Thomas Welch Gillespie

Human-caused wildfire ignitions have become increasingly important drivers of fire activity in California during the 21st century. This study applies a 6 year moving-window XGBoost framework to model monthly wildfire ignition probabilities across California for water years 2001–2020. The model shows strong predictive skill, with average AUC-receiver operating characteristic and AUC-precision–recall gain of 0.84 and 0.96, respectively, and broadly reproduces both the spatial distribution and seasonal cycle of observed ignitions, as well as their interannual fluctuations (Spearman’s ρ = 0.785, p < 0.001). Feature importance analysis identifies road density and maximum temperature as dominant predictors, indicating the growing influence of human infrastructure while confirming the continuing importance of weather-related factors. Further experiments reveal that interannual weather anomalies strongly affect wildfire ignition probability during the wet and early fire seasons, whereas anthropogenic drivers dominate during the peak fire season. The results show that such a temporally adaptive machine-learning framework has the potential to improve ignition prevention strategies in a warming, increasingly human-influenced fire regime.

We describe a highly contiguous and complete diploid genome assembly for the Chryxus Arctic, Oeneis chryxus (E. Doubleday, [1849]), a butterfly species complex spanning much of northern and western North America. One subspecies, the Ivallda Arctic (O. c. ivallda), is endemic to California’s Sierra Nevada and of particular biogeographic interest and conservation concern. Extreme alpine habitats occupied by this subspecies include the summit of Mt. Whitney, California, representing the highest elevation butterfly population in North America. The assembly presented here consists of two haplotypes, 738.92 and 770.85 Mb in length, with contig N50 values of 10.49 and 10.13 Mb, scaffold N50 values of 25.35 and 25.69 Mb, scaffold L50 values of 13 and 14, and BUSCO completeness scores of 96.5 and 98.3%, respectively. More than 97% of the assembly is organized into 29 scaffolds, which likely represent whole chromosomes. This assembly is the first major genomic resource for Oeneis, providing a foundational reference for future genomic studies on the taxonomy, evolutionary history, and conservation of the genus. As part of the California Conservation Genomics Project, we will use this assembly in conjunction with short-read resequencing to resolve patterns of evolutionary differentiation, adaptive genomic variation, and gene flow among remaining O. c. ivallda populations. These data can and will be used to inform the subspecies’ conservation as warming climatic conditions continue to lead to the loss and fragmentation of alpine habitats. We also provide genome assemblies for the O. chryxus mitochondrion and a Wolbachia endosymbiont.

Biodiversity monitoring is an almost inconceivable challenge at the scale of the entire Earth. The current (and soon to be flown) generation of spaceborne and airborne optical sensors (i.e., imaging spectrometers) can collect detailed information at unprecedented spatial, temporal, and spectral resolutions. These new data streams are preceded by a revolution in modeling and analytics that can utilize the richness of these datasets to measure a wide range of plant traits, community composition, and ecosystem functions. At the heart of this framework for monitoring plant biodiversity is the idea of remotely identifying species by making use of the ‘spectral species’ concept. In theory, the spectral species concept can be defined as a species characterized by a unique spectral signature and thus remotely detectable within pixel units of a spectral image. In reality, depending on spatial resolution, pixels may contain several species which renders species‐specific assignment of spectral information more challenging. The aim of this paper is to review the spectral species concept and relate it to underlying ecological principles, while also discussing the complexities, challenges and opportunities to apply this concept given current and future scientific advances in remote sensing.

The Akikiki (Oreomystis bairdi) and Akekee (Loxops caeruleirostris) are two honeycreepers endemic to Kauai, Hawaii, that were listed as federally endangered in 2010. Both species are rare, little‐studied, and occur in a remote, roadless area. We analyzed high‐resolution airborne lidar data to identify forest structure and topography metrics associated with Akikiki and Akekee nest locations (88 for Akikiki and 22 for Akekee) and occurrences (3706 for Akikiki and 1581 for Akekee) from 2012 to 2017 on the Alakai Plateau to predict their distribution in unsurveyed areas. Akikiki and Akekee nested in areas with similar forest structure at 10 m resolution, but different maximum tree heights. Akikiki and Akekee foraged in areas with significantly different forest structure (maximum tree height, mean canopy height, relative heights) and topography (slope) based on occurrences. Elevation was consistently one of the most important metrics for predicting both species nest locations and occurrences across scales (10, 100, 250 m) and it appears that both species are at the upper limits of their elevational range. We estimate that the area of suitable nesting habitat for Akikiki is 17.59 km²while the area of suitable nesting habitat for Akekee is 11.10 km²at 10 m resolution. The Akikiki has a potential range of 38 km²while the Akekee has a range of 58 km²at 100 m resolution. We produce predictive nest and occurrence maps at 10 m and 100 m resolutions to spatially target conservation actions. Results suggest that if avian malaria cannot be controlled and both species populations do not stabilize over the coming years, translocation may be needed to insure their viability.

