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Margaret Metz

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Papers by Margaret Metz

Emerging disease affects wildfire severity 1 2 Interacting disturbances : Wildfire severity affected by stage of forest disease invasion 4

Sudden oak death (SOD) is an emerging forest disease causing extensive tree mortality in coastal ... more Sudden oak death (SOD) is an emerging forest disease causing extensive tree mortality in coastal California forests. Recent California wildfires provided an opportunity to test a major assumption underlying discussions of SOD and land management: SOD mortality will increase fire severity. We examined pre-fire fuels from host species in a forest monitoring plot network in Big Sur, CA to understand the interactions between disease-caused mortality and wildfire severity during the 2008 Basin Complex wildfire. Detailed measurements of standing dead woody stems and downed woody debris one to two years prior to the Basin Fire provided a rare picture of the increased fuels attributable to SOD mortality. Despite great differences in host fuel abundance, we found no significant difference in burn severity between infested and uninfested plots. Instead, the relationship between SOD and fire reflected the changing nature of the disease impacts over time. Increased SOD mortality contributed to overstory burn severity only in areas where the pathogen had recently invaded. Where longer-term disease establishment allowed dead material to fall and accumulate, increasing log volumes led to increased substrate burn severity. These patterns help inform forest management decisions regarding fire, both in Big Sur and in other areas of California as the pathogen continues to expand throughout coastal forests.

Multi-scale phenological niches of seed fall in diverse Amazonian plant communities

Phenology has long been hypothesized as an avenue for niche partitioning or interspecific facilit... more Phenology has long been hypothesized as an avenue for niche partitioning or interspecific facilitation, both promoting species coexistence. Tropical plant communities exhibit striking diversity in reproductive phenology, but many are also noted for large synchronous reproductive events. Here we study whether the phenology of seed fall in such communities is non-random, what are the temporal scales of phenological patterns, and ecological factors that drive reproductive phenology. We applied multivariate wavelet analyses to test for phenological synchrony versus compensatory dynamics (i.e. anti-synchronous patterns where one species’ decline is compensated by the rise of another) among species and across temporal scales. We used data from long-term seed rain monitoring of hyperdiverse plant communities in the western Amazon. We found significant synchronous whole-community phenology at multiple time scales, consistent with shared environmental responses or positive interactions among...

Exploring the links between secondary metabolites and leaf spectral reflectance in a diverse genus of Amazonian trees

Ecosphere, 2021

Compound disease and wildfire disturbances alter opportunities for seedling regeneration in resprouter‐dominated forests

Ecosphere, 2019

Human-altered disturbance regimes and changing climatic conditions can reduce seed availability a... more Human-altered disturbance regimes and changing climatic conditions can reduce seed availability and suitable microsites, limiting seedling regeneration in recovering forest systems. Thus, resprouting plants, which can persist in situ, are expected to expand in dominance in many disturbance-prone forests. However, resprouters may also be challenged by changing regimes, and the mechanisms determining facultative seedling recruitment by resprouting species, which will determine both the future spread and current persistence of these populations, are poorly understood. In the resprouter-dominated forests of coastal California, interactions between wildfire and an emerging disease, sudden oak death (SOD), alter disturbance severity and tree mortality, which may shift forest regeneration trajectories. We examine this set of compound disturbances to (1) assess the influence of seed limitation, biotic competition, and abiotic conditions on seedling regeneration in resprouting populations; (2) investigate whether disease-fire interactions alter postfire seedling regeneration, which have implications for future disease dynamics and shifts in forest composition. Following a wildfire that impacted a preexisting plot network in SOD-affected forests, we monitored seedling abundances and survival over eight years. With pre-and postfire data, we assessed relationships between regeneration dynamics and disturbance severity, biotic, and abiotic variables, using Bayesian generalized linear models and mixed models. Our results indicate that postfire seedling regeneration by resprouting species was shaped by contrasting mechanisms reflecting seed limitation and competitive release. Seedling abundances declined with decreasing postfire survival of mature, conspecific stems, while belowground survival of resprouting genets had no effect. However, where seed sources persisted, seedling abundances and survival generally increased with the prefire severity of disease impacts, suggesting that decreased competition with adults may enhance seedling recruitment in this resprouter-dominated system. Species' regeneration responses varied with their relative susceptibility to SOD and suggest compositional shifts, which will determine future disease management and forest restoration actions. These results additionally highlight that mechanisms related to biotic competition, seed limitation, and opportunities for seedling recruitment beneath mature canopies may determine possible shifts in the occurrence of resprouting traits. This result has broad applications to other systems impacted by human-altered regimes where asexual persistence may be predicted to be a beneficial life history strategy.

