No description available.

The hemlock-silverbell (Tsuga canadensis-Halesia tetraptera) forest type is known to exist in only two places, the Great Smoky Mountains National Park (GRSM) and the Joyce Kilmer National Memorial Forest. The hemlock component of this forest type is currently threatened by the hemlock woolly adelgid (Adelgis tsugae), an invasive aphid-like insect native to Japan. This current status has given rise to the need to investigate the ecological resources of this rare forest type before the hemlock component dies out. The objectives of this study were to determine the nature of the plant/environment and plant/plant associations within this forest type. Within this forest type hemlock was negatively related to protection, aspect, and slope steepness and silverbell was positively related to aspect and slope steepness. This study also identified some interspecific associations such as the negative relationship in the understory between hemlock and striped maple, and provided evidence that understory stems are exhibiting a growth response to hemlock decline in these stands. The information obtained from this study characterizing the plant/environment interactions and even the structural and species components of this forest type will serve as a baseline of data from which to measure change and will provide insight into the mechanisms of species distribution and perhaps into short term scenarios of forest response to hemlock decline and mortality.

Adelges tsugae Annand is a non-native invasive insect threatening the survival of eastern hemlock (Tsuga canadensis) and Carolina hemlock (T. caroliniana). A. tsugae is established in over half of the total range of eastern hemlock and the entire range of Carolina hemlock. Its continued spread, establishment and associated hemlock mortality make research into biological control of A. tsugae crucial. Field surveys of predators associated with A. tsugae in the Pacific Northwest identified a strong correlation between A. tsugae abundance with Laricobius nigrinus and two species of silver fly, Leucopis argenticollis and Leucopis piniperda. Flies in the genus Leucopis are known specialist predators of adelgids and recent studies have shown a strong synchronization between the lifecycles of Leucopis spp. and A. tsugae. The purpose of this study was to test the potential establishment of Leucopis spp. at the southern and northern extent of A. tsugae infested eastern hemlock in eastern United States. In 2015 and 2016, western Leucopis spp. adults were released at two different densities into enclosed branches of A. tsugae infested T. canadensis in Tennessee and New York. A. tsugae on the branches were counted before putting on the enclosure. Four weeks after set-up, all of the enclosures were collected. The number of Leucopis spp. offspring were counted and then stored in ethanol. The number of Leucopis spp. offspring collected were positively related to adelgid density, but did not differ by the number of adult flies per enclosure. Flies collected from enclosures and from the source colony were identified as L.argenticollis and L. piniperda using DNA barcoding. These results show that Leucopis spp. from the Pacific Northwest feed and develop to the adult stage on A. tsugae in the eastern USA. They are able to tolerate environmental conditions during late spring and early summer at the southern and northern extent of the area invaded by A. tsugae in the eastern USA.

Breast height radial growth of 165 western red cedar (Thuja plicata Donn), 14.5 western hemlock (Tsuga heterophylla (Raf.) Sarg.) and 33 Douglas fir trees (Pseudotsuga menziesii (Mirb.) Franco), in young natural stands on the eastern side of the University of British Columbia Research Forest near Haney, B.C. was analysed. Individual tree parameters measured included breast height diameter, total height, age at breast height, radial growth over last five and ten years, crown width, live crown length, tree class, live crown ratio, height/age ratio, crown width/breast height diameter ratio, and height/ crown width. Stand parameters measured were number of trees per plot, average breast height diameter of plot, and basal area per acre of plot. Plots were of variable radius as determined in prism cruising. Growth was investigated from results of simple correlation coefficients and several multiple regression analyses computed on an IBM 7040. Causes of variation in growth were assessed by studying interaction of variables affecting growth patterns. Individual species have distinctly different modes of growth. Species react differently to changes in stand density. Radial growth can be determined from measurements of tree crowns; and crown development reflects changes in stand density. Difference between species are found as crown development varies with stand density changes. Crown dimensions of western hemlock are least sensitive to changes in stand density as measured by basal area per acre, crown width/breast height diameter, live crown ratio, or height/crown width. An understanding of how crown dimensions change with variation in stand density can be used to refine predictions of tree radial growth derived from crown measurements. / Forestry, Faculty of / Graduate

