Maria D. Tchakerian

Simulating the reciprocal interaction of forest landscape structure and southern pine beetle herbivory using LANDIS

The reciprocal interaction of landscape structure and ecological processes is a cornerstone of modern landscape ecology. We use a simulation model to show how landscape structure and herbivory interact to influence outbreaks of southern pine beetle (Dendroctonus frontalis Zimmermann) in a landscape representative of the southern Appalachian Mountains, USA. We use LANDIS and its biological disturbance agent module to simulate the effects of landscape composition (proportion of landscape in host area) and host aggregation on the size and severity of insect outbreaks and the persistence of the host species, Table Mountain Pine (Pinus pungens Lamb.). We find that landscape composition is less important in the modeled landscapes than host aggregation in structuring the severity of insect outbreaks. Also, simulated southern pine beetle outbreaks over time tend to decrease the aggregation of host species on the landscape by fragmenting large patches into smaller ones, thereby reducing the severity of future outbreaks. Persistence of Table Mountain pine decreases throughout all simulations regardless of landscape structure. The results of this study indicate that when considering alternative restoration strategies for insect-affected landscapes, it is necessary to consider the patterns of hosts on the landscape as well as the landscape composition.

Stage-structured matrix models for organisms with non-geometric development times

Matrix models have been used to model population growth of organisms for many decades. They are popular because of both their conceptual simplicity and their computational efficiency. For some types of organisms they are relatively accurate in predicting population growth; however, for others the matrix approach does not adequately model growth rate. One of the reasons for the lack of accuracy is that most matrix-based models implicitly assume a specific degree of variability in development times for the organism. Because the variability is implicit, the implied variances are often not verified with experimental data. In this paper, we shall present extensions to the stage-classified matrix models so that organisms with arbitrary means and standard deviations of development times can be modeled.

Computer-based synthetic data to assess the tree delineation algorithm from airborne LiDAR survey

Small Footprint LiDAR (Light Detection And Ranging) has been proposed as an effective tool for measuring detailed biophysical characteristics of forests over broad spatial scales. However, by itself LiDAR yields only a sample of the true 3D structure of a forest. In order to extract useful forestry relevant information, this data must be interpreted using mathematical models and computer algorithms that infer or estimate specific forest metrics. For these outputs to be useful, algorithms must be validated and/or calibrated using a sub-sample of ‘known’ metrics measured using more detailed, reliable methods such as field sampling. In this paper we describe a novel method for delineating and deriving metrics of individual trees from LiDAR data based on watershed segmentation. Because of the costs involved with collecting both LiDAR data and field samples for validation, we use synthetic LiDAR data to validate and assess the accuracy of our algorithm. This synthetic LiDAR data is generated using a simple geometric model of Loblolly pine (Pinus taeda) trees and a simulation of LiDAR sampling. Our results suggest that point densities greater than 2 and preferably greater than 4 points per m2 are necessary to obtain accurate forest inventory data from Loblolly pine stands. However the results also demonstrate that the detection errors (i.e. the accuracy and biases of the algorithm) are intrinsically related to the structural characteristics of the forest being measured. We argue that experiments with synthetic data are directly useful to forest managers to guide the design of operational forest inventory studies. In addition, we argue that the development of LiDAR simulation models and experiments with the data they generate represents a fundamental and useful approach to designing, improving and exploring the accuracy and efficiency of LiDAR algorithms.

Short communication: A simple stochastic weather generator for ecological modeling

Stochastic weather generators are useful tools for exploring the relationship between organisms and their environment. This paper describes a simple weather generator that can be used in ecological modeling projects. We provide a detailed description of methodology, and links to full C++ source code (http://weathergen.sourceforge.net) required to implement or modify the generator. We argue that understanding the principles of weather generation will allow ecologists to tailor a solution for their own requirements. The detailed, repeatable methodology we present demonstrates that weather generation is relatively straightforward for ecologists to implement and modify.

Restoration of Southern Pine Forests After the Southern Pine Beetle

The southern pine beetle (Dendroctonus frontalis Zimmermann) is the most destructive insect pest of pine (Pinus spp.) forests in the southern United States. Restoring and managing pine stands infested by southern pine beetle are critically important for forest health and sustainability in the region. The successful restoration of damaged pine forests requires the integration of information of beetle biology and behavior, pine ecology, and landscape restoration. Certain social, economic, and political issues also need to be considered concomitantly. The knowledge for effective restoration and management of southern pine forests has increased greatly in the past decade. In this chapter, we provide a synthesis of new and existing knowledge to address the goals, framework, implementation, social and political impacts on the restoration of the southern pine forests in the context of southern pine beetle. We also provide information on common restoration methods and cost estimates. More effective use and further development of such knowledge could substantially reduce the economic, ecological, and social impact of southern pine beetle within the southern United States and adjacent areas.

