Environmental factors driving the recovery of bay laurels from Phytophthora ramorum infections: An application of numerical ecology to citizen science

Phytophthora ramorum is an alien and invasive plant pathogen threatening forest ecosystems
in Western North America, where it can cause both lethal and non-lethal diseases. While the
mechanisms underlying the establishment and spread of P. ramorum have been elucidated, this is
the first attempt to investigate the environmental factors driving the recovery of bay laurel, the main
transmissive host of the pathogen. Based on a large dataset gathered from a citizen science program,
an algorithm was designed, tested, and run to detect and geolocate recovered trees. Approximately
32% of infected bay laurels recovered in the time period between 2005 and 2015. Monte Carlo
simulations pointed out the robustness of such estimates, and the algorithm achieved an 85% average
rate of correct classification. The association between recovery and climatic, topographic, and
ecological factors was assessed through a numerical ecology approach mostly based on binary logistic
regressions. Significant (p < 0.05) coefficients and the information criteria of the models showed
that the probability of bay laurel recovery increases in association with high temperatures and low
precipitation levels, mostly in flat areas. Results suggest that aridity might be a key driver boosting
the recovery of bay laurels from P. ramorum infections.