A not so cool Harlley's legacy: The catastrophic human-made Trindade Island devastation and its recovery

Highlights

• The revegetation of Trindade Island increased the soil microbiological function.

• There was no seasonal effect on microbial indicators for a same soil in the island.

• The revegetation of Trindade Island provides recovery of the soil quality.

Abstract

Human occupation of Trindade Island caused the decline of much of its vegetation and pronounced changes of the island's landscape. The main factor behind these changes was human colonization and the introduction of goats by Edmond Harlley in 1700. Without natural predators on the island, these animals proliferated uncontrolled and consumed almost all plant cover. High declivities in most parts of the island led to soil erosion and loss of surface soil. The goats were finally eradicated in 2005, allowing vegetation to recover since then. This work explored the hypothesis that the recovery of the island's vegetation was accompanied by the recovery of physicochemical characteristics and soil biological functions. Soils in revegetated areas showed higher values of microbial biomass, basal respiration, microbial quotient, mineralizable nitrogen, and enzymatic activities, and lower metabolic quotient. Principal component analyzes demonstrated that the correlations between the indicators and the principal components remained practically unchanged in two sampling periods (rainy and dry season). Biological indicators are more related to the presence or absence of vegetation than to the type of vegetation, soil physicochemical properties or time of sampling. The natural recovery of the vegetation, combined with the microbiological indicators of soil, demonstrate the improvement of the insular ecosystem after goats were eradicated.

Introduction

The myth of the noble savage, who lives in close harmony with nature and coexists peacefully with other creatures, has long been overthrown by the scientific community. Evidences from various parts of the world show that environmental destruction caused by ancient societies was often notable when considering their small technological development (Bentley, 2013). The extinction of many ancient civilizations is attributed to the environmental degradation triggered by the anthropic action and, in some cases, its effects are still notable (Diamond, 1994).

In pre-Columbian Central America, depletion and soil erosion, resulting from the deforestation of the region for agriculture, are pointed out as the main cause of the extinction of Mayan civilization (Abrams and Rue, 1996; Oglesby et al., 2010).

For insular ecosystems anthropogenic impacts are usually of great magnitude, since such environments do not have the resilience of continental biomes (Jeschke et al., 2018). Historical documents report that the artistically talented inhabitants of Easter Island had already begun their cultural decline long before Captain Cook discovered the island. Such fact would be related to the deforestation of the immense palm forest (Jubaea chilensis), a vital resource for the inhabitants of the island (Stevenson et al., 2015).

Currently, Haiti is a tragic example of how social and economic impacts, generated by an unsustainable model of natural resources exploration, can persist for generations. Since independence in 1858, little has been done to protect the ecosystems of this small country located in an island of the Caribbean Sea. Extensive deforestation, powered by charcoal production, decimated 99% of its original vegetation, contributing to soil erosion, desertification, and freshwater pollution (Williams, 2011). This extractive model did not bring wealth or economic development; on the contrary, the country is one of the poorest in the world and the poorest in the Americas. It is ranked 170th on the United Nations Human Development Index (HDI) and constantly suffers from a shortage of food and other natural resources.

Trindade Island, located 1160 km away from the Brazilian shoreline, has an interesting history of occupation and intense process of environmental degradation. It was discovered in 1501 by the Portuguese navigator João da Nova and later named Santíssima Trindade Island. At the time of the great navigations, the island was intermittently used as a maritime support point by slave traders and English pirates (SECIRM, 2020). It was disputed by Portugal and England and, in 1882, became part of the Brazilian territory. In 1957, the Oceanographic Post of Trindade Island was created, which has since been occupied by the Brazilian Navy (about 32 people on alternate stays), and eventually by a few researchers (Gasparini, 2004).

Degradation problems in Trindade island began in 1700, when Edmond Harlley, on board the HMS Paramour, passed through the island and left some goats (Capra hircus), pigs (Sus scrofa) and guinea fowl (Numida meleagris) (Alves, 1998; Duarte and Horta, 2012). The objective of the astronomer was to ensure that the next navigators or even castaways could survive in the island. In addition, the animals would facilitate a possible subsequent British occupation of that territory (Kämpf, 2016). In a few years, the lack of natural predators and competing herbivores has paved the way for the uncontrolled growth of the goat population, at the expense of the intense consumption of native vegetation. The natural vegetation of the island was practically eliminated. This, associated with the high slopes of the land, culminated in eroded areas and soil degradation (Alves, 1998; Clemente et al., 2011).

The tree Colubrina glandulosa, prevalent at that time, was strongly impacted by the action of these animals, which gnaw at the bark of the trees, in addition to eliminating the undergrowth that protected the soil from erosion (Alves, 1998; Duarte and Horta, 2012). The extractive action carried out in the colonization attempts undertaken by the Portuguese Crown in previous centuries further impacted a highly fragile ecosystem. In addition to presenting easy and fast combustion, native wood was also used for house construction by the new inhabitants who, together with the unsuccessful attempts to cultivate corn, aggravated the serious erosion problem due to the abundant rains from April to September (Alves, 1998).

Since the elimination of the last goat in 2005 by snipers from the Brazilian Navy, many research studies have been carried out on the island, in order to assess the impacts of this action on its macrofauna and flora (Alves et al., 2011; Silva and Alves, 2011; Silva et al., 2013; Salvador et al., 2014). The impacts in the landscape are evident, but the effects of degradation and further recovery on the invisible part of the island and, not less important, the microorganisms present in the soils, are not known.

Research on the soil microbiota of oceanic islands is scarce and still very recent. Of these, studies of the functional microbiota behavior under possible oil contamination stand out (Morais et al., 2016; Camacho-Montealegre et al., 2019), together with a study on biosurfactants-producing bacteria (Silva et al., 2015), both with soils from Trindade Island. However, there is no study on the impact of soil degradation on that island on microbiological indicators and how they respond to the restoration of vegetation in its degraded areas. This knowledge gap must be filled, aiming to generate information that can support interventions aimed to accelerate the recovery and subsequent preservation of degraded environments.

This work aimed to evaluate the hypothesis that the restoration of natural vegetation after the elimination of goats comes with physicochemical and microbial soil properties that are generally accepted to be characteristic for well-functioning vegetated ecosystems; thereby supporting that the ecosystem of Trindade Island is recovering from its devastation caused by anthropologic interference.