Earlier Phenology Research Articles

Early phenology and growth trait variation in closely related European pine species.

Closely related taxa occupying different environments are valuable systems for studying evolution. In this study, we examined differences in early phenology (bud set, bud burst) and early growth in a common garden trial of closely related pine species: Pinus sylvestris, P. mugo, and P. uncinata. Seeds for the trial were sourced from populations across the ranges of each species in Europe. Over first 4 years of development, clear differences were observed between species, while the most significant intraspecific differentiation was observed among plants from P. sylvestris populations from continental European locations. Trait differences within P. sylvestris were highly correlated with altitude and latitude of the site of origin. Meanwhile, P. mugo populations from the Carpathians had the earliest bud set and bud flush compared to other populations of the species. Overall, populations from the P. mugo complex from heterogeneous mountain environments and P. sylvestris from the Scottish Highlands showed the highest within‐population variation for the focal traits. Although the three species have been shown to be genetically highly similar, this study reveals large differences in key adaptive traits both among and within species.

Introgression from Populus balsamifera underlies adaptively significant variation and range boundaries in P.trichocarpa.

Introgression can be an important source of adaptive phenotypes, although conversely it can have deleterious effects. Evidence for adaptive introgression is accumulating but information on the genetic architecture of introgressed traits lags behind. Here we determine trait architecture in Populus trichocarpa under introgression from P.balsamifera using admixture mapping and phenotypic analyses. Our results reveal that admixture is a key driver of clinal adaptation and suggest that the northern range extension of P.trichocarpa depends, at least in part, on introgression from P.balsamifera. However, admixture with P.balsamifera can lead to potentially maladaptive early phenology, and a reduction in growth and disease resistance in P.trichocarpa. Strikingly, an introgressed chromosome 9 haplotype block from P.balsamifera restores the late phenology and high growth parental phenotype in admixed P.trichocarpa. This epistatic restorer block may be strongly advantageous in maximizing carbon assimilation and disease resistance in the southernmost populations where admixture has been detected. We also confirm a previously demonstrated case of adaptive introgression in chromosome 15 and show that introgression generates a transgressive chlorophyll-content phenotype. We provide strong support that introgression provides a reservoir of genetic variation associated with adaptive characters that allows improved survival in new environments.

Phenology, roots and reproductive allocation, but not the LHS scheme, shape ecotypes along an aridity gradient

This study tested systematically at two spatial scales for key traits shaping within-species ecotypic differentiation under increasing aridity. It assessed different plant strategy theories and considered potential implications for climate change.We studied the widespread Mediterranean grass Brachypodium hybridum. At large scale, we tested 14 populations along a steep natural aridity gradient (114–954mm annual rainfall). At small scale, we tested the micro-climatic contrast between plants originating from corresponding north (more mesic) and south (more arid) exposed hillslopes. Fifteen traits were measured in the greenhouse, including the popular traits of the Leaf-Height-Seed scheme (SLA, plant height, seed mass), several traits on phenology, architecture, growth, fitness, and rarely measured root traits.Clear trait shifts indicated ecotypic differentiation along the large-scale gradient. Earlier phenology, higher reproductive allocation and reduced root investment characterized arid ecotypes. Surprisingly, no trait of the Leaf-Height-Seed scheme shifted with aridity and root responses were opposite to the theory of optimal resource partitioning. Trait differences between north and south exposures were small, often inconsistent between sites, and poorly matched the trends across the large-scale gradient. South exposures thus appeared unlikely to harbour distinct ecotypes better adapted to aridity.Our findings highlight ecotypes as a crucial way how species span environmental gradients, yet underpinning their restriction at small spatial scales. In combination, this possibly renders populations more vulnerable to climate change. We draw attention to specific, partly unexpected traits and pose the question whether the Leaf-Height-Seed scheme has limited applicability for intraspecific investigations in drylands.

Exploring Niches for Short-Season Grain Legumes in Semi-Arid Eastern Kenya - Coping with the Impacts of Climate Variability.

