseries, the height of 2. MATERIALS AND METHODS of Corsican pine (Pinus nigra seedlings var. maritima Melv.) grown in containers Experiments 1 and 2 on Corsican and Scots is often uneven both within individual pine were carried out at the Forestry Commis- trays and across benches. Seedlings in the sion Research Station, Alice Holt Lodge, Farn- centre of benches are usually taller than ham, Surrey (UK) (latitude 51°11’ N), while those at the edges, suggesting that this seedlings of coastal origin Douglas-fir in exper- iments 3 and 4 were raised at the Northern species is particularly sensitive to seedling Research Station, Roslin, Midlothian (UK) density. The aim of the first experiment (latitude 55°53’ N). All seedlings were grown was to test if height growth of Corsican in peat-based growing media and were fertil- pine is particularly responsive to growing ized by applications of liquid fertilizer during density. Growth of Corsican pine at dif- growth (table I). ferent densities was compared with Scots pine and Douglas-fir in the second and third experiments. The interaction between 2.1. Experiment 1 cell volume and growing density on the growth of Douglas-fir seedlings was inves- Corsican pine seeds (UK Forestry Com- tigated in the fourth experiment. Finally, mission identity number 87(4032) Lot 10) were
ing three densities used wider diameter plastic sown in Lannen Ecopot (Lannen UK Ltd, Cam- bridge, UK) 308 trays (cell volume 53 cm at ) -3 tubes filled with the same volume of media as four densities ranging from 1 525 to about 200 used in the paper pot cells, arranged in an seedlings m This system was used because . -2 hexagonal pattern. Cultural details for grow- the cell walls are made from plastic laminated ing the seedlings were similar to those paper, which minimizes the lateral transfer of described in the first experiment. water, nutrients and roots between neighbour- Twenty seedlings were harvested from the ing cells. The cells in Ecopot trays were of each plot during the following winter centre arranged in an hexagonal arrangement such and the shoot height, root collar diameter and that each cell was bounded by six neighbours shoot and root dry weight were measured for and the four seedling densities were achieved each seedling. The variance in height, root col- by missing out selected cells in the trays. All lar diameter and dry weight tended to increase cells were sown to give the highest density of with mean plant size; thus, their relationships 1 525 plants m Omitting to sow three alter- . -2 with density were analyzed by fitting general- gave a density of 1 030 nate neighbours ized linear models to the reciprocal of the mea- , -2 plants m and by leaving one or two empty sured parameters using gamma error distribu- cells between produced densities of seedlings tion [3, 5]. The models were fitted using 384 and 192 plants m respectively. Each den- -2 procedures in Genstat [13]. Results are pre- sity treatment was replicated four times and sented as scatter plots and curves of observed trays were arranged in a randomized block and fitted values respectively. The fitted equa- design in an unheated polythene tunnel. tions summarized in table II. are Two seeds were sown in each cell during March. Seed was then covered with a thin layer of grit. A sheet of white polythene was placed 2.3. Experiment 3 over the trays until about 10 % of the seed had germinated, after germination seedlings were Douglas-fir seedlings of coastal Washington thinned to single plants per cell. Seedlings were origin were sown in April at five seedling den- grown on through the summer and seedling sities ranging from over 1 500 to about 100 m-2 height and root collar diameter were assessed in Lannen 308 Ecopots. Each density was repli- on 20 seedlings randomly selected from the cated four times and the trays were arranged centre of each plot in autumn after growth had in a randomized block design in a ventilated ceased. Linear and quadratic effects on seedling polythene tunnel. In mid-November, five growth were tested for by analysis of variance seedlings were randomly selected from the (ANOVA) using procedures in Genstat [13]. centre of each tray and shoot height, root col- lar diameter, shoot and root dry weight were measured on each seedling. Relationships Experiment 2 2.2. between these parameters and density were again analyzed using generalized linear mod- els and the results arc plotted on the same axes Seedlings of both Corsican pine and Scots as the results from experiment 2. pine (identity numbers 87(4032) Lot 10 and 86(2009), respectively) were each grown at Differences in light interception by the ten seedling densities ranging from just over canopy of seedlings grown at different densities 1 000 to about 130 m using a hexagonal -2 were followed throughout the summer by mea- arrangement of cells. Densities were obtained suring the percentage of the above-canopy pho- either missing out one or more of the six by tosynthetically active radiation, which was immediate neighbours around seedlings or by transmitted to the media surface using quan- having one or more empty cells separating tum sensors (SKP 200 Skye Instruments Ltd seedlings. Seven densities were set up using Llandrind-Wells, UK). Lannen 308 Japanese Paper Pots (cell volume 65 cm This system is used to produce com- ). 3 mercial crops of Corsican pine secdlings in the 2.4. Experiment 4 United Kingdom; however, for this experiment the cells were lined with thin plastic sheeting to prevent lateral movement of roots or nutrients The effects of cell volume and seedling den- and water between adjacent cells. The remain- sity on the growth of Douglas-fir seedlings was
