Droughts have a significant & long-lasting change on tree and liana regeneration in a monodominant Amazon forest

Monodominant tropical forests, especially those not associated with flooded environments, are rare and still poorly understood. In the transition between Cerrado and the Amazon rainforest biomes in Brazil, lies patches of monodominant forests of “Pau-Brasil” or Bloodwood cacique (Brosimum rubescens, Figure 1). The structure of these forests have trees of different sizes and represents about 80% of above-ground biomass (Marimon et al., 2001).

Figure 1: Monodominant forest of Brosimum rubescens in Cerrado-Amazonia transition, Brazil. Credits: Beatriz S. Marimon.

The mechanisms behind the dominance of few species and their temporal maintenance in tropical forests are varied and often distinctive (Elias et al., 2018). Analysis how regeneration occurs especially looking at the regrowth of younger and non-established individuals within a community (Figure 2), has been an effective way of finding answers to this occurrence of monodominance as well as helping us to understand the diversity (alpha and beta) found within tropical forests. The diversity seen in tropical forests is normally maintained by balancing or compensatory mechanisms that benefit rare species. As such, when monodominance occur, these regeneration mechanisms uncharacteristically favour common species and tree diversity remains low. Thus, evaluation of long-term regeneration dynamics should be able to determine whether changes in diversity occur with changes in disturbances, such as droughts, logging and anthropogenic climate change — all of which impact tree mortality, recruitment, carbon sequestration and species composition in Amazonia (Esquivel‐Muelbert et al., 2019; Phillips et al., 2009).

Figure 2: Young individuals from the natural regeneration of Brosimum rubescens monodominant forest. Credits: Paulo S. Morandi.

In our study published in Plant Ecology (Marimon et al., 2020), we analysed the number of different tree and liana species (species richness and alpha-diversity) and how they changed annually between 1996 and 2017 in a monodominant forest of Brosimum rubescens in the Cerrado-Amazonia transition in Brazil. The study area is marked by high annual climatic seasonality (~6 months), and in the last years the intensity of seasonal droughts and average temperature are increasing.

Twenty-one years of tree and liana regeneration were evaluated in four censuses in 30 plots. Within these subplots we nested smaller plots to sample vegetation in different size classes, totalling 30 per class: 1 m × 1 m (seedlings: height ≤ 30 cm), 2 m × 2 m (saplings: > 30 cm to ≤ 60 cm), 5 m × 5 m (poles or young stems: > 60 cm to ≤ 200 cm) and 10 m × 10 m (treelets: height > 200 cm and diameter < 5 cm). Our study represents by far the longest-running assessment of regeneration in monodominant forests to date anywhere in the Tropics, and is the first attempt in such system to explicitly account for the long-term regeneration of woody lianas and trees.

Our results show that stem density, species richness, tree diversity and evenness changed between regenerative classes over time. Removing the lianas from the analysis, in all regenerative size classes, tree species richness was highest in 2002 and declined substantially after 2007–2008 and 2015–2016 drought events. In all regenerative size classes the proportion of liana (species and abundance) increased, especially among seedlings and saplings. In 1997 lianas contributed less than 1% of the woody plant seedlings, but by 2018 they represented more than 50% of all woody plant seedlings (Figure 3). The abundance of B. rubescens seedlings declined markedly, from 85% in 1997 to 29% in 2018, after the most intense El Niño-driven drought, whereas the fraction contributed by other tree species changed little (Fig. 3). The regeneration community experienced a high rate of species turnover, with changes in the overall richness and species diversity determined principally by lianas and not trees.

Figure 3: Variation in seedlings stem density (lianas and B. rubescens) and climate over the time series (1996-2018). Credits: Dr. Fernando Elias.

In conclusion, we found unexpectedly large changes, including a dramatic decline in dominance of the smaller size classes of B. rubescens, and a compensatory shift towards dominance of the seedlings community by lianas. The nature and the timing of the shifts and the length of the observation window is consistent with drought events, especially the increase in temperature associated with water deficit experienced over the last two decades, and that may induce long-term shifts in the structure and floristic composition of forest regeneration (seedlings, saplings, poles and treelets), particularly via increases in liana richness and abundance, as observed for adult trees in other studies (Esquivel‐Muelbert et al., 2019; Phillips et al., 2009).

