Showing papers by "William J. McShea published in 2023"

Scale‐dependent diversity–biomass relationships can be driven by tree mycorrhizal association and soil fertility

Abstract: Diversity–biomass relationships (DBRs) often vary with spatial scale in terrestrial ecosystems, but the mechanisms driving these scale-dependent patterns remain unclear, especially for highly heterogeneous forest ecosystems. This study explores how mutualistic associations between trees and different mycorrhizal fungi, i.e., arbuscular mycorrhizal (AM) vs. ectomycorrhizal (EM) association, modulate scale-dependent DBRs. We hypothesized that in soil-heterogeneous forests with a mixture of AM and EM tree species, (i) AM and EM tree species would respond in contrasting ways (i.e., positively vs. negatively, respectively) to increasing soil fertility, (ii) AM tree dominance would contribute to higher tree diversity and EM tree dominance to greater standing biomass, and that as a result (iii) mycorrhizal associations would exert an overall negative effect on DBRs across spatial scales. To empirically test these hypotheses, we collected detailed tree distribution and soil information (e.g., nitrogen, phosphorus, organic matter, pH) from seven temperate and subtropical AM–EM mixed forest megaplots (16–50 ha). Using a spatial codispersion null model and structural equation modeling, we identified the relationships among AM or EM tree dominance, soil fertility, tree species diversity, and biomass and, thus, DBRs across 0.01- to 1-ha scales. We found the first evidence overall supporting the three aforementioned hypotheses in these AM–EM mixed forests: (i) In most forests, with increasing soil fertility, tree communities changed from EM-dominated to AM-dominated; (ii) increasing AM tree dominance had an overall positive effect on tree diversity and a negative effect on biomass, even after controlling for soil fertility and number of trees. Together, (iii) the changes in mycorrhizal dominance along soil fertility gradients weakened the positive DBR observed at 0.01- to 0.04-ha scales in nearly all forests and drove negative DBRs at 0.25- to 1-ha scales in four out of seven forests. Hence, this study highlights a soil-related mycorrhizal dominance mechanism that could partly explain why, in many natural forests, biodiversity–ecosystem functioning (BEF) relationships shift from positive to negative with increasing spatial scale.

Predicting vulnerability of forest patches to invasion by non-native plants for landscape scale management.

Abstract: As a leading cause of forest health degradation, non-native invasive plant species are a key focus for many forest management and conservation efforts. These efforts come at a high price for resource limited agencies and organizations making cost effectiveness an important objective of invasion response plans. In this paper we present an approach to guide the prioritization of locations for invasion management using species distribution models that account for the non-equilibrium of invasive species distributions and use readily available land use data as the primary explanatory variables. This approach takes advantage of the relatively high spatial resolution, as well as the broad, continuous geographic coverage, of land use data to provide results at a landscape scale relevant to practitioners responsible for invasive species management. In our example from northern Virginia, we simultaneously modeled a suite of invasive plant species to identify common indicators of invasion. We found that the proportions of surrounding non-forested land use types (grasses, crops, and development) were the most common and strongest indicators of invasion risk. These outcomes can guide managers of large protected areas to focus on major divides between forest and non-forest land over linear disturbances. We also found useful species-specific traits that can inform specific management actions. Additionally, we demonstrate through a case study how organizations that manage multiple smaller properties can take advantage of the projected distribution maps when considering acquiring or administering properties.

Harmonizing spatial scales and ecological theories to predict avian richness and functional diversity within forest ecosystems

Abstract: Classic ecological theory has proven that temperature, precipitation and productivity organize ecosystems at broad scales and are generalized drivers of biodiversity within different biomes. At local scales, the strength of these predictors is not consistent across different biomes. To better translate these theories to localized scales, it is essential to determine the links between drivers of biodiversity. Here we harmonize existing ecological theories to increase the predictive power for species richness and functional diversity. We test the relative importance of three-dimensional habitat structure as a link between local and broad-scale patterns of avian richness and functional diversity. Our results indicate that habitat structure is more important than precipitation, temperature and elevation gradients for predicting avian species richness and functional diversity across different forest ecosystems in North America. We conclude that forest structure, influenced by climatic drivers, is essential for predicting the response of biodiversity with future shifts in climatic regimes.

Seasonal shifts in large mammal activity relative to fruit availability and hunting risk along a protected area boundary in Borneo

Abstract: Understanding wildlife spatiotemporal dynamics at protected area boundaries is critical to conservation. In SE Asia, protected areas are often bordered by indigenous communities whose traditional practices result in increased landscape heterogeneity within their community managed forests (CF). Because SE Asian forests exhibit supra‐annual mast fruiting (3–7 yrs) and sustained fruit scarcity, wildlife using CF may benefit from greater availability of fruits and seeds encouraged by traditional management, but incur greater risk of being hunted. We examined shifts in wildlife activity in forests within and adjacent to Lanjak Entimau Wildlife Sanctuary (LEWS), in Sarawak, Malaysia. Using camera traps and surveys of fruiting phenology, we related presence of fruits and seeds to shifts in large mammal activity over 3 years (October 2016–2019). We first compared relative frequency of five focal species (sun bear, bearded pig, muntjac, mouse deer, and sambar) by forest type for a given survey year and season (rainy vs. dry). We then modeled activity to assess how fruit availability, landscape features, and proxies for hunting risk, influence seasonal shifts in habitat use. Our results suggested seasonal variation in concert with increased landscape heterogeneity influenced patterns of activity. We found no evidence that CF excluded any detected mammal species, suggesting CF contribute important habitat to wildlife, particularly during periods of fruit scarcity in primary forest. However, our findings also imply increased hunting risk for wildlife attracted to resources near human settlements, emphasizing the need to consider the influence of both annual and supra‐annual seasonality when developing best practices for the sustainable management.