Owen, K. C., A. D. Melin, F. A. Campos, L. M. Fedigan, T. W. Gillespie, and D. J. Mennill. 2020. Bioacoustic analyses reveal that bird communities recover with forest succession in tropical dry forests. Avian Conservation and Ecology 15(1):25. https://doi.org/10.5751/ACE-01615-150125

A combination of drought and high temperatures (“global-change-type drought”) is projected to become increasingly common in Mediterranean climate regions. Recently, Southern California has experienced record-breaking high temperatures coupled with significant precipitation deficits, which provides opportunities to investigate the impacts of high temperatures on the drought sensitivity of Mediterranean climate vegetation. Responses of different vegetation types to drought are quantified using the Moderate Resolution Imaging Spectroradiometer (MODIS) data for the period 2000–2017. The contrasting responses of the vegetation types to drought are captured by the correlation and regression coefficients between Normalized Difference Vegetation Index (NDVI) anomalies and the Palmer Drought Severity Index (PDSI). A novel bootstrapping regression approach is used to decompose the relationships between the vegetation sensitivity (NDVI–PDSI regression slopes) and the principle climate factors (temperature and precipitation) associated with the drought. Significantly increased sensitivity to drought in warmer locations indicates the important role of temperature in exacerbating vulnerability; however, spatial precipitation variations do not demonstrate significant effects in modulating drought sensitivity. Based on annual NDVI response, chaparral is the most vulnerable community to warming, which will probably be severely affected by hotter droughts in the future. Drought sensitivity of coastal sage scrub (CSS) is also shown to be very responsive to warming in fall and winter. Grassland and developed land will likely be less affected by this warming. The sensitivity of the overall vegetation to temperature increases is particularly concerning, as it is the variable that has had the strongest secular trend in recent decades, which is expected to continue or strengthen in the future. Increased temperatures will probably alter vegetation distribution, as well as possibly increase annual grassland cover, and decrease the extent and ecological services provided by perennial woody Mediterranean climate ecosystems as well.

Societal Impact Statement: People plant, remove, and manage urban vegetation in cities for varying purposes and to varying extents. The direct manipulation of plants affects the benefits people receive from plants. In synthesizing several studies of urban biodiversity in Los Angeles, we find that cultivated plants differ from those in remnant natural areas. This highlights the importance of studying cultivated plants in cities, which is crucial for the design and planning of sustainable cities. Residents have created a new urban biome in Los Angeles, and this has consequences for associated organisms, ultimately resulting in a responsibility for society to determine what type of biome we wish to create.Summary: Urbanization is a large driver of biodiversity globally. Within cities, urban trees, gardens, and residential yards contribute extensively to plant biodiversity, although the consequences and mechanisms of plant cultivation for biodiversity are uncertain. We used Los Angeles, California, USA as a case study for investigating plant diversity in cultivated areas. We synthesized datasets quantifying the diversity of urban trees, residential yards, and community gardens in Los Angeles, the availability of plants from nurseries, and residents’ attitudes about plant attributes. Cultivated plant diversity was drastically different from remnant natural areas; compared to remnant natural areas, cultivated areas contained more exotic species, more than double the number of plant species, and turnover in plant functional trait distributions. In cultivated areas, most plants were intentionally planted and dominated by exotic species planted for ornamental purposes. Most tree species sampled in Los Angeles were available for sale in local nurseries. Residents’ preferences for specific plant traits were correlated with the trait composition of the plant community, suggesting cultivated plant communities at least partially reflect resident preferences. Our findings demonstrate the importance of cultivated species in a diverse megacity that are driven in part through commercial distribution. The cultivation of plants in Los Angeles greatly increases regional plant biodiversity through changes in species composition and functional trait distributions. The pervasive presence of cultivated species likely has many consequences for residents and the ecosystem services they receive compared with unmanaged or remnant urban areas.

Despite worldwide knowledge of the importance of the Galápagos archipelago, there is little comparative plot data from the forests in the dry regions. We examined patterns of woody plant (≥2.5 cm diameter at breast height (DBH)) species richness and structure using Gentry’s transect method (0.1 ha) on the three largest islands in the Galápagos. We identified the conservation status of woody plants within the dry forest region, assessed forest cover and change in the region, and compared field results to other tropical dry forests in the Pacific. Of the 22 species encountered (11 native, 11 endemic), there were no non-native species and only one threatened species. Isabela, Santa Cruz and San Cristóbal have similar overall levels of species, genera, family and liana richness per site, but significantly different tree species richness, density and tree height per transect. Geospatial databases identified 51 species (native 40%, endemic 60%) of woody plants (≥2.5 cm DBH) within the dry forest region of the Galápagos and 13 species (10 from the genus Scalesia) on the IUCN Red List. There is an estimated 551.97 km2 of dry forest in the Galápagos and there has been little change (<0.01%) in forest cover from 2000 to 2015. Dry forests of the Galápagos have similar levels of species richness to Hawaii and the Marquesas but contain lower densities, basal areas and tree heights than other dry forests in the Pacific. These dry forests appear to be the best preserved and protected tropical dry forest in the Pacific.

The prolonged 2012–2016 California drought has raised many issues including concerns over reduced vegetation health. Drought impacts are complicated by geographical differences in hydroclimatic variability due to a climatic dipole influenced by the Pacific. Analysis of MODIS‐derived Normalized Difference Vegetation Index and self‐calibrated Palmer Drought Severity Index from 2000 to 2018 reveals differences in drought and vegetation responses in Northern versus Southern California (NorCal vs SoCal, see definition in section ). The greatest declines in Normalized Difference Vegetation Index were focused in the SoCal, while NorCal appears not severely affected thus far. It appears that both the strength of drought and the sensitivity of the vegetation to drought are larger in SoCal. The exacerbated aridity in SoCal is a trend extending throughout the past and present century. The spatial differences in hydroclimatology and vegetation responses are important considerations for statewide climate change adaptation—with SoCal potentially facing greater challenges.