Temporal coexistence mechanisms contribute to the latitudinal gradient in forest diversity

Nature, 2017

Changing disturbance regimes, ecological memory, and forest resilience

Frontiers in Ecology and the Environment, 2016

Ecological memory is central to how ecosystems respond to disturbance and is maintained by two ty... more Ecological memory is central to how ecosystems respond to disturbance and is maintained by two types of legacies-information and material. Species life-history traits represent an adaptive response to disturbance and are an information legacy; in contrast, the abiotic and biotic structures (such as seeds or nutrients) produced by single disturbance events are material legacies. Disturbance characteristics that support or maintain these legacies enhance ecological resilience and maintain a "safe operating space" for ecosystem recovery. However, legacies can be lost or diminished as disturbance regimes and environmental conditions change, generating a "resilience debt" that manifests only after the system is disturbed. Strong effects of ecological memory on post-disturbance dynamics imply that contingencies (effects that cannot be predicted with certainty) of individual disturbances, interactions among disturbances, and climate variability combine to affect ecosystem resilience. We illustrate these concepts and introduce a novel ecosystem resilience framework with examples of forest disturbances, primarily from North America. Identifying legacies that support resilience in a particular ecosystem can help scientists and resource managers anticipate when disturbances may trigger abrupt shifts in forest ecosystems, and when forests are likely to be resilient.

format_quoteChanges in climate and disturbance regimes critically impact forest resilience, raising key questions on ecological memory's role in future recovery under new conditions.format_quote

Habitat-specific divergence of procyanidins in Protium subserratum (Burseraceae)

Chemoecology, 2015

In Amazonian Peru, the neotropical tree Protium subserratum Engl. (Burseraceae) occurs as distinc... more In Amazonian Peru, the neotropical tree Protium subserratum Engl. (Burseraceae) occurs as distinct ecotypes on low nutrient white-sand (WS), intermediate fertility brown-sand (BS), and nutrient-rich clay (CS) soils. Genetic analysis indicates that these ecotypes are undergoing incipient speciation. Possible drivers of this divergence are habitat-specific herbivore faunas and differing resource availabilities. Protium subserratum, therefore, provides an ideal opportunity to investigate how defense chemistry evolves during lineage divergence. WS and BS races of P. subserratum are host to largely nonoverlapping herbivore communities and they differ in chlorogenic acid, flavonoid, and oxidized terpene chemistry. Here, we investigate how another important class of anti-herbivore chemicals, procyanidins (PCs), varies among the ecotypes. We isolated the PCs from leaves of juvenile and adult trees from each ecotype and used spectroscopic and chemical techniques to characterize the chemical structures of their component monomers. We found that WS, BS, and CS ecotypes accumulate ca. 17 % of leaf dry weight as PCs. Within ecotypes, we found very little difference in PC type, neither by site nor by life stage. Among ecotypes, however, we observed a marked divergence in PC composition that arose at least in part from differences in their terminal and extension subunits. In addition, the average polymer length of BS and CS PCs was significantly greater than in WS ecotypes. We conclude that phenotypic differences in PCs in the WS versus BS and CS ecotypes of P. subserratum are consistent with selection by herbivores in different soil types that differ strongly in nutrient availability and may contribute to the evolution of habitat specialization.

