Outbreaks of the winter moth on Sitka Spruce in Scotland are not influenced by nutrient deficiencies of trees,tree budburst,or pupal predation

Summary Since the early 1980s, the winter moth, Operophtera brumata L. (Lepidoptera: Geometridae) has emerged as a serious pest of Sitka Spruce, Picea sitchensis Bong. plantations in southern Scotland. Outbreaks are characterised by susceptible sites within plantations which can occur immediately adjacent to resistant sites. We investigated the level of some nutrients in the trees, the date of budburst of the trees, and the numbers of some potential predators of winter moth pupae. None could satisfactorily explain outbreak patterns. Although foliage analysis demonstrated that many trees were marginal or deficient in phosphorus, nitrogen and potassium, these deficiencies were not related to the susceptibility of a site. Within sites, the numbers and weights of O. brumata were positively related to phosphorus content and negatively related to calcium content of foliage. Other evidence suggests, however, that these correlations may not represent direct effects of phosphorus and calcium on larval growth and survival. Date of budburst, which commonly determines susceptibility of deciduous hosts to O. brumata, was unrelated to density, and pupal predators were more, not less, abundant in susceptible sites. Although it is difficult to distinguish between factors that initiate outbreaks and those that maintain them, these data suggest that nutrient deficiencies of trees, budburst date, and the distribution of pupal predators of the winter moth cannot explain patterns of outbreak of the winter moth on spruce.     

Herbivores and pathogens on willow: do they affect each other?

Abstract 1 Willows often need to cope with attack by both rust fungi and herbivores. We studied whether rust infection on willow affects the herbivore, and vice versa, whether herbivore feeding affects the fungal infection. The system investigated by laboratory bioassays and greenhouse experiments consisted of the willow hybrid Salix × cuspidata, the rust Melampsora allii‐fragilis and the willow leaf beetle Plagiodera versicolora. Effects were studied both on a local scale (rust infection and feeding on the same leaf) and systemically (rust infection and feeding on different, but adjacent leaves). 2 Rust infection was not affected by herbivore feeding on a local scale. Systemically, however, the willow's susceptibility towards rust infection was increased by herbivore feeding, as indicated by a higher number of rust sori on leaves adjacent to feeding‐damaged leaves. The herbivore's performance was detrimentally affected by rust infection: increase of mortality (systemically), decrease of larval weight (locally and systemically) and prolonging of developmental time (locally and systemically). 3 Previous rust infection enhanced systemically the willow's susceptibility towards subsequent fungal infection. Previous herbivore feeding on the willow had no effects on the herbivore's developmental time and mortality. However, feeding upon previously feeding‐damaged willow leaves significantly reduced larval weight.     

IS PINUS SYLVESTRIS RESISTANCE TO PINE TWIST RUST ASSOCIATED WITH FITNESS COSTS OR BENEFITS?

Seven-year-old Pinus sylvestris were studied in two field trials with respect to height growth and injury caused by the fungal pathogen Melampsora pinitorqua. Each trial comprised single-tree progenies from two to 11 parent trees from each of 45 pine populations in northern Sweden (open pollinated) and Finland (control pollinated with a pollen mixture from 22 north Swedish trees). Heritability estimates were in the range of 6-18%. Most of genetic variation in height growth and rust resistance in Swedish populations and in height growth in Finnish populations occurred within populations (86-100%). In populations of Finnish origin variation in rust resistance consisted of more equal among- and within-population components (68% and 32%, respectively). Family genetic correlations between pathogen resistance and tree height the previous year (disease-free environment) were positive among Finnish populations and Swedish coast populations, suggesting that pathogen resistance confers fitness benefits even in the absence of disease, whereas Swedish inland populations showed a negative correlation indicative of fitness costs. Patterns of genetic correlations at the population level tended to be just the reverse compared with those found at the family level. No genotype × trial interactions were detected for any of the examined characters. Prerequisites for establishment of a genecological balance between host and parasite are discussed.     

Balanced dispersal or source–sink–do both models describe wood mice in farmed landscapes?

