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Immediate Ecological Effects

  • Ariel E. Lugo
Chapter
Part of the SpringerBriefs in Energy book series (BRIEFSENERGY)

Abstract

The ecological systems appeared to have collapsed after hurricane María because the defoliation of vegetation was so extensive as to give the appearance that the vegetation was killed. In reality, the rapid re-greening of vegetation quickly reversed these visible effects. Forests continued to yield clean water from watersheds and began a process of change that would restore their structure and functioning, even if species composition might change as they matured. Extreme events such as María have positive long-term effects on Caribbean forests and contribute to adaptability of organisms to a changing world environment.

The newspapers were full of opinions about the effects of María on forests, mostly based on the visible effects of the hurricane and poor understanding of the ecology of Caribbean forests after hurricanes. Some generalizations were simply guesses. Here are some myths that were propagated:
  • That “all the trees are dead” evolved into “98 percent of adult trees are down”.

  • That the remaining forest structure cannot hold sediments and contributes to the filling of reservoirs.

  • That it will take 50 years for forests to recover.

Scientists from US National Laboratories and Universities published a satellite image showing the geographic distribution of affected vegetation after María (Fig. 3.1). Although the scientists were careful with the interpretation of the image, the press and the public understood that María had killed about 30 million trees. Even if true, 30 million trees killed are only 13% of the trees of those sizes in the island, reflecting a robust and resilient tree population. Nevertheless, determining which trees are dead and which are not is not possible so quickly or from a single satellite image because determining tree mortality is not trivial. Even decapitated trees can re-sprout and live productively. Similarly, it is hard to know what “adult trees” mean, but assuming it means the tall ones, it is a challenge to make such a generalization for any large area of forests without a systematic inventory. The worst affected parts of the Luquillo Mountains after hurricane Hugo had 37% tree mortality in small areas, and most “adult” trees remained standing. I made similar observations in the Luquillo Mountains after María with similar results.
Fig. 3.1

Satellite image depicting disturbance intensity of forests immediately after the passage of hurricane María over Puerto Rico [6]. The change in nonphotosynthetic vegetation (ΔNVP) after the hurricane relative to before the hurricane is the measure of disturbance shown here

A hurricane transfers canopy leaves and branches to the forest floor, in effect placing a carpet over the forest floor and protecting soil from erosion. Before these hurricanes, collaborating scientists of the International Institute of Tropical Forestry (Institute) conducted an experiment involving a stand clear-cut and removal of the debris from the site to see what happen to nutrient retention during rainfall events. The results indicated that the soil remains in place thanks to the root structure [34]. Measurements of water quality did not show significant leakage of sediments or nutrients. The issue of reservoir sedimentation in Puerto Rico has to do with exposed bare soils along roads, towns, and communities. The 100,000 landslides produced by María also contributed to sediments, as do exposed agricultural soils. Placing the blame of reservoir sedimentation on defoliated forests misleads the mitigation effort and incorrectly points to natural forces rather than human activity. After María, I saw clear water flowing out of our Bisley Experimental Watersheds in the Luquillo Mountains where we have been studying forest recovery after hurricane Hugo in 1989 (Picture 3.1).
Picture 3.1

Aerial view of the Río Espíritu Santo watershed in the Luquillo Mountains after the passage of Hurricane María. The forest is defoliated, but most of the trees alive, and clear water is flowing out of the watershed. Picture by Sharon Wallace, USDA Forest Service

After Hugo we learned about the resilience of ecological systems. When we first saw the effects of Hugo on the forests of the Luquillo Mountains, we erroneously thought that the recovery would take a long time. Some of the prevailing ecological paradigms of the 1980s viewed tropical forests as fragile and incapable of recovery from extreme events. This paradigm proved false, as our research between 1988 and the present demonstrated [18]. That research gave us a lot of confidence for predicting what the ecological response to María will be. The passage of María also gives us an opportunity to study certain details of forest response that escaped attention after Hugo. The most dramatic one is the role of microbial and soil organisms in processing the enormous quantities of woody and other vegetative material that piles on the ground as a result of the hurricane.

When I sat down to write a summary of what we had learned about ecological effects of hurricanes up to 2008, I recognized six effects that hurricanes have on the forests of the Caribbean (Box 3.1). Observations after María reinforced these effects. For example, the absence of flowers, nectar, and roosting places stressed pollinators and nectarivore organisms such as bees and some birds and bats. These organisms were observed disoriented and attracted to sugary materials such as sodas sold in fast food locations. People had to consume these materials indoors to avoid confrontations with starving insects and birds. Mortality was high in these organisms and many were observed roosting in unexpected locations in people’s yards.

Box 3.1 Summary of Visible and Invisible Effects of Hurricanes [14]

Hurricanes:
  • Change the ecological space available to organisms. The ecological space represents the envelope of environmental conditions that support the activities and survival of organisms. Each species is adapted to a particular set of environmental conditions, and hurricanes change that ecological space available to species and organisms. As ecological space changes, organisms have to move in search of the particular set of conditions to which they are adapted.

  • Set organisms in motion. This is in response to changes in ecological space.

  • Increase the heterogeneity of the landscape and the variability in ecosystem processes.

  • Rejuvenate the landscape and its ecosystems and redirect succession.

  • Shape forest structure, influence their species composition and diversity, and regulate their functioning.

  • Induce evolutionary change through natural selection, and ecological creativity through self-organization, i.e., nature finds its way to reorganize after an extreme event.

In short, hurricanes are a positive natural force that selects for organisms that thrive between hurricane events. These events make forests more productive and adaptive to deal with future uncertainties. Everybody in Puerto Rico saw the immediate visible effects of María and experienced the same surprise ecologists had after Hugo, but the public was much less aware of the “invisible” effects. “Invisible” hurricane effects need to be studied if they are to be uncovered. For example, the oldest trees in the Luquillo Mountains regenerated after hurricanes dating back to the XIX century. But who would know that? It is an invisible effect uncovered by Institute scientists [39].

The response to a hurricane lasts over a century, with the unfolding of an incredible number of invisible effects that only good scientists and keen observers can see. After 10 years most people will not “see” hurricane effects because the canopy has fully recovered and the forest appears green and healthy. The forests of Puerto Rico and the Caribbean have to substantially recover between hurricane passages if they are to maintain the current forest structure. On average, hurricanes return every 60 years over a particular geographic area of the Luquillo Mountains [32]. But the species composition and abundance of a forest does not return to the same level of relative species abundance as it had before the hurricane [10]. In fact, tree species composition and abundance is always changing. This level of dynamic change is what happens in our forests and is part of the message that we need to communicate to the public because many lessons can be learned from the recovery of ecological systems to make our social and technological ones more adaptive and resilient.

Copyright information

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Ariel E. Lugo
    • 1
  1. 1.San JuanPuerto Rico

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