Interactive effects of sudden oak death and fire on forest biomass and carbon losses in the Big Sur region in coastal California

Background/Question/Methods In California forests, Sudden Oak Death (SOD) related mortality and f... more Background/Question/Methods In California forests, Sudden Oak Death (SOD) related mortality and frequent wildfires have emerged as an important forest management concern. The forests of Big Sur are among the most impacted by SOD. Following tree death, above ground biomass act as fuel load which aggravate forest fire. We hypothesize that SOD has a positive feedback on forest fire and the effects may be confounded by site physiography, fire characteristics (direction, intensity), and weather conditions. However, the feedback of forest fires on SOD may be positive or negative depending on forest re-growth after fire. Our goal is to assess the interaction between SOD mortality and forest fire (both frequency and intensity), and their effects on above-ground biomass/carbon losses in the Big Sur region. We established 280 long term monitoring plots across the forest of Big Sur region, and surveyed for SOD incidence. We surveyed plot vegetation inventory consisting of tree species and diam...

Defense varies during leaf development in tropical seedlings, shedding light into herbivory-mediated patterns of biodiversity

Background/Question/Methods Many tropical forest tree species delay greening their leaves until f... more Background/Question/Methods Many tropical forest tree species delay greening their leaves until full expansion, either by delayed chlorophyll synthesis or delayed development of the chloroplasts themselves. This strategy is thought to provide newly flushing leaves with protection against damage by herbivores by keeping young leaves devoid of nutritive value. Because young leaves suffer the greatest predation from invertebrate herbivores, delayed greening could prevent costly tissue loss. Many species that delay greening also produce anthocyanin pigments in their new leaves, giving them a reddish or bluish tint. These anthocyanins may be fungicidal, protect leaves against UV damage, make leaves cryptic to herbivores blind to the red part of the spectrum, or even attract herbivores, diverting them from more costly older leaves. Here, we undertake a comprehensive survey of seedlings, saplings and mature trees in a hyper-diverse forest in western Amazonia and ask the following questions...

Mapping burn severity in a disease-impacted forest landscape using Landsat and MASTER imagery

International Journal of Applied Earth Observation and Geoinformation, 2015

Global environmental change has increased forest vulnerability to the occurrence of interacting d... more Global environmental change has increased forest vulnerability to the occurrence of interacting disturbances, including wildfires and invasive diseases. Mapping post-fire burn severity in a disease-affected forest often faces challenges because burned and infested trees may exhibit a high similarity in spectral reflectance. In this study, we combined (pre-and post-fire) Landsat imagery and (post-fire) high-spectral resolution airborne MASTER data [MODIS (moderate resolution imaging spectroradiometer)/ASTER (advanced spaceborne thermal emission and reflection radiometer)] to map burn severity in a California coastal forest environment, where a non-native forest disease sudden oak death (SOD) was causing substantial tree mortality. Results showed that the use of Landsat plus MASTER bundle performed better than using the individual sensors in most of the evaluated forest strata from ground to canopy layers (i.e., substrate, shrubs, intermediate-sized trees, dominant trees and average), with the best model performance achieved at the dominant tree layer. The mid to thermal infrared spectral bands (3.0-12.5 m) from MASTER were found to augment Landsat's visible to shortwave infrared bands in burn severity assessment. We also found that infested and uninfested forests similarly experienced moderate to high degrees of burns where CBI (composite burn index) values were higher than 1. However, differences occurred in the regions with low burn severity (CBI values lower than 1), where uninfested stands revealed a much lower burn effect than that in infested stands, possibly due to their higher resilience to small fire disturbances as a result of higher leaf water content.

Demographic consequences of chromatic leaf defence in tropical tree communities: do red young leaves increase growth and survival?

Annals of botany, 2013

Many tropical forest tree species delay greening their leaves until full expansion. This strategy... more Many tropical forest tree species delay greening their leaves until full expansion. This strategy is thought to provide newly flushing leaves with protection against damage by herbivores by keeping young leaves devoid of nutritive value. Because young leaves suffer the greatest predation from invertebrate herbivores, delayed greening could prevent costly tissue loss. Many species that delay greening also produce anthocyanin pigments in their new leaves, giving them a reddish tint. These anthocyanins may be fungicidal, protect leaves against UV damage or make leaves cryptic to herbivores blind to the red part of the spectrum. A comprehensive survey was undertaken of seedlings, saplings and mature trees in two diverse tropical forests: a rain forest in western Amazonia (Yasuní National Park, Ecuador) and a deciduous forest in Central America (Barro Colorado Island, Panamá). A test was made of whether individuals and species with delayed greening or red-coloured young leaves showed low...

