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PLANT DIVERSITY AND ENDEMISM IN THE CALIFORNIA FLORISTIC PROVINCE
Abstract
The California Floristic Province (CFP) is an area of high biodiversity and endemism corresponding roughly to the portion of western North America having a Mediterranean-type climate. High levels of diversity and endemism in the CFP are attributed to the unique geo-climatic setting of the region. In recent years, much has been learned about the origins of plant diversity in western North America. This work, however, has been hindered by a focus on political rather than biotic regions, such that much more is known about diversity and endemism in the state of California than the natural biotic region represented by the CFP. Here we present a preliminary list of native land plants (vascular plants and bryophytes) found in the CFP, as well as an analysis of diversity and endemism patterns at the level of both species and minimum rank taxa (MRT; species and infraspecific taxa). A total of 6,927 MRT are native to the CFP, including 6,143 vascular plants and 784 bryophytes. Of these, 2,612 vascular plants are endemic to the CFP (42%) compared to 37 endemic bryophytes (5%). Finally, 2,506 native CFP vascular plant MRT (41% of the CFP flora) and 454 CFP bryophyte MRT (58% of the CFP flora) are found outside California in the Oregon and Baja California parts of the CFP. This high degree of sharing across political boundaries among both vascular plants and bryophytes highlights the cohesiveness of the CFP, and the need to focus more research effort on biotic regions.
... Another biodiversity hotspot in North America is the California Floristic Province (CFP) (Calsbeek et al., 2003;Burge et al., 2016) and it is considered one of the world's top 25 most biologically rich and endangered terrestrial ecosystems (Myers et al., 2000). The CFP is an area with high plant diversity and endemism and exhibits a Mediterranean-type climate that extends to southern Oregon, western Nevada, and northern Baja California, Mexico (Raven and Axelrod, 1978). ...
... The CFP is an area with high plant diversity and endemism and exhibits a Mediterranean-type climate that extends to southern Oregon, western Nevada, and northern Baja California, Mexico (Raven and Axelrod, 1978). A total of 5006 species native to the CFP region exist with an estimate of 36.9 endemism (Burge et al., 2016). Compared to other areas of North America with high endemic plant and animal taxa, the CFP is the largest and has more identifiable subspecies than the central and northeastern United States and Canada combined (Calsbeek et al., 2003). ...
... California's flora, the Jepson Manual [5], classifies the state into ten ecoregions that represent different geographic divisions based on distinctive types of dominant vegetation, topographic, geologic and climatic conditions. Each ecoregion has a distinctive set of endemic species and communities adapted to specific climatic conditions [5,6] (see File S1 for a more detailed description). The ecoregions reveal the great vegetative diversity and climate variability that encompasses the state of California. ...
Climate change is affecting Mediterranean climate regions, such as California. Retrospective phenological studies are a useful tool to track biological response to these impacts through the use of herbarium-preserved specimens. We used data from more than 12,000 herbarium specimens of 29 dominant native plant species that are characteristic of 12 broadly distributed vegetation types to investigate phenological patterns in response to climate change. We analyzed the trends of four phenophases: preflowering (FBF), flowering (F), fruiting (FS) and growth (DVG), over time (from 1830 to 2023) and through changes in climate variables (from 1896 to 2023). We also examined these trends within California’s 10 ecoregions. Among the four phenophases, the strongest response was found in the timing of flowering, which showed an advance in 28 species. Furthermore, 21 species showed sequencing in the advance of two or more phenophases. We highlight the advances found over temperature variables: 10 in FBF, 28 in F, 17 in FS and 18 in DVG. Diverse and less-consistent results were found for water-related variables with 15 species advancing and 11 delaying various phenophases in response to decreasing precipitation and increasing evapotranspiration. Jepson ecoregions displayed a more pronounced advance in F related to time and mean annual temperature in the three of the southern regions compared to the northern ones. This study underscores the role of temperature in driving phenological change, demonstrating how rising temperatures have predominantly advanced phenophase timing. These findings highlight potential threats, including risks of climatic, ecological, and biological imbalances.
