Woody Ground Cover Research Articles

Sedimentary n-alkanes and n-alkanoic acids in a temperate bog are biased toward woody plants

Sedimentary plant waxes and their hydrogen and carbon (δ2H and δ13C) isotopes are important proxies for past hydrologic and vegetation change. However sedimentary waxes accumulate from diverse sources, integrating uncertainties from: (i) variable isotope fractionation among plant species, and (ii) unresolved processes controlling the transport of waxes from plants to sediments. We address these uncertainties by comparing the molecular and isotopic composition of n-alkanes and n-alkanoic acids in recent bog sediments with all major plant species growing in the catchment of Browns Lake Bog (BLB) in Ohio, USA. There are two distinct plant assemblages at BLB, including a forest dominated by trees and a bog shoreline composed of shrubs, woody groundcover, herbs and graminoids. n-Alkane concentrations in trees were 10–300 times higher than in shoreline plants, while n-alkanoic acid concentrations were generally lower and comparable across all species. The overall range of wax δ2H values among individual plants (77‰ for n-C29 alkane and 84‰ for n-C28 alkanoic acid) was likely driven by interspecies differences in biosynthetic δ2H fractionation as well as source water differences between forest and shoreline plants. A considerably smaller range of δ2Hwax values in the bog sediments (9‰ for n-C29 alkane and 11‰ for n-C28 alkanoic acid) suggests that sediments are either biased toward specific plants, or that signal averaging processes during or after deposition are constant. The combined δ2H and δ13C signatures of plant sources and sediments indicate a sediment bias mainly toward trees, with contributions from woody shrubs and groundcover growing in the bog shoreline. Within trees and woody shrubs, we observed δ2Hwax–δ13Cwax relationships of opposite sign for n-C29 alkane and n-C28 alkanoic acid, which we speculate may reflect contrasting seasonal timing of synthesis and plant metabolic status between compound classes. The net apparent δ2H fractionation between precipitation and wax (εapp) was approximately 30‰ larger for n-alkanes (−133‰) than for n-alkanoic acids (−103‰), both at the plant level and in sediments. These results demonstrate the sensitivity of sediments in a hydrologically closed basin to woody plants growing in the associated catchment and can guide εapp estimates for sedimentary records from similar depositional settings.

Survival, Movements, and Habitat Use of Fledgling Veeries (Catharus fuscescens) in Northeastern Pennsylvania

For most passerines, survival and behavior during the postfledging period are poorly known, even though these population characteristics are potentially important to demography and conservation. In 2013–2014 radiotelemetry was used to measure survival, movements, and habitat use of juvenile Veeries (Catharus fuscescens) during the postfledgingdependent period in a landscape dominated by mature forest in northeastern Pennsylvania. In total I tracked 29 juvenile Veeries and conducted habitat sampling at sites used by fledglings and at associated random sites. Survival during the first 21 d postfledging was high (0.78), with most mortalities occurring during the first 7 d, and all deaths attributed to predation. Fledglings moved gradually away from their nests as they aged, averaging 333±62 m by 19–21 d. However, there was much variation in movement patterns among individuals, perhaps reflecting differences in spatial distribution of important microhabitats or differences in timing of postfledging dispersal. Like fledglings of many other species of forest passerines, Veery fledglings preferred microhabitats with dense woody understory vegetation: compared to random sites, sites used by fledglings had, on average, greater woody ground cover, midstory cover, and sapling density but had lower density of eastern hemlock trees. However, unlike many other forest passerine species, Veery fledglings did not exhibit broad shifts to other nonnesting habitat types. These results provide the first detailed study of postfledging survival and behavior of the Veery and add generally to our understanding of postfledging ecology in forest passerines.

