Tropical Forest Ecology and Management for the Anthropocene

This Special Issue looks forward as well as backward to best analyze the forest conservation challenges of the Caribbean. This is made possible by 75 years of research and applications by the United States Department of Agriculture, International Institute of Tropical Forestry (the Institute) of Puerto Rico. It transforms Holocene-based scientific paradigms of the tropics into Anthropocene applications and outlooks of wilderness, managed forests, and urban environments. This volume showcases how the focus of the Institute’s programs is evolving to support sustainable tropical forest conservation despite uncertain conditions. The manuscripts showcased here highlight the importance of shared stewardship and a long-term, hands-on approach to conservation, research programs, and novel organizations intended to meet contemporary conservation challenges. Policies relevant to the Anthropocene, as well as the use of experiments to anticipate future responses of tropical forests to global warming, are reexamined in these pages. Urban topics include how cities can co-produce new knowledge to spark sustainable and resilient transformations. Long-term results and research applications of topics such as soil biota, migratory birds, tropical vegetation, substrate chemistry, and the tropical carbon cycle are also described in the volume. Moreover, the question of how to best use land on a tropical island is addressed. This volume is intended to be of interest to all actors involved in long-term sustainable forest management and research in light of the historical lessons and future directions that may come out of a better understanding of tropical cities and forests in the Anthropocene epoch

Methodological Considerations in the Study of Earthworms in Forest Ecosystems

Decades of studies have shown that soil macrofauna, especially earthworms, play dominant engineering roles in soils, affecting physical, chemical, and biological components of ecosystems. Quantifying these effects would allow crucial improvement in biogeochemical budgets and modeling, predicting response of land use and disturbance, and could be applied to bioremediation efforts. Effective methods of manipulating earthworm communities in the field are needed to accompany laboratory microcosm studies to calculate their net function in natural systems and to isolate specific mechanisms. This chapter reviews laboratory and field methods for enumerating and manipulating earthworm populations, as well as approaches toward quantifying their influences on soil processes and biogeochemical cycling

Effects of Hurricane-Felled Tree Trunks on Soil Carbon, Nitrogen, Microbial Biomass, and Root Length in a Wet Tropical Forest

Decaying coarse woody debris can affect the underlying soil either by augmenting nutrients that can be exploited by tree roots, or by diminishing nutrient availability through stimulation of microbial nutrient immobilization. We analyzed C, N, microbial biomass C and root length in closely paired soil samples taken under versus 20–50 cm away from large trunks of two species felled by Hugo (1989) and Georges (1998) three times during wet and dry seasons over the two years following the study conducted by Georges. Soil microbial biomass, % C and % N were significantly higher under than away from logs felled by both hurricanes (i.e., 1989 and 1998), at all sampling times and at both depths (0–10 and 10–20 cm). Frass from wood boring beetles may contribute to early effects. Root length was greater away from logs during the dry season, and under logs in the wet season. Root length was correlated with microbial biomass C, soil N and soil moisture (R = 0.36, 0.18, and 0.27, respectively; all p values < 0.05). Microbial biomass C varied significantly among seasons but differences between positions (under vs. away) were only suggestive. Microbial C was correlated with soil N (R = 0.35). Surface soil on the upslope side of the logs had significantly more N and microbial biomass, likely from accumulation of leaf litter above the logs on steep slopes. We conclude that decaying wood can provide ephemeral resources that are exploited by tree roots during some seasons

On the interaction between Autonomous Mobility-on-Demand systems and the power network: models and coordination algorithms

We study the interaction between a fleet of electric, self-driving vehicles servicing on-demand transportation requests (referred to as Autonomous Mobility-on-Demand, or AMoD, system) and the electric power network. We propose a model that captures the coupling between the two systems stemming from the vehicles' charging requirements and captures time-varying customer demand and power generation costs, road congestion, battery depreciation, and power transmission and distribution constraints. We then leverage the model to jointly optimize the operation of both systems. We devise an algorithmic procedure to losslessly reduce the problem size by bundling customer requests, allowing it to be efficiently solved by off-the-shelf linear programming solvers. Next, we show that the socially optimal solution to the joint problem can be enforced as a general equilibrium, and we provide a dual decomposition algorithm that allows self-interested agents to compute the market clearing prices without sharing private information. We assess the performance of the mode by studying a hypothetical AMoD system in Dallas-Fort Worth and its impact on the Texas power network. Lack of coordination between the AMoD system and the power network can cause a 4.4% increase in the price of electricity in Dallas-Fort Worth; conversely, coordination between the AMoD system and the power network could reduce electricity expenditure compared to the case where no cars are present (despite the increased demand for electricity) and yield savings of up $147M/year. Finally, we provide a receding-horizon implementation and assess its performance with agent-based simulations. Collectively, the results of this paper provide a first-of-a-kind characterization of the interaction between electric-powered AMoD systems and the power network, and shed additional light on the economic and societal value of AMoD.Comment: Extended version of the paper presented at Robotics: Science and Systems XIV, in prep. for journal submission. In V3, we add a proof that the socially-optimal solution can be enforced as a general equilibrium, a privacy-preserving distributed optimization algorithm, a description of the receding-horizon implementation and additional numerical results, and proofs of all theorem

