Shade Regimes Research Articles

Coffee agroecosystem performance under full sun, shade, conventional and organic management regimes in Central America

Changes in coffee economics are leading producers to reduce agrochemical use and increase the use of shade. Research is needed on how to balance the competition from shade trees with the provision of ecological services to the coffee. In 2000, long-term coffee experiments were established in Costa Rica and Nicaragua to compare coffee agroecosystem performance under full sun, legume and non-legume shade types, and intensive and moderate conventional and organic inputs. Coffee yield from intensive organic production was not significantly different from intensive conventional in Nicaragua, but in Costa Rica it was lower during three of the six harvests. Full sun coffee production over 6 years was greater than shaded coffee in Costa Rica (61.8 vs. 44.7 t ha−1, P = 0.0002). In Nicaragua, full sun coffee production over 5 years (32.1 t ha−1) was equal to coffee with shade that included Tabebuia rosea (Bertol.) DC., (27–30 t ha−1) and both were more productive (P = 0.03) than coffee shaded with Inga laurina (Sw.) Willd. (21.6 t ha−1). Moderate input organic production was significantly lower than other managements under all shade types, except in the presence of Erythrina poepiggina (Walp.) O.F. Cook. Inga and Erythrina had greater basal area and nutrient recycling from prunings than other shade species. Intensive organic production increased soil pH and P, and had higher K compared to moderate conventional. Although legume shade trees potentially provide ecological services to associated coffee, this depends on management of the competition from those same trees.

Insights into herbivore distribution and abundance: oviposition preferences of western hemlock and phantom hemlock loopers

AbstractKnowledge of the factors affecting host selection by herbivorous insects is essential to predictions of their distribution and abundance over landscapes. In the laboratory, we studied the oviposition preferences of two eruptive loopers (Lepidoptera: Geometridae) native to western Canada (western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst), and phantom hemlock looper, Nepytia phantasmaria (Strecker)) for different species and condition of hosts. When offered a choice, phantom hemlock loopers laid nearly three times as many eggs on western hemlock, Tsuga heterophylla (Raf.) Sarg. (Pinaceae) as on either western redcedar, Thuja plicata Donn ex D. Don (Cupressaceae) or western white pine, Pinus monticola Douglas ex D. Don (Pinaceae). Western hemlock loopers were less specific, laying equal numbers of eggs on western hemlock and western redcedar, though fewer eggs were deposited on western white pine when compared with western hemlock. When offered western hemlock trees grown under different nutrient and shading regimes, phantom hemlock loopers preferred to oviposit on high nutrient hosts, irrespective of shading; western hemlock loopers exhibited a preference for high-nutrient hosts only if they were grown without shading. These patterns of host preference can be combined with information regarding forest composition to help quantify the conditional probability of western and phantom hemlock looper distibution and abundance.

Light intensity is a limiting factor to the inland expansion of Cape ivy (Delairea odorata)

Cape ivy (Delairea odorata) is a highly invasive climbing perennial vine that is primarily distributed in coastal communities of California and Oregon, with patchy infestations in some inland riparian areas. In this study, we evaluated light as a potential environmental limitation to the spread of Cape ivy into inland regions of the western United States. Cape ivy was collected from four locations representing the north to south range. Plants were grown for 9 to 11 weeks in full sunlight and under two shade regimes (20 and 6% of full sunlight). The experiment was conducted twice at two temperature regimes. Results show some within- and among-population variability, with the southernmost San Diego County population having the highest biomass under the warmer growing conditions and the three northern populations responding most favorably in the cooler growing conditions. Despite the minor differences within and between populations, Cape ivy grew very poorly in full sunlight in both experiments. Although plants growing under 6% light grew better than those in full sunlight, they were far less robust compared to plants growing at 20% light. Our results indicate that while Cape ivy will not persist in areas with prolonged high intensity sunlight, characterized by much of the interior regions of California and Oregon, it is expected to invade and spread in areas with reduced light, including coastal regions frequently exposed to fog or cloudy conditions, or sub-canopy layers of riparian forests or woodlands. These communities should be the target areas for early detection and rapid response programs to prevent further Cape ivy invasion.

