Planting spacing affects canopy structure,biomass production and stem roundness in poplar plantations

To improve the productivity and wood quality of poplar plantations, effects of four planting spacing on canopy characteristics, biomass production and stem roundness in poplar plantations were evaluated over 8 years. Planting spacing influenced canopy characteristics of the plantations, and further affected the understory vegetation and plantation productivity. Understory vegetation biomass and Shannon-Wiener index were negatively correlated with leaf area index, but both diversity indexes and aboveground biomass of understory vegetation were higher in stands with a wider spacing. Tree diameter growth increased with increasing planting spacing, while the increment in plantations of square configurations (5?×?5 m and 6?×?6 m) was higher than those with rectangular configurations (3?×?8 m, 4.5?×?8 m). The highest poplar biomass production was achieved in the plantation with 5?×?5 m spacing at age 8. Moreover, poplar trees showed a tendency with better stem roundness in a square configuration. The results suggest that planting spacing not only affect canopy characteristics, understory vegetation and tree growth but also wood quality, and square configurations (5?×?5 m and 6?×?6 m) could be a better option for poplar plywood timber production at similar sites.     

Tree row spacing affected agronomic and economic performance of Eucalyptus-based agroforestry in Andhra Pradesh, Southern India

The 3 × 2 m spacing currently used for eucalyptus plantations in the state of Andhra Pradesh, southern India does not permit intercropping from the second year. This discourages small landholders who need regular income from taking up eucalyptus plantations and benefiting from the expanding market for pulpwood. Therefore, on-farm experiments were conducted near Bhadrachalam, Khammam district (Andhra Pradesh) for over 4 years from August 2001 to November 2005 to examine whether wide-row planting and grouping of certain tree rows will facilitate extended intercropping without sacrificing wood yield. Eucalyptus planted in five-spatial arrangements in agroforestry [3 × 2 m (farmers’ practice), 6 × 1 m, 7 × 1.5 m paired rows (7 × 1.5 PR), 11 × 1 m paired rows (11 × 1 PR) and 10 × 1.5 m triple rows (10 × 1.5 TR)] was compared with sole tree stands at a constant density of 1,666 trees ha^?1. Cowpea (Vigna unguiculata) was intercropped during the post-rainy seasons from 2001 to 2004, and fodder grasses (Panicum maximum and Brachiaria ruziziensis) were intercropped during both the seasons of 2005. At 51 months after planting, different spatial arrangements did not significantly affect height and diameter at breast height (dbh). Total dry biomass of eucalyptus in different spatial arrangements ranged between 59.5 and 52.9 Mg ha^?1, the highest being with 6 × 1 m and the lowest with 10 × 1.5 TR, but treatment differences were not significant. The widely spaced paired row (11 × 1 PR) and triple row (10 × 1.5 TR) arrangements produced 62–73% of sole cowpea yield in 2003, 59–66% of sole cowpea yield in 2004, and 79–94% of sole fodder in 2005. In contrast, the 3 × 2 m spacing allowed only 17–45% of sole crop yields in these years. The better performance of intercrops in widely spaced eucalyptus was likely because of limited competition from trees for light and water. Intercropping of eucalyptus in these wider rows gave 14% greater net returns compared with intercropping in eucalyptus spaced at 3 × 2 m, 19% greater returns compared with that from sole tree woodlot and 263% greater returns compared with that from sole crops. Therefore, in regions where annual rainfall is around 1,000 mm and soils are fairly good, eucalyptus at a density of 1,666 plants per ha can be planted in uniformly spaced wide-rows (6 m) or paired rows at an inter-pair spacing of 7–11 m for improving intercrop performance without sacrificing wood production.     

Intra-annual growth and mortality of four <Emphasis Type="Italic">Populus</Emphasis> clones in pure and mixed plantings

Intra-annual growth rates were assessed during 3 years for four Populus clones grown in pure and mixed clonal stands at square spacings of 0.5, 1.0 and 1.5 m in western Washington, USA. Height growth rate peaked in August, except at the 0.5-m spacing where it peaked in July and June in years 2 and 3, respectively. Diameter growth rate generally peaked in June. Seasonal growth patterns in mixed clonal stands, relative to those in pure clonal stands, varied by clone. Following early season moisture stress in year 2, growth of a P. balsamifera ssp. trichocarpa clone declined significantly relative to three P. balsamifera ssp. trichocarpa × P. deltoides clones; this trend was most evident at the 0.5-m spacing. During this period of moisture stress, P. balsamifera ssp. trichocarpa had 11 and 36% mortality in pure and mixed stands, respectively, at the 0.5-m spacing; this clone had no mortality at wider spacings during the same period. Although height rankings among clones shifted during the first growing season, rankings at the end of year 1 were very similar to those at the end of year 3.     

