Martin A. Spetich

Fire history of oak–pine forests in the Lower Boston Mountains, Arkansas, USA

Perspective on present day issues associated with wildland fire can be gained by studying the long-term interactions among humans, landscape, and fire. Fire frequency and extent over the last 320 years document these interactions north of the Arkansas River on the southern edge of the Lower Boston Mountains. Dendrochronological methods were used to construct three fire chronologies from 309 dated fire scars that were identified on 45 shortleaf pine (Pinus echinata) remnants. Fire frequency increased with human population density from a depopulated period (the late 1600s and early 1700s) to a peak in fire frequency circa 1880. Fire frequency then decreased as human population continued to increase. Fire frequency and human population density were positively correlated during an early period (1680–1880) with low levels of population, but negatively correlated during a later period (1881–1910) with high levels of population. We hypothesized that this difference is due to limits on fire propagation and ignition caused by land use and culture, as well as human population density. Relatively high human population densities (>5 humans/km 2 ) were associated with a peak in the maximum number of fires per decade in this highly dissected, ‘bluff and bench’ landscape compared to less dissected regions of the Ozarks. # 2002 Elsevier Science B.V. All rights reserved.

A large-scale forest landscape model incorporating multi-scale processes and utilizing forest inventory data

Two challenges confronting forest landscape models (FLMs) are how to simulate fine, stand-scale processes while making large-scale (i.e., >107 ha) simulation possible, and how to take advantage of extensive forest inventory data such as U.S. Forest Inventory and Analysis (FIA) data to initialize and constrain model parameters. We present the LANDIS PRO model that addresses these needs. LANDIS PRO adds density and size mechanisms of resource competition. This is achieved through incorporating number of trees and DBH by species age cohort within each raster cell. Forest change is determined by the interactions of species-, stand-, and landscape-scale processes. Species-scale processes include tree growth, establishment, and mortality. Stand-scale processes include density and size-related resource competition that regulates self-thinning and seedling establishment. Landscape-scale processes include seed dispersal, as well as natural and anthropogenic disturbances. LANDIS PRO is designed to be straightforwardly comparable with forest inventory data, and thus the extensive FIA data can be directly utilized to initialize and constrain model parameters before predicting future forest change. We initialized a large landscape (∼107 ha) from historical FIA data (1978) and the predicted forest structure and composition following 30 years of simulation were statistically calibrated against a prior time-series of sequential FIA data (1978 to 2008). The results showed that the initialized conditions realistically represented the historical forest composition and structure at 1978, and the constrained model parameters predicted reasonable outcomes at both landscape and land type scales. The subsequent evaluation of model predictions showed that the predicted forest composition and structure were comparable with old-growth oak forests; predicted forest successional trajectories were consistent with the expected successional patterns in oak-dominated forests in the study region; and the predicted stand development patterns were in agreement with the established theories of forest stand development. This study demonstrated a framework for forest landscape modeling including model initialization, calibration, and evaluation of predictions.

A framework for evaluating forest landscape model predictions using empirical data and knowledge

Evaluation of forest landscape model (FLM) predictions is indispensable to establish the credibility of predictions. We present a framework that evaluates short- and long-term FLM predictions at site and landscape scales. Site-scale evaluation is conducted through comparing raster cell-level predictions with inventory plot data whereas landscape-scale evaluation is conducted through comparing predictions stratified by extraneous drivers with aggregated values in inventory plots. Long-term predictions are evaluated using empirical data and knowledge. We demonstrate the applicability of the framework using LANDIS PRO FLM. We showed how inventory data were used to initialize the landscape and calibrate model parameters. Evaluation of the short-term LANDIS PRO predictions based on multiple metrics showed good overall performance at site and landscape scales. The predicted long-term stand development patterns were consistent with the established theories of stand dynamics. The predicted long-term forest composition and successional trajectories conformed well to empirical old-growth studies in the region. We present a framework for evaluating the short- and long-term forest landscape model predictions at site and landscape scales.Site-scale evaluation is conducted through comparing cell-level predictions with inventory plot data.Landscape-scale evaluation is conducted through comparing predictions stratified by extraneous drivers with aggregated values in inventory plots.We successfully evaluated the LANDIS PRO forest landscape model predictions using empirical data and knowledge and showed reasonable performances at both scales.

Modeling the effects of harvest alternatives on mitigating oak decline in a Central Hardwood Forest landscape

Oak decline is a process induced by complex interactions of predisposing factors, inciting factors, and contributing factors operating at tree, stand, and landscape scales. It has greatly altered species composition and stand structure in affected areas. Thinning, clearcutting, and group selection are widely adopted harvest alternatives for reducing forest vulnerability to oak decline by removing susceptible species and declining trees. However, the long-term, landscape-scale effects of these different harvest alternatives are not well studied because of the limited availability of experimental data. In this study, we applied a forest landscape model in combination with field studies to evaluate the effects of the three harvest alternatives on mitigating oak decline in a Central Hardwood Forest landscape. Results showed that the potential oak decline in high risk sites decreased strongly in the next five decades irrespective of harvest alternatives. This is because oak decline is a natural process and forest succession (e.g., high tree mortality resulting from intense competition) would eventually lead to the decrease in oak decline in this area. However, forest harvesting did play a role in mitigating oak decline and the effectiveness varied among the three harvest alternatives. The group selection and clearcutting alternatives were most effective in mitigating oak decline in the short and medium terms, respectively. The long-term effects of the three harvest alternatives on mitigating oak decline became less discernible as the role of succession increased. The thinning alternative had the highest biomass retention over time, followed by the group selection and clearcutting alternatives. The group selection alternative that balanced treatment effects and retaining biomass was the most viable alternative for managing oak decline. Insights from this study may be useful in developing effective and informed forest harvesting plans for managing oak decline.