Effect of shade regime on flower development, yield and quality in lisianthus

The effects of shading on lisianthus ( Eustoma grandiflorum) floral transition, plant development, flower yield and quality, and content of starch and soluble sugars were assessed in three cultivars, over two consecutive years. Shading nets affording 67% or 88% reduction in light intensity, were fitted at planting in the greenhouse for periods ranging from 3 to 8 weeks. Meristem morphology at floral transition was characterized by apical meristem widening and the appearance of two bract primordia. Floral transition time was affected by cultivars, but in general, longer and heavier shade treatments delayed floral transition; the longest delay (6 weeks) being recorded in Mariachi White under 88% shade for 7 weeks or under a combined shade treatment of 88% for 3 weeks followed by 67% for 5 weeks. Despite interactions between cultivar and shade treatment, consistent trends were discerned: the heaviest and most prolonged shading reduced yield (up to 40%), cut stem length (up to 15%), and number of flower buds/stem (up to 26%), within cultivar. Total carbohydrates levels were very low, and it is questionable whether changes observed in carbohydrate quantity following shade treatments had any effect on plant growth or flower yield. Rather, it appears that lisianthus is very dependent on current photosynthesis, so that even a brief shading interlude could reduce branching and flower quality. It may be concluded that the intensive shading usually applied is detrimental for lisianthus.

Influence of experimental warming and shading on host–parasitoid synchrony

AbstractAs the climate warms, many species are showing altered phenology patterns, potentially disrupting synchrony between interacting species. Recent studies have documented disrupted synchrony in plant–herbivore and predator–prey interactions. However, studies investigating climate‐related asynchrony in host–parasitoid interactions and exploring the relative responses of interacting hosts and parasitoids to climate change are lacking. This is an important gap in knowledge given the ubiquity of insect parasitoids and their importance in influencing the abundance and dynamics of their hosts. In the threatened marsh fritillary butterflyEuphydryas aurinia(Lepidoptera: Nymphalidae) and its specialized parasitoid,Cotesia bignellii(Hymenoptera: Braconidae) phenological synchrony (and consequently population fluctuations) are thought to be weather‐dependent. To assess the likely influence of climate and microenvironment change on synchrony betweenE. auriniaandC. bignellii, we experimentally manipulated the exposure of sensitive‐stage host larvae and parasitoid pupae to temperature (ambient or elevated) and shading (shaded or unshaded) regimes. We also analysed a 20‐year population dynamic dataset from the United Kingdom forE. auriniato investigate whether population variations could be explained by interannual variations in the thermal and sunshine environment. Development times were affected significantly by the experimental temperature and shading treatments forE. auriniabut not forC. bignellii. However, the contrasting responses were insufficient to significantly affect host availability for parasitoids. In the field, thermal and sunshine conditions did not influence population fluctuations, and population variations across a large (UK‐wide) scale were uncorrelated. Changes to the thermal and sunshine environment of the magnitude investigated in our experiment and within the range experienced by wildE. auriniapopulations over the last 20‐years thus seem unlikely to cause breakdown in host–parasitoid synchrony. We suggest that experiments investigating the mechanistic responses of interacting species to environmental change are needed to support the analysis and interpretation of observational data on species' phenology.

Effect of different moisture and shade regimes on the growth of D x P ex Kusi oil palm seedlings

The effect of three moisture levels and three shade regimes on the growth of D x P ex Kusi oil palm seedlings was investigated at the Oil Palm Research Institute, Kusi between July 1998 and February 2000 in a factorial experiment laid out in randomized complete block design with four replications. The moisture treatments investigated were W1 (50-60 % field capacity), W2 (65-75 % field capacity) and W3 (80-90 % field capacity). The shade treatments investigated were S1 (0 % shade), S2 (50 % shade) and S3 (75 % shade). Data was collected on leaf number per plant, plant height, butt circumference and leaf area as well as dry weight of plant parts and total dry matter. There were significant effects due to shade and shade x moisture interactions on seedling growth. Seedlings under 50% shade (50% full sunlight) in combination with low moisture supply (50-60% field capacity) were comparable in growth to those under 0% shade (100% full sunlight) with high moisture supply (80-90% field capacity). During the dry season when water is scarce, the application of up to 50% shade (50% full sunlight) in combination with reduced watering (50-60% field capacity) at the nursery will not adversely affect the growth of D x P oil palm seedlings.

