Charles A. Gresham

GENERALITY OF LEAF TRAIT RELATIONSHIPS: A TEST ACROSS SIX BIOMES

Convergence in interspecific leaf trait relationships across diverse taxonomic groups and biomes would have important evolutionary and ecological implications. Such convergence has been hypothesized to result from trade-offs that limit the combination of plant traits for any species. Here we address this issue by testing for biome differences in the slope and intercept of interspecific relationships among leaf traits: longevity, net pho- tosynthetic capacity (Amax), leaf diffusive conductance (Gs), specific leaf area (SLA), and nitrogen (N) status, for more than 100 species in six distinct biomes of the Americas. The six biomes were: alpine tundra-subalpine forest ecotone, cold temperate forest-prairie ecotone, montane cool temperate forest, desert shrubland, subtropical forest, and tropical rain forest. Despite large differences in climate and evolutionary history, in all biomes mass-based leaf N (Nmass), SLA, Gs, and Amax were positively related to one another and decreased with increasing leaf life span. The relationships between pairs of leaf traits exhibited similar slopes among biomes, suggesting a predictable set of scaling relationships among key leaf morphological, chemical, and metabolic traits that are replicated globally among terrestrial ecosystems regardless of biome or vegetation type. However, the intercept (i.e., the overall elevation of regression lines) of relationships between pairs of leaf traits usually differed among biomes. With increasing aridity across sites, species had greater Amax for a given level of Gs and lower SLA for any given leaf life span. Using principal components analysis, most variation among species was explained by an axis related to mass-based leaf traits (Amax, N, and SLA) while a second axis reflected climate, Gs, and other area-based leaf traits.

Relationships of leaf dark respiration to leaf nitrogen, specific leaf area and leaf life-span: a test across biomes and functional groups

Abstract Based on prior evidence of coordinated multiple leaf trait scaling, we hypothesized that variation among species in leaf dark respiration rate (Rd) should scale with variation in traits such as leaf nitrogen (N), leaf life-span, specific leaf area (SLA), and net photosynthetic capacity (Amax). However, it is not known whether such scaling, if it exists, is similar among disparate biomes and plant functional types. We tested this idea by examining the interspecific relationships between Rd measured at a standard temperature and leaf life-span, N, SLA and Amax for 69 species from four functional groups (forbs, broad-leafed trees and shrubs, and needle-leafed conifers) in six biomes traversing the Americas: alpine tundra/subalpine forest, Colorado; cold temperate forest/grassland, Wisconsin; cool temperate forest, North Carolina; desert/shrubland, New Mexico; subtropical forest, South Carolina; and tropical rain forest, Amazonas, Venezuela. Area-based Rd was positively related to area-based leaf N within functional groups and for all species pooled, but not when comparing among species within any site. At all sites, mass-based Rd (Rd-mass) decreased sharply with increasing leaf life-span and was positively related to SLA and mass-based Amax and leaf N (leaf Nmass). These intra-biome relationships were similar in shape and slope among sites, where in each case we compared species belonging to different plant functional groups. Significant Rd-mass−Nmass relationships were observed in all functional groups (pooled across sites), but the relationships differed, with higher Rd at any given leaf N in functional groups (such as forbs) with higher SLA and shorter leaf life-span. Regardless of biome or functional group, Rd-mass was well predicted by all combinations of leaf life-span, Nmass and/or SLA (r2≥ 0.79, P < 0.0001). At any given SLA, Rd-mass rises with increasing Nmass and/or decreasing leaf life-span; and at any level of Nmass, Rd-mass rises with increasing SLA and/or decreasing leaf life-span. The relationships between Rd and leaf traits observed in this study support the idea of a global set of predictable interrelationships between key leaf morphological, chemical and metabolic traits.

Rice fields of South Carolina: A resource inventory and management policy evaluation

Abstract Acreages and vegetative cover types of areas identified as former rice fields were determined from topographic maps and aerial photographs with verification by ground checks. Sixteen vegetative cover types were recognized and 74, 113 acres of former rice fields were located. Each drainage system studied had roughly the same acreage, but different proportions of cover types. A questionnaire was sent to selected rice field owners in the inventoried drainage systems and to selected owners in the Ashepoo, Combahee, and South Edisto River drainage system and the Savannah River drainage system. The questionnaire survey indicated that only about 32 percent of the former rice fields were being managed and that the rice fields were being managed for waterfowl. The regulatory and management problems associated with rice field utilization are discussed.

Associations Between Two Bottomland Hardwood Forest Shrew Species and Hurricane-Generated Woody Debris

Abstract We investigated associations between soricids and coarse woody debris (CWD) in bottomland hardwood forests impacted by Hurricane Hugo. The objectives were to evaluate CWD loadings at three forests disturbed by Hurricane Hugo, monitor soricid captures at these forests, and identify habitat associates of soricids Pitfall traps were used to sample soricids from January 2002–December 2003, and habitat parameters (CWD, vegetation, soils, and microsite) surrounding pitfalls were sampled. We found CWD volume was significantly higher at study sites that experi enced highest hurricane wind speeds. Captures of soricids were highest in forests with high CWD loadings, and regression models associated soricids with log cover and CWD volume. Sorex longirostris (southeastern shrew) was associated with logs in an advanced state of decay and woody litter. Blarina carolinensis (southern short tailed shrew)was associated with log cover and leaf-litter cover. Soricid captures also increased with close proximity of CWD. We found that major disturbances have lasting influence on bottomland hardwood communities, and forests with high load ings of deteriorating CWD provide habitat for S. longirostris and B. carolinensis.

A review of spatial aspects of forest damage and recovery on the South Carolina coast following hurricane Hugo

Southern US coastal forests are subject to damage by major Atlantic Hurricanes at a frequency that influences forest succession. Forest species may be: a) resistant: unchanged in mortality and growth; b) susceptible: increase in mortality and decrease in growth, and c) resilient: increase in mortality but increase in abundance and growth, or d) usurper: absent prior to disturbance and increase abundance and growth afterwards. Although there is a wide literature on resistance of temperate species found in the southern US to hurricane wind and salt damage, long-term ecological implications are poorly understood outside of the tropics. Hurricane Hugo struck the South Carolina Coast with an estimated wind speed of 60 m/s. Due to the relatively fast forward movement of the storm, high wind speed and severe forest damage extended nearly 100 km into the state. In depth studies of immediate damage were reported for four sites and seven forest types. Species resistance to hurricane damage was found to be similar to that reported after other major hurricanes (Camille, Katrina, and Rita) although mortality percentages were influenced by position in the wind field. Susceptible species were highly dependent on position (wind speed) and proximity to the ocean (salt water in storm surge). Loblolly pine (Pinus taeda) and sweetgum (Liquidambar styraciflua),varied between resilient and usurper roles in response to mortality percentage of susceptible species.