Classification and ordination of plant communities along an altitudinal gradient on the Presidential Range,New Hampshire,USA

An analysis of vegetation along an altitudinal gradient on the Presidential Range, New Hampshire, USA, using the Braun–Blanquet approach followed by multivariate data analysis is presented. Twelve main plant communities have been distinguished. Floristic information is presented in twelve tables and one appendix. The relationships of the communities to complex environmental gradients are analyzed using Correspondence Analysis. Floristic composition and community structure are controlled primarily by the altitudinal gradient (temperature, precipitation), and by mesotopographic conditions (snow accumulation, exposure and cryoturbation, slope position, and soil moisture).     

A survey of seasonal bark proteins in eight temperate hardwoods

Summary Bark proteins of eight temperate hardwoods were analyzed by SDS-PAGE at monthly intervals to determine whether an accumulation of specific proteins, potential storage proteins, occurred in the fall at the time of leaf senescence. Storage proteins were identified as proteins that accumulated during the fall and were present in reduced amounts in the summer. Total protein levels were higher in the winter than in the summer in Fagus sylvatica, Fraxinus americana, Tilia americana, Alnus glulinosa, Betula papyrifera and Querus rubra, but not in Gleditsia triacanthos or Robinia pseudoacacia. Betula contained the most abundant storage protein, although in all species minor bands, which fluctuated seasonally, could be identified. With the exception of Alnus and Betula, results generally correlated with previous microscopy studies of these tree species, which showed varying amounts of protein storage vacuoles present in phloem parenchyma cells during the winter, but not during the summer.     

Foliar physiology of yellow-poplar ( Liriodendron tulipifera L.) exposed to O3 and elevated CO2 over five seasons.

The chronic effects of ozone (O₃) alone or combined with elevated carbon dioxide (CO₂) on the foliar physiology of unfertilized field-grown yellow-poplar ( Liriodendron tulipifera L.) seedlings were studied from 1992 to 1996. Within open-top chambers, juvenile trees were exposed to the following: charcoal-filtered air (CF); 1× ambient ozone (1XO₃); 1.5× ambient ozone (1.5XO₃); 1.5× ambient ozone plus 700 ppm carbon dioxide (1.5XO₃+CO₂); or chamberless open-air (OA). Seasonal 24-h mean ambient O₃ concentrations ranged from 32 to 46 ppm over the five seasons. Averaged over 5 years, midseason net photosynthesis at saturating light ( A _sat) was reduced by 14% ( P =0.029) and stomatal conductance ( g _s) was reduced, albeit non-significant, by 13% ( P =0.096) in upper canopy foliage exposed to 1.5XO₃-air relative to CF controls. There were no significant differences over the 5 years in A _sat and g _s between trees grown in 1XO₃- and 1.5XO₃-air. Our results support the hypothesis that the magnitude of O₃ effects on A _sat and g _s decreases as saplings age. When averaged over the five seasons of exposure, total chlorophyll concentration ( chl) was not significantly affected by exposure to elevated O₃; however, in 1.5XO₃+CO₂-air, foliar chl was reduced by 33% relative to all others ( P <0.001). In 1.5XO₃+CO₂-air, A _sat was 1.4–1.9 times higher ( P <0.001) and g _s was 0.7 times lower ( P =0.022) than all others. O₃ uptake in juvenile trees exposed to elevated O₃ plus elevated CO₂ (1.5XO₃+CO₂-air) was most comparable to trees exposed to ambient air (1XO₃) throughout the study. These findings suggest that elevated CO₂ may minimize the negative effects of O₃ by reducing O₃ uptake through decreased stomatal conductance.     

Assessing Ecoregional-Scale Habitat Suitability Index Models for Priority Landbirds

ABSTRACT Emerging methods in habitat and wildlife population modeling promise new horizons in conservation but only if these methods provide robust population-habitat linkages. We used Breeding Bird Survey (BBS) data to verify and validate newly developed habitat suitability index (HSI) models for 40 priority landbird species in the Central Hardwoods and West Gulf Coastal Plain/Ouachitas Bird Conservation Regions. We considered a species’ HSI model verified if there was a significant rank correlation between mean predicted HSI score and mean observed BBS abundance across the 88 ecological subsections within these Bird Conservation Regions. When we included all subsections, correlations verified 37 models. Models for 3 species were unverified. Rank correlations for an additional 5 species were not significant when analyses included only subsections with BBS abundance >0. To validate models, we developed generalized linear models with mean observed BBS abundance as the response variable and mean HSI score and Bird Conservation Region as predictor variables. We considered verified models validated if the overall model was an improvement over an intercept-only null model and the coefficient on the HSI variable in the model was >0. Validation provided a more rigorous assessment of model performance than verification, and models for 12 species that we verified failed validation. Species whose models failed validation were either poorly sampled by BBS protocols or associated with woodland and shrubland habitats embedded within predominantly open landscapes. We validated models for 25 species. Habitat specialists and species reaching their highest densities in predominantly forested landscapes were more likely to have validated models. In their current form, validated models are useful for conservation planning of priority landbirds and offer both insight into limiting factors at ecoregional scales and a framework for monitoring priority landbird populations from readily available national data sets.     