The influence of overhead shade on the shade mortality of Abies xborisii-regis Mattf. seedlings and saplings in the central Rhodope mountains of north-eastern Greece

In order to examine how overhead shade affects the shade mortality of Abies xborisii-regis Mattf. seedlings and saplings in the central Rhodope mountains of Greece, two plots of 0.1 ha were established in two stands. In each plot, diameter in cm and height in m of all living trees was recorded. Over 50 increment cores and cross sections were used to determine the stand age structure. Moreover, in an area of 0.15–0.2 ha in each stand, all dead A. xborisii-regis trees were cut, and categorized according to their position in the vertical stand structure. In 91 of them, the ring width was measured, to the nearest 0.01 mm, in the stem base radius. The dead A. xborisii-regis trees showed high persistence in deep shade and very low growth rates. The various overhead shade regimes, as a result from the stand's vertical profiles, strongly affected the shade mortality of A. xborisii-regis seedlings and saplings. The major influence refers to the vertical arrangement of dead A. xborisii-regis trees in relation to the stand storeys. Consequently, it was the different overhead shade regimes that most strongly determined the growth pattern of the dead trees in the last years of their life. In particular, most of the dead A. xborisii-regis trees were close to living A. xborisii-regis trees, and died through lasting suppression. The top and branches of the dead trees were just below the foliage of taller living trees belonging to the same stratum. On the contrary, in the case of dead A. xborisii-regis trees whose branches and top were far below a stratum created by the foliage of living trees, only 32% died through lasting suppression, the rest experienced at least one growth increase, in terms of ring width, or the synergistic effect of a growth increase and a growth reduction, in the last 5 years of their life.

Browning reactions during storage of low-moisture Australian sultanas: Further evidence for arginine-mediated Maillard reactions during storage, and some effects of vine-shading and harvest date

Sultana grapevines (Vitis Vinifera L. cv. Sultana syn. Thompson Seedless) were subjected to four shading regimes: 50% shading (1), 25% shading (2), fully exposed-top of canopy (3) and beneath canopy (4) and harvested early (21 February) and late (13 March) in the 1996/1997 sultana season. Grapes from each of the eight field-treatment combinations represented a range of maturities (14.4 to 23.50°Brix). Grape samples from each of the treatments were dipped and dried to 18% moisture, with half of each of the sultana samples further reduced in moisture by sunfinishing on plastic sheets in direct sun. These field treatments resulted in sixteen unique dried sultana bulk samples with a range of initial chemico-physical properties; aw (0.481-0.691), skin-polyphenoloxidase (PPO) activity (4.40-9.05 µmol O2/g.minute) free arginine in skin tissues (1.0-5.10 mg/g) and protein (16.40-27.18 mg/g). Sultanas were stored at 10°C and 30°C in either the presence or absence of oxygen for 10 months, and changes in CIE L*a*b* tristimulus values, hue-angle (hab*) and chroma (Cab*) were monitored. Significant changes in sultana colour occurred in samples stored at 30°C, especially in higher aw non-sunfinished sultanas. Although browning was more intense in the presence of oxygen, significant browning also occurred in the absence of oxygen. Lower concentrations of 5-hydroxy methylfurfural, a key marker of Maillard browning in samples stored at 30°C in the presence of oxygen, indicated that the non-enzymatic reactions were sensitive to oxygen. Changes in the concentration of trans-caftaric acid, the main substrate of grape PPO, were also measured during sultana drying. Storage browning (changes in L*, b*, hab*, Cab*)in dried sultanas could be predicted by regression models using pre-storage aw, free-skin arginine or Kjeldahl protein after 10 months' storage between 10°C and 30°C. Non-enzymatic and Maillard-type reactions (sensitive to both oxygen and aw), made an important contribution to sultana storage browning. We provide only weak evidence that either shaded (immature) or green fruit was more susceptible to storage browning.