Intercropping ginger and turmeric with poplar (Populus deltoides ‘G-3’ Marsh.)

Performance of two rhizomatous crops i.e. ginger (Zingiber officinale Rosc.) and turmeric (Curcuma longa L.) was investigated under rainfed conditions in pure stands and as intercrops with 5-year-old poplars planted at three spacings viz., 5×5 m, 5×4 m and 5×3 m. The average illumination below the canopies was 53, 46 and 38% of incident radiation, respectively. Both crops performed better as intercrops than as pure stands. Survival was inversely correlated to light intensity. Plant height, tillers per plant and leaves per plant in ginger and leaf length and leaf breadth besides plant height in turmeric were significantly enhanced when intercropped. The rhizome length, rhizome breadth, yield per plant and yield per ha in ginger exceeded under poplars but showed a drastic reduction under the closest poplar spacing. In turmeric, the trend for the first two characters was the same, whereas yield per plant as well as yeild per ha were slightly greater in the open than under 5×3 m spacing. Dry matter content varied significantly with spacing. For quality parameters, only oil content in ginger and oleoresin in turmeric showed significant differences. The cultivation of turmeric proved more remunerative than ginger.Among the poplar spacings, 5×4 m for ginger and 5×5 m for turmeric were delineated as the best spacings.     

Influence of Initial Spacing on Growth and Branching Characteristics of Cordia africana Trees Established on Eritrean Highland

The study reports on the influence of initial spacing on growth and branching habit of Cordia africana trees established on Eritrean highland. The initial spacings used in this study were 1.0×1.0 m, 1.5×1.5 m, 2.0×2.0 m, 2.5×2.5 m, 3.0×3.0 m, and 3.5×3.5 m; these are equivalent to 1 m², 2.25 m², 4 m², 6.25 m², 9 m² and 12.25 m² in growing space per tree, respectively. No significant relationship between spacing and tree height was found, but increased spacing increased crown diameter and root-collar-diameter. On the other hand, an increase in spacing reduced wood quality because it increased branch diameter (knot size). Thus, from a wood quality perspective, adopting close spacing in plantations of C. africana could be advantageous.     

Effect of spacing on growth and quality parameters in sessile oak (Quercus petraea) stands in central Poland: results 7 years after planting

We examined the growth and quality of young oaks in stands established at three different spacings. The three densities were the traditional level, that is, 8000?seedlings?ha^?1 (1.5?×?0.85?m) plus two where the initial density was decreased by 50% and 70%, achieved by increasing the distance between the rows from 1.5 to 3 or 4.5?m. The experiment was located in central Poland on a moderately fertile site. In the two wider spacings, the intention was to use natural regeneration occurring between oak rows as a replacement of intraspecific competition for oaks. The mean height was only affected in the third and the fourth year after establishment. Subsequently, the differences between spacings with respect to both growth and quality traits were insignificant and small. At lower densities, natural regeneration of willow and aspen was abundant and inter-species competition replaced intra-species competition, thus explaining the absence of a spacing effect on growth and quality properties. In the study period, the wider spacings were economically beneficial compared to traditional densities. A strong competition affecting height growth caused by natural regeneration necessitated extensive tendings. More tendings are likely to be needed in the future and they might reduce the initial economical superiority of wider spacing. The study indicates that it is possible to decrease the initial spacing in oak plantations and simultaneously support good growing conditions by means of natural processes, for example, natural regeneration. However, economic efficiency of the method has to be studied in a longer perspective.     