Climate variability is the major risk to agricultural production in semi-arid agroecosystems and the key challenge to sustain farm livelihoods for the 500 million people who inhabit these areas worldwide. Short-season grain legumes have great potential to address this challenge and help to design more resilient and productive farming systems. However, grain legumes display a great diversity and differ widely in growth, development, and resource use efficiency. Three contrasting short season grain legumes common bean (Phaseolus vulgaris L.), cowpea (Vigna unguiculata (L.) Walp.] and lablab [Lablab purpureus (L.) Sweet] were selected to assess their agricultural potential with respect to climate variability and change along the Machakos-Makueni transect in semi-arid Eastern Kenya. This was undertaken using measured data [a water response trial conducted during 2012/13 and 2013/14 in Machakos, Kenya] and simulated data using the Agricultural Production System sIMulator (APSIM). The APSIM crop model was calibrated and validated to simulate growth and development of short-season grain legumes in semi-arid environments. Water use efficiency (WUE) was used as indicator to quantify the production potential. The major traits of adaptation include early flowering and pod and seed set before the onset of terminal drought. Early phenology together with adapted canopy architecture allowed more optimal water use and greater partitioning of dry matter into seed (higher harvest index). While common bean followed a comparatively conservative strategy of minimizing water loss through crop transpiration, the very short development time and compact growth habit limited grain yield to rarely exceed 1,000 kg ha−1. An advantage of this strategy was relatively stable yields independent of in-crop rainfall or season length across the Machakos-Makueni transect. The growth habit of cowpea in contrast minimized water loss through soil evaporation with rapid ground cover and dry matter production, reaching very high grain yields at high potential sites (3,000 kg ha−1) but being highly susceptible to in-season drought. Lablab seemed to be best adapted to dry environments. Its canopy architecture appeared to be best in compromising between the investment in biomass as a prerequisite to accumulate grain yield by minimizing water loss through soil evaporation and crop transpiration. This lead to grain yields of up to 2,000 kg ha−1 at high potential sites and >1,000 kg ha−1 at low potential sites. The variance of observed and simulated WUE was high and no clear dependency on total rainfall alone was observed for all three short-season grain legumes, highlighting that pattern of water use is also important in determining final WUEbiomass and WUEgrain. Mean WUEgrain was lowest for cowpea (1.5–3.5 kggrain ha−1 mm−1) and highest for lablab (5–7 kggrain ha−1 mm−1) reflecting the high susceptibility to drought of cowpea and the good adaptation to dry environments of lablab. Results highlight that, based on specific morphological, phonological, and physiological characteristics, the three short-season grain legumes follow different strategies to cope with climate variability. The climate-smart site-specific utilization of the three legumes offers promising options to design more resilient and productive farming systems in semi-arid Eastern Kenya.

Competitor phenology as a social cue in breeding site selection.

Predicting habitat quality is a major challenge for animals selecting a breeding patch, because it affects reproductive success. Breeding site selection may be based on previous experience, or on social information from the density and success of competitors with an earlier phenology. Variation in animal breeding phenology is often correlated with variation in habitat quality. Generally, animals breed earlier in high-quality habitats that allow them to reach a nutritional threshold required for breeding earlier or avoid nest predation. In addition, habitat quality may affect phenological overlap between species and thereby interspecific competition. Therefore, we hypothesized that competitor breeding phenology can be used as social cue by settling migrants to locate high-quality breeding sites. To test this hypothesis, we experimentally advanced and delayed hatching phenology of two resident tit species on the level of study plots and studied male and female settlement patterns of migratory pied flycatchers Ficedula hypoleuca. The manipulations were assigned at random in two consecutive years, and treatments were swapped between years in sites that were used in both years. In both years, males settled in equal numbers across treatments, but later arriving females avoided pairing with males in delayed phenology plots. Moreover, male pairing probability declined strongly with arrival date on the breeding grounds. Our results demonstrate that competitor phenology may be used to assess habitat quality by settling migrants, but we cannot pinpoint the exact mechanism (e.g. resource quality, predation pressure or competition) that has given rise to this pattern. In addition, we show that opposing selection pressures for arrival timing may give rise to different social information availabilities between sexes. We discuss our findings in the context of climate warming, social information use and the evolution of protandry in migratory animals.

