Michael R. Saunders

Epicormic buds in trees: a review of bud establishment, development and dormancy release

The formation of epicormic sprouts on the boles of trees is a phenomenon that has, until recently, been poorly understood. Renewed interest in the topic in the last two decades has led to significant advances in our knowledge of the subject, especially in regard to bud anatomy, morphology and ontogeny. There exists, however, no comprehensive synthesis of results from different disciplines across genera and geographical areas; this review seeks to fill that void and provide a comprehensive framework capable of guiding future research. A trees potential for producing epicormic branches is dependent on the number of buds that are produced on a growing shoot, the development of those buds and associated meristems over time and the factors that promote sprout formation or bud death. Based on the descriptions of a limited number of researched species, we were able to describe four different developmental strategies for epicormics based on characteristics of meristem development. Control over epicormic bud dormancy is complex, but it is clear that the traditional view of auxin-mediated dormancy release is incomplete. Genetic control over epicormic development is yet to be empirically proven. Future research should focus on clarifying these physiological and genetic controls of epicormic bud development as well as developing more robust methods for tracking epicormics in ecological and silvicultural studies.

Long-term spatial and structural dynamics in Acadian mixedwood stands managed under various silvicultural systems

Using inventory data from a long-term silviculture experiment in east-central Maine, spatial models were devel- oped to analyze 28 years (1974-2002) of stand structural dynamics. Differences in spatial pattern, species mingling, height differentiation, and relative stand complexity index (rSCI) were compared among five treatments: commercial clear-cutting, fixed diameter-limit, 5 year single-tree selection, three-stage shelterwood (both with and without precommercial thin- ning), and unharvested natural areas. Regardless of treatment, regeneration events (whether induced by natural breakup of the overstory or by harvesting) increased aggregation in spatial pattern and reduced species mingling, more so in the commercial clearcut and fixed diameter-limit treatments where hardwood densities were highest. Regular spatial patterns were rare. Height differentiation values for individual trees and stand-level mean rSCI were generally highest in untreated natural areas and 5 year selection treatments, intermediate in commercial clearcut and fixed diameter-limit treatments, and lowest in three-stage shelterwood treatments. After a brief adjustment period, precommercial thinning in a shelterwood treated stand generally increased species mingling, height differentiation, and rSCI. Two untreated natural areas exhibited divergent pathways of structural development. Dynamics in uneven-aged selection treatments more closely resembled that of the untreated natural areas than did the shelterwood, commercial clearcut, or fixed di- ameter-limit treatments.

Height-Diameter Models with Random Coefficients and Site Variables for Tree Species of Central Maine

Height-diameter models were developed for nine tree species common to the northeastern United States: Abies balsamea, Acer rubrum, Betula papyrifera, B. populifolia, Picea rubens, P. mariana, Pinus strobus, Populus tremuloides, and Tsuga canadensis. Stem heights and diameters were collected from 6 146 trees (between 136 and 2615 trees per species) on 50 plots within 10 structurally diverse stands that are part of a long-term silvicultural experiment in central Maine. The models were developed using both generalized nonlinear least squares (GNLS) and multi-level, mixed-effects approaches. Mixed-effects approaches were superior to GNLS, with inclusion of site covariates (tree density and basal area) accounting for some of the variability explained by the random coefficients in the full mixed-effect models. Analysis of plot-level parameter estimates suggested that differences in stand structure (even-aged vs. uneven-aged silvicultural practices) had a significant influence on the height-diameter relationships.RésuméDes modèles hauteur-diamètre ont été développés pour neuf essences courantes dans le Nord Est des USA : Abies balsamea, Acer rubrum, Betula papyrifera, Betula populifera, Picea rubens, Pinus strobus, Populus tremuloides et Tsuga canadensis. Le diamètre et la hauteur des troncs ont été recueillis sur 6 146 arbres (entre 136 et 2615 arbres par espèce) dans 50 placeaux de 10 des peuplements de diverses structures qui font partie d’une expérimentation à long terme dans le centre du Maine. Les modèles ont été développés en utilisant à la fois les moindres carrés non linéaires généralisés (GNLS) et des approches multi-niveaux à effets mixtes. Les démarches à multi-niveaux ont été supérieures au GNLS, avec des covariables de station (densité et surface terrière) représentant une partie de la variabilité expliquée par les coefficients aléatoires dans l’ensemble des modèles à effets mixtes. L’analyse des estimations des paramètres au niveau des placeaux suggère que les différences de structure de peuplement (pratiques sylvicoles en peuplement équiennes ou inéquiennes) ont un effet significatif sur les relations hauteur —diamètre.

