Late-successional Plant Research Articles

Successional Trends in Insect Herbivore Population Densities: A Field Test of a Hypothesis

Theory suggests that plants typical of early and late succession should possess qualitatively different anti-herbivore chemical defences. Differences in the structure, mode of action and effect of these chemicals should result in greater herbivore population levels on plants of early succession. This theory was tested for three separate insect taxa over a successional gradient in southern England. All taxa displayed greater population densities on short-lived plants of early succession than on birch, a plant of late succession. Although the results support theories which suggest a dichotomy of effect of the chemical defences of early and late successional plants, difficulties remain in reconciling the theory of plant chemical defences with existing data

Competitive ability of the bunchgrass Schizachyrium scoparium as affected by grazing history and defoliation

Herbivory by large animals is known to function as a selection pressure to increase herbivory resistance within plant populations by decreasing the frequency of genotypes possessing large, erect canopies. However, the increase in herbivory resistance of the remaining genotypes in the population may potentially involve a tradeoff with competitive ability. The perennial bunchgrass Schizachyrium scoparium was grown in a transplant garden to test the hypothesis that late successional plant populations with a history of grazing are at a competitive disadvantage relative to conspecific populations with no history of grazing in the presence of competition from mid-successional species. Plants with a history of grazing were found to possess a greater competitive ability than plants with no grazing history in the absence of herbivory. This unexpected response resulted from the capacity of plants with a history of grazing to recruit a greater number of smaller tillers than did plants with no grazing history. This response was only significant when plants with a history of grazing were nondefoliated and grown with the weakest of the mid-successional competitors, indicating that both defoliation and intense interspecific competition can mask the architectural expression of herbivore-induced selection. Individual tillers did not display any architectural differences between plants with contrasting grazing histories other than mean tiller weight. These data confirm that herbivory by domestic cattle may function as a selection pressure to induce architectural variation in grass populations within an ecological time frame (ca < 25 yrs). Nomenclature: Gould, F. W. 1975. The Grasses of Texas. Texas A&M Univ. Press, College Station, TX.

An Example of Site Classification in the Southeastern Coastal Plain Based on Vegetation and Land Type¹

Abstract A site classification system based on vegetation and land type was developed for the Savannah River Plant (SRP) in the upper coastal plain of South Carolina. Different positions of the landscape support distinctive plant communities. Late successional plant communities and their immediate predecessors were identified on eight site types along a moisture gradient ranging from dry, sandy uplands to flooded bottoms. Late successional, near-stable plant communities, even in the highly disturbed forest ecosystems of the Southeast, act as integrators of environmental factors to reflectsite potential. Vegetation can supplement information on soils and topography in the delineation and classification of forest sites. Knowledge of site-vegetative relationships would be especially useful in making management decisions regarding wildlife habitat evaluation, hazard rating for insects, diseases, and fires, and estimating potential uses for recreation. Application of the system by practicing foresters is discussed. South. J. Appl. For. 11(1):23-28.

Marsh community development in a central Florida phosphate surface-mined reclaimed wetland

As the nation’s acreage of productive freshwater marsh/wetlands continues to decrease the need for sucessful marsh restoration/reclamation increases. A variety of land uses including surface mining, residential development and agriculture create direct impacts on wetlands often resulting in a net loss of habitat if appropriate restoration or reclamation of the ecosystem is not obtained within a reasonable period of time. The 30 hectare freshwater marsh reclaimed from a phosphate mined area is part of a 148 hectare upland, 61 hectare wetland ecosystem (Agrico Swamp) reclaimed in 1981/82. Topsoil additions have been a successful means of establishing a marsh system within the site. This technique shows distinct advantages over natural revegetation of overburden. At the end of two full growing seasons the topsoiled area has higher species richness and cover values than the overburden areas. During this period a slight decline in the species richness in the topsoiled area was evident due in part to the aggressive nature ofPontederia cordata. Conversely, the species richness of the overburden areas increased significantly. Topsoiling appears to encourage the accelerated establisment of late successional plants in sufficient quantities to compete with aggressive weedy species such asTypha latifolia.

Instability of the snowshoe hare and woody plant interaction.

We show that Alaskan woody plants respond to browsing in two ways that might destabilize a plantherbivore interaction and account for snowshoe hare population 'cycles'. (1) Browse production of preferred, earliersuccessional woody plants increases in response to moderate levels of browsing. Such yield increases are potentially destabilizing. Later successional woody plants show decreases in yield after moderate browsing, which is consistent with the persistence of snowshoe hares in late successional 'refuge' habitats (Keith 1966, Wolff 1980). (2) Many woody plants are destructively overbrowsed or girdled at the peak of the snowshoe hare cycle. The more palatable and plastic, early to mid successional plants respond by sprouting accompanied by juvenile reversion. Sprouts are markedly less palatable than mature shoots. We show here that sprout palatability and twig biomass are restored in 2-3 years for earlier successional plants, but palatability may not recover for 4-10 years in sprouts of some mid to late successional plants. The decrease in palatability helps to account for the snowshoe hare 'crash' (assuming that damage to more palatable plants is widespread during the 'peak'), and the 2-3 year time lag for recovery of more palatable species could account for (May 1974) the observed 8-11 year period of the hare cycles. Browse yield increases acting during the snowshoe hare population nadir and increase, and sprouting with juvenile reversion acting during the hare peak and decline can in principle account for the oscillatory nature and the observed 8-11 year periodicity of the snowshoe hare cycle.

