Daniela F. Cusack

Stoichiometry of soil enzyme activity at global scale

Extracellular enzymes are the proximate agents of organic matter decomposition and measures of these activities can be used as indicators of microbial nutrient demand. We conducted a global-scale meta-analysis of the seven-most widely measured soil enzyme activities, using data from 40 ecosystems. The activities of beta-1,4-glucosidase, cellobiohydrolase, beta-1,4-N-acetylglucosaminidase and phosphatase g(-1) soil increased with organic matter concentration; leucine aminopeptidase, phenol oxidase and peroxidase activities showed no relationship. All activities were significantly related to soil pH. Specific activities, i.e. activity g(-1) soil organic matter, also varied in relation to soil pH for all enzymes. Relationships with mean annual temperature (MAT) and precipitation (MAP) were generally weak. For hydrolases, ratios of specific C, N and P acquisition activities converged on 1 : 1 : 1 but across ecosystems, the ratio of C : P acquisition was inversely related to MAP and MAT while the ratio of C : N acquisition increased with MAP. Oxidative activities were more variable than hydrolytic activities and increased with soil pH. Our analyses indicate that the enzymatic potential for hydrolyzing the labile components of soil organic matter is tied to substrate availability, soil pH and the stoichiometry of microbial nutrient demand. The enzymatic potential for oxidizing the recalcitrant fractions of soil organic material, which is a proximate control on soil organic matter accumulation, is most strongly related to soil pH. These trends provide insight into the biogeochemical processes that create global patterns in ecological stoichiometry and organic matter storage.

Changes in microbial community characteristics and soil organic matter with nitrogen additions in two tropical forests

Microbial communities and their associated enzyme activities affect the amount and chemical quality of carbon (C) in soils. Increasing nitrogen (N) deposition, particularly in N-rich tropical forests, is likely to change the composition and behavior of microbial communities and feed back on ecosystem structure and function. This study presents a novel assessment of mechanistic links between microbial responses to N deposition and shifts in soil organic matter (SOM) quality and quantity. We used phospholipid fatty acid (PLFA) analysis and microbial enzyme assays in soils to assess microbial community responses to long-term N additions in two distinct tropical rain forests. We used soil density fractionation and 13C nuclear magnetic resonance (NMR) spectroscopy to measure related changes in SOM pool sizes and chemical quality. Microbial biomass increased in response to N fertilization in both tropical forests and corresponded to declines in pools of low-density SOM. The chemical quality of this soil C pool reflected ecosystem-specific changes in microbial community composition. In the lower-elevation forest, there was an increase in gram-negative bacteria PLFA biomass, and there were significant losses of labile C chemical groups (O-alkyls). In contrast, the upper-elevation tropical forest had an increase in fungal PLFAs with N additions and declines in C groups associated with increased soil C storage (alkyls). The dynamics of microbial enzymatic activities with N addition provided a functional link between changes in microbial community structure and SOM chemistry. Ecosystem-specific changes in microbial community composition are likely to have far-reaching effects on soil carbon storage and cycling. This study indicates that microbial communities in N-rich tropical forests can be sensitive to added N, but we can expect significant variability in how ecosystem structure and function respond to N deposition among tropical forest types.

The role of native species plantations in recovery of understory woody diversity in degraded pasturelands of Costa Rica

