Low Structural Diversity Research Articles

Long-term impacts of stand management on ponderosa pine physiology and bark beetle abundance in northern Arizona: A replicated landscape study

Ponderosa pine ( Pinus ponderosa Dougl. ex Laws.) forests in northern Arizona have degraded due to overgrazing, logging, and fire suppression that accompanied Euro-American settlement in the late 1800s. Overstocked stands of suppressed trees with low structural diversity dominate the landscape. These conditions create high risk of catastrophic fires and insect outbreaks. We investigated long-term effects (8–16 years post-treatment) of thinning and thinning + prescribed burning on ponderosa pine water stress, leaf carbon isotope discrimination and nitrogen concentration, oleoresin exudation flow, phloem thickness, radial growth, and bark beetle abundance relative to unmanaged control stands over 2 years of measurement in 12 stands replicated across the landscape. Predawn water potential in late June, phloem thickness, and basal area increment were lower in unmanaged than managed stands. Oleoresin exudation flow in July was greater in unmanaged and thinned + burned stands than thinned stands, and greater in a warm year than a cooler year. Leaf nitrogen concentration differed between years, but not among treatments. Tree competition and water stress were positively correlated, and tree competition was negatively correlated with radial growth and phloem thickness. Pheromone-baited trap catches of Dendroctonus spp. ( D. brevicomis Leconte pooled with D. frontalis Zimmerman) were higher in unmanaged than managed stands, whereas catches of Ips spp. did not differ among treatments. We conclude that thinning with and without prescribed burning can have long-term effects on ponderosa pine water stress, growth, phloem thickness, resin flow, and bark beetle abundance. Low levels of tree mortality from bark beetles at our study sites suggest remarkable resistance of ponderosa pine in mid-elevation forests in northern Arizona, even at high tree densities.

Structural Analysis of Insulin Minisatellite Alleles Reveals Unusually Large Differences in Diversity between Africans and Non-Africans

The insulin minisatellite (INS VNTR) associates with susceptibility to a variety of diseases. We have developed a high-resolution system for analyzing variant repeat distributions applicable to all known minisatellite alleles, irrespective of size, which allows lineages of related alleles to be identified. This system has previously revealed extremely low structural diversity in the minisatellite among northern Europeans from the United Kingdom, with all alleles belonging to one of only three highly diverged lineages called "I," "IIIA," and "IIIB." To explore the origins of this remarkably limited lineage diversity, we have characterized an additional 780 alleles from three non-African and three African populations. In total, 22 highly diverged lineages were identified, with structural intermediates absent from extant populations, suggesting a bottleneck within the ancestry of all humans. The difference between levels of diversity in Africans and non-Africans is unusually large, with all 22 lineages identified in Africa compared with only three lineages seen not only in the United Kingdom but also in the other non-African populations. We also find evidence for overrepresentation of lineage I chromosomes in non-Africans. These data are consistent with a common out-of-Africa origin and an unusually tight bottleneck within the ancestry of all non-African populations, possibly combined with differential and positive selection for lineage I alleles in non-Africans. The important implications of these data for future disease-association studies are discussed.

Comparison of Coastal Fringe and Interior Forests as Reserves for Marbled Murrelets on Vancouver Island

Abstract Much of the protected habitat available to the threatened Marbled Murrelet Brachyramphus marmoratus and other old-growth associated species in the Pacific Northwest is in narrow strips along the coast (e.g., parks and scenic fringes). Using data over two years from three watersheds on southwest Vancouver Island, we show that such shoreline strip forests represent suboptimal habitat for murrelets. Murrelet detections, including circling and subcanopy behaviors, were significantly lower at 30 coastal stations (20–250 m from the shoreline edge) than at 30 interior stations (1.5–21.0 km inland). Densities of predators were significantly higher at the coastal stations. The coastal trees were of similar mean height and diameter, but they had lower structural diversity and provided fewer and less suitable (thinner epiphyte cover on large boughs) nesting platforms than trees in the interior. When possible, reserves for Marbled Murrelets should be placed in interior and not shoreline forests.

COMPARISON OF COASTAL FRINGE AND INTERIOR FORESTS AS RESERVES FOR MARBLED MURRELETS ON VANCOUVER ISLAND

Abstract Much of the protected habitat available to the threatened Marbled Murrelet Brachyramphus marmoratus and other old-growth associated species in the Pacific Northwest is in narrow strips along the coast (e.g., parks and scenic fringes). Using data over two years from three watersheds on southwest Vancouver Island, we show that such shoreline strip forests represent suboptimal habitat for murrelets. Murrelet detections, including circling and subcanopy behaviors, were significantly lower at 30 coastal stations (20–250 m from the shoreline edge) than at 30 interior stations (1.5–21.0 km inland). Densities of predators were significantly higher at the coastal stations. The coastal trees were of similar mean height and diameter, but they had lower structural diversity and provided fewer and less suitable (thinner epiphyte cover on large boughs) nesting platforms than trees in the interior. When possible, reserves for Marbled Murrelets should be placed in interior and not shoreline forests.