Harnessing Information Technology (IT) for Use in Production Agriculture

Internet based, Information Technology (IT) offers opportunities to agricultural scientists to share information important to production agriculture. We offer an objective view for how IT can be used to manipulate data, information, and knowledge. The application of these technologies in other domains serves as a lesson to how they might be used to benefit production agriculture. We discuss three related technologies that have the potential to improve information flow among agricultural stakeholders and identify a number of trends (increased robustness, standardization of data formats, and reduced cost of implementation) that make them impor- tant tools for production agriculture.

Forest landscape management in response to change: the practicality

In this chapter, we examined forest landscape management from a pragmatic (practical as opposed to idealistic) perspective. The discussion was framed in the context of the landscape: a spatially explicit geographic area consisting of recognizable and characteristic component ecosystems. This perspective provided two opportunities for management: the individual component ecosystems and the mosaic of ecosystems that form the landscape per se. A point of emphasis was that forest management is not a generic concept and requires specification of the purpose of management, the spatial unit(s) being managed, the type of forest being managed, and the projected desired outcome of management. Given these constraints, we considered how the principal drivers of landscape change (disturbances, climate, and domestication) influence forest management practices. We concluded with an examination of the concept of designed forest landscapes to provide human-valued goods and services and identified constraints to achieving this end.

An integrated approach to mapping forest conditions in the Southern Appalachians (North Carolina)

©2008 by the Board of Regents of the University of Wisconsin System. An Integrated Approach to Mapping Forest Conditions in the Southern Appalachians (North Carolina) Weimin Xi (Knowledge Engineering lab, texas a&M University, college station, tX 77843, xi@tamu.edu), lei Wang (Dept of geography and anthropology, louisiana state University, Baton Rouge, la 70803), andrew g. Birt (Knowledge Engineering lab), Maria D. tchakerian (Knowledge Engineering lab), Robert n. coulson (Knowledge Engineering lab), Kier D. Klepzig (U.s. Forest service southern Research station, 2500 shreveport Hwy, Pineville, la 71360)

An Optimization-Based System Model of Disturbance-Generated Forest Biomass Utilization

Disturbance-generated biomass results from endogenous and exogenous natural and cultural disturbances that affect the health and productivity of forest ecosystems. These disturbances can create large quantities of plant biomass on predictable cycles. A systems analysis model has been developed to quantify aspects of system capacities (harvest, transportation, and processing), spatial aspects of the biomass generation process, and deterioration impacts on biomass quality in the various inventory states (field stands, field-harvested inventories, transportation prepared inventories, and production facility inventories). Optimal decision alternatives can be used to guide responses to reclamation, utilization, mitigation, and control. This is particularly advantageous in insect and disease outbreaks, in which the process may last several years, with varying levels of intensity. The prescriptive system description, assuming capacities are fixed, results in a linear programming model. The time-dependent capacity decision model results in a mixed-integer programming model. The analytical model is developed in detail in this analysis.

The influence of nest site selection on the population dynamics of Africanized honey bees in an urban landscape

Urban landscapes provide habitat for many species, including domesticated and feral honey bees, Apis mellifera L. (Hymenoptera: Apidae). With recent losses of managed honey bee colonies, there is increasing interest in feral honey bee colonies and their potential contribution to pollination services in agricultural, natural, and urban settings. However, in some regions the feral honey bee population consists primarily of Africanized honey bees. Africanized honey bees (AHB) are hybrids between European honey bees and the African honey bee, Apis mellifera scutellataLepeletier, and have generated economic, ecological, and human health concerns because of their aggressive behavior. In this study, we used two long‐term datasets (7–10 years) detailing the spatial and temporal distribution of AHB colonies in Tucson, AZ, USA, where feral colonies occupy a variety of cavities including water meter boxes. A stage‐structured matrix model was used to elucidate the implications of nest site selection and the effects of colony terminations on the structure and dynamics of the AHB population. Our results suggest that Tucsons AHB population is driven by a relatively small number of ‘source’ colonies that escape termination (ca. 0.165 colonies per km2 or 125 colonies in total), although immigrating swarms and absconding colonies from the surrounding area may have also contributed to the stability of the Tucson AHB population. Furthermore, the structure of the population has likely been impacted by the number and spatial distribution of water meter boxes across the city. The study provides an example of how urban wildlife populations are driven by interactions among landscape structure, human management, and behavioral traits conferred by an invasive genotype.