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The reproductive ecology of the semi-serotinous species black spruce (Picea mariana (Mill.) BSP) in northern boreal forests remains poorly understood. There is a general lack of data on cone/seed production and viability as a function of biotic treelevel characteristics and abiotic variables. No studies currently exist to quantify these differences over a large gradient in temperature, elevation, and precipitation. Extensive physical, ecological, dendrometric, and reproductive data were collected from young to very old black spruce stands in northern Quebec. ANOVA and general linear mixed models were used to examine interannual cone production, and the relative importance of the biotic and abiotic explanatory factors in determining total cone production; length of the cone-bearing zone; filled seeds per cone; proportion of filled seeds; and seed viability. The results illustrate that the reproductive ecology of black spruce in northern cold forests is mainly explained by biotic variables such as age and diameter [DELTA]T breast height, and by abiotic variables related to temperature such as elevation, length of the growing season, and growing degree-days. Black spruce exhibits a lower reproductive potential in northern cold forests, making it possibly less resilient to increased fire frequency, particularly in unproductive and very young or very old stands. Key words: black spruce, reproductive ecology, cone production, seed production, germination, boreal forest, forest fire, seed viability, resilience, adaptation L'ecologie de la reproduction de l'espece semi-serotineuse, l'epinette noire (Picea mariana (Mill.) BSP) dans les forets boreales froides est encore peu documentee. Il existe un manque general de donnees sur la production des cones/graines et leur viabilite en fonction des caracteristiques biotiques au niveau de l'arbre et des variables abiotiques. Aucune etude n'existe actuellement pour quantifier ces differences sur un large gradient de temperature, d'altitude, et de precipitations. De nombreuses donnees physiques, ecologiques, dendrometriques et reproductives ont ete recueillies dans des peuplements d'epinette noire jeunes a tres ages dans le nord du Quebec. Des ANOVA et des modeles mixtes lineaires generaux ont ete utilises pour examiner la production annuelle de cones et l'importance relative des facteurs explicatifs biotiques et abiotiques dans la determination de la production totale de cones; la longueur de la cime comportant des cones; le nombre de graines pleines par cone; la proportion de graines pleines; et leur taux de germination. Les resultats indiquent que l'ecologie de la reproduction de l'epinette noire dans les forets boreales nordiques est expliquee par des variables biotiques telles que l'age et le DHP, et des variables abiotiques liees a la somme thermique regionale telles que l'altitude, la duree de la saison de croissance, et les degres-jours de croissance. L'epinette noire presente un potentiel reproductif plus faible dans les forets froides du nord, ce qui la rend moins resistante a l'augmentation de la frequence des feux, particulierement dans les peuplements improductifs et tres jeunes ou tres vieux. Mots-cles : epinette noire, ecologie de la reproduction, production des cones, production des graines, germination, foret boreale, feu de foret, taux de germination, resilience, adaptation, 1. Introduction Black spruce (Picea mariana (Mill.)) is one of the most common and commercially important conifer species in the boreal forest of eastern North America (Viereck and Johnston 1990), [...]

Masting behavior--variable and synchronized reproduction by a population of plants--has long been recognized as correlating with weather. How and why weather conditions influence seed production is, however, poorly understood. We investigated the relationships between acorn production and both local weather and long-term climate in 10 populations across the geographic range of the valley oak (Quercus lobata Nee), a California endemic that matures acorns in a single season. Acorn production was larger following a cold spring in the prior year and dry conditions in the winter and spring immediately preceding acorn maturation; similar patterns were also found, with minor differences, at all 10 individual sites. The strength of the relationships varied geographically in the case of the correlation between winter rainfall and annual acorn production, which was stronger (more negative) at wetter sites. Thus, in contrast to a recent study in Quercus petraea (Matt.) Liebl., weather had generally similar effects on acorn production throughout the range of Q. lobata. Similar to Q. petraea, however, the strength of the relationship between site-level annual acorn production and one of the weather factors affecting acorn production (winter rainfall in the case of Q. lobata) varied geographically in ways that may be related to differences among sites in the degree of pollen limitation. Understanding the mechanisms by which weather affects seed production is challenging but critical if we are to understand how climate change will affect masting behavior in the future. Key words: acorn production, masting, Quercus lobata, valley oak, variable reproduction. Il est depuis longtemps reconnu que la reproduction synchronisee et variable dans une population de plantes (<>) est correlee avec les conditions meteorologiques. Cependant, on comprend mal comment et pourquoi les conditions meteorologiques influencent la production de semences. Nous avons etudie les relations entre la production de glands et les conditions meteorologiques locales ainsi que le climat a long terme chez 10 populations dans l'aire de repartition du chene lobe (Quercus lobata Nee), un chene endemique de la Californie dont les glands arrivent a maturite en une seule saison. La production de gland etait plus abondante a la suite d'un printemps froid l'annee precedente et des conditions seches durant l'hiver et le printemps precedant immediatement la maturation des glands. Des patrons similaires ont ete observes, avec des differences mineures, dans l'ensemble des 10 stations individuelles. La force de la relation variait geographiquement dans le cas de la correlation entre la chute de pluie hivernale et la production annuelle de glands; la correlation etait plus forte (plus negative) dans les stations plus humides. Par consequent, contrairement a une etude recente qui portait sur Quercus petraea (Matt.) Liebl., les conditions meteorologiques avaient generalement des effets similaires sur la production de glands partout dans l'aire de repartition de Q. lobata. Comme avec Q. petraea cependant, la force de la relation entre la production annuelle de glands a l'echelle de la station et un des facteurs meteorologiques qui influencent la production de glands (chute de pluie hivernale dans le cas de Q. lobata) variait d'un endroit a l'autre. Cette variation pouvait etre reliee a des differences entre les stations concernant la disponibilite du pollen. Il est difficile mais essentiel de comprendre les mecanismes par lesquels les conditions meteorologiques influencent la production de semences si nous voulons comprendre de quelle facon le changement climatique affectera la reproduction synchronisee dans le futur. [Traduit par la Redaction] Mots-cles: production de glands, masting, Quercus lobata, vallee du chene, reproduction variable., Introduction Variable, synchronized seed production, known as mast-fruiting or masting behavior, is commonly observed in many taxa of plants and is particularly widespread among temperate and boreal trees. The evolutionary [...]

