Effects Of Dwarf Mistletoe Research Articles

Effects of dwarf mistletoe on stand structure of lodgepole pine forests 21-28 years post-mountain pine beetle epidemic in central Oregon.

Lodgepole pine (Pinus contorta) forests are widely distributed throughout North America and are subject to mountain pine beetle (Dendroctonus ponderosae) epidemics, which have caused mortality over millions of hectares of mature trees in recent decades. Mountain pine beetle is known to influence stand structure, and has the ability to impact many forest processes. Dwarf mistletoe (Arceuthobium americanum) also influences stand structure and occurs frequently in post-mountain pine beetle epidemic lodgepole pine forests. Few studies have incorporated both disturbances simultaneously although they co-occur frequently on the landscape. The aim of this study is to investigate the stand structure of lodgepole pine forests 21–28 years after a mountain pine beetle epidemic with varying levels of dwarf mistletoe infection in the Deschutes National Forest in central Oregon. We compared stand density, stand basal area, canopy volume, proportion of the stand in dominant/codominant, intermediate, and suppressed cohorts, average height and average diameter of each cohort, across the range of dwarf mistletoe ratings to address differences in stand structure. We found strong evidence of a decrease in canopy volume, suppressed cohort height, and dominant/codominant cohort diameter with increasing stand-level dwarf mistletoe rating. There was strong evidence that as dwarf mistletoe rating increases, proportion of the stand in the dominant/codominant cohort decreases while proportion of the stand in the suppressed cohort increases. Structural differences associated with variable dwarf mistletoe severity create heterogeneity in this forest type and may have a significant influence on stand productivity and the resistance and resilience of these stands to future biotic and abiotic disturbances. Our findings show that it is imperative to incorporate dwarf mistletoe when studying stand productivity and ecosystem recovery processes in lodgepole pine forests because of its potential to influence stand structure.

Effects of Dwarf Mistletoe on Climate Response of Mature Ponderosa Pine Trees

This research examines the influence of western dwarf mistletoe (Arceuthobium campylopodum) infection on the radial growth response of mature ponderosa pines (Pinus ponderosa) and its effects on dendroclimatic reconstructions. I hypothesize that trees with mistletoe have lower annual growth rates than uninfected trees, but exhibit higher mean sensitivities and stronger relationships between growth and climate variation. I tested these hypotheses using correlation and regression analyses to compare 100-year crossdated and standardized tree-ring chronologies from 26 infected and 29 uninfected trees. I compared both chronologies to climate variation as measured by changes in total precipitation, minimum, mean, and maximum temperature, and the Palmer Drought Severity Index (PDSI). Results show that trees infected with dwarf mistletoe have higher radial growth rates, exhibit greater sensitivity, and respond more strongly to climate variation. Both infected and uninfected chronologies are significantly correlated with the respective climate variables, but exhibit different patterns. The strongest correlations are between infected trees and PDSI for all months tested; significant correlations between uninfected trees and PDSI are limited to May through December lagged from the previous year. These results suggest mistletoe-infected trees are more sensitive to climatic factors than uninfected trees and may be useful for dendroclimatic analyses.

Characterizing the effects of dwarf mistletoe and other diseases for sustainable forest management

Many insects, fungi, and plants in forest ecosystems can damage trees and forests, depending on stand and environmental conditions. Natural disturbances, harvesting, and other forest practices can retard or increase the spread and the effects of dwarf mistletoe and other diseases on tree growth. To monitor the effects of diseases, certification and monitoring programs typically use incidence and severity of infestations as criteria and indicators. However, these are often insufficient to characterize the impact of the disease or to measure the effects of new management practices, such as variable retention silviculture, on sustainability. Long-term observations and models of stand development are advocated as better methods for characterizing disease effects. For dwarf mistletoe (Arceuthobium tsugense), we are designing and monitoring installations in infested stands of western hemlock (Tsuga heterophylla) and constructing a spatial and life history model of stand and disease development. Disease spread and effects are influenced by several factors including site quality, stand density, and the spatial arrangement of infected trees, which are sources of mistletoe spread into new stands. Potentially, these factors could be manipulated to either reduce or encourage the spread and the effects of dwarf mistletoe.