We suggest that if these trends (increase in lianas, hotter and more variable climate, and decline in B. rubescens regeneration) continue the structure and the floristic composition of this tropical monodominant forest will experience large changes, potentially becoming transformed into a mixed forest. Since ongoing land-use change, climatic changes, and increases in lianas appear to be almost ubiquitous among tropical forests of the Americas, our results suggest a high level of threat to the survival and maintenance of remaining Brosimum rubescens monodominant forests.

About the Author: Dr. Fernando Elias is a biologist and Postdoctoral Research Fellow in the Sustainable Amazon Network (www.rasnetwork.org) at Embrapa Amazônia Oriental in Brazil. He holds a PhD in Ecology at Universidade Federal do Pará/Embrapa Amazônia Oriental, and Master degree in Ecology and Conservation at Universidade do Estado de Mato Grosso. He has experience with forest ecology and restoration related to the assessment of carbon dynamics, biodiversity recovery, phytogeography and conservation biology. Twitter: @feliasbio. E-mail: fernandoeliasbio@gmail.com. ORCID: orcid.org/0000-0001-9190-1733

References

Elias, F., Marimon, B. S., Marimon-Junior, B. H., Budke, J. C., Esquivel-Muelbert, A., Morandi, P. S., … Phillips, O. L. (2018). Idiosyncratic soil-tree species associations and their relationships with drought in a monodominant Amazon forest. Acta Oecologica, 91(July), 127–136. https://doi.org/10.1016/j.actao.2018.07.004

Esquivel-Muelbert, A., Baker, T. R., Dexter, K. G., Lewis, S. L., Brienen, R. J. W., Feldpausch, T. R., … Phillips, O. L. (2019). Compositional response of Amazon forests to climate change. Global Change Biology, 25(1), 39–56. https://doi.org/10.1111/gcb.14413

Marimon, B. S., Felfili, J. M., & Haridasan, M. (2001). Studies in monodominant forests in Eastern Mato Grosso, Brazil: I. a Forest of Brosimum rubescens Taub. Edinburgh Journal of Botany, 58(1), 123–137. https://doi.org/10.1017/S096042860100049X

Phillips, O. L., Aragao, L. E. O. C., Lewis, S. L., Fisher, J. B., Lloyd, J., Lopez-Gonzalez, G., … Torres-Lezama, A. (2009). Drought Sensitivity of the Amazon Rainforest. Science, 323(5919), 1344–1347. https://doi.org/10.1126/science.1164033

Different logging schemes impact forest management in the Brazilian Amazon

Loud, gigantic, and scary! This was my first impression of a skidder – a heavy vehicle used in cutting trees. Multiple trees are crushed to access one large Amazonian log. This was the logging operations that occurred in the Jamari National Forest in the Rondônia State of Brazil. Logging tropical trees is simultaneously an art and a damaging activity, given that these trees play a crucial role in regulating Earth’s climate. Despite this importance, only a few operations follow certified sustainable forest management plans (SFMPs).

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Gold mining leaves deforested Amazon land barren for years

Travel through the rainforest in Guyana, in northern South America, and you’ll often hear the indigenous adage: “a forest has no end and no beginning” to explain their natural cycle of disturbance and recovery. For the people who live in these forests, their experiences are based on decades of slash and burn cultivation, from which forests are generally able to recover well. But does the adage hold true for forests abandoned after more intense land uses?

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Amplifying Global South Voices: Reflection & Actions

Since March 11 2020, our world has been disrupted by the COVID-19 pandemic and the existing and persistent inequalities of our systems are being painfully exposed. These inequalities also brought to the forefront the issue of systemic racism of people of colour and the power imbalances between Western societies and the Global South. As Amruta Byatnal, an Associate Editor at Devex mentions in her article on health and COVID-19, “Who controls the levers of development? It’s really people in the so-called global north. While global domination and structural inequality is inbuilt as constituted by economic power, it is reinforced and justified by racial power” 

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Where the Maya People Live: Land Management in Yucatán, Mexico

The Maya solar of Yucatán, in southeast Mexico, has historically supported an intricate indigenous system of land, livelihoods and identities. It remains the basic habitat unit in the region as a vital space for the continuous development of everyday activities (social, economic, cultural, and environmental). These everyday activities contribute towards the cohesion of the family unit and the community through preservation, enrichment and diffusion of knowledge shaping individual and social identities, allowing for the survival of their way of life. Moreover, it is in this place where people organise their self-provision in a series of spaces (e.g. kitchen, barn, and henhouse) connecting their livelihoods to the surrounding land. The solar has been produced and shaped in relation to the region’s specific environmental conditions.