Habitat selection differs across hierarchical behaviors: selection of patches and intensity of patch use

AbstractWhen animals select habitats, they integrate a suite of behaviors that are influenced by multiple competing resource requirements. Resources that influence decisions about habitat use are likely to differ across spatial scales and hierarchical behaviors. At coarser scales, animals are expected to select resources that are critical to fitness, and at finer scales, to intensively use resources that enhance fitness. Our goal was to contrast habitat selection at two hierarchical behavioral levels (patch selection and intensity of patch use) to test hypotheses about how resources shape habitat use. We applied a two‐stage hurdle model to quantify both initial selection and intensity of use of resource patches by a burrowing herbivore, the pygmy rabbit (Brachylagus idahoensis). We expected security from predation to influence initial selection of patches, and forage availability to influence intensity of use of selected patches. We monitored locations of adults fitted with radio‐collars during winter and summer. We measured vegetation, burrow characteristics, and concealment cover within patches that were used and unused by rabbits, and we quantified burrow densities surrounding patches in a GIS. Selection of used patches from available patches was largely influenced by security resources (presence and proximity of burrows, shrub height, and woody ground cover) during both seasons. Intensity of patch use was also influenced by forage availability and, consequently, differed between seasons. During winter, sagebrush is the primary forage, and greater sagebrush canopy within a patch was associated with increased intensity of use. During summer, rabbits more intensively used patches with greater availability of herbaceous forage. Elucidating how animals make choices about habitats across a diversity of spatial and temporal scales will continue to increase our understanding of the factors that govern distribution of populations and movements of individuals. By extending these concepts to hierarchical behaviors, we can enhance insights into the processes that shape the patterns of habitat use we observe.

Multi-scale responses of fox squirrels to land-use changes in Florida: Utilization mimics historic pine savannas

Pine savanna ecosystems in the southeastern United States are highly fragmented and degraded. Within these ecosystems, southeastern fox squirrels (Sciurus niger spp.) appear to be excellent bioindicators and serve important ecological roles. However, because of the loss of these areas, fox squirrel populations are patchily distributed and they are thought to be declining. To determine factors influencing their distribution, we conducted a multi-scale occupancy study throughout the range of the Sherman’s fox squirrel (S. n. shermani) in Florida. We surveyed 40 landscapes comprised of 200 grids and 1800 camera-trap points. We recorded 3170 camera-trap photos of fox squirrels at 8 of the 21 land cover classes surveyed, at 26 landscapes (65.0%), 70 grids (35.0%), and 210 of the camera-trap points (11.7%). At the landscape scale (7.65km2), the occurrence of fox squirrels increased as the amount of interspersion in tree cover increased, but decreased with increasing tree cover, supporting the need for open canopied areas interspersed with hardwoods and hardwood thickets at broad scales. At the finer grid scale (5.3ha), their occurrence increased with pine and oak densities and proximity to urban and residential development and was also negatively influenced by tree cover. At the grid and point scales, fox squirrels were more likely to occur in areas with increased canopy closure, supporting their association with patches of oak trees imbedded in open canopy forests similar to the pine savannas that once dominated the region. Fox squirrels’ occurrence was negatively influenced by woody understory and woody ground cover at all scales. Their preference for a midstory with an open canopy and clear understory also suggest a reliance on frequent disturbance such as fire to maintain their habitat. Fox squirrels appear to be highly adaptable as they occurred in land cover types and altered landscapes (e.g., developed, agriculture) outside of natural pine savannas. But, as indicators of pine savanna ecosystem health, their conservation along with other wildlife tied to these forests will necessitate management practices that include or emulate a fire regime to reduce tree canopy densities and the encroachment of the understory layer and woody ground cover, but also to maintain heterogeneity that intersperses requisites (food, shelter, and cover) across the landscape.

Impacts of Short-Rotation Early-Growing Season Prescribed Fire on a Ground Nesting Bird in the Central Hardwoods Region of North America.

