Persistence and expansion of ponderosa pine woodlands in the west‐central Great Plains during the past two centuries

Aim Woody plant expansion and infilling in grasslands and savannas are occurring across a broad range of ecosystems around the globe and are commonly attributed to fire suppression, livestock grazing, nutrient enrichment and/or climate variability. In the western Great Plains, ponderosa pine (Pinus ponderosa) woodlands are expanding across broad geographical and environmental gradients. The objective of this study was to reconstruct the establishment of ponderosa pine in woodlands in the west‐central Great Plains and to identify whether it was mediated by climate variability. Location Our study took place in a 400‐km wide region from the base of the Front Range Mountains (c. 105° W) to the central Great Plains (c. 100° W) and from Nebraska (43° N) to northern New Mexico (36° N), USA. Methods Dates for establishment of ponderosa pine were reconstructed with tree rings in 11 woodland sites distributed across the longitudinal and latitudinal gradients of the study area. Temporal trends in decadal pine establishment were compared with summer Palmer Drought Severity Index (PDSI). Annual trends in pine establishment from 1985 to 2005 were compared with seasonal PDSI, temperature and moisture availability. Results Establishment of ponderosa pine occurred in the study area in all but one decade (1770s) between the 1750s and the early 2000s, with over 35% of establishment in the region occurring after 1980. Pine establishment was highly variable among sites. Across the region, decadal pine establishment was persistently low from 1940 to 1960, when PDSI was below average. Annual pine establishment from 1985 to 2005 was positively correlated with summer PDSI and inversely correlated with minimum spring temperatures. Main conclusions Most ponderosa pine woodlands pre‐date widespread Euro‐American settlement of the region around c. ad 1860 and currently have stable tree populations. High variability in the timing of establishment of pine among sites highlights the multiplicity of factors that can drive woodland dynamics, including land use, fire history, CO₂ enrichment, tree population dynamics and climate. Since the 1840s, the influence of climate was most notable across the study area during the mid‐20th century, when the establishment of pine was suppressed by two significant droughts. The past sensitivity of establishment of ponderosa pine to drought suggests that woodland expansion will be negatively affected by predicted increases in temperature and drought in the Great Plains.     

Climate change and voltinism of Mythimna sequax: the location and choice of phenological models matter

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Red turpentine beetle primary attraction to β-pinene or 3-carene (with and without ethanol) varies in western US pine forests

1. Lure attraction strength for red turpentine beetle, Dendroctonus valens (Coleoptera: Curculionidae: Scolytinae) observed previously in US Pacific Northwest ponderosa pine forests is (−)-β-pinene+ethanol > (+)-3-carene+ethanol, but untested elsewhere in its western US range. Thus, both were tested with (−)-β-pinene, (+)-3-carene, ethanol, and a blank in Oregon and California sites burned by wildfire, whereas in Arizona the first four lures were tested in a thinned-unburned site.
2. The D. valens responses in burned Oregon and California sites were similar, (−)-β-pinene+ethanol > (−)-β-pinene > 3-carene = 3-carene+ethanol > ethanol > blank, whereas in the cut-unburned Arizona site it was 3-carene+ethanol > 3-carene = (−)-β-pinene+ethanol > (−)-β-pinene. Whether this variation was influenced by beetle genetic differences, or chemical and physical parameters in the different environments and remaining stressed host resources 1-year post disturbance warrants additional study.
3. Responses to (−)-β-pinene varied, from a stronger attractant than (+)-3-carene in Oregon and California, to a weaker lure than (+)-3-carene in Arizona. This (−)-β-pinene variability was minimized when released in combination with ethanol, making (−)-β-pinene+ethanol the most consistent attractant of those tested across the three states, and a reliable lure for detection, monitoring, and management projects for D. valens in western US pine forests.