Recent concern regarding the potential decline of quaking aspen (Populus tremuloides Michx.) forests in the western United States has sparked concern over whether the species can be effectively regenerated. Using a retrospective approach, we quantified the response of regenerating aspen stems to an ordinary set of silvicultural treatments conducted over approximately the past decade in southern Utah, USA. A suite of variables describing stand structure and composition, stand vigor, physiographic factors, herbivore pressure, and treatment types were measured to predict the possible controls, as well as their relative importance, on aspen regeneration. Results suggested that aspen regeneration was most strongly related to browsing pressure, site preparation technique, and the presence of advance reproduction before treatment, which is a novel finding. Secondary predictors included elevation, site index, and overstory conditions, which are generally characteristics of stand vigor. Management recommendations based on our results should recognize the strong primary control that browsing pressure exerts on regeneration. First, the height of advance reproduction is inherently dependent on antecedent herbivory and also indicative of present browsing and should be assessed before treatment. Second, the most effective site preparation techniques, namely broadcast burning and browsing reduction, will directly reduce browsing pressure, assuming ungulate populations are not too large. Any management targeting timely and effective aspen regeneration should incorporate monitoring and (or) controlling browsing pressure, both before and after treatment. Key words: browsing, coppice, herbivory, Populus tremuloides, silviculture. L'inquietude recente face au deperissement apprehende des forets de peuplier faux-tremble (Populus tremuloides Michx.) dans l'ouest des Etats-Unis a suscite un questionnement concernant la possibilite de regenerer efficacement cette espece. A l'aide d'une approche retrospective, nous avons quantifie la reponse de tiges de peuplier faux-tremble au stade de la regeneration a un ensemble ordinaire de traitements sylvicoles realises au cours de la derniere decennie dans le sud de l'Utah, aux Etats-Unis. Une serie de variables decrivant la composition et la structure du peuplement, la vigueur du peuplement, les facteurs physiographiques, la pression des herbivores et les types de traitement ont ete mesurees dans le but de determiner quels facteurs pourraient influencer la regeneration du peuplier faux-tremble ainsi que leur importance relative. Les resultats indiquent que la regeneration du peuplier faux-tremble est surtout influencee par la pression des herbivores, la preparation technique du terrain, et la presence de regeneration preetablie, c'est-a-dire avant le traitement, ce qui constitue un resultat inedit. Les predicteurs secondaires incluent l'altitude, l'indice de qualite de station et l'etat de l'etage dominant: generalement les caracteristiques de vigueur du peuplement. Selon nos resultats, les recommandations d'amenagement devraient reconnaitre que la regeneration est controlee principalement par la pression des herbivores. Premierement, la hauteur de la regeneration preetablie depend intrinsequement du broutage passe mais peut aussi donner une idee de l'impact actuel du broutage; elle devrait etre evaluee avant d'appliquer un traitement. Deuxiemement, les techniques de preparation de terrain les plus efficaces: le brulage extensif et la reduction du broutage, reduiront directement la pression des herbivores a condition que les populations d'ongules ne soient pas trop importantes. Tout amenagement visant a etablir une regeneration en temps opportun et efficace du peuplier fauxtremble devrait comprendre le suivi ou le controle de la pression des herbivores, ou les deux, avant et apres le traitement. [Traduit par la Redaction] Mots-cles: broutage, taillis, herbivorisme, Populus tremuloides, sylviculture., Introduction Quaking aspen (Populus tremuloides Michx.; hereafter, aspen) is an ecologically and economically important forest species throughout its range (Baker 1925). A prevalent theme in the aspen literature is concern [...]

The differential temperature (ΔT) model, based on the assumption that masting plants respond to the difference in the temperatures during the growing seasons 1 and 2 years prior to seed production, has recently been proposed to explain the proximate factor of masting. In this study, we used a 28-year series of data on pollen cone and seed production in Cryptomeria japonica D. Don in Japan and compared several models based on temperatures and resources to test whether ΔT acts as a cue or is a proxy for resource limitation. Of all the models tested, models including ΔT, previous summer absolute temperature [T.sub.n-1], and reproduction in the previous year provided the best fit. The number of pollen cones and seeds produced was proportional to the difference in the mean daily maximum temperature during June to August between the preceding two years. In addition, to test whether the double mast events in consecutive years was less common than consecutive warm summers, we used our dataset and 12 datasets of pollen dispersal of 17 years or longer of C. japonica in Japan. Although consecutive warm summers occurred in 4.4% of pairs, double mast events occurred in 1.0%. The ΔT model was a considerably better predictor of the rare phenomenon of double mast events, which occur only after a specific sequence of cold-moderate-hot absolute summer temperatures. Thus, ΔT acts as cue for masting in C. japonica. Key words: climate cue, Cryptomeria japonica, ΔT model, Japanese cedar, masting. Le modele de temperature differentielle (ΔT), fonde sur l'hypothese que les plantes reagissent a la difference de temperature entre les deux saisons de croissance qui ont precede une annee semenciere, a recemment ete propose pour expliquer la cause directe de ce phenomene. Dans cette etude, nous avons utilise une serie de donnees portant sur 28 annees de production de cones males et de graines chez Cryptomeria japonica D. Don au Japon et nous avons compare plusieurs modeles fondes sur les temperatures ainsi que les ressources pour verifier si le modele ΔT agit comme un signal ou est un indice de ressources limitees. De tous les modeles testes, les modeles qui incluaient ΔT, la temperature absolue de l'ete precedent [T.sub.n-1] et la reproduction au cours de l'annee precedente donnaient le meilleur ajustement. Le nombre de cones males et de graines produits etait proportionnel a la difference de temperature journaliere maximum moyenne durant les mois de juin et aout entre les deux annees precedentes. De plus, pour determiner si les annees semencieres doubles consecutives etaient moins frequentes que les etes chauds consecutifs, nous avons utilise notre base de donnees et 12 bases de donnees sur la dispersion du pollen sur 17 annees ouplus pour C. japonica au Japon. Bienque des etes chauds consecutifs soient survenus dans 4,4% des paires, les annees semencieres doubles sont survenues dans 1% des cas. Le modele ΔT predisait beaucoup mieux le phenomene rare des annees semencieres doubles qui survenaient seulement a la suite d'une sequence specifique de temperatures estivales absolues: froides-moderees-chaudes. Par consequent, ΔT agit comme un signal pour les annees semencieres chez C. japonica. [Traduit par la Redaction] Mots-cles: signal climatique, Cryptomeria japonica, modele ΔT, cedre du Japon, annee semenciere., Introduction Population-level fluctuations of large crops of seeds or flowers, known as masting or mass flowering, are common and important phenomena in plants (Silvertown 1980, Kelly and Sork 2002). Masting [...]

The study of floral traits and pollination for the plant genus Phlox has historically been focused on either surveys of general pollinator affinities across the genus or detailed research on pollinator-mediated evolution of floral color in a single species (Phlox drummondii). The purpose of this study was to explore a different kind of trait--floral scent in Phlox divaricata, a species noted for its strong scent. Specifically, we predicted the diel emission patterns of floral scent might covary with the daily abundance of diurnal moths, identified in a previous study as the most important pollinators in a Konza Prairie population of P. divaricata. Consistent with this prediction, we documented peaks in median floral scent emissions at 1000-1200 and 1930-2130, coinciding with peaks in moth visitation and resulting seed production. Two groups of scent compounds contributed to this pattern; linalool and its associated lilac aldehyde/alcohol compounds (especially lilac aldehyde B) contributed a greater proportion to scent at 1000-1200, while aromatic compounds (including benzaldehyde and benzyl acetate) contributed a greater proportion to scent at 1930-2130 and other afternoon time periods. These volatiles are known floral attractants for several lepidopteran pollinators, including noctuid moths. However, there is an additional peak in pollinator abundance (Hemaris diurnal hawkmoths) and seed set at a time when scent production is relatively low (1400-1600) suggesting additional factors mediate both pollinator behavior and floral volatile emissions. Future studies of P. divaricata should test for the presence of destructive floral enemies that might be attracted by floral volatiles during mid-afternoon periods, as well as the importance of visual floral traits (color, shape) in attracting diurnal moths, an important functional group of pollinators that has received minimal attention in North America., INTRODUCTION Studies of unique floral forms and functions for a number of different plant species have led to a greater understanding of the evolutionary history of relationships between plants and [...]