Object-based assessment of burn severity in diseased forests using high-spatial and high-spectral resolution MASTER airborne imagery

ISPRS Journal of Photogrammetry and Remote Sensing, 2015

Compared to PCA, MNF dramatically reduced image spectral variation, generating larger image objec... more Compared to PCA, MNF dramatically reduced image spectral variation, generating larger image objects with less complexity of object shapes. Whereas, PCA-based models delivered superior performance in most evaluated cases suggesting that some key spectral variability contributing to the accuracy of burn severity models in diseased forests may have been removed together with true spectral noise through MNF transformations.

format_quotePCA-based models performed better than MNF, suggesting that some key spectral information may be lost through MNF transformations.format_quote

Sudden oak death effects on the dynamics of dead wood

format_quoteFocus on accumulation rates of Bay Laurel, highlighting its ecological implications.format_quote

The relationship between wood density and mortality in a global tropical forest data set

New Phytologist, 2010

• Wood density is thought to be an important indicator of plant life history because it is couple... more • Wood density is thought to be an important indicator of plant life history because it is coupled to many aspects of whole-plant form and function. We used a hierarchical Bayesian approach to explain variation in mortality rates with wood density, drawing on data for 765 500 trees from 1639 species at 10 sites located across the Old and New World tropics. • Mortality rates declined with increasing wood density at five of 10 sites. Similar negative trends were detected at four additional sites, while one site showed no relationship. Our model explained 40% of variation in mortality on average. Both wood density and mortality rates show a high degree of phylogenetic conservatism. • Grouping species by family across sites in a second analysis, we found considerable variation in the relationship between wood density and mortality, with 10 of 27 families demonstrating a strong negative relationship. • Our results highlight the importance of wood density as a functional trait in tropical forests, as it is strongly linked to variation in survival. However, the relationship varied among families, plots, and even census intervals within sites, indicating that the factors responsible for the relationship between wood density and mortality vary spatially, taxonomically and temporally.

format_quoteMortality rates decrease with increasing wood density at five of ten tropical sites, suggesting a significant pan-tropical trend.format_quote

Temporal and spatial variability in seedling dynamics: a cross-site comparison in four lowland tropical forests

Journal of Tropical Ecology, 2008

Spatial and temporal variation in seedling dynamics was assessed using records of community-wide ... more Spatial and temporal variation in seedling dynamics was assessed using records of community-wide seedling demography collected with identical monitoring methods at four tropical lowland forests in Panama, Malaysia, Ecuador and French Guiana for periods of between 3 and 10 y. At each site, the fates of between 8617 and 391 777 seedlings were followed through annual censuses of the 370-1008 1-m 2 seedling plots. Within-site spatial and inter-annual variation in density, recruitment, growth and mortality was compared with among-site variability using Bayesian hierarchical modelling to determine the generality of each site's patterns and potential for meaningful comparisons among sites. The Malaysian forest, which experiences community-wide masting, was the most variable in both seedling density and recruitment. However, density varied year-to-year at all sites (CV among years at site = 8-43%), driven largely by high variability in recruitment rates (CV = 40-117%). At all sites, recruitment was more variable than mortality (CV = 5-64%) or growth (CV = 12-51%). Increases in mortality rates lagged 1 y behind large recruitment events. Within-site spatial variation and inter-annual differences were greater than differences among site averages in all rates, emphasizing the value of long-term comparative studies when generalizing how spatial and temporal variation drive patterns of recruitment in tropical forests.

format_quoteMean seedling density ranged significantly, from 8.9 seedlings/m² at Pasoh to 12.2 seedlings/m² at BCI, with year-to-year variations being notable.format_quote

An emergent disease causes directional changes in forest species composition in coastal California

