Functional Trait Differences Between Weedy And Non-Weedy Plants In Southern California

MacKinnon, Evan D.; Pratt, R. Brandon; Jacobsen, Anna L.

doi:10.3120/0024-9637-61.4.328

Cited by 4 publications

(7 citation statements)

References 45 publications

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“…Exotic annual grasses are the most important and widespread, but exotic forbs are locally important. These dicots function differently than grasses and can be more responsive to environmental changes (Zavaleta et al, 2003; MacKinnon et al, 2014). Black mustard is nonmycorrhizal and inhibits mycorrhizal growth and development, a trait shared by many Brassicaceae species (Pakpour and Klironomos, 2015).…”

Section: Challenges To Predicting Changes Due To Vegetation‐type Conversion Of Chaparralmentioning

confidence: 99%

Vegetation‐type conversion of evergreen chaparral shrublands to savannahs dominated by exotic annual herbs: causes and consequences for ecosystem function

Pratt

2021

American J of Botany

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Woody, evergreen shrublands are the archetypal community in mediterranean‐type ecosystems, and these communities are profoundly changed when they undergo vegetation‐type conversion (VTC) to become annual, herb‐dominated communities. Recently, VTC has occurred throughout southern California chaparral shrublands, likely with changes in important ecosystem functions. The mechanisms that lead to VTC and subsequent changes to ecosystem processes are important to understand as they have regional and global implications for ecosystem services, climate change, land management, and policy. The main drivers of VTC are altered fire regimes, aridity, and anthropogenic disturbance. Some changes to ecosystem function are certain to occur with VTC, but their magnitudes are unclear, whereas other changes are unpredictable. I present two hypotheses: (1) VTC leads to warming that creates a positive feedback promoting additional VTC, and (2) altered nitrogen dynamics create negative feedbacks and promote an alternative stable state in which communities are dominated by herbs. The patterns described for California are mostly relevant to the other mediterranean‐type shrublands of the globe, which are biodiversity hotspots and threatened by VTC. This review examines the extent and causes of VTC, ecosystem effects, and future research priorities.

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Section: Challenges To Predicting Changes Due To Vegetation‐type Conversion Of Chaparralmentioning

confidence: 99%

Vegetation‐type conversion of evergreen chaparral shrublands to savannahs dominated by exotic annual herbs: causes and consequences for ecosystem function

Pratt

2021

American J of Botany

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“…Consequently, much research has been devoted to understanding patterns and drivers of invasion in California's ecosystems. This work has taken a number of approaches, including comparative studies of native and invasive species' traits (MacKinnon et al, 2014;Funk et al, 2016), but few studies directly compare drought responses among species, and none, to our knowledge, has addressed effects on reproductive output.…”

Section: Introductionmentioning

confidence: 99%

Invasive annuals respond more negatively to drought than native species

et al. 2019

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Summary In his foundational list of ‘ideal weed’ characteristics, Baker (1965) proposed that weedy plants maximize reproductive output under high resource availability. Since then, the idea that invasive plant species are more responsive to fluctuating resources compared with native or noninvasive species has gained considerable traction, although few studies extend this hypothesis to include reproductive output. We revisit Baker's hypothesis in the context of invasion and drought in California grasslands, exploring whether invasives show greater growth and reproductive responses to water availability compared with the native wildflowers they displace. In an outdoor potted study, we grew eight native and eight invasive species of annuals commonly found in southern California grasslands to reproductive maturity under both well‐watered and drought conditions. While drought negatively impacted plant performance overall, invasives showed more negative responses for growth and reproductive traits. Invasives also grew larger than native species, especially under well‐watered conditions, and produced seed with higher rates of germination. Invasives may be more negatively impacted by drought compared with natives, but they are also able to capitalize on high resource conditions and greatly increase reproductive output. Such opportunistic responses exhibited by invasives might explain previously observed fluctuations in their abundance under variable precipitation.

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“…Drought‐adapted plants have evolved mechanisms to cope with unpredictable and low water availability (Osmond et al 1987, MacKinnon et al 2014). Despite adaptive mechanisms, seed germination and seedling recruitment are especially vulnerable to desert constraints.…”

Section: Introductionmentioning

confidence: 99%

A seed–seedling conflict forAtriplex polycarpashrubs competing with exotic grasses and their residual dry matter

et al. 2021

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Native saltbush, Atriplex polycarpa, shrub populations are widely diminished and fragmented in the southern San Joaquin Desert of California due to habitat conversion and invasion by exotic annual grasses of mostly Mediterranean origin. The role these grasses play in saltbush population demography is not well understood. We hypothesized that saltbush seedling recruitment and growth is limited by the competitive interactions with exotic grasses, preventing saltbush stands from maintaining their populations and expanding. We predicted that saltbush seedling recruitment would be reduced by (1) light and moisture competition with the grasses; and (2) the physical barrier of grass residual dry matter (RDM) formed during senescence. To test our predictions, we investigated saltbush seedling recruitment under field conditions across six saltbush populations. We examined how variations in edaphic structure and water availability by site may have affected saltbush seedling recruitment and longer-term population dynamics. In experimental plots where saltbush seeds were sowed, exotic grass RDM reduced saltbush seedling emergence compared to seeds sown in the absence of RDM; competition post-emergence was not significant. Saltbush seedlings transplanted into the field had lower mortality and less herbivory in invaded grassy habitats compared to seedlings planted in bare zones in between established, mature saltbush shrubs. Edaphic variation and water availability by site were likely key factors affecting the success of both grass invasion and saltbush recruitment. Our results suggest that there is a seed-seedling conflict: Sites favorable for saltbush seedling emergence (minimal grass cover among mature shrubs) are unfavorable for seedling survival due to high herbivory. Conversely, sites favorable for saltbush seedling survival (high grass coverage away from mature shrubs) are unfavorable for seedling emergence. The RDM produced by grasses represents an important stabilizing feedback favoring continued grass dominance.

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Functional Trait Differences Between Weedy And Non-Weedy Plants In Southern California

Cited by 4 publications

References 45 publications

Vegetation‐type conversion of evergreen chaparral shrublands to savannahs dominated by exotic annual herbs: causes and consequences for ecosystem function

Vegetation‐type conversion of evergreen chaparral shrublands to savannahs dominated by exotic annual herbs: causes and consequences for ecosystem function

Invasive annuals respond more negatively to drought than native species

A seed–seedling conflict forAtriplex polycarpashrubs competing with exotic grasses and their residual dry matter

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