Luquillo Data Sets By Insertion Order

This data set includes N. virginea densities and sizes relative to streambed substrate type, water depth, and habitat type in a low land reach in Río Mameyes near PR Route 3 bridge, and presence and inland extent of distribution of in 32 coastal rivers around the island. Hydrologic and water chemistry variables are reported as predictors of snail distribution at regional and stream-network scales.

Seedlings were measured before and after treatments to determine how alterations in canopy openness and detritus affect seedling densities and life histories (growth, mortality, recruitment). It was predicted that plots experiencing canopy openness with detritus removed would have the quickest increase in seedlings (recruitment and growth), especially of early successional (light demanding) species, such as Cecropia. Seedlings in plots that received no canopy manipulation but had detritus deposited is predicted to have near-total mortality initially (low light and high physical inhibition due to detritus). Treatment plots experiencing both canopy manipulation and addition of detritus would initially experience near-total mortality, with some light demanding seedlings establishing and growing through detritus with time.

This experiment was designed to decouple the effects of canopy opening from those of increased detrital inputs on rates of detrital processing and resultant community and ecosystem processes. In a study initiated after massive inputs of organic matter from Hurricane Georges in 1998, the forest floor returned to prehurricane values very quickly, within 2-10 months (Ostertag et al. 2003). However, it was unclear to what extent this homeostasis was caused by increased rates of decomposition. Furthermore, if accelerated decomposition was implicated in rapid recovery, the relative contributions of environmental and resource changes wrought by canopy opening versus green leaf deposition on the forest floor were unclear because these factors are confounded in hurricane damage. A full factorial design was therefore used to tease apart the separate and combined effects of simulated storm damage on rates of mass loss in pre-weighed senesced and green litter cohorts inserted into litter decomposition baskets following application of canopy trimming and debris deposition treatments. Natural litter cohorts (i.e., organic forest floor material and subsequent natural litterfall separated into 3-month cohorts) were also weighed when replicate baskets were harvested at approximately 3-month intervals. In addition to obtaining mass and percent moisture of litter cohorts, the extent of fungal connections between litter cohorts was quantified. Fungal connections between partly decomposed and fresh leaf litter have been shown to be important in importation of phosphorus (the most limiting major nutrient in decomposition of tabonuco forest litter) into the freshly fallen leaves in order to rapidly build fungal biomass and associated acceleration of decomposition (Lodge 1993, 1996). The thickest of these fungal colonization & translocation organs (rhizomorphs, cords and hyphal strands) are primarily basidiomycete fungi, which have an almost unique capacity to cause white-rot by breaking down lignin in low-quality litter. A few white-rot basidiomycetes produce finer connections comprised of diffuse wefts of hyphae (e.g., Marasmius leoninus and related species), but the majority may represent ascomycetes and water molds that lack enzyme systems for breaking down lignin. White-rot basidiomycetes were shown in separate experiments to accelerate rates of decomposition of tabonuco leaves (Dacryodes excelsa) by 15% to 20% (Santana et al. 2005; Lodge et al. 2008), so any changes in fungal connectivity by basidiomycete fungi in response to the treatments should be related to nutrient exchanges between litter cohorts and changes in rates of mass loss.

Litterbaskets are used to study decomposition and nutrient cycling questions, and are often a better for understanding interactions between different litter cohorts than are leaf decomposition bags. We know from previous work here and elsewhere that: 1) basidiomycete fungi rapidly colonize freshly fallen litter (within the first 3 weeks of litterfall) from partly decomposed litter on the forest floor using rhizomorphs and cords (Lodge & Asbury 1988); 2) these fungal root-like structures transport nutrients from the old food base in order to build their biomass in the freshly fallen leaves, and are capable of tripling the phosphorus content in a senesced tabonuco leaf as indicated using radioactive phosphorus tracer in microcosm experiments (Lodge 1993; 1996); and 3) basidiomycete colonization accelerates leaf decomposition in the LEF (Lodge et al. 2008). Fungal translocation of nutrients is probably responsible for the increase in total CONTENT of N and P in leaf litter above 100% in El Verde (as in Zou et al.) and elsewhere in the tropics within 3-6 weeks of leaf fall (see Lodge 1993). In contrast, temperate forest floor litter is not usually colonized by basidiomycete fungi from the forest floor until 9-15 months after litterfall. Translocation of phosphorus into tropical litter with low phosphorus concentrations likely contributes to accelerated rates of leaf decomposition associated with basidiomycete colonization in tabonuco forest (Lodge et al. 2008), but the enzymatic capacity of basidiomycete to degrade lignin is a contributing factor (Santana et al. 2005).

