Potential Host Trees Research Articles

Local population extinction and vitality of an epiphytic lichen in fragmented old‐growth forest

The population dynamics of organisms living in short-lived habitats will largely depend on the turnover of habitat patches. It has been suggested that epiphytes, whose host plants can be regarded as habitat patches, often form such patch-tracking populations. However, very little is known about the long-term fate of epiphyte individuals and populations. We estimated life span and assessed environmental factors influencing changes in vitality, fertility, abundance, and distribution of the epiphytic lichen species Lobaria pulmonaria on two spatial scales, individual trees and forest patches, over a period of approximately 10 years in 66 old-growth forest fragments. The lichen had gone extinct from 7 of the 66 sites (13.0%) where it was found 10 years earlier, even though the sites remained unchanged. The risk of local population extinction increased with decreasing population size. In contrast to the decrease in the number of occupied trees and sites, the mean area of the lichen per tree increased by 43.0%. The number of trees with fertile ramets of L. pulmonaria increased from 7 (approximately 1%) to 61 (approximately 10%) trees, and the number of forest fragments with fertile ramets increased from 4 to 23 fragments. The mean annual rate of L. pulmonaria extinction at the tree level was estimated to be 2.52%, translating into an expected lifetime of 39.7 years. This disappearance rate is higher than estimated mortality rates for potential host trees. The risk of extinction at the tree level was significantly positively related to tree circumference and differed between tree species. The probability of presence of fertile ramets increased significantly with local population size. Our results show a long expected lifetime of Lobaria pulmonaria ramets on individual trees and a recent increase in vitality, probably due to decreasing air pollution. The population is, however, declining slowly even though remaining stands are left uncut, which we interpret as an extinction debt.

Semiochemical‐mediated oviposition behavior by female peachtree borer, Synanthedon exitiosa

AbstractThe peachtree borer, Synanthedon exitiosa (Say) (Lepidoptera: Sesiidae), is an important pest of commercial cultivations of peach trees, Prunus persicae (L.) (Rosaceae). Identification of semiochemicals that mediate host selection by adult S. exitiosa may lead to the development of a new earth‐friendly tactic within integrated programs for control of S. exitiosa. Larvae develop in the phloem of peach trees where their feeding stimulates the production of gum frass, a mixture of tree phloem particles, tree sap (gum), and larval feces (frass). We tested the hypothesis that gum‐frass semiochemicals signal a potential host tree, and induce oviposition by female S. exitiosa. In coupled gas chromatographic‐electroantennographic detection analyses of Porapak Q‐collected gum frass volatiles, 21 compounds elicited responses from male or female S. exitiosa antennae. These compounds included four acids, four hydrocarbons, four ketones, three acetates, two aldehydes, γ‐decalactone, conophthorin, 2‐phenylethanol, and 2‐isopropyl‐3‐methoxypyrazine. In dual‐choice laboratory experiments, all groups of compounds, except the acetates, were needed to induce significantly more egg laying by female S. exitiosa on treatment than on unbaited control oviposition sites. By responding to gum frass semiochemicals, female S. exitiosa seem to exploit signals that are complex, detectable, and that reliably indicate a potential host tree for larval development.

EFFECTS OF STAND-LEVEL DISTURBANCES ON THE SPATIAL DISTRIBUTION OF A LICHEN INDICATOR

Due to its assumed dispersal limitation and susceptibility to disturbance, the epiphytic lichen Lobaria pulmonaria is used as an indicator of undisturbed forest stands. The hypothesis was tested that stand-level disturbances have a long-lasting negative impact on the occurrence of L. pulmonaria. Two 19th century stand-level disturbances were reconstructed using aerial photographs from 1933. For 7769 potential host trees within a random sample of 251 plots of 1 ha, the presence of L. pulmonaria, tree species, and diameter at breast height were recorded. An analysis of variance showed that neither historical stand-level disturbances nor current grazing reduced the proportion of colonized trees. Spatial analysis at the tree level revealed a patchy distribution of colonized trees, suggesting L. pulmonaria colonization from nearby sources. Spatial analysis at plot level even showed a positive spatial association of L. pulmonaria with historic disturbances. We conclude that the presence of L. pulmonaria may provide information about conservation value of a landscape, but not necessarily at a forest stand scale. Although indicator species, such as L. pulmonaria, may be an efficient means to assess the conservation value of a forest, spatially and temporally explicit knowledge of the species' life history characteristics is indispensable in order to prevent possible misinterpretation of ecological processes that the indicator aims to unravel.

