Alexander Cruz, Fellow of the American Ornithologists’ Union (AOU; now American Ornithological Society), died on May 15, 2018, in Boulder, Colorado, after a brief battle with pancreatic cancer. He will be remembered as an outstanding professor, mentor, and avian researcher in the Department of Ecology and Evolutionary Biology at the University of Colorado (CU). His boundless energy, contagious passion for science and conservation, and dedication to diversity touched thousands of students and colleagues both in the United States and abroad, especially in the West Indies. Alex was born in New York City to Puerto Rican parents, Florentino Cruz and Maŕıa Luisa Cruz, on July 12, 1941, and grew up speaking both English and Spanish at home. His father was a canary enthusiast, and Alex could not recall a life without birds. That early exposure sparked an interest in wild birds and other urban wildlife. A junior high school biology teacher in New York encouraged Alex, at the age of 14, to begin his lifelong interest in watching birds. Alex would also search vacant, weedy lots in the city for insects and anything else he could find. His interest in insects was keen enough that he knew them by scientific name—rather startling for a kid growing up in a neighborhood with street gangs. He recalled that gangs didn’t hassle him because spouting scientific names made him an unlikely candidate for recruitment, or because the gang members sensed he would ‘‘go somewhere’’ and just ‘‘let him go.’’ Frequent visits to relatives in Puerto Rico furthered his blossoming interests, offering Alex opportunities not available in the dense urban setting of his home. Birds were both more abundant and easier to observe on Puerto Rico than in New York City. Those early experiences played a crucial role in Alex’s later interests in tropical ecology and island biogeography. While an undergraduate at City University of New York (CUNY), Alex developed a close friendship with Matt Cormons, who would become a naturalist and artist. Each had a profound influence on the other, and they spent many weekends during and after college bird watching together. After completing his B.S. in biology at CUNY in 1964, Alex worked as a microbiologist for the New York City Health Department for five years. He and Cormons continued their bird excursions in New York, across the country, and in Mexico. Hungry for more than their jobs offered, they encouraged each other to attend graduate school. Cormons recalls that Alex ‘‘was the incentive for me to also attend grad school, which I am very grateful for. We were definitely a positive influence on each other.’’ Alex obtained a Ford Foundation Fellowship when he enrolled in the Department of Zoology and Ecology at the University of Florida in 1968. He returned to his beloved West Indies to study Jamaican Woodpeckers, which resulted in his 1973 Ph.D. dissertation, ‘‘Ecology and behavior of the Jamaican Woodpecker (Melanerpes radioAlexander Cruz enjoying Magellanic Penguins in Chile, 2016. Photo courtesy of Alex Cruz, Jr.

Developed waters may improve arid landscapes for birds, but their efficacy requires further study. I counted birds along five 300-m transects originating at point sources of water in a New Mexico grassland, and compared results with those from transects without water. Total birds were nearly three times more abundant on transects with water, but differences were greater in spring and winter than during the wet summer period. Twenty-two of 25 common species trended toward greater abundance on transects with water, eight of these at statistically significant levels, including Gambel's Quail, Mourning Dove, House Finch, and a variety of wintering sparrows. Sixty-four percent of detections along transects with water occurred <50 m from the water sources, at which birds regularly drank. Results suggest 1) that water attracted birds, especially in dry seasons, and 2) that proximity to water may influence the abundance and composition of avian assemblages in arid landscapes. (c) 2015 Elsevier Ltd. All rights reserved.

We measured fire damage to 250 riparian trees in 2003-2004, and again in 2012-2013, in a southeastern Arizona grassland burned by wildfires in 2002, 2009, or both. Following a single fire, combined mortality or survival only by ground-level resprout was 64% for desert willow (Chilopsis linearis), 57% for Fremont cottonwood (Populus fremontii), 48% for Arizona walnut (Juglans major), 32% for velvet ash (Fraxinus velutina), and 25% for Wright's sycamore (Platanus wrightii). A second fire burned 120 of the trees that happened to have been less damaged by the first fire. Distinctions among species in overall fire damage persisted after the second fire but to a lesser degree. By the conclusion of our study, 26% of the 250 trees had died completely while another 32% survived only as relatively small resprouts. We conclude that the fires substantially reduced both the abundance and crown volume of mature riparian trees in the study area.

Livestock grazing and fire influence the composition of desert grassland communities, including their rodent populations. However, there have been few studies of the interactions between grazing and wildfire in arid grasslands of the southwestern United States. We trapped rodents and measured vegetation on grazed versus ungrazed plots before (2001) and following (2002-2007) an intense 15,000 ha wildfire in southeastern Arizona. The fire reduced grass canopy on grazed plots for 2 y and on ungrazed plots for 3 y. Some rodents in the family Cricetidae (genera Baiomys, Reithrodontomys and Sigmodon) were more abundant on ungrazed plots before the fire. Cricetidae as a whole declined following the fire and did not return to preburn levels until the sixth postfire year (2007). Nine of ten cricetid species contributed to this general pattern. By contrast, the abundant species of Heteromyidae (Chaetodipus hispidus, C. baileyi, Perognathus flavus) increased following the fire, especially on ungrazed plots. These results are consistent with a model predicting that fire-caused reductions in grass cover should favor Heteromyidae over Cricetidae. Fires elsewhere in the Southwest have had little impact on rodent populations, but these were smaller and cooler burns with relatively minor effects on vegetation. Future studies of large wildfires of varying intensities would further elucidate the generality of the model.

