28
The climate and topography along which these forests develop determine a wide
variety of forest formations, soil types, and disturbance regimes, which greatly
influence in species distribution as well as in their patterns of genetic variation.
Then, the region is characterized by a high heterogeneity imposed by deep environmental gradients. First, the extension of these forests encompassing about 20° of
latitude generate a gradient in the photoperiod with earlier start and later end of the
daylight during the growing season toward the south, thus increasing day length.
Also light quality and quantity differ across latitude due to seasonal variation in the
distribution of semidarkness (twilight and moonlight) (Mills 2008) and the amount
of solar ultraviolet radiation that decreases toward the poles. In addition, air temperature has a poleward decrease. The latitudinal mean annual temperature (MAT)
gradient in the Southern Hemisphere is of −0.57 °C per degree of latitude (while in
the Northern Hemisphere is of −0.73 °C), although many factors influence the local
temperature making this relation less linear (i.e., vegetation, topography, winds,
cloud, and snow cover) (De Frenne et al. 2013). For species with geographic ranges
that span these gradients, local adaptation is often observed, with variation among
populations in growth and reproductive traits such as phenology, as a response to
light and temperature (Savolainen et al. 2007). Intraspecific variation in other key
life history traits like leaf N:P ratio and seed mass was found to decrease with latitude in natural populations of vascular plants (De Frenne et al. 2013).
The amount of precipitation is also a major determinant of the distribution of
vegetation. At latitudes between 35° S and 43° S in Chile, the Coastal range runs
parallel to the Andes, separated by the Central Depression. While the Andes reach
altitudes above 3000 m asl, the Coastal mountain range only reaches 2000 m asl at
its maximum heights (at 38° S; Armesto et al. 1995). South of 43° S, the Andes
gradually diminish in mean elevation. These two mountain ranges cause a rain
shadow effect that concentrates rainfall on the western slopes. This effect is more
pronounced in the Andes where precipitation decreases from more than 2000 mm to
under 200 mm over a west-to-east distance of 80 km (Roig and Villalba 2008). In
addition, precipitation increases from north (1500 mm at 35° S) to south (4500 mm
at 47° S) (Di Castri and Hajek 1976), decreasing again toward the continental
extreme (1400 mm at 55° S) (Arroyo et al. 1995). Not only does the precipitation
volume change from north to south but also its seasonality. For example, Valparaiso
(33° S) and Punta Arenas (53° S) have a quite similar annual mean, but in the first
case, almost 80% of the rainfall is concentrated in the winter months (May to
August), while in the second city, precipitation is homogeneously distributed over
the whole year (Donoso 1992). In addition, at mid-latitudes (42° – 44° S) northsouth- oriented mountain chains run parallel to the Andes, imposing another restriction to rains.
The precipitation gradient is associated with an increase in the daily thermal
amplitude as the forests give rise to the steppe (Hadad et al. 2019). These climatic
conditions enhance the likelihood of occurrence of frosts. Actually, the annual frostfree period is of only 90 days in eastern North Patagonia (December to March), with
records of late frost during the first days of December and early frost at middle of
March (Bustos 2001). Frost events occurring during the growing season can affect
P. Marchelli et al.
The climate and topography along which these forests develop determine a wide
variety of forest formations, soil types, and disturbance regimes, which greatly
influence in species distribution as well as in their patterns of genetic variation.
Then, the region is characterized by a high heterogeneity imposed by deep environmental gradients. First, the extension of these forests encompassing about 20° of
latitude generate a gradient in the photoperiod with earlier start and later end of the
daylight during the growing season toward the south, thus increasing day length.
Also light quality and quantity differ across latitude due to seasonal variation in the
distribution of semidarkness (twilight and moonlight) (Mills 2008) and the amount
of solar ultraviolet radiation that decreases toward the poles. In addition, air temperature has a poleward decrease. The latitudinal mean annual temperature (MAT)
gradient in the Southern Hemisphere is of −0.57 °C per degree of latitude (while in
the Northern Hemisphere is of −0.73 °C), although many factors influence the local
temperature making this relation less linear (i.e., vegetation, topography, winds,
cloud, and snow cover) (De Frenne et al. 2013). For species with geographic ranges
that span these gradients, local adaptation is often observed, with variation among
populations in growth and reproductive traits such as phenology, as a response to
light and temperature (Savolainen et al. 2007). Intraspecific variation in other key
life history traits like leaf N:P ratio and seed mass was found to decrease with latitude in natural populations of vascular plants (De Frenne et al. 2013).
The amount of precipitation is also a major determinant of the distribution of
vegetation. At latitudes between 35° S and 43° S in Chile, the Coastal range runs
parallel to the Andes, separated by the Central Depression. While the Andes reach
altitudes above 3000 m asl, the Coastal mountain range only reaches 2000 m asl at
its maximum heights (at 38° S; Armesto et al. 1995). South of 43° S, the Andes
gradually diminish in mean elevation. These two mountain ranges cause a rain
shadow effect that concentrates rainfall on the western slopes. This effect is more
pronounced in the Andes where precipitation decreases from more than 2000 mm to
under 200 mm over a west-to-east distance of 80 km (Roig and Villalba 2008). In
addition, precipitation increases from north (1500 mm at 35° S) to south (4500 mm
at 47° S) (Di Castri and Hajek 1976), decreasing again toward the continental
extreme (1400 mm at 55° S) (Arroyo et al. 1995). Not only does the precipitation
volume change from north to south but also its seasonality. For example, Valparaiso
(33° S) and Punta Arenas (53° S) have a quite similar annual mean, but in the first
case, almost 80% of the rainfall is concentrated in the winter months (May to
August), while in the second city, precipitation is homogeneously distributed over
the whole year (Donoso 1992). In addition, at mid-latitudes (42° – 44° S) northsouth- oriented mountain chains run parallel to the Andes, imposing another restriction to rains.
The precipitation gradient is associated with an increase in the daily thermal
amplitude as the forests give rise to the steppe (Hadad et al. 2019). These climatic
conditions enhance the likelihood of occurrence of frosts. Actually, the annual frostfree period is of only 90 days in eastern North Patagonia (December to March), with
records of late frost during the first days of December and early frost at middle of
March (Bustos 2001). Frost events occurring during the growing season can affect
P. Marchelli et al.