ALL GREENERY IS GOOD FOR THE ENVIRONMENT; THE MESQUITE TREE IN UAE IS LIVING PROOF!

Dr. Yousef Nazzal Zayed Universtiy Professor and Chair LES

While most countries and governments believe that planting greenery is always environmentally sustainable and friendly, and the UAE has been at the forefront of green strategy; yet, not all green vegetation is good.

The Mesquite tree, Ghweif in UAE, was introduced from South America by the UAE to green the deserts. However, it escaped the plantation and is currently covering huge areas in the UAE, especially the east regions of the country. As this tree has a very deep root system, it accesses and depletes the UAE’s groundwater resources at an alarming rate since 1990. These are the findings of a recent study conducted by researchers of the College of Natural and Health Sciences, Zayed University, and the Department of Applied Biology, College of Sciences, University of Sharjah.

Entitled “Changes in the Invasion Rate of Prosopis juliflora and Its Impact on Depletion of Groundwater in the Northern Part of the United Arab Emirates” a team of researchers included Fares M. Howari, Manish Sharma, Yousef Nazzal, Ali El-Keblawy, Shajrat Mir Cijo M. Xavier, Imen Ben Salem, Ahmed A. Al-Taani and Fatima Alaydaroos used high resolution satellite imagery dating from 1990 to 2019. They showed that Mesquite trees (Prosopis species) have invaded an area reaching maximum expansion in 2019 of 16 km2 compared to just 0.2 km2 in 1990. The study also unveiled that this increased expansion has come hand in hand with increased groundwater consumption.

The findings showed that these Mesquite trees consumed 22.2 million m3 of groundwater in 2019 in the study region; a 7372 % increase from 1990! All data recordings were obtained from the field spectroradiometer camera and were then decoded in ENVI software for analysis. This study monitored the spread and propagation of the invasive P. juliflora in newly invested areas in the Ajman and Sharjah Emirates. Researchers utilizing integrated geographic information systems (GIS), remote sensing images, and meteorological station data detected and quantified the rate of invasion around the most affected area in Ajman Emirate from the early 1990s to 2019. Researchers also calculated its impact on groundwater by estimating evapotranspiration using Sharjah Airport meteorological station data.

The Mesquite tree

Prosopis juliflora, known as Mesquite trees or Ghweif in UAE, was introduced in the 1970s for desert greening. According to international studies, there are over 40 juliflora is a formidable invader, capable of colonizing and dominating new habitats quickly.

Mesquite species native to South America, where the trees originate. There are also two species in the southwestern United States in Texas, mainly found along Texas rivers, creeks, and draws.

Prosopis juliflora (Mesquite) is a hardy and aggressive invasive species that has spread across various ecological landscapes, particularly in arid and semi-arid regions. The deep root system of this species is one of its primary strategies for colonization. A deep-penetrating root system not only allows Mesquite to access water from deeper layers of soil, often outcompeting native vegetation but also stabilizes sand dunes and soils, facilitating its dominance in a new environment. Mesquite roots have a symbiotic relationship with nitrogen-fixing bacteria, enhancing the plant's ability to thrive in nutrient-poor soils. Nitrogen-fixing can enrich soils, which makes the environment unfavorable for some native species adapted to low levels of nitrogen. It is also known for its robust bark and trunk, is valued by carpenters, and has been traditionally used by natives for making furniture and utensils. The roots of Mesquite trees make the soil under them highly resistant to erosion, preventing landslides.

The reproductive strategy of Mesquite is another significant advantage that aids its invading nature. The plant produces a multitude of seeds with a high germination rate and are known to remain viable in the soil for years. Many herbivores are attracted to these seeds because they are encapsulated in pods. Animals ingest these pods unharmed, and the seeds are dispersed in their droppings over vast areas, further facilitating the plant's spread. Due to its hardiness, nitrogen-fixing ability, and seed dispersal mechanisms, P.

The Mesquite dilemma in UAE

In the UAE, these trees have grown dramatically in several places. It dominates and covers a huge area in Sharjah, near the airport, Um Fannan, and Al Talla. According to Prof. Yousef Nazzal, the situation has become a problem, especially given the limited groundwater resources available in the UAE.