investigated by using four cell volumes result- same height as the 15-cm deep cells. Cultural conditions and measurements were the same ing from the factorial combination of two as described in the third experiment and the widths (3 and 5.6 cm) combined with two results were analyzed by ANOVA. and 15 cm) of Lannen Ecopots. depths (7.5 The manufacturer specifies cell size as a three digit code consisting of the nominal width (first number) and depth (last two numbers). Thus, 2.5. Experiment 5 the four sizes used in this experiment were 308, 315, 608 and 615. Trays of each cell size The field performance of Douglas-fir plants were sown in April at approximately the same from the five container densities in experiment three densities (table III). All treatments were 3 were tested in an outplanting experiment. replicated four times and arranged in a ran- The experiment was planted on a podzolic domized block design on benches in a poly- brown earth at 200 m a.s.l. in Monaughty For- thene tunnel. Trays with 5.6-cm deep cells were est, Grampian Region, Scotland (latitude 57°30’ N) in April 1991. The location has an placed on supports to raise the top surface to the
root collar diameter of Corsican pine annual rainfall of 850 mm and between 1 000 the and 1 375 day-degrees above 5.6 °C. The site seedlings (table IV). Shoot height showed had been clear-felled in spring 1990 and culti- a positive linear relationship with density vated with a double mouldboard plough in the (P < 0.001), increasing from about 5 cm at following September. Trees were sprayed with the lowest density to nearly 12 cm at full permethrin against Hylobius attack in May and stocking. In contrast, root collar diameter August 1991, April and September 1992 and showed a significant negative relationship April 1993. Competing vegetation, predomi- nantly bracken (Pteridium aquilinum (L.) with seedling density (P < 0.001), falling Kuhn), was cut back by hand in summer 1991 by about one quarter from 2.2 mm in and 1992. seedlings grown at 192 mto 1.7 mm at -2 Plants from the five container densities (i.e. . -2 m 1 525 100,180, 390, 780 and1 550 m were planted ) -2 in randomized block with four design repli- a cates. Plants chosen for the field experiment Experiment 2 3.2. were selected at random from the density treat- ments with no culling for size or forn. In addi- tion, plots of 2-year-old undercut seedlings of Corsican pine seedlings again showed another coastal provenance were included for significant positive relationship between a comparison with the container seedlings. A height and density (figure 1a). Seedlings 20-plant plot was used for all treatments except were on average only 7 cm tall at the low- the 100 m density where 16 plants were used. -2 est density (107 m but grew to just over ), -2 Survival, seedling height and root collar diam- eter were assessed at planting and at the end 12 cm at the highest density - an increase of the first and third growing seasons. Data of nearly 70 %. On average, Scots pine were statistically analyzed by ANOVA. Per- seedlings were about 50 % taller than Cor- centages were arcsine transformed before anal- sican pine seedlings and height increased ysis; however, non-transformed percentages from 12 to 17 cm across the range of den- are presented for clarity. sities. However, the relationship between height and density was weaker than for Corsican pine (table II) with evidence of 3. RESULTS systematic variation with density (fig- 1a). ure 3.1. 1 Experiment Root collar diameters of both species negatively related to seedling den- were had a highly signifi- sity (figure 1b) and the relationship was Seedling density effect again weaker for Scots pine than for Cor- both the shoot height and cant on
sican pine (table II). Stem diameters for The relationship between total dry mat- Scots pine averaged 3 mm at 107 production per tray (biomass) and ter seedlings mand declined to 2.1 mm at -2 seedling density was positive and nearly the closest spacing. Corsican pine showed identical in both species (figure 2a). The a highly significant negative effect of relationship was non-linear with about growing density on root collar diameters, 78 % of the total increase occurring when declining from 2.7 mm at the widest spac- density was increased from 134 to 584 m At higher growing densities, the . -2 ing to 1.7 mm at the closest spacing.