Tropical timber plantations provide a variety of environmental services, including recovery of biodiversity on degraded lands. For example, plantations can speed forest successional processes by improving microsite conditions and attracting seed dispersers, thus promoting woody regeneration. Timber species have been hypothesized to differ in understory recruitment success. In the present research, understory regeneration of woody plants was compared for six native timber species on tropical plantations in the Atlantic humid lowlands of Costa Rica. Timber species compared were: Calophyllum brasiliense Cambess, Hieronyma alchorneoides Allemao, Terminalia amazonia (J.F. Gmel.) Exell, Virola koschnyi Warb., Vochysia ferruginea Mart., and Vochysia guatemalensis Sprague. The six species were present at each of the three sites: one experimental plantation and two small-scale plantations belonging to farmers of the region. All plantations were 9–10 years. The experimental plantation was 100 m from continuous forest (i.e., seed source), and the farmers’ plantations were 1.3 and 2.5 km from continuous forest. Four plots were sampled for each timber species at each site using a randomized block design. All understory woody species were counted, identified, and separated by height class. Canopy openness and leaf litter biomass on the plantation floor were also evaluated. All of the plantations studied showed significantly higher levels of understory regeneration than control plots on abandoned pastures ðP < 0:05Þ. In this study, plantation site was the most significant factor affecting understory woody species diversity ðP < 0:0001Þ. Different timber species were most successful at recruiting understory regeneration in each of the three sites. On the experimental plantations at site 1, V. guatemalensis and C. brasiliense had the greatest recruitment success, with 75,581 and 69,219 regenerating individuals/ha, respectively. In the commercial plantations, T. amazonia (16,250 regenerating individuals/ ha) had the greatest recruitment success at site 2, and V. ferruginea (29,219 regenerating individuals/ha) had the greatest recruitment success at site 3. Across sites, plots with intermediate canopy openness had greater abundance of understory regeneration than plots with low or high percentages of canopy openness ðP ¼ 0:02Þ. There was no relationship between understory regeneration and leaf litter biomass. Of the planted species most successful at restoring understory diversity, V. guatemalensis, T. amazonia, and V. ferruginea have demonstrated good form and growth for timber, making them important species for reforestation in the region. # 2003 Published by Elsevier B.V.

Trends in Above and Belowground Carbon with Forest Regrowth After Agricultural Abandonment in the Neotropics

Increasing forest cover on lands which were recently forested (reforestation), as well as on lands which have not supported forest growth in recent times (afforestation), has been proposed by the Intergovernmental Panel on Climate Change (IPCC) to help mitigate anthropogenic C emissions from land-use change and fossil fuel use (Brown et al. 1995a, Watson et al. 2000, Metz et al. 2001). Recent research has suggested that these strategies would be most effective in the tropical latitudes (Gibbard et al. 2005). Tropical forests have higher potential carbon (C) uptake rates than forests in temperate or boreal biomes (Brown et al. 1995a, Watson et al. 2000). Globally, 40% of terrestrial biomass C is in tropical forests (Dixon et al. 1994), and 40% of this is in secondary forests (Brown and Lugo 1990). In addition to providing opportunities for C sequestration, reforestation can lead to the recovery of important forest ecosystem goods and services. These include, but are not limited to, watershed protection, erosion control, regional climate stabilization, wood and nontimber products, and habitat for biodiversity (Brown and Lugo 1990, Guariguata and Ostertag 2001, Naughton-Treves and Chapman 2002, De Walt et al. 2003). Although deforestation is still a dominant trend across the tropics, secondary forests resulting from human disturbance are becoming an increasingly important forest cover type (Brown and Lugo 1990). Just as rates of deforestation are difficult to establish with certainty (see Achard et al. 2002, DeFries et al. 2002, Eva et al. 2003, Fearnside and Laurance 2003), estimates for rates of secondary forest growth also differ, although most agree that the trend is positive. In the 1980s, tropical secondary forests were estimated to cover more than 600 million hectares (ha) globally with an annual rate of formation of 9 million hectares per year (ha/yr), and growing (Brown and Lugo 1990). In 1993, the estimated area of tropical America covered by secondary forests was 165 million ha (Weaver 1995 in Kammesheidt 2002). The United Nations Food and Agriculture Organization in 1990 classified 33 million ha of previously agricultural or pasture lands in Latin America as fallow (cited in Kammesheidt 2002). These fallow lands are key components of forest regrowth

Environmental Services of Native Tree Plantations and Agroforestry Systems in Central America

SUMMARY Besides supplying the growing demand for wood, plantations and agroforestry systems provide environmental services such as carbon sequestration and recovery of biodiversity. Several countries of Central America have recently started incentive programs to encourage plantation and agroforestry development. In Costa Rica, Payment for Environmental Services (PES) provides subsidies to farmers for plantations and agroforestry systems. Funding for these subsidies comes from a special tax on gasoline, and from external sources sought by FONAFIFO (National Fund for Forestry Financing). These plantations and agroforestry systems are established on degraded land by farmers who are often advised by local NGOs (non-governmental organizations) or by research institutions that have practical experience in the region. Gathering information on species selection, plantation silviculture, and environmental services provided by plantations and agroforestry systems is important to the success of these systems. These incentive programs can also serve as a model for starting or modifying similar programs in other countries with comparable ecological and socioeconomic conditions. This paper presents experiences with native species plantations over the past twelve years in Costa Rica. Data on volume, biomass production and recuperation of biodiversity are presented. We recommend the establishment of government incentives for reforestation and agroforestry systems with native Species.