Numerous factors contribute to the variability in treeline change; however, the potential role of insect predation in limiting seed productivity is not well documented. Conditions for seed germination, establishment, and survival are not limiting at the Mealy Mountains treeline (Labrador, Canada), but seedlings are rarely encountered, suggesting a seed-related bottleneck to recruitment. Mature cones were collected in 2008 from four tree species (black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.), balsam fir (Abies balsamea (L.) Mill.), eastern larch (Larix laricina (Du Roi) K. Koch), and white spruce (Picea glauca (Moench) Voss)) across three treeline zones (forest, transition, and krummholz) to assess potential seed limitation. During that year, an unexpectedly high diversity of insect larvae caused extensive reproductive loss and damaged the cones of ~85% of trees sampled, confirming that treeline change models should include seed predation. Seed germination was low and variable in all treeline zones, although significantly higher in black spruce and eastern larch. Most reproductive quality measures decreased significantly with elevation, although no differences among zones or tree species in the percentages of seeds damaged by insects were found (mean ± standard deviation: 31% [+ or -] 23%). Based on tree density and seed production, black spruce is predicted to lead the treeline expansion in the Mealy Mountains. Although climate warming may create conditions conducive for increased seed production, predispersal seed predation may limit future treeline expansion. Key words: climate change, forest-tundra ecotone, insect herbivory, multispecies, predispersal seed predation, reproductive bottleneck. Plusieurs facteurs contribuent a la variabilite de la modification de la limite des arbres mais le role potentiel des epidemies d'insecte dans la reduction de la productivite des graines a ete peu etudie. A la limite des arbres dans les montagnes Mealy (Labrador, Canada), les conditions sont adequates pour la germination, l'etablissement et la survie mais on trouve rarement des semis. Cela indique qu'il y a un probleme de recrutement relie aux graines. Des cones matures ont ete collectes en 2008 chez quatre especes (epicea noir (Picea mariana (Mill.) Britton, Sterns & Poggenb.), sapin baumier (Abies balsamea (L.) Mill.), meleze laricin (Larix laricina (Du Roi) K. Koch) et epicea blanc (Picea glauca (Moench) Voss)) dans trois zones de la limite des arbres (foret, transition et krummholz) pour evaluer les problemes potentiels relies aux graines. Durant cette annee, une diversite etonnamment elevee de larves d'insecte ont cause des pertes importantes en endommageant les cones d'environ 85 % des arbres echantillonnes. Cela a confirme que les modeles qui simulent les variations de la limite des arbres devraient inclure la predation par les insectes. La germination des graines etait faible et variable dans toutes les zones a la limite des arbres quoique significativement meilleure chez l'epicea noir et le meleze. La plupart des mesures de qualite de la reproduction diminuaient significativement avec l'altitude bien qu'aucune difference dans le pourcentage de graines endommagees par les insectes entre les zones ou les especes d'arbre n'ait ete observee (moyenne : 31% ± 23%ET). Sur la base de la densite des arbres et de la production de cones ou de graines, on prevoit que l'epicea noir dominera l'expansion de la limite des arbres dans les montagnes Mealy. Bien que le rechauffement du climat puisse creer des conditions favorables a l'augmentation de la production de graines, la predation des graines avant qu'elles n'aient ete dispersees pourrait limiter l'expansion future de la limite des arbres. [Traduit par la Redaction] Mots-cles : changements climatiques, ecotone entre la foret et la toundra, insectes herbivores, multiespeces, predation des graines avant leur dispersion, problemes de reproduction., Introduction At the global scale, upslope and northward advance of the thermally constrained forest-tundra ecotone (treeline; sensu Scott (1995)) is expected given projected warming scenarios associated with climate change (Grace [...]

Ranunculus ficaria is an invasive plant species in the northeastern United States, especially in urban riparian habitats. Changes in the frequency and intensity of flooding events in these urban riparian corridors create patches of heavy litter and patches of bare ground. Many plant species either cannot penetrate deep litter, or they are susceptible to freezing temperatures and drying conditions on bare ground. This can result in competitive advantages for invasive species that are adapted to these varying conditions. We conducted a field experiment to test the effects of leaf litter depth on R. ficaria biomass, bulbil production, flower production, and seed production under deep (20 cm) litter, intermediate (10 cm) litter, shallow (5 cm) litter, and bare ground along an urban stream in Louisville, Kentucky. Deep litter and lack of litter decreased plant biomass compared with shallow litter. Bulbil production was not significantly different across treatments. Flower and seed production were only reduced in deep litter. Ranunculus jicaria's ability to maintain production across a large range of litter depths may provide a competitive advantage over plant species not adapted to varying litter depths., INTRODUCTION Invasive plant species are important economic and environmental pests, posing threats to endangered species, altering native habitats, decreasing biodiversity, and facilitating the establishment of other invasive species (Pimentel et [...]

This article introduces the concept of 'robust selection', which proposes tree selection based on the stochastic simulation of economic values to account for the inherent uncertainty of economic weights used in tree selection for breeding programs. The proposed method uses both median ranking and ranking variability as criteria for breeding selection. Using consensus genetic and economic parameters from the New Zealand Radiata Pine Breeding Company program, we compare three selection strategies: deterministic application of economic weights from a vertically integrated bioeconomic model, an equal-weight index often used in operations, and robust selection. All strategies aim to increase value for a breeding objective that includes four traits, i.e., volume, stem sweep, branch size, and wood stiffness (measured as modulus of elasticity), based on a selection index that considers five criteria, i.e., stem diameter at breast height (1.3 m), straightness, branching score, wood density, and modulus of elasticity. Two-thirds of the selected trees were unique for each of the selection strategies. Robust selection achieved the best realised gain for three of the four selection criteria and was the middle performer in the last selection criteria. Considering the high intrinsic uncertainty of economic weights, we suggest that the relevant criterion for the selection of individuals is the maximum median ranking, subject to an acceptable level of variation in that ranking, rather than their narrow performance under a single economic scenario. This will lead to tree selections that perform well under a wide range of economic circumstances. Key words: breeding objectives, economic weights, simulation, economic evaluation, risk analysis. Cet article introduit le concept de << selection robuste >> qui propose une selection fondee sur la simulation stochastique de la valeur economique pour tenir compte de l'incertitude inherente du poids economique utilise pour la selection des arbres dans les programmes d'amelioration. La methode qui est proposee utilise le classement median et la variabilite du classement comme criteres pour la selection. A l'aide de parametres genetiques et economiques du programme de la New Zealand Radiata Pine Breeding Company qui font consensus, nous avons compare trois strategies de selection : l'application deterministique du poids economique provenant d'un modele bioeconomique verticalement integre, un indice de poids equivalent souvent utilise dans les operations et la selection robuste. Toutes les strategies visent a augmenter la valeur d'un objectif d'amelioration qui inclut le volume, la courbure du tronc, la dimension des branches et la rigidite du bois a partir d'un indice de selection qui tient compte du diametre du tronc, de sa rectitude, de la note de branchaison, de la densite du bois et du module d'elasticite. Les deux tiers des arbres selectionnes avec chacune des strategies etaient uniques. La selection robuste a produit le meilleur gain pour trois des quatre criteres de selection et occupe la position intermediaire pour l'autre critere. En tenant compte de l'importante incertitude intrinseque du poids economique, nous suggerons que le critere pertinent pour la selection des individus soit le classement median maximum, qui est sujet a un degre acceptable de variation dans ce classement, plutot que leur performance etroite dans le cadre d'un seul scenario economique. Cela va engendrer la selection d'individus qui performent bien dans une vaste gamme de conditions economiques. [Traduit par la Redaction] Mots-cles : objectifs d'amelioration, poids economique, simulation, evaluation economique, analyse de risques., Introduction The selection of superior trees is central to breeding programs, aiming to identify individuals with maximum economic-genetic value for a combination of characteristics of economic importance. These trees are [...]

