Bird Diversity and Composition in Even-Aged Loblolly Pine Stands Relative to Emergence of 13-year Periodical Cicadas and Vegetation Structure
In southern Arkansas, l&year periodical cicadas (Magicicada spp.) were expected to emerge in late April and early May of 1998. Presence of a superabundant food source, such as periodical cicadas, may attract greater numbers of b i r d s a n d m o r e s p e c i e s o f b i r d s t h a n i s u s u a l l y p r e s e n t i n a p a r t i c u l a r a r e a . T h r e e e v e n a g e d l o b l o l l y p i n e (Pinus faeda L . ) stands were surveyed for birds by using a fixed-width transect before, during, and after emergence of the periodical c i c a d a s . E m e r g i n g c i c a d a n y m p h s w e r e t r a p p e d a n d c o u n t e d t o o b t a i n a n e s t i m a t e o f c i c a d a d e n s i t y . T h e d e n s i t y o f cicadas in these pine stands was considerably lower than densities reported for other forest stands in the Eastern U.S. Bird d i v e r s i t y w a s v a r i a b l e b e t w e e n m o n t h s a n d s t a n d s b u t d i d n o t a p p e a r t o b e s t r o n g l y i n f l u e n c e d b y t h e p r e s e n c e o f p e r i o d i c a l c i c a d a s . B i r d c o m p o s i t i o n i n t h e s e m a n a g e d l o b l o l l y p i n e s t a n d s w a s s i m i l a r t o t h a t i n u n m a n a g e d , e v e n a g e d p i n e a n d p i n e / h a r d w o o d s t a n d s o f s i m i l a r a g e s . INTRODUCTION Emergence of periodical cicadas (Homoptera: Cicadidae: Magicicada) is a highly predictable occurrence. The l3-year race of periodical cicadas that occurs in Arkansas is a group of three species including Magicicada tredecim (Walsh and Riley), M. tfedecassirti (Alexander and Moore), and M. tredecula (Alexander and Moore). Adult cicadas synchronously emerge from the ground every 13 years, ascend the nearest tree, and cast their nymphal skin. Adult males aggregate in the forest canopy and form chorusing centers to attract females for mating (Williams and Smith 1991). Adults complete their reproductive cycle and die within 4 to 6 weeks. Adult populations of periodical cicadas can be very dense. Populations in previous emergences have been estimated at tens of thousands to hundreds of thousands of individuals per acre (Dybas and Davis 1962, Rodenhouse and others 1997, White and others 1962). This type of ephemeral, high density occurrence of insects can provide a superabundance of food that may attract greater numbers and more species of insectivorous birds than is usually present in a particular location. In this study, we investigated the influence of 13-year periodical cicadas on bird diversity in even-aged stands of loblolly pine (Pinus taeda L.) in southern Arkansas where periodical cicadas were observed during a previous emergence (personal observation, M.D. Cain, 1985). The study also provided an opportunity to examine bird composition relative to vegetation structure of loblolly pine stands that were managed to maximize pine development. Others have examined bird composition relative to vegetation structure in unmanaged, even-aged pine and pine/hardwood stands (Childers and others 1986, Conner and others 1979, Conner and others 1983, Dickson and Segelquist 1979, Kellner 1996), but this information is lacking for managed stands. Recent concern over declining populations of neotropical migratory songbirds and an increasing interest in managing forests at the ecosystem level warrants an examination of bird communities inhabiting forests managed for timber production (Finch and Stangel 1993). METHODS Study Sites Three plots were surveyed for birds and cicadas on the Crcssett Experimental Forest, Ashley County, Arkansas. Merchantable-sized trees (a3.5 in. d.b.h.) on all plots were primarily loblolly pine, but a few shortleaf pine (Pinus echinafa Mill.) and assorted hardwood species were present. Plot 5 is a 1 O-acre, 25year-old stand measuring 1,320 ft long and 330 ft wide. This stand was precommercially and commercially thinned and periodically prescribe burned in winter (Cain 1996). Burning was initiated in the ninth year to control understory vegetation. The most recent bum was conducted in February 1998. Plot 5 also had patches of unmanaged pine and