Plant responses to browsing can affect root and shoot morphology, which is important to subsequent herbivory, nutrient acquisition and competition. This paper examines the above- and below-ground responses of three browse species, with different growth strategies, to simulated browsing damage at different times of year. Saplings were grown in pots in sand culture to enable whole sapling analysis. At winter dormancy or budburst, 50% of previous year's shoots (and associated leaves/buds) were clipped. Subsequent sapling growth and morphology was compared with that of unclipped control saplings. Treatment differences in growth parameters of each species were observed, including changes in branching patterns, shoot lengths, diameters and ratios, leaf sizes and end-of-season bud numbers. Some responses were damage-induced per se; others differed according to timing of damage. Compensatory growth by the two deciduous species ( Betula pendula , Sorbus aucuparia ) resulted in few biomass differences by the end of the year of damage as compared to controls, but both above- and below-ground growth of clipped Pinus sylvestris was poor, particularly those damaged at budburst, giving strong differences between control, dormant, and budburst clipped saplings.     

Hydroseeding tackifiers and dryland moss restoration potential

Tackifiers are long‐chain carbon compounds used for soil stabilization and hydroseeding and could provide a vehicle for biological soil crust restoration. We examined the sensitivity of two dryland mosses, Bryum argenteum and Syntrichia ruralis, to three common tackifiers—guar, psyllium, and polyacrylamide (PAM)—at 0.5×, 1.0×, and 2.0× of recommended (×) concentrations for erosion control and revegetation. We measured moss shoot, gemma, and protonema production as well as moss organic matter and bound sand masses as indicators of growth and soil holding ability. We tested sand and tackifier chemistry to investigate potential nutrient and toxicant potential on moss growth. Groups of 10 fragments from field‐collected mosses were grown on sand in open petri dishes arranged in a growth chamber in replicated blocks containing each tackifier and concentration combination plus a distilled water control. Bryum (n = 10) and Syntrichia (n = 9) growth were measured at the end of 6 and 5 weeks, respectively. Overall model tests yielded statistically significant results (p < 0.001) for every variable in each species. When compared to water, guar tended to decrease growth, psyllium tended to increase growth, and PAM's effects were generally neutral to positive. Within tackifier types, increasing concentrations of guar tended to decrease growth, while increasing concentrations of psyllium tended to increase growth. Changes in PAM concentrations had little effect on growth. Increases in guar and psyllium lowered pH and increased P and K. Psyllium and PAM yielded promising results as potential agents of dispersal and adherence of dryland mosses in field restoration.     

Genetic relationships between growth characters in Salix viminalis grown in Sweden

From an eight by eight factorial crossing with Salix viminalis, 40 of the 64 families obtained were selected for further analysis. Fourteen seedplants from each of these 40 families were planted in two pairs of contrasting environments: sand and clay soil, and low and high nutrient supply. The material in the soil contrast was harvested after 1, 4 and 6 years of growth. The material in the nutrient contrast was harvested each year for 3 years and analysed after the first and the third harvests. The correlation between number of shoots and weight in the clay environment changed from being negative in the first harvests to positive at the last harvest, compared with the sand environment where this correlation was positive in all years. In the nutrient contrast this correlation was positive at the last harvest in the high nutrient environment, but no correlation could be detected in the low nutrient environment. The differences in correlations between environments may be due to a different allocation of nutrients in the plants, depending on whether the plant is under stress or not. The data suggests that the genetic relationship between growth components is the same over age and environments when the plants are grown without stress.     

Effectiveness of indirect selection for wheat yield in a stress environment

 Effectiveness of indirect selection for grain yield was investigated among eight bread wheat lines, selected in a stress environment in the East African Highlands, where they showed a wide response to yellow rust, the biotic factor causing the stress. The lines were intercrossed to give an 8×8F₁ diallel, which was grown in this same environment for three consecutive growing seasons during 1994 and 1995. Half of the last trial was sprayed with fungicide. From the estimates of narrow-sense heritabilities for yield and yellow rust severity, and the genetic correlation between them, indirect selection for yield in the unsprayed plots, obtained by choosing the most resistant 5% of this material was, on average, 12% higher than selecting for yield itself. In the fungicide-treated plots, indirect selection was only 73% as efficient as direct selection. The implications of these results for selecting for yield in stress environments are discussed. Received: 10 April 1998 / Accepted: 5 August 1998     

