Oak-pine forests in the U.S. Central Hardwood Forests are recovering from exploitative harvesting and clearing in the early twentieth century and are undergoing rapid succession changes. ...Unprecedented red oak borer (ROB,
Enaphalodes rufulus
) outbreaks in 1999–2003 are associated with the largest oak mortality event reported in the Central Hardwood Region since the arrival of Europeans. Predicting and evaluating the effects of ROB disturbance on forest composition has practical value for forest management plans that aims to minimize ecological and economic loss from ROB disturbances. However, such prediction at a regional scale is rare due to the limited approaches that could explicitly couple insect outbreak mechanisms with forest dynamics under changing climate. We used a newly developed climate-sensitive Biotic Disturbance Agent module in the LANDIS PRO framework to simulate species composition changes due to succession, climate change, and ROB disturbances in 13.5 million ha forests in the U.S. Central Hardwood Region from 2000 to 2300. Our simulation suggested that succession is more important than climate effects and ROB disturbance in predicting regional species composition changes. ROB disturbance interacting with climate change accelerated the decline of primary host species (e.g.,
Quercus rubra
) and then substantially changed forest succession trajectories under warming climates. Our modeling approach improved the simulation realism of ROB disturbance and more realistically projected how tree species will respond to ROB disturbance under changing climate, informing decision-making in silvicultural prescriptions and long-term management plans.
In the Gulf of Mexico coastal region, prescribed fire has been increasingly used as a management tool to restore declining native ecosystems, but it also increases the threat posed by biological ...invasion, since the treated sites are more susceptible to invasive species such as Chinese tallow (Triadica sebifera). We chose Mississippi Sandhill Crane National Wildlife Refuge (MSCNWR), a fire-managed landscape, to examine the potential effect of prescribed fire and landscape/community features on tallow invasion and spread. We took a complete survey of roadways and fire lines for tallow and measured a systematic sample of 144 10 × 3 m2 rectangular plots along two selected roadways and a simple random sample of 56 0.04-ha circular plots across burn units. We used pair correlation function for marked point pattern data, zero-inflated negative binomial models for count data, as well as multivariate Hotelling’s T2 test, to analyze the effect of prescribed fire and landscape/community characteristics on tallow invasion and spread along habitat edges and into interiors. Our results show that tallow spread along habitat edges and into interiors in a spatially clustered pattern. Tallow invasion risk decreases with the distance to seed trees and shrub coverage, and with the time since last fire if seed trees are outside the effective seed dispersal range (~300 m), but increases with the time since last fire if seed trees are within the effective seed dispersal range. Tallow seedling (≤2 years old) densities increase with the time since last fire and with increasing overstory tree basal area, but decrease with the distance to seed trees. Tallow-invaded interior plots have significantly shorter mean fire return intervals (2.7 years), lower shrub coverage (8.6%), and are closer to edges (20.3 m) than non-invaded plots (4.3 years, 18.4%, 167.6 m, respectively).
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.
Oak decline and related mortality have periodically plagued upland oak–hickory forests, particularly oak species in the red oak group, across the Ozark Highlands of Missouri, Arkansas and Oklahoma ...since the late 1970s. Advanced tree age and periodic drought, as well as Armillaria root fungi and oak borer attack are believed to contribute to oak decline and mortality. Declining trees first show foliage wilt and browning, followed by progressive branch dieback in the middle and/or upper crown. Many trees eventually die if severe crown dieback continues. In 2002, more than 4000 living oak trees ≥11
cm dbh in the relatively undisturbed mature oak forests of the Missouri Ozark Forest Ecosystem Project (MOFEP) were randomly selected and inventoried for tree species, dbh, crown class, crown width, crown dieback condition (healthy: <5% crown dieback, slight: >5–33%, moderate: 33–66%, and severe: >66%) and number of emergence holes created by oak borers on the lower 2.4
m of the tree bole. The same trees were remeasured in 2006 to determine their status (live or dead). In 2002, about 10% of the red oak trees showed moderate or severe crown dieback; this was twice the percentage observed for white oak species. Over 70% of trees in the red oak group had evidence of oak borer damage compared to 35% of trees in the white oak group. There was significant positive correlation between crown dieback and the number of borer emergence holes (
p
<
0.01). Logistic regression showed oak mortality was mainly related to crown width and dieback, and failed to detect any significant link with the number of oak borer emergence holes. Declining red oak group trees had higher mortality (3 or 4 times) than white oaks. The odds ratios of mortality of slightly, moderately, and severely declining trees versus healthy trees were, respectively, 2.0, 6.5, and 29.7 for black oak; 1.8, 3.8, and 8.3 for scarlet oak; and 2.6, 6.5 and 7.1 for white oaks.