... Furthermore, unlike tracheophytes whose distributions are usually constrained to narrower elevational bands and single continents (Patiño and Vanderpoorten, 2018), many moss species, including S. caninervis, have broad ecological amplitude (María Ros et al., 1999;FNA, 2007+;eFloras, 2023). Such broad niches are thought to result from the ability of mosses to exploit similar microhabitats across vastly different environments (Ladrón de Guevara and Maestre, 2022) often resulting in cross-continental or disjunct distributions (e.g., Burge et al., 2016;Carter et al., 2016;Brooks and Jauregui-Lazo, 2023). The broad elevational and fine-scale niche we observed for S. caninervis in the DNWR exemplifies such a pattern in which many shrub species provide similarly buffered microhabitats distributed across three unique elevation zones. ...
Premise
Mosses provide many ecosystem functions and are the most vulnerable of biocrust organisms to climate change due to their sensitive water relations stressed by summer aridity. Given their small size, moss stress resistance may be more dependent on fine‐scale habitat than macroclimate, but the sheltering role of habitat (i.e., habitat buffering) has never been compared to macroclimate and may have important implications for predicting critical biocrust moss refugia in changing climates.
Methods
We located three populations of a keystone biocrust moss, Syntrichia caninervis , spanning 1200 m of altitude, which comprised three macroclimate (elevation) zones of characterized plant communities in the Mojave Desert. We stratified 92 microsites along three aridity gradients: elevation zone, topography (aspect), and microhabitat (shrub proximity). We estimated summer photosynthetic stress ( F v / F m ) and aridity exposure (macroclimate, irradiance, and shade).
Results
Microsite aridity exposure varied greatly, revealing exposed and buffered microhabitats at all three elevation zones. Moss stress did not differ by elevation zone despite the extensive macroclimate gradient, failing to support the high‐elevation refugia hypothesis. Instead, stress was lowest on northerly‐facing slopes and in microhabitats with greater shrub shading, while the importance of (and interactions between) topography, irradiance, and shade varied by elevation zone.
Conclusions
Fine‐scale habitat structure appears physiologically more protective than high‐elevation macroclimate and may protect some biocrust mosses from the brunt of climate change in widespread microrefugia throughout their current ranges. Our findings support a scale‐focused vulnerability paradigm: microrefugia may be more important than macrorefugia for bolstering biocrust moss resistance to summer climate stress.
... To test whether grassland community compositions respond rapidly and consistently to climate change, we collected compositional data from long-term quantitative observations and manipulative experiments in the California Floristic Province (CFP), a global biodiversity hotspot 30,31 (Extended Data Fig. 1). Encompassing broad geographic, climatic and edaphic gradients, the CFP harbours over 5,000 native vascular plant species with over 30% endemism 32 , but is heavily invaded by non-native species 33 . We first compiled 12 long-term observational records (Extended Data Table 1 and Extended Data Fig. 2) across the regional climate gradient during a period of climate warming and drying (equation (1), Extended Data Fig. 3 and Supplementary Tables 1 and 2). ...
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. We estimated 349 vascular plant species’ climatic niches from 829,337 occurrence records, compiled 15 long-term community composition datasets from 12 observational studies and 3 global change experiments, and analysed community compositional shifts in the climate niche space. We show that communities experienced significant shifts towards species associated with warmer and drier locations at rates of 0.0216 ± 0.00592 °C yr⁻¹ (mean ± s.e.) and −3.04 ± 0.742 mm yr⁻¹, and these changes occurred at a pace similar to that of climate warming and drying. These directional shifts were consistent across observations and experiments. Our findings contrast with the lagged responses observed in communities dominated by long-lived plants and suggest greater biodiversity changes than expected in the near future.
