Search

Changes in landscape patterns may influence a variety of natural features including wildlife abundance, nutrient flow, and lake productivity. Data suggest that cyclic changes in landscape diversity occur on areas of 100 km2 in Yellowstone National Park. When properly managed, large wilderness areas provide the best and probably the only locale for studying the kind of landscape changes that occurred for millenia in presettlement times. (Accepted for publication 12 May 1982)

Multivariate analysis of the preference responses of 483 children to landscape photographs allowed the identification of three independent preference dimensions: the 1st and 3rd dimensions (illuminated vs shadowed; rough, harsh vs bland, smooth texture or relief) were considered as forms of a more general ‘risk, uncertainty factor’ often influencing landscape preference. Younger children (11 years old) showed less preference for both shadowed, less illuminated scenes (1st dimension) and harsh, rough scenes with aggressive forms (3rd dimension) than older children (16 years old). There were no significant differences for the 2nd dimension (landscape diversity).

Fire is now recognized as a major ecosystem process and Yellowstone National Park has recently implemented a fire management plan that permits lightning fires to burn without interference under certain conditions. To predict the kinds of wildfires we can now expect in the Park, and to evaluate the effectiveness of this plan in restoring fire to the Yellowstone ecosystem, it is important to know the natural frequency and size of wildfires under pristine conditions. This study, which began in 1977 and was completed in August 1979, had the following objectives: (1) to determine the incidence and size of major fires during the last 300-400 years on the 73-km2 Little Firehole River watershed, an area dominated by extensive lodgepole pine and some spruce-fir forests; (2) to determine average fire frequency, i.e., the time interval between successive major fires on any particular sites; (3) to determine the relationships between stand age or successional stage and fuel accumulation or the probability of fire; and (4) to examine the effect of fire on patterns of landscape diversity. Three components of landscape diversity were recognized - richness, evenness, and patchiness. Richness is simply the number of different community types represented, while evenness is an expression of the proportion of the landscape covered by each community type (maximum evenness occurring when every type occupies an equal area). The patchiness component is based on the size and interspersion of the community types.

The landscape diversity of California provides abundant opportunity for the geographical investigation of physical and cultural problems. Air pollution has been one major environmental problem long identified in California. With relatively rapid population growth and urban development over the 1940 to 1970 period, the problem seems to have intensified. The map of air quality prepared by Middleton provided an initial geographical portrayal of the problem of air quality in California and gave particular attention to the existence of several centers of relatively high air pollution concentration (Figure 1).1 The purpose of the following will be to discuss the distribution of air pollution in California through (1) the introduction of a method of measurement of the distribution of air quality, and (2) the explanation of the distribution interms of a spatial interaction model of air quality.