Influence of Intensity and Duration of Invasion by Amur Honeysuckle (Lonicera maackii) on Mixed Hardwood Forests of Indiana

Abstract The expansion of populations of invasive species continues to compromise the ecological and economic integrity of our natural resources. The negative effects of invasive species on native biota are widely reported. However, less is known about how the duration (i.e., age of oldest invaders) and intensity (i.e., density and percent cover) of an invasion influences native plant diversity and abundance at the microsite scale. We examined the influence of density, percent cover, and age of Amur honeysuckle (a nonnative invasive shrub), and several environmental factors on native plant taxa at 12 mixed hardwood forests in Indiana, USA. Overall, study sites with the greatest taxonomic diversity (Shannons Diversity; H′), richness (S), percent cover, and density of native vegetation also had the lowest percent cover of Amur honeysuckle in the upper vertical stratum (1.01 to 5 m). Based on linear mixed model analyses, percent cover of Amur honeysuckle in the upper vertical stratum was consistently and negatively correlated with H′, S, total percent cover, and woody seedling density of native taxa at the microsite scale (P < 0.05). Duration of Amur honeysuckle at the microsite scale was not significant when percent cover of Amur honeysuckle in the upper vertical stratum was included in models. However, duration of Amur honeysuckle invasion was significantly correlated with dependent variables and with upper-stratum honeysuckle cover, suggesting that older Amur honeysuckle in a microsite resulted in greater light competition from above for native understory plant species. Beyond increased cover and shading, our results do not provide evidence of duration-related effects from long-term dominance of honeysuckle in our sampled mixed hardwood forest sites. Nomenclature: Amur honeysuckle; Lonicera maackii (Rupr.) Herder. Management Implications: Nonnative invasive plants continue to pose one of the most serious threats to ecosystems worldwide. While the negative effects of invasive plants have been well documented, it is still unclear how the combined effect of duration of invasion and intensity (amount of occupied growing space) of an invader can influence native diversity at the microsite scale. We addressed this knowledge gap by examining how the duration and intensity of Amur honeysuckle invasion influenced the diversity and abundance of native plants in hardwood ecosystems of Indiana. Our results indicated that while percent cover of Amur honeysuckle in the upper vertical stratum (1.01 to 5 m) exhibited a strong negative correlation with native plant diversity and abundance at the microsite scale, duration of Amur honeysuckle invasion was not important when honeysuckle percent cover was included in the statistical models. However, when only duration of invasion was considered, it did show a significant negative correlation with native plant diversity and abundance and upper-stratum honeysuckle cover. It therefore appears that microsites where Amur honeysuckle has persisted longer contain a greater percent cover of this invasive shrub, resulting in greater light competition from above and reduced diversity and abundance of native flora. Information about the combined effects of Amur honeysuckle invasion intensity and duration can help forest managers prioritize control efforts in areas where existing sources of native plant propagules are present in microsites where Amur honeysuckle invasion is less intense. Also, our results suggest that the rate of community recovery after honeysuckle removal may not be heavily influenced by cumulative effects related to the duration of invasion. Such information is important for management efforts to support the long-term recovery of native plant communities in invaded ecosystems. Such information may be critical to the long-term recovery of native plant communities in these invaded ecosystems.

Accumulation and connectivity of coarse woody debris in partial harvest and unmanaged relict forests.

When a tree dies, it continues to play an important ecological role within forests. Coarse woody debris (CWD), including standing deadwood (SDW) and downed deadwood (DDW), is an important functional component of forest ecosystems, particularly for many dispersal-limited saproxylic taxa and for metapopulation dynamics across landscapes. Processes, such as natural disturbance or management, modify forest composition and structure, thereby influencing CWD abundance and distribution. Many studies have compared older forests to forests managed with even-aged silvicultural systems and observed a prolonged period of low CWD occurrence after harvesting. With fine-scale spatial data, our study compares the long-term impacts of light partial harvesting on the CWD structure of eastern deciduous hardwood forests. We mapped and inventoried DDW and SDW using variable radius plots based on a 10 m×10 m grid throughout an unmanaged, structurally-complex relict forest and two nearby forests that were partially harvested over 46 years ago. The relict stand had significantly larger individual pieces and higher accumulations of DDW and SDW than both of the partially harvested stands. Connectivity of CWD was much higher in the relict stand, which had fewer, larger patches. Larger pieces and higher proportion of decay-resistant species (e.g. Quercus spp.) in the relict forest resulted in slower decomposition, greater accumulation and increased connectivity of CWD. Partial harvests, such that occur with selection forestry, are generally considered less disruptive of ecosystem services, but this study highlights the long-term impacts of even light partial harvests on CWD stocks and distribution. When planning harvesting events, forest managers should also consider alternative methods to ensure the sustainability of deadwood resources and function.