Previous research in temperate forests shows a positive effect of increased litter depth on colonization by basidiomycete fungi. Unpublished data of Lodge & Asbury showed that drying of the litter layer reduced or eliminated basdiomycete colonization, while Lodge & Cantrell (1995) showed disappearance of some basidiomycete colonies in canopy gaps on ridges at El Verde after hurricane Hugo, or replacement of drought-sensitive strong nutrient translocators (i.e., Collybia johnstonii) with more drought tolerant species that translocated less P32. There were no previous data on effects of litter depth on basidiomycete fungi from tropical forests. We knew from studies after Hurricane Georges that 1. forest floor mass in secondary forest returned to pre-hurricane levels in about a year (Ostertag, Silver & Scatena?), but we did not know whether this was due to accelerated decomposition or reduced litter inputs after the storm. Thus, it was not really clear what mechanisms were involved in control of forest floor decomposition following hurricane disturbance.

This litterbasket decomposition experiment was designed to mimic as closely as possible post-hurricane conditions in order to follow mass loss and nutrient content of specific litter cohorts. To this end, a layer of SURFACE AIR-DRIED tabonuco leaves was placed between two screens on top of the existing forest floor layer in the litterbaskets (on the ground). In debris-addition plots, green leaves of Dacryodes, Manilkara and Sloanea IN HURRICANE AMOUNTS (as determined in Lodge et al. 1991) were added on top of the senesced litter layer screen after the canopy manipulations were completed in the CTE plots. Additional cohorts of litterfall were demarcated using screens added to remaining baskets when these were harvested ca. quarterly.

So far, we know that 1) canopy opening inhibited fungal connectivity between litter cohorts (mostly basidiomycete fungi, but the highest counts may be from diffuse hyphal connections by ascomycetes and water molds); 2) addition of green litter buffered the layers below from drying, mostly compensating for the effects of canopy opening; 3) fungal connectivity to the weighed layer of senesced tabonuco leaves was positively and significantly correlated with rates of leaf decomposition; 4) litter decomposition rates were higher than in dried leaf litter in a litterbag experiment in the CTE (González et al, unpublished), as in previous unpublished comparisons of dried versus undried litter; 5) but despite this, forest floor mass had not returned to pre-hurricane levels 1.5 years after CTE initiation. The data of Cantrell and Ortíz (lterdb165) on microbial composition in the litter cohorts from these baskets used methods that cannot distinguish basidiomycetes from other fungi. The results, however, suggest that colonization by basidiomycetes colonize accelerates the rate of early leaf decomposition and changes the trajectory of community succession. Nutrient analyses to determine if increases followed by decreases in inorganic nutrient pools, especially phosphorus, are associated with changes in patterns of fungal connectivity between the litter cohorts, and whether cohorts with low connectivity at the beginning have net losses rather than net gains in N & P stores.

Electronic sensors are placed at the field location to support other activities. Data set includes measurementes from several climate stations in the northeast section of the Luquillo Experimental Forest. These stations are surround the Bisley Experimental watersheds and the Sabana Field Station that are operated by the USFS and the USGS.

Small-scale experiments in tropical streams have suggested that freshwater shrimps play a critical role in determining the quality and quantity of benthic organic matter and overall nutrient dynamics. We quantified the effects of a whole-reach shrimp poisoning event in the Sonadora, a second-order stream draining the Luquillo Experimental Forest in northeastern Puerto Rico. The illegal poisoning (for shrimp harvest) caused massive mortality of shrimps and aquatic insects. Atyid and xiphocaridid shrimp abundances in pools of the poisoned reach were reduced by ~95%, relative to abundances in an upstream reference reach. A survey of poisoned vs. reference pools, combined with a manipulative experiment (in which atyid and xiphocaridid shrimps were added to 3 poisoned pools), showed that reduced shrimp abundances due to the poisoning had strong impacts on benthic resources. The benthos of poisoned pools, where shrimp abundances were reduced, had 4 times more chlorophyll a, 6 times more algal biovolume, 4 times more fine particulate organic matter, 14 times more fine particulate inorganic matter, 5 times more carbon, and 4 times more nitrogen than did the benthos of pools in the reference reach. These increases in benthic resources were consistent with increases in algae, organic/inorganic matter, and nutrients in previous small-scale shrimp exclusion experiments conducted in the study river and tributaries. Effects of shrimp poisoning on the benthos varied by habitat, with riffles showing fewer significant differences than did pools. Compared to reference riffles, poisoned riffles had higher standing stocks of fine particulate inorganic matter, nitrogen, and biovolume of filamentous algae, and lower epilithic C:N ratios. Overall, previous small-scale exclusion experiments were highly predictive of the direction of effects due to large-scale shrimp removal by poisoning. Our study provides a tropical data set to add to the short list of stream studies that examine the predictive power of small-scale experiments for larger scales.