Nitrogen absorption, growth of stock plants, and adventitious rooting of Pelargonium × hortorum cuttings as affected by the form and dosage of nitrogen

SummaryEffective modern production of young Pelargonium hortorum L.H. Bailey plants requires a reliable rooting response of shoot tip cuttings from stock plants. This study was conducted to explore the N demand and the influence of the form and dosage of N on the growth of stock plants in aerated nutrient solutions (A, C) and thin-layer peat substrates (B). The effects of three N dosages at 1, 7, and 13 mmol N l–1 (A) or 0.5, 1.5, and 4.0 g N m–2 week–1 (B) were examined. Futhermore, at uniform dosages of 7 mmol N l–1, graduated substitutions of NO3– by NH4+ were investigated using six NH4+:NO3– ratios of 0:100, 20:80, 40:60, 60:40, 80:20, and 100:0 (C). The quality, survival and rooting capacity of cuttings were determined in response to NH4+ or NO3– alone (A), NH4+ and NO3– fertigation (B), or the NH4+:NO3– ratio (C). Natural irradiation and different shading regimes during Spring and Summer cultivation ensured adequate light [photosynthetic photon flux density (PPFD) = 314 µmol m–2 s–1], while limiting light during Autumn (PPFD = 135 µmol m–2 s–1) interfered with the N treatments. The N status, survival rate, and rooting of cuttings were examined in samples of cuttings provided by propagators worldwide. In solution-culture, NH4+:NO3– ratios of 20:80 and 40:60 provided optimised growth and quality of cuttings at 7 mmol N, regardless of light level. Compared with NO3–-only nutrient solutions, these ratios enhanced the branching of stock plant roots, NO3– absorption in shoot tissues, overall cutting yield, and adventitious root formation in cuttings. Although NH4+:NO3– ratios above 60:40 impaired fresh weight and the number of tip cuttings per plant, the rooting capacity of such cuttings was promoted further, as long as adequate light was available. We hypothesise that the ratio of N form shifts hormone levels and carbon fluxes which, in turn, influence the root and shoot morphology of stock plants, as well as the rooting of cuttings. Cultivation in peat substrate resulted in the highest yields and best rooting of cuttings at weekly N doses of 1.5 g N m–2. The high dose of N (4 g) did not enhance yield, but rather reduced the rooting of cuttings at adequate light levels.This dose also resulted in increased NO3–-N and salt accumulation in the peat. Moreover, while reduced rooting at a low N dose (i.e., 0.5 g) indicated N limitation, the impaired rooting seen at a high N dose may have been induced by osmotic stress to the stock plants.

Shade avoidance inTrifolium repens: costs and benefits of plasticity in petiole length and leaf size

We tested whether the degree of shade-induced plasticity in petiole length and leaf area is related to the mean trait value expressed under high-light conditions, and to what extent trait values expressed under high-light and shaded conditions affect plant performance. Thirty-four Trifolium repens genotypes were used with a wide range of petiole lengths and leaf areas. Plants were subjected to a high-light environment and two shading regimes: homogeneous shading and a vertical light gradient. Absolute petiole elongation in response to both shading treatments and absolute leaf area expansion in response to homogeneous shading were independent of the trait values expressed in high light. Consequently, relative plasticity was higher for genotypes with lower high-light trait values. Plasticity was associated with enhanced plant performance in a vertical light gradient but not in homogeneously shaded conditions. We also found costs associated with the ability to express plasticity. Our results suggest that selection can act separately on trait values expressed under high-light conditions and on the degree of plasticity.

