Academic journal article Estonian Journal of Ecology

Naturalness of Quercus Robur Stands in Latvia, Estimated by Structure, Species, and Processes/ Hariliku Tamme Quercus Robur Puistute Looduslikkus Latis, Hinnatuna Struktuuri, Liikide Ja Arengu Jargi

Academic journal article Estonian Journal of Ecology

Naturalness of Quercus Robur Stands in Latvia, Estimated by Structure, Species, and Processes/ Hariliku Tamme Quercus Robur Puistute Looduslikkus Latis, Hinnatuna Struktuuri, Liikide Ja Arengu Jargi

Article excerpt

INTRODUCTION

Due to intensive forest harvest and exploitation for agriculture, all Western European forests of the temperate zone are to a great extent disturbed by man (Peterken, 1996). Very few fragments of the past virgin forest remain (Jones, 1945), causing a deficiency of reference areas to study structure and disturbance dynamics. In northern European forests in the temperate--boreal transition zone, human activities were responsible for a decline of broad-leaved forests and expansion of spruce (Bradshaw & Hannon, 1992; Lindbladh et al., 2000; Niklasson et al., 2002), particularly in the past 300 years (Lindbladh & Foster, 2010). The largest old-growth broad-leaved (Quercus robur, Fraxinus excelsior, Ulmus spp., Tilia cordata, Acer spp.) woodland in lowland Europe is the Bialowieza Primeval Forest on the Polish and Belarusian border (Falinski, 1986). However, even there the territory suffered from felling and overgrazing due to use as a hunting reserve in the late 1800s-1900s (Falinski, 1988), which caused an expansion of Picea abies (Mitchell & Cole, 1998).

The coverage of broad-leaved species in Latvia reached a maximum in the Atlantic period about 6000 years ago (Zunde, 1999). Since that time, climate cooling and human impact caused a decline of broad-leaved forest in Latvia, particularly in the 17th and 18th centuries to supply growing export of Q. robur for ship-building and slash and burn clearage of forest by peasants (Dumpe, 1999; Liepina, 1999). In northern Latvia, the total forest area dropped from 59.2% in 1710 to 19.4% in 1914 (Vasilevskis, 2007). In 1924, broad-leaved forest occupied only 2.3 thousand ha (0.2% of forests) in Latvia (Matiss, 1987). However, by 2008, the forest area had increased to 53%, of which broad-leaved forests contributed 1.1% (data from the Latvian State Forest Register 2009). The Q. robur stands in Latvia are presently mostly small (< 2 ha) and highly fragmented (Zunde, 1999).

It has been argued that the Q. robur primeval forest in lowland Europe formed an open landscape, due to grazing by large herbivores (Vera, 2000). According to this view, wooded meadows and pastures in the rural landscape today might resemble the forests of pre-industrial forestry. In contradiction to the grazing hypothesis, some palaeoecological evidence suggests that the natural Q. robur woodland that existed prior to human settlement formed a closed canopy, with or without grazers (Mitchell, 2005). Thus, knowing that regeneration of Q. robur is limited by light availability caused by competition with vegetation (Humphrey & Swaine, 1997; Kussner, 2003; Harmer & Morgan, 2007), natural disturbances such as fire, wind, and water-logging probably created gaps favouring regeneration (Bradshaw et al., 2003; Bradshaw & Hannon, 2004; Whitehouse & Smith, 2004). Regeneration of Q. robur and other broad-leaved species can be successful in floodplains (Kussner, 2003; Dobrowolska, 2008) and under conifer canopies, provided sufficiently lit conditions free from competitive vegetation (Gotmark et al., 2005; Dobrowolska, 2006; Goris et al., 2007). In Poland (Falinski, 1986) and Russia (Nfesterovs, 1954), Q. robur mostly occurs in mixed woods with a closed canopy, and the tree species in mixed stands with Q. robur differ depending on the growth conditions. The controversy regarding whether Q. robur woods naturally occurred as open of closed woodland may never be fully resolved, but in Eastern Europe there is no evidence that an open landscape with oak existed before human settlement.

In Latvia, open parkland landscapes were created by slash and burn agriculture, whereby scattered Q. robur trees survived within tilled land, hayfields, and pastures (Dumpe, 1999). Regeneration of Q. robur on agricultural land can be successful in patches of unpalatable or spiny vegetation unfavoured by large herbivores, which can provide an explanation for long-term persistence of Q. …

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