rate of increase in biomass decreased. In sity was increased to 584 m The rela- . -2 contrast, the dry weight of individual between shoot dry weight and tionship seedlings decreased with growing density density was the same for both pines and (figure 2b). Seedlings of both species followed a similar pattern to the trend for grown at the closest spacing were about total seedling dry weight (figure 3a); shoot half the weight of those raised at the widest weight was halved across the density spacing, and again about 70 % of the range, and the majority of the weight loss (70 %) had occurred at 584 m . -2 decrease in weight had occurred as den-
Growing density had the largest effect 584 m Unlike shoot weight, the roots . -2 the weight of the root systems of both on of Scots pine were heavier than Corsican species (figure 3b, table II). The roots of pine (figure 3b). The larger reduction in seedlings grown at the highest density root dry weight compared with shoot were only about one third the weight of weight resulted from a decrease in the allo- those grown at the widest spacing, and cation of dry matter to root system as den- again more than 70 % of this reduction took place as density was increased to sity was increased (figure 3c).
height of Corsican pine seedlings tioning of dry matter between The shoot and negatively correlated with both shoot (figure 3c). root was and root dry weight, but there was no cor- The percentage of incident light trans- relation between the height and weight of mitted to the surface of the trays depended Scots pine seedling (table V). There was a on the growing density (figure 4). The strong positive correlation in both species amount of light transmitted through between root collar diameter and the seedlings grown at the widest spacing was weight of both shoots and roots. between 70 to 80 % throughout the sum- mer. At intermediate densities of 179 and 372 m the percentage transmission -2 3.3. Experiment 3 decreased from about 65 to 50 % after 14 weeks from sowing. At 780 mtrans--2 mission had declined to only 10 % after The response of Douglas-fir seedlings 16 weeks, while all of the light was inter- being grown at different densities was to cepted at the highest density after 14 generally similar to the results of the pre- weeks. vious experiment (figures 1-3). However, seedling height was unaffected by density (figure 1a). Both biomass production and 3.4. Experiment 4 total dry weight were about 20 % lower in Douglas-fir seedlings than with the pines (figure 2). Shoot dry weight was The effects of changes in cell dimen- very similar for all three species across sions on seedling growth depended on the range of densities (figure 3a), whereas growing density (figure 5). At the high- est density (D3, 400 m there was no ), -2 Douglas-fir had the lowest root dry weight (figure 3b). Unlike the pines, there was statistically significant difference in shoot no effect of growing density on the parti- and root dry weight, and stem diameter
est densities were just significantly shorter between seedlings grown in any of the four container sizes. As density was at 88 and 76 cm, respectively (figure 6b). Plants raised at 390 and 780 mproduced -2 decreased, the weight and root collar diam- eter of seedlings grown in the smallest the greatest height increment (13.6 cm) during the first year after planting. This volume containers (308) remained unchanged, but seedling size increased in was significantly higher than in seedlings the other larger three container sizes. At that had been raised at both lower and higher densities (5.7 and 8.9 cm, respec- the lowest density, seedlings grown in 615 containers were four times heavier than tively). Height increments were similar at an average of 68 cm over the following 2 those grown in 308 containers, and were more than twice the size of seedlings years for all densities except the highest raised in the same size container at where the increment was significantly less 400 m(figures 5a and b). Root collar -2 at 56 cm. diameter showed a similar response to the A very similar pattern occurred with the increases in cell size and growing density increase in root collar diameter between dry weight (figure 5c). Although as seedlings raised at different densities (fig- seedling height increased with cell size, ure 6c). The greatest increments in root it tended not to respond to changes in den- collar diameter occurred at intermediate sity within any particular container size densities. This resulted in the negative rela- (figure 5d). The increased growth in larger tion between diameter and density which containers at low densities did not appear existed at planting, changing to a distribu- to be related just to increasing cell vol- tion with a distinct optimum at 780 m -2 ume, since growth in 315 and 608 cells where stem diameter peaked at 19 mm and was generally similar despite the fact that fell to 16 and 13 mm at the lowest and their respective volumes were 106 and highest densities. 