Western hemlock seedlings were grown for 8 months in a greenhouse with fertilizer amendments of N, P, N+P, and lime. Humus material was used as a growth medium. It was collected from low-productive sites identified by Lewis (1985) as the cedar-hemlock phase of the Thuja plicata - Tsuga heterophylla - Gautheria shallon - Rhytidiadelphusloreus ecosystem association unit designated as S1CH , on his ecosystem maps of Tree Farm Licences 6 and 25, which are located on northern Vancouver Island. A combination of 100 kg/ha N and 150 kg/ha P produced the most favourable seedling growth and foliar nutrient status. N or P added separately at these rates also gave superior seedling growth compared to the control. Neither lime, nor high rates of N (at 300 kg/ha with or without P) increased seedling growth. High N additions also restricted root development. N fertilization reduced foliar P concentrations, and P addition decreased foliar N concentrations. Foliar Mg concentrations increased when P fertilizers were added. N and/or P additions caused a decrease in foliar B concentrations. A combination of N and P increased foliar Zn concentrations and S, but reduced Mn absorption. Foliar R was inversely related to seedling productivity. Management recommendations for the S1CH sites include fertilizing with P, and increasing available N either by cultivation to increase mineralization or by low rates of N fertilization / Land and Food Systems, Faculty of / Graduate

Throughout the eastern United States, the spread of the hemlock woolly adelgid, Adelges tsugae Annand, has caused high mortality of eastern hemlocks Tsuga canadensis (L.). We recorded overwintering survival and fecundity of A. tsugae, and tree new growth at sites in the northeastern and southeastern United States and in a common garden experiment in Massachusetts. Overwintering mortality of A. tsugae was much higher in the north (87%) than the south (37%) in 2009, and showed significantly positive density-dependence in the north only. In 2010, overwintering mortality decreased in both regions but remained higher in the north (54%) than the south (34%), and, unlike 2009, density-dependent mortality was strongly negative in the north, and positive in the south. In both years, sistens fecundity was significantly higher in the south than the north, but we observed no density-dependent trends, and fecundity measurements were similar in the two years. The regional discrepancies in fecundity suggested the possibility of an evolutionary trade-off between overwintering mortality and sistens fecundity. However, when we reared samples in a common garden, we found that source region had no effect on either sistens fecundity or overwintering mortality, which suggests observed regional differences can be attributed to environmental factors rather than genetic differences. In our regional studies, branch samples from the north had significantly more new growth than those from the south in both 2009 and 2010, even though A. tsugae densities were comparable. This difference persisted in the common garden wherein branches inoculated with northern-derived A. tsugae had significantly higher new growth than those infested with southern-derived A. tsugae. These findings raise the possibility that A. tsugae may be evolving towards reduced virulence. If true, these findings may help explain why A. tsugae is killing hemlocks much more slowly now in New England than it did when it first invaded this region more than 20 years ago, or as it is doing now in more recently invaded regions in the southern United States.

Temperate mixed forests are complex ecosystems composed of multiple vegetation types with very different physiological characteristics which are distributed over the landscape. This dissertation investigates the influence of these mixed plant landscapes on eddy-covariance flux data, and in particular, uses an ecohydrological model to study the influence of climate variability and insect infestation on a mixed forest at the Harvard Forest Long Term Ecological Research site in Massachusetts. There are significant seasonal and interannual variabilities in the extent and the orientation of the footprints of a flux tower (EMS-tower) as the Harvard Forest. The Gross Primary Productivity (GPP) flux was found to be largely dependent on the vegetation density during the green-up and senescence periods, but not during the mature period. Half of the interannual anomalies in the mature period GPP flux can be explained by the variation in the proportion of coniferous evergreen needleleaf forest (ENF) in the footprint. Every 1% decrease of ENF resulted in the increase of the GPP flux by 20 gC m-2. The spatially-distributed process-based Regional Hydro-Ecological Simulation System (RHESSys) model was implemented in two headwater catchments at the Harvard Forest to simulate water and carbon cycles from 1992 to 2008. Results were evaluated using field measurements such as streamflow and the GPP and evapotranspiration (ET) fluxes at two flux towers. The simulated annual GPP flux of the deciduous forest showed strong and significant long-term increases, six times higher than the GPP flux of the coniferous forest, while the increase in ET flux of both forests was small yet significant. The Harvard Forest was infested by Hemlock Woolly Adelgid (HWA) between 2004 and 2008, and although there has not yet been a significant increase in the total annual mortality, the small stature stands have started to die off by 5.7%. The HWA infestation has already resulted in an increased streamflow in the catchment dominated by hemlock stands (44% in area). In 2014, the increased annual streamflow was estimated as 81 mm using the RHESSys model with an embedded representation of the HWA-induced loss of water conductivity (calibrated using the Hemlock tower ET flux).

