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In the United States, people of color are disproportionally more likely to live in environments with poor air quality, in close proximity to toxic waste, and in locations more vulnerable to climate change and extreme weather events.

Studies conducted in forests have resulted in much of the ecological theory we build upon today. However, our basic understanding of forest ecology comes almost exclusively from the study of trees, even though they represent only a small fraction of the plant diversity present in forests. In recent decades there has been an increasing number of studies of forest herbs, broadening our understanding of plant community ecology in forest ecosystems. Here we highlight ten recent studies examining patterns and drivers of, as well as threats to, herbaceous plant diversity in forests. We first examine local, regional, and global patterns of herbaceous diversity in forests and how such patterns differ for woody versus herbaceous species. We then focus on ecological mechanisms that contribute to forest herb diversity, including the role of abiotic and biotic interactions. We end by discussing some major anthropogenic impacts on forest herb diversity, identifying where herbs are particularly susceptible or particularly resilient to current and predicted changes in comparison to trees. The studies we feature demonstrate that patterns and drivers of diversity often differ between woody and herbaceous plant communities. To facilitate cross-site comparisons, there is great need for more standardized survey methods for herbaceous plants, for simultaneous measurements of multiple plant growth forms, and for incorporating herbs into long-term forest monitoring networks. In addition, the selected studies reveal how land-use history, overabundant herbivores, invasive species, and climate change are all impacting forest herb communities. Some common characteristics of herbaceous plants, such as limited dispersal and small stature, may make forest herb communities more susceptible to these anthropogenic impacts, while others (e.g., resprouting ability, clonal reproduction) may make them more resilient compared to forest trees. More research is needed from both plant ecologists and applied forest practitioners to predict how herbaceous forest diversity will change in the future.

In this paper, a case is made for the use of model-based approaches for the analysis of community data. This involves the direct specification of a statistical model for the observed multivariate data. Recent advances in statistical modelling mean that it is now possible to build models that are appropriate for the data which address key ecological questions in a statistically coherent manner. Key advantages of this approach include interpretability, flexibility, and efficiency, which we explain in detail and illustrate by example. The steps in a model-based approach to analysis are outlined, with an emphasis on key features arising in a multivariate context. A key distinction in the model-based approach is the emphasis on diagnostic checking to ensure that the model provides reasonable agreement with the observed data. Two examples are presented that illustrate how the model-based approach can provide insights into ecological problems not previously available. In the first example, we test for a treatment effect in a study where different sites had different sampling intensities, which was handled by adding an offset term to the model. In the second example, we incorporate trait information into a model for ordinal response in order to identify the main reasons why species differ in their environmental response.

Principal component analysis (PCA) is a standard technique to summarize the main structures of a data table containing the measurements of several quantitative variables for a number of individuals. Here, we study the case where some of the data values are missing and propose a review of methods which accommodate PCA to missing data. In plant ecology, this statistical challenge relates to the current effort to compile global plant functional trait databases producing matrices with a large amount of missing values. We present several techniques to consider or estimate (impute) missing values in PCA and compare them using theoretical considerations. We carried out a simulation study to evaluate the relative merits of the different approaches in various situations (correlation structure, number of variables and individuals, and percentage of missing values) and also applied them on a real data set. Lastly, we discuss the advantages and drawbacks of these approaches, the potential pitfalls and future challenges that need to be addressed in the future.

Extreme fire seasons in both hemispheres in 2019 and 2020 have highlighted the strong link between climate warming and altered fire regimes. While shifts in fire regimes alone can drive profound changes in plant populations, communities, and ecosystems, the direct effects of warming climate conditions can impose added stress on key demographic processes prior to and immediately following fire. Altered survival-, growth-, and reproductive- rates in periods between fires, coupled with post-fire recruitment failure from increasingly stressful environmental conditions (including both heatwave and drought) can pose serious threats for conservation in fire-adapted ecosystems worldwide, raising concerns of ecosystem conversion and state change. In this special issue, a collection of 11 papers from fire-prone ecosystems in both hemispheres documents key insights into how changes are unfolding—and mechanisms underpinning such changes—across a diverse range of species and ecosystems. Here, we synthesize this work that uses latitudinal observational surveys, experiments, and simulation modeling to understand how climate warming and altered fire regimes are reshaping our planet. We place these studies in the context of broader advances, and highlight additional research directions to uncover how altered fire regimes, fires interacting with other disturbances, and pre-and post-fire demographic processes can erode resilience in a warming climate.

The Great Basin of the western USA is an arid region characterized by high spatial and temporal variability. The region experienced high levels of ecological disturbance during the early period of Euro-American settlement, especially from about 1870–1935. The principal plant communities of the Great Basin are sagebrush steppes, dominated by various Artemisia shrubs and perennial bunchgrasses that represent the largest rangeland ecosystem in North America. In low to mid-elevation sagebrush communities, exotic annual grasses have displaced native plant species and are associated with a dramatic increase in size and frequency of wildfires. Degradation in this region is driven by processes that cause the loss of mature bunchgrasses, which, when intact, limit exotic annual grass invasion. Historically, large economic investments to restore degraded Great Basin rangeland through establishment of native bunchgrasses, principally utilizing heavily mechanized agronomic approaches, have been met with limited success. A multitude of environmental factors contribute to the lack of restoration success in this region, but seedling mortality from freezing and drought has been identified as a primary demographic limitation to successful bunchgrass establishment. Novel approaches to overcoming limitations to bunchgrass establishment will be required for restoration success. Increased national concern and a near listing of the greater sage-grouse, a steppe-obligate species, to Endangered Species status, has spurred greater regional support and collaboration across a diversity of stakeholder groups such as state and federal land and wildlife management agencies, county planners, and ranchers.