Canopy structure and photosynthesis modelling of grapevines (Vitis vinifera L. cv. Sultana) grown on an overhead (parronal) trellis system in Chile

Most table grapes in Chile are produced on an overhead (parronal) trellis system with typically high values for leaf area index (LAI). An apparent lack of sunlight inside such canopies often raises questions as to the photosynthetic effectiveness of shaded leaves, and the comparative importance of successive leaf layers (top to bottom) for the total canopy carbon balance. In particular, are some leaves parasitic with respect to daily carbon balance? Accordingly, we undertook a study of canopy architecture, light climate and photosynthetic physiology to address those issues. Canopy photosynthesis was inferred from a process-based model using measured values for: the vertical distribution of (1) leaf angle, (2) LAI, (3) the fraction of sunlit leaves and (4) single-leaf photosynthetic capacity. Photon flux densities (PFD) and measured values of CO2 assimilation by leaves located on different parts of the canopy were obtained at flowering (mid-October) and during active berry growth (mid-December). Results of leaf angle revealed that Sultana canopies on this system behave in an erectophile manner with an average leaf inclination of 60o above horizontal. Modelling the contribution made by different leaf layers to overall canopy photosynthesis demonstrated that leaf layers contributing most were those under a shade plus sunfleck regime. They were located between 20 and 40 cm above the horizontal trellis structure itself. Indeed, some photoinhibition was observed in leaves under continuous direct radiation towards the top of the canopy, and located above 40 cm layer. However, such leaves represented only a small proportion of total LAI, and thus compromised canopy photosynthesis to only a limited extent. Outcomes from our simulation studies imply that LAI values commonly reached by canopies managed according to the parronal system of grape trellising do not result in parasitic leaves.

Effect of light intensity and rooting hormone on propagation of Bambusa vulgaris Schrad ex Wendl. by branch cutting

Untreated and treated (with 0.2% solution of rooting hormone IBA) branch cuttings of Bambusa vulgaris Schrad ex Wendl. were allowed to root under four different light regimes, viz ., open sun, tree shade, partial shade and deep shade. Rooted cuttings were then grown under the open sun for 6 months to assess the performance of stecklings. Rooting ability of cuttings and growth performance of stecklings were found affected significantly both by light intensity and IBA treatment. Highest rooting percentage (84%) was in IBA treated cuttings rooted in the tree shade followed by untreated cuttings under the same light regime (73.3%) and the lowest (60%) was under the deep shade. The number of roots per cutting was also the highest (7.9) in the treated cuttings rooted under tree shade and the lowest (4.1) for untreated cuttings grown under the open sun. However, the longest root was in cuttings rooted under tree shade (17.1 cm) without IBA and the shortest (9 cm) was in deep shade regime. The highest survival percentage was 95.2% in treated cuttings rooted in the open sun and the lowest was in case of deep shade without IBA treatment, while maximum number of shoots were developed in treated cuttings rooted under tree shade. Shoot length was the highest in treated cuttings rooted under partial shade.

The impact of shade on establishment of shrubs adapted to the high light irradiation of semi-arid environments

Light may be an important limiting resource that influences community structure of chenopod shrublands. As part of a larger study that aimed to determine the factors that influence chenopod community structure, the focus of this study was the influence of plant canopy on the growth and establishment of smaller plants. We therefore measured the height and cover of three chenopods ( Enchylaena tomentosa, Maireana brevifolia and Maireana georgei) when growing within and outside of the canopy of Atriplex bunburyana under field conditions. All three chenopods had lower cover and E. tomentosa was taller when growing within the canopy of A. bunburyana in comparison to those growing outside of the canopy. The chenopods were then grown under three artificial shade regimes. Plant height, cover, biomass, relative leaf area and photosynthetic surface area measurements showed that each species responded differently to shade. E. tomentosa biomass was facilitated by shade. This was inferred by an increase in total plant biomass. M. brevifolia, in contrast, tolerated shade by increasing above-ground biomass allocation. M. georgei was adversely affected by the shade regimes: root biomass decreased in response to shade. Competition for light is, therefore, likely to influence chenopod community structure of semi-arid and arid environments.

