World collection of pines and research station

The suitable arboretum plot was found in the northern part of Plzeň, in the Bolevec lakes recreational area, at the edge of a large forested territory, at the elevation of 330-350 m a.s.l., on a slight slope facing the south (49° 47' 21'' N, 13° 23' 9'' E). Since 1965, the arboretum has been housing a meteorological station, incorporated in 1969 into the climatologic network controled by the Czech Institute of Hydrometeorology. Situation of the lower part of the plot (inversion site) and soil type (Permo-Carboneous clay sands and arkoses) with insufficient thermo-accumulation result in high occurence of extreme temperatures. Prevailing vegetation type in this area is acidophilous oak forest.

Climatologic Characteristics of the Sofronka Arboretum

• mean annual precipitations: 525 mm (min. 364 mm – 1991, max. 813 mm – 1965)

• mean annual sunshine: 1.260 hours ( 1.050, 1.570)

• mean annual temperature: 7,3 ^oC (6,4 ^oC, 9,1 ^oC )

• maximum temperature: 40,1 ^oC (1983)

• minimum temperature: - 28,0 ^oC (1985)

• minimum above-ground temperature: - 30,0 ^oC (1985)

• maximum daily precipitations: 146 mm (1965)

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Mean monthly temperatures and precipitations within the last 25 years:

The arboretum plot is characterized by very poor sandy soil with minimum contents of nutrients and minimum amount of humus, climatically arid, with frequent temperature extremes and high occurrence of early and late frosts. These conditions limit the survival of majority of introduced species. The ones that successfully survived local conditions can be grown in most Central-European localities.

Part of the Sofronka research area are parallel comparison plots in Southern and Eastern Bohemia. The Bědovice near Týniště plot in Eastern Bohemia was established on Diluvial sands of the Orlice river terraces. The other one located in Southern Bohemia lies on a very poor stand (”lichenous pinetum ”) within the Mláka u Třeboně forest district. The plots have been utilized for comparison of identical pine provenances in different environments.

Other research areas were founded after 1983, particularly in connection with research of ecological potential of several pine species located in stress conditions of immision – stricken areas of the Ore Mountains (former Klášterec n. O. forest management). Parallel plots were established in Sofronka and Průhonice near Prague.

All plantations were carried out in a manner common in forest management, i.e. in regular distance of 1 x 1m or 2 x 2m. Individual parcels form squares or rectangles containing 100-200 seedlings of each population sample, so that habitus of each sample could be judged not only from the viewpoint of gene-ecological differentiation, but also in terms of production. A great number of population samples enables a study of species variability within its entire range.

Our research approach had been inspired by N. I. Vavilov, a prominent Russian geneticist and phytogeographer, model of the arboretum design was the Placerville, Cal. Arboretum containing 90 pine species, founded by James Eddy in 1926, later renamed as Institute of Forest Genetics.

The entire planting material has been grown in our own Sofronka nursery from seeds acquired from scientist and research workers from various countries thanks to private connections of the founder, or by exchange of seeds with other scientific institutions. The nursery and outplantings have not been exposed to any fertilization not chemical protection. Pruning and thinning of outplantings have not been used either. Cultures are subjected to natural development determined merely by natural selection, as the objective of all research institutions is not production of timber but gaining info about the intrinsic abilities and evolution of the treated species only within natural environmental conditions.

Since the establishment of the arboretum 62 pines species from all corners of the Northern hemisphere have been planted on the area of 22 hectares, which made the collection one of the largest on the Euro-Asian continent. Currently, Sofronka hosts 16 representative clusters of pine species, fruitful and naturally regenerating. Another 14 species have survived in numbers ranging from one to several specimens. The other tested species died out either after the first winter period or in the course of a few years.

In species represented by a great number of origins, i.e. in samples from various parts of their range, the objects of study was biology, life strategies and migration following the retreat of the last glaciation. This way a lot of original information on numerous important natural laws directly connected with methods of their silviculture has been accumulated. Evidence has been gathered that each species evolves in accordance with changes of its own environment. So its own evolution takes place parallelly with the evolution of its range and that way also parallelly with the evolution of its forest ecosystem. From the above findings a new branch of dendrology, called ”evolutionary dendrology” has been derived.

The new approach has given rise to numerous theories and hypotheses on solving the catastrophic events in the Ore Mts. Caused by immissions. Sofronka has become the only forestry working site in our country engaged in forest evolution applied in ecosystem concept of forest treatment, that is in biological silviculture. This approach respects natural properties of plant species, their role in forest succession, and also their genetic adaptations. It excludes all insensitive human interventions into forest ecosystems, which approach is closely related to current concept of forest care.

During its existence, Arboretum Sofronka has been visited by numerous prominent guests from around the globe, and its importance surpasses the Czech borders. That is why it has been included in the international list of the most outstanding botanical gardens and arboreta in the central Reading register (U.K.).