Mismatch between Herbivore Behavior and Demographics Contributes to Scale-Dependence of Host Susceptibility in Two Pine Species

Abstract The impacts on forests of tree-killing bark beetles can depend on the species composition of potential host trees. Host susceptibility might be an intrinsic property of tree species, or it might depend on spatial patterning of alternative host species. We compared the susceptibility of loblolly pine (Pinus taeda) and Virginia pine (P. virginiana) to southern pine beetle (Dendroctonus frontalis) at two hierarchical levels of geographic scale: within beetle infestations in heterospecific stands (extent ranging from 0.28 to 0.65 ha), and across a forest landscape (extent 72,500 ha) that was dominated by monospecific stands. In the former, beetles preferentially attacked Virginia pine (tree mortality = 65–100% in Virginia pine versus 0–66% in loblolly pine), but in the latter, loblolly stands were more susceptible than Virginia stands. This hierarchical transition in host susceptibility was predicted from knowledge of (1) a behavioral preference of beetles for attacking loblolly versus Virginia pine, (2) a negative correlation between preference and performance, and (3) a mismatch in the domain of scale between demographics and host selection by individuals. There is value for forest management in understanding the processes that can produce hierarchical transitions in ecological patterns. FOR. SCI. 51(6):522–531.

Host associations of the strangler fig Ficus watkinsiana in a subtropical Queensland rain forest

Abstract The distribution of epiphytic organisms is limited by the availability of, and dispersal to suitable hosts. We examined the distribution of a hemi‐epiphytic strangler fig, Ficus watkinsiana (Moraceae) in Cooloola National Park (Queensland, Australia), in order to determine whether this species exhibits a preference for certain host species and why. We assessed host bark roughness and flakiness, fruit type, and size to explain the observed distribution of F. watkinsiana. We surveyed over 1900 potential host trees of the 30 most common forest canopy species and found that host size measured by diameter at breast height accounted for most variation in fig prevalence (Binary Logistic Regression log‐likelihood = −588.178, G = 314.494, d.f. = 1, P < 0.005). After controlling for host size, F. watkinsiana prevalence still differed significantly between host species (χ2 = 54.612, d.f. = 24, P < 0.005), a difference that was only partly explained by variation in the bark roughness of host trunks. These results suggest that variation in the rate at which tree species host strangler figs are primarily related to individual tree size – figs may simply be more likely to colonize and thrive upon host species that grow larger.

Ecological Relationships among Hypogeous Fungi and Trees: Inferences from Association Analysis Integrated with Habitat Modeling

Association analyses by contingency tables and generalized linear modeling were compared to infer relationships among hypogeous (belowground-fruiting) ectomycorrhizal fungi and potential host tree species from 136 study plots in forested habitats in southeastern mainland Australia. Results from both types of statistical approaches were highly congruent. As with previous experimental studies, no exclusive fungus-host tree associations were identified. However, the likelihood of occurrence of some species of fungi increased significantly in the presence of particular host tree species, suggesting fungal host preference or shared habitat preferences. Similarly, while most associations among fungal species were nonsignificant, a few taxa were more likely to be found in the presence of certain others. These were termed positively associated and are thought to share common climatic and microhabitat requirements or host preferences. In contrast, other combinations of fungal species were negatively associated with one another, perhaps indicating different habitat preferences. Furthermore, the finding that some fungi occurred more frequently in the presence of certain tree species provides a starting point for selection of compatible host-fungus combinations that could be used for forest nursery and restoration applications.

