Rapid shifts in grassland communities driven by climate change.

Many terrestrial plant communities, especially forests, have been shown to lag in response to rapid climate change. Grassland communities may respond more quickly to novel climates, as they consist mostly of short-lived species, which are directly exposed to macroclimate change. Here we report the rapid response of grassland communities to climate change in the California Floristic Province.

Extreme pre-fire drought decreases shrub regeneration on fertile soils.

Extreme drought and increasing temperatures can decrease the resilience of plant communities to fires. Not only may extremely dry conditions during or after fires lead to higher plant mortality and poorer recruitment, but severe pre-fire droughts may reduce the seed production and belowground vigor that are essential to post-fire plant recovery, and may indirectly facilitate invasion. We studied survival, recruitment, and growth of shrubs and herbs in chaparral (shrubland) communities in Northern California after a 2015 fire that immediately followed California's extreme 3-yr drought.

Trait-based signatures of cloud base height in a tropical cloud forest.

Premise: Clouds have profound consequences for ecosystem structure and function. Yet, the direct monitoring of clouds and their effects on biota is challenging especially in remote and topographically complex tropical cloud forests. We argue that known relationships between climate and the taxonomic and functional composition of plant communities may provide a fingerprint of cloud base height, thus providing a rapid and cost-effective assessment in remote tropical cloud forests.

Vulnerability and resistance in the spatial heterogeneity of soil microbial communities under resource additions.

Spatial heterogeneity in composition and function enables ecosystems to supply diverse services. For soil microbes and the ecosystem functions they catalyze, whether such heterogeneity can be maintained in the face of altered resource inputs is uncertain. In a 50-ha northern California grassland with a mosaic of plant communities generated by different soil types, we tested how spatial variability in microbial composition and function changed in response to nutrient and water addition.

Invasive species interact with climatic variability to reduce success of natives.

Plants have evolved resource-conservative and resource-acquisitive strategies to deal with variability in rainfall, but interactions with dominant invasive species may undermine these adaptations. To investigate the relative effect of invaders on species with these two strategies, we manipulated rainfall and invasive grass presence and measured demographic rates in three resource-acquisitive and three resource-conservative native annual forbs. We found that invasive grasses were harmful to all of the target species, but especially the resource-acquisitive ones, and that these effects were stronger under experimental drought.

Seed banks of native forbs, but not exotic grasses, increase during extreme drought.

Extreme droughts such as the one that affected California in 2012-2015 have been linked to severe ecological consequences in perennial-dominated communities such as forests. In annual communities, drought impacts are difficult to assess because many species persist through facultative multiyear seed dormancy, which leads to the development of seed banks. Impacts of extreme drought on the abundance and composition of the seed banks of whole communities are little known.

Climate-driven diversity change in annual grasslands: Drought plus deluge does not equal normal.

Climate forecasts agree that increased variability and extremes will tend to reduce the availability of water in many terrestrial ecosystems. Increasingly severe droughts may be exacerbated both by warmer temperatures and by the relative unavailability of water that arrives in more sporadic and intense rainfall events. Using long-term data and an experimental water manipulation, we examined the resilience of a heterogeneous annual grassland community to a prolonged series of dry winters that led to a decline in plant species richness (2000-2014), followed by a near-record wet winter (2016-2017), a climatic sequence that broadly resembles the predicted future in its high variability.

Shading and litter mediate the effects of soil fertility on the performance of an understorey herb.

Background And Aims: Soil fertility and topographic microclimate are common determinants of plant species distributions. However, biotic conditions also vary along these abiotic gradients, and may mediate their effects on plants. In this study, we investigated whether soils and topographic microclimate acted directly on the performance of a focal understorey plant, or indirectly via changing biotic conditions.

Landscape structure affects specialists but not generalists in naturally fragmented grasslands.

Understanding how biotic communities respond to landscape spatial structure is critically important for conservation management as natural habitats become increasingly fragmented. However, empirical studies of the effects of spatial structure on plant species richness have found inconsistent results, suggesting that more comprehensive approaches are needed. We asked how landscape structure affects total plant species richness and the richness of a guild of specialized plants in a multivariate context.

Resource colimitation governs plant community responses to altered precipitation.

Ecological theory and evidence suggest that plant community biomass and composition may often be jointly controlled by climatic water availability and soil nutrient supply. To the extent that such colimitation operates, alterations in water availability caused by climatic change may have relatively little effect on plant communities on nutrient-poor soils. We tested this prediction with a 5-y rainfall and nutrient manipulation in a semiarid annual grassland system with highly heterogeneous soil nutrient supplies.

Climate-driven diversity loss in a grassland community.

