Geology topics

Daniel C. Laughlin

Publications and source records attributed to Daniel C. Laughlin.

6 recordsLinked to original sources

USGS2025

Divergent responses of seed banks and aboveground vegetation to drought and deluge in grasslands across an elevational gradient

Increased variability in precipitation associated with climate change creates extreme conditions of drought and deluge that can have profound effects on the abundance and composition of plant communities. Responses to these extremes likely vary across climatic gradients and depend on local plant community composition, which includes the emergent, aboveground vegetation as well as belowground seed banks. Because seed banks can both buffer the effects of environmental change and influence the future trajectories of communities, it is critical to understand seed bank responses to precipitation extremes in relation to the aboveground vegetation and how patterns vary across environmental gradients. Here we quantified the responses of aboveground and seed bank communities at five perennial grass-dominated sites across an elevational gradient to 6 years of extreme drought and deluge, by implementing experimental water exclusion and water addition treatments. Responses were stronger for drought than for deluge. Drought decreased abundance aboveground, while seed bank abundances were generally unaffected. Similarly, drought decreased richness and diversity of aboveground vegetation at intermediate elevations, without concurrent changes in seed banks. Surprisingly, the lowest and middle elevation sites showed stronger shifts in functional composition and dissimilarity in response to treatments, despite the expectation of greater buffering in seed banks in more arid environments. The relatively attenuated responses of seed bank communities to drought and deluge suggest potential for resistance and recovery, though species and functional composition may show greater responses to change particularly in more arid, lower elevation sites.

Arizona↗

USGS2025

Why are non-native plants successful? Consistently fast economic traits and novel origin jointly explain abundance across US ecoregions

Are non-native plants abundant because they are non-native, and have advantages over native plants, or because they possess ‘fast’ resource strategies, and have advantages in disturbed environments? This question is central to invasion biology but remains unanswered. We quantified the relative importance of resource strategy and biogeographic origin in 69 441 plots across the conterminous United States containing 11 280 plant species. Non-native species had faster economic traits than native species in most plant communities (77%, 86% and 82% of plots for leaf nitrogen concentration, specific leaf area, and leaf dry matter content). Non-native species also had distinct patterns of abundance, but these were not explained by their fast traits. Compared with functionally similar native species, non-native species were (1) more abundant in plains and deserts, indicating the importance of biogeographic origin, and less abundant in forested ecoregions, (2) were more abundant where co-occurring species had fast traits, for example due to disturbance, and (3) showed weaker signals of local environmental filtering. These results clarify the nature of plant invasion: Although non-native plants have consistently fast economic traits, other novel characteristics and processes likely explain their abundance and, therefore, impacts.

conterminous United States↗

USGS2025

Using plant invasions to compare occurrence- and abundance-based calculations of biotic homogenisation: Are results complementary or contradictory?

Aim Beta diversity quantifies the similarity of ecological assemblages. Its increase, known as biotic homogenisation, can be a consequence of biological invasions. However, species occurrence (presence/absence) and abundance-based analyses can produce contradictory assessments of the magnitude and direction of changes in beta diversity. Previous work indicates these contradictions should be less frequent in nature than in theory, but a growing number of empirical studies report discrepancies between occurrence- and abundance-based approaches. Understanding if these discrepancies represent a few isolated cases or are systematic across a diversity of ecosystems would allow us to better understand the general patterns, mechanisms and impacts of biotic homogenisation. Location United States. Time Period 1963–2020. Major Taxa Studied Vascular plants. Methods We used a dataset of more than 70,000 vegetation survey plots to assess differences in biotic homogenisation with and without invasion using both occurrence- and abundance-based metrics of beta diversity. We estimated taxonomic biotic homogenisation by comparing beta diversity of invaded and uninvaded plots with both classes of metrics and investigated the characteristics of the non-native species pool that influenced the likelihood that these metrics disagree. Results In 78% of plot comparisons, occurrence- and abundance-based calculations agreed in direction, and the two metrics were generally well correlated. Our empirical results are consistent with previous theory. Discrepancies between the metrics were more likely when the same non-native species was at high cover at both plots compared for beta diversity, and when these plots were spatially distant. Main Conclusions In about 20% of cases, our calculations revealed differences in direction (homogenisation vs. differentiation) when comparing occurrence- and abundance-based metrics, indicating that the metrics are not interchangeable, especially when distances between plots are high and invader diversity is low. When data permit, combining the two approaches can offer insights into the role of invasions and extirpations in driving biotic homogenisation/differentiation.

