The Effects of Fire on Forest Community Composition, Structure, and Pattern in Florida Sandhills.

The influence of fire on turkey oak (Quercus laevis Walt.) and sand live oak (Q. geminata Small) populations was examined in experimental fires in sandhills near Tampa. Turkey oak crown survival was positively related to oak dbh, distance to the nearest longleaf pine (Pinus palustris Mill.), and dbh of the nearest pine. The pyrogenic litter of pines adversely affected survival of small turkey oaks within 10-20 m of the nearest pine, depending on fire severity. Resprouting of crown-killed turkey oaks was inversely related to oak dbh and, in one field, distance to the nearest pine. Poor resprouting away from pines was associated with delayed crown mortality and incomplete release from apical dominance. Turkey oaks were weakly clumped to randomly distributed at most scales in unburned fields. Four-year changes in a plot unburned for $\u3e$21-25 yr suggested that as stands mature, trees become more randomly distributed. Initial fires reduced turkey oak densities by 41-57% and (1) reduced the scale of maximal clumping, (2) increased clumping intensity, and (3) created large-scale randomness and uniformity. Patchiness of surviving trees was probably related to spatial variation in fire intensity, particularly with distance from pines. Repeated fires increased clumping intensity and gradually eroded large-scale randomness and uniformity, with most trees surviving only in a few isolated patches. Mainly small sand live oaks ($\u3c$10 cm dbh) were killed by initial fires, and subsequently larger trees were lost only very slowly from repeated annual and biennial fires. Although fuel characteristics within sand live oak groves display fire-retarding characteristics, fire mortality was mainly dependent on the size of individual trees, and not with grove size or location of trees within a grove. Trees suffered high crown mortality from intense fires occurring near longleaf pines, although mortality rates tapered off rapidly beyond the perimeter of the pine\u27s crown. Age-class structures of groves recovering from fire suggested that even-aged cohorts of resprouts develop after some fires, but new sprouts are also produced annually as part of normal clonal growth and expansion. Sand live oaks are well adapted to sandhill as well as less frequently burned scrub and hammock communities

Natural disturbances and the physiognomy of pine savannas : A phenomenological model

Abstract. Question: The decline of the Pinus palustris ecosystems has resulted from anthropogenic influences, such as conversion to pine plantation forestry, agriculture and land development, all of which are closely related to increases in human populations. Other effects, however, have arisen from alterations in disturbance regimes that maintain the structure and function of these ecosystems. How have alterations of the disturbance regime altered the physiognomy of ‘old-growth’ stands, and what are the implications for ecosystem conservation and restoration? Methods: In contrast to models that emphasize close interactions among the vertically complex strata, we develop a conceptual phenomenological model for the physiognomic structure of Pinus palustris stands. We relate two natural disturbances (tropical storms and fire) that affect different stages of the life cycle to different aspects of the physiognomic structure. We then compare overstorey stand structure and ground cover composition of two old-growth longleaf stands near the extremes of different composite disturbance regimes: the Wade Tract (frequent hurricanes and fire) and the Boyd Tract (infrequent hurricanes and long-term fire exclusion). Results: We predict that tropical storms and fires have different effects on stand physiognomy. Tropical storms are periodic, and sometimes intense, whereas fires are more frequent and less intense. Hurricanes directly influence the overstorey via wind-caused damage and mortality, and indirectly influence the herb layer by altering the spatial distribution of shading and litter accumulation. Fire exerts direct effects on juvenile stages and indirect effects on the herb layer via fine fuel consumption and selective mortality of potential competitors of P. palustris juveniles. These differences in effects of disturbances can result in widely different physiognomies for P. palustris stands. Finally, some global climate change scenarios have suggested that changes may occur in tropical storm and fire regimes, altering frequency and severity. Such changes may greatly affect pine stands, and ultimately entire pine savanna ecosystems. Conclusions: Our phenomenological model of disturbance regimes in Pinus palustris old-growth produces very different physiognomies for different disturbances regimes that reflect natural process and human management actions. This model can be used to derive restoration strategies for pine savannas that are linked to reinstitution of important ecological processes rather than specific physiognomic states

Stabilization of Valence Through Coordination: I. The Stabilities of Some Complexes of Alpha-Amino Acids With Divalent Metals. Ii. A Polarographic Study of the Complexes of Hydrazine With Zinc and Cadmium

90 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1954.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Stabilization of Valence Through Coordination: I. The Stabilities of Some Complexes of Alpha-Amino Acids With Divalent Metals. Ii. A Polarographic Study of the Complexes of Hydrazine With Zinc and Cadmium

90 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1954.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD