Larval feeding behaviour affects the impact of staminate flower production on the suitability of balsam fir trees for spruce budworm

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing indicated that the feeding behaviour of the larvae, which is affected by the insect population density, significantly influenced the impact of balsam fir, Abies balsamea, staminate flowering on spruce budworm biology. At low budworm density, the production of pollen in the midcrown of host trees reduced the insect development time by 5 days without affecting pupal weight, fecundity and survival. However, at high budworm density, the small amount of current-year foliage produced by flowering branches forced old larvae (sixth instar) either to feed on 1-year-old foliage (backfeeding) or to move from the midcrown to the lower crown section where staminate flowers are absent and more current-year foliage is available. When old larvae fed on old foliage, they exhibited reduced pupal weight and fecundity without losing the advange in development time that they obtained from feeding on pollen during their early stages of development. On the other hand, when old larvae moved to the lower crown section, they avoided the negative effects of backfeeding but lost the advantage in development time that was gained from feeding on pollen. Results from this study indicated that the production of staminate flowers by balsam fir trees could have opposite effects on spruce budworm population dynamics depending upon the insect population density when flowering occurs.     

Growth response of subalpine fir (Abies lasiocarpa) to climate in the Olympic Mountains, Washington, USA

Growth response of subalpine fir (Abies lasiocarpa) to climate was studied across its local geographical and elevation range in the Olympic Mountains, Washington. A dendroecological analysis of subalpine fir across a range of elevations (1350-1850 m) and annual precipitation (125-350 cm y^?1), was used to compare environmental factors affecting growth. Climate-growth relationships were explored using Pearson product-moment correlation coefficients; partial correlation analysis was used to assess relationships among site chronologies and climatic variables. Radial growth is negatively correlated with winter precipitation at high elevation and wet sites, but not at low and middle elevation dry sites. Growth is positively correlated with current growing season temperature at all sites; however, growth is negatively correlated with previous year August temperature, indicating that climate affects growth in subsequent years. Positive correlations between growth and summer precipitation during the growing season at low and middle elevation dry sites suggest that soil moisture is partially limiting to growth on these sites. If the climate of the Pacific Northwest becomes warmer and drier, then subalpine fir growth may increase at high elevation and wet sites, but may decrease at lower elevation dry sites in the Olympic Mountains. However, the growth response of subalpine fir to potentially rapid climate change will not be uniform because subalpine fir grows over a wide range of topographic features, habitats, and local climates at different geographical scales. A comparison of growth response to current growing season temperature suggests that the temperature-related growth response of subalpine fir is not adequately described by the parabolic curve used in JABOWA-based models.     

Impact of balsam fir flowering on pollen and foliage biochemistry in relation to spruce budworm growth, development and food utilization