openings that supported grasses and forbs. Plots 37N and 37s are both 15-year-old loblolly pine stands. Plot 37N is 1,000 ft long and 165 ft wide (3.8 acres), and plot 37s is 660 ft long and 330 ft wide (5.0 acres). As part of one ongoing study, plots 37N and 37s have been similarly managed (Cain 1997). Both plots were precommercially and commercially thinned and competing vegetation was controlled with herbicides, manual removal, or both during the first 5 years of pine development. These two plots also had patches of unmanaged pine. All plot boundaries were well-defined by mowed fire lanes. Bird Survey Birds were surveyed using a fixed-width transect (Mikol 1980). A transect was established through the center of each plot. Bird surveys were conducted along each transect for 2 days each in early-April, mid-May, and mid-June of 1998. Each 2-day survey was completed within a 4-day period. All birds detected by sight or sound within the plot boundary were recorded and plotted on a map as the observer slowly traversed the transect. In addition, all birds detected within 80 ft outside the plot boundary were recorded and mapped for two reasons. First, birds were not confined to our artificially-defined boundaries. Second, birds in the periphery were observed using the study plots. ’ P a p e r p r e s e n t e d a t t h e T e n t h B i e n n i a l S o u t h e r n S i l v i c u l t u r a l R e s e a r c h C o n f e r e n c e , S h r e v e p o r t , L A , F e b r u a r y 1 6 1 8 , 1 9 9 9 . ’ Biological Science Technician and Research Forester, USDA Forest Service, Southern Research Station, P.O. Box 3516, Monticello, AR 71656,
Relationships Between Bird Communities and Forest Age, Structure, Species Composition and Fragmentation in the West Gulf Coastal Plain
-Bird communities of the West Gulf Coastal Plain are strongly influenced by the stage of forest succession, species composition of understory and overstory vegetation, and forest structure. Alteration of plant communities through forest management and natural disturbances typically does not eliminate birds as a fauna1 group from the area affected, but will replace some species with others and cause changes in the abundance and species composition of bird communities. Upland, tire disclimax pine Savannah communities composed of primarily longleaf pine (Pinuspalustris) provide mature pines for Red-cockaded Woodpeckers (Picoides borealis) and Brown-headed Nuthatches (Sitta pusilla) while simultaneously providing grassland ‘ground cover for Bachman’s Sparrows (Airnophila aestivalis) and Henslow’s Sparrows (Ammodramus henslowii). On the mesic mid-slopes where there is an increasing presence of loblolly (P’tnus taeda) and shortleaf (Pinus echinata) pine and hardwood species, Northern Cardinals (Cardinalis cardinalis) and White-eyed Vireos (Vireo griseus) find habitat in the understory and midstory vegetation, whereas canopy hardwoods and pines provide habitat for Red-eyed Vireos (Vireo olivaceus) and Summer Tanagers (Piranga rubra). Transition into the wet bottomland hardwood forests increases the abundance of bird species associated with deciduous wetlands such as Prothonotary Warblers (Protonotaria citrea) and Swainson’s Warblers (Limnothlypis swainsonii), whereas species associated with conifers and grassland savannahs are lost. Anthropogenic or natural disturbances that set back mature stages of forest succession can dramatically alter the species composition of bird communities. Depending on patch size, forest removal can initiate forest succession and provide habitat for early succession bird species such as Blue Grosbeaks (Guiraca caerulea), Field Sparrows (Spizella pusilla), Prairie Warblers (Dendroica discolor), Painted Buntings (Passerina ciris), Indigo Buntings (Passerina cyanea), and Yellow-breasted Chats (Icteria virens). Although current data are inconclusive, patch size, forest fragmentation, edge effect, and landscape use patterns appear to influence bird communities by affecting area-sensitive species. Of greatest concern are forest-interior bird species that appear to be area sensitive such as the Cerulean Warbler (Dendroica cerulea), Northern Panda (Parula americana), Louisiana Waterthrush (Seiurus motacilla), American Redstart (Setophaga ruticilla), and