Pollen gene flow, male reproductive success, and genetic correlations among offspring in a northern red oak (Quercus rubra L.) seed orchard.

Northern red oak is a high-value hardwood used for lumber, furniture and veneer. Intensively managed northern red oak seed orchards are required to obtain genetic gain for trait improvement. Data from conifer seed orchards and natural and managed stands of hardwood trees have shed light on the distance over which pollen can move, and underscore the need for managerial attention to seed orchard design, placement, and maintenance. We used eleven microsatellite markers to investigate pollen gene flow, female mate choice, and male reproductive success in a clonal seed orchard of northern red oak based on paternity analysis of seed orchard offspring in progeny tests. Nearly all (93%) offspring were sired by a male parent within the seed orchard. The mean number of male parents per year was 69.5, or 47.6% of all clones in the seed orchard. Female clones in the early phenology group had more offspring sired from extra-orchard pollen (13%) than clones in the intermediate (5%) and late (1%) phenology groups. Distance was the largest influence on pollination success, and pollination occurred most often by male trees in the same subline as the maternal tree. Males in the early phenology group sired more offspring overall in the progeny pool and more offspring per mother tree than males in the intermediate or late phenology groups. Average genetic correlations among all OP progeny ranged between 0.2557 and 0.3529 with a mean of 0.28±0.01. The importance of progeny test genotyping for northern red oak improvement likely is increasing with the demand for improved varieties. The current study demonstrated the feasibility of post hoc assembly of full-sib families for genetic analysis.

Tolerance and phenological avoidance of herbivory in tarweed species.

Avoidance and tolerance of herbivory are important components of plant interactions with herbivores. Their relationship to each other and to plant defense is important in understanding how plants maximize fitness in the face of herbivore pressure. Various tarweed species have populations comprised of both early-season and late-season flowering individuals. Late-season flowering individuals employ a recently described indirect defense against herbivores in which the accumulation of dead insects on their sticky surfaces attracts predatory insects that eat herbivores. In two tarweed species (Hemizonia congesta and Madia elegans), we observed that key herbivores rarely interact with early-season individuals in the field, and early-season individuals did not invest in dense glandular trichomes that cause indirect defense. We conducted field and greenhouse bud-removal experiments to assess tolerance of M elegans to herbivore damage. We found that late-season individuals were more tolerant of simulated herbivory than early-season individuals in both the field and the greenhouse. Late-season individuals that were forced into an earlier phenology with a 24-h light cue lost their tolerance to simulated herbivory. One possible mechanism linking phenological avoidance of herbivores with decreased tolerance is that early-season individuals invested less in below-ground biomass than late-season individuals, which may accumulate belowground resources for regrowth at the expense of early flowering.

Phenology, Thermal Integral and Agronomic Yield of Cotton (Gossypium arboreum L) at a Function of Date of Planting in Dry Weather

The aim of this study was to know the effect of planting date (early and late) on the phenology and thermal integral of an accession of Gossypium arboreum L. to evaluate fiber and seed yields and harvest index. Design randomized complete block with four replications (4x3) = 12 experimental units was used. The experiment was carried out at the Universidad de la Canada in Teotitlan de Flores Magon, Oaxaca, Mexico, from May to October 2012. The experiment was conducted in the field, fertilizing the soil and with a topological arrangement (0.30 x 0.30 x 1.0). Both seed and fiber Original Research Article Loeza-Corte et al.; AJEA, 10(2): 1-7, 2016; Article no.AJEA.21054 2 yields were determined gravimetrically, and harvest index by the ratio between the agronomic yield and the biological yield. The results indicate that the highest seed yield, fiber and seed harvest index, was achieved in early planting dates and crop phenology was not altered by treatment effect. From this study it could be concluded that the cotton might be an option to plant under the conditions of the tropical dry forest of Oaxaca.

