Global Change and the Vulnerability of Chaparral Ecosystems

Underwood, Emma C.; Franklin, Janet; Molinari, Nicole A.; Safford, Hugh D.

doi:10.1002/bes2.1460

Cited by 7 publications

(6 citation statements)

References 17 publications

(26 reference statements)

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“…For example, once‐dominant vegetation types may transition to different types and lead to cascading ecological impacts. A classic example of this is vegetation type conversion (VTC) from native woody shrublands to invasive annual grasslands in Southern California, one of the five Mediterranean‐climate ecosystems in the world (Underwood, Franklin, et al, 2018). Chaparral shrublands provide a wide range of ecosystem services, and their support of exceptional species richness in one of the world's biodiversity hotspots makes their decline an issue of global significance (Rundel, 2018; Underwood, Hollander, et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Fire‐driven vegetation type conversion in Southern California

Syphard

Brennan²,

Rustigian‐Romsos³

et al. 2022

Ecological Applications

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One consequence of global change causing widespread concern is the possibility of ecosystem conversions from one type to another. A classic example of this is vegetation type conversion (VTC) from native woody shrublands to invasive annual grasslands in the biodiversity hotspot of Southern California. Although the significance of this problem is well recognized, understanding where, how much, and why this change is occurring remains elusive owing to differences in results from studies conducted using different methods, spatial extents, and scales. Disagreement has arisen particularly over the relative importance of short‐interval fires in driving these changes. Chronosequence approaches that use space for time to estimate changes have produced different results than studies of changes at a site over time. Here we calculated the percentage woody and herbaceous cover across Southern California using air photos from ~1950 to 2019. We assessed the extent of woody cover change and the relative importance of fire history, topography, soil moisture, and distance to human infrastructure in explaining change across a hierarchy of spatial extents and regions. We found substantial net decline in woody cover and expansion of herbaceous vegetation across all regions, but the most dramatic changes occurred in the northern interior and southern coastal areas. Variables related to frequent, short‐interval fire were consistently top ranked as the explanation for shrub to grassland type conversion, but low soil moisture and topographic complexity were also strong correlates. Despite the consistent importance of fire, there was substantial geographical variation in the relative importance of drivers, and these differences resulted in different mapped predictions of VTC. This geographical variation is important to recognize for management decision‐making and, in addition to differences in methodological design, may also partly explain differences in previous study results. The overwhelming importance of short‐interval fire has management implications. It suggests that actions should be directed away from imposing fires to preventing fires. Prevention can be controlled through management actions that limit ignitions, fire spread, and the damage sustained in areas that do burn. This study also demonstrates significant potential for changing fire regimes to drive large‐scale, abrupt ecological change.

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Section: Introductionmentioning

confidence: 99%

Fire‐driven vegetation type conversion in Southern California

Syphard

Brennan²,

Rustigian‐Romsos³

et al. 2022

Ecological Applications

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“…These threats include destruction of habitat, propagation of exotic herbs, and abnormally frequent fires resulting from artificial ignitions, extreme föhn winds, and elevated vapor pressure deficits linked to changing climate (Syphard et al, 2007;Moritz et al, 2010;Seager et al, 2015). Potential consequences of frequent fire in chaparral warrant scientific study to support management of fuels, watersheds, and conserved lands (Underwood et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Does short-interval fire inhibit postfire recovery of chaparral across southern California?