Landscape-scale short-rotation early-growing season prescribed fire, hereafter prescribed fire, in upland hardwood forests represents a recent shift in management strategies across eastern upland forests. Not only does this strategy depart from dormant season to growing season prescriptions, but the strategy also moves from stand-scale to landscape-scale implementation (>1,000 ha). This being so, agencies are making considerable commitments in terms of time and resources to this management strategy, but the effects on wildlife in upland forests, especially those dominated by hardwood canopy species, are relatively unknown. We initiated our study to assess whether this management strategy affects eastern wild turkey reproductive ecology on the Ozark-St. Francis National Forest. We marked 67 wild turkey hens with Global Positioning System (GPS) Platform Transmitting Terminals in 2012 and 2013 to document exposure to prescribed fire, and estimate daily nest survival, nest success, and nest-site selection. We estimated these reproductive parameters in forest units managed with prescribed fire (treated) and units absent of prescribed fire (untreated). Of 60 initial nest attempts monitored, none were destroyed or exposed to prescribed fire because a majority of fires occurred early than a majority of the nesting activity. We found nest success was greater in untreated units than treated units (36.4% versus 14.6%). We did not find any habitat characteristic differences between successful and unsuccessful nest-sites. We found that nest-site selection criteria differed between treated and untreated units. Visual concealment and woody ground cover were common selection criteria in both treated and untreated units. However, in treated units wild turkey selected nest-sites with fewer small shrubs (<5 cm ground diameter) and large trees (>20 cm DBH) but not in untreated units. In untreated units wild turkey selected nest-sites with more large shrubs (≥5cm ground diameter) but did not select for small shrubs or large trees. Our findings suggest that wild turkey have not benefited from the reintroduction of prescribed fire to the WRERA.

Understory plant biomass dynamics of prescribed burned Pinus palustris stands

Longleaf pine (Pinus palustris Mill.) forests are characterized by unusually high understory plant species diversity, but models describing understory ground cover biomass, and hence fuel load dynamics, are scarce for this fire-dependent ecosystem. Only coarse scale estimates, being restricted on accuracy and geographical extrapolation, are available. We analyzed the dynamics of ground cover biomass under different prescribed burning regimes in longleaf pine stands in the southeastern United States. We developed a set of functions to simulate ground cover biomass dynamics in stands of varying age, basal area and fire management history. The subsequent models allow for estimation of ground cover biomass for unburned stands and living woody and herbaceous ground cover biomass for burned stands. Woody ground cover was highly reduced as fire frequency increased, and also affected by stand basal area when time since last burning was longer than two years. Herbaceous ground cover was affected little by burning frequency but was reduced as basal area increased. This novel model system is a useful tool that can be incorporated into fire management and carbon balance models.

Box Huckleberry Roots at Highest Percentages From Softwood Stem Cuttings

Box huckleberry [Gaylussacia brachycera (Michx.) Gray] is a slow-growing, dwarf evergreen woody groundcover that is native to both the mountains and coastal plains of eight states in the mid-Atlantic region of the United States. It grows as a low, dense, spreading mat and is affected by few major disease or insect pests. While uncommon in the wild, it has potentially high ornamental value as an evergreen groundcover, growing well in dry shade and acidic soil. Unfortunately, knowledge on the optimal asexual propagation of box huckleberry is lacking. In order to identify optimal propagation timing, we took stem cuttings from five genotypes of box huckleberry every month for two years. Although some genotypes differed, on average 90% or more of the cuttings rooted for those taken during May to July, 30% or fewer for September to December cuttings, and 40 to 70% for cuttings taken in other months. Cuttings generally formed roots faster in months with a higher rooting percentage. Based on these results, the best time to take stem cuttings for box huckleberry propagation is late spring to early summer which corresponds to softwood or semi-hardwood growth.

Disturbance Type and Plant Successional Communities in Bahamian Dry Forests

ABSTRACTDifferent disturbances in similar habitats can produce unique successional assemblages of plants. We collected plant species composition and cover data to investigate the effects of three common types of disturbances—fire, anthropogenic clearing (‘cleared’), and clearing followed by goat grazing (‘cleared‐and‐grazed’)—on early‐successional coppice (dry forest) community structure and development on Eleuthera, Bahamas. For each disturbance type, both the ground layer (&lt;0.5 m height) and shrub layer (&gt;0.5 m height) were sampled in eight patches (&gt;1 ha) of varying age (1–28 yr) since large‐scale mature coppice disturbance. Overall, plant communities differed among disturbance types; several common species had significantly higher cover in the shrub layer of fire patches, and cleared‐and‐grazed patches exhibited higher woody ground cover. Total percent cover in the shrub layer increased in a similar linear fashion along the investigated chronosequence of each disturbance type; however, cover of the common tree species, Bursera simaruba, increased at a notably slower rate in cleared‐and‐grazed patches. The pattern of increase and subsequent decrease in cover of Lantana spp. and Zanthoxylum fagara in the shrub layer was characterized by longer persistence and higher covers, respectively, in cleared‐and‐grazed patches, which also exhibited low peak cover and fast decline of nonwoody ground cover. Our results suggest that goats may accelerate some aspects of succession (e.g., quickly removing nonwoody ground cover) and retard other aspects (e.g., inhibiting growth of tree species and maintaining early‐successional shrubs in the shrub layer). These effects may lead to different successional trajectories, and have important conservation implications.