Exponential fertilization has been shown to be a useful technique for improving seedling quality during nursery production. In this study, we evaluated (i) the impact of exponential vs. conventional fertilization on trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) seedlings during nursery production and (ii) the growth performance and nitrogen (N) utilization of those seedlings in response to foxtail barley (Hordeum jubatum L.) competition after the transplantation of seedlings in a greenhouse experiment. Exponential fertilization with an application rate higher than the conventional fertilization increased the internal N reserve in trembling aspen and white spruce seedlings during nursery production and also increased new leaf, new stem, and old stem biomass and N retranslocation rates in trembling aspen seedlings but not in white spruce seedlings after transplantation. Foxtail barley competition decreased N concentrations in seedlings and soil N uptake by the seedlings; however, increased N retranslocation rates with foxtail barley competition were observed in white spruce seedlings but not in trembling aspen seedlings. Our results suggest that the growth performance of seedlings was improved by N loading, whereas the impact of vegetation management was species specific. Key words: exponential fertilization, internal N reserve, N-loaded seedling, net N retranslocation rate, vegetation competition. La fertilisation exponentielle s'est averee utile pour ameliorer la qualite des semis lors de la production en pepiniere. Dans cette etude, nous avons evalue (i) l'impact de la fertilisation exponentielle vs conventionnelle sur les semis de peuplier faux-tremble (Populus tremuloides Michx.) et d'epicea blanc (Picea glauca (Moench) Voss) lors de la production en pepiniere, et (ii) la croissance de ces semis et leur utilisation de N en reaction a la competition de l'orge queue-d'ecureuil (Hordeum jubatum L.) apres les avoir transplantes en serre suivant un dispositif experimental. La fertilisation exponentielle, dont le taux d'application est plus eleve que la fertilisation conventionnelle, a augmente les reserves internes de N chez les semis de peuplier faux- tremble et d'epicea blanc durant la production en pepiniere et a augmente la biomasse des nouvelles feuilles, des nouvelles et des vieilles tiges ainsi que le taux de retranslocation de N apres la transplantation chez les semis de peuplier faux-tremble mais pas chez les semis d'epicea blanc. La competition de l'orge queue-d'ecureuil a reduit les concentrations de N dans les semis et l'absorption de N dans le sol par les semis; cependant, en presence de l'orge queue-d'ecureuil une augmentation du taux de retranslocation de N a ete observee chez les semis d'epicea blanc mais pas chez les semis de peuplier faux-tremble. Nos resultats indiquent que la croissance des semis a ete amelioree par une surcharge de N tandis que l'impact de la maitrise de la vegetation dependait de chaque espece. [Traduit par la Redaction] Mots-cles : fertilisation exponentielle, reserves internes de N, semis surcharges en N, taux net de retranslocation, competition de la vegetation., Introduction Vegetation management is one of the most critical silvicultural practices for maximizing postplanting tree seedling survival and growth during the early establishment phase of plantations (Lowery et al. 1993; [...]

Natural regeneration-based silviculture has been increasingly regarded as a reliable option in sustainable forest management. However, successful natural regeneration is not always easy to achieve. Recently, new concerns have arisen because of changing future climate. To date, regeneration models have proved helpful in decision-making concerning natural regeneration. The implementation of such models into optimization routines is a promising approach in providing forest managers with accurate tools for forest planning. In the present study, we present a stochastic multistage regeneration model for Pinus pinea L. managed woodlands in Central Spain, where regeneration has been historically unsuccessful. The model is able to quantify recruitment under different silviculture alternatives and varying climatic scenarios, with further application to optimize management scheduling. The regeneration process in the species showed high between-year variation, with all subprocesses (seed production, dispersal, germination, predation, and seedling survival) having the potential to become bottlenecks. However, model simulations demonstrate that current intensive management is responsible for regeneration failure in the long term. Specifically, stand densities at rotation age are too low to guarantee adequate dispersal, the optimal density of seed-producing trees being around 150 stems-ha-1. In addition, rotation length needs to be extended up to 120 years to benefit from the higher seed production of older trees. Stochastic optimization confirms these results. Regeneration does not appear to worsen under climate change conditions; the species exhibiting resilience worthy of broader consideration in Mediterranean silviculture. Key words: multistage models, transition probability, stochastic spatial optimization, stochastic simulation, climatic change. Resume: La sylviculture fondee sur la regeneration naturelle est de plus en plus consideree comme une option fiable pour l'amenagement forestier durable. Cependant, il n'est pas toujours facile de reussir a etablir une regeneration naturelle. Recemment, de nouvelles preoccupations ont ete soulevees en raison des futurs changements climatiques. Jusqu'a present, les modeles de regeneration se sont averes utiles pour la prise de decision concernant la regeneration naturelle. L'application de ces modeles dans des routines d'optimisation est une approche prometteuse pour fournir aux amenagistes forestiers des outils precis pour la planification forestiere. Dans la presente etude, nous presentons un modele de regeneration stochastique multistage pour les forets amenagees de Pinus pinea L. du centre de l'Espagne ou la regeneration a historiquement ete infructueuse. Le modele est en mesure de quantifier le recrutement en fonction de differentes methodes sylvicoles et de divers scenarios climatiques, en plus d'optimiser le calendrier d'amenagement. Le processus de regeneration de cette espece a montre une forte variation interannuelle et tous les sous-processus (production, dispersion, germination et predation des graines ainsi que survie des semis) peuvent devenir des goulots d'etranglement. Cependant, les simulations du modele montrent que l'amenagement intensif presentement applique est responsable de l'echec de la regeneration a long terme. Specifiquement, la densite des peuplements a l'[caret.a]ge d'exploitabilite est trop faible pour garantir une dispersion adequate, la densite optimale des arbres semenciers etant d'environ 150 tiges h[a.sup.-1]. De plus, la duree de la rotation doit etre allongee jusqu'a 120 ans pour tirer profit de la plus forte production de semences des plus vieux arbres. L'optimisation stochastique confirme ces resultats. L'etablissement de la regeneration ne semble pas devenir plus difficile sous des conditions de changement climatique; l'espece fait preuve d'une resilience qui merite d'etre mieux consideree par la sylviculture mediterraneenne. [Traduit par la Redaction] Mots-cles: modeles multistages, probabilite de transition, optimisation spatiale stochastique, simulation stochastique, changements climatiques., Introduction One of the main aims of sustainable forest management is to guarantee forest persistence over time (Nyland 2002). This general objective implies that managed stands need to be successfully [...]