185 cm respectively. 3 Survival of the undercut bare-root was similar to the survival of seedlings container seedlings grown at densities 3.5. Experiment 5 below 1 550 m(figure 6a), but the pat- -2 tern of height and stem diameter growth An average of 86 % of the Douglas-fir was different. At planting, the undercut seedlings raised at densities between 100 seedlings were nearly twice as tall and and 780 msurvived by the end of the -2 thick as the container seedlings. However, first growing season after planting in the increases in height and diameter were neg- forest (figure 6a). but survival was sig- ligible during the first year after planting, nificantly reduced to 54 % in plants raised and over the next 2 years these increments at the highest density (1 550 m Subse- ). -2 were only about the same as for the small- quent losses over the next 2 years were est seedlings that had been grown at the the same for each treatment and averaged highest container density. Consequently, about 7 % by the end of the third grow- the initial size advantage of the bare-root ing season. There was a high Hylobius seedlings had disappeared by the end of population during the first two seasons, the third year. which was responsible for some of the losses. 4. DISCUSSION By the end of the third year after plant- ing, plants raised at 780 m were the -2 tallest at just over 100 cm, whilst seedlings The results of the first three experi- grown at the lowest as well as the high- showed that growing density, with ments
rooting volume held constant, has a strong species showed a similar negative response influence on the growth and development density for root dry weight and root col- to lar diameter, although individual species of Corsican pine, Scots pine and Dou- differed in the relative size of these param- glas-fir. The relationship between pro- duction of biomass, total and shoot dry eters. The response of seedling height was weight with density was very similar in much more variable between the three conifers. The height of Douglas-fir all three species. In addition, all three
differences between species in the way seedlings was unaffected by growing den- sity, while the two pine species showed a shoot elongation responds to density war- positive response to growing density with rants further investigation. the tallest seedlings being produced at the Since the root systems of individual highest density. In this study, the height were isolated from each other, seedlings of Corsican pine seedlings was particu- the effects of density on the growth of larly strongly affected by growing den- these seedlings were caused by the effects sity, suggesting that density effects are in of mutual shading on the interception of part responsible for the uneven distribu- light by seedlings and on changes in asso- tion of seedling heights between the cen- ciated environmental factors, such as tem- tre and edges of trays and benches during perature, within the seedlings. Reciprocal commercial production. equations have been widely used to describe relationships between mean plant The reductions in seedling dry weight size and density [5]. The close relation- and root collar diameter with increasing ships obtained between the reciprocals of density found in these three species are mean seedling weights and density would similar to those reported in other studies be expected if the effects of competition on using container seedlings where the effects plant size are due to the partitioning of of density alone have been investigated available growing space between individ- [1, 14, 16]. The differences between Dou- ual seedlings. In the absence of root com- glas-fir and the two pines in the effects of petition, the density over which competi- growing density seedling height are on tion intensifies is a function of the size also apparent in other studies on both these and geometry of the seedling canopy in and other species. The positive relation- relation to the space available. The rela- ship between seedling height and density tionship between area and density is non- found in Cosican and Scots pine has been linear with the area available per seedling reported in interior spruce seedlings where increasing substantially at densities less shoot length increased by more than 60 % than about 500 m(figure 7), corre- -2 as growing density was increased from sponding to the density range where the 100 to over 1 000 m [14]. Hulten [8], -2 majority of the increases in root and shoot however, found that the height of Scots dry weight occurred in these experiments. pine seedlings only increased substantially At densities above 400 mthe canopy -2 as growing density was increased to 400 plants m at higher densities up to ; -2 of Douglas-fir seedlings intercepted nearly 1 200 mheight was slightly reduced. In -2 all of the incident radiation. At wider spac- contrast to the lack of response of the ings, more light is utilized by individual height of Douglas-fir seedlings to density seedlings