Quantifying the relationship of different grass functional groups to increasing woody plant cover is necessary to better understand the effects of woody plant encroachment on grasslands. This study explored biomass production responses of three perennial grass groups based on photosynthetic pathway and potential canopy height (C4 short-grasses, C3 midgrasses, and C4 midgrasses) to different percent canopy covers of the surrounding deciduous woody legume, honey mesquite (Prosopis glandulosa). Two methods were used to determine mesquite canopy cover, line-intercept and geospatial analysis of aerial images, and both were used to predict production of the three grass groups. Five years of grass production data were included in the mesquite cover/grass production regressions. Two yr had extreme grass production responses, one due to drought and the other to high rainfall. Of the 3 remaining yr, best-fit curves were negative linear for C4 short-grasses and C3 midgrasses and negative sigmoidal for C4 midgrasses using both cover determination methods, although slopes of the curves differed between cover determination methods. C4 midgrasses were more sensitive than the other grass groups to increasing mesquite cover. Loss of production potential when mesquite cover increased from 0% to 35% was 75.5%, 28.7%, and 23.2% for C4 midgrasses, C3 midgrasses, and C4 short-grasses, respectively. Moreover, production potential of C4 midgrasses under no mesquite cover was 3 and 6 times greater than C3 midgrasses or C4 short-grasses, respectively. Spatial settings of the different grass groups in relation to mesquite tree size and size of intercanopy areas provided indirect evidence that the process of mesquite encroachment in the past 50−100 yr may have negatively impacted C4 midgrasses more than the other grass groups. Results suggest that gains in grass production following mesquite treatment would be limited if the system has degraded to where only C3 midgrasses and C4 short-grasses dominate.
Ungulates are important components of a variety of ecosystems worldwide. This dissertation integrates aspects of ungulate and forest ecology to increase our understanding of how they work together in ways that are of interest to natural resource managers, educators, and those who are simply curious about nature. Although animal ecology and ecosystem ecology are often studied separately, one of the general goals of this dissertation is to examine how they interact across spatial and temporal scales. Forest ecosystems are heterogeneous across a range of scales. Spatial and temporal habitat use patterns of forest ungulates tend to be congregated in patches where food and/or cover are readily available. Ungulates interact with ecosystem processes by selectively foraging on plants and excreting waste products in concentrated patches. Positive feedbacks may develop where these activities increase the value of habitat through soil fertilization or the alteration of plant chemistry and architecture. Heterogeneity in ecosystem processes and plant community structure, observed at both stand and local scales, may be the integrated outcome of feedbacks between ungulate behavior and abiotic resource gradients.
There are three common conceptualizations of resilience: persistence, recovery, and adaptability. While researchers apply all three in studies of forest ecosystems, the conceptualization used can have important empirical implications. We conducted a systematic literature review of empirical studies of forest resilience in the US from 2010 to 2020 to determine how researchers conceptualized, measured, and reflected the concept of resilience in reporting and interpreting their results. We determined that most studies defined resilience as recovery to the original state post‐disturbance, focused on the state of individual species within the ecosystem rather than the state of the ecosystem itself, and measured the impacts of a single disturbance rather than impacts of multiple disturbances. As climate change and other stressors exacerbate impacts to ecosystems, it is important to move beyond the persistence of or recovery to the original state as the goal for resilient ecosystems and to focus instead on maintaining ecosystem functions and enhancing their adaptability.
Many land-grant institutions with agriculture and natural resource programs in the United States offer online courses to meet student demand. The goal of this study was to understand how major educational stakeholders, including instructors and students, perceive the benefits and limitations of online teaching and learning in agriculture and natural resource sciences. This study utilized a mixed mode data collection method, which involved informal meetings as well as online survey administration. The data were analyzed through strengths, weaknesses, opportunities, and threats (SWOT)-Analytic Hierarchical Process (AHP) framework. The study results offer novel perspectives on the perceived utility and challenges of several attributes of online learning including work-home balance, lack of social interactions, virtual classroom opportunities for working professionals, and academic integrity and cyber scam issues among others. Our findings may be beneficial to academic administrators, instructors, and institutions in identifying opportunities, challenges, and adopting programmatic strategies to improve effectiveness of online learning.
Concentrated foraging in forest canopy gaps by large ungulates may produce a pulsed spatial resource subsidy with cascading effects on the composition and developmental trajectory of gap vegetation. To test this hypothesis, we investigated the influence of white-tailed deer (Odocoileus virginianus) use of 12 artificial canopy gaps in a hemlock-northern hardwood forest. Ground-layer vegetation was monitored and available reactive nitrogen was assayed using resin beads deployed under the snowpack (March–April) and soon after snowmelt (May). Deer use of openings was consistent with the forage maturation hypothesis, with the greatest levels of use occurring in small gaps. Allometric relationships suggest that mean localized winter pulses of deer-excreted N may be on par and/or in excess of annual atmospheric N deposition in the region. Correspondingly, deer access plots contained significantly more reactive N than exclosure plots soon after snowmelt (P = 0.036) in April. While the pulse was indistinguishable by May, our nonmetric multidimensional scaling ordination results suggest that plant community composition in exclosure and control plots reflects this pulsed gradient in N availability. Given the importance of canopy disturbances and gaps to the perpetuation of forest ecosystems, localized and/or heterogeneous impacts may be magnified as forests turn over.
While hunting is employed as a means to control overabundant populations of white-tailed deer (Odocoileus virginianus) and reduce the negative effects of herbivory, few studies have examined whether recovery of forest regeneration occurs following a long-term controlled hunting program. In Indiana state parks, controlled hunts were implemented in the 1990s to reduce deer population abundance and allow vegetation communities to recover. In 1996 and 1997, long-term vegetation monitoring plots were established in 16 state parks and six historically hunted reference areas to monitor vegetation response to hunting. We resampled these plots in 2010 to examine how deer reductions affected woody stem density and species composition in three height classes: < 50 cm, 50–200 cm, and > 200 cm. We also examined changes in species richness (S), evenness (E), and Shannon-Wiener diversity (H′) between 1996–97 and 2010. Temporal changes were tested with generalized linear mixed models. Density in the < 50 cm height class increased significantly in both state parks and reference areas. Density in the 50–200 cm height class increased significantly in parks, but not in reference areas. Species richness increased significantly in all three height classes in parks, but only in the > 200 cm class in reference areas. Density of Fraxinus americana and Acer saccharum increased greatly in the < 50 cm and 50–200 cm height classes in both state parks and reference areas. While still abundant in the parks, two unpalatable species, Asimina triloba and Lindera benzoin exhibited reduced relative density in the < 50 cm height class. Within parks and reference areas, the density of these species increased in the > 200 cm height class. These results indicate that the void in forest understories created by chronic herbivory in Indiana state parks is being filled by a diverse array of species following deer population reductions. In addition, the species composition of parks has become more similar to that of reference areas through time.