Frost sensitivity of leaves and flowers of subalpine plants is related to tissue type and phenology

Summary Harsh abiotic conditions – such as low temperatures that lead to spring and summer frost events in high‐elevation and high‐latitude ecosystems – can have strong negative consequences for plant growth, survival and reproduction. Despite the predicted increase in episodic frost events under continued climate change in some ecosystems, our general understanding of the factors associated with frost sensitivity of reproductive and vegetative plant structures in natural plant communities is limited. The timing of growth and reproduction may be an important strategy by which plants can avoid frost. In this study, we experimentally investigated the frost sensitivity of eight long‐lived perennial herbaceous plant species from a subalpine ecosystem in the Colorado Rocky Mountains, USA. The study taxa represent four congeneric pairs from four flowering plant families; within each pair, there is a species with early and late growth and reproductive phenology. Thus, we control for evolutionary history – and therefore additional traits shared through common ancestry – to some degree, while examining the influence of phenology on frost sensitivity. Specifically, we compared frost sensitivity of vegetative and reproductive structures for each species and asked whether frost sensitivity was similar between species within congeneric pairs or, instead, was related to phenology (i.e. differences in the timing of growth and reproduction). For most species (6 of 8), flowers were more sensitive to frost than leaves. Within most congeneric pairs (3 of 4), the leaves of species with later phenology were significantly more sensitive to frost than the leaves of species with earlier phenology. For flowers, the later flowering species were more sensitive in two of the four congeneric pairs. Synthesis. This study contributes to our general understanding of factors related to interspecific differences in plant sensitivity to episodic frost events of naturally occurring species. The increased frost sensitivity of reproductive structures compared to vegetative structures may be a widespread pattern for long‐lived perennial plants. Furthermore, we find evidence for a trade‐off between phenology and frost sensitivity, whereby species with later phenology exhibit higher frost sensitivity compared to species with earlier phenology. These results have implications for plant populations, species interactions and ecological communities.

Contemporary evolution of plant reproductive strategies under global change is revealed by stored seeds.

Global change is expected to impose new selection pressures on natural populations. Phenotypic responses, such as earlier phenology in response to climate warming, have been repeatedly observed in the field. The recent pollinator decline is also expected to change selection on reproductive traits in flowering plants. However, it remains unclear whether short-term adaptation of plant reproductive strategies occurs in response to global change. In this study, we report the evolution of some important reproductive traits of the annual self-incompatible weed Centaurea cyanus. In a common garden experiment, we germinated stored seeds, sampled 18years apart from the same location, in a region where warmer springs and indices of pollinator decline have been reported. Compared to the ancestral population (1992), our results showed that plants of the descendant population (2010) flowered earlier and also produced larger capitula with longer receptivity and a larger floral display. QST -FST comparisons indicated that natural selection has likely contributed to the evolution of some of the traits investigated. Lower FST within temporal samples than among spatial samples further suggests a limited role of gene flow from neighbouring populations. We therefore propose that trait shifts could partly be due to adaptation to global change.

Relating adaptive genetic traits to climate for Sandberg bluegrass from the intermountain western United States.

Genetic variation for potentially adaptive traits of the key restoration species Sandberg bluegrass (Poa secunda J. Presl) was assessed over the intermountain western United States in relation to source population climate. Common gardens were established at two intermountain west sites with progeny from two maternal parents from each of 130 wild populations. Data were collected over 2 years at each site on fifteen plant traits associated with production, phenology, and morphology. Analyses of variance revealed strong population differences for all plant traits (P < 0.0001), indicating genetic variation. Both the canonical correlation and linear correlation established associations between source populations and climate variability. Populations from warmer, more arid climates had generally lower dry weight, earlier phenology, and smaller, narrower leaves than those from cooler, moister climates. The first three canonical variates were regressed with climate variables resulting in significant models (P < 0.0001) used to map 12 seed zones. Of the 700 981 km2 mapped, four seed zones represented 92% of the area in typically semi-arid and arid regions. The association of genetic variation with source climates in the intermountain west suggested climate driven natural selection and evolution. We recommend seed transfer zones and population movement guidelines to enhance adaptation and diversity for large-scale restoration projects.

