Ashley E. Askew

Characterization of Three-Dimensional Spatial Aggregation and Association Patterns of Brown Rot Symptoms within Intensively Mapped Sour Cherry Trees

BACKGROUND AND AIMS Characterization of spatial patterns of plant disease can provide insights into important epidemiological processes such as sources of inoculum, mechanisms of dissemination, and reproductive strategies of the pathogen population. Whilst two-dimensional patterns of disease (among plants within fields) have been studied extensively, there is limited information on three-dimensional patterns within individual plant canopies. Reported here are the detailed mapping of different symptom types of brown rot (caused by Monilinia laxa) in individual sour cherry tree (Prunus cerasus) canopies, and the application of spatial statistics to the resulting data points to determine patterns of symptom aggregation and association. METHODS A magnetic digitizer was utilized to create detailed three-dimensional maps of three symptom types (blossom blight, shoot blight and twig canker) in eight sour cherry tree canopies during the green fruit stage of development. The resulting point patterns were analysed for aggregation (within a given symptom type) and pairwise association (between symptom types) using a three-dimensional extension of nearest-neighbour analysis. KEY RESULTS Symptoms of M. laxa infection were generally aggregated within the canopy volume, but there was no consistent pattern for one symptom type to be more or less aggregated than the other. Analysis of spatial association among symptom types indicated that previous years twig cankers may play an important role in influencing the spatial pattern of current years symptoms. This observation provides quantitative support for the epidemiological role of twig cankers as sources of primary inoculum within the tree. CONCLUSIONS Presented here is a new approach to quantify spatial patterns of plant disease in complex fruit tree canopies using point pattern analysis. This work provides a framework for quantitative analysis of three-dimensional spatial patterns within the finite tree canopy, applicable to many fields of research.

Spatio-temporal Patterns of Pre-harvest Brown Rot Epidemics within Individual Peach Tree Canopies

Tree canopies are architecturally complex and pose several challenges for measuring and characterizing spatial patterns of disease. Recently developed methods for fine-scale canopy mapping and three-dimensional spatial pattern analysis were applied in a 3-year study to characterize spatio-temporal development of pre-harvest brown rot of peach, caused by Monilinia fructicola, in 13 trees of different maturity classes. We observed a negative correlation between an index of disease aggregation and disease incidence in the same tree (r = −0.653, P < 0.0001), showing that trees with higher brown rot incidence had lower aggregation of affected fruit in their canopies. Significant (P ≤ 0.05) within-canopy aggregation among symptomatic fruit was most pronounced for early-maturing cultivars and/or early in the epidemic. This is consistent with the notion of a greater importance of localized, within-tree sources of inoculum at the beginning of the epidemic. Four of five trees having >10 blossom blight symptoms per tree showed a significant positive spatial association of pre-harvest fruit rot to blossom blight within the same canopy. Spatial association analyses further revealed one of two outcomes for the association of new fruit rot symptoms with previous fruit rot symptoms in the same tree, whereby the relationship was either not significant or exhibited a significant negative association. In the latter scenario, the newly diseased fruit were farther apart from previously symptomatic fruit than expected by random chance. This unexpected result could have been due to uneven fruit ripening in different sectors of the canopy, which could have affected the timing of symptom development and thus led to negative spatial associations among symptoms developing over time in a tree.

Potential effects of climate on downhill skiing and snowboarding demand and value at U.S

Annually, 23 million recreationists participate in downhill skiing on over 180,000 acres of skiable land in the U.S. National Forest system, making it the second most popular outdoor activity in the system. While the emerging literature on climate science reveals changing climatic conditions in ski areas, the extent of climate change impact on the demand for and economic value of downhill skiing is unknown. By combining trip data collected from on-site surveys of skiers in national forests across the nation with climatic data collected through nearby weather stations, this study developed an aggregated travel cost model to estimate the net economic benefit of downhill skiing and snowboarding, and the projected impact of climate change on the demand and value. Per person per trip net economic benefit of downhill skiing was estimated to be in the range of

Outdoor recreation participation in the United States - projections to 2060: a technical document supporting the Forest Service 2010 RPA Assessment

91 to

Spatial Patterns of Brown Rot Epidemics and Development of Microsatellite Markers for Analyzing Fine-Scale Genetic Structure of Monilinia fructicola Populations Within Peach Tree Canopies

185 depending on the assumptions about skiers’ opportunity cost of time. When aggregated across visits and national forests, the total economic value of downhill skiing in the U.S. National Forest system ranged from

Federal outdoor recreation trends: Effects on economic opportunities

2.16 to

Climate change and outdoor recreation participation in the Southern United States

4.39 billion, annually. Climate variables including temperature, snow depth, and rainfall were correlated with ski demand, and projected changes in these climate variables could affect the economic benefits from skiing. Findings contribute to understanding the net economic benefit of maintaining downhill skiing on national forests, and will help recreation planners and tourism entrepreneurs develop adaptive strategies to sustain the skiing industry. Subscribe to JPRA