Ecological relationships among hypogeous fungi and trees: inferences from association analysis integrated with habitat modeling

Association analyses by contingency tables and generalized linear modeling were compared to infer relationships among hypogeous (belowground-fruiting) ectomycorrhizal fungi and potential host tree species from 136 study plots in forested habitats in southeastern mainland Australia. Results from both types of statistical approaches were highly congruent. As with previous experimental studies, no exclusive fungus-host tree associations were identified. However, the likelihood of occurrence of some species of fungi increased significantly in the presence of particular host tree species, suggesting fungal host preference or shared habitat preferences. Similarly, while most associations among fungal species were nonsignificant, a few taxa were more likely to be found in the presence of certain others. These were termed positively associated and are thought to share common climatic and microhabitat requirements or host preferences. In contrast, other combinations of fungal species were negatively associated with one another, perhaps indicating different habitat preferences. Furthermore, the finding that some fungi occurred more frequently in the presence of certain tree species provides a starting point for selection of compatible host-fungus combinations that could be used for forest nursery and restoration applications.

Bayesian Mapping of Lichens Growing on Trees

Suitability of trees as hosts for epiphytic lichens are studied in a forest stand of size 25 ha. Suitability is measured as occupation probabilites which are modelled using hierarchical Bayesian approach. These probabilities are useful for an ecologist. They give smoothed spatial distribution map of suitability for each of the species and can be used in detecting high- and low-probability areas. In addition, suitability is explained by tree-level covariates. Spatial dependence, which is due to unobserved spatially structured covariates, is modelled through an unobserved Markov random field. Markov chain Monte Carlo method has been applied in Bayesian computation. The extensive spatial data consist of the occurrences of eight lichen species and one bryophyte on all of the 1253 potential host trees. In addition, coordinates of the trees and several tree characteristics have been recorded. The data have been analysed for four most abundant species: Lobaria pulmonaria, Nephroma bellum, Nephroma parile and Peltigera praetextata. The tree level parameters, subject to estimation, consist of the occurrence probabilities for each tree and for each lichen species. Model validation is discussed in detail and, in addition to Bayesian validation tools, the autologistic model and case-control design based on logistic regression have been suggested for validation of covariate effects. As a result we present suitability maps for the four lichen species. We observed, that among the observed tree covariates, the diameter at breast height (DBH) correlates with lichen occurrence. Our modelling approach has close connections to disease mapping in spatial epidemiology.

Strangler Figs in a Stand of Dry Rainforest in the Lower Hunter Valley, NSW

A complete census was conducted of all hemi-epiphytic Ficus individuals within a single stand of dry rainforest. Substrate analyses were conducted on the material from potential hemi-epiphyte germination sites in an attempt to understand the factors influencing the distribution of hemi-epiphytic Ficus individuals within the stand. In all, 191 individuals of Ficus macrophylla ssp. macrophylla (Moreton Bay fig) and 65 individuals of Ficus superba var. henneana (deciduous fig) were found within the stand, providing a mean hemi-epiphyte density of 13.5/ha. Clear host preferences were shown for both fig species with two species, Olea paniculata (native olive) and Drypetes deplanchei (yellow tulip), shown to host 60 per cent and 21 per cent, respectively, of all hemi-epiphytes within the stand. These host trees are characterised by humus pockets that accumulate in depressions on their branches and trunk, as well as in branch axils. Their host potential is thought to be enhanced by the increased visitation of birds that feed on the fruit from both the hemi-epiphytes and these potential host trees. Substrate analyses revealed that while the highly organic epiphytic and rock-surface substrates had a high field capacity, their moisture holding capacity was low. The ponding of water and the reduced desiccation afforded by the microtopography of the germination sites ensures that these sites are more likely to maintain a viable moisture content. It appears that desiccation of the germination substrate could be the major cause of the high rate of juvenile hemi-epiphytic Ficus mortality.