Patterns of jack pine (Pinus banksiana Lambert) pollen cone production are of interest because they may help explain jack pine budworm (Choristoneura pinus pinus Freeman) outbreak patterns. We used generalized linear mixed models to analyze pollen cone production in 180 permanent plots in Ontario, Canada between 1992 and 2008. Pollen cone production increased with stand age, and large trees in sparsely-populated stands produced more pollen cones. Defoliation decreased the propensity of trees to produce pollen cones for at least two years. We also identified important patterns that are not explained by defoliation and stand characteristics. Pollen cone production is spatially synchronized among years, trees in central Ontario produced more pollen cones than trees in northwestern Ontario, and background cone production increased over time in the central region but not in more northwestern plots. Synchronized reproduction is common among tree species, but has not previously been noted for jack pine pollen cones. Increasing cone production in central Ontario may be evidence of changing forest and (or) climatic conditions and deserves further investigation. Our model can be used to quantitatively predict pollen cone production and assess the risk of jack pine budworm defoliation. Key words: Choristoneura pinus pinus, Pinus banksiana, population dynamics, spatial synchrony, insect plant interactions. Resume: Les profils de production de cones males chez le pin gris (Pinus banksiana Lambert) presentent un interet parce qu'ils pourraient contribuer a expliquer le comportement des epidemies de tordeuse du pin gris (Choristoneura pinus pinus Freeman). Nous avons utilise des modeles lineaires mixtes generalises pour analyser la production de cones males dans 180 placettes permanentes en Ontario, au Canada, entre 1992 et 2008. La production de cones males augmentait avec l'age du peuplement et les gros arbres dans les peuplements clairsemes produisaient plus de cones males. La defoliation reduisait la propension des arbres a produire des cones males pendant au moins deux ans. Nous avons aussi identifie des profils importants qui ne sont pas expliques par la defoliation ni par les caracteristiques du peuplement. La production de cones males est spatialement synchronisee d'une annee a l'autre: les arbres produisaient plus de cones males dans le centre que dans le nord-ouest de l'Ontario, et la production historique de cones males a augmente avec le temps dans la region centrale mais pas dans les placettes les plus eloignees vers le nord-ouest. La reproduction synchrone est courante parmi les especes d'arbre mais n'avait pas jusqu'ici ete observee chez les cones males du pin gris. La production accrue de cones males dans le centre de l'Ontario pourrait etre un indice que les conditions climatiques et la foret changent et merite d'etre davantage etudiee. Notre modele peut etre utilise pour predire de facon qualitative la production de cones males et evaluer le risque de defoliation par la tordeuse du pin gris. [Traduit par la Redaction] Mots-cles: Choristoneura pinus, Pinus banksiana, dynamique des populations, synchronisme spatial, interactions entre les plantes et les insects., Introduction Many animal populations undergo large, spatially synchronized changes in abundance over time, and determining the causes of these patterns is a central topic in population ecology (Bjornstad and Grenfell [...]

Simple, operational tools are required for forest managers to quantify the effects of soil fertility on tree growth and ecosystem sustainability leading to precise, sustainable forest management. The simplified process-based 3-PG model (Landsberg, J.J., and Waring, R.H., For. Ecol. Manage. 95: 209-228, 1997) provides a useful framework for operational prediction of forest growth. However, no simple objective method for relating the effects of available soil nutrients to the model fertility parameter fertility rating (FR) is yet available. The present study aimed to compare several general modeling approaches for the estimation of FR values from soil relative nutrient contents (RNCs) to maximum nonlimiting values, measured in the whole soil profile, at continuous inventory plots of Eucalyptus globulus Labill. in several locations under different parent materials in northwestern Spain. The modeling approaches tested provided good predictions of FR values from RNCs. In particular, using the minimum value of the most significant RNCs showed considerable potential for modeling FR values and plantation growth responses to them. This modeling approach showed promise to be further tested as a generally applicable strategy for estimating the effect of soil nutrients on forest plantations growth. Resume: Des outils simples et operationnels sont necessaires aux amenagistes forestiers pour quantifier les effets de la fertilite du sol sur la croissance des arbres et la durabilite des ecosystemes menant a un amenagement forestier precis et soutenu. Le modele 3-PG simplifie, fonde sur des processus ecophysiologiques (Landsberg, J.J., et Waring, R.H., For. Ecol. Manage. 95: 209-228, 1997), offre un cadre utile de prevision operationnelle de la croissance forestiere. Cependant, aucune methode simple et objective n'est encore disponible pour faire le lien entre les effets de la disponibilite des nutriments du sol et le parametre d'indice de fertilite (IF) du modele. La presente etude vise a comparer plusieurs approches generales de modelisation pour estimer des valeurs d'IF a partir du contenu relatif en nutriments du sol (CRN) pouvant atteindre des valeurs maximales non limitatives. Le CRN a ete mesure dans le profil complet du sol de parcelles d'inventaire continu d'Eucalyptus globulus Labill. etablies a plusieurs endroits sur differents materiaux parentaux dans le nord-ouest de l'Espagne. Les approches de modelisation testees ont produit de bonnes previsions des valeurs d'IF a partir des CRN. En particulier, l'utilisation de la valeur minimale des CRN les plus significatifs a montre un potentiel considerable pour modeliser les valeurs d'IF de meme que son effet sur la reaction de croissance des plantations. Cette approche de modelisation prometteuse merite d'etre davantage testee comme strategie d'application generale pour estimer l'effet des nutriments du sol sur la croissance des plantations forestieres. [Traduit par la Redaction], Introduction In spite of the well-documented relevance of soil nutrition on tree growth (e.g., Merino et al. 2003, Laclau et al. 2010), there is a scarcity of practical modeling tools [...]

