Canopy spectral reflectance detects oak wilt at the landscape scale using phylogenetic discrimination

Abstract

The oak wilt disease caused by the invasive fungal pathogen Bretziella fagacearum is one of the greatest threats to oak-dominated forests across the Eastern United States. Accurate detection and monitoring over large areas are necessary for management activities to effectively mitigate and prevent the spread of oak wilt. Canopy spectral reflectance contains both phylogenetic and physiological information across the visible near-infrared (VNIR) and short-wave infrared (SWIR) ranges that can be used to identify diseased red oaks. We develop partial least square discriminant analysis (PLS-DA) models using airborne hyperspectral reflectance to detect canopies at early stages of disease development and assess the importance of VNIR, SWIR, phylogeny, and physiology for oak wilt detection. We achieve high accuracy through a three-step phylogenetic process in which we first distinguish oaks from other species (90% accuracy), then red oaks from white oaks (Quercus macrocarpa) (93% accuracy), and, lastly, infected from non-infected trees (80% accuracy). Including SWIR wavelengths increased model accuracy by ca. 20% relative to models based on VIS-NIR wavelengths alone; using a phylogenetic approach also increased model accuracy by ca. 20% over a single-step classification. SWIR wavelengths include spectral information important in differentiating red oaks from other species and in distinguishing diseased red oaks from healthy red oaks. We determined the most important wavelengths to identify oak species, red oaks, and diseased red oaks. We also demonstrated that several multispectral indices associated with physiological decline can detect differences between healthy and diseased trees. The wavelengths in these indices also tended to be among the most important wavelengths for disease detection within PLS-DA models, indicating a convergence of the methods. Indices were most significant for detecting oak wilt during late August, especially those associated with canopy photosynthetic activity and water status. Our study suggests that coupling phylogenetics, physiology, and canopy spectral reflectance provides an interdisciplinary and comprehensive approach that enables detection of forest diseases at large scales even at early disease stages. These results have potential for direct application by forest managers for early detection to initiate actions to mitigate the disease and prevent pathogen spread.

Plant Disease Sensing: Studying Plant-Pathogen Interactions at Scale

“…The foundational components of the spectranomics approach are that plants have chemical fingerprints that become increasingly unique when additional constituents are incorporated ( 9 ) and spectroscopic signatures determine a portfolio of chemicals found in plants ( 15 ). This approach has since been extended to phylogenetics ( 16 , 17 ), conservation biology ( 14 ), and plant metabolic functioning ( 18 ) with great success. Plant pathologists have recently begun to take advantage of the spectranomics trail blazed by terrestrial ecologists, yielding the nascent discipline of plant disease sensing ( 17 ).…”

“…This approach has since been extended to phylogenetics ( 16 , 17 ), conservation biology ( 14 ), and plant metabolic functioning ( 18 ) with great success. Plant pathologists have recently begun to take advantage of the spectranomics trail blazed by terrestrial ecologists, yielding the nascent discipline of plant disease sensing ( 17 ). Both beneficial ( 19 ) and parasitic ( 20 ) plant-microbe interactions impact a variety of plant traits that can be sensed.…”

Neighbors consistently influence growth and survival in a frequently burned savanna

“…A second possible explanation for the decline in the strength of neighbor facilitation involves the arrival of oak wilt (Bretziella fagacearum ) in east-central Minnesota several decades ago (Gibbs and French 1980), and which is thought to have spread rapidly at CCESR since 2010 (Sapes et al 2021, Pellegrini et al 2021). The fungus is spread primarily through root grafting among neighboring trees and by sap beetles (Nitidulidae) (Kuntz andRiker 1956, Jagemann et al 2018).…”

Plant spectra as integrative measures of plant phenotypes

“…Today's applications of spectroscopy range from modelling and predicting leaf (Asner et al, 2014; Serbin et al, 2014) and canopy traits (Asner et al, 2017; Singh et al, 2015), to detecting plant stress (Asner et al, 2016) and natural enemies (Pontius et al, 2005; Sapes et al, 2022 ), to differentiating species and broader taxonomic clades (Féret & Asner, 2013; Meireles et al, 2020; Sapes et al, 2022). Indeed, maps of species (Roth et al, 2015), functional group composition (Schmidtlein et al, 2012; Schweiger et al, 2017), and traits of individual plants (Asner & Martin, 2009) or plant communities (Cavender‐Bares et al, 2022) are highly valuable for investigating a plethora of ecological questions beyond the scale of individual research plots.…”