The fate of next generation trees

A few years ago, an old lemon tree that towered over the garden of my parents’ house died, but before that, the tree left us a parting gift – a new lemon tree that grew right next to it. Today, this young lemon tree is now mature and producing many healthy, ripe fruits.

In a home garden, an event like this is often unforeseen and seen as nothing more than a happy accident, but in forests, the ability to sprout subsequent generations of saplings remains essential for providing ecosystem services and sustainable habitat for humans and wildlife. .

According to a new israeli study, however, climate change-induced reduced rainfall presents serious threats to natural forest regeneration, especially in Israeli forests. For regeneration to be successful, enough sprouts must germinate and survive to grow into healthy saplings. These processes were examined by a team of researchers from the Weizmann Institute of Science (including Professor Dan Yakir), JNF and the Volcani Institute. Funded by the JNF and published in the scientific journal “Forest Ecology and Management”, the study was carried out between 2015-2020 in the Yatir ForestIsrael’s largest planted forest (an area of ​​30,000 dunams or 7,413 acres) located in a semi-arid region between the Judean and Negev mountains, at the edge of the pine range (the furthest point where the species grows).

At first, the researchers observed abundant growth of sprouts during March and April, but this regeneration quickly faded.

“In season, we saw very large and massive sprouting, so the forest seemed to be growing normally and well,” says Ella Pozner, a graduate student in the Department of Plant and Environmental Sciences at the Weizmann Institute of Science and one study researchers. editors.

However, the trend quickly reversed and only a fraction of the sprouts – at most 10% – survived the summer until September. Over the 6 years of study, only a few shoots managed to grow into saplings; a maximum of 20 trees on average per dunam per year. For comparison, the Malachim-Shachariya Forest near Kiryat Gat, has an average of several hundred saplings per dunam per year.

Compromised regeneration

According to the researchers, the shoots in the Yatir forest struggled to reach maturity mainly due to the lack of rainfall. This was especially noticeable during dry years, especially between 2017 and 2019, when the summer shoot survival rate dropped to near zero. In addition, the study found that animal grazing, during which wildlife tramples and eats shoots, and high tree density, which reduces sunlight penetration and the amount of water available in soil, also affect the ability of forests to regenerate.

“If you come to Yatir Forest after the rain, everything will be green and beautiful, but you won’t see a field of ‘children’ in the forest – young trees that will one day replace older, dying trees,” explains Dr. Tamir Klein of the Weizmann Institute of Plant and Environmental Sciences. According to him, the few trees that have managed to grow beyond their germination stages are very short and look like shrubs rather than tall trees. Klein warns against the possibility that in thirty years the forest will no longer exist.

It’s all about drought

Regeneration failure is a problem with many forests, especially those at the edge of ranges. As the study reveals, the regeneration of large areas of the Yatir Forest in Israel is already disrupted, especially during years of intense drought. In these areas, some tree species are at risk of extinction, that is, the complete disappearance of a species in a specific area or region.

“The climate crisis is driving many changes around the world, as well as an increase in global temperatures and the frequency of drought years and extreme weather events,” says Pozner. “Ultimately, even forests that are considered wetter and retain higher humidity levels will encounter and struggle with drought conditions.”

Over the past decade, many studies have been conducted around the world on the regenerative capacity of forests in the age of the modern climate crisis. Difficulties in regenerating various species have been observed in pine and fir species in the Rocky Mountains forests in the United States, whose vegetation is also suffering from wildfires born from drought. Spatial shifts and compositional shifts in tree populations have also been observed in boreal forests (very cold coniferous to deciduous forests that extend over high altitude areas in Asia and North America) and in wetlands tropical regions of East Asia.

It should be noted that other studies specifically address the adaptive mechanisms that develop in trees at the cellular level that allow them to regenerate more easily and cope with local climatic changes. Such mechanisms have been found in forests in Greece, Brazil and elsewhere.

What is the answer ?

So what can be done to improve the situation and help the forests to regenerate, despite the difficult conditions?

According to Klein, there are many forest interface tools that can be used to help with regeneration, such as: placing a protective plastic sheath around softwoods in their first year that protects them from strong winds and animals grazing, establishing low dams near rainwater from the lake, building low dams near trees to rainwater from the lake, selection of drought resistant trees for future plantings and thinning trees to increase the amount of water available in the soil as well as the sunlight that penetrates through the forest canopies. With measures like these and additional research, next-generation sprouts may be better equipped to persist in harsh summer conditions and preserve some of the world’s most valuable and beloved forests.

The article was prepared by Zavit – The Israeli Society for Ecology and Environmental Sciences News Agency