Five fumigation treatments (a conventional methyl bromide - chloropicrin application and four reduced-rate alternative fumigant treatments) and a nonfumigated treatment were evaluated at two forest nurseries in Oregon and one forest nursery in Washington for their effects on soil pathogen populations, weeds, and seedling morphology during a 2-year study. The effect of plastic tarp composition on fumigant efficacy was also evaluated (virtually impermeable film versus high-density polyethylene). All fumigant treatments reduced soil populations of Fusarium and Pythium for up to 7 months after fumigation and resulted in seedlings with significantly less pathogen colonization than those from the nonfumigated treatment. All fumigant treatments were more effective against pathogen inoculum buried at 15 cm rather than at 30 cm. Fusarium commune Skovgaard, O'Donnell et Nirenberg, Fusarium oxysporum Schlect. emend. Snyder & Hansen, isolates from the Gibberella fujikuroi Saw. complex, Pythium irregulare Buisman, Pythium aff. spiculum B. Paul 2006, Pythium sylvaticum Campbell & Hendrix, and Pythium 'vipa' Hermansen & Klemsdal were the most commonly isolated pathogens. Weed biomass and weeding times were significantly reduced by fumigation, but only at the Washington nursery with high weed pressure. No significant differences were observed in efficacy between the conventional methyl bromide - chloropicrin treament and any of the reduced rate fumigants or between the two types of plastic tarp. Conifer seedling height, diameter, shoot volume, and root volume were significantly greater in all fumigated treatments compared with the nonfumigated treatment. Resume: Cinq traitements de fumigation (une application conventionnelle de bromure de methyle et de chloropicrine et quatre autres traitements de fumigation a taux reduit) ainsi qu'un traitement sans fumigation ont ete evalues dans deux pepinieres forestieres en Oregon et une autre pepiniere forestiere dans l'Etat de Washington. L'etude a dure deux ans et a porte sur l'effet des traitements sur les populations de pathogenes du sol, les mauvaises herbes et la morphologie des semis. L'effet de la composition de la bache en plastique sur l'efficacite du fumigant a aussi ete evalue (pellicule pratiquement imper-meable versus polyethylene haute densite). Tous les traitements de fumigation ont reduit les populations de Fusarium et de Pythium pendant une periode dont la duree pouvait aller jusqu'a sept mois apres la fumigation et les semis etaient significa-tivement moins colonises par les pathogenes que ceux qui n'avaient pas ete fumiges. Tous les traitements de fumigation ont ete plus efficaces contre l'inoculum des pathogenes enfoui a 15 cm plutot qu'a 30 cm. Fusarium commune Skovgaard, O'Donnell et Nirenberg, Fusarium oxysporum Schlect. emend. Snyder & Hansen, des isolats appartenant au complexe Gibberella fujikuroi Saw., Pythium irregulare Buisman, Pythium aff. spiculum B. Paul 2006, Pythium sylvaticum Campbell & Hendrix et Pythium ≪ vipa ≫ Hermansen & Klemsdal sont les pathogenes qui ont ete le plus souvent isoles. La fumigation a reduit de facon significative la biomasse des mauvaises herbes et la duree du desherbage mais seulement dans la pepiniere de l'Etat de Washington ou la pression des mauvaises herbes etait forte. Aucune difference significative d'efficacite n'a ete observee entre le traitement conventionnel, avec le bromure de methyle et la chloropicrine, et n'importe quel des traitements de fumigation a taux reduit, ni entre les deux types de bache en plastique. La hauteur, le diametre, le volume des pousses et le volume des racines des semis de conifere avaient des valeurs significativement plus elevees dans tous les traitements de fumigation comparativement au traitement sans fumigation. [Traduit par la Redaction], Introduction Forest nurseries of the Pacific Northwest (PNW) of the United States (Oregon, Washington, and Idaho) produce field-grown bareroot tree seedlings to regenerate lands that have been harvested or destroyed [...]

In forestry, science-based seed transfer systems, the foundation of effective reforestation programs, will likely be used in some form to mitigate the negative effects of climate change. In this study, we developed fixed and focal point seed transfer systems for interior spruce (Picea glauca (Moench) Voss, Picea engelmannii Parry ex Engelm., and their hybrids) in British Columbia, Canada, and compared the effectiveness of both systems. Growth, phenology, and physiology traits were measured for 112 populations, and population means were transformed to principal components that were modeled using climate variables and multiple regression analysis. Compared with the fixed seed zone system, the focal point system had a greater area of seed use for a given risk of maladaptation. The relationship between growth and adaptive distance (i. e., adaptive similarity between test populations and populations local to test sites) was used to calculate critical seed transfer distances for focal point seed zones, which were defined according to expected forfeiture of growth. Changes in climate observed over the past 100 years and predicted in the next one third of a rotation were used to calculate appropriate assisted migration distances and develop methods for incorporating assisted migration into a focal point seed transfer system. Resume: etant le fondement de programmes efficaces de reboisement en foresterie, les systemes de transfert de semences qui reposent sur des donnees scientifiques seront probablement utilises sous une forme ou une autre afin d'attenuer les effets negatifs des changements climatiques. La presente etude avait pour but de developper des systemes de transfert des semences bases sur les points fixes et focaux pour l'epinette de l'interieur (Picea glauca (Moench) Voss, Picea engelmannii Parry ex Engelm. et leurs hybrides) en Colombie-Britannique, au Canada, et de comparer l'efficacite des deux types de systeme. Des caracteres relies a la croissance, la phenologie et la physiologie ont ete mesures chez 112 populations et les moyennes de populations ont ete transformees en composantes principales qui ont ete modelisees a l'aide des variables climatiques et de l'analyse de regression multiple. Comparativement au systeme de zones semencieres base sur les points fixes, le systeme a points focaux produisait de plus grandes zones d'utilisation des semences pour un risque donne de mesadaptation. La relation entre la croissance et la distance reliee a l'adaptation (c.-a-d. la similitude d'adaptation entre les populations d'elevage et les populations locales en reference aux sites experimentaux) a ete utilisee pour estimer les distances critiques de transfert des semences pour les zones semencieres basees sur les points focaux, telles que definies selon la baisse anticipee de croissance. Les changements climatiques observes durant les 100 dernieres annees et predits pendant le premier tiers de la revolution ont ete utilises pour estimer les distances appropriees de migration assistee et pour developper des methodes qui incorporent la selection assistee au systeme de transfert des semences base sur les points focaux., Introduction Climate change is expected to result in forests becoming increasingly maladapted in many regions as the climates they experience depart from the climates in which they evolved (Schmidtling 1994; [...]