History, Administration, Goals, Value, and Long-Term Data of Russia's Strictly Protected Scientific Nature Reserves

ABSTRACT: One of the most comprehensive attempts at biodiversity conservation in Russia and the former Soviet Union has been the establishment of an extensive network of protected natural areas. Among all types of protected areas in Russia, zapovedniks (strictly protected scientific preserves) have been the most effective in protecting biodiversity at the ecosystem scale. Russia has 101 zapovedniks with a total area of 34.3 million ha, representing 2% of Russian territory. The mission of zapovedniks is to protect native biodiversity and ecosystem processes as well as to facilitate the study of natural ecosystem processes and functions. In this manuscript, we provide a brief history of Russian ecosystem preservation and outline the goals and administrative organization of the Russian zapovednik system as it currently functions, as well as the characteristics, problems, and values of the system.

Ridgetop Fire History of an Oak-Pine Forest in the Ozark Mountains of Arkansas

Abstract A total of 53 fire-scarred Pinus echinata (shortleaf pine) trees were examined to reconstruct a ridgetop fire chronology of an oak-pine forest in the Ozark Mountains of north-central Arkansas. This process yielded 104 fire scars dating to 61 separate fire years. Fire frequency was greatest during the Euro-American Settlement Period (1820–1900), when the median fire interval (MFI) was 1.9 years. Most of the sample trees established during this period. Fire remained prevalent through the Regional Development (1901–1930) and Modern (1931–2003) Periods, when the MFI was 2.1 and 2.6 years, respectively. Palmer Drought Severity Index mean values from 1823–2003 did not differ (p = 0.76) between fire years and non-fire years, suggesting that fires in the study area were predominantly anthropogenic in origin.

Oak Decline in Central Hardwood Forests: Frequency, Spatial Extent, and Scale

Oak decline is a widely distributed disease that results from an interacting set of factors in the Central Hardwood Region. Episodes of decline have been reported since before the turn of the twentieth century and from every state in the region. It is a stress-mediated disease that results from the interactions of physiologically mature trees, abiotic and biotic stressors that alter carbohydrate physiology, and opportunistic fungal pathogens and inner bark-feeding insects. Symptoms include reduced radial growth and slow, progressive crown dieback. Decline occurs over several years or decades, ending in death of vulnerable trees. Patterns of oak decline vary from a few trees in stands with diverse species composition and age structure, to areas covering several thousand ha in landscapes with more uniform composition of susceptible, physiologically mature red oak group species. Prolonged periods of drought that occur in combination with repeated spring defoliations by leaf-feeding insects exacerbate decline. Past disturbances have shaped current forest species composition and age structure, favoring physiologically mature stands with a large oak component, and are thus inextricably linked to oak decline vulnerability. Noteworthy examples are the functional extirpation of the American chestnut by the non-indigenous chestnut blight pathogen, combined with changing disturbance patterns, including fire suppression and reduced harvesting, during the early twentieth century. Data from extensive regional surveys have been used to develop models predicting the probability and impacts of oak decline events as part of the Forest Vegetation Simulator.

Spatial Trends and Factors Associated with Hardwood Mortality in the Southeastern United States

Hardwood species play an integral role in forested ecosystems in the southeastern United States. This necessitates an assessment of mortality patterns in these species as well as factors associated with them. This study assessed mortality patterns for hardwood species utilizing Forest Inventory Analysis (FIA) data from the United States Forest Service for two consecutive inventory cycles using kernels smoothing and Classification and Regression Tree (CART) modeling. The first inventory cycle (2000–2004) reveals a patterns and associated factors that can be associated with decline events that have recurred throughout the region while the second inventory cycle (2005–2009) exhibits a different pattern in mortality than cycle one. Mortality patterns and their associated factors should be monitored in the hope that methods can be developed to mitigate extreme impacts to these vitally important species.

Effects of species biological traits and environmental heterogeneity on simulated tree species distribution shifts under climate change

Demographic processes (fecundity, dispersal, colonization, growth, and mortality) and their interactions with environmental changes are not well represented in current climate-distribution models (e.g., niche and biophysical process models) and constitute a large uncertainty in projections of future tree species distribution shifts. We investigate how species biological traits and environmental heterogeneity affect species distribution shifts. We used a species-specific, spatially explicit forest dynamic model LANDIS PRO, which incorporates site-scale tree species demography and competition, landscape-scale dispersal and disturbances, and regional-scale abiotic controls, to simulate the distribution shifts of four representative tree species with distinct biological traits in the central hardwood forest region of United States. Our results suggested that biological traits (e.g., dispersal capacity, maturation age) were important for determining tree species distribution shifts. Environmental heterogeneity, on average, reduced shift rates by 8% compared to perfect environmental conditions. The average distribution shift rates ranged from 24 to 200myear-1 under climate change scenarios, implying that many tree species may not able to keep up with climate change because of limited dispersal capacity, long generation time, and environmental heterogeneity. We suggest that climate-distribution models should include species demographic processes (e.g., fecundity, dispersal, colonization), biological traits (e.g., dispersal capacity, maturation age), and environmental heterogeneity (e.g., habitat fragmentation) to improve future predictions of species distribution shifts in response to changing climates.