Fuelwood production from Leucaena leucocephala established in fodder crops at Mtwapa,Coast Province,Kenya

Fuelwood production from a high density leucaena-based fodder production experiment at Mtwapa, Coast Province, Kenya is reported. Leucaena with and without other fodder crops namely, Cassava, Bana and Napier grass, formed the main-plot treatments while leucaena densities ranging from 6,250 to 100,000 ha^–1 planted in single- or double-line planting arrangements formed the sub-plot treatments of the split-plot design used. Each treatment was replicated four times. The experiment was established and maintained without the use of fertilizer, pesticides, irrigation. Hand weeding was done only during the first year.After 2.7 years growth, height and diameter measurements were taken before cutting back the leucaena stems to 0.5 m above ground. Utilizable fuelwood (twigs greater than 0.5 mm diameter) was then sun-dried for 3 months and dry weights taken.Fuelwood yields were significantly reduced by the fodder intercrops. Yield from leucaena intercropped with fodder crops were, on average, 30% lower than yield from sole stands of leucaena. Mean yields of the single-line plantings ranged from 13.7 to 21.2 tons ha^–1. Yield from the double-line plantings were lower (on average 10%) than that of single-line plantings and were as well highly variable. Unlike tree heights, diameters in the single-line planting arrangement were not affected significantly by the fodder intercrops. In the single line plantings, yield of fuelwood from sole stand of leucaena was higher at all in-row spacings than the yield from intercropped leucaena. Increase in in-row spacing of leucaena generally led to reduced yield of fuelwood.Fodder yields of intercropped Cassava, Bana and Napier grasses were near normal in the first year but zero or negligible in the remaining 1.7 years. Implications of the prolonged tree establishment period on fodder yields after opening of the canopy are discussed.     

Stand responses to initial spacing in Norway spruce plantations in Norway

Abstract

Using data from nine spacing experiments of Norway spruce (Picea abies (L.) Karst.) in Norway, covering wide ranges of site index and initial spacing, this study evaluated stand basal area and volume responses to initial spacing and examined whether these responses varied by stand ages or site quality. We developed nonlinear regression models that described the standing basal area or volume responses to initial spacing along with site index and stand ages. The results show that closer spacings produced higher standing basal area and volume than wider spacings. The response curves are highly nonlinear in younger stands and become nearly linear in mid-rotation stands, indicating stronger responses at younger ages and weaker responses as age increases. Furthermore, for young stands, spacing effects are stronger at closer than at wider spacings. The basal area and volume responses to initial spacing tend to be similar across site indices. However, the interaction of site index and stand age on spacing responses makes it difficult to isolate the effect of site index on spacing responses. Mortality is higher and begins earlier at closer spacings than wider. The mean diameter of the largest 100, 400, 600, and 800 trees ha^?1 increased with spacing in three out of the nine experiments. Dominant height did not vary by initial spacing for any of the experiments. The findings suggest that the extra volume production in stands of closer initial spacing is restricted to early stand development.     

Effect of tree spacing on growth and wood density of 38-year-old Cariniana legalis trees in Brazil

Average wood density of 38-year-old Cariniana legalis (Mart.) Kuntze, a Brazilian native forest species, was found to increase with faster growth and lower stocking, while decreasing from pith to bark. A complete randomised block design was planted with five blocks. Ten trees were harvested in each of three spacing treatments. We hypothesised that the stand stemwood production would not significantly differ depending on tree spacing. However, tree growth would be higher in the wider spacing and wood density would be higher in the narrower spacing. The diameter growth of trees was higher at 3 m × 2.5 m than at 3 m × 2 m and 3 m × 1.5 m. Nevertheless, this higher individual tree growth at 3 m × 2.5 m did not compensate for the greater tree stock density at 3 m × 1.5 m with stand stemwood production at 38 years of 530 m3 ha^?1 and 649 m³ ha^?1, respectively. These results suggest that C. legalis, which can produce up to 17 m³ ha^?1 y^?1 of medium-to high-density timber – about 800 kg m^?3 – is a promising native species for forest plantations in Brazil.     

Yield, maturation, and forage quality of alfalfa in a black walnut alley-cropping practice

There is interest in producing alfalfa as an alley crop because alfalfa (Medicago sativa L.) is the most profitable hay crop in the USA. Field experiments were conducted near Stockton, MO in 2003 and 2004. Treatments consisted of alfalfa grown in open plots and in plots that were alley cropped between 20-year-old black walnut trees (Juglans nigra L.) planted in rows 24.4- and 12.2-m apart. Alfalfa was sampled for three harvest cycles each year. In the alley-cropping plots, samples were taken beneath the canopy (2.5 m from the tree row) and in the center of the alleys. Data were taken on dry-matter yield, maturity, and forage quality. At all harvest dates over both years, yields from beneath the canopy of both alleys and the narrow alley centers were less than yields from the wide alley centers and open plots. Yield from the wide alley centers was similar to that in open plots in every harvest but the final harvest of 2004. Transects across the plots indicated that yields increased linearly from the tree row to the center of both alleys. Alfalfa tended to mature faster in the open and wide alley centers compared to beneath the canopy of both alleys and the narrow alley centers. Forage quality differences were inconsistent across treatments. Alfalfa yield was significantly reduced and maturity was delayed by the narrow 12.2 m tree spacing, but yield was not reduced in the centers of the wider 24.4 m alleyways.     