... California is recognized as both a global biodiversity (14,15) and Indigenous cultural diversity (16) hotspot. Over millennia, Indigenous people's stewardship of country within California's cultural regions exemplifies adaptation to changing environmental conditions to meet diverse ecocultural objectives including influences on fire, water, and biodiversity (17)(18)(19) and ensure social and ecological resilience. ...
The climate crisis has exacerbated many ecological and cultural problems including wildfire and drought vulnerability, biodiversity declines, and social justice and equity. While there are many concepts of social and ecological resilience, the exemplar practices of Indigenous stewardship are recognized in having sustained Indigenous peoples and their countries for millennia and past climate change events. California has been at the crossroads of many of these issues, and the historic and current contributions of Indigenous peoples to addressing these provide an excellent study of ecocultural stewardship and leadership by Indigenous peoples to achieve climate resilience.
... The Jepson Ecoregions (88) used in these analyses divide the state into major ecological regions sharing similar climate, topography, flora, and vegetation mosaics. Eighty percent of the state lies within the California Floristic Province-CFP (Northwestern, Cascade Range, Sierra Nevada, Great Valley, Central Western, and Southwestern ecoregions)-characterized by a Mediterranean-type climate (cool wet winters, warm dry summers) and exceptionally high plant diversity with 20% of all vascular plant species found in the United States, 37% of which are endemic (89,90). Vegetation of the CFP spans chaparral (evergreen shrublands), coastal scrub, and oak woodlands and grasslands in the south and at lower elevations in valleys and foothills, to mixed evergreen, conifer, montane, and subalpine forests in the north and at higher elevations. ...
An increasing amount of California’s landscape has burned in wildfires in recent decades, in conjunction with increasing temperatures and vapor pressure deficit due to climate change. As the wildland–urban interface expands, more people are exposed to and harmed by these extensive wildfires, which are also eroding the resilience of terrestrial ecosystems. With future wildfire activity expected to increase, there is an urgent demand for solutions that sustain healthy ecosystems and wildfire-resilient human communities. Those who manage disaster response, landscapes, and biodiversity rely on mapped projections of how fire activity may respond to climate change and other human factors. California wildfire is complex, however, and climate–fire relationships vary across the state. Given known geographical variability in drivers of fire activity, we asked whether the geographical extent of fire models used to create these projections may alter the interpretation of predictions. We compared models of fire occurrence spanning the entire state of California to models developed for individual ecoregions and then projected end-of-century future fire patterns under climate change scenarios. We trained a Maximum Entropy model with fire records and hydroclimatological variables from recent decades (1981 to 2010) as well as topographic and human infrastructure predictors. Results showed substantial variation in predictors of fire probability and mapped future projections of fire depending upon geographical extents of model boundaries. Only the ecoregion models, accounting for the unique patterns of vegetation, climate, and human infrastructure, projected an increase in fire in most forested regions of the state, congruent with predictions from other studies.
While investigating the potential for Arctostaphylos species to hybridize in the mixed populations of Point Sal and Burton Mesa in Santa Barbara County, California, we discovered that Arctostaphylos from the Nipomo Mesa (San Luis Obispo County), formerly considered a northern population of A. rudis, are genetically and morphologically distinct. We name this new taxon A. nipumu after the ytt (Northern Chumash language) word for the Nipomo Mesa region. For morphological and molecular analyses, we sampled 54 plants, focusing on A. purissima, A. rudis, and A. crustacea from multiple species and comparative single species populations. Parametric and nonparametric clustering analyses (STRUCTURE and PCA) of ddRADseq data show that Arctostaphylos from the Nipomo Mesa segregate from all other samples in the dataset. In mixed populations A. purissima and A. crustacea samples cluster with samples from other unmixed populations of the same species but A. rudis samples form two distinct clusters. One is composed of the mixed populations in Santa Barbara County, and the other consists of the Nipomo Mesa population. Additionally, the Santa Barbara County A. rudis samples are admixed in STRUCTURE analysis unlike the samples from the Nipomo Mesa. A principal component analysis of eight morphological characters shows that A. rudis individuals from Santa Barbara County tend to be phenotypically variable, occurring in a wide morphological cluster that overlaps with the tight clusters formed by A. purissima, A. crustacea, and Arctostaphylos from the Nipomo Mesa. Based on this evidence we describe the Nipomo Mesapopulation as a new species of Arctostaphylos. Given its limited and fragmented distribution we believe that A. nipumu is of critical conservation concern.