Consequence of altered nitrogen cycles in the coupled human and ecological system under changing climate: The need for long-term and site-based research

Anthropogenically derived nitrogen (N) has a central role in global environmental changes, including climate change, biodiversity loss, air pollution, greenhouse gas emission, water pollution, as well as food production and human health. Current understanding of the biogeochemical processes that govern the N cycle in coupled human–ecological systems around the globe is drawn largely from the long-term ecological monitoring and experimental studies. Here, we review spatial and temporal patterns and trends in reactive N emissions, and the interactions between N and other important elements that dictate their delivery from terrestrial to aquatic ecosystems, and the impacts of N on biodiversity and human society. Integrated international and long-term collaborative studies covering research gaps will reduce uncertainties and promote further understanding of the nitrogen cycle in various ecosystems.

Commimity-Based Ecotourism and Sustainability: Cases in Bocas del Toro Province, Panama and Talamanca, Costa Rica

Abstract Tourism is one of the fastest growing industries in the global economy. Ecotourism, a sector of the larger tourism industry, focuses on protecting natural ecosystems while bringing benefits to local communities. To be sustainable, ecotourism projects must be carefully managed so that visitors do not damage isolated natural areas and cultures. Projects must be continually monitored to ensure they are run sustainably. Here, we establish a framework of sustainability indicators for evaluating community-based ecotourism projects. We then evaluate six ecotourism projects around Parque Internacional La Amistad, an international biosphere shared by Panama and Costa Rica. Evaluations are based on field visits conducted as part of a rapid assessments course at the Yale University School of Forestry and Environmental Studies. Finally, we recommend that the sustainability of projects can be increased through goal-setting, establishment of partnerships, and monitoring and evaluation of established projects.

An interdisciplinary assessment of climate engineering strategies

Mitigating further anthropogenic changes to the global climate will require reducing greenhouse-gas emissions ( abatement ), or else removing carbon dioxide from the atmosphere and/or diminishing solar input ( climate engineering ). Here, we develop and apply criteria to measure technical, economic, ecological, institutional, and ethical dimensions of, and public acceptance for, climate engineering strategies; provide a relative rating for each dimension; and offer a new interdisciplinary framework for comparing abatement and climate engineering options. While abatement remains the most desirable policy, certain climate engineering strategies, including forest and soil management for carbon sequestration, merit broad-scale application. Other proposed strategies, such as biochar production and geological carbon capture and storage, are rated somewhat lower, but deserve further research and development. Iron fertilization of the oceans and solar radiation management, although cost-effective, received the lowest ratings on most criteria. We conclude that although abatement should remain the central climate-change response, some low-risk, cost-effective climate engineering approaches should be applied as complements. The framework presented here aims to guide and prioritize further research and analysis, leading to improvements in climate engineering strategies.

Global change effects on humid tropical forests: Evidence for biogeochemical and biodiversity shifts at an ecosystem scale