Two challenges confronting forest landscape models (FLMs) are how to simulate fine, stand-scale processes while making large-scale (i.e., >10
7
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 (∼10
7
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.
In the southeastern United States, drought can pose a significant threat to forests by reducing the amount of available water, thereby stressing trees. Destructive changes in crown conditions provide ...the first visible indication of a problem in a forested area, making it a useful indicator for problems within an ecosystem. Forest Health and Monitoring (FHM) and Palmer's Drought Severity Index (PDSI) data from 11 states in the southeastern United States were obtained in an effort to determine the role that drought, forest type, and ecoregion have in indicating differences in crown dieback. Analyses were conducted by species groups using classification and regression tree (CART) analysis. The greatest amount of total relative crown dieback occurred in red oak (18%), followed by other hardwoods (14%), and white oak (11%). Relative crown dieback varied by forest type and ecoregion with a relationship to drought in both red oak and white oak. This information will be useful for focusing future research and modeling efforts to predict forest health conditions affected by changing climate variables.
► Shortleaf pine sprout from a basal crook after top-kill from fire. ► Sprouting is reduced due to high temperatures and crown scorch. ► Sprouts survive best after sprouted if seedlings are between ...0.6 and 1.6
cm in ground line diameter. ► Shortleaf pine sprouts can be used as a source of advanced regeneration.
Shortleaf pine (
Pinus echinata) is a fire dependent species that is declining across the southeastern US. Its unique basal crook is an adaptation that protects dormant buds from fire and facilitates prolific sprouting of seedling rootstocks following top-kill. Understanding what influences shortleaf pine sprouting after fire could greatly increase success of natural regeneration efforts. We examined the relationship between sprouting and seedling size, basal crook depth, and maximum basal crook temperature of shortleaf pine seedlings following a mid-intensity prescribed fire in the Ozark-St. Francis National Forest of northwestern AR, US. We hypothesized that larger seedlings with deeper buried crooks would exhibit greater sprouting after top-kill from fire. A total of 195 seedlings were measured for a variety of site, size, and fire damage characteristics. ‘Simulated crooks’ were constructed and calibrated to estimate basal crook temperature and were buried adjacent to each seedling. Prescribed fires were implemented during the early growing season, resulting in a wide range of seedling damage from slightly charred stems to complete immolation of aboveground biomass. Fourteen of 195 seedlings were not top-killed and were larger and experienced lower crown scorch than those that were top-killed. Of the 181 seedlings that suffered top-kill, 72 did not sprout and died. Over the course of the growing season 40 of the sprouted seedlings died. Sprouted seedlings that survived the entire growing season had similar size and crook soil depths as seedlings that initially died and were smaller (ground line diameter of 1.5 vs. 3.1
cm) with shallower crook depth (0.2 vs. 0.7
cm) than seedlings that sprouted and later died. Crook temperature and crown scorch values were similar among sprouted seedlings that lived and died, but were lower than for seedlings that never sprouted. These results suggest that the ability of top-killed seedlings to sprout following fire is sensitive to heat and fire damage, while the ability of a seedling to survive once sprouted decreases with seedling size. Low intensity fires when seedlings are 1–2
cm in diameter can be used to bank seedlings until adequate stocking is achieved or until regeneration cutting can be timed with a bumper seed crop to supplement existing advanced regeneration.