水肥胁迫对尾叶桉无性系生长及叶片变异的影响研究

为选择尾叶桉(Eucalyptus urophylla)优良无性系,以20个尾叶桉无性系为材料,采用2因素(水分、养分)3水平完全随机区组设计,对水肥胁迫半年后尾叶桉苗木生长和叶片性状变异进行分析和评估。结果表明,尾叶桉的叶尖角、叶长、叶宽、叶周长和叶面积在不同水肥处理下差异显著,表明水分和养分会影响叶片的大小。苗木生长和叶片性状间大多数呈显著或极显著正相关,少数呈显著负相关或一定的负相关性。13种性状可综合为4个主成分,其累计贡献率达98%,说明这些性状具有极强的代表性。除地径的水分×养分互作不显著外,生长性状在水分、养分及水分×养分互作上达显著和极显著的水平。无性系在树高、地径和冠幅上的方差分量为2.19~149.59,重复力为0.16~0.45。以20%入选率,采用基因型值筛选出4个优良无性系:LDUA10、ZQUA9、ZQUA8和LDUA24,他们的树高、地径和冠幅比对照分别高出5.0%、12.8%和14.5%,为后续骨干亲本选择及优良无性系推广提供依据。     

Rust disease (Melampsora epited) of willow (Salix spp.) grown as short rotation coppice (SRC) in inter- and intra-species mixtures

Twenty inter‐ and intra‐species genotypes of willows (Salix spp.) were grown in large mono‐plots and incorporated into five, 10,15 and 20–way mixtures. In each growing season from 1996 to 2001 the level of rust disease caused by Melampsora epitea was recorded on each genotype where it was growing as a mono‐plot or as part of a mixture. Three genotypes, S. schwerinii×viminalis×dasyclados’V7531′, S. schwerinii×aquatica‘V7533’ and S. viminalis‘Gigantea’ remained virtually rust free through the six yr of the trial. It is, however, argued that there are benefits of including such genotypes in a mixture in order to reduce the risk of them developing rust susceptibility. S. burjatica‘Germany’, S. dasyclados×aquatica‘V7511’ and S. dasyclados×caprea‘V794’ were severely affected by rust, although levels tended to be less when included in mixtures. The levels of rust on S. mollissima‐undulata‘SQ83’ were much higher in the first three‐year harvest cycle than during the second cycle. On a number of genotypes, e.g. S. burjatica‘Germany’ and S. dasyclados×aquatica‘V7511’ rust was more severe on the regrowth from freshly coppiced stools.     

Influence of intra-tree variation in time of budburst of white spruce on herbivory and the behaviour and survivorship of Zeiraphera canadensis

Abstract.

• 1 Field studies were carried out to determine the effects of intra-tree variation in the time of budburst of white spruce, Picea glauca Moench (Voss.), on the behaviour and survivorship of, and herbivory by, the spruce bud moth, Zeiraphera canadensis Mutt. & Free.
• 2 There was significant variation in the time of budburst among whorls, shoots and buds. Budburst was acropetal, with buds in the interior of the lower crown bursting first and terminal buds on terminal shoots in the upper crown bursting last.
• 3 Bud moths laid the greatest proportion of their eggs in the middle of the crown and egg hatch was usually best synchronized to budburst in this region. Many eggs hatched before terminal buds on terminal shoots in the upper crown had burst and thus intra-tree variation in budburst decreased the probability that first-instar larvae would colonize the most important plant parts for growth.
• 4 However, many later instars dispersed upwards and outwards in the crown and colonized the late bursting buds in the upper crown. Such dispersal reduces the effectiveness of intra-plant variation in budburst to reduce herbivory and permits Z.canadensis to eat young nutritious buds for a longer period of time.
• 5 Intra-tree variance in the date of budburst was greater than that between trees but there were no consistent differences between the intra-tree variance of trees in half-sib families with high or low susceptibility to Z.canadensis. Differences between trees in herbivory, bud moth density and survivorship were not related to the amount of intra-tree variation in budburst.