Effects of artificial shade on attack by the mahogany shoot borer, Hypsipyla robusta (Moore)

Abstract Swietenia macrophylla King (Meliaceae: Swietenioideae) provides one of the premier timbers of the world. The mahogany shoot borer Hypsipyla robusta Moore (Lepidoptera: Pyralidae) is an economically important pest of S. macrophylla throughout Asia, Africa and the Pacific. No viable method of controlling this pest is known. Previous observations have suggested that the presence of overhead shade may reduce attack by H. robusta, but this has not been investigated experimentally. This research was therefore designed to assess the influence of light availability on shoot‐borer attack on S. macrophylla, by establishing seedlings under three different artificial shade regimes, then using these seedlings to test oviposition preference of adult moths, neonate larval survival and growth and development of shoot borer larvae. Oviposition preference of shoot borer moths was tested on leaves from seedlings grown under artificial shade for 63 weeks. A significant difference in choice was recorded between treatments, with 27.4 ± 1.5 eggs laid under high shade and 87.1 ± 1.8 under low shade. Neonate larval survival on early flushing leaflets of S. macrophylla did not differ significantly between shade treatments. Larval growth rate, estimated by measuring daily frass width, was significantly higher for those larvae fed on seedlings from the high and medium shade treatments (0.1 mm/day), than the low shade treatment (0.06 mm/day). In laboratory‐reared larvae, the total mass of frass produced was significantly higher in the high shade treatment (0.4 g) than under the low shade treatment (0.2 g). Longer tunnel lengths were bored by larvae in plants grown under high shade (12.0 ± 2.4 cm) than under low shade (7.07 ± 1.9 cm). However, pupal mass under low shade was 48% higher than that under the high shade treatment, suggesting that plants grown under high shade were of lower nutritional quality for shoot borer larvae. These results indicate that shading of mahogany seedlings may reduce the incidence of shoot borer attack, by influencing both oviposition and larval development. The establishment of mahogany under suitable shade regimes may therefore provide a basis for controlling shoot borer attack using silvicultural approaches.

SHADE-INDUCED PLASTICITY AND ITS ECOLOGICAL SIGNIFICANCE IN WILD POPULATIONS OF ARABIDOPSIS THALIANA

In laboratory studies of Arabidopsis thaliana, plants shaded by neighboring vegetation (or subject to treatments mimicking shade) flower at a younger developmental stage, and sometimes earlier in time. We examined whether this shade avoidance response varies among and within natural populations of A. thaliana, and whether it corresponds to variable selection regimes at shaded and unshaded field sites, by conducting a two-year reciprocal transplant study and a parallel greenhouse study that manipulated the presence and timing of shade. In the field, shading had limited or inconsistent impacts on survivorship across several phases of the growing season. The date of bolting was earlier at the shadier site compared to the less shady site, but in the greenhouse there was no significant shade- induced plasticity for this trait. In both studies, we detected directional selection gradients favoring earlier bolting in shade, but gradients favoring earlier bolting were as strong in nonshaded conditions. The number of rosette leaves at bolting (i.e., the developmental stage of flowering) was significantly reduced by shade in both studies. However, there was either no directional selection on this trait, or selection to flower with more rather than fewer leaves. Despite the contrast in habitats, there was limited differentiation between populations for survivorship, reproductive fitness, size-related or flowering time traits, and no differ- entiation for trait plasticities. Some traits were variable among families within populations. A trade-off between age and developmental stage may limit the response to selection for flowering time, possibly explaining limited local adaptation. The adaptive significance of shade-induced flowering time plasticity remains equivocal. Future studies of the plasticity of flowering time in A. thaliana should investigate the effects of shading regimes together with other environmental variables on size- and timing-related traits.

Compensation and Plasticity in an Invasive Plant Species

Plant plasticity under varying resources is one character that contributes to competitiveness and invasibility. The plasticity of plant modules of the invasive Japanese stilt grass (Microstegium vimineum) was examined under different light and nutrient levels using a balanced field and greenhouse study. Ample light and nutrients resulted in the greatest biomass accumulation in all plant modules. However, M. vimineum showed extreme plasticity, producing stolons and flowers (reproductive structures) under a wide range of environmental conditions except infertile, low light. The addition of nutrients under various shading regimes compensated for lower light levels, rendering little change in the allocation of carbon to reproductive structures. Data from the field study corroborate the greenhouse results, but also suggest plasticity in response to competition.

