Kiyoko Miyanishi

Testing the assumptions of chronosequences in succession

Many introductory ecology textbooks illustrate succession, at least in part, by using certain classic studies (e.g. sand dunes, ponds/bogs, glacial till, and old fields) that substituted space for time (chronosequence) in determining the sequences of the succession. Despite past criticisms of this method, there is continued, often uncritical, use of chronosequences in current research on topics besides succession, including temporal changes in biodiversity, productivity, nutrient cycling, etc. To show the problem with chronosequence-based studies in general, we review evidence from studies that used non-chronosequence methods (such as long-term study of permanent plots, palynology, and stand reconstruction) to test the space-for-time substitution in four classic succession studies. In several cases, the tests have used the same locations and, in one case, the same plots as those in the original studies. We show that empirical evidence invalidates the chronosequence-based sequences inferred in these classic studies.

FIRE FREQUENCY AND THE SPATIAL AGE MOSAIC OF THE MIXED‐WOOD BOREAL FOREST IN WESTERN CANADA

One approach to ecosystem management is to emulate the effects of natural disturbance in producing landscape patterns; this approach requires a spatial analysis of the pattern and an understanding of the processes producing the pattern. Forested landscapes exhibit mosaic patterns of both stand types and ages. This study investigates the spatial mosaic of stand ages produced by high-intensity stand-replacing fires in the mixed-wood boreal forest of western Canada. A high-resolution, accurately dated, time-since-fire map for a large (3461 km2) contiguous area is used to produce the landscape survivorship distribution in which both spatial and temporal changes in fire cycle are statistically tested. Spatial multivariate analysis of the time-since-fire map is also used to investigate the spatial assembly of the age mosaic. Significant changes in fire cycle can be explained by climatic change as well as land use change in the surrounding area. The shift from a short (15 yr) fire cycle to a longer (75 yr) cycle after 1890 in the northern half of the study area coincides with climatic change at the end of the Little Ice Age. In the southern half of the study area, the short fire cycle continues after 1890 due to the spread of human-caused fires from the adjacent area which was settled and cleared for agriculture during the first half of the 20th century. Upon completion of settlement in 1945, the fire cycle becomes significantly longer due to the fragmentation of the once continuous forest that surrounded the study area and from which the majority of large fires propagated in the past. The different fire cycle histories of the two parts of the study area also explain the spatial mosaic pattern of stand ages, sizes, and shapes. The extended period of the short fire cycle through the first half of this century in the southern region results in it being dominated by younger, larger, oblong-shaped polygons with irregular edges: characteristics that describe the shapes of large burns. The northern region has generally older and smaller, more circular, compact polygons that are the remnants of larger much earlier burns that have since been overburned. The polygons in the northern region are more similar in size and shape but less similar in age to adjacent polygons than are those in the southern region. Thus, this study shows how spatial heterogeneity in the landscape mosaic pattern can be characterized and related to the disturbance history of an area. Furthermore, it provides evidence of the impacts on the age mosaic due to forest fragmentation in surrounding areas.

Creating New Landscapes and Ecosystems

Extraction of oil from the Alberta Oil Sands through surface mining involves the removal of the overburden and oil sand to a depth of up to 100 m and over extremely large areas. While the operation of the bitumen processing plants has serious environmental impacts on downstream habitats, this article focuses on the reclamation of areas from which the oil sands have been removed, processed, and returned. This reclamation following closure of the mines will entail the complete re‐creation of landforms and ecosystems at a landscape scale, with the goal of producing suitable habitats for plants, animals, and people. Such projects will require a reasonable understanding of the geophysical and ecological processes that operate at a wide range of scales. Some information is provided on the climate, hydrology, vegetation, and land use (past and current) of the Oil Sands area, situated within the Boreal Plain ecozone, to provide a framework for discussion of issues to be addressed in, and proposed guidelines for, such large‐scale reclamation. Although none of the mines has yet closed, numerous consultant reports have been produced with recommendations for various aspects of such reclamation projects (e.g., wetland hydrology, vegetation, wildlife habitat). The scientific basis of such reports is found to vary with respect to depth of understanding of the relevant processes.

