The green-up of vegetation in spring brings a pulse of food resources that many animals track during migration. However, green-up phenology is changing with climate change, posing an immense challenge for species that time their migrations to coincide with these resource pulses. We evaluated changes in green-up phenology from 2002 to 2021 in relation to the migrations of 150 Western-Hemisphere bird species using eBird citizen science data. We found that green-up phenology has changed within bird migration routes, and yet the migrations of most species align more closely with long-term averages of green-up than with current conditions. Changing green-up strongly influenced phenological mismatches, especially for longer-distance migrants. These results reveal that bird migration may have limited flexibility to adjust to changing vegetation phenology and emphasize the mounting challenge migratory animals face in following en route resources in a changing climate.

Climate change, interacting with and exacerbating anthropogenic modifications to the landscape, is altering ecosystem structure and function, biodiversity, and species distributions. Among the most visible short‐term impacts are the altered ecological roles of foundation species—those species, native or non‐native—that create locally stable environmental conditions and strongly influence ecosystem services. Understanding the future of these species is crucial for projecting impacts on ecosystem services at both local and regional scales. Here we present foundation species by ecoregion study cases across the US South‐Central Region (Louisiana, New Mexico, Oklahoma, and Texas), including C₄ grasses, mesquite, and northern bobwhite in the Southern Great Plains, mangroves and nutria in coastal Louisiana wetlands, tiger salamanders and sandhill cranes in wetlands of the Southern Great Plains, and post and blackjack oaks and eastern redcedar in the Cross Timbers ecoregion. These case studies explore the impacts of climate change on foundation species and the consequences for ecosystem services, the outlook for climate adaptation efforts, and the sustainability of restoration in these systems. We underscore risks and vulnerabilities that stakeholders should consider when managing or restoring natural resources and conserving ecosystem services in an increasingly extreme and variable climate. We show that past management, through a lack of understanding or implementation of actions, has exacerbated shifts in invasive species, resulting in significant changes in ecosystem structure and function. These changes, interacting with landscape fragmentation and shifting land use and exacerbated by climate change, can result in critical losses of biodiversity. Unfortunately, lack of public understanding may hinder political support for restoration efforts and climate adaptation strategies crucial for the continued supply of traditional ecosystem services. Furthermore, the resulting invaded systems may provide opportunities for income via new ecosystem services valued by society that may reduce support for restoration to historical baselines, thus further shifting management priorities. These priorities should be informed by an understanding of past and ongoing ecological trends in region‐specific situations, such as those we present, to highlight the immediacy of climate change impacts on the environment and society and provide evidence for the critical nature of informed management decisions.

In the Southern Great Plains (SGP) of the United States, encroachment of the native invasive woody legume, honey mesquite (Prosopis glandulosa Torr.), has caused a decline in C₄ mid‐grass abundance. Prosopis glandulosa invasion has also facilitated growth of the C₃ mid‐grass species, Texas wintergrass (Nassella leucotricha [Trin & Rupr.] Pohl) initially beneath its canopy but extending to interspaces between P. glandulosa as stand density increases. Little is known about the stability of the Prosopis/Nassella association or C₄ grass recovery following P. glandulosa disturbance. We quantified C₃ and C₄ grass production in interspaces, and basal cover in interspaces and P. glandulosa subcanopy microsites for 9 years following P. glandulosa suppression (top‐kill) and compared this to untreated P. glandulosa woodland (woodland). The Prosopis/Nassella association limited the window of C₄ mid‐grass recovery to only a few years. Nassella leucotricha dominated grass production during the first 3 years after top‐kill. C₄ mid‐grass recovery began in year 4, but was interrupted by severe drought in years 5 through 7. Recovery resumed in year 8, due to above‐average summer rainfall, but P. glandulosa regrowth was large enough by this time to limit C₄ mid‐grass production to a third of its potential. Nassella leucotricha basal cover remained dominant and stable in woodland subcanopy microsites, even during drought, and only briefly declined in top‐kill subcanopy microsites before returning to pretreatment levels by year 8 as P. glandulosa regrowth increased and provided shade. Synthesis and applications. A single suppression event had little impact on disrupting the Prosopis/Nassella association and allowing C₄ mid‐grass recovery. The coupling of a deciduous, N‐fixing C₃ woody species with this C₃ perennial grass may be a vegetative “state” that is resistant to multiple woody suppression disturbances and permanently limits the transition back to C₄ grassland.

Honey mesquite (Prosopis glandulosa) is an invasive native woody plant in the southern Great Plains, USA. Treatments used to slow the invasion rate have either killed the plant (“root-kill”) or killed above-ground tissue (“top-kill”). Top-killing provides temporary suppression, but stimulates multi-stemmed regrowth. This study from north central Texas quantified soil moisture, grass production and mesquite resprout architecture following a mechanical clearing treatment that top-killed mesquite (cleared) compared to untreated mesquite woodland (woodland) over a 10-year period. During an extreme drought at 5 and 6 years post-clearing, soil moisture at 60-cm depth became lower in cleared than in woodland, suggesting that, as early as 5 years after top-kill, water use by regrowth mesquite could be greater than that by woodland mesquite. Perennial grass production was greater in cleared treatments than in woodland treatments in all years except the extreme drought years. Mesquite regrowth biomass increased numerically each year and was independent of annual precipitation with one exception. During the year 5 and 6 drought, mesquite stopped lateral expansion of larger stems and increased growth of smaller stems and twigs. In summary, top-killing mesquite generated short-term benefits of increased grass production, but regrowth created potentially negative consequences related to soil moisture.

Prescribed fire is used to reduce woody plant invasion and restore herbaceous production and diversity in grasslands and savannas worldwide. Here, we determined whether a concentrated series of repeated‐winter, repeated‐summer, or alternate‐season (winter and summer) fires in a short timeframe (“transition fires”) could catalyze the restoration of C₄perennial grasses in Southern Great Plains, USA grasslands that had become dominated by a fire‐tolerant C₃woody N₂‐fixer (honey mesquite,Prosopis glandulosa) and a C₃perennial bunchgrass (Texas wintergrass,Nassella leucotricha). We applied transition fires over a 5‐yr span and maintenance fires on a portion of each plot 7 or 8 yr later. We measured herbaceous standing biomass and cover and soil variables (soil organic C, N, δ¹³C, and δ¹⁵N) in unburned, transition‐burned, and maintenance‐burned treatments. Greater δ¹³C at 10–20 (−17‰) than 0–10 (−20‰) cm depth increment confirmed that vegetation was historically mostly C₄grassland that shifted toward C₃dominance. Transition treatments with summer fire were most effective at top‐killing mesquite, but no treatments root‐killed >3%. Regrowth of top‐killed mesquite was similar in all treatments and reached pre‐fire height by 9–10 yr post‐fire. Herbaceous production and cover responses showed that: (1) Alternate‐season transition fires increased C₄mid‐grass, but did not change Texas wintergrass; (2) repeated‐summer fires reduced Texas wintergrass, but did not change C₄mid‐grass; and (3) repeated‐winter fires did not change C₄mid‐grass or Texas wintergrass compared with the unburned control. All maintenance fires stimulated Texas wintergrass biomass and cover, thus eliminating the reduction of Texas wintergrass caused by repeated‐summer transition fires. There were no long‐term effects of transition fires on soil C, N, δ¹³C, or δ¹⁵N. Results advance our understanding of the expectations and limitations of prescribed fire in shifting a woodland alternate state toward what was historically a fire supported C₄grassland/savanna.