Comparative patterns of phenology and growth form diversity in two winter rainfall deserts: the Succulent Karoo and Mojave Desert ecosystems

A comparative study of community structure and seasonal growth dynamics in the arid winter rainfall regions of the Succulent Karoo in South Africa and the Mojave Desert of the United States suggests that remarkably divergent patterns of resource use and resultant growth form diversity exist in regions with outwardly similar climatic regimes. An understanding of these divergent patterns in the two winter rainfall deserts allows predictions to be made on vegetation response to global change. Above-ground plant growth in the Succulent Karoo begins with the first significant rains in late summer and continues through winter because moderate minimum temperatures allow continued growth. These communities have low structural diversity above-ground, but also below-ground, where root systems commonly do not exceed 20 cm in depth. These shallow root systems harvest water from upper soil horizons soon after rain falls, and growth declines as rainfall decreases in late spring. In contrast, low temperatures during winter inhibit growth in the Mojave Desert until early spring at a time when a mean 74% of the hydrologic year precipitation (July-June) has already occurred. Thus species in this structurally diverse system rely on deeper stores of water for growth in spring and early summer. A global change scenario of a 2 to 4 °C increase in mean annual temperature and increased summer rainfall in the Mojave desert would be expected to produce similar conditions in the Mojave Desert to those that exist in the Succulent Karoo today. Assuming no genetic constraints on phenotypic plasticity, this would suggest increased species diversity and a decline in structural diversity in the Mojave Desert over evolutionary time. Increased summer rainfall in the Succulent Karoo would be expected to lead to invasions of grasses and thus increased competitive pressure reducing community diversity.

Current problems with tuberculosis treatment

Natural product drug discovery has regained interest due to low production costs, structural diversity, and multiple uses of active compounds to treat various diseases. Attention has been directed towards medicinal plants as these plants have been traditionally used for generations to treat symptoms of numerous diseases.It is established that plants harbour microorganisms, collectively known as endophytes. Exploring the as-yet untapped natural products from the endophytes increases the chances of finding novel compounds. The concept of natural products targeting microbial pathogens has been applied to isolate novel antimycobacterial compounds, and the rapid development of drug-resistant Mycobacterium tuberculosis has significantly increased the need for new treatments against this pathogen. It remains important to continuously screen for novel compounds from natural sources, particularly from rarely encountered microorganisms, such as the endophytes.This review focuses on bioprospecting for polyketides and small peptides exhibiting antituberculosis activity, although current treatments against tuberculosis are described. It is established that natural products from these structure classes are often biosynthesised by microorganisms. Therefore it is hypothesised that some bioactive polyketides and peptides originally isolated from plants are in fact produced by their endophytes. This is of interest for further endophyte natural product investigations.

Pleistocene Rhine gravel: deposits of a braided river system with dominant pool preservation

Abstract An example of a gravelly braided river deposit is described which exhibits a rather low structural diversity as compared to other ancient and modern braided river sediments. The presented model is based on a study of the Rhine gravel, formed in front of the Würm stage extension of the Rhine glacier (northern part of Switzerland). The observations in the Rhine gravel suggest that only processes which operate generally at a low topographic level of the braided river system generate a response in the geological record, i.e. (1) pool deposits produced at the junction of two channels (cross-bedded trough fills); (2) channel sediments which reflect thin bedload sheets deposited by moderate-magnitude flow stages with low suspension concentrations; (3) sheet flow deposits produced by extraordinary high-magnitude flow stages with high suspension concentrations, probably due to outbursts from glacial lakes. Therefore, we postulate that in the Rhine gravel system only a limited number of braided river structures have a significant preservation potential: any deposit generated at an elevated geometric level, such as flood plain deposits or bars, are successively destroyed by channel formation and are replaced by channel deposits, which in turn may be reworked by pools which operate at the lowest geometric level. It is suggested that similar preservational hierarchies could eventually exist also in other braided river deposits.

Cuticular Anatomy of Angiosperm Leaves from the Lower Cretaceous Potomac Group. I. Zone I Leaves

Angiosperm leaf cuticles from the oldest part of the Potomac Group reinforce previous paleobotanical evidence for a Cretaceous flowering plant diversification. Dated palynologically as Zone I of Brenner (Aptian?), these remains show a low structural diversity compared to later Potomac Group and modern angiosperms. All cuticle types conform to a single plan of stomatal construction that is unusual in its extraordinary plasticity: both the number of subsidiary cells and their arrangement vary greatly on a single epidermis, such that the stomata might be classified as paracytic, anomocytic, laterocytic, and intermediate. Such stomatal diversity is uncommon in extant angiosperms but is known from a few Magnoliidae. Many species possess secretory cells comparable to the oil cells of modern Magnoliidae, and a few show the bases of probable uniseriate hairs. None of the cuticle types can be assigned to a single modern family, but several show similarities with Chloranthaceae and Illiciales. These results support the concept that subclass Magnoliidae includes some of the most primitive living angiosperms.

CUTICULAR ANATOMY OF ANGIOSPERM LEAVES FROM THE LOWER CRETACEOUS POTOMAC GROUP. I. ZONE I LEAVES

Angiosperm leaf cuticles from the oldest part of the Potomac Group reinforce previous paleobotanical evidence for a Cretaceous flowering plant diversification. Dated palynologically as Zone I of Brenner (Aptian?), these remains show a low structural diversity compared to later Potomac Group and modern angiosperms. All cuticle types conform to a single plan of stomatal construction that is unusual in its extraordinary plasticity: both the number of subsidiary cells and their arrangement vary greatly on a single epidermis, such that the stomata might be classified as paracytic, anomocytic, laterocytic, and intermediate. Such stomatal diversity is uncommon in extant angiosperms but is known from a few Magnoliidae. Many species possess secretory cells comparable to the oil cells of modern Magnoliidae, and a few show the bases of probable uniseriate hairs. None of the cuticle types can be assigned to a single modern family, but several show similarities with Chloranthaceae and Illiciales. These results support the concept that subclass Magnoliidae includes some of the most primitive living angiosperms.