The Mediterranean Basin is one of the World’s plant diversity hotspots and a region prone to several anthropic pressures, besides being one of the World’s areas most susceptible to climate change. In this region, which hosts a high percentage of threatened species, there has been a large increase in practical conservation actions to prevent the extinction of many plants or improve their conservation status. In this framework, plant translocations have become increasingly important. To obtain a picture of the status and to depict possible directions, data on plant translocations was collected through the available databases, national experts, and the grey literature available online. Overall, a list of 836 translocations relating to 572 plant species was found. These actions are mainly concentrated in Spain, France, and Italy (c. 87%) and, except for some pioneering actions, translocations have strongly increased starting from 2010. A subsequent in-depth bibliographic search of the scientific databases was conducted to determine how much information about plant translocations was documented in the scientific literature. This search resulted in a list of 133 peer-reviewed papers, of which only 17 describing one or more translocations and, as a whole, reporting 101 experiences carried out on 56 plant species. Our research highlighted a great discrepancy between the scarce scientific documentation in comparison to the large number of practical conservation actions carried out. The great experience gained in these translocations constitutes an enormous heritage potentially available to implement the necessary conservation actions to preserve the plant diversity of the Mediterranean Basin.

Global climate models predict increases in the frequency and severity of drought worldwide, directly affecting most ecosystem types. Consequently, drought legacy effects (drought-induced alterations in ecosystem function postdrought) are expected to become more common in ecosystems varying from deserts to grasslands to forests. Drought legacies in grasslands are usually negative and reduce ecosystem function, particularly after extended drought. Moreover, ecosystems that respond strongly to drought (high sensitivity) might be expected to exhibit the largest legacy effects the next year, but this relationship has not been established. We quantified legacy effects of a severe regional drought in 2012 on postdrought (2013) aboveground net primary productivity (ANPP) in six central US grasslands. We predicted that (1) the magnitude of drought legacy effects measured in 2013 would be positively related to the sensitivity of ANPP to the 2012 drought, and (2) drought legacy effects would be negative (reducing 2013 ANPP relative to that expected given normal precipitation amounts). The magnitude of legacy effects measured in 2013 was strongly related (r² = 0.88) to the sensitivity of ANPP to the 2012 drought across these six grasslands. However, contrary to expectations, positive legacy effects (greater than expected ANPP) were more commonly observed than negative legacy effects. Thus, while the sensitivity of ANPP to drought may be a useful predictor of the magnitude of legacy effects, short-term (1-year) severe droughts may cause legacy effects that are more variable than those observed after multiyear droughts.

Understanding the effects of seed predation, dispersal, and recruitment on the population dynamics of rare plant species is essential for generating effective management strategies. Unfortunately for most rare plants, the parameterization of these processes is limited and generally not included in demographic analyses. This exclusion can lead to biased estimates of vital rates and overall population growth rates, as well as limit inferences about inter-population processes like colonization and demographic rescue that can affect population viability. Based on previous empirical studies from Fort Liberty (formerly Fort Bragg) North Carolina (USA), we constructed a spatially explicit demographic model that accounts for pre-dispersal seed predation, dispersal, and habitat suitability for Lindera subcoriacea (bog spicebush), a rare shrub in the southeastern United States. We demographically modeled three scenarios: S1 did not include any of the three parameters; S2 accounted for seed predation and dispersal; and S3 included all three of the parameters. Results suggested that pre-dispersal seed predation, dispersal, and habitat suitability negatively impact the population growth rates of bog spicebush relative to the naïve demographic model. After 100 annual time steps, scenarios S1, S2, and S3 led to a 96%, 49%, and 1% increase in population size, respectively. In addition, over the course of 100 years, results of scenarios S2 and S3 demonstrated limited increases in site occupancy, with newly occupied areas located < 1 km from previously occupied habitat. Our results suggest additional parameterization of plant demographic models may be an informative endeavor and warranted, even in the absence of empirical data.

Understanding plant adaptive strategies to aridity is crucial for ecological research, particularly in the current context of climate change and increasing drought. This study focuses on the intraspecific phenotypic variation of the wild olive (Olea europaea subsp. europaea var. sylvestris), one of the most emblematic species of the Mediterranean Basin, widely distributed in Morocco. The research is based on measuring nine leaf and plant-size related traits in 130 trees across 13 populations under varying climate conditions and vegetation covers. The study explores the adaptive strategies of wild olive trees in response to increasing aridity and aridification. The results indicate that the nine traits exhibit significant covariation trends along environmental gradients, reflecting plant strategies related to resource acquisition, resource investment, and water use. Wild olive trees demonstrate substantial intraspecific variation both among and within populations in response to these environmental gradients. Climate, altitude, and vegetation cover together explain 93.8% of the trait covariations. The study elucidates the mechanisms underlying the adaptive strategies of wild olive trees to cope with stressful conditions. The findings suggest that wild olive trees adapt to stressful environments by adopting a conservative strategy, characterized by lower resource investment and higher water-use efficiency. This research underscores the importance of considering intraspecific variation in plant responses to environmental stressors and demonstrates the utility of trait-based approaches in understanding plant strategies under such conditions.