Storey

Stow

O’Leary

et al. 2021

Science of The Total Environment

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Regrowth after fire is critical to the persistence of chaparral shrub communities in southern California, which has been subject to frequent fire events in recent decades. Fires that recur at short intervals of 10 years or less have been considered an inhibitor of recovery and the major cause of 'community type-conversion' in chaparral, primarily based on studies of small extents and limited time periods. However, recent sub-regional investigations based on remote sensing suggest that short-interval fire (SIF) does not have ubiquitous impact on postfire chaparral recovery. A region-wide analysis including a greater spatial extent and time period is needed to better understand SIF impact on chaparral.This study evaluates patterns of postfire recovery across southern California, based on temporal trajectories of Normalized Difference Vegetation Index (NDVI) derived from June-solstice Landsat image series covering the period 1984-2018. High spatial resolution aerial images were used to calibrate Landsat NDVI trajectory-based estimates of change in fractional shrub cover (dFSC) for 294 stands. The objectives of this study were (1) to assess effects of time between fires and number of burns on recovery, using stand-aggregate samples (n = 294) and paired single-and multiple-burn sample plots (n = 528), and (2) to explain recovery variations among predominant single-burn locations based on shrub community type, climate, soils, and terrain. Stand-aggregate samples showed a significant but weak effect of SIF on recovery (p < 0.001; R 2 = 0.003). Results from paired sample plots showed no significant effect of SIF on dFSC among twice-burned sites, although recovery was diminished due to SIF at sites that burned three times within 25 years. Multiple linear regression showed that annual precipitation and temperature, chaparral community *

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“…Mediterranean-type ecosystems (MTEs) are biodiversity hotspots, accounting for almost 20% of the world's species in 5% of its area [1,2]. Heterogeneity in climate, topography, and fire regimes contributes to these high levels of species diversity [3][4][5]; however, climate change, frequent fire, urbanization, and non-native plant invasions are threatening the biodiversity of MTEs, leading to species extinctions as well as rapid changes in vegetation cover [2,4,6]. Therefore, it is essential to understand the trends in species loss and monitor changes in biodiversity [7].…”

Section: Introductionmentioning

confidence: 99%

“…Average time to complete vegetation-cover survey by method (point-intercept vs. Photogrid) and by Photogrid configuration(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). Configuration 1 is the most detailed photo survey containing 420 gridpoints per plot, and configuration 12 is the least detailed with only 45 gridpoints.…”

mentioning

confidence: 99%

A Camera-Based Method for Collecting Rapid Vegetation Data to Support Remote-Sensing Studies of Shrubland Biodiversity

et al. 2022

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The decline in biodiversity in Mediterranean-type ecosystems (MTEs) and other shrublands underscores the importance of understanding the trends in species loss through consistent vegetation mapping over broad spatial and temporal ranges, which is increasingly accomplished with optical remote sensing (imaging spectroscopy). Airborne missions planned by the National Aeronautics and Space Administration (NASA) and other groups (e.g., US National Ecological Observatory Network, NEON) are essential for improving high-quality maps of vegetation and plant species. These surveys require robust and efficient ground calibration/validation data; however, barriers to ground-data collection exist, such as steep terrain, which is a common feature of Mediterranean-type ecosystems. We developed and tested a method for rapidly collecting ground-truth data for shrubland plant communities across steep topographic gradients in southern California. Our method utilizes semi-aerial photos taken with a high-resolution digital camera mounted on a telescoping pole to capture groundcover, and a point-intercept image-classification program (Photogrid) that allows efficient sub-sampling of field images to derive vegetation percent-cover estimates while reducing human bias. Here, we assessed the quality of data collection using the image-based method compared to a traditional point-intercept ground survey and performed time trials to compare the efficiency of various survey efforts. The results showed no significant difference in estimates of percent cover and Simpson’s diversity derived from the point-intercept and those derived using the image-based method; however, there was lower correspondence in estimates of species richness and evenness. The image-based method was overall more efficient than the point-intercept surveys, reducing the total survey time by 13 to 46 min per plot depending on sampling effort. The difference in survey time between the two methods became increasingly greater when the vegetation height was above 1 m. Due to the high correspondence between estimates of species percent cover derived from the image-based compared to the point-intercept method, we recommend this type of survey for the verification of remote-sensing datasets featuring percent cover of individual species or closely related plant groups, for use in classifying UAS imagery, and especially for use in MTEs that have steep, rugged terrain and other situations such as tall, dense-growing shrubs where traditional field methods are dangerous or burdensome.

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Global Change and the Vulnerability of Chaparral Ecosystems

Cited by 7 publications

References 17 publications

Fire‐driven vegetation type conversion in Southern California

Fire‐driven vegetation type conversion in Southern California

Does short-interval fire inhibit postfire recovery of chaparral across southern California?

A Camera-Based Method for Collecting Rapid Vegetation Data to Support Remote-Sensing Studies of Shrubland Biodiversity

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