A STUDY OF CO-RELATIONSHP BETWEEN INTERNAL TEMPERATURE OF BUILDINGS AND TREE SHADING IN HOT AND DRY CLIMATE

The study of tree shade on the internal temperature of a building in hot dry climate was examined using a computer – based model. Clear and hazy atmospheric conditions with solar radiation blocked (as if by trees) were considered for the study. Three shading conditions and ten shading regimes were chosen. It was found that tree shading has the most effective impact on the internal temperature of the building if the walls and roof are shaded. Using a regression analysis a test of linearity was conducted to determine the relationship between the internal temperature of a building and an increase in tree shade. It was found that a negative linear relationship exists between the internal temperature and the amount of shade.

Rehabilitation of diseased cacao fields in Peru through shade regulation and timing of biocontrol measures

The objective of this case study was to test the effectiveness of biocontrol for the rehabilitation of abandoned, diseased (moniliasis, witches’ broom and black pod) cocoa and to develop testable hypotheses regarding the effect of shade and biocontrol timing. Three trial fields differed in their shade regimes. Biocontrol was administered starting either at flowering or pod filling. Disease incidence and yield were compared with cultural control alone. Biocontrol reduced moniliasis from 49% to 25%, independent of the shading regime and application time. Witches’ broom was most severe without shade and unaffected by biocontrol. No significant effects on black pod were observed. Although biocontrol increased percentage healthy fruit independent of shading and timing, only the shaded plot with biocontrol from flowering onwards responded with increased yield. Our hypothesis is: ‘In the rehabilitation of abandoned cacao, only fields under sustainable shade management and early onset of biocontrol can realise their production potential.’

Environmental and genotypic influences on isoquinoline alkaloid content in Sanguinaria canadensis.

In a common garden, we investigated genetic and environmental influences on alkaloid production using Sanguinaria canadensis as a model. Nutrient and shade regimes were applied to replicated clones over one growing season, and induction of alkaloid production in bloodroot was tested on a whole-plant basis using jasmonic acid as an elicitor. Alkaloid concentrations increased with decreasing light intensity and fertilizer levels. Induction was not achieved by foliar application of jasmonic acid. Genetic influences represented by clone effects may be indicated by variation in alkaloid concentration by clone, but this experimental design did not allow us to distinguish genetic from pre-experiment environmental influences on the rhizomes.

Designing pest-suppressive multistrata perennial crop systems: shade-grown coffee in Central America

During most of its cultivation in Central America, coffee (Coffea arabica L.) suffered few serious pest problems. However, over the past three decades, three factors contributed to significantly increase pest levels and losses: the recent introduction of new pests; more favorable conditions for existing pests, diseases, and weeds due to lower shade levels; and secondary pest problems caused by pesticide use. The strategy of maximizing coffee production with pest control dominated by synthetic pesticides has not only increased yields substantially, but also production costs, pesticide resistance, and both human health and environmental risks. An analysis of the response of the food web in coffee plantations to varying levels of light and humidity associated with different shade levels provides the basis for identifying the optimum shade conditions which minimize the entire pest complex and maximize the effects of beneficial microflora and fauna acting against it. These optimum shade conditions for pest suppression differ with climate, altitude, and soils. The selection of tree species and associations, density and spatial arrangement, as well as shade management regimes are critical decisions for shade strata design. Site-specific knowledge of the seasonal food web dynamics permits growers to determine the appropriate seasonal shade management in order to further suppress pest levels. For example in a low-elevation dry coffee zone, 35 to 65% shade promotes leaf retention in the dry season and reduces Cercospora coffeicola, weeds, and Planococcus citri; at the same time, it increases the effectiveness of microbial and parasitic organisms without contributing to increased Hemileia vastatrix levels or reducing yields. In these conditions, shade should be at a maximum early in the dry season and at a minimum by the middle of the rainy season. Further research is needed on: the effects of individual tree species on the food web; the role of canopy architecture for coffee vigor, photosynthesis, leaf drying, pest susceptibility, and pruning regimes; and on simple observation methods and decision criteria for farmer management of tree-coffee-food web interactions.