Heartsill-Scalley T.

Long-term dynamics of organic matter and elements exported as coarse particulates from two Caribbean montane watersheds

Heartsill Scalley, T., Scatena, F.N., Moya S., Lugo A.E., 2012 Long-term dynamics of organic matter and elements exported as coarse particulates from two Caribbean montane watersheds. Journal of Tropical Ecology. Vol 28. pp 127-139. doi:10.1017/S0266467411000733

RIPARIAN VEGETATION AND STREAM CONDITION IN A TROPICAL AGRICULTURE–SECONDARY FOREST MOSAIC

Heartsill-Scalley T, Aide TM. 2003. Riparian vegetation and stream condition
in a tropical agriculture–secondary forest mosaic. Ecological
Applications 13: 225–234.

Abstract: 
Changes in land cover from forest to agriculture often alter riparian vegetation, which modifies the physical conditions of streams. To understand the impacts of different categories of land cover on riparian and stream habitats, we sampled riparian vegetation and stream conditions in three adjacent watersheds in southeastern Puerto Rico. Land cover categories (pasture, mixed, and forest) were determined using aerial photographs. Vegetation structure and composition and characteristics of streams were assessed for 35 riparian sites. Sites were located along first-order streams, at 400–600 m elevation in the wet-forest life zone. Understory vegetation in the forest sites was mainly shrubs, herbs, and ferns, whereas the mixed and pasture sites were dominated by grasses, vines, and bare soil. Syzygium jambos and Spathodea campanulata, nonnatives, and Guarea guidonia, a native, were the most common tree species in the riparian areas. Surrounding land cover explained .60% of the variation among stream sites. There was a positive relationship between tree cover and percentage of dissolved oxygen, and a negative relationship between tree cover and percentage of substrata covered by sediments from eroded soil. The amount of woody debris in the streams tended to increase with forest cover. Overall, land cover is a landscape feature that effectively characterized riparian understory cover, tree species composition, and stream condition

Effects of drought and hurricane disturbances on headwater distributions of palaemonid river shrimp (Macrobrachium spp.) in the Luquillo Mountains, Puerto Rico

Covich, Alan P.; Crowl, Todd A.; Heartsill-Scalley, Tamara 2006. Effects of drought and hurricane disturbances on headwater distributions of palaemonid river shrimp (Macrobrachium spp.) in the Luquillo Mountains, Puerto Rico.. J. N. Am. Benthol. Soc., 25(1):99-107.

Abstract: 
Extreme events (hurricanes, floods, and droughts) can influence upstream migration of macroinvertebrates and wash out benthic communities, thereby locally altering food webs and species interactions. We sampled palaemonid river shrimp (Macrobrachium spp.), dominant consumers in headwaters of the Luquillo Mountains of northeastern Puerto Rico, to determine their distributions along an elevational gradient (274–456 m asl) during a series of disturbances (Hurricane Hugo in 1989, a drought in 1994, and Hurricane Georges in 1998) that occurred over a 15-y period (19882002).We measured shrimp abundance 3 to 6 times/y in Quebrada Prieta in the Espiritu Santo drainage as part of the Luquillo Long-Term Ecological Research Program. In general, Macrobrachium abundance declined with elevation during most years. The lowest mean abundance of Macrobrachium occurred during the 1994 drought, the driest year in 28 y of record in the Espiritu Santo drainage. Macrobrachium increased in abundance for 6 y following the 1994 drought. In contrast, hurricanes and storm flows had relatively little effect on Macrobrachium abundance.

Effects of different types of conditioning on rates of leaf-litter shredding by Xiphocaris elongata, a Neotropical freshwater shrimp

Crowl, Todd A.; Welsh, Vanessa; Heartsill-Scalley, Tamara 2006. Effects of different types of conditioning on rates of leaf-litter shredding by Xiphocaris elongata, a Neotropical freshwater shrimp.. J. N. Am. Benthol. Soc., 25(1):198-208.

Abstract: 
Temperate headwater streams with closed canopies rely on inputs of terrestrially derived organic matter to provide the major energy basis for their food webs. Microbial colonization, or conditioning, makes leaf litter more nutritional and palatable to stream detritivores, but few studies have investigated the relative importance of litter source to macroshredders in tropical streams. We determined the source (terrestrial, aquatic, or aerial), quantity, and species composition of allochthonous inputs into the Quebrada Prieta, a tropical headwater stream in Puerto Rico, as a first step toward understanding the importance of conditioning history to rates of tropical leaf-litter processing by decapod consumers. Fresh leaves of 4 common species of leaves were treated by exposing them to different conditions for 2 wk. These exposure treatments (conditioning histories) represented routes by which leaves might enter streams and included submersion (aquatic input), incubation on the streambank soil (terrestrial input), and suspension above the ground (aerial input). Conditioned leaves were placed in small experimental microcosms with or without shrimp (Xiphocaris elongata) for 20 d. Shrimp significantly increased the rate of decomposition of all leaf species independent of conditioning history. Conditioning history had little effect on breakdown rates independent of the presence of shrimp. One species (Rourea surinamensis) had faster mass loss when the leaves were conditioned as aquatic inputs rather than as terrestrial or aerial inputs. Our results indicate that conditioning history has little effect on the ability of some macroconsumers to alter detrital foodweb dynamics in tropical streams. Tropical stream ecosystems may function differently from temperate ecosystems because of the dominance of large detritivores such as shrimps.