     

Changes in voltinism in a pine moth <Emphasis Type="Italic">Dendrolimus spectabilis</Emphasis> (Lepidoptera: Lasiocampidae) population: implications of climate change

Climate change induces an alteration in the life cycle of many poikilothermic organisms, resulting in changes in the structure and function of communities. Changes in voltinism in the pine moth Dendrolimus spectabilis (Butler), which is known to be univoltine in South Korea, were studied to elucidate the effects of climate change on their voltinism. The developmental stages of the pine moth were evaluated through field surveys, and the developmental rate was estimated at five different temperatures: 17, 20, 25, 28, and 32°C. Field surveys showed that the moths completed two generations per year, indicating that the phenology of the pine moth in this area had changed from univoltinism to bivoltinism. Laboratory experiments showed that increasing the temperature could induce a change in voltinism in the pine moth population. Generations of the bivoltine population displayed phenotypic plasticity: the fitness of the first generation was greater than that of the second generation with regard to size and fecundity. The difference in fitness between the first and second generations could be due to the influence of factors such as low food quality and heat stress on the second generation. Therefore, changes in thermal conditions due to climate change have offered this species the chance to develop a bivoltine population, but they have also exerted ecological costs, especially for the second generation of the pine moth.     

Effect of temperature on the reproductive success,developmental rate and brood characteristics of Ips sexdentatus (Boern.)

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The effect of temperature on the development and life cycle regulation of the pine weevil Hylobius abietis and the potential impacts of climate change

• 1 The pine weevil Hylobius abietis is widely distributed in the Palaearctic region where it is a major pest. Although predominantly semi‐voltine, with a 2‐year life cycle, the generation time across its range can vary from 1 to 4 years. The duration of the life cycle and the seasonal timing of weevil activity affect the economic impact and management of this pest, all of which are likely to change in a warming climate.
• 2 To determine the effect of temperature and tree species on weevil growth and development, laboratory experiments were performed with eggs, larvae, prepupae, pupae and adults, using, as appropriate, the host species Scots pine Pinus sylvestris L. and Sitka spruce Picea sitchensis (Bong.) Carr. under constant or alternating temperatures.
• 3 The development rate was linearly related to temperature, with developmental thresholds for eggs, larvae and pupae of 8, 4.5 and 7.3 °C, respectively. Day‐degrees were estimated for each life stage. Larval development was affected by tree species, being slower on Sitka spruce than on Scots pine, and was faster under alternating than constant temperatures.
• 4 The development time for prepupae was highly variable, with an apparent facultative prepupal diapause initiated by temperature. The temperature range 20–17.5 °C marked the transition between median prepupal development times of approximately 25 and 90 days. The prepupal stage may serve to minimize the risk of overwintering mortality in the pupal stage and help to synchronize the life cycle.
• 5 Larval and adult mass was positively related to developmental temperature, demonstrating an inverse temperature size rule, and weevils were heavier when developing on Scots pine than Sitka spruce. Development in alternating temperatures reduced weevil mass on Scots pine. The influence of temperature on weevil mass is likely to have a positive effect on fecundity and overwintering survival. The effects of climate change on development, voltinism and weevil mass are discussed.

     

Global warming affects phenology and voltinism of Lobesia botrana in Spain

• 1 Climate change is promoting alterations of a very diverse nature in the life cycle of an array of insect species, including changes in phenology and voltinism. In Spain, there is observational evidence that the moth Lobesia botrana Den. & Schiff. (Lep.: Tortricidae), a key vine pest that is usually trivoltine in Mediterranean latitudes, tends to advance spring emergence, displaying a partial fourth additional flight, a fact that is potentially attributable to global warming.
• 2 To verify this hypothesis, local temperatures were correlated with L. botrana phenology in six vine‐growing areas of southwestern Spain during the last two decades (1984–2006) by exploiting the database of flight curves obtained with sexual pheromone traps. The dates of second and third flight peaks of the moth were calculated for each area and year and then correlated with both time (years) and local temperatures.
• 3 The results obtained demonstrated a noteworthy trend towards local warming (as a result of global warming) in the last two decades, with mean increases in annual and spring temperatures of 0.9 and 3.0°C, respectively. Therefore, L. botrana phenology has significantly advanced by more than 12 days. Moreover, the phenological advance contributed to increased moth voltinism in 2006 by promoting a complete fourth additional flight, a fact that has never been reported previously to our knowledge in the Iberian Peninsula.
• 4 The potential impact of an earlier phenology and increased voltinism in L. botrana is discussed from an agro‐ecological perspective.

