Direct and indirect effects of environmental variability on growth and survivorship of pre‐reproductive Joshua trees, <i>Yucca brevifolia</i> Engelm. (Agavaceae)

Esque, Todd C.; Medica, Philip A.; Shryock, Daniel F.; DeFalco, Lesley A.; Webb, Robert H.; Hunter, Richard B.

doi:10.3732/ajb.1400257

Cited by 18 publications

(25 citation statements)

References 26 publications

(41 reference statements)

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“…While recruitment for this species may be infrequent due to multiple factors (Reynolds et al 2012), this study as well as the study of Barrows and Murphy-Mariscal (2012) found many trees under 1 m (presumably younger than approximately 20-30 yr by the calculations of Esque et al 2015) in height across the park. The macroplots represented a wide range of densities, especially of juveniles, with one macroplot containing none at all, to more than 70 juveniles.…”

Section: Discussionmentioning

confidence: 46%

“…As a proxy for age of Joshua trees (see Gilliland et al 2006 andEsque et al 2015 for discussion), teams measured height to the tallest part of the crown (along the axis of the trunk for trees that were leaning), living condition (a qualitative, categorical rating scale for overall plant condition from 2 (few shoots alive) to 5 (most shoots alive), and number of clonal sprouts on all living trees that we encountered within the macroplots. Macroplots were censused using a walking inventory navigating with the use of GPS units, covered generally in 25-m swaths by small teams of 3-5 individuals.…”

Section: Field Data Collectionmentioning

confidence: 99%

“…❖ www.esajournals.org Using height as a proxy for age, we identified juvenile individuals as those below a height of 60 cm, likely about 10-20 yr in age (using the calculations of Esque et al 2015 for MAP = 120 mm/yr) but which were pre-reproductive (trees may flower starting at 200 cm height; N. Frakes, N. Graver, and T. Green, unpublished data). We tallied the number of living trees per macroplot and the number of juvenile trees under 60 cm.…”

Section: Field and Model Output Analysismentioning

confidence: 99%

“…Joshua tree annual survivorship is age-and precipitation-dependent; low precipitation levels have an inordinate negative impact on survivorship of smaller plants (Esque et al 2015, DeFalco et al 2010. Joshua tree annual survivorship is age-and precipitation-dependent; low precipitation levels have an inordinate negative impact on survivorship of smaller plants (Esque et al 2015, DeFalco et al 2010.…”

Section: Introductionmentioning

confidence: 99%

“…Following on that study, Barrows and Murphy-Mariscal (2012), using a finer scale, a more restricted extent focusing on populations of the western Joshua tree, and a uniform maximum temperature increase of 3°C, predicted persistence of JTNP Joshua trees, but within an area that was just 10% of their current distribution. Others have examined key components of Joshua tree demography, such as survivorship following fires, juvenile growth, pollination, fruit production, and seed predation, all within a climate change context (DeFalco et al 2010, Esque et al 2015, Borchert and DeFalco 2016, Harrower and Gilbert 2018.…”

Section: Introductionmentioning

confidence: 99%

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Congruence between future distribution models and empirical data for an iconic species at Joshua Tree National Park