Global Ecology and Biogeography↗

USGS2023

Testing the hierarchy of predictability in grassland restoration across a gradient of environmental severity

Ecological restoration is critical for recovering degraded ecosystems but is challenged by variable success and low predictability. Understanding which outcomes are more predictable and less variable following restoration can improve restoration effectiveness. Recent theory asserts that the predictability of outcomes would follow an order from most to least predictable from coarse to fine community properties (physical structure > taxonomic diversity > functional composition > taxonomic composition) and that predictability would increase with more severe environmental conditions constraining species establishment. We tested this “hierarchy of predictability” hypothesis by synthesizing outcomes along an aridity gradient with 11 grassland restoration projects across the United States. We used 1829 vegetation monitoring plots from 227 restoration treatments, spread across 52 sites. We fit generalized linear mixed-effects models to predict six indicators of restoration outcomes as a function of restoration characteristics (i.e., seed mixes, disturbance, management actions, time since restoration) and used variance explained by models and model residuals as proxies for restoration predictability. We did not find consistent support for our hypotheses. Physical structure was among the most predictable outcomes when the response variable was relative abundance of grasses, but unpredictable for total canopy cover. Similarly, one dimension of taxonomic composition related to species identities was unpredictable, but another dimension of taxonomic composition indicating whether exotic or native species dominated the community was highly predictable. Taxonomic diversity (i.e., species richness) and functional composition (i.e., mean trait values) were intermittently predictable. Predictability also did not increase consistently with aridity. The dimension of taxonomic composition related to the identity of species in restored communities was more predictable (i.e., smaller residuals) in more arid sites, but functional composition was less predictable (i.e., larger residuals), and other outcomes showed no significant trend. Restoration outcomes were most predictable when they related to variation in dominant species, while those responding to rare species were harder to predict, indicating a potential role of scale in restoration predictability. Overall, our results highlight additional factors that might influence restoration predictability and add support to the importance of continuous monitoring and active management beyond one-time seed addition for successful grassland restoration in the United States.

Continental United States↗

USGS2019

Discoveries and novel insights in ecology using structural equation modeling

As we enter the era of data science (Lortie 2018), quantitative analysis methodologies are proliferating rapidly, leaving ecologists with the task of choosing among many alternatives. The use of structural equation modeling (SEM) by ecologists has increased in recent years, prompting us to ask users a number of questions about their experience with the methodology. Responses indicate an enthusiastic endorsement of SEM. Two major elements of respondent’s experiences seem to contribute to their positive response, (1) a sense that they are obtaining more accurate explanatory understanding through the use of SEM and (2) excitement generated by the discovery of novel insights into their systems. We elaborate here on the detection of indirect effects, offsetting effects, and suppressed effects, and demonstrate how discovering these effects can advance ecology.

Ecology and Evolution↗

USGS2017

Tree mortality across biomes is promoted by drought intensity, lower wood density and higher specific leaf area

Drought events are increasing globally, and reports of consequent forest mortality are widespread. However, due to a lack of a quantitative global synthesis, it is still not clear whether drought-induced mortality rates differ among global biomes and whether functional traits influence the risk of drought-induced mortality. To address these uncertainties, we performed a global meta-analysis of 58 studies of drought-induced forest mortality. Mortality rates were modelled as a function of drought, temperature, biomes, phylogenetic and functional groups and functional traits. We identified a consistent global-scale response, where mortality increased with drought severity [log mortality (trees trees −1 year −1 ) increased 0.46 (95% CI = 0.2–0.7) with one SPEI unit drought intensity]. We found no significant differences in the magnitude of the response depending on forest biomes or between angiosperms and gymnosperms or evergreen and deciduous tree species. Functional traits explained some of the variation in drought responses between species (i.e. increased from 30 to 37% when wood density and specific leaf area were included). Tree species with denser wood and lower specific leaf area showed lower mortality responses. Our results illustrate the value of functional traits for understanding patterns of drought-induced tree mortality and suggest that mortality could become increasingly widespread in the future.

Ecology Letters↗