Growth of silver birch (Betula pendula Roth.) in plantations on farmlands in Latvia | Kārpainā bērza (Betula pendula Roth.) jaunaudžu augšanas gaita stādījumos lauksaimniecības augsnēs Latvijā

Letón. Pētījuma mērķis - novērtēt bērzu jaunaudžu augšanas gaitu stādījumos lauksaimniecības augsnēs un salīdzināt to ar bērzu mežaudžu augšanas gaitas prognožu tabulu datiem. Pētījuma ietvaros analizēti pieci bērzu stādījumi, kuru vecums uzmērīšanas brīdī bija no 11 līdz 14 gadiem. Visas pētījumā ietvertās bērzu jaunaudzes ierīkotas neizmantotās lauksaimniecības zemēs, normāla mitruma minerālaugsnēs. Stādījumi izmērīti 2010. gada agrā pavasarī, pirms veģetācijas sezonas sākšanās. Stumbru analīžu veikšanai katrā audzē nozāģēti trīs paraugkoki - viens I Kraft a klases un divi II Kraft a klases koki. Paraugkoki sadalīti metru garās sekcijās, un stumbru šķērsgriezuma ripas iegūtas atbilstoši klasiskās stumbru analīzes metodes prasībām. Audžu augšanas gaitas aproksimācijai pielietota Ričarda-Čapmena funkcija. Pētījumā analizētie bērzu stādījumi lauksaimniecības augsnēs ir ļoti ātraudzīgi, un koku augstumi pārsniedz bērzu mežaudžu augšanas gaitas tabulās prognozētos augstumus attiecīgajā vecumā. Bērzu stādījumu augšanas gaitas un produktivitātes prognozēšanai nepieciešami jauni matemātiskie modeļi, kuru pamatā būtu mūsu apstākļos iegūts empīriskais materiāls. Pagaidām bērzu stādījumu augšanas gaitas prognozēm izmantojami attiecīgie Somijas dienvidu daļai izstrādātie augšanas modeļi.

Inglés. In Latvia, afforestation of abandoned agricultural lands largely by birch started at the end of the last century. By now the age of the first birch plantations thus established is more than ten years. Evaluating the performance of these stands can give an indication of the growth potential of birch on former farmlands. The aim of the given study was to investigate the growth of silver birch in farmlands and compare it with the expected growth rates following the existing yield tables developed for natural birch stands in the conditions of Latvia. The growth of birch on five 10- to 14-year-old plantations established on well-drained mineral soils was investigated. Three of them (Dikļi, Bukas, Stružāni) were established by using container seedlings (Rootrainer Sherwood containers) and two (Salgale 1 and Salgale 2) – by using bareroots. The stand parameters (d. b. h. and height) were measured within circular sample plots subjectively chosen in the most typical spots of the stand (four sample plots per stand). For stem analysis in each stand three dominant trees were felled and crosscut discs at the end of every 1m section of the log and also at the height of 1.3 m were sawn off. The discs were scanned and digital images were measured using the Windendro soft ware. The stems were analyzed by using the Winstem soft ware. Chapman-Richards growth function was used to model the height growth. For the models obtained graphic comparison was made with the models worked out for natural birch stands (Tauriņš, 1968) and those developed for simulating the growth of plantation-cultivated birch in southern Finland (Oikarinen, 1983). The growth in height of analyzed birch plantations substantially exceeds the growth for natural birch stands following the existing yield tables. Thus, the tables for predicting the growth of regular forest stands appear to be unsuitable for modelling the growth of intensively managed stands of birch in plantation cultivation. The data of the given study show that the Oikarinen’s yield tables for birch plantations in southern Finland may be useful for evaluating the growth potential of plantation-cultivated birch on farmlands in Latvia. However, according to our results the growth in height of the most productive birch plantations in Latvia can exceed the site index H50 = 30 indicated for the growth of most productive birch plantations in Finland. It is obvious that we ought to work out growth and yield tables based on the local data for plantation-cultivated forest crops.