THE COXIFEROUS forests of the northern Sierra Nevada usually are described as pine (Pinus) or fir (Abies) dominated. The pines of this region are designated as fire-type vegetation because pine seed germination after fires is common. There are many statements in the literature about this natural process of reforestation, but we have found little or no quantitative data on the phenomenon. In this study we have attempted to gather detailed information on conifer regeneration on the Donner Ridge burn, near the University of California Sagehen Creek Field Station, Nevada County, California.

This chapter describes the impacts of rural exurban development on the abundance and variety of plants and animals in North American ecosystems. The principles of landscape ecology provide a framework for considering the ways that exurban development can impact biodiversity. We survey the literature and describe the responses of varying components of biodiversity to rural exurban development in North America. Results suggest that habitat loss and landscape fragmentation have relatively minor impacts on exurban biodiversity, except at the highest housing densities. In contrast, perforation edge effects and land-use changes are highly important in most cases. Positive perforation effects include the provision of resources such as water and shade that otherwise can be scarce in natural habitats. Negative perforation effects include competition, predation, and nest parasitism from household pets and other human commensal species and escapes of exotic vegetation from landscaped areas into adjacent natural ecosystems. The chapter concludes by suggesting ways in which planners and property owners can mitigate or avoid impacts on habitat and wildlife.

Ranches are being converted to exurban housing developments in the southwestern United States, with potentially significant but little‐studied impacts on biological diversity. We counted birds in grasslands and savannas in southeastern Arizona that were grazed by livestock, embedded in low‐density exurban housing developments, or both, or neither. Species richness and bird abundance were higher in exurban neighborhoods than in undeveloped landscapes, independent of livestock grazing. The positive response to development was particularly evident among doves, quail, hummingbirds, aerial insectivores, and some but not all ground‐foraging sparrows. Effects of livestock grazing were comparatively minor and mostly involved birds with requirements for tall ground cover or the lack of it. The average rank correlation between counts of individual species and housing density was positive across all transects. However, this relationship disappeared among the exurban transects alone, and bird species richness on the exurban transects was negatively correlated with the number of homes nearby. These results suggest that the positive influence of exurban development on avian abundance and variety was greatest at the lowest housing densities. We attribute the attraction of many birds to exurban development to an oasis effect, in which resources otherwise scarce in arid southwestern environments (shade, nectar, nest sites, and especially water) are relatively abundant around exurban home sites. This finding is consistent with the hypothesis that exurban home sites represented resource supply points inside birds' home ranges otherwise consisting mostly of natural vegetation.

Fire was a common prehistoric disturbance in most southwestern grasslands, oak savannas, and coniferous forests, but not in Sonoran and Mojave desertscrub, or in riparian ecosystems. Prescribed burning should be applied, but under experimental conditions that facili- tate studying its impacts on birds and other components of biodiversity. Fire plays a critical role in maintaining a balance between desert grassland and Chihuahuan desertscrub, but unburned areas also are important for birds dependent upon woody vegetation and/or heavy grass cover. Understory fire probably once played a critical role in maintaining relatively open oak (Quercus spp.), pinyon-juniper (Pinus- Juniperus), and ponderosa pine (Pinus ponderosa) woodlands and their bird assemblages, while stand replacement fires sustained aspen groves (Populus tremuloides) at higher elevations. Carefully controlled prescribed burning, thinning, and grazing management will be needed to return fire to its prehistoric role in these habitats. There is an urgent need for cooperative effort between man- agers and researchers to implement replicated burns to quantify avian responses in appropriate habitats.

Livestock grazing may or may not be an exogenous disturbance facilitating the spread of exotic grasses, perhaps depending on the historical importance of native ungulates in a particular grassland. We compared canopy cover of native grasses and two African lovegrasses (Eragrostis spp.) over 22 years in ungrazed versus livestock grazed desert grasslands in southeastern Arizona. The exotics comprised <1% of the total grass canopy in either treatment in 1984, but by 2006 this number had risen to 24% in grasslands ungrazed since 1968, and to 65% on adjacent cattle ranches. The exotics increased from 79% to 99% canopy over the same time period in ungrazed areas where they had been planted. Results indicate that: (1) protection from grazing reduced the rate of exotic invasions into native grasslands; (2) areas deliberately planted with the exotics developed into near monocultures even under livestock exclusion, and (3) livestock grazing is an exogenous disturbance in southeastern Arizona, to which exotics are better adapted than most native grasses. It remains to be determined whether ungrazed native desert grasslands will resist further incursions by the African species.