Bryum flabelliforme, a new facultative rheophytic moss, is described based on detailed morphological and molecular evidence. Examination of historical and recent specimens revealed that this moss has had a long history of confusion with several members of the Bryaceae that have rounded leaf apices. It has a broad distribution in North America, from California and Oregon eastward to Oklahoma and Kansas. A detailed description and photographs, known distribution, ecological data, and distinctions from similar-looking taxa are included. The unique rhizoidal tuber morphology of this species was previously unknown among North American bryaceous mosses. Splachnobryum valdiviae Müll.Hal. from temperate areas of the Southern Hemisphere was re-confirmed to belong to the Bryaceae rather than the Splachnobryaceae. This transfer to Bryum was corroborated by molecular data and subsequently formalized here.
Based on data of bryophyte invasions into 82 regions on five continents of both hemispheres, we aim here at a first comprehensive overview of the impacts that bryophytes may have on biodiversity and socio-economy. Of the 139 bryophytes species which are alien in the study regions seven cause negative impacts on biodiversity in 26 regions, whereas three species cause negative impacts on socio-economic sectors in five regions. The vast majority of impacts stem from anecdotal observations, whereas only 14 field or experimental studies (mostly on Campylopus introflexus in Europe) have quantitatively assessed the impacts of an alien bryophyte. The main documented type of impact on biodiversity is competition (8 alien bryophytes), with native cryptogams being most affected. In particular, C. introflexus (9 regions) and Pseudoscleropodium purum (7 regions) affect resident species composition. The few socio-economic impacts are caused by alien bryophytes which form dense mats in lawns and are then considered a nuisance. Most negative impacts on biodiversity have been recorded in natural grasslands, forests, and wetlands. Impacts of alien bryophytes on biodiversity and socio-economy are a recent phenomenon, with >85 % of impacts on biodiversity, and 80 % of impacts on socio-economy recorded since 1990. On average, 40 years (impacts on biodiversity) and 25 years (impacts on socio-economy) elapsed between the year a bryophyte species has been first recorded as alien in a region and the year impacts have been recorded first. Taking into account the substantial time lag between first record and first recorded impact in a region, it seems to be likely that the currently moderate impacts of alien bryophytes will continue to increase. As quantitative studies on impacts of alien bryophytes are rare and restricted to few environments and biogeographic regions, there is a need for addressing potential impacts of alien bryophytes in yet understudied settings.
The California Floristic Province exhibits one of the richest floras on the planet, with more than 5500 native plant species, approximately 40% of which are endemic. Despite its impressive diversity and the attention it has garnered from ecologists and evolutionary biologists, historical causes of species richness and endemism in California remain poorly understood. Using a phylogenetic analysis of 16 angiosperm clades, each containing California natives in addition to species found only outside California, we show that CA's current biodiversity primarily results from low extinction rates, as opposed to elevated speciation or immigration rates. Speciation rates in California were lowest among Arcto-Tertiary lineages (i.e., those colonizing California from the north, during the Tertiary), but extinction rates were universally low across California native plants of all historical, geographic origins. In contrast to long-accepted ideas, we find that California diversification rates were generally unaffected by the onset of the Mediterranean climate. However, the Mediterranean climate coincided with immigration of many desert species, validating one previous hypothesis regarding origins of CA's plant diversity. This study implicates topographic complexity and climatic buffering as key, long-standing features of CA's landscape favoring plant species persistence and diversification, and highlights California as an important refuge under changing climates.
