Kenneth H. Orvis

A multi-scale analysis of landscape statistics

It is now feasible to monitor some aspects of landscapeecological condition nationwide using remotely-sensed imagery andindicators of land cover pattern. Previous research showedredundancies among many reported pattern indicators andidentified six unique dimensions of land cover pattern. Thisstudy tested the stability of those dimensions and representativepattern indicators across different types of land cover maps. Themaps were derived from Landsat Thematic Mapper images of theTennessee River and Chesapeake Bay watersheds, and they differedin resolution, number of attributes, and method of delineatinglandscape unit boundaries. A multivariate analysis of patternmetrics was conducted separately for each map, and the resultswere then compared among types of maps. Measures of land coverdiversity, texture, and fractal dimension were more consistentthan measures of average patch shape or compaction among the landcover maps.

PATTERNS OF ICE ACCUMULATION AND FOREST DISTURBANCE DURING TWO ICE STORMS IN SOUTHWESTERN VIRGINIA

Major ice storms deposit heavy loads of freezing rain on trees, causing catastrophic forest disturbance in eastern North America. During 1994, two ice storms struck southwestern Virginia within a three-week period. Heavy ice deposition occurred during each storm when warm, moist air was advected over a shallow subfreezing layer at the surface. Cold-air damming helped trap the cold surface air, as is typical for ice storms in parts of the Appalachians and Piedmont. Heaviest forest damage occurred on mountain slopes facing south and east. Ice damage in these topographic positions removed approximately 30% to 60% of total basal area and created large canopy openings. Several processes may have contributed to topographic variations in ice accretion, including orographic effects on rainfall and influences of wind on twig surface and raindrop thermodynamics. [Key words: ice storms, freezing rain, forest disturbance, Virginia, Appalachian Mountains.]

Assessing the Potential Impacts to Riparian Ecosystems Resulting from Hemlock Mortality in Great Smoky Mountains National Park

Hemlock Woolly Adelgid (Adelges tsugae) is spreading across forests in eastern North America, causing mortality of eastern hemlock (Tsuga canadensis [L.] Carr.) and Carolina hemlock (Tsuga caroliniana Engelm.). The loss of hemlock from riparian forests in Great Smoky Mountains National Park (GSMNP) may result in significant physical, chemical, and biological alterations to stream environments. To assess the influence of riparian hemlock stands on stream conditions and estimate possible impacts from hemlock loss in GSMNP, we paired hardwood- and hemlock-dominated streams to examine differences in water temperature, nitrate concentrations, pH, discharge, and available photosynthetic light. We used a Geographic Information System (GIS) to identify stream pairs that were similar in topography, geology, land use, and disturbance history in order to isolate forest type as a variable. Differences between hemlock- and hardwood-dominated streams could not be explained by dominant forest type alone as forest type yields no consistent signal on measured conditions of headwater streams in GSMNP. The variability in the results indicate that other landscape variables, such as the influence of understory Rhododendron species, may exert more control on stream conditions than canopy composition. The results of this study suggest that the replacement of hemlock overstory with hardwood species will have minimal impact on long-term stream conditions, however disturbance during the transition is likely to have significant impacts. Management of riparian forests undergoing hemlock decline should, therefore, focus on facilitating a faster transition to hardwood-dominated stands to minimize long-term effects on water quality.

The Earliest Evidence of Ostionoid Maize Agriculture from the Interior of Hispaniola

Abstract. Considering the abundance of archaeological sites and the numerous archaeological surveys conducted throughout the Caribbean region, evidence of prehistoric cultivation of maize (Zea mays subsp. mays) is surprisingly rare. The rarity of botanical or other evidence of maize agriculture hampers efforts to chart the spread of this cultigen through the Caribbean and to understand its local and regional importance at different times. To better constrain and understand the biogeography and chronology of maize in the Caribbean we searched for evidence of maize agriculture in lake sediments from two mid-elevation lakes in the Dominican Republic, Laguna Castilla and Laguna de Salvador. The two sedimentary records contain abundant maize pollen dating back to around A.D. 1060. These prehistoric maize pollen grains constitute the earliest evidence of maize from the interior of Hispaniola and represent some of the earliest and most securely dated evidence of maize agriculture on the island of Hispaniola and from the Caribbean as a whole.