Seed orchards' parental reproductive success is often assessed through surveys of seed-and pollen-cone production (reproductive investment). Although the reliability of this approach has been questioned, its speed and ease made it the method of choice for providing approximate estimates for the genetic quality and quantity of seed orchard crops. In this study, reproductive investment data from various female and male phenotypic assessment methods from three seed orchards (lodgepole pine (Pinus contorta Dougl. ex. Loud. var. latifolia Engelm.), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), and western larch (Larix occidentalis Nutt.)) were compared with reproductive success estimates based on DNA fingerprinting and parentage analyses. The use of reproductive investment as a proxy to reproductive success on estimating seed crop's volume genetic worth and diversity (measured by effective number of parents) was evaluated. Regression analyses indicated that the phenotypic assessment methods reflect the true parental reproductive success and that estimates of seed-and pollen-cone volume production appear to be the most appropriate indicators of female and male reproductive success, respectively. Although the best combination of female-male survey methods produced inflated effective number of parents estimates, the genetic worth estimates were similar to those based on DNA, highlighting their robustness to fertility variation assessment. Resume: Le succes de reproduction des semenciers d'un verger a graines est souvent determine par des inventaires de production des cones seminiferes et polliniferes (investissement dans la reproduction). Quoique la fiabilite de cette approche ait ete remise en question, sa simplicite et sa rapidite en ont fait la methode de choix pour obtenir des estimations approximatives de la qualite genetique et du volume de la production semenciere des vergers a graines. Dans la presente etude, les auteurs ont compare les donnees relatives a l'investissement dans la reproduction obtenues par differentes me-thodes d'evaluation phenotypique de l'effort femelle et de l'effort male aux estimations de succes basees sur l'analyse des empreintes d'ADN et l'analyse de parente dans trois vergers a graines (pin tordu latifolie (Pinus contorta Dougl. ex. Loud. var. latifolia Engelm.), Douglas vert (Pseudotsuga menziesii (Mirb.) Franco) et meleze de l'Ouest (Larix occidentalis Nutt.)). L'emploi de l'investissement dans la reproduction comme indication du succes de reproduction afin d'estimer la valeur genetique du volume de la production semenciere et sa diversite (evaluee par le nombre effectif de parents) a aussi ete evalue. Les analyses de regression ont indique que les methodes d'evaluation phenotypique refletent le succes parental reel de reproduction et que les estimations du volume de production de cones seminiferes et polliniferes semblent etre les indicateurs les plus appropries du succes reproducteur femelle et male. Meme si la meilleure combinaison des methodes de determination de l'effort femelle et de l'effort male produisaient des estimations gonflees du nombre effectif de parents, les estimations de la valeur genetique etaient similaires a celles qui etaient basees sur l'ADN, mettant en evidence leur robustesse relativement a l'evaluation de la variation de la fertilite. [Traduit par la Redaction], Introduction Forest tree recurrent selection programs attain their goals through two distinctive streams, namely breeding and production. Breeding with its classical three steps, crosses, testing, and selection, leads to the [...]

Timing of pollen arrival may affect the level of seeds fertilized by pollen from outside seed orchards, especially in seed orchards of Scots pine (Pinus sylvestris L.) established in southern Finland with stock from northern populations. We performed sequential pollination experiments with Scots pine pollen collected from seed orchard clones originating from southern and northern Finland and recipient strobili in clones originating from southern Finland. When southern pollen was introduced first, seeds were sired equally by northern and southern genotypes. When northern pollen was introduced first, northern genotypes were found in 75% of the resulting seeds. When both pollen types were introduced at the same time, the resulting seed crop was split almost equally between northern and southern genotypes. These results do not unconditionally support the idea that the first pollen grain in the pollen chamber always fertilizes the ovum; instead, they suggest a more complex way of competition between pollen grains. Le moment ou le pollen arrive peut affecter la quantite de graines fertilisees par le pollen provenant de l'exterieur des vergers a graines, particulierement dans les vergers a graines de pin sylvestre (Pinus sylvestris L.) etablis dans le sud de la Finlande avec du materiel provenant de populations nordiques. Nous avons realise des experiences de pollinisation sequentielle avec du pollen de pin sylvestre collecte dans des vergers a graines de clones originaires du sud et du nord de la Finlande et des strobiles recepteurs chez des clones originaires du sud de la Finlande. Lorsque le pollen provenant du nord etait introduit en premier, 75 % des graines produites correspondaient aux genotypes du nord. Lorsque les deux types de pollen etaient introduits en meme temps, les graines etaient reparties presque egalement entre les genotypes du nord et du sud. Ces resultats ne supportent pas inconditionnellement l'idee que le premier grain de pollen dans la chambre pollinique fertilise toujours l'ovule. Au contraire, ils laissent entrevoir un mecanisme plus complexe de competition entre les grains de pollen. [Traduit par la Redaction], Introduction While pollen competition that leads to nonrandom mating is well studied in angiosperms (Skogsmyr and Lankinen 2002; Bernasconi 2003), few experiments have focused on coniferous species such as Scots [...]

Abstract: Clonal and cutting stem morphology variations in rooting ability were simultaneously examined in Allanblackia floribunda Oliv. using leafy stem cuttings in two experiments. The hypothesis tested is that clonal [...]

Abstract: A total of 2561 slash pine (Pinus elliottii Engelm. var. elliottii) grafts were topgrafted in the winter of 2003 and evaluated in January of 2004. The objectives of this [...]

Abstract: Mating system pattern (selfing or outcrossing and correlated matings levels) comparisons between two interior spruce seed orchard designs (clonal-row and random) managed under intensive crown and pollen management were [...]

Abstract: Field trials established with clones and seedlings from the same families provide an opportunity for comparing full-sib family performance across propagule types. More than 1200 different clones together with [...]

Abstract: We studied flower stimulation in two young miniaturized seed orchards of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) in Oregon. In experiment 1, female and male flowering were substantially [...]

We studied the pollination biology of 18 common insect-pollinated plant species on Kent Island, a boreal island in the Bay of Fundy, New Brunswick, Canada. Under natural conditions, fruit set was relatively high in most of the species studied [although it was very low ( Overall, our results demonstrate that for many insect-pollinated plant species on Kent Island, pollinators are likely to be limiting, autogamy is common and inbreeding depression is negligible. Although pollinator limitation and autogamy regularly occur in mainland habitats as well, a review of the literature suggests that they may be more common on islands such as Kent Island. If such island-mainland differences are general, they may arise because genotypes and species capable of self-fertilization are more likely than obligate outcrossers to colonize and become established in isolated habitats.

The nonindigenous invasive, Lonicera japonica, is a woody vine with a well-documented capacity for vegetative spread. In contrast, few data exist on its potential for establishment by seed. Lonicera japonica is biotically pollinated and xenogamous, requiring pollen from a genetically distinct individual for fruit set. We conducted hand-pollinations to determine if the fruit set of L. japonica in Arkansas was pollinator limited. Naturally pollinated control shoots produced fruit from 17.4% of their flowers, but the hand-pollinated flowers had a fruit set of 78.7%. Shoots with pollinators excluded set fruit on only 2.1% of the flowers. To determine geographic patterns in fruit set we surveyed seven different sites along the western edge of the naturalized range of L. japonica. Average fruit set on primary shoots was 13 [+ or -] 4.1% (mean [+ or -] SE), whereas the secondary shoots averaged 23 [+ or -] 6.7%. These results support our conclusion that sexual reproduction in populations of L. japonica along the western edge of its naturalized range is limited by a lack of pollination.

I studied several factors that affected rates of seedling establishment for northern blazing star (Liatris scariosa var. novae-angliae) at Kennebunk, Maine. Fire stimulated blazing star fecundity in four ways: (1) There was a four-fold increase in the number of flowering plants in recently burned units (10.6%) compared to plants in units that had not been burned for 4 y (2.4%). (2) The number of seeds per flower head was greater in recently burned units. (3) Among flower heads that had been infested with predacious moth larvae, the percentage of depredated seeds (40-50%) was lower in recently burned units than in units that had not been burned for two or more years (78-93%). (4) Under natural conditions, seedling establishment was much greater in management units that had been burned 20 mo previously than in management units that had been burned either within the past 8 mo, or units that had not been burned for more than 4 y. These results suggest that northern blazing star benefits from fire and that these four factors are temporally linked. Fire reduced levels of seed predation and increased seed production, providing a large supply of viable seeds. Fire also reduced litter, thus providing a suitable substrate for seedling establishment and development.

