The structure, function and value of urban forests in California communities

McPherson, E. Gregory; Xiao, Qingfu; Doorn, Natalie S. van; Goede, John de; Bjorkman, Jacquelyn; Hollander, Allan D.; Boynton, Ryan; Quinn, James; Thorne, James H.

doi:10.1016/j.ufug.2017.09.013

Cited by 62 publications

(48 citation statements)

References 37 publications

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“…The logic has been that if a tree species is on that list, then all individuals of that species, at all sites, are at risk of being killed by an infestation. McPherson et al (2017) used this logic to predict that nearly 12 million urban trees were at risk in coastal southern California and the asset value lost due to the invasive shot hole borers could be greater than $9 billion over 10 years. By the current logic, many millions of riparian trees in southern California are at risk of being killed by the shot hole borers, and all of these trees have the same high risk.…”

Section: Discussionmentioning

confidence: 99%

“…For instance, according to the Enriched Tree Hypothesis the predictions that the borers will (1) damage other natural sites as severely as the Tijuana River Valley (Greer, Rice & Lynch, 2018), (2) kill all the sycamores ( Platanus racemosa Nutt.) in California (Raver, 2018), and (3) cause billions of dollars worth of damage to urban trees (McPherson et al, 2017) likely overstate the threat.…”

Section: Discussionmentioning

confidence: 99%

“…First, they usually do not indicate where the impacts will be greatest within the range; as Venette, Coleman & Seybold (2015: 237) state, “ the magnitude of impact remains the most difficult component of any pest risk assessment to forecast. ” Second, these maps assume that all individuals of a host tree species are the same (McPherson et al, 2017) when in fact, as shown here within the Tijuana River Valley, trees of the same species growing under different conditions have different wood characteristics and very different KSHB infestation rates. Therefore, while a pest risk map will be useful in predicting the ultimate range of the KSHB, the Enriched Tree Hypothesis can direct us to sites within the range where the KSHB is likely to have the most impact.…”

Section: Discussionmentioning

confidence: 99%

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Impacts of the invasive shot hole borer (Euwallacea kuroshio) are linked to sewage pollution in southern California: the Enriched Tree Hypothesis

Boland¹,

Woodward

2019

PeerJ

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The Kuroshio Shot Hole Borer (KSHB, Euwallacea kuroshio) and the Polyphagous Shot Hole Borer (E. whitfordiodendrus; Coleoptera: Curculionidae: Scolytinae) have recently invaded southern California and are attacking live trees in commercial agriculture groves, urban parks and native riparian forests. Among native forests the worst impacts observed to date have been in the Tijuana River Valley in south San Diego County, where approximately 30% of the native willows (Salix spp.), or 120,000 trees, have died as a result of a KSHB infestation. This paper examines wood densities, wood moisture contents, KSHB infestation rates, and KSHB-induced mortality rates in two willow species (Salix lasiolepis and S. gooddingii) at sites near and far from sewage input. Comparisons were made on two spatial scales: broadly among sites within San Diego County; and locally among sites within the Tijuana River Valley. The results showed that, on average, willow trees growing closest to sewage pollution had significantly lower wood density, higher wood moisture content, higher KSHB infestation rates, and higher KSHB-induced willow mortality rates than those growing farther away. We present the Enriched Tree Hypothesis to explain the link between sewage pollution and KSHB impacts; it is as follows: (A) Riparian trees subject to nutrient enrichment from frequent sewage pollution grow quickly, and their fast growth results in wood of low density and high moisture content. If attacked by the KSHB, the trunks and branches of these nutrient-enriched trees provide an environment conducive to the fast growth of the symbiotic fungi upon which the KSHB feeds. With an abundant food supply, the KSHB population increases rapidly and the trees are heavily damaged by thousands of KSHB galleries in their trunks and branches. (B) Riparian trees not subject to frequent sewage pollution grow more slowly and have denser, drier wood. Conditions in their trunks and branches are not conducive to the fast growth of the KSHB’s symbiotic fungi. The KSHB generally ignores, or has low abundances in, these slow-growing trees. This new hypothesis explains current patterns of KSHB impact in San Diego County and focuses attention on the important roles of the environment and preexisting conditions of trees in determining the extent of KSHB impact. It highlights the Tijuana River Valley as an unusual site due to high sewage inputs and predicts that the high KSHB-induced willow mortality seen there should not occur in other natural riparian habitats in southern California. Most importantly, by identifying sewage pollution (or nutrient enrichment) as a major risk factor for KSHB impacts, the hypothesis ratchets down the KSHB-threat level for most riparian sites in southern California and directs attention to other nutrient-enriched sites as those most at risk.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Impacts of the invasive shot hole borer (Euwallacea kuroshio) are linked to sewage pollution in southern California: the Enriched Tree Hypothesis