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Rethinking trees in a multi-cultural urban area

This article was researched and written in early 2019. A shorter version was published in September 2019 in Mongabay, who originally commissioned the piece. 

“Cherry, mango, star apple, pam, cashew, pomegranate,” Carol Dabie, 37, rattles off a list of trees that once filled her family’s yard. She recalls climbing them as a child, impatiently waiting for the small, round, sweet pam fruits with their shiny black skin to drop.

As in many backyards across Georgetown – Guyana’s expanding coastal capital – Dabie’s childhood trees were eventually cut down and the fertile earth entombed beneath concrete. It’s a shift reflected in the city’s architecture too, with breezy wooden structures slowly being replaced by low-maintenance concrete blocks.

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Monitoring the loss of trees in the Amazon forests: How satellites, lasers, cloud computing, and artificial intelligence are helping in the fight against deforestation and degradation

Within the last few decades, forest loss in the Amazon forests has been monitored using satellites such as Landsat (30m resolution) and MODIS Terra and Aqua (250-1000m resolution). Detecting deforestation is relatively easy due to the abrupt changes in the landscape, from vegetation/forest to exposed soil or pasture. This shift causes large changes in the spectral signal (different types of surfaces reflect radiation differently, like its own fingerprint, and is a function of wavelength) measured by the satellite sensors, especially in the near infrared wavelength. The difficulty stands on reliably and systematically assessing the whole Amazon forests (>5.5 million km²) every year in order to guide public policies and action. In this sense, Brazil is a reference for deforestation monitoring through the PRODES program of INPE – the Brazilian National Institute for Space Research (Figure 1). PRODES, allied with another system that produces real-time deforestation alerts (DETER), are the core of the Brazilian efforts on reducing deforestation, with great success during the past decade.

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In Guyana, Sustainability is the Journey and the Destination

A Long-standing Commitment to Responsible Travel 

South America’s best kept secret is not much of a secret anymore. From its Low Carbon Development Strategy to the more recent Green State Development Strategy (GSDS), Guyana has had a long-standing commitment to a sustainability agenda. This coupled with nine Indigenous Nations who have been stewards of their ancestral lands for a millennia illustrates that sustainability is a core value and a way of life for many Guyanese. 

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Whale shark interactions in the Philippines: To Feed or not to feed?

Tourism based on marine wildlife interaction is booming worldwide. In the Philippines, it has been gaining popularity for the past six years, particularly swimming with whale sharks. Anyone who has ‘swimming with whale sharks’ on their bucket list is certain to have the Philippines on there too. And recently, that means going to the town of Oslob in Cebu.

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The Exchange of Fruits: How past Indigenous Communities shaped the forest in Brazil

During an archaeological survey in Roraima State, Brazil, in July 2019, I was mistaken as a Macuxi, an indigenous person, by a landowner, whom quickly expelled me from his property. In my country, landowners often assume indigenous persons enter their property to reclaim the land. It wasn’t until the archaeological coordinator explained I wasn’t an indigenous person in disguise that I was allowed back onto his property. The landowner then proceeded to offer me mangos, oranges, and macaxeira as an apology for his mistake. His use of fruits to make amends for treating me poorly is a common gesture among traditional communities in Amazonia, where the circulation of plants flows with the social interplays of everyday life. A visit to a relative, neighbour or friend is an opportunity for the exchange of fruits, seeds, condiments, medicines, seedlings, and ornamental plants. I’ve witnessed and participated in this botanical exchange from an early age, growing up in a small village on the bank of the Guamá River in Pará State, Brazil.

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