Four new Ophiostoma species associated with hardwood-infesting bark beetles in Norway and Poland

Ophiostoma spp. (Ophiostomatales, Ascomycota) are well-known fungi associated with bark and ambrosia beetles (Curculionidae: Scolytinae, Platypodinae). Fungi in the Ophiostomatales include serious tree pathogens as well as agents of timber blue-stain. Although these fungi have been extensively studied in the northern hemisphere, very little is known regarding their occurrence on hardwoods in Europe. The aims of the present study were to identify and characterize new Ophiostoma spp. associated with bark and ambrosia beetles infesting hardwoods in Norway and Poland, and to resolve phylogenetic relationships of Ophiostoma spp. related to the Norwegian and Polish isolates, using multigene phylogenetic analyses. Results obtained from five gene regions (ITS, LSU, β-tubulin, calmodulin, translation elongation factor 1-α) revealed four new Ophiostoma spp. These include Ophiostoma hylesinum sp. nov., O. signatum sp. nov., and O. villosum sp. nov. that phylogenetically are positioned within the Ophiostoma ulmi complex. The other new species, Ophiostoma pseudokarelicum sp. nov. reside along with Ophiostoma karelicum in a discrete, well-supported phylogenetic group in Ophiostoma s. stricto. The results of this study clearly show that the diversity and ecology of Ophiostoma spp. on hardwoods in Europe is poorly understood and that further studies are required to enrich our knowledge about these fungi.     

Biotechnological applications of tissue culture to forest tree improvement

Plant tissue culture techniques are of tremendous potential value to forest tree improvement. The technology is envisaged as playing a complementary role to traditional methods through exploiting spontaneous or induced genetic and epigenetic variability in culture, by use of haploidy and by the use of protoplasts. Haploids and protoplasts will aid in shortening breeding cycles and allow for unconventional crosses respectively. Clonal propagation is an integral part of any tree improvement program, and in addition can play an independent role in reforestation, clonal orchard establishment and in energy foresting. The goals, problems and limitations of these applications of tissue culture technology to forest tree improvement are indicated and assessed.     

Does canopy position affect wood specific gravity in temperate forest trees?

The radial increases in wood specific gravity known in many tree species have been interpreted as providing mechanical support in response to the stresses associated with wind loading. This interpretation leads to the hypothesis that individuals reaching the canopy should (1) be more likely to have radial increases in specific gravity and (2) exhibit greater increases than individuals in the subcanopy. Wood specific gravity was determined for three species of forest trees (Acer rubrum, Fagus grandifolia and Tsuga canadensis) growing in central Massachusetts, USA. Acer rubrum shows radial increases in specific gravity, but these increases are not more pronounced in canopy trees; the other two species show a pattern of radial decreases. The degree of radial increase or decrease is influenced by tree height and diameter. Of the dominant tree species for which we have data, A. rubrum, Betula papyrifera and Pinus strobus show radial increases in specific gravity, whereas F. grandifolia, T. canadensis and Quercus rubra show decreases. The occurrence of radial increases in B. papyrifera and P. strobus, which are often canopy emergents, suggests that it is overall adaptive strategy that is important rather than position (canopy vs. subcanopy) of any individual tree. It is suggested that radial increases in specific gravity are associated with early-successional status or characteristics and decreases with late-successional status or persistence in mature forest.     

Response of xylem parenchyma by suberization in some hardwoods after mechanical injury

Summary Wound responses of xylem parenchyma by suberization were investigated in some hardwoods by light and electron microscopy. Suberized ray and axial parenchyma cells form a distinct boundary around the wound in all investigated species. Vessels and fibres within and close behind the suberized area appeared more or less occluded; vessels in Fagus, Quercus, and Populus contained suberized tyloses, those in Betula and Tilia contained amorphous and fibrillar deposits. A common mechanism for suberin deposition in the parenchyma cells became evident. Cisternae of the endoplasmic reticulum were apparently involved in suberization. Suberin compounds are extruded by cytoplasmic vesicles, which fused with the plasma membrane, in order to release their content. The suberin layer exhibited the typical lamellated structure; cytoplasmic continuity between suberized cells by plasmodesmata was maintained through the suberin layer. Fagus revealed the most intense suberized area as compared with the other species. Within the reaction zone of Fagus and Quercus, some individual ray and axial parenchyma cells exhibited a subdivision into 2 or 3 compartments prior to suberization. Subdivision was achieved by the formation of a primary wall-like layer. Subsequently, the compartments became individually suberized. Wounding during winter did not induce suberization. Also, samples wounded and kept under water during the vegetation period showed no response. The role of suberization in the effectivity of wound-associated compartmentalization is discussed.     

Tree composition and structure in disturbed stands with varying dominance by Pinus spp. in the highlands of Chiapas,México

We studied soil and forest floor conditions, regeneration patterns oftrees, and forest structure and floristic composition along a gradient ofdominance by Pinus spp. in disturbed stands in thehighlands of Chiapas, southern Mexico. Seedlings, saplings, and adults of treespecies were counted and measured in 2-3 circular plots (1000m² each) in 36 forest stands (a total of 38 treespecies). Dominance of broadleaved trees other thanQuercusspp. was negatively correlated with basal area of Pinusspp. (P < 0.001). Soils of pine-dominated stands weremore compacted, less acidic, and less fertile (lower C.E.C., nitrogen, andorganic matter content). Numerous broadleaved trees may depend on anoak-dominated canopy to regenerate, and changes associated to pinelandsexpansion may compromise their long-term persistence. However, seedlings andsaplings of Quercus spp. were abundant in stands with bothan oak- or pine-dominated canopy. The results suggest that a plan forsustainable forest utilization in the study region, and in other similarpopulated tropical highlands, could take advantage of the abundant oakregeneration and coexistence with pines in the canopy.