A spatially explicit forest succession and disturbance model is used to delineate the extent and dispersion of oak decline under two fire regimes over a 150-year period. The objectives of this study ...are to delineate potential current and future oak decline areas using species composition and age structure data in combination with ecological land types, and to investigate how relatively frequent simulated fires and fire suppression affect the dynamics of oak decline. We parameterized LANDIS, a spatially explicit forest succession and disturbance model, for areas in the Boston Mountains of Arkansas, USA. Land type distribution and initial species/age class were parameterized into LANDIS using existing forest data. Tree species were parameterized as five functional groups including white oak (
Quercus alba L.,
Quercus stellata Wangenh.,
Quercus muehlenbergii Engelm.), red oak (
Qurecus rubra L.,
Quercus marilandica Muenchh.,
Quercus falcata Michx.,
Quercus coccinea Muenchh.), black oak (
Quercus velutina Lam.), shortleaf pine (
Pinus echinata Mill), and maple (
Acer rubrum L.,
Acer saccharum Marsh.) groups. Two fire regimes were also parameterized: current fire regime with a fire return interval of 300 years and a historic fire regime with an overall average fire return interval of 50 years. The 150-year simulation suggests that white oak and shortleaf pine abundance would increase under the historic fire regime and that the red oak group abundance increases under the current fire regime. The black oak group also shows a strong increasing trend under the current fire regime, and only the maple group remains relatively unchanged under both scenarios. At present, 45% of the sites in the study area are classified as potential oak decline sites (sites where red and black oak are >70 years old). After 150 simulation years, 30% of the sites are classified as potential oak decline sites under the current fire regime whereas 20% of the sites are potential oak decline sites under the historic fire regime. This analysis delineates potential oak decline sites and establishes risk ratings for these areas. This is a further step toward precision management and planning.
The disturbance history of six mature white oak (Quercus alba L.) - northern red oak (Quercus rubra L.) - hickory (Carya spp.) stands in the Ozark Mountains of northern Arkansas were reconstructed ...using tree-ring and fire-scar analysis. Results indicate that all six stands originated in the early 1900s following timber harvesting and (or) fire. These disturbances initiated a pulse of oak-dominated establishment. Most sites were periodically burned during the next several decades. Abrupt radial growth increases in all stands during the 1920s to 1940s reflected additional disturbances. These perturbations likely provided growing space for existing trees, but did not result in increased seedling establishment. Thus, multiple disturbances were important in the origin and development of the stands studied. By the 1930s and 1940s, oak establishment was replaced by shade-tolerant, fire-intolerant non-oak species; few oak recruited into tree size classes after the 1950s. The decrease in oaks and the increase in non-oaks coincided with fire suppression. Few scars were recorded during the past 60-70 years. Prescribed fire may be an important management tool in regenerating oak forests in northern Arkansas.
Celotno besedilo
Dostopno za:
BF, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
AimsUsing a network of permanent plots, we determined how multiple old-growth forests changed over an 18-19-year period at a state-wide scale. This examination of change allowed us to assess how the ...compositional and structural stability of each forest varied with site characteristics (topography, physiography and productivity) and stochastic disturbance.MethodsIn 2011, we resampled 150 plots distributed across five old-growth hardwood forests in Indiana, USA that were originally sampled in 1992-1993. Within each plot, we relocated and remeasured the diameter at breast height (dbh) of all trees (≥10.0cm) present during the 1992-1993 sample, which allowed us to track their individual fates through time for growth and mortality calculations. Trees that grew to ≥10.0cm dbh since plot establishment were designated as ingrowth. The dbh and species of all saplings (stems ≥2.0cm but <10.0cm dbh) were also recorded. For each forest, we calculated density (stems ha -1 ), basal area (BA; m2 ha-1 ) and importance value (relative density + relative BA)/2) of trees by species. For saplings, density per ha was calculated by species for each forest. We also calculated annual mortality rate (AMR) for three diameter classes (10-29.9, 30-59.9 and ≥60cm) and species richness (S), evenness (E) and Shannon-Weiner diversity (H') for the tree and sapling layers. Differences between years were compared for each forest using paired t-tests and Wilcoxon signed rank tests.Important FindingsAlthough we observed commonality in changes across some sites, our results suggest that these forests differ in their rates and trajectories of change. Changes in total stand BA and density varied across sites and were influenced by past disturbance and mortality rates. We observed a general increase in the overstory dominance of Acer saccharum coupled with a general decrease in the dominance of Quercus section Lobatae (red oak group) species. Mortality of overstory trees present in 1992-1993 ranged from 27% to 49% over the study period (mean AMR 1.6-3.7%). Most sites experienced greater mortality of early and mid-successional species, but one site experienced heavy mortality of Fagus grandifolia, a shade-tolerant late-successional species. Shade tolerant species, A. saccharum in particular, dominated the sapling layer at most sites. However, recruitment of this species into larger size classes did not occur uniformly across all sites and the species was comparatively uncommon at one site. Overall, our results suggest that old-growth remnants, even within a single state, cannot be viewed as equivalent units with regard to research or management. Stochastic disturbance events and surrounding land use may have amplified effects on small scattered remnants. Therefore, continued monitoring of these rare, but biologically important forests is critical to their long-term management and protection.
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