     

Resistance toMelampsora larici-epitea leaf rust inSalix: analyses of quantitative trait loci

Quantitative resistance ofSalix toMelampsora larici-epitea leaf rust was studied in 2Salix mapping populations. One population was a backcross between aS. schwerinii ×S. viminalis hybrid andS. viminalis, and the other was an F₂ population betweenS. viminalis andS. dasyclados. A leaf disc bioassay was used to study the components of quantitative resistance (latent period, uredinia number, and uredinia size) to 3 isolates of the leaf rust. The analysis of quantitative trait loci (QTLs) revealed 9 genomic regions in the backcross population and 7 genomic regions in the F₂ population that were important for rust resistance, with QTLs explaining 8–26% of the phenotypic variation. An important genomic region was identified for the backcross population in linkage group 2, where QTLs were identified for all resistance components for 2 of the rust isolates. Four of the QTLs had overlapping mapping intervals, demonstrating a common genetic background for latent period, uredinia diameter, and uredinia number. QTLs specific to some rust isolates and to some resistance components were also found, indicating a combination of common and specific mechanisms involved in the various resistance components. Breeding implications in relation to these findings are discussed.     

Predicted changes in the synchrony of larval emergence and budburst under climatic warming

Summary The impact of climatic warming on the synchrony of insect and plant phenologies was modelled in the case of winter moth (Operophtera brumata) and Sitka spruce (Picea sitchensis) in the Scottish uplands. The emergence of winter moth larvae was predicted with a thermal time requirement model and the budburst of Sitka spruce was predicted from a previously published model (Cannell and Smith 1983) based on winter chilling and thermal time. The date of emergence of winter moth larvae was predicted to occur earlier under climatic warming but the date of budburst of Sitka spruce was not greatly changed, resulting in decreased synchrony between larval emergence and budburst. The general question of how a change of climate might affect phenological synchrony and insect abundance is discussed.     

White pine weevil performances in relation to budburst phenology and traumatic resin duct formation in Norway spruce

1 As the phenological window hypothesis was reported to be significant in influencing the fitness of many herbivores feeding on tree foliage, could it also explain the performance of an insect such as the white pine weevil Pissodes strobi mainly attacking the bark phloem of conifers? 2 Under field conditions, adult weevils were caged on Norway spruce trees presenting a natural variation in their shoot growth phenology. 3 We evaluated white pine weevil biological performances, including oviposition, the number of emerged insects, survival, adult mean weight and tree defense responses as reflected by the production of induced resin canals. 4 None of the white pine weevil biological parameters was significantly affected by Norway spruce phenology. 5 The number of eggs per hole, the number of oviposition holes per leader, the number of emerged adults and their mean weight were not affected by host phenology. 6 The intensity of the traumatic response observed was variable and not correlated with budburst phenology. 7 Trees with higher traumatic responses, forming two or more layers of traumatic ducts, had lower adult emergence and estimated survival. 8 The distance between the first layer of traumatic resin ducts and the start of the annual ring was not correlated with the number of emerged weevils. 9 Norway spruce, which is an exotic tree in North America and a relatively recent host for the white pine weevil, might not possess the defense mechanisms necessary to fight off the white pine weevil.     

Nutrient Relations of Groundsel (Senecio vulgaris) Infected by Rust (Puccinia lagenophorae) at a Range of Nutrient Concentrations I. Concentrations, Contents and Distribution of N, P and K

Groundsel (Senecio vulgaris L.), healthy or infected with therust fungus Puccinia lagenophorae was grown in sand and fedwith a complete nutrient medium diluted to give a range of concentrations.Analysis of bulked, dried tissues of the plant showed that undernutrient-rich conditions rust infection resulted in increasedconcentrations of total (Kjeldahl) nitrogen and potassium buthad little effect on phosphorus concentration. Thus, despitereduced dry weight growth, total plant nitrogen contents wereno less in rusted than control plants. Although total contentsof phosphorus and potassium were reduced by rust, effects wereprobably related to loss of these nutrients in fungal spores. Interactions between rust infection and nutrient supply weresignificant but differed between nutrients: rust caused increasednitrogen concentrations only under nutrient-rich conditionsbut increased phosphorus concentrations only when nutrient supplywas limited. Increased concentrations were not confined to infectedtissues. Mechanisms underlying rust-nutrient interactions appearto be complex and to depend inter alia on the partitioning andrecycling of the particular nutrient within the plant. Rust-inducedincreases in potassium concentration occurred under both highand low nutrient conditions but were confined to infected tissues.Potassium accumulation in nutrient deficient conditions wasprobably due to increased transpirational flux into infectedtissues, but under nutrient-rich conditions reduced potassiumexport appeared to assume greater significance. The possible implications of the changed nutrient relationsfor the wider interactions of rust-infected plants in naturalvegetation are discussed. Senecio vulgaris, Puccinia lagenophorae, rust infection, nutrient deficiency, nutrient content, nutrient concentration, nutrient distribution     

EFFECTS OF MATERNAL AND PATERNAL ENVIRONMENT AND GENOTYPE ON OFFSPRING PHENOTYPE IN SOLIDAGO ALTISSIMA L.