since fewer of their needles found in this study, Timmis and Tanaka would have been below the light com- [16] reported that seedlings were signifi- pensation point. Also in Douglas-fir, Tim- cantly taller when grown at a high den- mis and Tanaka [16] estimated that ten sity of 1 080 plants m however, at lower ; -2 times as much visible radiation reached densities (270 and 810 m there were ) -2 the lower needles of wider-spaced only small although statistically signifi- seedlings; the greater light interception at cant differences in height. Loblolly pine low densities resulted in an increase in dry grown over a wide range of densities (452 matter production by individual seedlings to 1 808 plants m showed a similar ) -2 as well as an increased allocation of carbon response to Douglas-fir in this study with for root growth. At wider spacings the no simple relationship at all between increased absorption of radiation at the height and density [ 1].The basis for these compost surface resulted in warmer stem
only effective at the containers temperatures [16], warmer root tempera- was size at lower growing tures and possibly drier growing media increasing seedling densities. Thus, when shoot competition than at closer spacings. Changes in leaf and leaf-air vapour pressure differ- was less intense at wider spacings, con- area tainer volume then became the limiting would also affect water use by ence seedlings at different densities. Close spac- factor for seedling growth. ing will also modify the quality of light Morphological features of seedlings beneath the canopy, especially the red:far like height and diameter are frequently red ratio, and this probably has an impor- used to grade seedling stock. Root collar tant role in increasing the extension growth diameter is considered to be a better pre- of seedlings at high density [12, 17]. dictor of outplanting performance than shoot height since it is often correlated The interaction between container den- sity and volume found in experiment 4 with seedling weight and the size of the suggests that at high seedling densities, root system [11]. Growing density pro- intense competition for light is the limiting duced strong positive correlations between factor affecting seedling size. The weight root collar diameter and shoot and root of Douglas-fir seedlings grown at 400 m -2 weight in all three species, whereas plant height was either negatively correlated did not increase when container volume with weight in Corsican pine, or was not was increased; increasing the volume of
significantly correlated in Scots pine and Height growth in the nursery was unaf- Douglas-fir. Specification of seedling size fected by spacing, but root collar diameter, root and shoot dry weight all increased at in terms of shoot height alone is not a good measure of seedling size since height wider spacings. However, 2 years after growth of container seedlings grown at outplanting, survival and height growth of plants raised at an intermediate density close spacing is a response to mutual shad- of 150 mwas better than those grown -2 ing, rather than to an increase in dry mat- at wider or closer spacings. One may spec- ter accumulation by seedlings; root collar diameter is a useful indicator of ulate that there could be an interaction more between spacing and physiological con- seedling size. dition such as the number of bud initials, which affects outplanting growth and war- Taller seedlings generally remain taller rants further investigation. in the years following outplanting (e.g. [14]). The results of the outplanting exper- All three species in this investigation iment with Douglas-fir showed that the often produced in British nurseries at are smallest seedlings, which were raised at densities ranging from 800 to 1 200 m . -2 the highest density, had significantly Good survival and growth of these poorer survival, presumably because their seedlings can be achieved after outplanting smaller root collar diameter and lesser root on suitable sites given adequate ground volume made them more vulnerable to preparation and proper weed control and site-induced stresses after planting such protection. There may be instances, such as weed competition and shoot damage as planting on a weedy and/or uncultivated by the large pine weevil Hylobius abietis. site, where a larger specification seedling However, subsequent growth did not show may prove advantageous. To obtain sub- a simple relationship with initial size, since stantially heavier plants, the results of this the greatest growth occurred in plants study suggest that seedlings would have raised at intermediate densities of around to be grown at densities below 400 m -2 800 m with the larger plants that had , -2 in larger volume cells to reduce competi- been raised at lower container densities tion for light and to allow seedlings to growing significantly less. Indeed, the respond to increased availability of mineral increment of the plants from the widest nutrients and water. In