Forage production of woody fodder species and herbaceous vegetation in a silvopastoral system in northern Greece

Introduction of woody plants in silvopastoral systems could be an appropriate land-use for the poor sandy soils of the Mediterranean semiarid zone. Forage production of four woody fodder species and herbaceous vegetation in relation to plant spacing and animal (sheep) grazing was studied in a silvopastoral system on such a site in Macedonia, northern Greece. The woody fodder species tested were Robinia pseudoacacia L., Gleditsia triacanthos L., Amorpha fruticosa L. and Morus alba L. They were planted at the spacings 1.5 × 1.5 m,2.5 × 2.5 m and 3.5 × 3.5 m and kept in a shrubby form by topping. They were grazed by sheep (stocking rate of 1.1 sheep/ha/year) in early July and late August of 1992, 1993 and 1994. Among the species Robinia yielded the highest forage production (394 kg/ha). The spacing 1.5 × 1.5 m had the highest (P ≥ 0.05) forage production per area unit (280 kg/ha) while the spacing 3.5 × 3.5 m had the highest forage production per plant (91.8 g/plant). No competition was observed between the woody and the herbaceous plants in the various spacings probably due to topping of the woody species every winter. Percent utilisation of the native herbage dropped as forage of the woody species increased. This revised version was published online in June 2006 with corrections to the Cover Date.     

Introduction of Raikhanim (Ficus semicordata) in a Maize and Finger-Millet Cropping System: An Agroforestry Intervention in Mid-Hill Environment of Nepal

Fodder trees are integral part of farming system in the hills of Nepal, but designed agroforestry interventions targeted to particular trees and crops are not widely available. This paper examines the joint productivity of an agroforestry practice in which Raikhanim (Ficus semicordata) is planted in a maize (Zea mays) and finger-millet (Eleusine coracana) cropping system at Keware Bhanjyang of the western mid-hills of Nepal. Raikhanim seedlings were planted in a row on terrace risers 2, 4 and 6 m apart in ordinary farming conditions, in a randomized block design with three replications. Maize and finger-millet were grown on the terraces as intercrops with a control plot without trees on risers in each replicate. Growth parameters of Raikhanim—height, diameter at 30 cm above ground (D₃₀) and survival rate—were recorded annually in December until trees were lopped for fodder biomass, and crop yields were measured to determine tree-crop interaction effects. Tree height and D₃₀ differed significantly between spacings until trees reached the lopping stage 3½ years after planting, with the highest growth in 4 m spacing. Tree lopping checked the height growth but the diameter growth continued to increase and differed among spacings after lopping. Fodder biomass increased with tree age and was highest under 4 m spacing (7.294 t/ha) followed by 6 m (5.256 t/ha) and 2 m (3.84 t/ha). Finger-millet yield in the experimental plots decreased with tree age due to shading effects, while maize yield was not substantially affected. Among spacings, control plots produced the highest finger-millet yield (1,624 kg/ha) while the 6 m spacing produced the highest maize yield (2,463 kg/ha). It is concluded that planting Raikhanim at 6 m intervals will produce additional fodder without significant effect on maize yield and only a moderate effect on finger-millet yield. The agroforestry practice of planting fodder trees on under-utilised terrace risers is a viable option for mid-hill farmers for simultaneous production of fodder and cereal crops while sustaining the hill farming system.     