Facilitation as a Successional Mechanism in a Rocky Intertidal Community

The mechanism by which the surfgrass Phyllospadix scouleri Hook. (Potamogetonaceae), a dominant late successional plant, replaces algae during secondary succession was investigated in a rocky intertidal community on the Oregon coast. Experiments suggest some, but not all, middle successional species are necessary for surfgrass recruitment. The barbed form of surfgrass seeds allows them to become attached to algal species with a central axis approximately 1 mm in diameter, such as erect coralline algae and the red algae Rhodomela larix and Odonthalia floccosa, but not to algae with other forms. Observations suggest this interaction is obligate facilitation (sensu Connell and Slatyer 1977).

Photosynthetic acclimation to variability in the light environment of early and late successional plants.

Fourteen plant species from early-, mid-, and late-successional habitats were grown for a period of 25 to 50 days in each of two light environments, i.e. full sunlight and in deep shade. The rate of photosynthesis for newly formed leaves was measured as a function of light intensity for plants from each light environment. Photosynthetic flexibility, measured as the difference in response between sun- and shade-grown plants, was determined for each of 5 parameters including dark respiration, quantum yield, light compensation, half-saturating irradiance for photosynthesis, and the photosynthetic rate at 1,400 μE m-2 s-1. We found photosynthetic flexibility to be high for early successional annuals, intermediate for midsuccessional species, and low for late successional species.

Effect of night temperature on daytime stomatal conductance in early and late successional plants.

Sixteen annuals, biennials, and herbaceous and woody perennials characteristic of early and late successional old field ecosystems and upland and floodplain habitats were analyzed for their response of stomatal conductance to changes in night temperature. Early successional species that germinate in early spring when temperatures are low, but above freezing are insensitive to cool nights, i.e., their conductance in the following days is unaffected by low night temperature. Later spring and summer-emerging species' stomatal conductance is inhibited by low temperatures. Tree species show the same effects and in some an enhancement of stomatal conductance by low night temperatures was observed. However, adaptive differences in response to night temperatures appear related to both phenology of germination and growth and habitat types.

The Physiological Ecology of Plant Succession

Succession is a process of continuous colonization of and extinction on a site by species populations. The process has long been central in ecological thinking; much theory and many data about succession have accumulated over the years. Since nearly all species in all communities participate in successional interactions, and because physiological ecology encompasses everything that a plant does during its life cycle, a complete review of physiological ecology of all species in all successions is not possible. Thus in this review I discuss the physiological adaptations of species of one successional gradient-from open field to broad-leaved deciduous forest. I concentrate on the physiological adaptations of early successional plants to environmental variability and collate the literature on tree physiology to make comparisons with early successional plants. My discussion may not be applicable to seres where there is little difference in physiognomy between early and late successional plants or where the designation of species as early or late successional is unjustified (e.g. for certain desert and tundra habitats). I discuss the nature of successional environments, seed germination, seedling and mature plant development, plant growth, photosynthesis, water use, and the physiological ecology of competition and interference.

Difference in Pollination Niche Relationships in Early and Late Successional Plant Communities

Alpha—niche parameters involving pollination resources were examined for plants in communities of 3 different successional ages. Niche breadths and overlaps were compared in early successional annual, early perennial, and prairie communities. Niche axes examined were seasonal time of flowering, species of flower visitor, daily time of visit, and 2—dimensional parameter, species of visitor x daily time. Seasonal flowering was clumped in all communities. It occurred fairly synchronously in midsummer in the annual community and in the fall in the perennial community. Flowering in the winter annual and prairie communities occurred at 3 distinct seasonal times; spring, summer and fall. In this annual community, the different flowering times reflected varied life history strategies demonstrating adaptations mainly to the physical environment. In the prairie, the same 3 seasonal flowering aggregations were most likely formed through adaptation to the biotic environment. The prairie species had smaller seasonal flowering niche breadths, but showed no reduction in seasonal niche overlap. In fact, there was some evidence for convergence in flowering time of species attracting similar vector species. There was little difference in daily time of flowering for most species pairs in all communities. Only in early and midsummer was there evidence for niche separation in daily time of visitation. In early spring and fall, mean overlaps between species were &gt; in comparable random data sets, suggesting convergence in daily time of insect visitation. The relative proportions of general types of visitor differed among the communities. There were tendencies for annuals to be visited more by halictid bees and syrphid flies and there were strong tendencies for prairie species to be visited more by apid and megachilid bees and by lepidopterans. Because of the latter groups are considered to be more effective pollinators, significantly more of the visits could have effected cross—pollination in the prairie than in annual communities. Niche overlaps of species of visitor were significantly lower than random for all communities, indicating some niche differentiation on that axis. The mean similarities of species of visitor and the 2—dimensional visitor species x daily time for the prairie plants were significantly lower than the means for the annuals, and showed a tendency to be lower than the means of the early perennials. Niche breadths on the same 2 parameters were also lower in the prairie. Therefore, species of the late successful community, the tallgrass prairie, showed more niche specialization and separation than did species of early successional communities. We conclude that α—scale differentiation on these pollination parameters does occur between plant species, and the degree to which it occurs increases with the successional age of the community. These results support the hypothesis that selection to reduce competition has resulted in greater niche differentiation in late successional communities.