Canopy Gap Characteristics of an Oak-Beech-Maple Old-Growth Forest in Northeastern Ohio

Author Institution: School of Natural Resources, The Ohio State UniversityForests are gap-driven systems as openings within the tree canopy directly influence species composition, structure, and regeneration. Most gap studies have occurred in small, mesic, old-growth remnants. This study sought to further the understanding of gap characteristics by examining gaps in one of Ohio's largest old-growth forests, which has wet-mesic site conditions and high species diversity. A modification of the methodology recommended by Runkle (1992) was used to obtain data on gap characteristics. An important portion (17.7%) of this old-growth forest was in gaps. Most of the gaps sampled were large (100-400 m2), and multiple-tree gaps were significantly larger than single-tree gaps. Tip-up and basal shear of a canopy tree were the primary means by which a gap was created (origin type). These findings differ from some other similar gap studies, and the contrasts may be due to the advanced age and particular species composition of this forest, the poor soil drainage conditions, and the large size and stressed condition of the overstory trees

University of Maine Proposal for Joining the NSF Center for Advanced Forestry Systems

University of Maine (UM) is planning to join the existing multi-university Industry/University Cooperative Research Center (I/UCRC) entitled The Center for Advanced Forestry Systems (CAFS) which was established in 2007 with four member institutions: North Carolina State University (lead university), Oregon State University, Purdue University and Virginia Tech. The primary focus of the proposed research site within CAFS will be modeling the productivity of managed natural forests. This research focus will be addressed at multiple scales ranging from the individual tree to the regional forest. UM has a long history of applied research in the management of naturally regenerated forests as well as a strong relationship with the forest products industry. The proposed activities at UM will augment current CAFS projects, and will more fully address the needs for scientific and technological advances for enhancing the competitiveness of the US forestry sector. The effort at UM has the potential to improve the competitiveness of the forest products industry by solving key problems using applied research and enhanced institutional collaboration. The broader scientific community will benefit through refereed publications and presentations at scientific meetings that focus on key nationwide research questions. Enhanced graduate student research opportunities will increase the number of trained professionals able to address these future forest resource challenges. UM also plans to address employee and student diversity issues

Examining approaches for modeling individual tree growth response to thinning in Norway spruce

Using periodic measurements from permanent plots in non-thinned and thinned Norway spruce (Picea abies (L.) H. Karst.) stands in Norway, individual-tree growth models were developed to predict annual diameter increment, height increment, and height to crown base increment. Based on long-term data across a range of thinning regimes and stand conditions, alternative approaches for modeling response to treatment were assessed. Dynamic thinning response functions in the form of multiplicative modifiers that predict no effect at the time of thinning, a rapid increase followed by an early maximum before the effect gradually declines to zero could not be fitted to initially derived baseline models without thinning related predictors. However, alternative approaches were used and found to perform well. Specifically, indicator variables representing varying time periods after thinning were statistically significant and behaved in a robust manner as well as consistent with general expectations. In addition, they improved overall prediction accuracy when incorporated as fixed effects into the baseline models for diameter and height to crown base increment. Further, more simply, including exponentially decreasing multiplicative thinning response functions improved prediction accuracy for height increment and height to crown base increment. Irrespective of studied attribute and modelling approach, improvement in performance of these extended models was relatively limited when compared to the corresponding baseline models and more pronounced in trees from thinned stands. We conclude that the largely varying and often multi-year measurement intervals of the periodic data used in this study likely prevented the development of more sophisticated thinning response functions. However, based on the evaluation of the final models’ overall performance such complex response functions may not to be necessary to reliably predict individual tree growth after thinning for certain conditions or species, which should be further considered in future analyses of similar nature.publishedVersio

Alterations in Douglas-fir crown structure, morphology, and dynamics imposed by the Swiss needle cast disease in the Oregon Coast Range

