Winter in Bosque Pehuén: Reflecting on the ecological and hydrological processes in the Andean Araucanía

In the midst of snow-capped mountains, temperatures below 0ºC, snow, reduced daylight hours and prolonged rains, species of flora, fauna and fungi in Bosque Pehuén undergo vital transformations. Winter has been very present in the Andean Araucanía, however, climate change and other factors are rapidly changing the natural cycles. What is currently happening during winter in these Andean ecosystems? What are some of the relevant processes taking shape during this period? These are some of the questions that come up at this point of the year.

Inhabited by centuries-old araucarias, coihues, lengas and raulíes, Bosque Pehuén –a conservation area managed by Fundación Mar Adentro– is situated in the Andean Araucanía, between the Rucapillán (or Villarica) and Quetrupillán volcanoes. This protected area stands out for its rich biodiversity, abundant native vegetation and the presence of endemic species typical of the temperate forest ecosystems of southern South America. Throughout the year, the seasons are clearly defined and during the final days of autumn, everything tends to be covered in snow, announcing the beginning of a new winter period which is essential to the balance of nature’s ecological processes. 

Rainfall that nourishes vital cycles

The climate of the Araucanía region varies according to the altitude and the predominant relief. For example, in the Andes Mountains, a cold high altitude climate prevails, characterized by low temperatures and abundant rainfall of 3,000 mm per year. At this altitude –over 1,500 meters above sea level (masl)– precipitation occurs in the form of snow and temperatures tend to remain below 0°C.

In the specific case of Bosque Pehuén, the information for the 2019-2023 period provided by the Tres Hermanas meteorological station (located at 1,240 m asl) shows that during this year 1,310 mm of rainfall were registered, with 2021 being the driest year of the period.

The water that falls as rain or snow favors the growth of dense and abundant forests, so that the forest’s soil and plants receive the rainwater that infiltrates the soil, which is then absorbed by the plant roots and used for growth during the spring and summer months. In addition, the water contributes to the flows of rivers and estuaries of this mountain basin, which has a pluvio-nival regime that plays an essential role in the water supply of the lower altitude areas.

Due to winter rains and spring thaws, this basin is characterized by its high water flows in winter and late spring. Although the trees grow during spring and summer (from September to March), –stopping during autumn-winter and forming the characteristic growth rings within the trunks– in some cases the rates of growth, development and reproduction are strongly related to the amount of rainfall during the previous winter.

Warmer summers

The weather conditions that used to prevail during the winters of the Andean Araucanía have changed, now with higher temperatures, abundant environmental humidity and accelerated melting snow. Currently, the snow remains on the ground for less time than usual and, therefore, there is less snow accumulation, impacting the availability of water for plants and the replenishment of underground aquifers and changing the water flows in summer. In August 2021 and June 2023, the highest average monthly winter temperatures were recorded in Bosque Pehuén since the Tres Hermanas station began its monitoring in 2018. It is therefore necessary to continue carrying out research that explores the possible changes caused by these climatic anomalies in species and ecosystems. 

Similarly to what happened in the country’s central zone during this winter (event of June 21 and 26, 2023), the high zero isotherm meant that raindrops did not freeze, therefore resulting in liquid precipitations at altitudes where snow usually falls. The presence of an elevated zero isotherm can entail risks, as liquid precipitations can drag sediments and trigger floods in the high areas of the mountain range. 

The consequences of the rapid changes seen in the climate during the past few decades can also generate significant impacts both in human well-being and in various components of ecosystems, their diversity and ecological and evolutionary processes. 

The reproductive cycle of the Araucaria araucana

Winter and its low temperatures are significantly related with the reproductive process of the araucarias and the development of its seed, the piñón (Araucaria pine nut, in Spanish). The Araucaria araucana, or pewen in Mapudungun, is an ancient tree that has been present since the Paleozoic era, over 200 million years ago. 

In Bosque Pehuén, it is estimated that some of the araucarias may be several hundred years old. The reproductive stage –that is, the expression of reproductive traits such as the masculine and feminine cones of the longest living individuals growing in the territory– began centuries ago. The seasonality and characteristics of the winters have been essential to their reproductive cycles, as well as for the growth of new sprouts, the germination of seeds and the development of roots and other vegetative organs. 

In the Araucaria, the development of the seedlings begins with the germination of the seeds, stimulated by low temperatures, and with a growth that is accelerated during the southern hemisphere’s summer. An essay by Washington State University in the 1970s studied the germination process of the Araucaria araucana with seeds collected from the Andes Mountains. It found that the seed’s viability (germination potential) is short (the seeds remain viable up to 120 days after maturation), and that the seeds that remain under the snow during winter germinate when the snow melts, confirming the positive relationship between winter snow cover and the germination and development of Araucaria seedlings. 

In conclusion, winters in the Andean Araucanía play a vital role in the ecological and hydrological processes of its ecosystems. Rains and snowfall feed the biodiversity and ensure the region’s water supply, while low temperatures have an essential role in the reproductive processes of species such as the Araucaria. However, climate change and the observed alterations in the climate are challenging the stability of these natural cycles. It is therefore relevant to continue researching and reflecting on these processes, in order to continue contributing to the care, protection and conservation of biodiversity. 






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