Transcript Feb 25
EEES4760/6760 Landscape Ecology Jiquan chen Feb. 25, 2009 1. Fragmentation 2. Island Biogeographic Theory (IBT) 1km 50 m 1km 30 m 81 ha 69 ha 59 ha Case 7.2 (A) Degree of fragmentation of major river basins of the world 7.4 A fragmentation sequence 7.8 A constellation of separate habitat patches may be critical to the survival of individuals or populations 7.9 Many animals require a suite of different habitats or resources to meet life history needs 7.13 Roads can be significant barriers to the movement of small vertebrates and invertebrates EFFECTS OF FRAGMENTATION • • • • • • • • • • • • • • • • • • • • Landscape structure · Patch density · Patch size · Inter-patch distance · Connectivity · Boundary length · Interior/edge ratio · Maximum of core (interior forest) · Total interior · Stepping stones · Corridors Species · Isolation · Number of generalist · Exotic species · Nest predation · Extinction rate · Dispersal of interior species · Large-home-range species · Richness of interior species • • • • • Others · Metapopulation dynamics · Genetic inbreeding · Size of disturbance patches · Cumulative effects (rain, snow and flooding effects) The Checkerboard Landscape Patterns of clearcutting development under various models(a-c) Progression of clearcutting using the dispersed patch model in which areas are selected for cutting so as to be distributed regularly across the landscape: shown are 25, 50, and 75% cutover points. (ef) Pattern of cutting at 50% point using single, four nucleus, and aggressiveparallel cutting systems. (Franklin & Forman 1987) Susceptibility of forests in the Douglas-fir region to various damaging agent along a landscape cutting gradient as shown by the checkerboard model (Franklin & Forman 1987) Creating Land Mosaics An old-growth patch surrounded by a long rotation island that is cut in a programmed sequence such ( Harris 1984). Conclusions • The number, size, and arrangement of the patches in a mosaic created by forest managers strongly influence the degree to which management objectives are fulfilled. • Two recommendations are: (1) reduce the emphasis on dispersing small clearcut patches through the forest landscape, and (2) identify and reserve large patches of primeval forest in the landscape for maintenances of interior and amenity values. • SLOSS debate What do we want to know about fragmentation? • • • • • What are the relationships among patch area, shape, isolation, edge, the interaction of these factors, and various population and ecosystem? How do various landscape elements (e.g., corridors, linear networks, and matrix) affect ecosystem processes and the connectivity of populations in fragmented landscapes? How do pattern-process linkages function in spatially and temporally dynamic landscapes across the range of spatial and temporal scales? What levels of habitat loss and fragmentation does population viability decline drastically? How long does it take population and ecosystem processes to respond to physical changes in the landscape associated with fragmentation? Island Biogeographic Theory 1. Early interest in habitat fragmentation arose from island biogeographic theory (MacArthur & Wilson 1963 & 1967). (MacArthur and Wilson, 1963) 19.4 – fish 1982 (Preston, 1962; Nilsson et al. 1988) 19.3 – mammal 1989 The equilibrium model of island biogeography by MacArthur and Wilson (1963) Manipulative and Mensurative Experiment - Two Major Approaches • • Manipulative experiment • Physically manipulates some attribute of the system in a controlled manner, while holding all other attributes constant. Mensurative experiment • Simply observes or measures the system at different locations or times • The treatment is the different conditions in space or time. • Generally, manipulative experiments lead to stronger inferences and therefore more reliable knowledge than mensurative experiments. • An ideal manipulative experiment requires • • • • • • The similarity among landscape minimizes the experimental error The size of the landscape are functionally relevant to the process/organism(s) under consideration Areal extent and configuration manipulation is needed to assess independent and interactive of processes Replication and random Temporal and spatial controls (natural variability) Observing the delayed effect Mensurative Experiment • Can overcome some of the important limitations • The practical and logistical difficulties of implementing large-scale treatment • No practical limit to the spatial or temporal scale of the study system • Flexibility in time lag effect • Still problems … • Additional sources of variation associated with inconsistent and uncontrolled past perturbations • Lack in pretreatment control – owing to substituting space for time – inherent variability and autocorrelation Lack in … • • • • Landscape level study Isolation of a process Extinction threshold/ time lag/ synergisms between habitat area and configuration Inequity in the organismal focus • • • Invertebrates, reptiles, and amphibians Replication / poorly controlled Spatial information