What Seeds to Plant in the Great Basin? Comparing Traits Prioritized in Native Plant Cultivars and Releases with those that Promote Survival in the Field

Restoration in the Great Basin is typically a large-scale enterprise, with aerial, drill, and broadcast seeding of perennial species common after wildfires. Arid conditions and invasive plants are significant barriers to overcome, but relatively simple changes to seeds used for restoration may improve success. Here we summarize: 1) the composition of seed mixes used in recent postfire seedings in Nevada, 2) traits that were valued when cultivars and other native seed materials were named and released, and 3) traits that have been demonstrated to increase native perennial grass performance in invaded systems. A review of 420 seeding treatments on public shrublands in Nevada between 2006 and 2009 indicated that native perennial grasses and native shrubs were most frequently included in these projects, followed by exotic and native forbs, and lastly, exotic perennial grasses. Native perennial grasses made up the bulk of seeds used in these treatments, with multiple species of grasses (average of 3.4 species) typically seeded per treatment, while the richness of other functional groups in seed mixes was closer to 1 species per treatment. Traits prioritized in cultivars and native seed material releases included, in order of frequency: forage quality and yield, seed yield, seedling vigor, ability to establish and persist, and drought tolerance, with many other traits mentioned with less frequency. Traits that had consistent support for improving native perennial grass performance in the field were related to early phenology, small size, and higher root allocation. Further tests to determine which traits improve shrub and forb establishment under field conditions could further refine seed source selection, and help maintain diversity in Great Basin systems.

Unexpected phenological responses of butterflies to the interaction of urbanization and geographic temperature

Urbanization and global climate change can profoundly alter biological systems, yet scientists often analyze their effects separately. We test how the timing of life cycle events (phenology) is jointly influenced by these two components of global change. To do so, we use a long‐term phenological data set of 20 common butterfly species from 83 sites across the state of Ohio, USA, with sites that range from rural undeveloped areas to moderately sized cities. These sites span a latitudinal gradient in mean temperature of several °C, mimicking the range of projected global climate warming effects through the end of the century. Although shifts toward earlier phenology are typical of species' responses to either global climate change or urbanization, we found that their interaction delayed several Ohio butterfly species' first appearance and peak abundance phenology. Exploitative species exhibited smaller delays in first appearance and peak abundance phenology in areas that were urbanized and geographically warm. Our results show that phenological responses to urbanization are contingent upon geographic variation in temperature, and that the impacts of urbanization and global climate change should be considered simultaneously when developing forecasts of biological responses to environmental change.

The Influence of Altered Rainfall Regimes on Early Season N Partitioning Among Early Phenology Annual Plants, a Late Phenology Shrub, and Microbes in a Semi-arid Ecosystem

In Mediterranean-type ecosystems, nitrogen (N) accumulates in soil during dry summer months and rapidly becomes available during early season rain events. The availability of early season N could depend on the size of rainfall events, soil microbial activity, and phenology of the plant community. However, it is poorly understood how precipitation patterns affect the fate of early season N. Microbes and plants with early phenology may compete strongly for early season N but theory suggests that microbial N storage can meet plant N demands later in the season. Using a 15N tracer and rainfall manipulation we investigated the fate of early season N. N allocation patterns differed substantially between microbes, early and late phenology plants. As expected early phenology annuals and microbes took up 15N, within 1 day, whereas a late-phenology shrub allocated 15N to leaves later in the season. We saw no evidence for microbial storage of early season N; the peak of 15N in shrub leaves did not coincide with detectable levels of 15N in the microbial biomass or labile soil pool. This suggests that shrubs were able to access early season N, store and allocate it for growth later in the season. Although we saw no evidence of microbial N storage, N retention in soil organic matter (SOM) was high and microbes may play an important role in sequestering N to SOM. Plant N uptake did not respond significantly to 1 year of rainfall manipulation, but microbes were sensitive to dry conditions. 1 year after 15N addition shrubs had resorbed up to half of the N from leaves whereas N in annuals remained as dead leaf litter. Differences in end-of-season N partitioning between dead and living biomass in the two vegetation types suggest that plant species composition could affect N availability in the following growing season, but it may take several years of altered precipitation patterns to produce rainfall-dependent changes.

