Over last spring – summer – autumn season (although autumn is only beginning now) I have taken my early morning walks along a trail which leads through patches of habitats.
These are mainly riparian habitats where riparian forest is followed by riparian hay meadows, (too) close-to-river arable fields.
However, there is also a vaster forest stand adjacent to larger cropfields and this forest stand has a resprouting clearing.
I have observed what is already known in science, i.e., that denser forest stands tend to fluctuate less in the temperature (warmer than open habitats during cool periods and somewhat cooler during very hot periods).
Meanwhile, openings tend to be much cooler in the pre-dawn hours and the sense of cold is augmented by the moisture rising from the river which often causes fog to form over the open riverside habitats.
The clearings and the larger agricultural fields (which are further from the river) appeared even colder than the riparian meadows during early springtime (but less so in summer).
These differences between habitats that lie quite nearby to one another made me wonder about thermoregulation in the local mammal assembly (although, of course, they also affect other taxa which, however, is frequently adapted to the specific habitat patch, e.g., grassland species, forest ecotone species etc.).
The contrast between open habitats and closed forest habitats was at times stark and I thought about the impact of fragmented forests (lack of ‘deeper’ forest patches) on species thermoregulation (and the respective energy gains/costs, survival, reproductive success etc.).
The cooler temperatures of the riparian forest openings and clearings might provide refuge during times of day when the global warming has caused the temperatures to rise to a level which is no longer comfortable for native species.
For example, I can see how these openings might benefit such species as the wild boar that finds it difficult to regulate its own body temperature during periods of hot weather.
Herbivores might use ecotones and small openings to mitigate the global warming effects, especially, during late spring and early summer allowing to forage longer before the hot weather sets in.
Perhaps, historically, crepuscular herbivory in ecotones has evolved as a strategy to avoid the warmth of the forest as well as to utilize vegetation that perhaps develops more slowly in these forest edge habitats that experience cooler mornings.
I am not certain that ecotones would decelerate plant phenology because cooler morning temperatures are accompanied with greater light influx.
(Still, it would be interesting to assess whether ecotones near larger forests and smaller adjacent open habitats have slower phenology rates compared to ecotones near smaller forests and larger adjacent open habitats.)
However, once the temperature has risen, it can be higher in these openings preventing additional daytime foraging during periods when the weather has disrupted foraging during twilight hours.
Also, what once used to be ecotones, now have been turned into larger habitat patches where the microclimate is no longer mitigated by the presence of the forest.
Thus, for example, any cooling effects that would have perhaps slowed down phenology on small riparian meadows, are offset by the heat of the Sun during later hours (late morning, day).
These escalating temperature contrasts observed in larger habitats adjacent to forests (that are relatively more thermally stable) might prove more difficult for the young of the year as well as any species that use ecotones for hunting but that are not as efficient at thermoregulation – not during hot spells, not during cold spells.
Such species would be, for example, mustelids with their elongated bodies where thermoregulation has been exchanged for agility and ability to squeeze into burrows and holes accommodating much smaller prey species.
If forests become smaller while the adjacent open habitats become larger and this causes stark temperature fluctuations in ecotones, the ecotones might create higher thermoregulation costs in, e.g., mustelids than they used to, historically.
Also, there might be species (or stages during the individual’s development) where deeper forest and its stable microclimate is crucial in order to survive, for example, the cold of the night and the heat of the day.
This is especially relevant for denning, nesting, hibernating in species that are seeking a stable microclimate (without fluctuations and without above-average or below-average temperatures).
Forests that are too small and that are interspersed with clearings might no longer offer such microhabitats for species that would have otherwise sought rest under the conditions of its stable temperatures.
I believe that research should be conducted to determine whether forest fragmentation affects the stability of its microclimate in the intact patches and whether larger open habitats adjacent to the forests affect the microclimate of ecotones.
Such studies would be important to ensure conservation measures for species with lower thermoregulation capacity (regarding high and/or low temperatures).
However, such research should also look at the potential benefits of ecotones in offering refuge habitats during heat stress which is the side effect of the global warming.
Foraging behaviour (of herbivores but possibly also of ecotone/grassland predators) might be studied in order to determine if the use of habitats changes according to temperature fluctuations during the diel period as well as due to temperature differences on a day-to-day basis (i.e., whether the individual chooses to forage on open habitats as the pre-dawn turns to post-dawn and whether the individual chooses to forage on open habitats in mornings that are warmer than average mornings.)
Notes by Ieva 