Effects of clump spacing on nutrient distribution and root activity of <Emphasis Type="Italic">Dendrocalamus strictus</Emphasis> in the humid region of Kerala,peninsular India

The humid agroclimatic conditions of Kerala, India permit the cultivation of an array of bamboo species of which Dendrocalamus strictus Roxb. (Nees.) is an important one on account of its high growth rate and multiple uses. Stand density, a potential tool in controlling the productivity of woody ecosystems, its effect on growth and root distribution patterns may provide a better understanding of productivity optimization especially when bamboo-based intercropping options are considered. Growth attributes of 7-year-old bamboo (D. strictus) stands managed at variable spacing (4 × 4 m, 6 × 6 m, 8 × 8 m, 10 × 10 m, 12 × 12 m) were studied. Functional root activity among bamboo clumps were also studied using a radio tracer soil injection method in which the radio isotope ³²P was applied to soil at varying depths and lateral distances from the clump. Results indicate that spacing exerts a profound influence on growth of bamboo. Widely spaced bamboo exhibited higher clump diameters and crown widths while clump heights were better under closer spacing. Clump height was 30% lower and DBH 52% higher at the widest spacing (12 × 12 m) compared to the closest spacing (4 × 4 m). With increasing soil depth and lateral distance, root activity decreased significantly. Root activity near the clump base was highest (809 counts per minute, cpm; 50 cm depth and 50 cm lateral distance) at 4 × 4 m. Tracer study further showed wider distribution of root activity with increase in clump spacing. It may be concluded that the intensive foraging zone of bamboo is within a 50-cm radius around the clump irrespective of spacing. N, P and K content in the upper 20 cm was 2197, 21, and 203 kg/ha respectively for the closely spaced bamboo (4 × 4 m) which were significantly higher than corresponding nutrient content at wider spacings. About 50% of N, P and K were present within the 0–20 cm soil layer, which decreased drastically beyond the 20 cm depth. The results suggest that stand management practices through planting density regulation can modify the resource acquisition patterns of D. strictus which in turn can change growth and productivity considerably. Such information on root activities, spatial and temporal strategies of resource sharing will be helpful in deciding the effective nutrition zone for D. strictus. Further, the study throws light on the spatial distribution of non-competitive zones for productivity optimization yields, especially when intercropping practices are considered.     

西南桦造林密度与林木生长的关系

西南桦不同密度6a的试验结果显示:西南桦属速生树种,人工林初期生长很快,树高生长(1　5年生)达1 22　1 90m,胸径生长(3　6年生)达1 12　2 91cm。密度对树高生长有影响但不显著,而与胸径生长呈显著负相关。最大和最小密度林分间平均胸径相差2 88cm,3m×3m林分比1 5m×2m林分林木生长量高32 3%,比2m×2m林分高28 4%,比2m×3m林分高11 6%;单株材积生长与密度亦呈负相关关系,其关系式可用V=ax-b来表示。而林分蓄积则与密度呈正相关关系,即密度大林分蓄积量高,反之则小。随林龄增长,不同密度林分间蓄积差异逐渐缩小。要培育中大径材的西南桦人工林,造林密度不宜大,可考虑采用2m×3m及3m×3m的株行距。     

Effect of spacing on growth and biomass production of Gliricidia sepium (jacq) walp in an alley cropping system in Sierra Leone

This paper describes a study into the influences of spacing on the early performance and biomass production of Gliricidia sepium in an alley cropping system in southern Sierra Leone. Four between-row spacings of 2, 4, 6 and 8 m were combined with three within-row spacings (0.25, 0.50 and 1.00m) in a split plot experimental design.Survival, tree height and leaf nitrogen content were not affected by between- or within-row spacings. For the other parameters measured, namely root-collar diameter, branch production, total biomass and nitrogen yields per hectare, it was found that for equivalent tree densities, the lower the rectangularity of planting, the better the performance of the individual trees, and consequently the greater the yields per hectare.Total biomass production per unit area was, expectedly, greatest where the spacings between hedgerows were closest, while production per plant decreased with closer within-row spacings. The total fresh and dry weights of leaves and stems, as well as leaf nitrogen yields per unit area were strongly influenced by between-row spacing and less so by within-row spacing.     