A numerical analysis of a model in which selfing rate is controlled by a single locus having two alleles, designated A and a, was conducted. The selfing rates of genotypes AA, Aa and aa were designated s1,s2 and s3. One limitation of the model is that it did not allow for the joint evolution of inbreeding depression as selfing rate evolved. Results demonstrate that relaxing the assumption of equal inbreeding-depression effects greatly changes the dynamics of mating system evolution by permitting evolutionary stability of mixed-mating systems.

The incidence of infection and reproductive success of Phoradendron californicum (desert mistletoe) on its host, Acacia gregii (catclaw), was quantitatively investigated in two localities of the Las Vegas Valley, Nevada, from March through November 1997. Similar patterns were detected between the two study sites. The abundance of Phoradendron was significantly positively correlated with age of Acacia trees, and more positively correlated with size. Phoradendron-infested trees were significantly older and larger, and had significantly lower diurnal and seasonal water potentials than adjacent uninfested trees. Phoradendron-infested trees were significantly more water-stressed than uninfested trees of similar age and size. Infested Acacia trees occurring on an extensive terrace surface were significantly more water-stressed than Acacia occurring along an intermittent wash during the dry summer season. Phoradendron canopy cover and fruit production were significantly larger on Acacia trees occurring along the wash than on the terrace. High levels of Phoradendron infestation greatly increased host-plant water stress, and low host-plant water potentials significantly reduced the canopy cover and fruit production of Phoradendron. However, characteristics of Phoradendron fruits were not significantly different between the two geomorphic surfaces. A combination of age, size and water status of Acacia trees largely influences the infection and reproductive success of Phoradendron in the Las Vegas Valley of southern Nevada., INTRODUCTION Parasitism occurs when one organism (parasite) benefits at the expense of the host organism. All Phoradendron spp. show some degree of parasitism or dependence on a host plant (Fisher, [...]

Horsenettle (Solanum carolinense. Solanaceae) plants possess the ability to bear both hermaphroditic and male flowers on the same plant, a breeding system referred to as andromonoecy. As part of an ongoing investigation into the evolution and maintenance of andromonoecy in horsenettle we conducted a field investigation that addressed the following questions: 1. Are fruit and seed production in horsenettle populations pollen limited? 2. Do pollen additions affect sex expression? 3. Is the size of the floral display or the percentage of flowers that are male associated with percentage fruit set, and therefore possibly related to the attraction of pollinators? We conducted pollen additions on 25 planks in each of two populations, and monitored 25 open pollinated control plants at each site. Mean percentage fruit set and seed set per fruit was significantly greater in the pollen addition treatment than in the control, which indicates that both populations were pollen limited. The percentage of flowers on a plant that were male was significantly greater in the pollen addition treatment than in the control, which suggests that pollen addition affects sex expression in horsenettle. Percentage fruit set did not correlate with total flower number or percentage of male flowers, which indicates that a larger floral display does not affect pollinator behavior in ways that influence female reproductive success. The results document the existence of pollen limitation in the two horsenettle populations studied and suggest that future studies should determine if male flower production influences male fitness or vegetative reproduction., INTRODUCTION The ability of individual plants to bear both male and hermaphroditic flowers characterizes the andromonoecious breeding system. Andromonoecy can be maintained in a population if plants that possess the [...]

This study documents variation in the number of florets per flower head and the number of flower heads per flowering shoot for individuals of Solidago macrophylla, a perennial composite, on an elevational gradient in the White Mountains of New Hampshire, and asks if variation in floret distribution vs. plant insect attack predicts variation in reproductive success. Fifteen populations were censused over 2-3 yr to document the number of florets per head, the number of heads per shoot, aphid infestation and seedling emergence per flowering shoot. Additionally, levels of seed predation by tephritid flies were measured during the final year. Flowering shoots in populations at higher elevations produced significantly more florets per head and fewer flowering heads than flowering shoots in populations at lower elevations. Overall, populations at lower elevations produced more florets than populations at higher elevations. However, this difference in reproductive potential did not result in differential reproduction in either 1993 or 1994. Populations at higher elevations had fewer plants with aphids than populations at lower elevations. In 1993 neither aphid infestation levels nor floral life history traits predicted the mean number of emerging seedlings per shoot in the greenhouse. In 1994 the percent of flowering shoots per population with aphids was a significant negative predictor of the mean number of emerging seedlings per shoot in the greenhouse, whereas the number of seed predators per head per shoot was a significant positive predictor of the number of emerging seedlings. Floral life history traits did not predict reproduction in 1994. Finally, patterns of seedling emergence over the environmental gradient resulted in a greater opportunity for selection in lower vs. higher elevation populations., INTRODUCTION Life history traits have been shown to determine demographic processes in both theoretical (Cole, 1954; Lande, 1982; Caswell, 1989) and empirical studies (Bierzychudek, 1982; Kalisz and McPeek, 1992). While [...]

Simulated grazing can have a positive effect on the lifetime seed production of the strict biennial herb Gentianella campestris. It is shown that overcompensation occurs in populations exposed to a high risk of damage but not in those wherein the risk of damage is predictably low. Overcompensation pertains to higher vegetative productivity and seed yield as a consequence of natural or simulated grazing. These and previous results show that the capacity for overcompensation is an adaptive trait with an evolutionary history associated with habitats with a high and predictable risk of damage.

Conflicting predictions have been made concerning the outcome of natural selection in obligately asexual populations. The general-purpose genotype hypothesis predicts that environmental fluctuations over time should eliminate asexual lineages that possess narrow ecological tolerances, and that therefore asexual populations should evolve to become more broadly tolerant of environmental variation than their sexually reproducing relatives. I tested this prediction by comparing the responses of a sexual and an asexual species of Erigeron (Asteraceae), E. philadelphicus and E. annuus, to four environmental treatments in a greenhouse experiment. Environmental treatments were created by varying the levels of competition from grass and the levels of shading that different individuals experienced. Overall, the treatment variables had roughly similar effects on both species. For both species, the presence of grass caused over 25% delays in the timing of bolting, and over 50% declines in biomass and the numbers of inflorescences produced. The effects of the shade treatment were entirely nonsignificant for both species. However, contrary to the prediction of the general-purpose genotype hypothesis, there were no significant differences in the magnitudes of these responses between the two species, which implies that asexual Erigeron individuals are no more general-purpose than sexuals. This lack of support for the general-purpose genotype hypothesis may indicate that biotic interactions such as competition, which are likely to promote the ecological specialization of lineages over generalist strategies, are more relevant in determining the evolution of niche width in these species., INTRODUCTION There is no doubt that sexual reproduction has come to dominate the life histories of plants, animals and fungi. Much of the morphological, structural and behavioral variation between groups [...]

A study of the reproductive biology of outliers and of rare plants reveals that they produce lesser seeds per flower than plants within local populations but are capable of interbreeding over long distances. Outliers from large gatherings of interbreeding plants are the major sources of extrinsic pollen and seeds, disturbing the spacing of local populations forming the nuclei for new populations. Outliers serve as interpopulation links for pathogens and herbivores.