The impact of balsam fir (Abies balsamea (L.) Miller) flowering on nutritional and allelochemical quality of pollen, current-year and one-year-old foliage is studied in relation to spruce budworm (Choristoneura fumiferana Clem.) (Lepidoptera: Tortricidae) growth, development and utilization of food and nitrogen. In the laboratory, using fresh food from the field, we simulated conditions of low larval population density, in which there is no current-year foliage depletion during the spruce budworm feeding period. Similarly, we simulated conditions of high larval population density when current-year foliage depletion occurs.Because of the high nutritive value of pollen (high amounts of amino acids and minerals, especially nitrogen; low monoterpene content), insects from flowering trees reached the fifth instar five days earlier than those from non-flowering trees, and had heavier dry- and nitrogen-weights at the beginning of the fifth instar. At budbreak, switching from pollen to current-year foliage negatively affected conversion efficiencies and digestibilities of food and nitrogen (AD; ADN; ECDN; ECI; ECIN). The switch from pollen to new foliage had a detrimental impact on fifth-instar survival and on newly-moulted sixth-instar dry- and nitrogen-weights. Moreover, during the fifth instar, balsam fir flowering reduced the nutritive value of current-year foliage, which in turn, might have contributed to the reduced larval growth. Nevertheless, during the sixth instar, balsam fir flowering affected the biochemistry of current-year foliage in ways that enabled larvae to compensate for their low fifth-instar biological performance; larvae also managed to reach pupal dry weight similar to larvae reared on non-flowering trees. Current-year foliage from flowering trees contained less nitrogen, total soluble sugars and total monoterpenes. Those foliar characteristics enabled larvae to increase food and nitrogen consumption rates (RCR; RNCR), because of lower repellency and/or post-ingestional feedback from monoterpenes.As for current-year foliage, balsam fir flowering reduced nitrogen, total soluble sugar and total monoterpene contents in one-year-old foliage during the sixth-instar feeding period. These characteristics enabled sixth-instar larvae, fed on old foliage from flowering trees, to have high relative food and nitrogen consumption rates (RCR; RNCR). Larvae were also able to reach higher relative growth rates (RGR) and relative nitrogen accumulation rates (RNAR) compared to larvae reared on one-year-old foliage from non-flowering trees. Finally, larvae on flowering trees had pupal dry weight similar to those from non-flowering trees, but reached the adult stage nine days earlier.Regardless the foliage type consumed by spruce budworm larvae during the sixth instar, pollen consumption during early larval stages reduced total development time, and thus exposure time to natural enemies. This phenomenon might increase larval survival. Balsam fir flowering changed the biochemistry of one-year-old and current-year foliages, but did not affect pupal dry weights of larvae reared on flowering trees compared to those reared on non-flowering trees. Thus, at low population density, spruce budworm populations in balsam fir flowering stands might be favoured over those in balsam fir non-flowering stands. In addition, when larvae consumed one-year-old foliage during the entire sixth instar, those on flowering trees are probably favoured over those on non-flowering trees. However, because flowering trees produce less new foliage than non-flowering trees, current-year foliage depletion may occur earlier on flowering trees than on non-flowering trees. Thus, at similar larval population density, larvae on flowering trees might have to feed on one-year-old foliage earlier than those on non-flowering trees. In that case, spruce budworm populations on non-flowering stands would be favoured over those on flowering stands.     

云南亚高山云冷杉林林窗的研究

研究了云南碧塔海两块亚高山云冷杉（Ｐｉｃｅａ－Ａｂｉｅｓ）林内中小尺度林窗的干扰体系,结果表明：林窗和扩展林窗分别占林地面积的１９％和４１％,平均面积为４４ｍ２和１３９ｍ２,林窗的形成频率为０．００５～０．００７／ｙ。估计平均林窗周期为１６７年。大多数林窗（占８７％）的制造林窗树木（ｇａｐ－ｍａｋｅｒ,简记为ＧＭ）为１个以上,平均每个林窗的ＧＭ为２．９个,同一林窗内的ＧＭ常常死于不同的时间。在所有调查的ＧＭ中,折断占６０％,而根拔和直立死亡分别为２８％和１２％     

Freeze-protection of overwintering monarch butterflies in Mexico: critical role of the forest as a blanket and an umbrella

Abstract. 1. At their high-altitude overwintering sites in Mexico, monarch butterflies frequently are subjected to sub-zero°C temperatures during December-March. Although monarchs have moderate supercooling ability, two ecological factors strongly influence their capacity to resist freezing: wetting and exposure to the clear night sky. 2. As shown in Fig. 2, 50% of a population of butterflies with water on their body surfaces freeze at warmer sub-zero temperatures (-4.2°C) compared to butterflies with no water on their bodies (-7.7°C). 100% mortality occurs, respectively, at ?7.7°C and ?15°C. 3. Comparative measurements of rainfall within a large overwintering colony in Mexico indicated that the intact canopy acts as an umbrella that reduces butterfly wetting during winter storms. 4. Variable experimental exposure of butterflies to the clear night sky indicated that openings in the forest canopy increases radiational cooling and causes monarch body temperatures to drop as much as 4°C below ambient air temperature. Monarchs under dense cover had body temperatures approximately the same as the ambient air temperature, but more exposed individuals had body temperatures below ambient in direct proportion to the degree of exposure. Consequently, forest thinning increases the probability that the butterflies will freeze to death. 5. Whereas both wetting and exposure are increased by disturbance of the forest canopy, the interaction of these two factors exacerbates freezing mortality during winter storms: 50% of dry and unexposed butterflies froze at ?8°C, whereas wetted and fully exposed butterflies froze at only ?0.5°C. 6. Butterflies inside and on the bottom of the fir bough clusters are better protected from wetting than those on the outside. This supports the hypothesis that the structure of the butterfly clusters has evolved through individual selection to avoid wetting. 7. The data strongly reinforce previous evidence that forest thinning should be totally prevented within and adjacent to the overwintering sites in order to minimize both wetting and exposure of the butterflies that synergistically increase winter mortality at the overwintering sites in Mexico.     