et al. 2019

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U.S. national parks protect a natural heritage of global significance; those parks, especially those in the arid southwest, are threatened by climate change. Identifying climate refugia within our national parks using not only statistical models, but also validating predictions using robust field data should provide focus for managers in their stewardship of parks' biological resources. In the region surrounding Joshua Tree National Park (JTNP), which straddles the Colorado and Mojave deserts in southern California, previous research has predicted the widespread demise of its namesake iconic species, the Joshua tree (Yucca brevifolia) due to climate change. In order to assess whether climate refugia exist for Joshua trees in the future at JTNP, we employed both field measurements and statistical models. We used current distribution point data together with historic climate data, to match conditions when the existing Joshua trees established, in order to predict the distribution of continuously suitable conditions (refugia) at the end-of-century. While the high and moderate mitigation could result in refugia for approximately 19% and 14% of the original area within JTNP, respectively, the business-as-usual scenario indicated an almost complete elimination of Joshua trees from the park. In order to validate model predictions, using teams of community scientists, we measured the demographic patterns of Joshua tree stands from low to upper elevations within JTNP. Recruitment within stands shows a strong concordance with modeled climate refugia; high-recruiting stands were within or closer to modeled refugia and in areas with lower climatic water deficit, higher precipitation, and lower maximum temperature than low-recruiting stands. These findings most importantly indicate the importance of regional to global mitigation strategies for carbon emissions, as reflected in the difference between maintenance of refugia vs. an almost complete elimination of the species from the park by the end-of-century. This also underscores the need to protect areas predicted to support refugia from multiple management threats. Rather than an ominous prediction of extinction, climate refugia provide land stewards with targets for focusing protective management, giving desert biodiversity places to weather the future.

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Section: Discussionmentioning

confidence: 46%

Section: Field Data Collectionmentioning

confidence: 99%

Section: Field and Model Output Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Congruence between future distribution models and empirical data for an iconic species at Joshua Tree National Park

et al. 2019

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Resilience and alternative stable states after desert wildfires

Abella

Gentilcore

Chiquoine

2020

Ecological Monographs

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Improving models of community change is a fundamental goal in ecology and has renewed importance during global change and increasing human disturbance of the biosphere. Using the Mojave Desert (southwestern United States) as a model system, invaded by nonnative plants and subject to wildfire disturbances, we examined models of resilience, alternative stable states, and convergent‐divergent trajectories for 36 yr of plant community change after 31 wildfires in communities dominated by the native shrubs Larrea tridentata or Coleogyne ramosissima. Perennial species richness on average was fully resilient within 23 yr after disturbance in both community types. Perennial cover was fully resilient within 25 yr in the Larrea community, but recovery was projected to require 52 yr in the Coleogyne community. Species composition shifts were persistent, and in the Coleogyne community, the projected compositional recovery time of 550 yr and increasing resembled a deflected trajectory toward potential alternative states. Disturbed sites contained a perennial species composition of predominately short‐statured forbs, subshrubs, and grasses, contrasting with the larger‐statured shrub and tree structure of undisturbed sites. Auxiliary data sets characterizing species recruitment, annual plants including nonnative grasses, biocrust communities, and soils showed persistent differences between disturbed and undisturbed sites consistent with positive feedbacks potentially contributing to alternative stable states. Resprouting produced limited resilience for the large shrubs L. tridentata and Yucca spp. important to population persistence but did not forestall long‐term reduced abundance of the species. The nonnative annual grass Bromus rubens increased on disturbed sites over time, suggesting persistently abundant nonnative plant fuels and reburn potential. Biocrust cover on disturbed sites was half and species richness a third of amounts on undisturbed sites. Soil nitrogen was 30% greater on disturbed sites and no significant trend was evident for it to decline on even the oldest burns. Disturbed desert plant communities simultaneously supported all three models of resilience, alternative stable states, and convergent‐divergent trajectories among community measures (e.g., species richness, composition), timeframes since disturbance, and spatial resolutions. Accommodating expression within ecosystems of multiple models, including those opposing each other, may help broaden theoretical models of ecosystem change.

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Yucca AGAVACEAE

Thiede¹

2019

Monocotyledons

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Direct and indirect effects of environmental variability on growth and survivorship of pre‐reproductive Joshua trees, Yucca brevifolia Engelm. (Agavaceae)

Cited by 18 publications

References 26 publications

Congruence between future distribution models and empirical data for an iconic species at Joshua Tree National Park

Congruence between future distribution models and empirical data for an iconic species at Joshua Tree National Park

Resilience and alternative stable states after desert wildfires

Yucca AGAVACEAE

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