On the shoulders of giants: Continuing the legacy of large-scale ecosystem manipulation experiments in Puerto Rico

There is a long history of experimental research in the Luquillo Experimental Forest in Puerto Rico. These experiments have addressed questions about biotic thresholds, assessed why communities vary along natural gradients, and have explored forest responses to a range of both anthropogenic and non-anthropogenic disturbances. Combined, these studies cover many of the major disturbances that affect tropical forests around the world and span a wide range of topics, including the effects of forest thinning, ionizing radiation, hurricane disturbance, nitrogen deposition, drought, and global warming. These invaluable studies have greatly enhanced our understanding of tropical forest function under different disturbance regimes and informed the development of management strategies. Here we summarize the major field experiments that have occurred within the Luquillo Experimental Forest. Taken together, results from the major experiments conducted in the Luquillo Experimental Forest demonstrate a high resilience of Puerto Rico’s tropical forests to a variety of stressors

Disturbance reduces fungal white-rot litter mat cover in a wet subtropical forest

Fungi that bind leaf litter into mats and produce white-rot via degradation of lignin and other aromatic compounds influence forest nutrient cycling and soil fertility. Extent of white-rot litter mats formed by basidiomycete fungi in Puerto Rico decreased in response to disturbances—a simulated hurricane treatment executed by canopy trimming and debris addition in 2014, a drought in 2015, a treefall, and two hurricanes 10 days apart in September 2017. Percent fungal litter mat cover ranged from 0.4% after Hurricanes Irma and Maria to a high of 53% in forest with undisturbed canopy prior to the 2017 hurricanes, with means mostly between 10% and 45% of fungal litter mat cover in undisturbed forest. Drought decreased litter mat cover in both treatments, except in one control plot dominated by a drought-resistant fungus, Marasmius crinis-equi. Percent fungal litter mat cover sharply declined after hurricanes, a treefall, and a simulated hurricane treatment. Solar radiation was significantly inversely correlated with relative humidity (RH) and percent litter mat cover within each of the four climatic seasons. Solar radiation was also directly correlated with prior month litterfall, while RH was moderately correlated with throughfall, rain, and litter wetness. However, rainfall was inversely correlated with litter mat cover, possibly due to erosion or saturation during high rainfall events. Canopy opening reduced leaf fall and litter mat cover but these variables were not correlated except in winter. The main factor inhibiting basidiomycete fungi that bind leaf litter into mats was likely lower litter moisture associated with drought and increased solar radiation from canopy opening but secondary compounds in green litterfall may have contributed. Although higher litterfall likely increases fungal mat cover under closed canopy, changes in environmental factors apparently had a stronger inhibitory effect following canopy disturbances. Drought tolerance of some basidiomycete fungal litter mat species provided some resilience to drought

Characterizing Predictability of Fire Occurrence in Tropical Forests and Grasslands: The Case of Puerto Rico

Global estimates of fire frequency indicate that over 70% of active fires occur in the tropics, and the size and frequency of fires are increasing every year. The majority of fires in the tropics are an unintended consequence of current land-use practices that promotes the establishment of grass and shrubland communities, which are more flammable and more adapted to fire than forests. In the Caribbean, wildland fires occur mainly in dry forests and in grasslands and crop lands. Climate change projections for the Caribbean indicate increasing area of drylands and subsequent increasing potential for wildland fire. We assessed the last decade of fire occurrence records for Puerto Rico to quantify the relative importance of time, climate, land cover, and population to inform predictive models of fire occurrence for projecting future scenarios of fire risk. Kruskal-Wallis, generalized linear models, robust regression, simple and multiple regressions, and tree models were used. We found that hour of the day (time), mean minimum temperature (climate), and percent forest cover (land cover) significantly influenced fire occurrence, while population showed a weak effect. Many variable interactions showed to be important. These significant variables and interactions should be considered in fire-predicting models for the island