No description available.

Competitive interactions among two specialist predators, <i>Laricobius nigrinus</i> Fender (Coleoptera: Derodontidae) and <i>Sasajiscymnus tsugae</i> Sasaji and McClure (Coleoptera: Coccinellidae), and a generalist predator, <i>Harmonia axyridis</i> Pallas (Coleoptera: Coccinellidae), of hemlock woolly adelgid were evaluated using laboratory, field and video studies. The two specialist predators are part of a biological control program for <i>A. tsugae</i>, and the potential for competition among these species and previously established generalist predators is unknown. In laboratory studies of predator groups in Petri dish assays, the only significant negative effects from competition occurred among conspecifics, resulting in reduced net egg production by <i>L. nigrinus</i> and <i>H. axyridis</i> and reduced feeding by <i>H. axyridis</i>. In contrast, heterospecific combinations showed non-interference. In longer duration field studies of predator groups, held in branch enclosures, predator survival and feeding were not significantly affected by additional predators. Net reproduction was again significantly reduced by conspecifics, while heterospecifics showed non-interference for all predator responses. All predators reduced the number of <i>A. tsugae</i> nymphs of the next generation relative to no-predator controls; however, <i>L. nigrinus</i> had much greater impact overall due to the large number of progeny produced. Video studies revealed that predator behavior varied qualitatively and quantitatively by species, and did not appear to be coordinated temporally or spatially. All species exhibited continuous activity patterns that were punctuated by longer periods of rest. The specialist predators were more selective of feeding and oviposition sites, and rested at more concealed locations than <i>H. axyridis</i>. Conspecifics significantly altered the time allocated to specific behaviors for <i>L. nigrinus</i> and <i>H. axyridis</i>, resulting in reduced predator effectiveness due to increased searching and decreased feeding and oviposition. All predator groups maintained a high degree of spatial separation relative to assay size, suggesting that chemical or tactile cues may be used to regulate their distributions. Overall, these studies suggest that the three predator species will be compatible in this system. Management implications include using multiple-predator species combinations over single-species for biological control of <i>A. tsugae</i> and implementing low-density releases to reduce the potential negative effects of intraspecific competition. / Ph. D.

Laricobius nigrinus is an insect predator introduced into the eastern United States for the biological control of hemlock woolly adelgid, Adelges tsugae. Laricobius nigrinus dispersal characteristics and predation on A. tsugae were evaluated by monitoring its immature life stages that were distinguished from larvae of the native, L. rubidus using a portion of the cytochrome oxidase subunit one gene. Conventional polymerase chain reaction (PCR) followed by restriction fragment length polymorphism produced DNA fragment sizes that were unique to each species. Real-time PCR used a TaqMan assay with two species-specific nucleotide sequence probes labeled with fluorescence molecule VIC or FAM that indicated the DNA template was L. nigrinus or L. rubidus, respectively. Laricobius nigrinus beetles released in the lower hemlock crown (< 7 m) dispersed to the upper crown (>15 m) for oviposition. Four years post-release, its rate of spread into the surrounding forest was 75 m/yr and the number of L. nigrinus detected on hemlock trees was positively correlated with the density of A. tsugae, regardless of proximity to the release area. Adelges tsugae survival rate was lower on release trees than on geographically separated control trees for three years at a L. nigrinus release site in each Pennsylvania and North Carolina. Yet, the density of A. tsugae remained greater on release trees than control trees. In the eastern United States, the average density of A. tsugae was 3.8 times greater than the upper 95% confidence interval in the native range of L. nigrinus and A. tsugae, as observed in Seattle, WA. This contributed to the average ratio of predator to prey remaining 4.6 times lower than the 95% confidence interval observed in WA. Five to seven years post-release, hemlock health of release and geographically separated control trees declined at similar rates, though the average A. tsugae infestation level was 35% greater on release trees at the time of L. nigrinus release. The full efficacy of L. nigrinus predation was likely underestimated because this study assessed experimental release sites. Interactive roles of biotic and abiotic pressures on A. tsugae should continue to be evaluated at L. nigrinus introduction sites. / Ph. D.