Performance of Alternative European Wine Grape Cultivars in Southwestern Idaho: Cold Hardiness, Berry Maturity, and Yield

The cold tolerance, phenology, yield, and fruit maturity of alternative red- and white-skinned wine grape cultivars (Vitis vinifera) of European origin were compared with those of ‘Merlot’ and ‘Cabernet Sauvignon’ over two growing seasons in southwestern Idaho. Variability among alternative cultivars was detected for cold hardiness, onset of phenological events, yield, and fruit composition. The red-skinned cultivars Montepulciano and Tinto Cão were the least cold hardy of the alternative cultivars. The red-skinned cultivars Aleatico, Aglianico, and Graciano had similar yield but matured later than the leading cultivars Merlot and Cabernet Sauvignon and were among the more cold-sensitive alternative cultivars. ‘Grüner Veltliner’, ‘Sauvignon Gris’, and ‘Trousseau’ cold acclimated early, had high midwinter bud cold hardiness, and had similar or higher yield and fruit maturity as the leading cultivars. The white-skinned cultivars Verdelho, Fernão Pires, Sauvignon Blanc Musqué, and Sauvignon Gris had similar or less vine injury, similar or earlier phenology, and similar yield and fruit maturity as the leading cultivars. The large berry size of the red-skinned cultivars Trousseau and Touriga Brasiliera warrants evaluation for wine quality. The cultivar variability identified in this study for cold hardiness, phenology, cluster architecture, and yield provides a useful guide for cultivar site selection.

Structural, compositional and trait differences between native‐ and non‐native‐dominated grassland patches

Summary Non‐native species with growth forms that are different from the native flora may alter the physical structure of the area they invade, thereby changing the resources available to resident species. This in turn can select for species with traits suited for the new growing environment. We used adjacent uninvaded and invaded grassland patches to evaluate whether the shift in dominance from a native perennial bunchgrass, Nassella pulchra, to the early season, non‐native annual grass, Bromus diandrus, affects the physical structure, available light, plant community composition and community‐weighted trait means. Our field surveys revealed that the exotic grass B. diandrus alters both the vertical and horizontal structure creating more dense continuous vegetative growth and dead plant biomass than patches dominated by N. pulchra. These differences in physical structure are responsible for a threefold reduction in available light and likely contribute to the lower diversity, especially of native forbs in B. diandrus‐dominated patches. Further, flowering time began earlier and seed size and plant height were higher in B. diandrus patches relative to N. pulchra patches. Our results suggest that species that are better suited (earlier phenology, larger seed size and taller) for low light availability are those that coexist with B. diandrus, and this is consistent with our hypothesis that change in physical structure with B. diandrus invasion is an important driver of community and trait composition. The traits of species able to coexist with invaders are rarely considered when assessing community change following invasion; however, this may be a powerful approach for predicting community change in environments with high anthropogenic pressures, such as disturbance and nutrient enrichment. It also provides a means for selecting species to introduce when trying to enhance native diversity in an otherwise invaded community.

Testing a growth efficiency hypothesis with continental-scale phenological variations of common and cloned plants

Variation in the timing of plant phenology caused by phenotypic plasticity is a sensitive measure of how organisms respond to weather and climate variability. Although continental-scale gradients in climate and consequential patterns in plant phenology are well recognized, the contribution of underlying genotypic difference to the geography of phenology is less well understood. We hypothesize that different temperate plant genotypes require varying amount of heat energy for resuming annual growth and reproduction as a result of adaptation and other ecological and evolutionary processes along climatic gradients. In particular, at least for some species, the growing degree days (GDD) needed to trigger the same spring phenology events (e.g., budburst and flower bloom) may be less for individuals originated from colder climates than those from warmer climates. This variable intrinsic heat energy requirement in plants can be characterized by the term growth efficiency and is quantitatively reflected in the timing of phenophases-earlier timing indicates higher efficiency (i.e., less heat energy needed to trigger phenophase transitions) and vice versa compared to a standard reference (i.e., either a uniform climate or a uniform genotype). In this study, we tested our hypothesis by comparing variations of budburst and bloom timing of two widely documented plants from the USA National Phenology Network (i.e., red maple-Acer rubrum and forsythia-Forsythia spp.) with cloned indicator plants (lilac-Syringa x chinensis 'Red Rothomagensis') at multiple eastern US sites. Our results indicate that across the accumulated temperature gradient, the two non-clonal plants showed significantly more gradual changes than the cloned plants, manifested by earlier phenology in colder climates and later phenology in warmer climates relative to the baseline clone phenological response. This finding provides initial evidence supporting the growth efficiency hypothesis, and suggests more work is warranted. More studies investigating genotype-determined phenological variations will be useful for better understanding and prediction of the continental-scale patterns of biospheric responses to climate change.