     

Effect of temperature on fecundity,development, and emergence of the invasive ambrosia beetle Euwallacea kuroshio (Coleoptera: Scolytinae)

1. The Kuroshio shot hole borer (KSHB) Euwallacea kuroshio is an invasive ambrosia beetle pest in Southern California, where it causes Fusarium dieback in a number of different host tree species.
2. Since its discovery in California in about 2014, the KSHB has established or been identified across a wide geographic range along the California coast, spanning north from the Mexican border to San Luis Obispo.
3. KSHB were reared at temperatures ranging from 16 to 32 °C to determine the effect of temperature on development and emergence rates, brood size, and colonization success.
4. The highest total emergence and number of successful colonies occurred when KSHB was reared at 28 °C. Mean days until first offspring emergence decreased as temperature increased up to 30 °C, after which emergence ceased.
5. The thermal constant was estimated to be 318 degree-days. Using this approximation in conjunction with weather data from the California Irrigation Management Information System, we predict the annual number of generations of KSHB in several locations across its invasive range in California. Results can be used to predict the timing and number of generations in other invaded areas, as well as estimate the range of this pest.

     

Use of historical temperature data for timing insecticide applications of the Nantucket pine tip moth (Lepidoptera: Tortricidae): evaluation of damage and volume increment efficacy

• 1 The effectiveness of optimal spray period intervals based on mean daily temperatures were evaluated as a spray‐timing tool to control high density populations of the Nantucket pine tip moth Rhyacionia frustrana (Comstock).
• 2 Initial tree growth realized from first generation R. frustrana control was compared to that from conventional applications of one insecticide treatment scheduled for each of three annual generations.
• 3 The optimal spray period intervals provided by Fettig et al. (2000a) were highly effective for controlling R. frustrana infestations. The control group averaged 47.0 ± 2.2% whole tree damage for all sites and generations as compared to 0.6 ± 0.2% for the treated group.
• 4 Volume gains attributable to R. frustrana control averaged 16.9%, 46.4% and 98.6% for first generation control, and 46.6%, 72.7% and 146.3% for conventional applications of one insecticide treatment scheduled for each of three annual R. frustrana generations at Northampton, Halifax I and Halifax II, respectively. Growth returns increased as mean damage estimates increased for both treatments, suggesting that returns realized from a single, first generation application are likely to increase with population density.

     

Predators and competitors of the mountain pine beetle Dendroctonus ponderosae (Coleoptera: Curculionidae) in stands of changing forest composition associated with elevation

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Winter warming effects on overwinter survival,energy use,and spring emergence of Cerotoma trifurcata (Coleoptera: Chrysomelidae)

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β-Pinene + ethanol attracts more red turpentine beetles than carene+ ethanol,with or without traces of frontalin,at prescribed burn or thinned sites

1. Red turpentine beetle, Dendroctonus valens LeConte (Coleoptera: Curculionidae: Scolytinae), previously responded more strongly to (−)-β-pinene + ethanol than (+)-3-carene + ethanol lures at sites burned the prior year by wildfire in Oregon and northeastern California, whereas at a thinned-unburned Arizona site (+)-3-carene + ethanol was the stronger attractant. This discrepancy was further examined to tease apart whether D. valens attraction varies by region or previous forest disturbance types.
2. Here, (−)-β-pinene + ethanol and (+)-3-carene + ethanol lures were tested in pine stands at two Oregon sites disturbed the previous year by a prescribed burn or thinning only. Both lures were tested also with or without trace amounts of the pheromone frontalin, as its presence enhanced attractions in China but had not been tested in North America.
3. At both sites, regardless of prior forest disturbance, (−)-β-pinene + ethanol lures attracted the most beetles. Lures releasing trace frontalin attracted more beetles than their corresponding lures without it at both sites, except in one case.
4. Overall, previous year disturbances from disparate management treatments had minimal influence on lure attraction to D. valens. For detection, monitoring or management (−)-β-pinene + ethanol + frontalin in trace amounts attracts the most beetles of lures tested to date in Pacific Northwest pine forests.

     

Effects of the time of drought occurrence within the growing season on growth and survival of Pinus ponderosa seedlings

Key message

A drought event during spring produces a stronger and long lasting decrease in growth of ponderosa pine seedlings than a summer drought event. However, survival is not differentially affected.