Habitat requirements and conservation of Pytho kolwensis, a beetle species of old-growth boreal forest

The host-tree and habitat requirements of an endangered saproxylic beetle species, Pytho kolwensis, which inhabits fallen spruce ( Picea abies) trunks were studied. Host-tree quality of 150 potential host trees, 60 of which were inhabited, and stand characteristics were measured at six sites in eastern Finland. All of the P. kolwensis habitats were virgin spruce-mire forests with a stand continuity of at least 170–300 years, and a high volume of dead wood (73–111 m 3/ha). Decay-class distribution of large-diameter logs was very even, indicating that the recruitment rate of large, fallen trunks had remained nearly constant for at least 100 years. Microclimate and host-tree quality were not likely factors explaining the habitat confinement of the species. We suggest that P. kolwensis is mainly restricted to spruce-mire forests because of the long-term continuous availability of suitable host trees in these habitats.

Migration in spruce bark beetles (Ips typographis L.) and the efficiency of pheromone traps

AbstractMark‐release‐recapture experiments with both newly emerged and flight experienced Ips typographus L. were performed in a pine forest near Prague. Three concentric trap circles around the release site with a radius of 5 m, 200 m and 500 m, and intertrap distances of 6 m, 16 m and. maximally, 40 m, were installed with the intention of collecting all dispersing bark beetles ready to respond to pheromone lures. The results show that even without wind and no potential host trees in the surroundings, only about one‐third (35.4%) of the emerging beetles in an infested site can be eliminated locally with phermomone traps. At least 12.2% of the emerging beetles (25.7% of the recaptures), perform an adaptive migration flight, which brings them beyond the range of local pheromone traps. The estimated proportion of emigrants can rise over 50%, if most of the freshly emerged beetles that have never been recaptured are assumed to have left the experimental area. Electroantennograms recorded in the laboratory at different times after emergence indicate that the delayed response to aggregation pheromones in migrating bark beetles is not the result of a delayed maturation of the antennal receptor cells, but obviously governed by the central nervous system. The notion of precopulatory migration in 25–50% of the individuals in an I. typographus population can explain why pheromone traps can never eliminate all emerging beetles, and why so many bark beetles can be collected far away from any breeding sites.

Host Associations of Two Adventitious-Root-Climbing Vines in a North Queensland Tropical Rain Forest

The abundance of adventitious-root-climbing vines, predominantly Freycinetia excelsa and Piper caninum, on potential host trees was investigated in a north Queensland tropical rain forest. All trees 10 cm DBH and greater were measured and assessed for adventitious-root-climber presence. Additional trees of the 17 most abundant species were examined giving a total of 833 trees. Some 1694 adventitious-root-climbing vines were recorded from the study area. Distribution over the rain forest trees was not homogeneous, but exhibited host associations. Interspecific differences between potential host trees were analyzed in terms of allelopathy, bark characteristics, and gross morphological features. Bark characteristics are proposed. as the main factor for the relative absence of adventitious-root-climbing vines on trees of Syzygium papyraceum and Austromyrtus shepherdii. Thin, peeling, sloughable bark characterize these members of the Myrtaceae. Trees heavily infested by adventitious-root climbers include Beilschmiedia collina with non-descript (though slightly rough) bark providing a good, stable climbing surface with little phytotoxicity, and Citronella smythii, with thick, corky, fissured bark, also lacking allelopathic materials. Allelopathic effects of bark phytochemicals seem to be predominantly responsible for the absence of infestation of Alphitonia petriei by adventitious-root climbers.

Host Preferences of Rhus Radicans (Anacardiaceae) in a Southern Deciduous Hardwood Forest

Rhus radicans, a root—climbing liana, is not distributed randomly among potential host tree species in old—growth mixed mesophytic forest on the southern Cumberland Plateau of north Alabama, USA. Vines are more abundant than expected on Carya ovata and Quercus rubra, but less abundant than expected on Juglans nigra, Acer saccharum, and Sassafras albidum. Seed germination and early seedling growth in the presence of bark extracts suggest allelochemical interactions may influence the observed host preferences.