PUBLICATIONS Reviews of Geophysics REVIEW ARTICLE 10.1002/2015RG000510 Key Points: • Negative effects of all global change factors were found for humid tropical forest biogeochemical processes • All global change factors except carbon dioxide fertilization are likely to promote warming and/or greenhouse gas emissions • Effects of drying and deforestation are relatively clear; effects of CO 2 fertilization and N deposition are less certain Supporting Information: • Supporting Information S1 • Table S1 Correspondence to: D. F. Cusack, dcusack@geog.ucla.edu Citation: Cusack, D. F., J. Karpman, D. Ashdown, Q. Cao, M. Ciochina, S. Halterman, S. Lydon, and A. Neupane (2016), Global change effects on humid tropical forests: Evidence for biogeochemical and biodiversity shifts at an ecosystem scale, Rev. Geophys., 54, doi:10.1002/ 2015RG000510. Received 31 OCT 2015 Accepted 5 JUL 2016 Accepted article online 12 JUL 2016 Global change effects on humid tropical forests: Evidence for biogeochemical and biodiversity shifts at an ecosystem scale Daniela F. Cusack 1 , Jason Karpman 2 , Daniel Ashdown 1 , Qian Cao 1 , Mark Ciochina 1 , Sarah Halterman 1 , Scott Lydon 1 , and Avishesh Neupane 1 Department of Geography, University of California, Los Angeles, California, USA, 2 Department of Urban Planning, University of California, Los Angeles, California, USA Abstract Government and international agencies have highlighted the need to focus global change research efforts on tropical ecosystems. However, no recent comprehensive review exists synthesizing humid tropical forest responses across global change factors, including warming, decreased precipitation, carbon dioxide fertilization, nitrogen deposition, and land use/land cover changes. This paper assesses research across spatial and temporal scales for the tropics, including modeling, field, and controlled laboratory studies. The review aims to (1) provide a broad understanding of how a suite of global change factors are altering humid tropical forest ecosystem properties and biogeochemical processes; (2) assess spatial variability in responses to global change factors among humid tropical regions; (3) synthesize results from across humid tropical regions to identify emergent trends in ecosystem responses; (4) identify research and management priorities for the humid tropics in the context of global change. Ecosystem responses covered here include plant growth, carbon storage, nutrient cycling, biodiversity, and disturbance regime shifts. The review demonstrates overall negative effects of global change on all ecosystem properties, with the greatest uncertainty and variability in nutrient cycling responses. Generally, all global change factors reviewed, except for carbon dioxide fertilization, demonstrate great potential to trigger positive feedbacks to global warming via greenhouse gas emissions and biogeophysical changes that cause regional warming. This assessment demonstrates that effects of decreased rainfall and deforestation on tropical forests are relatively well understood, whereas the potential effects of warming, carbon dioxide fertilization, nitrogen deposition, and plant species invasions require more cross-site, mechanistic research to predict tropical forest responses at regional and global scales. 1. Introduction Humid tropical forests are one of the planet’s greatest natural resources, serving as a terrestrial warehouse for organic carbon (C), protecting nearby communities from runoff and soil erosion, and providing habitat for a spectacular diversity of living organisms. The potential for anthropogenic climate change to disrupt ecosys- tem processes has long been recognized [Vitousek, 1994], but the effects of individual and interacting global change factors have not been comprehensively reviewed. The need for such a review is particularly urgent. Human populations and the extraction of resources continue to increase [Lutz et al., 2001; Watson et al., 2001], and a suite of global-scale consequences are rapidly unfolding on ecosystems across the globe. While climate change is broadly recognized as the most important global change that humans and natural ecosystems face, other factors are also likely to have important effects on all ecosystems, with unique and potentially more accelerated effects on tropical ecosystems. This paper is organized around different aspects of global change that are impacting humid tropical ecosystems. The global change factors are presented in two broad groups that each includes several specific aspects of change. Within (2.1) Changing Cycles we include (2.1.1) Climate Change, (2.1.2) CO 2 Fertilization, and (2.1.3) Nitrogen (N) Deposition. Within (2.2) Land Use/Land Cover Change we include (2.2.1) Deforestation and (2.2.2) Unmanaged Land Cover Change, which explore successional trajectories of lands abandoned postdeforestation. A brief introduction to each of these global change factors is provided at the beginning of each section. ©2016. American Geophysical Union. All Rights Reserved. CUSACK ET AL. Within each of these five sections, we synthesize how a particular global change factor is currently altering key ecosystem processes and properties. We focus on five ecosystem properties that are crucial for ecosystem function and which will determine whether tropical humid forests of the future will resemble those of the past TROPICAL FORESTS AND GLOBAL CHANGE

Is pretenure interdisciplinary research a career risk

Despite initiatives to promote interdisciplinary research, early-career academics continue to perceive professional risks to working at the interface between traditional disciplines. Unexpectedly, the inherent practical challenges of interdisciplinary scholarship, such as new methodologies and lexicons, are not the chief source of the perceived risk. The perception of risk is pervasive across disciplines, and it persists despite efforts to support career development for individuals with common interests [Mitchell and Weiler, 2011]. Suggestions that interdisciplinary work can go unrewarded in academia [Clark et al., 2011] foster a concern that targeting interdisciplinary questions, such as those presented by climate change, will pose problems for acquiring and succeeding in a tenure-track position. If self-preservation limits the questions posed by early-career academics, a perceived career risk is as damaging as a real one to new transdisciplinary initiatives. Thus, institutions should address the source of this perception whether real or specious.