Functional diversity response to hardwood forest management varies across taxa and spatial scales

Contemporary forest management offers a trade-off between the potential positive effects of habitat heterogeneity on biodiversity, and the potential harm to mature forest communities caused by habitat loss and perforation of the forest canopy. While the response of taxonomic diversity to forest management has received a great deal of scrutiny, the response of functional diversity is largely unexplored. However, functional diversity may represent a more direct link between biodiversity and ecosystem function. To examine how forest management affects diversity at multiple spatial scales, we analyzed a long-term data set that captured changes in taxonomic and functional diversity of moths (Lepidoptera), longhorned beetles (Coleoptera: Cerambycidae), and breeding birds in response to contemporary silvicultural systems in oak-hickory hardwood forests. We used these data sets to address the following questions: how do even- and uneven-aged silvicultural systems affect taxonomic and functional diversity at the scale of managed landscapes compared to the individual harvested and unharvested forest patches that comprise the landscapes, and how do these silvicultural systems affect the functional similarity of assemblages at the scale of managed landscapes and patches? Due to increased heterogeneity within landscapes, we expected even-aged silviculture to increase and uneven-aged silviculture to decrease functional diversity at the landscape level regardless of impacts at the patch level. Functional diversity responses were taxon-specific with respect to the direction of change and time since harvest. Responses were also consistent across patch and landscape levels within each taxon. Moth assemblage species richness, functional richness, and functional divergence were negatively affected by harvesting, with stronger effects resulting from uneven-aged than even-aged management. Longhorned beetle assemblages exhibited a peak in species richness two years after harvesting, while functional diversity metrics did not differ between harvested and unharvested patches and managed landscapes. The species and functional richness of breeding bird assemblages increased in response to harvesting with more persistent effects in uneven- than in even-aged managed landscapes. For moth and bird assemblages, species turnover was driven by species with more extreme trait combinations. Our study highlights the variability of multi-taxon functional diversity in response to forest management across multiple spatial scales.

Local-scale Habitat Components Driving Bird Abundance in Eastern Deciduous Forests

Abstract Declining populations of forest songbirds in the eastern U.S. have emphasized a need for scientists and managers to understand habitat selection by birds in remnant patches of contiguous forest. Past work has identified effects of landscape-scale covariates on bird occurrence and abundance; however, less is known about the effects of local-scale forest structure. We applied a combination of forest inventory data and LiDAR-derived canopy height data to derive variables of local-scale forest structure in a managed forest. We then assessed the effects of these variables on the abundance of 18 forest bird species obtained from point counts, while accounting for imperfect detection using a combined distance and time-removal model. We found mean canopy height and terrain variables including elevation, slope, and aspect affected the local-scale abundance of the largest number of bird species and also had the largest effect sizes. Variables associated with vertical structure of the canopy were not important predictors of abundance. Our results confirm the importance of canopy height and terrain on abundance of multiple forest songbirds and emphasize the value of fine-scale spatial data for assessing bird habitat use.

Individual and interactive effects of white-tailed deer and an exotic shrub on artificial and natural regeneration in mixed hardwood forests

We experimentally excluded deer and removed an invasive shrub (Amur honeysuckle) to determine their effects on the survival of planted tree seedlings and the abundance and diversity of natural seedlings. The presence of honeysuckle or deer alone resulted in similar declines in the survivorship of planted oak seedlings, but the presence of deer alone resulted in lower survival of planted chestnut seedlings than the presence of honeysuckle alone. While deer and honeysuckle did not affect the abundance or diversity of natural seedlings, the presence of both factors increased the dominance of shade-tolerant, unpalatable, and/or browse tolerant species.

Effects of Woody Biomass Harvests on a Population of Plethodontid Salamanders in Southeast Indiana

Abstract Biomass harvesting removes unmarketable vegetative material from timber harvests for use as cellulosic bioenergy, leaving only leaf litter. To test whether biomass harvests negatively affect red-backed salamander (Plethodon cinereus) populations, we set up coverboard arrays at 10 sites (mean 3.29 ha, range 2.35–4.61 ha) with varying degrees of biomass harvesting at the Southeast Purdue Agricultural Center (SEPAC) in Jennings County, Indiana. We monitored salamander artificial cover object (ACO) arrays within each site from spring 2012 to fall 2015 and marked all salamanders with visible implant elastomers, generating capture histories for all individuals. Using Program MARK and Pollocks robust design we developed 10 a priori candidate models to test salamander population parameters, with variations on capture probability, recapture probability, survival, emigration, and immigration, as well as a set of models comparing preharvest and postharvest data. To incorporate precipitation events, we classified sessions as wet or dry based on total rainfall prior to sampling. The best performing models were those that incorporated the year, season, and amount of precipitation when estimating capture probabilities. Linear regression results showed percentage of canopy cover and Downed Coarse Woody Derbies (DCWD) were significant predictors of salamander abundance. We also found no significant relationships between survival, DCWD, and canopy cover. Our results suggest DCWD has some impact on variations in population sizes of red-backed salamanders, although other factors are likely contributing as well.