Spatial distribution of ectomycorrhizal mats in coniferous forests of the Pacific Northwest, USA

Ectomycorrhizal mats in forest soils have a wide global distribution and have been noted as potentially important elements in forest soil nutrient cycling. To elucidate the relationship between ectomycorrhizal mats and their environment, we undertook field studies and spatial analyses of mat distributions at different spatial scales. We used two experimental approaches to study mat-forming ectomycorrhizal fungi in coniferous forests of the Pacific Northwest in the United States. In the first approach, ectomycorrhizal mats and other forest floor features were mapped in 2 × 10 m plots and digitized into a geographical information system (GIS) for spatial pattern analysis. In order to examine larger-scale phenomena, a second approach involving other sites was taken; soil cores were taken along 30-m transects, and distance to the closest living potential host tree was calculated for each core. Mat patterns were studied at two scales: (1) within-stand level (i.e. variability attributed to distribution of other mat species, forest floor attributes, and understory vegetation); and (2) stand level (i.e. variability expressed along a successional gradient). Mat distribution was influenced by: (1) the proximity of one mat to another; (2) the distance from the mat to the closest living tree; (3) the density of living trees in a stand; and (4) the successional stage of the stand. Although GIS analysis indicated that mats of different morphologies did not physically overlap, there was a tendency for clustering of mats. No apparent correlations were observed between forest floor features and mats located within the 2 × 10 m grids. On the scale of tens of meters, mats decreased with distance from the closest potential host tree. Spatial patterns of mat distributions in harvested sites suggest that these mats may persist at least 2 years after their host trees have been cut. For Gautieria mats, total mat area, size, and frequency differed with stand age. This study has demonstrated the importance of both spatial scaling and forest stand age when the natural distribution of mycorrhizal fungi is examined. Results suggest the need for mat research directed at higher-order scales (e.g. stand and watershed) that will provide accurate information for managing forests to ensure their survival and normal function. ei]J H Graham

Seedling establishment in an epiphytic orchid: an experimental study of seed limitation.

Will increased fruit and seed production in a severely pollination-limited orchid stimulate population growth? We tested whether safe sites for germination and seedling establishment are limiting for the twig epiphyte, Tolumnia variegata, by manipulating fruit set and monitoring subsequent seedling establishment for two seasons (1991-1992, 1992-1993). In the Cambalache Forest Reserve of Puerto Rico, we established 36 plots along a transect. Each plot consisted of nine trees. A center tree was designated as the site for attaching Tolumnia and manipulating fruit set. The other eight potential host trees were 1-3 and 3-5 m from the center tree in each of the cardinal directions. A 1-m length of stem 1 m from the ground was monitored for recruits on each of the nine trees of 24 fruit-enhanced plots and 12 controls (23 and 13, respectively for the 1992-1993 season). Fruit enhancement plots were divided among two treatments: one-fruit and five-fruit additions for the 1st year and one to five and more than five fruits for the 2nd year. Availability of suitable host species was not limiting. T. variegata showed little specificity for host tree species, good host trees and shrubs were common, and there was no evidence that the orchid had a preference for small branches, despite possessing the entire suite of characteristics thought to respresent "obligate" twig epiphytes. Fruit enhancement increased seed rain and seedling establishment consistently in only the high-fruit treatment plots. Most recruitment occurred near fruiting plants. Over the 2-year period, mortality was 18% for adults and 85.5% for the 1991-1992 cohort of recruits. Net recruitment was positive for both the treatment (average = 1.74) and control plots (average = 0.67). Seedling establishment at our study site was not microsite-limited. If selection for increased pollinator attraction occurs, then an increase in seed output should result in population growth.

Effects of fire regimen on two species of epiphytic orchids in tropical savannas of the Northern Territory

AbstractThe effect of four fire regimens (early dry season annual, late dry season annual, early dry season biennial, unburnt) on the numbers of epiphytic orchids in a savanna community in Kakadu National Park was investigated. These fire regimens had been maintained on I ha plots for 16 years. Two species of epiphytic orchid were present — Cymbidium canaliculatum and Dendrobium affine. The numbers of Cymbidium plants were insufficient to enable statistical analysis, but plants were present in the unburnt, early annual and early biennial fire treatments. Dendrobium occurred in substantial numbers irrespective of fire treatment, but the extent of colonization of all available host trees was greater in the unburnt than the burnt treatments.The lower numbers of Dendrobium plants in burnt treatments was due to a lower proportion of potential host trees being colonized and a lower number of orchids on each colonized tree. The proportion of small trees colonized was markedly lower in burnt treatments. Frequent fires late in the dry season may prevent recruitment of the main host species. Eucalyptus tectifica. The survival of orchids despite frequent fires depended on the availability of relatively protected sites for colonization and the ability of the orchids to withstand some fire damage.