Introduction. The boreal forest and global change

The boreal forest is the second largest biome in the world containing 33% of the Earths forest cover ([FAO 2001][1]) of which approximately 25% is natural. It is circumpolar and shares similar taxa across its range. It has approximately 20 300 identified species. Along with the tropics, the

The boreal forest as a cultural landscape

Because of its generally low density of humans and few settlements, the circumpolar boreal forest is often viewed as an untouched wilderness. However, archeological evidence indicates that humans have inhabited the region since the continental glaciers disappeared 8,000–12,000 years ago. This paper discusses the ecological impacts that humans have had on the boreal forest ecosystem through their activities in prehistoric, historic, and recent times and argues that the boreal forest has always been a cultural landscape with a gradient of impacts both spatially and temporally. These activities include hunting, trapping, herding, agriculture, forestry, hydroelectric dam projects, oil and natural gas development, and mining. In prehistoric times, human impacts would generally have been more temporary and spatially localized. However, the megafaunal extinctions coincident with arrival of humans were very significant ecological impacts. In historic times, the spread of Europeans and their exploitation of the boreals natural resources as well as agricultural expansion has altered the composition and continuity of the boreal forest ecosystem in North America, Fennoscandia, and Asia. Particularly over the last century, these impacts have increased significantly (e.g., some hydroelectric dams and tar sands developments that have altered and destroyed vast areas of the boreal forest). Although the atmospheric changes and resulting climatic changes due to human activities are causing the most significant changes to the high‐latitude boreal forest ecosystem, any discussion of these impacts are beyond the limits of this paper and therefore are not included.

Strengthening Fire Ecology's Roots

Publisher Summary Ecologists have been interested in how fires change the composition and structure of ecological systems. The approach that has been taken to investigate these issues has, in general, involved describing patterns of fire effects and correlating these to environmental factors. This approach does not immediately lead to a concern with the mechanism of interaction between fire processes and ecosystem processes. One could read the ecological literature for a long time before finding any discussions that indicate an appreciation that the processes of combustion and heat transfer lie at the heart of fire ecology. Fire ecology is a part of both environmental biophysics and ecology. Consequently, it is concerned with combustion, transfer of heat, mass and momentum in wildfires, heat transfer between the fire and the organism, and finally, how these physical processes affect ecological processes. Research on the connection between wildfires and ecological systems goes back to the early discovery that natural disturbances were a recurrent phenomenon in ecosystems and, as such, required an understanding of their effects on ecosystem structure and function. However, connecting wildfires to ecological systems has proceeded slowly. This is probably because forestry and ecology, the two fields primarily interested in wildfire effects on ecosystems, have been sidetracked by their traditional approach to studying ecological systems. Foresters are mostly interested in extinguishing or eliminating wildfires or in managing burns to produce certain effects in the forest.

8 – Coastal Dune Succession and the Reality of Dune Processes

Coastal dunes are one of the first ecological systems studied in detail, and observation of the distribution of vegetation on coastal dunes gave rise to the idea of succession, defined as the sequential replacement of dominant species over time in the absence of disturbance. The early studies of coastal dune vegetation, particularly of the Indiana Dunes of Lake Michigan, are some of the first to apply the chronosequence method based on the ergodic hypothesis of substituting spatial sequences of vegetation for the temporal sequences of vegetation development. The method covered in this chapter is subsequently used for the study of other types of succession, such as on glacial until following glacial retreat and on abandoned agricultural land. It is used extensively today to study succession. However, as discussed in chapter, the chronosequence based successional sequences encounter problems as soon the assumptions of this space-for-time substitution are examined.

The role of mammals in maintaining plant species richness in a floating Typha marsh in southern Ontario

Animals are known to influence and sometimes help maintain plant species richness in terrestrial systems. This study investigated the effects of mammals in influencing plant species richness of a floating Typha marsh at Point Pelee National Park. The extent of use of the marsh by terrestrial mammals was documented by mapping mammal trails from air photographs. Trail densities ranging from 70 to 1550 m ha−1 in various areas of the marsh, provided evidence for widespread, and in some places frequent, mammal activity. Plant surveys indicated a pattern of increased species richness and frequency associated with these trails, particularly in late summer when Typha biomass increased off trails. Three mechanisms by which mammals might influence species richness: disturbance of the dominant Typha, nutrient enrichment, and seed dispersal, were investigated using field and lab experiments. Two types of disturbance, trampling and herbivory, at two levels of intensity were simulated within 2×2m plots with and without fertilizer added. Disturbance significantly affected species richness; high levels of trampling decreased while high levels of clipping increased species richness. Nutrients had no effect; there were no significant disturbance×nutrients interactions. The importance of seed dispersal by raccoon was studied by collecting raccoon scat from within the marsh, incubating scat in a growth chamber and comparing the species that emerged to those growing in the marsh. Although substantial numbers of viable seeds of terrestrial species were found in scat, only one of these species was actually part of the Typha mat community. We concluded that mammals do influence plant species richness in this marsh primarily through disturbance of the dominant Typha.