Latitudinal scaling of aggregation with abundance and its consequences for coexistence in species rich forests

Abstract: The complex spatial structure and dynamics of ecological communities continue to defy explanation by simple principles despite decades of attention from ecologists and theoreticians. For example, the relationship between plant spatial distributions and species coexistence is often challenging to resolve in empirical settings. By analysing the spatial patterns of trees in 21 large forest plots we find a general and strong latitudinal gradient in the relationship between conspecific aggregation and abundance of tree species, with stronger negative abundance-dependency as latitude increases. To derive theoretical expectations for how interactions between multiple spatial pattern and processes can impact species coexistence, we incorporate the observed spatial patterns together with neighbourhood crowding competition into a mathematical model to estimate the local extinction risk of species. Strikingly, we find simple relationships that predict species local extinction risk from their demography and spatial distribution. Compared to a corresponding non-spatial analysis, accounting for spatial patterns reduces the 1000-year extinction risk on average by 52% when species invade from low abundances of 50 individuals. Additionally, based on their current abundances, only 8% of the species had an extinction risk greater than 5%. Our approach opens up new avenues for integrating observed spatial patterns with multiple ecological processes into mathematical theory. Our results demonstrate that emerging spatial patterns can contribute substantially to coexistence in species-rich forests, emphasizing the need to understand the interacting multiple processes underpinning spatial patterns in greater detail than has previously been appreciated.

Ungulates’ Behavioral Responses to Humans as an Apex Predator in a Hunting-Prohibited Area of China

Abstract: Simple Summary Large mammals’ behavioral responses to humans as predators may be impacted by hunting intensity. Using a playback experiment, we found that two wild ungulates exhibited reactive (flee) rather than proactive responses (decrease habitat use) to human vocalizations at a hunting-prohibited site in North China. The wild ungulates had equal or even higher flight probabilities upon hearing vocalizations of humans than the native extant large carnivore (leopard). We also found habituation-type responses featured as progressively decreased responses to the vocalizations in both ungulates. Abstract Large mammals can perceive humans as predators and therefore adjust their behavior to achieve coexistence with humans. However, lack of research at sites with low hunting intensity limits our understanding of how behavioral responses of animals adapt to different predation risks by humans. At Heshun County in North China, where hunting has been banned for over three decades and only low-intensity poaching exists, we exposed two large ungulates (Siberian roe deer Capreolus pygarus and wild boar Sus scrofa) to the sounds of humans, an extant predator (leopard Panthera pardus) and a control (wind), and examined their flight responses and detection probabilities when hearing different type of sounds. Both species showed higher flight probabilities when hearing human vocalization than wind, and wild boar were even more likely to flee upon hearing human vocalization than leopard roar, suggesting the behavioral response to humans can equal or exceed that of large carnivores in these two ungulates even in an area without hunting practices. Recorded sounds had no effect on detection probability of both ungulates. Additionally, with repeated exposure to sounds, regardless of treatment, roe deer were less likely to flee and wild boars were more likely to be detected, indicating a habituation-type response to sound stimuli. We speculate that the immediate flight behavior rather than shifts in habitat use of the two species reflect the low hunting/poaching pressure at our study site and suggest further examination of physiological status and demographic dynamics of the study species to understand human influence on their long-term persistence.

Modeling alternative future scenarios for direct application in land use and conservation planning

Abstract: Land use is one of the largest threats to biodiversity, ecosystem function, and ecosystem services. These losses can be mitigated through strategic land use planning efforts that balance the social, economic, and environmental needs of society and the ecosystems that support it. A crucial component in the development of strategic plans is a concrete understanding of land use change and the impacts and influence of it on the landscape. Land change models are one method for quantifying the effect of these relationships and projecting the resulting changes on landscapes of the future. However, in order for the resulting model products to be useful to planners, policy makers, and conservationists, they must be focused on addressing questions of relevance to the community they intend to serve. Scenario planning offers a framework for integrating community‐developed visions of the future with land change models in order to increase relevancy and uptake of products. We developed a land change model for five future scenarios of land use change in northwestern Virginia, integrating regional stakeholder knowledge throughout the process. Across scenarios, we found consistent increases in development across our study area, but the form and configuration of land use types varied sub‐regionally. This manuscript describes not only our results, but the process of integrating stakeholder input throughout. We describe our model outputs in the context of usefulness for planners, policy makers, and conservation decision makers, often through the lens of the importance of geographic scale. This work serves as an additional example of land use modeling across scenarios. We conclude with guidance for scientists interested in integrating similar approaches in their work.