Are vegetation—environment relationships different between herbaceous and woody groundcover plants in barrens with shallow soils?

The extent to which woody vegetation exhibits more expansive community structures and different relationships with environmental variables than herbaceous plants is poorly understood in savannas and barrens worldwide, especially those with shallow soils. We explored this question in oak barrens, which are savanna habitats characterized by shallow soils, in southern Ohio, USA. Groundcover plant aerial cover and environmental data were collected using 75 randomly located 1-m2 quadrats in 3 barrens. A combination of non-metric multidimensional scaling (NMDS) and β-flexible cluster analysis revealed 3 distinct herbaceous plant assemblages that varied in abundances of C4 and C3 graminoid species and several forbs. Herbaceous vegetation patterns were correlated with soil acidity, soil depth, plant available water, and especially soil organic matter and quadrat slope. By contrast, woody plants were more widely distributed than herbs, and woody vegetation patterns were strongly correlated only with soil organic matter, although they were weakly associated with quadrat slope and an index of tree influence. The expansion of woody plants into barrens is likely not restricted by most edaphic factors; thus, barrens are highly susceptible to woody plant encroachment that has been fostered by anthropogenic alterations to natural fire regimes (suppression, dormant season fires). We hypothesize that fires that are intended to mimic natural lightning fires during the growing season will be most effective in deterring woody plant encroachment.

Beach Dune Sand Hydrophobicity Due to the Presence of Beach Vitex (Vitex rotundifolia L. f.)

Conservation and preservation concerns have led to efforts to understand mechanisms of invasiveness and the effects these mechanisms have on the environment. Vitex rotundifolia L. f. [beach vitex (BV)] was introduced as a salt-tolerant woody ground cover, but it has since become invasive on primary and secondary dunes in coastal areas of the southeastern United States. Much of its invasive potential may be the result of intense substrate hydrophobicity underneath established stands, which is believed to prohibit seedling establishment by other plants including native plant species. This research was conducted to better understand BV-induced sand hydrophobicity by carrying out dune surveys of BV-infested areas of the South Carolina coast, identifying the compounds responsible for this activity via chemical analysis, and quantifying hydrophobicity persistence by resampling sites following removal of above-ground BV. The findings indicated that sand under BV cover was significantly hydrophobic, that cuticular alkanes from leaves and fruits were responsible for this hydrophobicity, and that extreme substrate hydrophobicity persisted for >3 years following BV removal.

Drought during canopy development has lasting effect on annual carbon balance in a deciduous temperate forest

* Climate change projections predict an intensifying hydrologic cycle and an increasing frequency of droughts, yet quantitative understanding of the effects on ecosystem carbon exchange remains limited. * Here, the effect of contrasting precipitation and soil moisture dynamics were evaluated on forest carbon exchange using 2 yr of eddy covariance and microclimate data from a 50-yr-old mixed oak woodland in northern Ohio, USA. * The stand accumulated 40% less carbon in a year with drought between bud-break and full leaf expansion (354 +/- 81 g C m(-2) yr(-1) in 2004 and 252 +/- 45 g C m(-2) yr(-1) in 2005). This was caused by greater suppression of gross ecosystem productivity (GEP; 16% = 200 g) than of ecosystem respiration (ER; 11% = 100 g) by drought. Suppressed GEP was traced to lower leaf area, lower apparent quantum yield and lower canopy conductance. The moisture sensitivity of ER may have been mediated by GEP. * The results highlight the vulnerability of the ecosystem to even a moderate drought, when it affects a critical aspect of development. Although the drought was preceded by rain, the storage capacity of the soil seemed limited to 1-2 wk, and therefore droughts longer than this are likely to impair productivity in the region.