To predict the possible evolutionary response of a plant species to a new environment, it is necessary to separate genetic from environmental sources of phenotypic variation. In a case study of the invader Solidago altissima, the influences of several kinds of parental effects and of direct inheritance and environment on offspring phenotype were separated. Fifteen genotypes were crossed in three 5 × 5 diallels excluding selfs. Clonal replicates of the parental genotypes were grown in two environments such that each diallel could be made with maternal/paternal plants from sand/sand, sand/soil, soil/sand, and soil/soil. In a first experiment (1989) offspring were raised in the experimental garden and in a second experiment (1990) in the glasshouse. Parent plants growing in sand invested less biomass in inflorescences but produced larger seeds than parent plants growing in soil. In the garden experiment, phenotypic variation among offspring was greatly influenced by environmental heterogeneity. Direct genetic variation (within diallels) was found only for leaf characters and total leaf mass. Germination probability and early seedling mass were significantly affected by phenotypic differences among maternal plants because of genotype ( genetic maternal effects ) and soil environment ( general environmental maternal effects ). Seeds from maternal plants in sand germinated better and produced bigger seedlings than seeds from maternal plants in soil. They also grew taller with time, probably because competition accentuated the initial differences. Height growth and stem mass at harvest (an integrated account of individual growth history) of offspring varied significantly among crosses within parental combinations ( specific environmental maternal effects ). In the glasshouse experiment, the influence of environmental heterogeneity and competition could be kept low. Except for early characters, the influence of direct genetic variation was large but again leaf characters (= basic module morphology) seemed to be under stricter genetic control than did size characters. Genetic maternal effects, general environmental maternal effects, and specific environmental maternal effects dominated in early characters. The maternal effects were exerted both via seed mass and directly on characters of young offspring. Persistent effects of the general paternal environment ( general environmental paternal effects ) were found for leaf length and stem and leaf mass at harvest. They were opposite in direction to the general environmental maternal effects, that is the same genotypes produced “better mothers” in sand but “better fathers” in soil. The general environmental paternal effects must have been due to differences in pollen quality, resulting from pollen selection within the male parent or leading to pre- or postzygotic selection within the female parent. The ranking of crosses according to mean offspring phenotypes was different in the two experiments, suggesting strong interaction of the observed effects with the environment. The correlation structure among characters changed less between experiments than did the pattern of variation of single characters, but under the competitive conditions in the garden plant height seemed to be more directly related to fitness than in the glasshouse. Reduced competition could also explain why maternal effects were less persistent in the glasshouse than in the garden experiment. Evolution via selection of maternal effects would be possible in the study population because these effects are in part due to genetic differences among parents.     

Effect of nutrient supply on growth of blue mussels (Mytilus edulis) in a landlocked bay

The growth of blue mussels (Mytilus edulis) was studied in the landlocked bay Hopavågen in central Norway for 3 years, of which in 2 years (1998 and 1999) nutrients were added to increase the primary production. Nutrients (N:Si:P) were added daily from May to October in 1998 (molar ratio 15:5:4.1) and 1999 (molar ratio 16:8:1). The doses of nutrients correspond to 0.4 and 0.8 g P l^–1 day^–1 in 1998 and 1999 respectively. The growth of blue mussels (Mytilus edulis) in 1997 was followed at four depths (1, 2, 4 and 7 m). In 1998 and 1999 growth was followed at 2 and 10 m depths at four locations in Hopavågen and at a control station outside on the coast. The nutrient supply in 1998 only slightly increased the algal biomass (chlorophyll a), whereas mean daily primary production during the summer remained at the same level as the previous year. The increased nutrient supply in 1999 caused a nearly 50 and 100% increase in mean summer biomass and daily primary production, respectively. The growth of blue mussels in Hopavågen in 1997 and 1998 was within the same size range during the summer. In 1999 the shell length of blue mussels kept at 2 m depth was significantly higher than in the previous year at end of the growth season. The recorded growth was also significant higher than for mussels at 2 m depth at the control station. No difference in shell length was observed on mussels grown at 10 m depth in Hopavågen and in the control stations in 1998 and 1999. A higher tissue content was found in blue mussels grown at 2 m depth in Hopavågen, both in 1998 and 1999 when compared to the control groups. At 10 m depth no differences were recorded.     