Boland¹,

Woodward

2019

PeerJ

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“…Urban ecology studies regularly use areabased statistics, such as tree density (Staudhammer et al 2015, McPherson et al 2017). When sampling schemes use identical selection criteria, area-based variables are unaffected by plot size differences in theory; however, their variances decrease with increases in plot size (Zeide 1980), leading to different levels of uncertainty for each plot size.…”

Section: Introductionmentioning

confidence: 99%

“…When sampling schemes use identical selection criteria, area-based variables are unaffected by plot size differences in theory; however, their variances decrease with increases in plot size (Zeide 1980), leading to different levels of uncertainty for each plot size. On the other hand, when such studies utilize datasets with disparate sampling schemes or select trees within plots with different probabilities, comparisons must be adjusted for unequal plot sizes using a bootstrap process to construct means and standard errors (McPherson et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Assessing methods for comparing species diversity from disparate data sources: the case of urban and peri‐urban forests

2018

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Multi-scale forest inventory and monitoring data are increasingly being used in studies assessing forest diversity, structure, disturbance, and carbon dynamics. Also, local-level urban forest inventories are providing plot data and protocols to study tree diversity and ecosystem services in urban forests worldwide. But, differences in the sampling methods underlying these disparate protocols and data sources is a non-trivial concern in formulating comparative analyses. We assess commonly used methods for comparing tree diversity in peri-urban and urban forests when available data have different sample sizes, plot sizes, and sampling intensities. We present methods for appropriately evaluating species richness, as well as methods for comparing species distributions via community data matrices. Using permanent plot data from the southeastern United States, we present a case study comparing urban and peri-urban forests along a north-south gradient, and assessing species richness and the ecological homogenization hypothesis. Our findings indicate that comparisons of tree species richness among communities, or forest types, are often inconclusive since commonly used sample sizes do not provide precise estimates of the number of species present. While the ecological homogenization hypotheses can be tested under conditions of unequal sampling effort, we suggest robust methods such as PERMANOVA and the Raup-Crick dissimilarity index. A framework for selecting appropriate methods is also discussed. As forests are increasingly being altered by anthropogenic drivers, future studies using disparate data sources must account for differences in measurements and sampling protocols in order to produce results that are both statistically defensible and useful for science-based management.

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Exploring Bark‐Water Interaction Effects on Stemflow Nutrient Concentrations in Urban Trees

Lima,

Mathias,

Guandique

et al. 2024

Hydrological Processes

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This study investigates the influence of bark properties on nutrient fluxes in urban environments, focusing on the relationship between bark wettability, chemical composition, and the concentrations of nutrients in stemflow and adjacent soil across eight urban tree species. Through a comprehensive analysis involving chemical assays and ecohydrological measurements, we explored how variations in bark characteristics affect water interaction and subsequent chemical dynamics within urban landscapes. Contrary to the initial hypothesis that bark properties would significantly influence nutrient flux, results revealed a complex scenario where environmental and anthropogenic factors in urban settings seemingly overshadow the direct impact of bark characteristics on nutrient dynamics. Our findings indicate that while bark properties such as wettability and chemical composition do vary among tree species, these variations do not directly correlate with significant differences in stemflow or soil nutrient concentrations. This suggests a homogenising effect of urban environments on ecohydrological processes, highlighting the need for a broader understanding of urban forest ecology that incorporates both biological traits and urban‐specific environmental influences. This research contributes to the field of urban ecohydrology by underscoring the complexity of nutrient fluxes in urban forests and suggesting that effective urban tree management requires an integrated approach that considers the interplay between tree physiological traits and urban environmental conditions. Our study calls for further research to unravel the intricate dynamics of urban ecosystems, aiming to enhance the sustainability and ecological benefits of urban forests.

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The structure, function and value of urban forests in California communities

Cited by 62 publications

References 37 publications

Impacts of the invasive shot hole borer (Euwallacea kuroshio) are linked to sewage pollution in southern California: the Enriched Tree Hypothesis

Impacts of the invasive shot hole borer (Euwallacea kuroshio) are linked to sewage pollution in southern California: the Enriched Tree Hypothesis

Assessing methods for comparing species diversity from disparate data sources: the case of urban and peri‐urban forests

Exploring Bark‐Water Interaction Effects on Stemflow Nutrient Concentrations in Urban Trees

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