Effects of Reintroduction of Fire into Fire Suppressed Coastal Scrub and Longleaf Pine Communities Along the Lower Gulf Coastal Plain

The Northwest Florida coastal landscape consists of a mosaic of sand pine scrub, longleaf pine, and ecotonal communities. Fire suppression has altered the structure and composition of these communities. The effects of environmental variation and the recent reintroduction of fire on plant distribution and abundance across this landscape were investigated. Relative cover of herbaceous and woody ground cover species and density of sapling and canopy trees along with elevation, percent bare ground, percent canopy cover, and litter depth were determined in burned and long-unburned treatments for all community types. Canonical correspondence analysis (CCA) identified elevation and time since fire as the most influential environmental variables for species distribution and abundance. Species most closely associated with lower sites included Gaylussacia mosieri Small, Ilex glabra (L.) Gray, Kalmia hirsuta Walt., Magnolia virginiana L., Pinus palustrus P. Mill., Vaccinium myrsinites Lam., Aristida L. species, and Calamovilfa curtissii (Vasey) Schribn.. Species associated most closely with higher sites included Ilex vomitoria Ait., Quercus chapmanii Sarg., Quercus geminata Small, Quercus myrtifolia Willd., Vaccinium stamineum L., Baptisia lanceolata (Walt.) Ell., Cladonia Hill ex P. Browne species, Eriogonum tomentosum Michx., Rhynchospora megalocarpa Gray, and Yucca filamentosa L. Eight months post fire, burned sites had lower density of woody overstory and saplings compared to long-unburned sites. Herbaceous species richness did not differ between burned and long-unburned sites. Repeated prescribed fires during the growing season and direct seeding may be needed to promote flowering and establishment of additional herbaceous species.

A Comparison of Planted Loblolly Pine (Pinus taeda) Growth in Areas Receiving Different Levels of Establishment Regime Intensity

Management intensity of southeastern US pine (Pinus spp.) plantations has increased during past decades, emphasizing timber production. Managers need more information about tree growth responses to different establishment intensities to successfully meet their economic and ecological objectives. We established a comparison of five loblolly pine (P. taeda) plantation establishment regimes in the Mississippi Lower Coastal Plain (LCP, n = 4), using a gradient of mechanical and chemical site preparation and herbaceous weed control intensities. Treatments varied from “low intensity” to “high intensity” and were expected to produce a gradient in vegetative and pine growth response. We monitored herbaceous and woody ground cover, woody stem density, pine survival, and pine growth during years one and two post-treatment (2002 and 2003). Herbaceous cover, woody cover, and woody stem density decreased as treatment intensity increased. Pine survival was less on Treatment 5 and decreased slightly on all treatments during 2003. Pine height and diameter increased as treatment intensity increased, except for the treatment with no mechanical preparation, indicating the importance of subsoiling and bedding in the LCP. After two growing seasons, a combination of mechanical and chemical site preparation followed by one or two years of broadcast herbaceous weed control maximized pine growth.

Effects of forest structure on the distribution of southern flying squirrels (Glaucomys volans) in urban parks

Although southern flying squirrels (Glaucomys volans) are present in many urban parks, squirrel-habitat relationships in such areas are poorly understood, limiting conservation efforts. Our objective was to quantify the effects of forest structure at multiple scales on flying squirrel distribution in New York City (NYC) parks. From 18 June–24 August 2001, we captured flying squirrels in 5 New York City parks and measured forest structure at the ground, shrub, understory, and overstory levels at trap sites. To examine the importance of forest structure to squirrels, we compared (1) habitat variables between trap stations where squirrels were captured and not captured and (2) habitat variables between parks with and without documented squirrel populations. Our data suggest that areas with forests containing smaller trees at higher densities, dense woody ground cover, and little herbaceous ground vegetation may not provide the food, cavities, ease of movement, or allow predator detection necessary to be used by or support flying squirrel populations. Other factors, such as the size and density of stumps and snags may be important to non-urban squirrel populations, but not populations in NYC parks. Because NYC parks contain almost all of the remaining woodlands within the City, forests within these areas should be a conservation priority.