Increases of velvet mesquite (Prosopis velutina Woot.) in southwestern grasslands might have been caused by livestock consumption of fuels that once burned with sufficient frequency and intensity to kill the trees. However, attempts to control mesquite with fire usually have failed. We measured fire damage and 5 years of postfire recovery for 225 mesquite trees > 1 m tall, following a 2002 wildfire that included grasslands differing in fire history, presence vs. 34-year livestock exclusion, and predominance of native vs. exotic grasses. The fire burned 100% of ground cover in ungrazed areas and 65% on grazed lands. Top-kill was 100% for trees in exotic ungrazed grasslands (the areas with highest fuel loads), 79% for trees in ungrazed native grasslands, and 28% for trees in grazed grasslands. Most top-killed trees produced ground sprouts, so that by 2006 the combined foliage volume from ground sprouts and surviving branches was 78% (± 3.2 SE) of preburn foliage volume in grazed areas, 66% (± 3.3) in ungrazed exotic grasslands, and 57% (± 4.0) in ungrazed native grasslands. Fire damage was greater among surviving trees in ungrazed areas that had burned twice (1987 and 2002) than among those that had burned only once since 1968 (in 2002), especially in native grasslands where postfire foliage recovery for twice-burned trees was only 47% (± 6.3) by 2006. Only 1 of 84 trees died in the area burned once, whereas 12 of 66 (18.2%) died in the area burned twice, including several individuals > 3 m tall. These results suggest that repeated fires likely could have prevented the historic spread of velvet mesquite into southwestern grasslands, but probably could be used to control mesquite today only in areas where abundant herbaceous growth provides sufficient fine fuels.

Species richness and evenness are components of biological diversity that may or may not be correlated with one another and with patterns of species abundance. We compared these attributes among flowering plants, grasshoppers, butterflies, lizards, summer birds, winter birds, and rodents across 48 plots in the grasslands and mesquite-oak savannas of southeastern Arizona. Species richness and evenness were uncorrelated or weakly negatively correlated for each taxonomic group, supporting the conclusion that richness alone is an incomplete measure of diversity. In each case, richness was positively correlated with one or more measures of abundance. By contrast, evenness usually was negatively correlated with the abundance variables, reflecting the fact that plots with high evenness generally were those where all species present were about equally uncommon. Therefore richness, but not evenness, usually was a positive predictor of places of conservation value, if these are defined as places where species of interest are especially abundant. Species diversity was more positively correlated with evenness than with richness among grasshoppers and flowering plants, in contrast to the other taxonomic groups, and the positive correlations between richness and abundance were comparatively weak for grasshoppers and plants as well. Both of these differences can be attributed to the fact that assemblages of plants and grasshoppers were numerically dominated by small subsets of common species (grasses and certain spur-throated grasshoppers) whose abundances differed greatly among plots in ways unrelated to species richness of the groups as a whole.

Ranches are being converted to exurban housing developments in the southwestern United States, with potentially significant impacts on biological diversity. We surveyed butterflies on 48 plots in grasslands, mesquite savannas, and oak savannas in southeastern Arizona that were grazed by livestock, embedded in low-density housing developments, or both, or neither. Results suggest that livestock grazing had little impact on butterfly species richness or abundance, while exurban development had minor impacts compared to negative effects that have been documented elsewhere in more fully developed urban and suburban landscapes. However, our data indicate that conversion of ranchland to exurban development has not been without consequence to butterflies. First, relatively immobile species with multiple broods and/or generalized diets were positively associated with development in grasslands, unaffected in mesquite savannas, and often negatively associated with development in oak savannas. Second, while abundance and variety of butterflies were positively correlated with plant species richness and cover in undeveloped landscapes, such correlations were not present in exurban areas. These results suggest that increased resources associated with housing development, including water, shade, and nectar, and possible negative impacts of increased avian predation and pesticide use, caused relationships between butterflies and native vegetation to be less tightly coupled in exurban than in undeveloped landscapes.

Ranches are being converted to exurban housing developments in the southwestern United States, with potentially significant but little-studied impacts on biological diversity. We captured rodents on 48 traplines in grasslands, mesquite savannas, and oak savannas in southeastern Arizona that were grazed by livestock, embedded in exurban housing developments, grazed and embedded in development, or neither grazed nor embedded in development. Independent of habitat or development, rodent species richness, mean rank abundance, and capture rates of all rodents combined were negatively related to presence of livestock grazing or to its effects on vegetative ground cover. Exurban development had no obvious effects on rodent variety or abundance. Results suggest southwestern exurban developments can sustain a rich assemblage of grassland and savanna rodents if housing densities are low and houses are embedded in a matrix of natural vegetation with little grazing.