Ecosphere, 2012

Non-native forest pathogens can cause dramatic and long-lasting changes to the composition of for... more Non-native forest pathogens can cause dramatic and long-lasting changes to the composition of forests, and these changes may have cascading impacts on community interactions and ecosystem functioning. Phytophthora ramorum, the causal agent of the emergent forest disease sudden oak death (SOD), has a wide host range, but mortality is concentrated in a few dominant tree species of coastal forests in California and Oregon. We examined interactions between P. ramorum and its hosts in redwood and mixed evergreen forest types over an 80,000 ha area in the Big Sur ecoregion of central California, an area that constitutes the southernmost range of the pathogen and includes forest stands on the advancing front of pathogen invasion. We established a network of 280 long-term forest monitoring plots to understand how host composition and forest structure facilitated pathogen invasion, and whether selective mortality from SOD has led to shifts in community composition. Infested and uninfested sites differed significantly in host composition due to both historical trends and disease impacts. A reconstruction of pre-disease forest composition showed that stands that eventually became infested with the pathogen tended to be more mature with larger stems than stands that remained pathogen-free, supporting the hypothesis of aerial dispersal by the pathogen across the landscape followed by local understory spread. The change in species composition in uninfested areas was minimal over the study period, while infested stands had large changes in composition, correlated with the loss of tanoak (Notholithocarpus densiflorus), signaling the potential for SOD to dramatically change coastal forests through selective removal of a dominant host. Forest diversity plays an important role in pathogen establishment and spread, and is in turn changed by pathogen impacts. Asymmetric competency among host species means that impacts of P. ramorum on forest diversity are shaped by the combination and dominance of hosts present in a stand.

Insect herbivores, chemical innovation, and the evolution of habitat specialization in Amazonian trees

Ecology, 2013

Herbivores are often implicated in the generation of the extraordinarily diverse tropical flora. ... more Herbivores are often implicated in the generation of the extraordinarily diverse tropical flora. One hypothesis linking enemies to plant diversification posits that the evolution of novel defenses allows plants to escape their enemies and expand their ranges. When range expansion involves entering a new habitat type, this could accelerate defense evolution if habitats contain different assemblages of herbivores and/or divergent resource availabilities that affect plant defense allocation. We evaluated this hypothesis by investigating two sister habitat specialist ecotypes of Protium subserratum (Burseraceae), a common Amazonian tree that occurs in white-sand and terra firme forests. We collected insect herbivores feeding on the plants, assessed whether growth differences between habitats were genetically based using a reciprocal transplant experiment, and sampled multiple populations of both lineages for defense chemistry. Protium subserratum plants were attacked mainly by chrysomelid beetles and cicadellid hemipterans. Assemblages of insect herbivores were dissimilar between populations of ecotypes from different habitats, as well as from the same habitat 100 km distant. Populations from terra firme habitats grew significantly faster than white-sand populations; they were taller, produced more leaf area, and had more chlorophyll. White-sand populations expressed more dry mass of secondary compounds and accumulated more flavone glycosides and oxidized terpenes, whereas terra firme populations produced a coumaroylquinic acid that was absent from white-sand populations. We interpret these results as strong evidence that herbivores and resource availability select for divergent types and amounts of defense investment in white-sand and terra firme lineages of Protium subserratum, which may contribute to habitat-mediated speciation in these trees.

format_quoteWhite-sand populations produced more secondary metabolites compared to terra firme, demonstrating divergent defense strategies influenced by habitat conditions.format_quote

Widespread density‐dependent seedling mortality promotes species coexistence in a highly diverse Amazonian rain forest