This data set includes N. virginea densities and sizes relative to streambed substrate type, water depth, and near-bed water velocity in three sites in a low land segment in Río Mameyes near PR Route 3 bridge: 1) 50 m upstream from bridge, 2) immediately downstream from bridge, and 3) 200 m downstream from bridge (upper Westin Riomar Golfcourse). In addition, above variables are reported for pools and riffles located at PRASA Intake (Río Mameyes) and at La Curvita (Río Espíritu Santo).

Our primary objective is to understand the linkage between surface-subsurface water interactions and ecosystem processes in neotropical lowland streams over an extended time frame (>25 yrs). Proposed research will occur at La Selva Biological Reserve in Costa Rica, which is owned and operated by the Organization for Tropical Studies

In tectonically active regions of Central America, it is common for solute-rich groundwater to emerge at gradient breaks within the complex volcanic topography of mountains and foothills which intergrade with the coastal plain. These groundwaters can significantly influence solute chemistry and related ecological and ecosystem-level processes in receiving surface waters. Many solute-rich groundwaters are associated with underlying volcanic activity which has altered the chemistry of receiving streams throughout Central America. Geothermally-modified groundwaters, surfacing at the gradient break between the Central Mountain range and the coastal plain at La Selva Biological Station, have high levels of P (up to 400 mg SRP L-1) and other solutes (Ca, Cl, Mg, SO4) but are not elevated in temperature. Spatial patterns in stream solute chemistry are determined by geomorphic features of the volcanic landscape that include: upland lavas drained by P-poor streams; a gradient break (~50 m.a.s.l.), at or near where P-rich springs emerge; and lowland alluvial areas drained by streams that are both P-rich and P-poor depending on whether they receive the input of solute-rich springs.

Our project is the first to determine long-term effects of nutrient enrichment in a detrital-based stream within the wet tropics. We will continue to build upon our ‘long-term' (1988-present) data set on stream solute chemistry, which is the only one that we are aware of for lowland primary rainforest of Central America. The proposed project will build on 18 years of past research which has shown that landscape patterns in stream solute chemistry (resulting from variation in solute-rich groundwater inputs) reflect ecosystem processes such as rates of primary production and decomposition of organic material. Specifically, we are: (1) continuing our evaluation of long-term trends in the solute chemistry of these lowland tropical streams as related to large scale climatic phenomena (e.g., El Nino Southern Oscillation Events); (2) examining how stream segments draining three major geomorphic subfeatures of the lowland tropical landscape respond to temporal (wet versus dry season) changes in precipitation; (3) examining stoichiometric mechanisms behind elevated levels of insect growth and biomass turnover rates in phosphorus-rich streams; and finally (4) concluding (and build upon) an ongoing long-term whole-stream phosphorus enrichment by determining the storage, fate and transport of the artificially-introduced phosphorus (that has been injected over an 8 year period) and examining related effects on detrital foodwebs.

Stream solute chemistry and ecosystem process-oriented data are of fundamental importance to our understanding and management of tropical forests and in predicting effects of regional (and potentially global) environmental change on these threatened ecosystems. Our long-term program will provide new insights into how large scale climatic phenomena interact with subsurface hydrologic factors and geothermal activity to influence stream solute chemistry and related ecosystem processes. We will continue to link the data sets generated from our LTREB Project to those from other long term sites for both tropical (e.g., Luquillo LTER site in Puerto Rico) and temperate research (Coweeta LTER site in North Carolina USA). Finally, the project will contribute to our ongoing environmental outreach program Water for Life, which includes local outreach in communities near La Selva Biological Station and an internationally accessible web page equipped with teaching tools on river conservation and water quality and quantity issues at the high school- level in both Spanish and English.

Seven tree species were selected to represent early (Cecropia, Prestoea) and late (Dacryodes, Manilkara, Sloanea) successional, and overstory (Cecropia, Dacryodes, Manilkara, Sloanea) and understory (Prestoea, Miconia, Psychotria), species in forests at El Verde. These trees were sampled in all CTE plots.

Identification, number and dry weight of invertebrates recovered from each litterbag.