Subalpine and alpine regions in California are rapidly warming. In response, high-elevation plants may acclimate or adapt to the new climate, move to higher elevations or latitudes, persist in refugia, or go extinct. Although shifts in high-elevation plant communities have been documented in other regions of the world, such changes have not yet been studied in Yosemite National Park. To assess high-elevation plant community shifts in Yosemite National Park, we resurveyed historic vegetation plots spanning 2800 to 3800 m from conifer forests to alpine fell-fields. Over the past 30 yr, in the subalpine zone, species richness declined by 7% on average. In the alpine zone, vegetation cover increased by 31% and species richness increased by 11% on average. Community composition shifted slightly towards lower-elevation assemblages, with no significant change in community climate affinity. Notably, Pinus albicaulis Engelm. appears to be transitioning from krummholz to upright growth, with 42.1% of previously alpine plots now supporting upright trees. These trends may indicate early stages of ecosystem transition under climate change.
Allium crenulatum Wiegand was originally described from the Olympic Mountains of Washington, where it occurs primarily on basalt-derived substrates. Field and herbarium studies reveal that populations historically assigned to A. crenulatum from the Wenatchee Mountains of central Washington differ consistently from Olympic Mountains plants and those in northwestern Oregon in floral and vegetative morphology, including tepal apices, tepal orientation at anthesis, and pedicel length. Wenatchee Mountain populations occur on ultramafic substrates at elevations of 900–2240 m and exhibit erect, narrowly ovate flowers with blunt tepals that remain nearly erect through fruiting, contrasting with the spreading, acute-tipped tepals of coastal populations. Given the Wenatchee Mountains plants' consistent morphological distinctions, disjunction from the core Allium crenulatum distribution, and occurrence in an area with a relatively high level of narrow endemics exhibiting edaphic specialization, we recognize these plants as a new variety, Allium crenulatum var. wenatchense Y.Li & Giblin.
We compared long-term data on acorn production of Tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S.H.Oh) with those of California true oaks (Quercus spp.) to test the hypothesis that Tanoak, as a largely insect-pollinated species, exhibits less evidence of masting behavior than wind-pollinated true oaks. Our results confirmed that variability in annual acorn production was reduced in Tanoak by several indices. Furthermore, Tanoak did not show evidence of resource depletion due to acorn production based on lag-1 autocorrelations and exhibited local spatial synchrony in acorn production over a much shorter distance than true oaks. Tanoak provides a contrast to true oaks that potentially offers new insights into the evolution of masting behavior.
Selection of genotypes to use in habitat restoration requires consideration of specific restoration goals, such as retaining genetic or species diversity, as well as challenges, such as climate change and the location and quality of extant source populations. Typically, if local source populations are readily available, practitioners will use local material which prioritizes local genetic integrity and adaptation. If local material is not available, seed purchased from non-local sources may have the benefit of providing broader genetic diversity for changing environmental conditions. Along the south coast of California, climate change is predicted to cause more intense but fewer winter storm events, resulting in prolonged dry seasons and episodic dry periods during the rainy season. In vernal pool grassland landscapes, these drought conditions may favor invasive species such as exotic annual grasses, especially if local native populations cannot tolerate severe drought. Yet, intraspecific geographic variation may have created populations that differ in their responses to drought or interspecific competitors. We set up a common garden greenhouse experiment focusing on Juncus bufonius L. (Toad Rush), a species common in, but not endemic to, vernal pools. We collected seeds from Santa Barbara and San Diego populations, the latter having evolved under longer seasonal droughts and lower annual rainfall. We exposed seeds from these populations to different drought regimes and competition with an invasive species, Festuca perennis (L.) Columbus & J.P.Sm. (Italian Ryegrass), in a controlled setting. We found intraspecific differences among geographic genotypes in aboveground growth and biomass, mortality, reproduction, and competition effects in response to drought and competition. The Santa Barbara population generally performed the worst under drought conditions, but there was not one population that consistently outperformed the others in all plant response variables. This intraspecific variation in response to drought and competition may affect a population's ability to persist under climate change, which suggests that the establishment and sustainability of restored populations can be maximized if we can identify specific source populations with adaptations to future climate conditions. Lacking specific climate predictions or population adaptations, maximizing genetic diversity by sourcing seed from multiple populations may also increase a restored population's performance under climate change.
Disturbance legacies can shape plant communities long after the initial event. The persistence and scale of these effects remain complicated, however, which in many instances can conflict with restoration efforts. Santa Cruz Island (SCI), California, presents a compelling case study in legacy effects. It was subject to over a century of intensive grazing by non-native cattle and feral sheep and rooting by feral pigs (Sus scrofa), and later to large-scale eradication and fire management interventions. We resurveyed 40 permanent grassland plots in southwestern SCI that were originally sampled in the 1990s—during the height of pig activity—and compared them to surveys conducted in 2023, 17 years after pig eradication. Using redundancy analysis (RDA), we asked: 1) did fine-scale pig rooting influence vegetation composition during the 1990s, 2) did rooting legacies on composition persist into the present, and 3) does current vegetation reflect longer-term legacy effects of non-native plant invasion? We found that rooting intensity and frequency explained significant variation in composition in the 1990s, but that these effects had largely dissipated by 2023. Instead, long-term changes were characterized by shifts among invasive herbaceous species, with no evidence of native shrub expansion or return to pre-disturbance states. Our results suggest that while pig disturbance had acute short-term effects, the most enduring legacy may be the non-native-dominated communities that became established in the late 19th century. These findings demonstrate the context dependence of ecological recovery, the deep ecological memory of intensively altered grasslands, and the need for active, tailored restoration approaches where passive recovery has stalled.