Ecology, 2010

Negative density-dependent mortality can promote species coexistence through a spacing mechanism ... more Negative density-dependent mortality can promote species coexistence through a spacing mechanism that prevents species from becoming too locally abundant. Negative density-dependent seedling mortality can be caused by interactions among seedlings or between seedlings and neighboring adults if the density of neighbors affects the strength of competition or facilitates the attack of natural enemies. We investigated the effects of seedling and adult neighborhoods on the survival of newly recruited seedlings for multiple cohorts of known age from 163 species in Yasunı´National Park, Ecuador, an ever-wet, hyper-diverse lowland Amazonian rain forest. At local scales, we found a strong negative impact on firstyear survival of conspecific seedling densities and adult abundance in multiple neighborhood sizes and a beneficial effect of a local tree neighborhood that is distantly related to the focal seedling. Once seedlings have survived their first year, they also benefit from a more phylogenetically dispersed seedling neighborhood. Across species, we did not find evidence that rare species have an advantage relative to more common species, or a community compensatory trend. These results suggest that the local biotic neighborhood is a strong influence on early seedling survival for species that range widely in their abundance and life history. These patterns in seedling survival demonstrate the role of density-dependent seedling dynamics in promoting and maintaining diversity in understory seedling assemblages. The assemblage-wide impacts of species abundance distributions may multiply with repeated cycles of recruitment and density-dependent seedling mortality and impact forest diversity or the abundance of individual species over longer time scales.

Palms, peccaries and perturbations: widespread effects of small-scale disturbance in tropical forests

BMC Ecology, 2012

Background: Disturbance is an important process structuring ecosystems worldwide and has long bee... more Background: Disturbance is an important process structuring ecosystems worldwide and has long been thought to be a significant driver of diversity and dynamics. In forests, most studies of disturbance have focused on largescale disturbance such as hurricanes or tree-falls. However, smaller sub-canopy disturbances could also have significant impacts on community structure. One such sub-canopy disturbance in tropical forests is abscising leaves of large arborescent palm (Arececeae) trees. These leaves can weigh up to 15 kg and cause physical damage and mortality to juvenile plants. Previous studies examining this question suffered from the use of static data at small spatial scales. Here we use data from a large permanent forest plot combined with dynamic data on the survival and growth of > 66,000 individuals over a seven-year period to address whether falling palm fronds do impact neighboring seedling and sapling communities, or whether there is an interaction between the palms and peccaries rooting for fallen palm fruit in the same area as falling leaves. We tested the wider generalisation of these hypotheses by comparing seedling and sapling survival under fruiting and non-fruiting trees in another family, the Myristicaceae. Results: We found a spatially-restricted but significant effect of large arborescent fruiting palms on the spatial structure, population dynamics and species diversity of neighbouring sapling and seedling communities. However, these effects were not found around slightly smaller non-fruiting palm trees, suggesting it is seed predators such as peccaries rather than falling leaves that impact on the communities around palm trees. Conversely, this hypothesis was not supported in data from other edible species, such as those in the family Myristicaceae. Conclusions: Given the abundance of arborescent palm trees in Amazonian forests, it is reasonable to conclude that their presence does have a significant, if spatially-restricted, impact on juvenile plants, most likely on the survival and growth of seedlings and saplings damaged by foraging peccaries. Given the abundance of fruit produced by each palm, the widespread effects of these small-scale disturbances appear, over long timescales , to cause directional changes in community structure at larger scales.

format_quoteOne-year survival of seedlings near mature palms was significantly lower compared to those further away, revealing direct homing effects.format_quote

Habitat Specialization by Birds in Western Amazonian White-sand Forests

Biotropica, 2013

In the Peruvian Amazon, white-sand forests are patchily distributed and restricted to a few local... more In the Peruvian Amazon, white-sand forests are patchily distributed and restricted to a few localities in the North. Although recent studies have documented patterns of habitat specialization by plants in these unique forests, very few studies of the fauna of these habitats have been conducted. The species composition of the avifauna of the white-sand forests at six localities in the region was sampled by conducting transects and point counts. Surrounding habitats were also sampled to compare avifaunal communities and to determine the degree of restriction of bird species to white-sand habitats. Non-metric multidimensional scaling analysis showed that bird communities of white-sand forests were more similar to each other than they were to terra firme or flooded forest communities. Sites on either side of the Amazon-Marañ on barrier were the most similar within habitat type consistent with the hypothesis that these rivers represent a major biogeographic barrier. Twenty-six species, belonging to 13 families, were to some degree specialized to white-sand forests. This is the first comprehensive ornithological assessment carried out on these habitats in Peru. The high degree of habitat specialization found in these 26 bird species highlights the need for conservation and management measures that will protect white-sand forests.