HURRICANE-INDUCED CHANGES IN VEGETATION STRUCTURE, COMPOSITION AND STOICHIOMETRY IN A SUBTROPICAL WET FOREST

Abstract: 
This paper compares aboveground forest structure and macronutrient stoichiometry over 5 15 years of hurricane induced secondary succession by species, life history groups, community 6 species composition, and geomorphic setting. Stem density continually increased after the 7 impact of the Category 4 hurricane Hugo and 15 years later, it was greater than pre-hurricane. 8 There were significant spatial and temporal differences in the number of species, the diversity 9 index per plot, forest structure, and biomass. The greatest compositional differences occurred 10 between the post-Hugo and the 15-year census. Prior to hurricane Hugo most plots had very 11 similar species composition and abundances, and thus occupied a small area in non-metric 12 multidimensional species space. Following the hurricane new species combinations occurred 13 and the location of plots was spread in multidimensional space. Diversity indices were 14 significantly different among geomorphic settings before and immediately after hurricane Hugo. 15 However, these differences were not observed again until the 15-year census where they returned 16 to pre-hurricane levels. Plant associations based on abundance, life history traits, and landscape 17 position had measurable differences in their structure, composition, aboveground nutrient 18 storage, and stoichiometry. However, these differences were reflected in a variety of ways at 19 different spatial scales. At the species level differences in macronutrient tissue concentrations 20 were apparent when comparing co-existing primary forests dominants, early successional 21 dominants, high-light and low-light species, and species whose stem densities are negatively 22 correlated. Community level differences were greater for forest structure and total nutrient 23 storage compared to the mass weighted concentrations of macronutrients. The largest differences observed were in Mg and can be attributed to the succession of pioneer species 2 following the hurricane. Over the entire 15-year period, the watershed average aboveground 3 stoichiometry was relatively consistent and this is linked to the biomass dominance of a few 4 species. The successional history recorded here also suggests that community level differences 5 in species composition, structure, and stoichiometry were well established after 10 to 15 years of 6 secondary succession.

Disturbance and long-term patterns of rainfall and throughfall nutrient fluxes in a subtropical wet forest in Puerto Rico

Heartsill-Scalley, T.; Scatena,F.N.; Estrada,C.; McDowell,W.H.;Lugo,A.E. 2007. Disturbance and long-term patterns of rainfall and throughfall nutrient fluxes in a subtropical wet forest in Puerto Rico. Journal of Hydrology 333, :472- 485.

Abstract: 
Nutrient fluxes in rainfall and throughfall were measured weekly in a mature subtropical wet forest in NE Puerto Rico over a 15-year period that included the effects of 10 named tropical storms, several prolonged dry periods, and volcanic activity in the region. Mean annual rainfall and throughfall were 3482 and 2131 mm yr1, respectively. Average annual rainfall and throughfall fluxes of K, Ca, Mg, Cl, Na, and SO4–S were similar but somewhat larger than those reported for most tropical forests. Rainfall inputs of nitrogen were comparatively low and reflect the relative isolation of the airshed. More constituents had seasonal differences in rainfall fluxes (6 out of 12) than throughfall fluxes (4 out of 12) and all volume weighted throughfall enrichment ratios calculated for the 15-year period were greater than one. However, median weekly enrichment ratios were less than 1 for sea salts and dissolved organic carbon, between 1 and 2 for Mg, Ca, SiO2 and SO4–S, and greater than 10 for NH4–N, PO4–P, and K. Droughts tended to reduce enrichment ratios of cations and sea-salts, but increased enrichment ratios of NH4–N, PO4–P, and K. In the weeks following hurricanes and tropical storms, relative throughfall tended to be higher and enrichment ratios tended to be lower. Saharan dust and the activity of Caribbean volcanoes can also be detected in the time series. Nevertheless, the impacts of particular events are variable and modified by the magnitude of the event, the preand post-event rainfall, and the time since the previous event. Rainfall, throughfall, rainfall pH, and rainfall fluxes of seven constituents had decreasing trends over the 15-year period. However, these decreases were small, less than inter-annual and annual varia-tions, and not considered to be ecologically significant. These long-term observations indicate that physical and biological processes associated with water passing through the canopy act to buffer internal nutrient cycles from inter-annual and seasonal variations in rainfall inputs.

Changes in Structure, Composition, and Nutrients During 15 Yr of Hurricane-Induced Succession in a Subtropical Wet Forest in Puerto Rico

Heartsill Scalley, Tamara; Scatena, Frederick N.; Lugo, Ariel E.; Moya, Samuel; Estrada Ruiz, Carlos R. 2010. Changes in structure, composition, and nutrients during 15 years of hurricane-induced succession in a subtropical wet forest in Puerto Rico. Biotropica. 42(4): 455-463.

Abstract: 
The trajectory of hurricane-induced succession was evaluated in a network of forest plots measured immediately before and 3 mo, 5, 10, and 15 yr after the direct impact of a Category 4 hurricane. Comparisons of forest structure, composition, and aboveground nutrients pools were made through time, and between species, lifehistory groups and geomorphic settings. The hurricane reduced aboveground biomass by 50 percent, causing an immediate decrease in stem density and diversity indices among all geomorphic settings. After 15 yr, basal area and aboveground biomass returned to pre-hurricane levels, while species richness, diversity indices, and stem densities exceeded pre-hurricane levels. Differences in species composition among geomorphic settings had not returned after 15 yr but differences in stem densities and structure were beginning to emerge. Significant differences were observed in the nutrient concentration of the three species that comprised the most aboveground biomass, and between species categorized as secondary high-light species and primary, low-light species. Species whose abundance was negatively correlated with the mature forest dominant also had distinct nutrient concentrations. When total aboveground nutrient pools were compared over time, differences in leaf nutrients among species were hidden by similarities in wood nutrient concentrations and the biomass dominance of a few species. The observed successional trajectory indicates that changes in species composition contributed to fast recovery of aboveground biomass and nutrient pools, while the influence of geomorphic setting on species composition occurs at time scales 415 yr of succession.
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