Changes in the arrangement of cellulose microfibrils associated with the cessation of cell expansion in tracheids

 The relationship between the cessation of cell expansion and formation of the secondary wall was investigated in the early-wood tracheids of Abies sachalinensis Masters by image analysis and field emission scanning electron microscopy. The area of the lumen and the length of the perimeter of the lumen of differentiating tracheids increased from the cambium towards the xylem. These increases had just ceased in the case of tracheids closest to the cambium in which birefringence was first detected by observations with a polarizing light microscope. Cellulose microfibrils (MFs) deposited on the innermost surfaces of radial walls were not well ordered during the expansion of cells, but well ordered MFs were deposited at the subsequent stage of cell wall formation. The first well ordered MFs were oriented in an S-helix. The well ordered MFs had already been deposited at the tracheids where birefringence was first detected under the polarizing light microscope. These results indicate that the deposition of the well ordered MFs, namely, the formation of the secondary wall, begins before the cessation of cell expansion of tracheids. Therefore, it seems that the expansion of tracheids is restricted by the deposition of the secondary wall because the cell walls become rigid simultaneously with the development of the secondary wall and, therefore, the yield point of cell walls exceeds the turgor pressure of the cell. Received: 3 July 1996 / Accepted: 24 September 1996     

Natural hybridization in eastern-Mediterranean firs: The case of Abies borisii-regis

The genus Abies is represented in southern Balkans by A. alba, A. cephalonica, and A. borisii-regis. To infer the status of southern-Balkans firs, as well as the extent and patterns of introgression within this taxonomical complex, we analyzed genetic variation patterns of 29 indigenous fir populations in Bulgaria, Macedonia, Greece, and Calabria using a combination of maternally and biparentally inherited markers. Three mitochondrial lineages were observed, one comprising Calabrian populations and two distributed in the Balkans, coinciding with A. alba and A. cephalonica. The boundary between lineages is sharp; only two populations containing a mixture of haplotypes were found. Bayesian analysis of population structure based on seven nuclear microsatellite (nSSR) loci revealed the existence of two clusters whose proportions exhibited a latitudinal cline with a width of 2.3° ( ≈ 255 km). Populations in the center of the latitudinal cline exhibit the most symmetrical, the flattest, and the broadest distributions of cluster proportions within individual tree genomes. A neighbor-net network reflects the cline resulting from the Bayesian analysis. The observed variation patterns are not consistent with the hypothesis of A. borisii-regis as a monophyletic taxon or a stabilized hybridogenous species resulted from ancient hybridization; the taxon rather is a product of recent introgression.     

Isolation of cuticular membranes from various conifer needles

Summary A method of isolating intact needle cuticles is presented. Cuticles were separated enzymatically from needles of Abies alba Mill., Picea abies (L.) Karst., Picea pungens Engelm., Pinus mugo Turra, and Taxus baccata L. Cuticle separation depended on the enzyme concentration, the developmental stage of the needles and the duration of incubation in the hydrolytic pectinase/cellulase solution. Cuticles could not be removed from needles older than 2 years. Scanning electron micrographs of enzymatically isolated cuticles are presented. The permeance coefficients for water and oxygen transport across the isolated cuticular membranes indicate their functional intactness. But permeance coefficients also show that isolation of cuticular membranes with chromic acid is an unacceptable method, since they are lo longer structurally or functionally intact following isolation by this method.     

Seasonal variation of growth and development of the roots of five second year conifer species in the nursery

Every other week over their second growing season, stem height, collar diameter, shoot and root dry masses, number of lateral roots and length of the tap root were measured on nursery grown seedlings ofAbies balsamea L. Mill.,Pinus banksiana Lamb.,Pinus resinosa Ait.,Picea mariana Mill. BSP andPicea glauca Moench Voss. Root elongation, branching and mycorrhizal development were also recorded.Given species showed distinct seasonal growth patterns. The rate and timing of maximum root growth (mg/dry weight/week) differed markedly between species.Except for the increase in height ofPinus banksiana, root and shoot growth were not negatively correlated.The results are discussed in relation to the performance of tree seedlings in the nursery.