Forests & climate

Scientific findings prove that global warming, observed over the past 50 years, is caused by human activity.

Since 1861, when sys­tem­atic record­ing of me­te­o­ro­log­i­cal data began, the global av­er­age tem­per­a­ture has in­creased by 0.6°C (+/- 0.2°C). The av­er­age sur­face tem­per­a­ture of the north­ern hemi­sphere over the past cen­turies is likely to have risen at a higher rate than it did in sim­i­lar pe­ri­ods over the last 1000 years. Ex­perts argue that, by 2100, tem­per­a­tures might rise by 1.4 to 5.8°C rel­a­tive to 1990 (IPCC 2001)- a rise that exceeds all nat­ural tem­per­a­ture fluc­tu­a­tions ob­served dur­ing the past few cen­turies.

More­over, these processes are ex­tra­or­di­nar­ily dy­namic, with tem­per­a­ture changes occuring at a speed never before seen, in the the last 10,000 years.

Cli­mate change in Aus­tria

In Aus­tria tem­per­a­tures went up by 1.8°C dur­ing the 20th cen­tury; a trend that was ob­served at all al­ti­tudes. A fur­ther cli­mate-in­duced rise in the av­er­age an­nual tem­per­a­ture is pro­jected, with the tem­per­a­ture rise ob­served in the Alpine area being sig­nif­i­cantly above the global av­er­age.

Re­search find­ings by the Hadley Cen­tre in Great Britain pre­dict an in­crease in sum­mer tem­per­a­tures by 5 to 11 de­grees in the west­ern parts of Aus­tria - a rise that, by far, ex­ceeds ear­lier pro­jec­tions. Further, the findings regarding pre­cip­i­ta­tion pattern was inconclusive, with the level and distribution of rainfall dif­fering greatly be­tween the in­di­vid­ual cli­mate mod­els used.

Cli­mate change also al­ters pre­cip­i­ta­tion pat­terns

Changes in rainfall patterns will prob­a­bly dif­fer widely between re­gions. Gen­er­ally speaking, ex­treme weather events, such as storms, dry pe­ri­ods, and heavy pre­cip­i­ta­tion, are ex­pected to occur more fre­quently. Moreover, as the im­pacts of man-made cli­mate change are al­ready being felt, and are only ex­pected to get worse in the coming decades, the microclimates found within for­ests will drastically change in both the immediate and distant future.

As a result, there is some doubt over the extent of the impact forestry can have on mitigating the effects of climate change. Nevertheless de­vel­op­ing and im­ple­ment­ing mea­sures, such as planting specially chosen tree species, improving the struc­ture of for­est stocks, and implementing various op­er­a­tional plans to ensure that forests can adapt to the im­pacts of cli­mate change is an ur­gent ne­ces­sity.

Study: Im­pacts of cli­mate change in Aus­tria

A 2001 study by Lexer et al ex­plored the con­se­quences that would emerge in Austria, should the average temperature increase by 2°C and should the total volume of rainfall reduce by 15%- thereby simulating the effects of one model of climate change. Their results, up to the year 2050, give the following expectations:

It is highly likely that, dur­ing the next few decades, the higher temperatures will result in the death of numerous trees and tree species at low-altitude areas, as they will no longer be able to grow. This is es­pe­cially true for sec­ondary spruce forests that are found in low­-altitude areas and, as a result, the reg­u­lated man­age­ment of these spruce stands, which even now are often in­ap­pro­pri­ate for the lo­ca­tion they are grown in (due to temperatures), will no longer be pos­si­ble. That said, due to forward-thinking for­est management policies, such forest stands ac­count for only a small per­cent­age of the overall for­est area.

Furthermore, the re­sults of mod­el­ling sug­gest that short- to medium-term im­pacts will be less ev­i­dent at higher al­ti­tudes. These cal­cu­la­tions are based on the as­sump­tion that the pro­duc­tiv­ity of for­est stands would rise.

The pro­jected long-term ef­fects of this particular scenario will be more pro­nounced in high-al­ti­tude areas than at lower altitude areas . This is due to the fact that, in the warmer con­di­tions that will emerge, de­cid­u­ous trees will now be able to com­pete with the currently dom­i­nat­ing conifers- thereby giving for­est man­agers a more diverse range of tree species to plant, since they can now grow in the warmer conditions

In low-altitude areas, where tem­per­a­tures are higher al­ready, beech trees will con­tinue to be one of the po­ten­tial nat­ural tree species; the com­pet­i­tive strength of oak will rise com­pared to beech.

The risk of de­ser­ti­fi­ca­tion is re­al­is­tic only for a small num­ber of sites that are already experiencing ex­treme weather con­di­tions. How­ever, dry areas are very sen­si­tive even to minor changes in pre­cip­i­ta­tion regimes.

New for­est man­age­ment prac­tices?

Sci­entific research can, and should, pro­vide a basis for plan­ning and de­ci­sion-mak­ing in for­est man­age­ment. This can be achieved through dy­namic sim­u­la­tion mod­els, or computer models that are used to determine how the behaviour of a system over a certain amount of time, of for­est ecosys­tems, as they allow individuals to make quan­ti­ta­tive as­sess­ments regarding the effectiveness of particular policies. Yet, one must always contextualise any con­clu­sion drawn from mod­el­ling as some for­est ecosys­tems have taken a very long time to be­come what they are today. Cur­rent fore­casts sug­gest that climate change is occuring at a very fast rate, which results in the emergence of certain fears, such as that the changes are occuring too quickly for the nat­ural adap­tive ca­pac­ity of for­est ecosys­tems to en­sure their sta­bil­ity or eco­log­i­cal func­tion­ing- or even that forest will no longer be able to perform their various roles in the facilitation of natural cycles.

The con­stantly chang­ing climate is a great chal­lenge for forestry. On the one hand, there are el­e­ments of un­cer­tainty in all fore­casts, while on the other ex­treme in­di­vid­ual events can change pro­jected trends and estimates dra­mat­i­cally. Due to knowledge deficits and natural factors, the scope and effectivness of  silvicultural adaptation measures over the short, medium, and long term are limited.

Current and previous ex­pe­ri­ence sug­gest that both near-nat­ural for­est stands and forests based on nat­ural se­lec­tion with species that are suitable to their sites can adapt to their environment more effectively than ar­ti­fi­cially es­tab­lished forest stands comprising non-na­tive tree species. There are di­verg­ing views among ex­perts as re­gards the po­ten­tial ad­van­tages and dis­ad­van­tages of cul­ti­vat­ing alien, non-in­dige­nous tree species. (Source: The Aus­trian For­est Pro­gramme)

published at 03.07.2018, Kommunikation und Service (Abteilung Präs. 5)