Local ecological communities represent the scale at which species coexist and share resources, and at which diversity has been experimentally shown to underlie stability, productivity, invasion resistance, and other desirable community properties. Globally, community diversity shows a mixture of increases and decreases over recent decades, and these changes have relatively seldom been linked to climatic trends. In a heterogeneous California grassland, we documented declining plant diversity from 2000 to 2014 at both the local community (5 m(2)) and landscape (27 km(2)) scales, across multiple functional groups and soil environments.

Historical and ecological controls on phylogenetic diversity in Californian plant communities.

We addressed the classic question of whether community diversity is determined from the bottom up by the breadth and partitioning of niche space or from the top down by historical and evolutionary forces. Specifically, we contrasted local and regional explanations for the diversity of Californian plant communities using phylogenetic and functional analyses. Our communities were sets of four field plots that sampled alpha (within-plot) and beta (among-plot) sources of variation in diversity.

Disentangling the drivers of β diversity along latitudinal and elevational gradients.

Understanding spatial variation in biodiversity along environmental gradients is a central theme in ecology. Differences in species compositional turnover among sites (β diversity) occurring along gradients are often used to infer variation in the processes structuring communities. Here, we show that sampling alone predicts changes in β diversity caused simply by changes in the sizes of species pools.

Can spatial isolation help predict dispersal-limited sites for native species restoration?

When the distribution of species is limited by propagule supply, new populations may be initiated by seed addition, but identifying suitable sites for efficiently targeted seed addition remains a major challenge for restoration. In addition to the biotic or abiotic variables typically used in species distribution models, spatial isolation from conspecifics could help predict the suitability of unoccupied sites. Site suitability might be expected to increase with spatial isolation after other factors are accounted for, since isolation increases the chance that a site is unoccupied only because of propagule limitation.

Is plant community richness regulated over time? Contrasting results from experiments and long-term observations.

There is considerable debate among ecologists as to whether or not communities are saturated. In saturated communities, species richness should remain relatively constant over time, despite compositional turnover, because richness is negatively correlated with colonization and positively correlated with local extinction. Few studies have tested for saturation using temporal observational data as well as diversity-perturbation experiments.

Navigating the multiple meanings of β diversity: a roadmap for the practicing ecologist.

A recent increase in studies of β diversity has yielded a confusing array of concepts, measures and methods. Here, we provide a roadmap of the most widely used and ecologically relevant approaches for analysis through a series of mission statements. We distinguish two types of β diversity: directional turnover along a gradient vs.

Origins and consequences of serpentine endemism in the California flora.

Habitat specialization plays an important role in the creation and loss of biodiversity over ecological and evolutionary time scales. In California, serpentine soils have a distinctive flora, with 246 serpentine habitat specialists (i.e.

Niche conservatism as an emerging principle in ecology and conservation biology.

The diversity of life is ultimately generated by evolution, and much attention has focused on the rapid evolution of ecological traits. Yet, the tendency for many ecological traits to instead remain similar over time [niche conservatism (NC)] has many consequences for the fundamental patterns and processes studied in ecology and conservation biology. Here, we describe the mounting evidence for the importance of NC to major topics in ecology (e.

Phylogeny, niche conservatism and the latitudinal diversity gradient in mammals.

Biologists have long searched for mechanisms responsible for the increase in species richness with decreasing latitude. The strong correlation between species richness and climate is frequently interpreted as reflecting a causal link via processes linked to energy or evolutionary rates. Here, we investigate how the aggregation of clades, as dictated by phylogeny, can give rise to significant climate-richness gradients without gradients in diversification or environmental carrying capacity.

Temporal variability and nestedness in California grassland species composition.

Nestedness occurs when species-poor assemblages contain a subset of the species that occur in more species-rich communities and is a commonly observed pattern in spatial data sets. Examination of nested distribution patterns across time rather than space are rarely conducted, even though they may have important implications for species coexistence. Nested temporal assemblages can occur when most species respond similarly to interannual variation in conditions.

Evolution and the latitudinal diversity gradient: speciation, extinction and biogeography.

A latitudinal gradient in biodiversity has existed since before the time of the dinosaurs, yet how and why this gradient arose remains unresolved. Here we review two major hypotheses for the origin of the latitudinal diversity gradient. The time and area hypothesis holds that tropical climates are older and historically larger, allowing more opportunity for diversification.

Effects of habitat fragmentation and isolation on species richness: evidence from biogeographic patterns.

Habitat subdivision by geography or human activity may be an important determinant of regional species richness. Cumulative species-area relationships for vertebrates, land plants, and insects on island archipelagoes show that collections of small islands generally harbor more species than comparable areas composed of one or a few large islands. The effect of the degree of habitat subdivision in increasing species richness appears to increase with the distance from potential sources of colonists.