As mentioned by Prof. Ali El-Keblawy,the Mesquite tree was introduced during the 1970s to combat desertification in the Abu-Dhabi Emirate. However, as seeds of the tree can be disseminated by domestic livestock such as goats, cattle, mules, camels, and wild fauna such as gazelles, it invaded large areas in the northern and western Emirates, such as Ras Al-Khaimah, Fujairah, Ajman, Sharjah, Dubai, and Umm Al Quwain. The higher rainfall, in addition to shallow groundwater in the northern and western Emirates, makes these regions even more suitable for the invasion of P. juliflora.

As Prof. Yousef Nazzal explains, “As a professor in the field of environmental science researching water management, it is known that the groundwater in UAE is limited and deteriorating due to overconsumption in the agricultural and industrial sectors. With limited rainfall and heat, the country consumes more than it saves. Evapotranspiration (ET), the sum of evaporation and plant transpiration, also increases the problem of groundwater resources. So, we needed to understand how much woody plant life was utilizing fresh groundwater. When quantifying the patterns of hydraulic redistribution by Mesquite and assessing how this affects tree water use and productivity, we found that Prosopis juliflora (Mesquite) switches between shallow lateral and deep taproots, which allows them to extract more groundwater.

The study sheds light on the fact that the increase in the number of introduced invasive species can change the social–ecological systems of a particular region. The biological invasion by Mesquite is recognized as a primary threat to indigenous biodiversity.

Nazzal warns that based on the study, if the Mesquite tree is not controlled, it will continue to spread and consume more groundwater, making it detrimental to agriculture, fresh drinking water, and other areas where it is utilized.

He outlines the consumption of the Mesquite tree and how it has increased over the years and in certain months during the year, especially summertime. He gives an example of how in June 1990, consumption was 420,000 cubic meters increasing to 3 million cubic meters in June 2019. He emphasizes if this is not managed the groundwater consumption of these trees will become too much to handle.

He explains, “Agriculture will be strongly affected especially because Mesquites are growing next to huge agriculture areas in Ajman and Sharjah, yet it will also affect our chances of recharging groundwater which is already very slow in arid regions especially if we consume more than we can get back.”

The solution

As a result, Prof Nazzal believes that there needs to be a management plan for the sustainable use of this species in the UAE region in particular and other similar countries in the arid land regions that are suffering from freshwater depletion because of Prosopis invasion. This could include countries in the GCC region as well as Sudan where it was introduced in the 19th century to combat desertification and as a source of fuelwood.

He adds “As a scientist we publish papers for decisionmakers to review. We are open to any approach from the government or private sector and are ready to support it. We need to remove and control these trees in the study area as well as carry out a full assessment of the cost and benefits. In the future, we need to have a national strategy plan to guide the management of green plants and criteria for choosing which ones to allow in the UAE because not every tree is good for the country.”

According to Nazzal, we have to look at vegetation that does not need large amounts of water, whether surface water or groundwater. Species which can be stated as being wholly native and still widespread in the UAE are the Ghaf Tree (Prosopis cineraria), Samur or Salam (Acacia Tortilis), Garath (Acacia Arabica), Sidr (Ziziphus Spinachristi), and the Date Palm (Phoenix Dactylifera). The researchers will be carrying out further studies in the future on this subject.

It is noteworthy that in 2017 Dr. Taoufik Ksiksi, a professor in the Department of Biology at UAE University in Al Ain, in a paper published in the Emirates Journal of Food and Agriculture, Landscaping with native plants in the UAE: calls for the increased use of native plants in the Emirates.

He discussed how the Mesquite tree has created havoc and is a nasty species, as it stifled the growth of native plant species because of the chemicals in its leaves, lowering the biodiversity in the desert.

Prof. El-Keblawy indicated that Mesquite is very hard to control, i.e., eradicated. The Ministry of the Global Environment and all Environmental agencies and municipalities in the different emirates are trying to eliminate it but with limited success. Therefore, we should live with the problem. Prof. El-Keblawy mentioned that we can transform this plant from a curse to a blessing by converting it into different sources of biofuels or quality charcoal.

So, for many reasons, it seems the Mesquite tree needs to be eradicated or at least highly controlled despite its needed green color because sustainability and the UAE’s groundwater are in danger.

Title of Published Paper:

Changes in the Invasion Rate of Prosopisjuliflora and Its Impact on Depletion of Groundwater in the Northern Part of the United Arab Emirates.

Published in: Plants

The impact Factor: 3.899

It is published by MDPI AG

The Journal is indexed UGC CARE Scopus

The SJR ( SCImago Journal Rank) 0.656