John M. Zobel

Whole stand yield models serve forest managers by providing projections of useful stand metrics such as height and volume. Climate shifts are currently being observed in the Lake States, including changes in forest composition and species’ ranges. Basswood ( Tilia americana L.) has potential to become a climate winner but lacks whole stand yield model parameters to adequately predict forest conditions. This paper aims to extend the utility of an existing whole stand yield model to basswood dominated stands in the Lake States to enable adaptation to shifting climatic conditions. Basal area, quadratic mean diameter, trees per acre, volume, and height models were fit using nonlinear least squares estimation. Models were validated with cross-validation, independent stand inventory data collected from a local forest management area, and national forest inventory data from more southerly states to evaluate model performance under climate conditions the Lake States could see in the future. Fit statistics for these models were consistent with other modeling efforts in the region, and validation statistics showed applicability of the models to broad basswood ranges and potential stability under changing climates. Forest managers can now utilize these new yield models to improve current and future management of the increasingly important basswood forest type.

Systems of whole‐stand yield models facilitate projections of forest attributes, but their inputs may be difficult to measure accurately. This study conducted sensitivity analyses to examine the effect of systematic and stochastic measurement errors on outputs from a representative system of equations. Simulated error was added to explanatory variables stand age, site index, or both. Results showed that large systematic error in one variable tended to produce moderate to large percent changes in all models, particularly the height and volume equations (often >50% change). Systematic error in both variables amplified this effect, especially for young, less productive stands. Stochastic error dramatically increased estimate variability (some relative standard errors >50%), particularly in the height and volume models at young ages and low site indices. These results suggest that measurement error may considerably alter projections and increase uncertainty when using whole‐stand yield models, highlighting the need for careful crew training.

Shortleaf pine site index on the Cumberland Plateau is one of the least studied silvics of the species. To obtain site index information, practitioners must use site index curves from outside the region. This research proposes a novel approach to using USDA Forest Service, Forest Inventory and Analysis data to develop a shortleaf pine site index equation specific to the Plateau. Shortleaf pine site trees (n = 410) were grown forward or backward until base age of 50 years, using site specific, mixed-model parameters. Over thirty height models were then fit using traditional methods and the algebraic difference approach (ADA). Fit and cross-validation statistics, along with examinations of model behavior, showed that a derivation of the Lundqvist-Korf model provided the best estimates. The model was rearranged to directly estimate site index, and a traditional site index graph is provided. Site index estimates had average validation results nearly four times better than the currently recommended site index curve developed off the Plateau. Forest practitioners now have access to improved site index estimation for restoring and managing shortleaf pine on the Cumberland Plateau.

Many forestry models require the input of stand size class information, a variable with multiple definitions across forest inventories. This work describes a crosswalk between stand age class and stand size class for several forest type groups in Minnesota to facilitate consistency and availability of the latter information. Refinements to the crosswalk include ratio adjustments that redistribute the number of plots (or hectares) from one estimated size class to another, based on known crosswalk error rates. The results showed that 61.9% of all plots were correctly classified, and 95.5% were within one size class. Correct classifications for individual forest type/size class combinations ranged from 16.7–79.2%. Applying the crosswalk to a validation dataset produced percent errors from −46.4% to 49.4%, but with the ratio adjustment, errors dropped to −20.1% to 14.4%. These results suggest that the crosswalk and ratio adjustments provide a coarse, yet reasonable, substitute to using more complex stand size classification methodologies, particularly when forecasting future stand conditions.

In 2018, the Minnesota Department of Natural Resources conducted the Sustainable Timber Harvest Analysis that resulted in the 10-year Stand Exam List (SEL). The SEL includes stands that will be assessed for potential management action from 2021 to 2030, but the location, number, and impact of stands actually harvested remains unknown. This study sought to use modeling to assess potential habitat changes from the SEL for five threatened, endangered, or special concern wildlife species. Three simulation scenarios captured the potential range of harvest from the SEL, and the Wildlife Habitat Indicator for Native Genera and Species model assessed associated habitat changes. The most realistic simulation scenario resulted in statistically insignificant habitat changes of less than ±6%, while two scenarios providing the upper and lower extremes of harvest resulted in statistically significant changes for one species each. Scenarios that resulted in less harvest and more mature forests benefited the five species, reflecting their habitat preferences. The tempering of habitat change values in the most realistic simulation scenario provides evidence for forest management tradeoffs between different wildlife species habitat requirements, as well as other forest resource management objectives.

Over the last four decades, forest management goals have transitioned to multiuse objectives, begging the question of their impact on wildlife habitat. Using USDA Forest Service Forest Inventory and Analysis data and the WHINGS (Wildlife Habitat Indicator for Native Genera and Species) model, the trends in wildlife habitat were quantified from 1977 to 2018 across Minnesota. Statewide, 35.5% of species experienced significant improvement in habitat, 29% significant reductions, and 35.5% nonsignificant change. The extent of habitat (acreage) increased for 100% of species, but the quality declined for 63% of species. Results were explained by the reduction in acreage of larger size classes of the aspen, balsam, and birch forest type and increases in smaller, younger forest area. Specifically, forest management that converted aspen stands to other forest types benefited certain wildlife species over others. Future forest management should consider the balance between the habitat requirements of the diverse native species in Minnesota.Study Implications: Trends in forest wildlife habitat over the last four decades across Minnesota highlight that forest management often favors one species at the expense of another. Statewide, wildlife species with preferences for larger, older aspen experienced diminished habitat, whereas habitat for species preferring younger forest types or older nonaspen types increased. Regionally, the forested ecoregions in Minnesota (northeast) generally saw reduced habitat, whereas the prairie/agricultural regions (south and northwest) saw the largest increases. Through this and further applications, forest and wildlife managers can rapidly assess the habitat implications of proposed management, whether for environmental review, forest planning, or harvest scheduling.

Forest fragmentation may negatively affect plants through reduced genetic diversity and increased population structure due to habitat isolation, decreased population size, and disturbance of pollen‐seed dispersal mechanisms. However, in the case of tree species, effective pollen‐seed dispersal, mating system, and ecological dynamics may help the species overcome the negative effect of forest fragmentation. A fine‐scale population genetics study can shed light on the postfragmentation genetic diversity and structure of a species. Here, we present the genetic diversity and population structure ofCercis canadensisL. (eastern redbud) wild populations on a fine scale within fragmented areas centered around the borders of Georgia–Tennessee, USA. We hypothesized high genetic diversity among the collections ofC. canadensisdistributed across smaller geographical ranges. Fifteen microsatellite loci were used to genotype 172 individuals from 18 unmanaged and naturally occurring collection sites. Our results indicated presence of population structure, overall high genetic diversity (H_E = 0.63,H_O = 0.34), and moderate genetic differentiation (F_ST = 0.14) among the collection sites. Two major genetic clusters within the smaller geographical distribution were revealed by STRUCTURE. Our data suggest that nativeC. canadensispopulations in the fragmented area around the Georgia–Tennessee border were able to maintain high levels of genetic diversity, despite the presence of considerable spatial genetic structure. As habitat isolation may negatively affect gene flow of outcrossing species across time, consequences of habitat fragmentation should be regularly monitored for this and other forest species. This study also has important implications for habitat management efforts and future breeding programs.