Soil organic matter dynamics during 80 years of reforestation of tropical pastures

Our research takes advantage of a historical trend in natural reforestation of abandoned tropical pastures to examine changes in soil carbon (C) during 80 years of secondary forest regrowth. We combined a chronosequence approach with differences in the natural abundance of ¹³C between C3 (forest) and C4 (pasture) plants to estimate turnover times of C in the bulk soil and in density fractions. Overall, gains in secondary forest C were compensated for by the loss of residual pasture-derived soil C, resulting in no net change in bulk soil C stocks down to 1 m depth over the chronosequence. The free light fraction (LF), representing physically unprotected particulate organic matter, was most sensitive to land-use change. Reforestation replenished C in the free LF that had been depleted during conversion to pastures. Turnover times varied with model choice, but in general, soil C cycling rates were rapid for the 0–10 cm depth, with even the heavy fraction (HF) containing C cycling in decadal time scales. Turnover times of C in the free LF from the 0–10 cm depth were shorter than for the occluded and HFs, highlighting the importance of physical location in the soil matrix for residence time in the soil. The majority of the soil C pool (82±21%) was recovered in the mineral-associated density fraction. Carbon-to-nitrogen ratios and differences in natural abundance ¹⁵N of soil organic matter (SOM) showed an increasing degree of decomposition across density fractions with increasing mineral association. Our data show that the physical distribution of C in the soil has a large impact on soil C turnover and the ability of soils to maintain SOM stocks during land-use and land-cover change.     

Disease of Red Mangrove (Rhizophora mangley) in Southwest Puerto Rico Caused by Cytospora rhizophorae1

A high frequency of dieback and mortality was found in Rhizophora mangle (red mangrove) in coastal mangrove forests of southwest Puerto Rico. Eight plots were established in a variety of mangrove environments to assess the extent and severity of the dieback and mortality. The imperfect fungus Cytospora rhizopborae was isolated consistently from stem dieback and associated canker tissues. No other pathogenic microorganisms were isolated. Pathogenicity was demonstrated in greenhouse and field inoculation experiments with C. rhizophorae using young R. mangle seedlings. In field studies of seedlings inoculated, mortality was 33 percent, and greenhouse mortality was as high as 50 percent. Cytospora rhizophorae was isolated consistently from diseased mangrove tissue; the fungus was grown in pure culture and then inoculated into healthy red mangroves, causing cankers. Koch's postulates were fulfilled by infecting R. mangle with C. rhizophorae, producing disease symptoms, and successfully re‐isolating C. rhizophorae from the diseased tissue. This is the first documentation of the pathogenicity of C. rhizophorae associated with mortality in red mangrove. In the coastal mangrove forests of southwest Puerto Rico, C. rhizophorae may play an important role in the frequency of dieback and mortality in R. mangle, producing slow stem diameter growth and causing frequent stem and root wounds.     

Patterns of litter production across a salinity gradient in a Pterocarpus officinalis tropical wetland

Historically, Pterocarpus officinalisJacq. (Leguminoseae) dominated freshwater wetlands in the coastal plains of Puerto Rico, but deforestation has reduced its distribution to small patches adjacent to mangrove forests in areas of higher salinity. The objective of this study was to determine how a gradient in soil salinity affected litter, flower, and fruit production in a Pterocarpus officinalis.Three 100 m² plots were established in each of three sites along a salinity gradient: pasture/Pterocarpus edge (low salinity, mean salinity at 60 cm–9.7 g Kg^–1), Pterocarpus forest (intermediate salinity, 11.5 g Kg^–1) and a Pterocarpus/mangrove ecotone (high salinity, 15.0 g Kg^–1). Across this gradient, P. officinalis accounted for 100% of the relative basal area in the low and intermediate sites and 43% in the high salinity site which was domimated by Laguncularia racemosa. The basal area of P. officinalis decreased along the gradient from 73.5 m² ha^–1 in the low salinity site to 42.0 m² ha^–1 in the high salinity site. Litterfall was sampled on average every 23 days in 45 0.25 m² traps (5 traps per plot) for two years. Annual litterfall for the forest was 11.9 Mg ha^–1 yr^–1. Peaks in litterfall were associated with high precipitation in May 1995 and tropical storms in September 1995. Leaf fall of P. officinalis was significantly higher in the low salinity site (4.8 Mg ha^–1 yr^–1) than the high salinity site (1.8 Mg ha^–1 yr^–1), but total stand litterfall was greatest in the area of high salinity due to the greater contribution of L. racemosa. Pterocarpus flower and fruit production was approximately 10 times greater in low and intermediate salinity sites in comparison with the high salinity site. An increase in global temperature, will lead to higher sea level and higher soil salinity in costal wetlands. To conserve this wetland forest type it is critical to expand the distribution into areas of lower salinity where this species occurred historically.     

Reproduction in an aggregating grouper,the red hind,epinephelus guttatus

Synopsis We examined the reproductive pattern of an aggregating grouper, the red hind,Epinephelus guttatus, in Puerto Rico. Macroscopic and histological examination of gonads confirmed that, although mature, ripe ovaries are found over a three-month period, spawning activity is limited to about 2 weeks each year. Females are determinate spawners and individuals are able to spawn more than once during the course of the annual spawning season. The red hind is protogynous and 50% maturity is attained at 215 mm fork length. In western Puerto Rico, spawning occurs in aggregations at several sites within loosely defined areas located towards the edge of the insular platform. Sex ratios of individuals taken by hook and line at one of the aggregation areas over a consecutive six-year period, suggest considerable intra- and inter-annual variation most likely attributable to a combination of differential ingress and egress by males and females during the course of an aggregation and to fluctuations in recruitment, differential mortality by sex and sex change among years. A comparative assessment of the reproductive patterns of seven western AtlanticEpinephelus spp. suggests that aggregation-spawning is associated with medium- to large-sized groupers, while smaller groupers do not aggregate. Mating systems vary among congeners in association with trends in male-female size dimorphism, sexual pattern and sperm competition. The short-term, localized, nature of spawning aggregations renders species with this reproductive mode particularly vulnerable to fishing pressure at spawning sites. Aggregating species, therefore, may require special management consideration.     