practice, seedling significantly greater treatments not was density and cell volume are interrelated than that of the plants grown at the closest since selecting a larger container size spacings. It is not clear why this variation results in both an increase in volume and in growth response with growing density a decrease in seedling density. However, should have occurred. The better-than- there has to be a compromise between expected growth of the seedlings grown selecting a growing density that will pro- at the closest density could be due to ini- duce seedlings of the desired specifica- tial mortality occurring amongst the small- tion, against the financial constraint of est and most vulnerable seedlings in this reducing the yield of seedlings that can treatment, leaving only the better quality be grown on a given area of a tunnel or plants to grow on. Reasons for the poorer- glasshouse. than-expected performance of the plants grown at the widest spacing are less evi- dent. However, similar results were ACKNOWLEDGEMENTS reported by Deans et al. [4] and Mason et al. [10] in bare-root Douglas-fir. In these We thank the staff of the nurseries at Alice studies plants were produced over 2 years Holt Lodge and the Northern Research Station at four densities from 286 to 74 plants m . -2 for raising the container seedlings, and the staff
Producing Uniform Conifer Planting Stock, of the Newton field station for planting and Forestry Suppl. 62, 1989, pp. 1-12. maintaining the field experiment. Ian Wright and Andrew Peace helped with the statistical [9] Landis T.D., Containers: types and functions, in: Landis T.D., Tinus R.W., McDonald S.E., analysis, and John Morgan commented on the Bamett J.P. (Eds.), The Container Tree Nursery draft text. Manual, vol. 2, Agricultural Handbook. 674. U.S. Department of Agriculture, Forest Ser- vice, Washington, DC, 1990, pp. 1-39. REFERENCES [10] Mason W.L., Sharpe A.L., Deans J.D., Grow- ing regimes for bare-root stock of Sitka spruce, Douglas-fir and Scots pine. II. Forest perfor- [1]Barnett J.P., Brissette J.C., Producing south- mance, in: Mason W.L., Deans J.D., Thompson ern pine seedlings in containers, Gen. Tech. S. (Eds.), Producing Uniform Conifer Planting Rep. SO-59 (1986) USDA Forest Service, Stock, Forestry Suppl. 62, 1989, pp. 275-284. Southern Experiment Station, New Orleans, [11]Mexal J.G., South D.B., Bareroot seedling cul- LA, 71 p. ture, in: Duryea M.L., Dougherty P.M. (Eds.), [2] Carlson L.W., Endean F., The effect of root- Forest Regeneration Manual, Kluwer Academic ing volume and container configuration on the Publishers, Netherlands, 1991, pp. 89-115. early growth of white spruce seedlings, Can. [12] Morgan D.C., Rook D.A., Warrington I.J., J. For. Res. 6 (1976) 221-224. Turnbull H.L., Growth and development of [3]Crawley M.J., GLIM for Ecologists, Blackwell Pinus radiata D. Don: the effect of light qual- Scientific Publications, Oxford, 1993. ity, Plant Cell Environ. 6 (1983) 691-701. [4] Deans J.D., Mason W.L., Cannell M.G.R., [13] Payne R.W., Lane P.W., Digby P.G.N., Hard- Sharpe A.L., Sheppard L.J., Growing regimes ing S.A., Leech P.K., Morgan G.W., Todd for bare-root stock of Sitka spruce, Douglas-fir A.D., Thompson R., Tunnicliffe Wilson G., and Scots pine. I. Morphology at the end of the Welham S.J., White R.P., Genstat 5 Release 3 nursery phase, in: Mason W.L., Deans J.D., Reference Manual, Clarendon Press, Oxford, Thompson S. (Eds.), Producing Uniform 1993. Conifer Planting Stock, Forestry Suppl. 62, [14] Simpson D.G., Growing density and container 1989, pp. 275-284. volume affect nursery and field growth of inte- [5] Drew T.J., Flewelling J.W., Some recent rior spruce seedlings, North J. Appl. For. 8 Japanese theories of yield-density relationships (1991) 160-165. and their application to Monterey pine planta- [15] Sutherland D.C., Day R.J., Container volume tions, For. Sci. 23 (1977) 517-534. affects survival and growth of white spruce, [6] Endean F., Carlson L.W., The effect of root- black spruce, and Jack pine seedlings: a litera- ing volume on the early growth of lodgepole ture review, North J. Appl. For. 5 (1988) pine seedlings, Can. J. For. Res. 5 (1975) 185-189. 55-60. [16] Timmis R., Tanaka Y., Effects of container [7] Hocking D., Mitchell D.L., The influences of and plant water stress on growth and density rooting volume - seedling espacement and sub- cold hardiness of Douglas-fir seedlings, For. stratum density on greenhouse growth of lodge- Sci. 22 (1976) 167-172. pole pine, white spruce, and Douglas-fir grown [17] Warrington I.J., Rook D.A., Morgan D.C., in extruded peat cylinders, Can. J. For. Res. 5 Turnbull H.L., The influence of simulated (1975) 440-451. shadelight and daylight on growth, develop- [8] Hulten H., Current levels of planting stock uni- ment and photosynthesis of Pinus radiata, formity and grading - a Scandinavian view, in: Agathis australis and Dacrydium cupressinum, Mason W.L., Deans J.D., Thompson S. (Eds.), Plant Cell Environ. 12 (1989) 343-356.