Leaf drop affects herbivory in oaks

Leaf phenology is important to herbivores, but the timing and extent of leaf drop has not played an important role in our understanding of herbivore interactions with deciduous plants. Using phylogenetic general least squares regression, we compared the phenology of leaves of 55 oak species in a common garden with the abundance of leaf miners on those trees. Mine abundance was highest on trees with an intermediate leaf retention index, i.e. trees that lost most, but not all, of their leaves for 2-3 months. The leaves of more evergreen species were more heavily sclerotized, and sclerotized leaves accumulated fewer mines in the summer. Leaves of more deciduous species also accumulated fewer mines in the summer, and this was consistent with the idea that trees reduce overwintering herbivores by shedding leaves. Trees with a later leaf set and slower leaf maturation accumulated fewer herbivores. We propose that both leaf drop and early leaf phenology strongly affect herbivore abundance and select for differences in plant defense. Leaf drop may allow trees to dispose of their herbivores so that the herbivores must recolonize in spring, but trees with the longest leaf retention also have the greatest direct defenses against herbivores.

Genetic variation in adaptive traits and seed transfer zones for Pseudoroegneria spicata (bluebunch wheatgrass) in the northwestern United States.

A genecological approach was used to explore genetic variation in adaptive traits in Pseudoroegneria spicata, a key restoration grass, in the intermountain western United States. Common garden experiments were established at three contrasting sites with seedlings from two maternal parents from each of 114 populations along with five commercial releases commonly used in restoration. Traits associated with size, flowering phenology, and leaf width varied considerably among populations and were moderately correlated with the climates of the seed sources. Pseudoroegneria spicata populations from warm, arid source environments were smaller with earlier phenology and had relatively narrow leaves than those from mild climates with cool summers, warm winters, low seasonal temperature differentials, high precipitation, and low aridity. Later phenology was generally associated with populations from colder climates. Releases were larger and more fecund than most of the native ecotypes, but were similar to native populations near their source of origin. Differences among native populations associated with source climates that are logical for survival, growth, and reproduction indicate that genetic variation across the landscape is adaptive and should be considered during restoration. Results were used to delineate seed transfer zones and population movement guidelines to ensure adapted plant materials for restoration activities.

Clinal variation for only some phenological traits across a species range

Phenology is the timing of life cycle events of an organism. Alterations in phenology can have profound effects on individual fitness, population growth, and community dynamics. Recent changes in climate have altered the phenology of many organisms, which may result in selection to shift phenological traits. Understanding the relationship between local climates and population differentiation in phenology will allow us to anticipate responses to novel selective environments caused by global climate change. We evaluated population differentiation in the number of days to germination, first flower, and fruit maturation for 33 populations throughout the range of Campanulastrum americanum (American Bellflower). Germination and fruit maturation had geographical clines with earlier timing in populations from northern latitudes. Northern sites were cooler and drier, suggesting potential adaptive differentiation of the shorter life cycle associated with earlier phenology. Similarly, higher elevations were cooler and had earlier fruit maturation. However, seed germination was later in higher elevation populations. Although there was substantial variation in the day to first flower, ranging 40 days between population means, it was idiosyncratic and not related to latitude, suggesting differentiation in response to selective factors distinct from those on germination and fruit maturation. Thus, germination and fruit maturation in C. americanum may shift in response to selection by rising temperatures. However, such changes are not expected for flowering time, a typical indicator of climate change.