Plants respond to defoliation in many different and complex ways, depending on their growth habit and form as well as the extent and duration of the defoliation. Tree crowns have been shown to be quite sensitive to disturbances such as defoliation, however quantitative relationships have rarely been developed, making the true biological meaning of crown condition assessments quite difficult to decipher. The sudden emergence of Swiss needle cast (SNC) in the Oregon Coast Range prompted investigation of the response of Douglas-fir crown structure, crown morphology, and foliage dynamics to extended defoliation. Using data from permanent plots and 82 destructively sampled trees, hypotheses regarding the response of trees to defoliation were tested with linear and nonlinear models. Responses of crowns were investigated at multiple levels including the needle, branch, tree, and stand scales. At the individual-needle level, SNC has resulted in foliage that is smaller in length, width, and projected area; lower in dry mass; and higher in specific leaf area. The disease has influenced the foliage age structure by increasing the proportion in the younger age classes with greater SNC severity. The disease has also resulted in crowns that have a greater proportion of their current and 1-year-old needles located higher in the crown than Abstract approved Douglas A. Maguire normal, while the 2-, 3- and 4-year-old needles are shifted towards the crown base relative to healthy trees. At the branch-level, the disease has modified growth patterns as well as dry matter production and allocation. The number of secondary lateral branches on a primary branch declined in response to the disease, as did the foliated branch length and diameter for a given position in the crown. The ratio of branch length to branch diameter, however, increased with disease severity, which suggests altered elongation patterns. Branches in the lower portion of the heavily diseased crowns were elongating faster than normal, while elongation of branches in the mid-crown was slower. Elongation of branches in the upper crown was unaffected. The disease significantly reduced branch foliage dry matter and area for a given position in the crown and diameter. Branches, however, allocated more dry matter to higher order branches, but less dry matter to primary branch elongation. At the tree-level, the disease has led to crowns that are shorter than normal, while the largest measured standing width remains unaffected. Crown radii and maximum branch diameter profiles suggested that changes within the crown might be occurring at different levels due to variations in SNC damage within the crown. The number of primary interwhorl branches decreased with greater disease severity. SNC also significantly reduced total foliage and branchwood dry matter. Overall, the vertical distribution of foliage dry matter was less skewed and more uniform with increased disease severity. At the stand-level, SNC has significantly increased crown recession rates, woody litterfall, the specific leaf area of the litter, and growth efficiency. The disease caused a decline in foliage litterfall rates as well as leaf area index. In addition, the seasonal distribution of foliage litterfall was altered, with a greater amount occurring in the summer than normal. Crown condition, as assessed by foliage retention and the crown sparseness index, varied with SNC and other site factors. Within-tree variability of foliage retention was significantly higher than between-tree or between-plot variability. Although assessments of foliage retention were found to be highly variable, the sample size required to attain a sufficiently precise estimate for a given tree and stand are lower than the sample sizes currently being collected. The crown sparseness index was found to be significantly less variable than foliage retention and was primarily influenced by stand factors such as age and stand density. Defoliation caused significant changes at the individual needle, branch, tree, and stand levels, complicating efforts to accurately predict growth responses to defoliation. This detailed analysis of crown and foliage dynamics helps to establish links among current SNC studies. For example, growth losses associated with SNC are due to the reduction of foliage area, but also to changes in the size and vertical distribution of the needles. In addition, crown assessment indices such as foliage retention and crown length to sapwood area ratio represent different aspects of crown condition. Crown attributes are sensitive to the direct and indirect effects of SNC, which have important implications for tree growth and stand management. Important direct effects include the premature loss of foliage, while important indirect effects of SNC include changes in the within-crown light environment. Integrating measures of crown condition into forest models, therefore, represents an important step towards incorporating physiological-mechanisms into models for predicting growth responses to environmental changes such as tree disease and for understanding the complex responses of tree morphology and growth

Development of a hybrid modeling framework for intensively managed Douglas-fir plantations in the Pacific Northwest

Forest growth models in the Pacific Northwest are predominantly empirical. Predictions of yield under alternative silvicultural regimes cannot rely completely on field trials; yet empirical growth models are often inadequate for extrapolating untested regimes and genotypes. The limitations of current models include (1) long time-steps (e.g. 5-10 years); (2) insufficient detail for characterizing crowns; and (3) inability to capture physiological mechanisms. The overall goal of this dissertation was to test the ability of a hybrid model (empirical + process-based) to predict the growth of intensively managed plantations. The first step of model development was to refine current characterizations of Douglas-fir crown structure across several silvicultural treatments. The effects of fertilization, thinning, precommercial thinning, vegetation control, and disease intensity (Swiss needle cast) were found to influence important structural attributes of the crown. Among the crown attributes affected, maximum branch size and total- and nonfoliated-crown profile were the most dynamic attributes. Conversely, treatments had no effect on the number of branches or on branch angle. Equations based solely on bole and crown variables predicted crown structural attributes reasonably well across these varied stand conditions. Annualized empirical equations for individual tree diameter and height growth were developed next and found to outperform similar models with a longer time-step. The parameters of these empirical equations showed very few meaningful relationships with physiography, soil, or climate, suggesting that representation of key physiological processes was a necessary next step. Individual branch growth and mortality were significantly influenced by fertilization, thinning, precommercial thinning, vegetation control, and Swiss needle cast. Dynamic equations developed from this dataset significantly improved predictions of crown recession, compared to a traditional empirical approach. The improvements, however, had a relatively minor impact on short-term stand volume growth. The combination of these equations into a hybrid framework showed improvements in leaf area index and periodic annual increment when compared to other stand-level hybrid models. At the individual tree-level, the use of both empirical and mechanistic components was necessary to achieve a level of bias slightly better than that of a purely empirical approach. Beyond growth predictions, this hybrid model offers many other uses