Effects of ramet clipping and nutrient availability on growth and biomass allocation of yellow nutsedge

A glasshouse experiment was conducted to examine how the interactions of nutrient availability and partial ramet clipping affect growth, reproduction and biomass allocation of Cyperus esculentus, an invasive sedge. The plants sprouting from tubers were grown at low and high nutrient levels, and were subject either to no clipping, one, two or three clippings, with each clipping cutting half of the existing ramets at soil level. Our results show that nutrient availability and clipping frequency tended to independently affect most of growth, reproduction and biomass allocation parameters of Cyperus esculentus examined in the present study. Increased supply of nutrients led to an increase in plant productivity and its associated traits. All of the traits, except for the number of ramets, displayed a decreasing pattern with increasing clipping frequency, indicating that Cyperus esculentus had undercompensatory responses to ramet clipping. It is likely that the patterns of plants response to clipping are species specific, and depend on morphological characters of species. Its susceptibility to ramet clipping can offer opportunities for controlling this invasive species through mechanical methods such as mowing. Clipping had little effects on biomass allocation; however, root weight fraction increased with increasing clipping frequency. While nutrient availability and clipping frequency had no influence on leaf carbon concentration at harvest, both of them increased leaf nitrogen concentration, and hence reduced leaf C/N ratio.     

Potentiality of actinobacteria to combat against biotic and abiotic stresses in tea [Camellia sinensis (L) O. Kuntze]

Tea (Camellia sinensis (L) O. Kuntze) is a long-duration monoculture crop prone to several biotic (fungal diseases and insect pest) and abiotic (nutrient deficiency, drought and salinity) stress that eventually result in extensive annual crop loss. The specific climatic conditions and the perennial nature of the tea crop favour growth limiting abiotic factors, numerous plant pathogenic fungi (PPF) and insect pests. The review focuses on the susceptibility of tea crops to PPF/pests, drought, salinity and nutrient constraints and the potential role of beneficial actinobacteria in promoting tea crop health. The review also focuses on some of the major PPF associated with tea, such as Exobasidium vexans, Pestalotiopsis theae, Colletotrichum acutatum, and pests (Helopeltis theivora). The phylum actinobacteria own a remarkable place in agriculture due to the biosynthesis of bioactive metabolites that assist plant growth by direct nutrient assimilation, phytohormone production, and by indirect aid in plant defence against PPF and pests. The chemical diversity and bioactive significance of actinobacterial metabolites (antibiotics, siderophore, volatile organic compounds, phytohormones) are valuable in the agro-economy. This review explores the recent history of investigations in the role of actinobacteria and its secondary metabolites as a biocontrol agent and proposes a commercial application in tea cultivation.     

Influence of mineral nutrient availability on growth of tree seedlings from the tropical deciduous forest

The effects of different nutrient availabilities on growth and biomass partitioning in seedlings from the tropical deciduous forest in Mexico were compared. The tree species studied were Heliocarpus pallidus, a species associated with disturbed parts of the forest, and Caesalpinia eriotachys, Jacquinia pungens and Recchia mexicana, species from mature, undisturbed habitats. The tropical deciduous tree seedlings were grown in pure silica sand for 50 days inside growth chambers under four nutrient regimes; 5, 20, 100 and 200% Long Ashton nutrient solutions. Data showed contrasting responses among species to different nutrient availabilities. Except Jacquinia pungens, all species had increased growth and productivity as nutrient level increased from 5 to 100%; however, no significant differences in these parameters were detected between 100 and 200% in all species. Compared with mature forest species, pioneer species showed higher variations in biomass production, relative growth rate and net assimilation rate. In contrast to mature forest species, root/ shoot ratios in Heliocarpus pallidus were greater and thus showed higher biomass allocation to roots when nutrient supply was limited. This response suggests higher phenotypic plasticity in pioneer species. Species from mature parts of the forest (Caesalpinia eriostachys, Recchia mexicana) showed less dependency on nutrient supply than pioneer species. These responses appear to support observations from studies with temperate plants investigating growth responses to soil fertility.