The effects of dwarf mistletoe, witches' brooms, stand structure, and site characteristics on the crown architecture of lodgepole pine in Oregon

We investigated the importance of lodgepole pine dwarf mistletoe (Arceuthobium americanum Nutt.) in determining the height to crown top (HCT), height to crown base (HCB), and live crown ratio (LCR) of 2025 lodgepole pine (Pinus contorta var. murrayana (Grev. & Balf.) Engelm.) growing over a 24-km2 study site in central Oregon. We compared the effects of infection and associated witches' brooms with those of site topography, soil type, shrub cover, stand density, and the abundance of mature ponderosa pine (Pinus ponderosa Dougl. ex P. Laws. & C. Laws). using multiple regression and path analysis. The density of dominant-size P. contorta was consistently the most important factor influencing HCT, HCB, and LCR across the study site. In dense stands, trees tended to have elevated crown bases due to self-pruning and, hence, lower values of LCR. Dwarf mistletoe and related witches' brooms uniquely explained 6.9% of the variance in LCR, which was close to that of dominant P. contorta (7.1%) and more than that of soil type (3.0%), but explained only 2.6% of the variance in HCB, which was less than that of dominant P. contorta (6.5%) and soil type (4.6%). Regression models suggest that heavily infected trees should be 18% shorter and have crown bases 37% lower than uninfected trees, while moderately infected trees should have an LCR over 20% larger than that of uninfected and heavily infected trees. We also found that the largest 25 heavily infected trees sampled were approximately 19% shorter and 11–13% smaller in diameter than the largest 25 uninfected trees. The results suggest that dwarf mistletoe can be an important factor in determining the crown dimensions of P. contorta but that these effects may be interpreted only in the context of site characteristics and stand structure.

Effects of dwarf mistletoe on the response of young Douglas-fir to thinning

Four sites from two forests were examined to determine the effect of various levels of infection by Arceuthobiumdouglasii on the growth of Pseudotsugamenziesii in precommercially thinned stands. We found less than 1% mortality among the trees that we examined. Changes in level of infection did occur; we estimate that changes to levels of infection sufficient to cause significant reductions in diameter growth occurred among 19% of the infected trees that we studied. Height growth was significantly reduced in both forests, while diameter growth was reduced by infection in one forest. Trees of lower infection rating (dwarf mistletoe rating 0–2) showed a significant increase in radial growth following thinning in both forests, while more heavily infected trees (dwarf mistletoe rating 5 and 6) did not. Trees that were heavily infected and had spike tops consistently showed significant reductions in diameter growth in both forests.

Distribution of Arceuthobium divaricatum and Phoradendron juniperinum (Viscaceae) on the South Rim of Grand Canyon, Arizona

The distribution and effects of the mistletoes Arceuthobium divaricatum Engelm. on Pinus edulis Engelm. and Phoradendron juniperinum Engelm. on Juniperus osteosperma (Torr.) Little on the pinyon-juniper vegetation type on the south rim of Grand Canyon National Park were investigated. Fire was the most limiting factor in the distribution of the mistletoes. The incidence of infection increased as trunk diameter and height increased in both pinyon and juniper. Arceuthobium divaricatum had the more serious impact on its host in respect to both vigor and mortality. Both mistletoes appear to be in equilibrium with their hosts at this time. Two mistletoes of the pinyon-juniper ecosystem of the Grand Canyon are Arceuthobium divaricatum Engelm. and Phoradendron juniperinum Engelm. Research on A. divaricatum and P. juniper- inum has been extremely limited because the trees infected have not been economically important as timber resources. With rising in- terest in utilization of the resources of the pinyon-juniper vegetation type, especially in a recreational capacity, effective management of these stands will be paramount in national parks and recreation areas (Clary 1975). Information on the site preferences and environmental factors that predispose the host trees to mistletoe infection will fa- cilitate management of diseased stands. This study was conducted to determine the distribution and effects of dwarf mistletoe on pinyon (Pinus edulis Engelm.) and true mistletoe on juniper (Juniperus osteosperma (Torr.) Little) on the South Rim at Grand Canyon Na- tional Park, Arizona.