Aim Biogeographical regionalizations, such as zoogeographical regions, floristic kingdoms or ecoregions, represent categorizations central to many basic and applied questions in biogeography, ecology, evolution and conservation. Traditionally established by experts based on qualitative evidence, the lack of transparency and quantitative support has set constraints on their utility. The recent availability of global species range maps, novel multivariate techniques and enhanced computational power now enable a quantitative scrutiny and extension of biogeographical regionalizations that will facilitate new and more rigorous uses. In this paper we develop and illustrate a methodological roadmap for species‐level biogeographical regionalizations at the global scale and apply it to mammals.
Location Global.
Methods We explore the relative usefulness of ordination and clustering methods and validation techniques. The performance of nine different clustering algorithms is tested at different taxonomic levels. The grain of regionalization (i.e. the number of clusters) will usually be driven by the purpose of the study, but we present several approaches that provide guidance.
Results Non‐metric multidimensional scaling offers a valuable first step in identifying and illustrating biogeographical transition zones. For the clustering of regions, the nine different hierarchical clustering methods varied greatly in utility, with UPGMA (unweighted pair‐group method using arithmetic averages) agglomerative hierarchical clustering having consistently the best performance. The UPGMA approach allows a tree‐like phenetic representation of the relative distances of regions and can be applied at different levels of taxonomic resolution. We find that the new quantitative biogeographical regions exhibit both striking similarities to and differences from the classic primary geographical divisions of the world’s biota. Specifically, our results provide evidence that the Sahara, northern Africa, the Arabian Peninsula and parts of the Middle East should be regarded as part of the Afrotropics. Further, the position of the New Guinean continental shelf, Lydekker’s Line, is supported as an appropriate border to separate the Oriental and Australian regions.
Main conclusions We propose that this sort of new, quantitative delineation and relationship assessment across taxonomic and geographical grains is likely to offer opportunities for more rigorous inference in historical and ecological biogeography and conservation.
Identification of global biodiversity hotspots is a leading conservationpriority ( Hotspots.Conservation International, Washington, DC; Precious Heritage: The Statusof Biodiversity in the United States. Oxford University Press, Oxford, UK), but weknow little about the nature and structure of such hotspots. Botanical richnessin one recently identified hotspot, the California Floristic Province, has longbeen attributed by evolutionists to edaphic and climatic heterogeneity. Here we demonstrate that the flora restricted (endemic) toserpentine soil, the state's most botanically distinctive substrate, showsunusually high ' diversity' – i.e., spatial variation inspecies composition – among regions, although ''diversity within any given region is low. Conservation of an endemic-rich florarequires a network of sites to capture this among-region or spatial component ofdiversity.
Rieseberg, L. H. & Brouillet, L.: Are many plant species paraphyletic? – Taxon 43: 21‐32. 1994. – ISSN 0040‐0262.
The phylogenetic Status of plant species has become a critical issue in systematic and evolutionary botany, due in part to the influence of Hennigian principles on organismal classification. This paper reviews various modes of speciation and their frequency in plants, and discusses predicted phylogenetic consequences of different modes of speciation. The classic model of allopatric speciation by subdivision will typically generate monophyletic daughter species, whereas most geographically local models of speciation (e.g., the founder effect model), will produce a paraphyletic progenitor and monophyletic derivative species. Due to the theoretical difficulty of transforming widespread population systems through gene flow or selection, allopatric speciation by subdivision is likely to be less frequent than geographically local models of speciation. Low levels of gene flow will also increase the time required for the progenitor species to achieve monophyly. Thus, many plant species are likely to be paraphyletic, and predictably a species classification based on the criterion of monophyly is unlikely to be an effective tool for describing and ordering biological diversity.