Fossil ascopores of the parasitic fungus Ustulina deusta in Eemian deposits in Denmark

Records of spores of the parasitic ascomycete Ustulina deusta were compared with the pollen records of potential host trees in Eemian deposits. The results indicate that the distance between sample site and forest has a considerable influence on the frequency records of the fungal spores. Spores are absent in deposits from the relatively large lakes at Hollerup and Herning. The deposit in a small (5 × 5m) hollow at Egernsund shows high frequencies of Ustulina in the vegetational phase 3 ( Fraxinus phase). In phase 4a, dominated by Corylus, the spores of Ustulina were almost absent, whereas phase 4b, dominated by Tilia, shows extremely high frequencies of the ascospores. The relationship between the fungus and its arboreal hosts at Egernsund ( Tilia, Fraxinus) reflects the weak parasitic character of the fungus. Corylus apparently was not infected, which is in agreement with its absence in the records of host plants of Ustulina deusta in the mycological literature.

Stand and Site Conditions Related to Southern Pine Beetle Susceptibility

Abstract Stand/site data from infested stands were compared with those from the general forest. Findings supported earlier research relating high basal area, high stand density, high proportion of pines, reduced radial growth rate, low soil pH, and high site index to increased southern pine beetle activity in the West Gulf Coastal Plain. Also, increased understory vegetation and thicker bark of potential host trees were found to favor beetle attack. Discriminant models were derived from data obtained from infested and general stand (baseline) plots and can be used to rank forest stands as to susceptibility to southern pine beetle attack. Forest Sci. 25:656-664.

Mineral Cycling and the Niche of Spanish Moss, Tillandsia usneoides L.

On the southeastern coastal plain, the occurrence and abundance of the epiphyte Spanish moss (Tillandsia usneoides L.; Bromeliaceae) are linked to the availability of minerals in the canopy of potential host trees. Trees with high rates of foliar leaching (e.g., cypress and oaks) provide an abundant supply of minerals (Ca, Mg, K, and P) in precipitation collected beneath the canopy. In forests of these species Spanish moss is more abundant and has higher mineral concentrations than in pine forests (e.g., phosphorus 0.04–0.06% dry weight versus 0.03–0.04%). In growth-chamber experiments the growth of Spanish moss increased in response to added phosphorus in the range of concentrations observed in field precipitation collections (0–200 μg/l). In addition to the availability of minerals, the rate of bark sloughing from host trees and allelopathic effects may also control the local distribution of Spanish moss. Light and moisture appear to be less important factors. Thus, within a favorable climatic range, mineral and bark characteristics of host trees may be used to illustrate a niche hypervolume for this species.

MINERAL CYCLING AND THE NICHE OF SPANISH MOSS, TILLANDSIA USNEOIDES L

On the southeastern coastal plain, the occurrence and abundance of the epiphyte Spanish moss (Tillandsia usneoides L.; Bromeliaceae) are linked to the availability of minerals in the canopy of potential host trees. Trees with high rates of foliar leaching (e.g., cypress and oaks) provide an abundant supply of minerals (Ca, Mg, K, and P) in precipitation collected beneath the canopy. In forests of these species Spanish moss is more abundant and has higher mineral concentrations than in pine forests (e.g., phosphorus 0.04–0.06% dry weight versus 0.03–0.04%). In growth‐chamber experiments the growth of Spanish moss increased in response to added phosphorus in the range of concentrations observed in field precipitation collections (0–200 μg/l). In addition to the availability of minerals, the rate of bark sloughing from host trees and allelopathic effects may also control the local distribution of Spanish moss. Light and moisture appear to be less important factors. Thus, within a favorable climatic range, mineral and bark characteristics of host trees may be used to illustrate a niche hypervolume for this species.