According to Sten Mander, head gardener at the University of Tartu Botanical Garden, this winter has been unusual: "Only on New Year's Eve did the temperature drop to between -15 degrees Celsius and -20 degrees Celsius and now, as March arrives, it has risen sharply above freezing."

Plants overwintered well, he said, because a sufficiently thick layer of snow covered much of the lower-growing species. "In addition, cold winters like this help regulate the spread of many diseases and pests," Mander added.

For some species, however, it is the warm spring sun that can prove fatal. "If the ground freezes very deeply, evergreen plants cannot access water from it. As the days grow brighter and sunnier, water inevitably evaporates from the leaves. If they cannot get additional moisture from the frozen soil, the plant simply dries out. This is a fairly typical phenomenon, for example, in rhododendrons or non-native conifers and is associated precisely with cold and sunny weather in March," Mander explained.

If the weather remains warm, however, it is favorable for plants, as the growing season begins earlier and they can better prepare for the next winter. "For example, sap may already begin to flow in maples during sunny weather," Mander said. In his view, sap enthusiasts in particular should welcome daily temperature fluctuations, which help the sap flow more freely.

Advice for sap enthusiasts

Ivar Sibul, associate professor of dendrology and forest entomology at the Estonian University of Life Sciences, urges readers not to drill a hole into a tree to collect sap. "Especially if it is a tree in your home garden. As children, we saw holes drilled into trunks and then plugged afterward, but I do not recommend doing this with birch and even less so with maple," Sibul explained.

According to Sibul, maples are very sensitive to bark damage and rot spreads quickly into the wood. "I have seen a picture where, over the years, rot moved a meter up and a meter down from a sap-tapping hole. You should not seal a trunk wound with a plug because it is a foreign object that prevents the wound from closing. Moisture and fungal spores remain there and begin to grow as if in an incubator," Sibul said.

So where should maple sap be collected? If the canopy extends close to the ground, Sibul recommends selecting a branch about the thickness of a finger, cutting it at an angle and attaching a bottle to the end with string. "Be sure to choose the southern side where the sun warms the canopy. My experience shows that at least half a liter of sap per day can come from a single branch," he added.

If, however, a hole is drilled into the trunk, it should be as small as possible and as high as possible. "The higher the hole, the richer the sap is in sugar. Birch sap taken at a height of two meters is also sweeter than sap collected at knee height because on its journey upward from the roots, the water becomes significantly enriched with sugars," Sibul explained.

Sibul confirmed that maple sap begins to flow when the roots are still in frozen ground but the sun warms the canopy. Birch sap, however, flows around the clock due to pressure, or osmosis, in the roots and canopy. "People often ask why maple does not run at night, but birch does. One reason is osmosis and another is that with nighttime temperatures below freezing, the liquid in maple simply cannot move," he added.

Movement in the insect kingdom

According to biologist and nature photographer Urmas Tartes, most insects overwinter in the ground or in cracks in tree bark and even the harsher cold spells this winter did not disturb them. A separate group consists of species that have adapted their adult life stage specifically to the winter months. "This winter, I have had very few opportunities to observe them because in severe cold they do not come out onto the snow and must carry out their activities beneath it," Tartes explained.

According to Tartes, spring warmth has two important thresholds: at four degrees Celsius, plant growth and photosynthesis begin and at 10 degrees Celsius, broader flight activity among insects gets underway. Although temperatures have not yet risen that high this spring, the photographer still recommends keeping one's eyes open in the forest. "You may still encounter classic winter insects, such as winter crane flies or snow fleas. A harbinger of spring, however, is the dark brown and hairy ruby tiger caterpillar, which comes out onto the snow quite literally to sunbathe," Tartes added.

He himself recently managed to photograph the fly species Crumomyia pedestris in Taevaskoja. "Their larvae develop in decaying organic matter, including the droppings of larger animals. One possible hypothesis about its winter activity, as well as that of many other flies, is that over the winter a considerable amount of large animal droppings accumulates on the snow, allowing them to be the first to lay eggs in it," Tartes explained.

As for the most pressing question — the abundance of mosquitoes in the coming summer — Tartes said it is still too early to look for answers. "Mosquito numbers depend on whether it rains in the coming period and whether mosquito pools persist until May. Generally, we rarely experience a mosquito-free season. For that to happen, spring would have to be very long and dry," Tartes reassured mosquito enthusiasts.

--

Follow ERR News on Facebook and X and never miss an update!