Effect of spacing on 23-year-old lodgepole pine (Pinus contorta Dougl. var. latifolia) in southern Sweden

Abstract

The objective of this study was to compare volume growth and external timber quality properties of lodgepole pine (Pinus contorta Dougl. var. latifolia) stands planted in different spacings (1.41×1.41, 2.00×2.00, 2.83×2.83, 4.00×4.00) in southern Sweden. In northern Sweden lodgepole pine has been grown for a long time and shows superior volume production compared to Scots pine (Pinus Sylvestris L.). The Swedish Forestry Act restricts establishment of lodgepole pine plantations in southern Sweden. However, it is important to increase the knowledge about lodgepole pine and its potential use also in this part of the country. Two experiments in southern Sweden were studied. Each trial was designed as a random block experiment with two blocks. Both investigated stands had an age of 23 years at the time of assessment. The mean diameter and the volume production differed significantly between the spacings. The highest volume production was found in the narrowest spacing, 313% compared to the widest spacing. Significant differences between spacings were also found concerning external quality traits. The frequency of dominant and co-dominant trees without defects was 24% in the most open spacing compared to 46% in the narrowest one. Under current circumstances approximately 2500 seedlings/ha in the initial stand seems to be a reasonable compromise between growth, diameter development and timber quality.     

Three-year growth studies of Leucaena leucocephala (1094) and L. pulverulenta (1001) at two spacings in Texas

The productivity of Leucaena leucocephala and a superior L. pulverulenta family were examined over a 3-year period at spacings (1.5 m×1.5 m and 1.5×3.0 m) chosen to compare two mechanical weeding operations. Leucaena pulverulenta was examined since faster-growing families of this cold-hardy, low-mimosine leucaena species were recently identified. There was no significant difference in yields between the species (P = 0.9060) but there was a significant difference between spacings (P = 0.0491). There was no significant spacing×species, species×year or spacing×year interaction. The annual growth rates for the first, second, and third seasons' growth for L. leucocephala were 3.73, 10.11 and 6.00 t ha⁻¹ at the close spacing and 3.03, 7.14 and 5.04 for the wider spacing. The annual growth-rates for the first, second and third seasons' growth for L. pulverulenta were 2.03, 8.35 and 8.31 t ha⁻¹ at the close spacing and 1.25, 9.38 and 5.29 at the wider spacing. Despite the fact that L. leucocephala froze to the ground in the first and second winter when L. pulverulenta was nearly undamaged, the L. leucocephala coppice resprout was greater than the second year's growth for L. pulverulenta.     

Influence of initial spacing and tree class on the basic density of Picea abies

The effects of initial spacing and tree class on the basic density of Norway spruce were evaluated in a stand on a fertile site in southwestern Sweden. The basic density at 0 and 4 m above ground level was significantly higher for trees planted with an initial spacing of 1.5 m than for trees planted with wider initial spacings. A decrease in initial square spacing from 2.5 m to 1.5 m had little effect, of small practical importance, on the basic density. The density at 0 and 4 m above ground was significantly higher for the suppressed trees than for the intermediate and dominant ones, and for the intermediate trees compared with the dominant trees. Differences in basic density appeared to be due mainly to differences in growth‐ring width. Basic density decreased outwards from the pith to the bark at 1.3 and 4 m above ground.     

闽南山地桉树造林株行距配置效应研究

对巨尾桉、尾叶桉 3种株行距配置造林试验研究表明 ,在同为 16 6 5株·hm-2 造林密度的情况下 ,不同株行距配置对林分生长、抗逆性、林内光照强度、林下凋落物及林地土壤肥力的影响有所差异。闽南山地造林采用 2m× 3m或 1 5m× 4m的配置并按“品”字型排列植穴所形成的营养空间较为合理 ,有利于林分生长和地力维持 ;而 1m× 6m的配置 ,表现出风折木多、林下植被旺盛、枯枝落叶量少、土壤养分含量少及林分生产力低等特点。     

Trees on farms in Bangladesh: 5. Growth of top- and root-pruned trees in wetland rice fields and yields of understory crops

Growth of trees and seasonal yields of understory crops were measured over a 5-year period for 4 crops grown under 17 tree species at 8 × 8 m spacing in wetland rice fields. All tree species grew well in rice fields, at rates comparable to their growth in forest plantations. Top and root pruning reduced average tree girths by up to 19% and average tree volumes by up to 41%, depending on intensity of pruning. The crops monitored were Oryza sativa, Triticum aestivum, Corchorus olotorius, and Lens culinaris. Crop yields under the trees averaged 93% of the corresponding yields outside the tree canopy. The most important factor affecting the yields of undercrops was tree size (height and/or girth). Differences among tree species and the interaction with species of undercrops were not significant after controlling for tree size. Pruning of roots and branches significantly improved crop yields under trees by amounts proportional to the intensity of root or top pruning. This revised version was published online in June 2006 with corrections to the Cover Date.