Geographic determinants of spatial patterns of Quercus robur forest stands in Latvia: biophysical conditions and past management


Most of the forest area dominated by pedunculate oak (Quercus robur L.) in Latvia was lost to arable land several centuries ago and the remnant patches of Q. robur stands are small and spatially scattered. We hypothesized that a large part of the present Q. robur stands in the Eastern Baltic area of the hemiboreal forest zone developed around the past manor houses in the period of social and political turmoil and subsequent agricultural land abandonment. Our aim was to determine the relationship of Q. robur stand occurrence with soil properties, climatic conditions and proximity to past manor houses. Our study area was the entire territory of Latvia (64.589 km2), divided into 16 landscape regions. We used the State Forest Inventory database to filter out all stands dominated by Q. robur (n=3746). Spatial aggregation of the stands was tested by multi-distance spatial clustering analysis (Ripley’s K method). Mean stand area and Euclidean nearest-neighbour distance for stands were calculated for landscape regions. Binary logistic regression with the calculation of autocovariates showed that winter temperature, soil texture, carbonate concentration and distance to closest manor house were the independent factors significantly (p<0.01) related to the probability of occurrence of Q. robur stands. The results showed that Q. robur is spatially clustered, i.e., significantly different from a random distribution (p<0.05). Higher densities of stands occurred in landscape regions with milder maritime climatic conditions. The largest proportional area of stands established between 1885 and 1914 in the period when peasants gained title to lands and manor lords lost control over their land holdings. In addition, in the landscape regions of Rietumkursa, Austrumkursa and Rietumzemgale, the abundance of Q. robur stands coincided with high densities of past manor houses. Thus, establishment of the Q. robur stands likely responded to suitable conditions (open canopy) made available for tree colonization during the land reform occurred 100 years ago. Our results suggest that priority for conservation should be given to spatial aggregations of stands with high connectivity and on richer soils in more maritime conditions.

iForest - Biogeosciences and Forestry