A new genus and species of 'giant hutia' (Tainotherium valei) from the Quaternary of Puerto Rico: an extinct arboreal quadruped?

A large incomplete rodent femur from a Quaternary cave deposit near Barahona, Puerto Rico, is established as the holotype of Tainotherium valei , a new extinct genus and species. Although biogeographic and body size similarities suggest that it may be related to the Puerto Rican giant hutia Elasmodontomys , the Antillean large-bodied rodent family Heptaxodontidae is now interpreted as invalid, and it is impossible to assign Tainotherium to a particular caviomorph family in the absence of associated craniodental material. Tainotherium differs from other West Indian species in possessing a large femoral head, a proximally angled femoral neck, a short greater trochanter and a medially positioned lesser trochanter unconnected by an intertrochanteric crest, and a transversely flattened, anteroposteriorly bowed shaft lacking well-defined ridges. These characters are all associated with arboreal life habits in other mammal groups. The Puerto Rican land mammal fauna was dominated by a rodent radiation occupying a wide variety of niches before human arrival in the West Indies, but although arboreality is correlated with increased likelihood of survival in Quaternary mammalian extinction events, all of this fauna is now extinct. It is unlikely that decreasing aridity and the reduction of Puerto Rican savanna-type environments at the end of the Pleistocene contributed to the extinction of the arboreal Tainotherium , and habitat destruction by pre-Columbian Amerindians may instead have been responsible.     

Turquoise is the new green: Restoring and enhancing riparian function in the Anthropocene

Riparian ecosystems are hotspots for ecological restoration globally because of the disproportionately high value and diversity of the ecological functions and services which they support and their high level of vulnerability to anthropogenic pressures, including climate change. Degraded riparian ecosystems are associated with many serious anthropogenic problems including increased river bank erosion, water quality decline, increased flood risk and biodiversity loss. Conventional approaches to riparian restoration, however, are frequently too narrow in focus – spatially, temporally, ecologically and socially – to adequately or equitably address the goals to which they aspire. Climate change, along with the intensification of other human pressures, means that static, historically oriented restoration objectives focused solely on prior ecological composition and structure are unlikely to be defensible, achievable or appropriate in the Anthropocene. Conversely, open‐ended restoration strategies lacking clear objectives and targets entail substantial risks such as significant biodiversity losses, especially of native species. A functional approach to planning and prioritising riparian restoration interventions offers an intermediate alternative that is still framed by measurable targets but allows for greater consideration of broader temporal, spatial and cultural influences. Here, we provide an overview of major riparian functions across multiple scales and identify key drivers of, and threats to, these. We also discuss practical approaches to restoring and promoting riparian functions and highlight some key concerns for the development of policy and management of robust riparian restoration in the Anthropocene.     

How do frugivores track resources? Insights from spatial analyses of bird foraging in a tropical forest

Frugivores often track ripe fruit abundance closely across local areas despite the ephemeral and typically patchy distributions of this resource. We use spatial auto- and cross-correlation analyses to quantify spatial patterns of fruit abundance and avian frugivory across a 4-month period within a forested 4.05-ha study grid in Puerto Rico. Analyses focused on two tanager species, Spindalis portoricensis and Nesospingus speculiferus, and their principal food plants. Three broad questions are addressed: (1) at what spatial scales is fruit abundance and frugivory patchy; (2) at what spatial scales do frugivores respond to fruit abundance; and (3) to what extent do spatial patterns of frugivory overlap between bird species? Fruit patch size, species composition, and heterogeneity was variable among months, despite fruit patch locations remaining relatively consistent between months. Positive correlations between frugivory and fruit abundance suggested tanagers successfully tracked fruit abundance. Frugivory was, however, more localized than fruit abundance. Scales of spatial overlap in frugivory and monthly variation in the foraging locations of the two tanager species suggested that interspecific facilitation may have been important in determining bird foraging locations. In particular, S. portoricensis, a specialist frugivore, may have relied on the loud calls of the gregarious generalist, N. speculiferus, to find new foraging areas. Such a mechanism could help explain the formation of mixed species feeding flocks and highlights the potential importance of facilitation between species that share resources.     

<Emphasis Type="Italic">Isla Evangelista—</Emphasis>A Story of Church and State: Puerto Rico’s Faith-Based Initiatives in Drug Treatment

This article describes the debates leading to Puerto Rico’s Mental Health Law of 2000, which defined addiction as a spiritual and social problem rather than a mental disorder, in order to trace three competing approaches to addiction in Puerto Rico: evangelist, biomedical, and harm-reductionist. Highlighting the ways in which the evangelist approach of Puerto Rican street ministries challenges the individualism underlying US faith-based initiatives and the punitive approach of the US War on Drugs, this article concludes that the virtues of the evangelist approach to addiction would be best supported by public funding for biomedical and harm-reduction approaches within a pluralistic system of treatment for addiction.