We asked whether evolutionary transitions to serpentine endemism are associated with transitions to more favorable environments. Theory and observation suggest that benign (e.g., high rainfall and less extreme temperatures) climates should favor the evolution of habitat specialism, both because such climates may facilitate persistence of small populations with novel adaptations, and because competition with non-specialists may be stronger in benign climates. Non-climatic factors, such as habitat availability, should also be associated with transitions to habitat specialism. We examined phylogenetic transitions to serpentine endemism in 23 Californian plant taxa. We contrasted transitions from serpentine-intolerant ancestors, where speciation entails novel adaptations to serpentine, with transitions from serpentine-tolerant ancestors, where the formation of a new serpentine-endemic taxon may result from an altered competitive environment. We found that transitions to endemism were strongly associated with transitions to regions with more benign climates, but only in the case of endemics arising from intolerant ancestors. In contrast, transitions to endemism from both types of ancestor were associated with transitions to regions with greater habitat availability. These results are consistent with the expectation that benign climates promote the persistence of small populations with novel adaptations both before and after speciation.
Abstract This paper addresses some of the conceptual issues involved in the analysis of the age and origin of mediterranean-climate plant taxa, paying particular attention to three topics: (1) the importance of an explicit time frame in the definition of biogeographical origins, (2) the distinction between the age of traits and the age of taxa, and (3) the idea of mediterranean-type ecosystems as environmental islands. (1) In California, recent analyses demonstrate that the diversity of species derived from different biogeographical origins is significantly correlated with temperature and precipitation gradients. These patterns support the hypothesis that niche conservatism is an important factor structuring modern diversity gradients. However, depending on how far back in time one looks, a species may be assigned to different origins; future discussions of biogeographical origins need to address the appropriate time frame for analysis. (2) Past research has demonstrated distinctive trait syndromes among woody plants of the Mediterranean, Chile, California and Mexico, and proposed that the syndromes are associated with lineages of different age in these floras. Reanalysis of individual traits demonstrates greater variability among regions than previously reported. The classification of plants into ‘old’ and ‘new’ genera is re-evaluated, and it is suggested that greater attention be paid to the age of traits, rather than to the age of taxa, especially at an arbitrary rank such as genus. (3) The idea of mediterranean-climate regions as ‘climatic islands’ is examined. Space–time diagrams of climate enable one to view the emergence of distinctive climatic regions in a continental context. The terms ‘synclimatic’ and ‘anticlimatic’ are proposed, referring to migration routes that parallel climate contours in space and time versus those that cross contours (including the case of geographic stasis in the face of climate change), respectively. Mediterranean-climate regions have served as important case studies in plant ecology and evolution, and merit continued close examination in the light of continued advances in phylogenetics and palaeoecology.
Question: Can we recognize areas of high endemism and high endemic richness, using data from collections, and what are the ecological variables that best explain these areas?
Location: Peninsula of Baja California, Mexico.
Methods: We analysed the distribution of 723 endemic vascular plants species along the peninsula of Baja California and neighbouring islands distributed in 218 cartographic cells 15’ x 20’ in size. By means of a residual analysis, we identified areas of significantly high endemic species richness, and we calculated the degree of endemicity (or rarity) in each cell by giving to each species a weight factor inversely proportional to the land area it covers.
Results: Nine regions of high-endemicity and/or high endemic species richness were found.
Discussion and conclusions: The analyses of rarity and endemic species richness showed two contrasting scenarios: High endemicity values in oceanic and sky islands accounts for a high number of species with a restricted distribution, promoted most likely by genetic isolation and high environmental heterogeneity. High endemic richness along the peninsular coast is related to ecotonal transition along vegetation types. After correcting for collection effort (i.e. the number of specimens collected within a cell), we found the phytogeographic region and altitudinal heterogeneity to be the variables that best predicted endemic richness. Both high endemism and high endemic richness have distinct geographic patterns within our study region. The nine endemic regions provide elements for priority definitions in future conservation programs.