Center for Research on Sustainable Forests 2019 Annual Report

The Center for Research on Sustainable Forests (CRSF) and Cooperative Forestry Research Unit (CFRU) continued to move forward on multiple fronts with a particularly productive and rewarding FY18-19. This included leadership on several key new initiatives such as the Forest Climate Change Initiative (FCCI), Intelligent GeoSolutions (IGS), and a funded National Science Foundation (NSF) Track 2 EPSCoR grant (INSPIRES). This is in addition to ongoing leadership and support for important CRSF programs such as NSF’s Center for Advanced Forestry Systems (CAFS), the Northeastern Research Cooperative (NSRC), and FOR/Maine. In short, CRSF is on a bold upward trajectory that highlights its relevance and solid leadership with a rather bright future

Managing the middle ground: forests in the transition zone between cities and remote areas

In many parts of the world there are extensive landscapes where forests and people strongly intermingle, notably in the suburbs and exurbs of cities. This landscape of transitional forest generally receives limited attention from policy makers and researchers who tend to be rooted in traditions centered on either urban planning or management of natural resources in rural areas. The transitional forest is on the periphery of both perspectives, but it is a large area that provides numerous important values (biodiversity, ecosystem function, forest products, and amenities) to the people that live in them and their neighboring cities. Here we argue for increased attention to transitional forests, identify major challenges, and suggest changes to planning and management practices needed to ensure that the values of these forests are sustained

Center for Research on Sustainable Forests 2020 Annual Report

FY20 saw exciting changes in CRSF with several new initiatives launched, while progress continues on many other ongoing efforts. In particular, FY20 saw the start of two National Science Foundation funded and CRSF-led research projects. The first is the INSPIRES project, a multi-year research collaboration between Maine, New Hampshire, and Vermont focused on harnessing Big Data to better understand and forecast the region’s forest given current as well as future uncertainties. The other effort was a successful Phase 3 reboot of the National Science Foundation Industry-University Collaborative Research Center, Center for Advanced Forestry System (CAFS), for which I have served as Director since 2016. CAFS provides direct connections among several additional universities across the United States, including North Carolina State University, Oregon State University, Purdue University, University of Georgia, University of Idaho, and University of Washington, as well as to forest industry partners. Phase 3 of CAFS will be a five-year effort and, I hope, will lead to the successful graduation of the IUCRC

Linking remote sensing and various site factors for predicting the spatial distribution of eastern hemlock occurrence and relative basal area in Maine, USA

Introduced invasive pests are perhaps the most important and persistent catalyst for changes in forest composition. Infestation and outbreak of the hemlock woolly adelgid (Adelges tsugae; HWA) along the eastern coast of the USA, has led to widespread loss of hemlock (Tsuga canadensis (L.) Carr.), and a shift in tree species composition toward hardwood stands. Developing an understanding of the geographic distribution of individual species can inform conservation practices that seek to maintain functional capabilities of ecosystems. Modeling is necessary for understanding changes in forest composition, and subsequent changes in biodiversity, and one that can be implemented at the species level. By integrating the use of remote sensing, modeling, and Geographic Information Systems (GIS) coupled with expert knowledge in forest ecology and disturbance, we can advance the methodologies currently available in the literature on predictive modeling. This paper describes an approach to modeling the spatial distribution of the less common but foundational tree species eastern hemlock throughout the state of Maine (∼84,000 km2) at a high resolution. There are currently no published accuracy assessments on predictive models for high resolution continuous distribution of eastern hemlock relative basal area that span the geographic extent covered by our model, which is at the northern limit of the species’ range. A two stage mapping approach was used where presence/absence was predicted with an overall accuracy of 85% and the continuous distribution (percent basal area) was predicted with an accuracy of 84%. Overall, these findings are quite good despite high variability in the training dataset and the general minor component that eastern hemlock represents in the primary forest types in Maine. Eastern hemlock occurs along the southern half of the state stretching the east-west span with little to no occurrence in the northern regions. Several environmental and site characteristics, particularly average yearly maximum and minimum temperatures, were found to be positively correlated with hemlock occurrence. Eastern hemlock dominated stands appeared predominantly in the southwest corner of the state where HWA monitoring efforts can be focused. Given the importance of climate variables in predicting eastern hemlock, forecasts of future range shifts should be possible using data generated from climate scenarios