ummary Various savannah reserves are examined to determine whether they are likely to lose substantial numbers of large herbivores if they become isolated. The relationship between the number of ungulate species and the size of each reserve is examined and compared to predictions established from existing island biogeographic studies. In the case of the savannah reserves, no significant relationship was found. However, when the data were re-analysed for reserves of similar habitat, significant though low z-values of 0.04 and 0.08 were established. For discrete ecosystems rather than reserves a steeper z-value of 0.14 was found. It is suggested that the z-value for the savannah ecosystems is lower than the typical value of 0.22 for other land mass islands because of the ubiquitous distribution of most large herbivore species and their long history of co-evolution. The significance of island biogeographic theory to the design of nature reserves is limited, at least in the savannahs. Most of the variation in the number of species in areas which can be practically established as reserves can be explained by habitat and landscape diversity. Whether the savannah reserves became faunal islands will be decided by political and economic policies and practices rather than the principles of ecological design. The design of reserves in the past is considered to have been based on sound ecological principles in most cases, even though these were not recognized at the time. Resume Diverses reserves a savane sont examinees afin de determiner si elles sont susceptibles de perdre un nombre important de grands herbivores si elles deviennent isolkes. La relation entre le nombre d'especes d'ongules et la taille de chaque reserve est examinee et comparee aux predictions etablies a partir d'etudes sur des ilots biogeographiques isoles. Dans le cas des reserves e savane, aucun type de relation significative n'a ete trouve. Cependant, lorsque les donnees furent analysees a nouveau pour des reserves a habitat similaire, des valeurs significatives bien que faibles de z= 0.04 a 0.08 ont eteetablies. Pour des ecosystemes discrets au lieu de reserves, une valeur plus raide de z= 0.14 fut trouvee. Il est suggere que la valeur de z pour les ecosystemes de savane est plus faible que la valeur typique de 0.22 pour les autres ilots de massifs terrestres a cause de la distribution uniquiste de la plupart des especes de grands herbivores et la longue histoire de leur co-evolution. L'application de la theorie des ilots biogeographiques au cas de reserves naturelles est limitee, du moins en ce qui concerne les savanes. La plupart des variations du nombre des especes dans les zones qui pourraient etre erigees en reserve peuvent etre expliquees par la diversite des habitats. Les reserves a savane deviendront des ilots faunistiques davantage selon les decisions politiques et economiques que les principes ecologiques. On considere que la gestion des reserves fut base dans le passe sur les principes ecologiques de base, meme si ceux-ci n'etaient pas encore reconnus a cette epoque.

Fire history was determined by fire scar analysis in a 73—km2 subalpine watershed in Yellowstone National Park, Wyoming, USA. Evidence was found for 15 fires since 1600, of which 7 were major fires that burned >4 ha, destroyed the existing forest, and initiated secondary succession. Most of the upland forest area was burned by large, destructive fires in the middle and late 1700's. Fires since then have been small and have occurred at long intervals. Fire frequency in this area is partly controlled by changes in the fuel complex during succession. Fuels capable of supporting a crown fire usually do not develop until a stand is 300—400 yr old, and ignitions prior to that time usually extinguish naturally before covering more than a few hectares. Thereafter a destructive crown fire is likely whenever lightning ignites small fuels during warm, dry, windy weather. On the extensive subalpine plateaus of Yellowstone National Park there appears to be a natural fire cycle of 300—400 yr in which large areas burn during a short period, followed by a long, relatively fire—free period during which a highly flammable fuel complex again develops. The 73—km2 study area appears to be about midway between major fire events in this cycle. This, rather than human fire suppression, apparently is the major reason for the small number and size of fires in the area during the last 180 yr. On the basis of the fire history data, the sequence of vegetation mosaics during the last 200 yr was reconstructed for the watershed. Indices of landscape diversity were computed for each reconstruction, treating forest types and successional stages as taxa and incorporating components of richness, evenness, and patchiness. Landscape diversity was highest in the early 1800's following the large fires in the 1700's, then declined in the late 1800's during a 70—yr period when no major fires occurred and the landscape was dominated by even—aged forests developing on the areas burned in the 1700's. Landscape diversity has increased somewhat during the last half—century as a result of two small fires and the effects of the mountain pine beetle. These landscape reconstructions for the last 200 yr suggest that the Yellowstone subalpine ecosystem is a nonsteady—state system characterized by long—term, cyclic changes in landscape composition and diversity. Such cyclic patterns may significantly influence wildlife habitat, streamflow, nutrient cycling, and other ecological processes and characteristics within the Park, and they may be an important consideration in judging whether recent ecological changes are natural or man induced. The landscape reconstructions were also made using a simulation model based on hypothetical fire management policies of total fire exclusion and selective fire control (permitting only small fires to burn). These hypothetical management policies generally reduced the richness and patchiness of the landscape compared to the natural fire regime, but they increased the evenness and reduced the magnitude of periodic fluctuations in overall landscape diversity. At times, overall landscape diversity may actually be higher with a fire control policy than with a natural fire regime. At other times, fire significantly increases landscape diversity, as would be expected.