Abstract

Although there is certainty about the increasing frequency of extreme climatic events, the consequences of changing patterns of drought events within the growing season on the growth and survival of different species are much less certain. In particular, little knowledge is available on the differential effect on tree seedlings of a drought event at different times within the growing season. The objective of this study was to quantify the effect of a drought event imposed at different times over the growing season on the growth, survival and some related morphological and physiological variables of Pinus ponderosa seedlings from two seed sources. Four treatments were applied: control conditions; spring drought; summer drought and spring plus summer drought (SpSuD). A drought event in spring reduced stem growth and biomass accumulation in ponderosa pine seedlings during the occurrence of the drought and afterwards, even when plant water status had recovered. The lack of growth recovery could not be associated with loss of stem hydraulic conductivity or reduction in stomatal conductance after drought. However, the spring drought did not differentially affect plant survival, as was the case with prolonged drought in the SpSuD treatment. The summer drought event had a significant but much smaller impact on plant growth. Our results suggest different consequences of a drought event in spring or in summer in ponderosa pine seedlings. This knowledge may be relevant to understand and predict tree seedlings responses to changing patterns of drought events within the growing season in the framework of climatic change.     

Drought responses of conifers in ecotone forests of northern Arizona: tree ring growth and leaf δ<Superscript>13</Superscript>C

We sought to understand differences in tree response to meteorological drought among species and soil types at two ecotone forests in northern Arizona, the pinyon-juniper woodland/ponderosa pine ecotone, and the higher elevation, wetter, ponderosa pine/mixed conifer ecotone. We used two approaches that provide different information about drought response: the ratio of standardized radial growth in wet years to dry years (W:D) for the period between years 1950 and 2000 as a measure of growth response to drought, and ¹³C in leaves formed in non-drought (2001) and drought (2002) years as a measure of change in water use efficiency (WUE) in response to drought. W:D and leaf ¹³C response to drought for Pinus edulis and P. ponderosa did not differ for trees growing on coarse-texture soils derived from cinders compared with finer textured soils derived from flow basalts or sedimentary rocks. P. ponderosa growing near its low elevation range limit at the pinyon-juniper woodland/ponderosa pine ecotone had a greater growth response to drought (higher W:D) and a larger increase in WUE in response to drought than co-occurring P. edulis growing near its high elevation range limit. P. flexilis and Pseudotsuga menziesii growing near their low elevation range limit at the ponderosa pine/mixed conifer ecotone had a larger growth response to drought than co-occurring P. ponderosa growing near its high elevation range limit. Increases in WUE in response to drought were similar for all species at the ponderosa pine/mixed conifer ecotone. Low elevation populations of P. ponderosa had greater growth response to drought than high-elevation populations, whereas populations had a similar increase in WUE in response to drought. Our findings of different responses to drought among co-occurring tree species and between low- and high-elevation populations are interpreted in the context of drought impacts on montane coniferous forests of the southwestern USA.     

Contrasting responses of black fly species (Diptera: Simuliidae) to experimental whole-stream warming

1. As global temperatures continue to rise, assessment of how species within ecological communities respond to shifts in temperature has become increasingly important. However, such assessments require detailed long-term observations or ecosystem-level manipulations that allow for interactions among species and the potential for species dispersal and exchange with the regional species pool.
2. We examined the effects of experimental whole-stream warming on a larval black fly assemblage in southwest Iceland. We used a paired-catchment design, in which we studied the warmed stream and a nearby reference stream for 1 year prior to warming and 2 years during warming and estimated population abundance, biomass, secondary production, and growth rates for larvae of three black fly species.
3. Experimental warming by 3.8°C had contrasting effects on the three black fly species in the assemblage. The abundance, biomass, growth, and production of Prosimulium ursinum decreased in the experimental stream during the warming manipulation. Despite increasing in the reference stream, the abundance, biomass, and production of another species, Simulium vernum, decreased in the experimental stream during warming.
4. In contrast, warming had an overall positive effect on Simulium vittatum. While warming had little effect on the growth of overwintering cohorts of S. vittatum, warming led to an additional cohort during the summer months and increased its abundance, biomass, and production. Overall, family-level production was enhanced by warming, despite variation in species-level responses.
5. Our study illustrates that the effects of climate warming are likely to differ even among closely related species. Moreover, our study highlights the need for further investigation into the uneven effects of warming on individual species and how those variable effects influence food web dynamics and ecosystem function.