Worm-eating Warbler (Helmitheros vermivorus). Forest bird communities of the West Gulf Coastal Plain are influenced primarily by forest age and structure, and tree species composition. Across the forest landscape, anthropogenic effects, that determine the spatial mosaic of forest age-classes and size of forest patches, also influence avian species composition and abundance. Seasonally, bird communities in the West Gulf Coastal Plain are affected by spring influx 124 THETEXASJOURNALOFSCIENCE-VOL,49(3)SUPPLEMENT, 1997 and departure of nearctic and neotropical migrants as they arrive from southerly latitudes to establish breeding territories, or stop briefly to feed and then quickly depart for more northerly breeding grounds. Until the mid 18OOs, the landscape of eastern Texas was primarily forest habitat with longleaf pine ecosystems dominating the frequently burned upland sites, bottomland hardwood forests in the lower mesic to wet sites, and loblolly and shortleaf mixed-pine hardwood forests spanning a dynamic zone between the sites of moisture extremes (Maxwell & Baker 1983; Walker 1991). During the late 1800s the rate of timber harvesting in the West Gulf Coastal Plain increased dramatically. A “bonanza era” of timber harvesting occurred from 1880 to 1930 which eliminated the majority of old-growth forests in eastern Texas (Maxwell & Baker 1983; McWilliams & Lord 1988). Upland pine forests and bottomland hardwood forests were both heavily logged. Some of the cut-overforest lands were reforested by artificial planting, some by natural seeding, while other lands were converted to agricultural uses and reservoirs (Truett & Lay 1984; Walker 1991). Thus, the present-day forests that provide habitat for bird communities are secondgrowth forests, which have again been affected by harvesting during the past several decades (McWilliams & Lord 1988). This paper presents an abbreviated glimpse of general relationships between birds and their habitats using selected species as illustrations. Our objective is to demonstrate that avian communities are variable, but are also dependent on forest stand age, tree species composition, season, special habitat features such as snags, and the mosaic of age classes across the forest landscape that affect forest fragmentation. Relationships between selected sensitive species, loss of old-growth habitat, and forest fragmentation will also be examined. THE INFLUENCE OF FOREST STAND A GE ON AVIAN CO M M U N I T I E S Timber harvesting, and largeand small-scale natural disturbances greatly affect the species composition of bird communities. Typically in the South, species are not eliminated from the forest landscape, but are temporally replaced by others as timber stand age is affected by forest management and natural forest succession (Odum 1950; Conner & Adkisson 1975; Conner et al. 1979; Dickson et al. 1993a; 1993b). Early succession seres created by disturbances such as wind throw, bark beetle infestation, or timber harvesting provide breeding habitat for field CONNER & DICKSON 125 EARLY SUCCESSION SPECIES
Noctilucent cloud observations over Greenland by a Rayleigh lidar
We report on the detection of noctilucent clouds (NLCs) by a Rayleigh lidar system located on the west coast of Greenland during operations in July and August 1994. The lidar detected NLCs in the zenith on three nights (July 28–29, July 31–August 1, and August 4). The lidar measurements are presented at temporal (1 minute) and spatial (192 meter) resolutions exceeding previously reported lidar measurements of NLCs and reveal significantly more structure in the clouds. Unique cloud features are observed for each night NLCs were detected. Because of the large backscatter ratio associated with NLCs, the volume backscatter coefficient for the cloud particles can be determined more accurately from the lidar signal than the backscatter ratio as the upper mesospheric molecular number density is negligible in the volume backscatter coefficient calculation. The volume backscatter coefficient values determined from the three nights of NLC observations would be classified by current models as moderate to extreme. The extreme backscatter from NLC measurements on August 4 tests the assumptions used in existing models.