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While trees in the biome lose their leaves to reduce water consumption, the species brought from Peru keeps its canopy alive, produces pods, and forms dense areas in the northeastern Sertão.
As the drought drags on and much of the Caatinga takes on a dry and gray appearance, the algaroba stands out for remaining green. In some areas of the Sertão, the tree remains laden with pods even under high temperatures and months of little rain.
This resilience is tied to a set of characteristics, including an extensive and deep root system. While many plants primarily depend on moisture found in the upper layers of soil, the algaroba is able to tap into reserves much deeper beneath the surface.
Studies conducted in arid regions show that specimens of the genus Prosopis can reach groundwater located dozens of meters below. However, the actual depth achieved varies according to soil type, the age of the tree, water availability, and environmental conditions.
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This ability helps the algaroba maintain activity during the dry season. Research published in Scientific Reports found that Prosopis juliflora trees can utilize groundwater during rainless periods, sustaining their foliage when other species reduce their activities.
A Different Strategy than Native Plants
The leaf loss observed in many Caatinga species does not mean the plants have died. It is a strategy to reduce transpiration and conserve water. When the rains return, the vegetation quickly re-sprouts, and the landscape regains its green color.
The algaroba follows a different strategy. Its root system combines lateral roots capable of exploiting moisture close to the surface after rains, with deep roots that can seek water during droughts.
Therefore, stating that all algarobas reach exactly 30 meters deep would be inaccurate. It is more correct to say that the species can develop roots that extend dozens of meters under favorable conditions, accessing reserves that remain out of reach for many smaller plants.
Tree Arrived in the Northeast in 1942
The algaroba is not part of the original flora of the Caatinga. The species was introduced to Brazil’s Northeast in 1942, in the municipality of Serra Talhada, Pernambuco, through seeds from the Piura region of Peru, according to the Joaquim Nabuco Foundation.
The tree was brought to the Semi-arid region for its resistance to droughts and its economic potential. Its pods became used for animal feed, while its wood found applications as fuel, charcoal, stakes, and raw material for various rural activities.
According to the National Institute of the Semi-arid Region, the algaroba can reach heights of four to 15 meters, tolerates long drought periods, and can thrive in rocky, sandy, and salinized soils.
Resistance Also Brought Environmental Problems
The same characteristics that made algaroba a viable option for arid areas have also contributed to its uncontrolled spread. The tree grows rapidly, disperses seeds through pods consumed by animals, and can form dense clusters.
In invaded environments, these clusters compete for space, water, nutrients, and light with native vegetation. A study on the Caatinga concluded that the presence of Prosopis juliflora reduced growth and increased mortality of the evaluated native species.
Research also indicates allelopathic effects, a phenomenon where substances released by the plant or its residues interfere with the germination and development of other species. The intense shade and the accumulation of leaves beneath the canopy may exacerbate this challenge.
Thus, the green canopy that stands out during the dry season reveals both the impressive adaptation of algaroba and the problem posed by its expansion. While useful for various economic activities, the species requires controlled management to ensure its resilience does not lead to the replacement of the native flora of the Caatinga.