     

Bark beetle and woodborer responses to stand thinning and prescribed fire in northeastern US coastal and inland pitch pine barrens

1. Southern pine beetle, Dendroctonus frontalis, has expanded its range further into the northeastern United States. This expansion threatens rare and ecologically valuable interior and coastal pitch pine barrens.
2. Pitch pine barrens restoration and southern pine beetle infestation suppression often involve leaving downed dead wood that saproxylic insects can exploit.
3. Semiochemical-baited traps were used to investigate the response of bark beetles and woodborers to restoration treatments at Rocky Point State Forest and the Albany Pine Bush Preserve, examples of coastal and interior pitch pine forests, respectively.
4. A total of 29,598 saproxylic insects from 116 species of bark beetles and woodborers were captured at Rocky Point State Forest, while 23,117 individuals from 67 species were captured at Albany Pine Bush Preserve.
5. Ips spp. were abundant at both sites with 28%–47% and 42%–74% of total collections at Rocky Point State Forest and Albany Pine Bush Preserve, respectively.
6. Ips grandicollis did not respond to treatments at either site. However, Ips pini was found in higher numbers in thinned blocks in Rocky Point State Forest.

     

Phenology and growth of Fagus sylvatica and Quercus robur seedlings in response to temperature variation in the parental versus offspring generation

• Plants are known to respond to warming temperatures. Few studies, however, have included the temperature experienced by the parent plant in the experimental design, in spite of the importance of this factor for population dynamics.
• We investigated the phenological and growth responses of seedlings of two key temperate tree species (Fagus sylvatica and Quercus robur) to spatiotemporal temperature variation during the reproductive period (parental generation) and experimental warming of the offspring. To this end, we sampled oak and beech seedlings of different ages (1–5 years) from isolated mother trees and planted the seedlings in a common garden.
• Warming of the seedlings advanced bud burst in both species. In oak seedlings, higher temperatures experienced by mother trees during the reproductive period delayed bud burst in control conditions, but advanced bud burst in heated seedlings. In beech seedlings, bud burst timing advanced both with increasing temperatures during the reproductive period of the parents and with experimental warming of the seedlings. Relative diameter growth was enhanced in control oak seedlings but decreased with warming when the mother plant experienced higher temperatures during the reproductive period.
• Overall, oak displayed more plastic responses to temperatures than beech. Our results emphasise that temperature during the reproductive period can be a potential determinant of tree responses to climate change.

     

Native root xylem embolism and stomatal closure in stands of Douglas-fir and ponderosa pine: mitigation by hydraulic redistribution

Hydraulic redistribution (HR), the passive movement of water via roots from moist to drier portions of the soil, occurs in many ecosystems, influencing both plant and ecosystem-water use. We examined the effects of HR on root hydraulic functioning during drought in young and old-growth Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] and ponderosa pine (Pinus ponderosa Dougl. Ex Laws) trees growing in four sites. During the 2002 growing season, in situ xylem embolism, water deficit and xylem vulnerability to embolism were measured on medium roots (2–4-mm diameter) collected at 20–30 cm depth. Soil water content and water potentials were monitored concurrently to determine the extent of HR. Additionally, the water potential and stomatal conductance (g_s) of upper canopy leaves were measured throughout the growing season. In the site with young Douglas-fir trees, root embolism increased from 20 to 55 percent loss of conductivity (PLC) as the dry season progressed. In young ponderosa pine, root embolism increased from 45 to 75 PLC. In contrast, roots of old-growth Douglas-fir and ponderosa pine trees never experienced more than 30 and 40 PLC, respectively. HR kept soil water potential at 20–30 cm depth above –0.5 MPa in the old-growth Douglas-fir site and –1.8 MPa in the old-growth ponderosa pine site, which significantly reduced loss of shallow root function. In the young ponderosa pine stand, where little HR occurred, the water potential in the upper soil layers fell to about –2.8 MPa, which severely impaired root functioning and limited recovery when the fall rains returned. In both species, daily maximum g_s decreased linearly with increasing root PLC, suggesting that root xylem embolism acted in concert with stomata to limit water loss, thereby maintaining minimum leaf water potential above critical values. HR appears to be an important mechanism for maintaining shallow root function during drought and preventing total stomatal closure.     

