Both diagnoses from space show critical developments for spruces and Co. Between 2018 and 2020, the trees in more than twelve percent of German coniferous forests had to contend with increasing water stress. And the vitality index shows how badly this affected the health of the trees: on more than 11,800 square kilometers and thus seven percent of the area under consideration, the canopy of forests, trees and shrubs was no longer as green as before after the three extreme summers. Trees had even died on one percent of the area. “It looks particularly bad in regions with large-scale spruce monocultures,” says Pierre Ibisch. “But there are also worrying signals in pine forests.” In the spruce forests, the drought not only changed entire landscapes. One also has to reckon with the fact that the ecosystems of the forests are nowhere near as efficient as before. “All of this didn’t just start in 2018,” emphasizes the researcher. The view from space shows a decline in vitality values in more than 20 percent of coniferous forests for the years 2013 to 2020. “What we saw in these analyzes is a loss of vitality of historic proportions,” says Ibisch.
Recipes for the forest of the future
But what to do when the combined forces of heat, drought and bark beetles have deforested entire landscapes? Ibisch advocates leaving the dead trees where they are for the time being so that they can shade the ground and create a cooler and wetter microclimate for future plant generations. Nor does he think it’s a good idea to plow the ground and then plant new trees. Instead of conserving the soil in the interest of a new forest, it is only compacted. Then he loses even more of his water storage capacity.
If, on the other hand, the areas are protected and natural regeneration is allowed, according to his observations, pioneer species such as elder and mountain ash would appear first. And these could then create more humus with their rotting leaves and thus the basis of life for other tree species. Ibisch knows about areas in Saarland where species-rich mixed deciduous forests are already growing under dead spruce trees.
Other currents in forestry, on the other hand, advocate planting new trees – but ones that are better equipped to deal with climate change than their predecessors. After all, all plants adapt to the special challenges of their habitat over the course of generations. Shouldn’t it be possible to find survivors in particularly dry regions who can cope better with a lack of water? Andreas Bolte and his team pursued this idea as part of the “Spruce Dryness” project network. In the greenhouse, they planted 100 young spruce trees from eight different areas in Germany, France, Poland and Romania in pots and then gradually let them dry out. In fact, the spruces from the wetter high altitudes in Bavaria delivered the worst performance. On the other hand, the saplings with the highest survival rate and the most resin canals in the wood came from the dry location of Nochten in Saxony.
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Reforestation in the Taunus | Preprogrammed to fail? Seedlings were planted on a bare and cleared area – in the hope that a new “forest” would develop here. However, the trees often wither quickly in the extreme microclimate that prevails in these open spaces.
“So spruces can actually adapt to drought to a certain extent and pass this tolerance on to their offspring,” summarizes Andreas Bolte. However, this says nothing about the fate of the old trees. The drought specialists may survive the difficult youth phase better. However, they are then just as exposed to the massive attacks of the bark beetles as all other conspecifics. And all the adjustments don’t seem to help. The most drought-tolerant stock in Nochten fell completely victim to the bark beetle in 2018. “I am therefore currently skeptical as to whether it will help much to plant spruce trees from drier regions elsewhere,” says Andreas Bolte. It is better to introduce other, more drought-tolerant tree species into the emerging natural regeneration in the dead spruce stands and thus increase the adaptability of the forests.
losers and winners
All in all, the “bread tree” that was once so popular in forestry seems to have fallen out of time. “We still have a lot of spruce forests in Germany,” says the researcher. “But since the Second World War there hasn’t been as much damage to these trees as in recent years.” In fact, according to the 2012 National Forest Inventory, the spruce is the only tree species whose stocks in German forests have decreased since 2002. And at least four percent. According to Andreas Bolte, it may still have a future as a mixed tree at higher altitudes. But the times when it dominated entire landscapes elsewhere are probably over.