LABORATORY PRODUCTION OF VOUCHERED REFERENCE CHARCOAL FROM SMALL WOOD SAMPLES AND NON-WOODY PLANT TISSUES

Abstract Taxonomic identification of small fragments of burned plant tissue in lake sediment profiles can enhance reconstructions of past vegetation, fire regimes, and climate. Vouchered reference collections of charcoal prepared from both soft and woody plant tissues, analogous to modern pollen reference collections, will be required for making rigorous identifications and for knowing the level of certainty achieved. Published methods of laboratory production of charcoal may only poorly mimic pyrolysis as it occurs in wildfires, and tend to require large volumes of plant material. We present a method for preparing reference charcoal from dried plant specimens that is simple, provides a high degree of control, yet requires only small tissue samples. Based on results of a series of experiments, we recommend placing dried samples in 25 cm3 perforated-base porcelain Gooch filtering crucibles, surrounded by 250–500 µm sand; saturating the sand with water and draining; and placing for eight to nine minutes in a furnace heated to 550°C. The wet sand delays heating so that temperature rise is steep. Pyrolysis is brief and occurs under hypoxic conditions due to temporary oxygen flushing by water vapor. Using our method we achieved excellent results on both woody and soft tissues from a variety of plant taxa.

Modeling the Geography of Migratory Pathways and Stopover Habitats for Neotropical Migratory Birds

Intact migratory routes are critical for the stability of forest-dwelling, neotropical, migratory bird populations, and mortality along migratory pathways may be significant. Yet we know almost nothing about the geography of available stopovers or the possible migratory pathways that connect optimal stopovers. We undertake a spatial analysis of stopover habitat availability and then model potential migratory pathways between optimal stopovers in the eastern United States. Using models of fixed orientation and fixed nightly flight distance between stopovers during spring migration, we explore whether a simple endogenous migratory program is sufficient to ensure successful migration across the modern landscape. Our model runs suggest that the modern distribution of optimum stopovers in the eastern United States can be adequately exploited by birds following migratory pathways defined by fixed-orientation and fixed-distance nightly flights. Longer flight distances may increase the chances of success by enabling migrants to bypass locales offering little habitat. Our results also suggest that most southwest–northeast migratory pathways through the Appalachian mountains are intact. Lack of optimal habitat at key locations in the Southeast causes many modeled pathways to fail. We present a speculative view of regional migration patterns implied by predominant ideas found in stopover ecology literature, and demonstrate the need for broad-scale migration research, in the hope that our approach will foster other continentaland regional-scale projects.

Recent land use and vegetation history from soil pollen analysis; testing the potential in the lowland humid tropics

Abstract We investigated the potential of soil pollen analysis to provide information about recent land use and vegetation history in the lowland humid tropics. Our initial work at the La Selva Biological Station in Costa Rica revealed that pollen was surprisingly well preserved in mineral soil, with pollen concentrations in the upper 10 cm of our soil cores as high as values for some lake sediment samples. Pollen percentages in our initial core samples showed down‐core variations that appeared to relate to what we knew about past episodes of forest clearance, pasture establishment, and secondary succession at our sampling sites. We carried out further tests of soil pollen analysis by collecting and analyzing additional soil cores from the La Selva Biological Station. Based on these new results, we conclude that soil pollen analysis in the lowland humid tropics does not hold the promise suggested by our initial work. Most pollen in our soil cores may be only a few decades old, and rapid downwash and/ or b...

Modern surface pollen from three transects across the southern Sonoran Desert margin, northwestern Mexico

Surface pollen samples collected along three transects that cross the southern margin of the Sonoran Desert east of the Gulf of California reflect regional vegetation gradients but also show strong local variability, notably within the southern desert. Chenopodiaceae‐Amaranthaceae (Cheno‐Am) and Gramineae pollen dominate in tropical deciduous forest; Pinus and Quercus in temperate‐climate vegetation at high elevations; and Gramineae and High‐Spine Compositae in the central Sonoran Desert (>29° N). The ERA group (composed largely of Euphorbiaceae, Rutaceae, Anacardiaceae), Gramineae, Cheno‐Am, and High‐Spine Compositae pollen inter‐vary but dominate as a group in the southern desert; Cheno‐Am here may signal irrigated agriculture. Coastal sites differ from the above, with Cheno‐Am pollen strongly dominant in saline conditions.

High-Elevation Savanna Landscapes in the Cordillera Central, Dominican Republic, Hispaniola: Dambos in the Caribbean?

Abstract Headwater unincised savanna (sabana) landscapes in the Cordillera Central, Dominican Republic, have a vegetation cover dominated by the native tussock grass, Danthonia domingensis. Sites occur on gentle-relief upland surfaces approximately between 2000 and 2400 m, mainly in José del Carmen Ramírez National Park (JCR) and Juan B. Pérez Rancier National Park (JBPR). Surface and subsurface data from 1 site constrain regolith age overlying granitoid saprolite to <12,570 14C years BP. We conclude that the savannas studied are dambos that developed in response to environmental change during and after the Pleistocene–Holocene transition. Dambos elsewhere are widely regarded as reliable indicators of major Quaternary environmental change. Dambos have unique hydrological, ecological, scenic, and utilitarian attributes; their importance will increase with greater tourism, as will the concerns for their sustainable use. This first publication on dambos in the Caribbean signals the need for more research into their origin, evolution, and state of equilibrium.