Predicting the distribution of Eccritotarsus catarinensis, a natural enemy released on water hyacinth in South Africa

Water hyacinth [Eichhornia crassipes (Mart.) Solms (Pontederiaceae)] is the most damaging aquatic weed in South Africa, where five arthropod biological control agents have been released against it. The most recent introduction of Eccritotarsus catarinensis (Carvalho) (Heteroptera: Miridae) has failed to establish permanent populations at a number of sites in South Africa where water hyacinth is a problem. Cold winter temperatures at these sites are assumed to be the reason for these establishment failures. This assumption was tested by investigating the thermal physiology of the mirid, then incorporating these data into various predictive distribution models. Degree‐day models predict 3–14 generations per year at different localities in South Africa, and five generations at a Johannesburg site where the mirid failed to overwinter. The inability to develop sufficiently rapidly during winter months may hinder overwintering of this insect, which was predicted to develop through only one generation during the winter months of April to August in Johannesburg. A CLIMEX model also showed that cold stress limits the mirid's ability to overwinter in the interior of the country, while determination of the lower lethal limit (–3.5 °C) and critical thermal minimum (1.2 ± 1.17 °C) also indicated that extreme temperatures will limit establishment at certain sites. It is concluded that E. catarinensis is limited in its distribution in South Africa by low winter temperatures.     

Classification tree and minimum-volume ellipsoid analyses of the distribution of ponderosa pine in the western USA

Aim Ponderosa pine (Pinus ponderosa Douglas ex Lawson & C. Lawson) is an economically and ecologically important conifer that has a wide geographic range in the western USA, but is mostly absent from the geographic centre of its distribution – the Great Basin and adjoining mountain ranges. Much of its modern range was achieved by migration of geographically distinct Sierra Nevada (P. ponderosa var. ponderosa) and Rocky Mountain (P. ponderosa var. scopulorum) varieties in the last 10,000 years. Previous research has confirmed genetic differences between the two varieties, and measurable genetic exchange occurs where their ranges now overlap in western Montana. A variety of approaches in bioclimatic modelling is required to explore the ecological differences between these varieties and their implications for historical biogeography and impending changes in western landscapes. Location Western USA. Methods We used a classification tree analysis and a minimum‐volume ellipsoid as models to explain the broad patterns of distribution of ponderosa pine in modern environments using climatic and edaphic variables. Most biogeographical modelling assumes that the target group represents a single, ecologically uniform taxonomic population. Classification tree analysis does not require this assumption because it allows the creation of pathways that predict multiple positive and negative outcomes. Thus, classification tree analysis can be used to test the ecological uniformity of the species. In addition, a multidimensional ellipsoid was constructed to describe the niche of each variety of ponderosa pine, and distances from the niche were calculated and mapped on a 4‐km grid for each ecological variable. Results The resulting classification tree identified three dominant pathways predicting ponderosa pine presence. Two of these three pathways correspond roughly to the distribution of var. ponderosa, and the third pathway generally corresponds to the distribution of var. scopulorum. The classification tree and minimum‐volume ellipsoid model show that both varieties have very similar temperature limitations, although var. ponderosa is more limited by the temperature extremes of the continental interior. The precipitation limitations of the two varieties are seasonally different, with var. ponderosa requiring significant winter moisture and var. scopulorum requiring significant summer moisture. Great Basin mountain ranges are too cold at higher elevations to support either variety of ponderosa pine, and at lower elevations are too dry in summer for var. scopulorum and too dry in winter for var. ponderosa. Main conclusions The classification tree analysis indicates that var. ponderosa is ecologically as well as genetically distinct from var. scopulorum. Ecological differences may maintain genetic separation in spite of a limited zone of introgression between the two varieties in western Montana. Two hypotheses about past and future movements of ponderosa pine emerge from our analyses. The first hypothesis is that, during the last glacial period, colder and/or drier summers truncated most of the range of var. scopulorum in the central Rockies, but had less dramatic effects on the more maritime and winter‐wet distribution of var. ponderosa. The second hypothesis is that, all other factors held constant, increasing summer temperatures in the future should produce changes in the distribution of var. scopulorum that are likely to involve range expansions in the central Rockies with the warming of mountain ranges currently too cold but sufficiently wet in summer for var. scopulorum. Finally, our results underscore the growing need to focus on genotypes in biogeographical modelling and ecological forecasting.