Corresponding author: Jennie Sandström ( jennie.sandstrom@miun.se ) Academic editor: Klaus Henle
© 2020 Jennie Sandström, Mattias Edman, Bengt Gunnar Jonsson.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Sandström J, Edman M, Jonsson BG (2020) Rocky pine forests in the High Coast Region in Sweden: structure, dynamics and history. Nature Conservation 38: 101-130. https://doi.org/10.3897/natureconservation.38.34870
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Almost all forests in Sweden are managed and only a small fraction are considered natural. One exception is low productive forests where, due to their limited economical value, natural dynamics still dominate. One example is the Scots pine (Pinus sylvestris L.) forests occurring on rocky and nutrient-poor hilltops. Although these forests represent a regionally common forest type with a high degree of naturalness, their dynamics, structure and history are poorly known. We investigated the structure, human impact and fire history in eight rocky pine forests in the High Coast Area in eastern Sweden, initially identified as good representatives of this forest type. This was done by sampling and measuring tree sizes, -ages, fire-scarred trees, as well as dead wood volumes and quality along three transects at each site. The structure was diverse with a sparse layer of trees (basal area 9 m2 and 640 trees larger than 10 cm ha-1) in various sizes and ages; 13 trees ha-1 were more than 300 years old. Dead wood (DW), snags and logs in all stages of decay, was present and although the actual DW (pine) volume (4.4 m3 ha-1) and number of units (53 ha-1) was low, the DW share of total wood volume was 18% on average. Dead wood can be present for several centuries after death; we found examples of both snags and logs that had been dead more than 300 years. Frequent fires have occurred, with an average cycle of 40 years between fires. Most fires occurred between 1500-1900 and many of them (13) during the 1600s. However, fires were probably small since most fire years were only represented at one site and often only in one or a few samples. The rocky pine forests in the High Coast Area are representative of undisturbed forests with low human impact, exhibiting old-growth characteristics and are valuable habitats for organisms connected to sun-exposed DW. Management of protected rocky pine forests may well include small-scale restoration fires and the limited DW volumes should be protected.
boreal, coarse woody debris, dendrochronology, fire history, natural forest, pine heath forest, shingle field pine forest
Human influence on boreal forests has varied considerably over time and has dramatically transformed forests in Fennoscandia during the last centuries (
In Sweden, nutrient poor forests with low productivity (< 1 m3 ha-1 yr-1) have been exempted from regular forestry by the Forest Act since the 1970s (
Rocky pine forests can frequently be found in the High Coast Area in the eastern parts of Northern Sweden (Fig.
Study area. Location of the study area in the High Coast Area, Västernorrland County, in the southern boreal zone of central Sweden. Forest structure was investigated at eight sites with rocky pine forest (shown by stars, GB Gropberget, PB Porsmyrberget, VB Vårdkallberget, FA Fanön, GA Gårdberget, SU Southern Ulvön, SK Skuleskogen National Park, HU Hummelvik Nature Reserve)
The low productivity in rocky pine forests in the High Coast Area, together with their inaccessibility, partly explains why many of these forests have escaped extensive human use. These forests mostly have continuity in old-growth characteristics with diverse canopy structure, old trees and dead wood. Hence, these types of forests could function as small refuges for organisms dependent on old-growth conditions. For example, many threatened insects are dependent on dead wood (
To date, very few studies about the structure and history of nutrient-poor, rocky pine forests have been made. This is true not only for Northern Europe but also on a more general, global scale. Some studies have been made on rocky black pine (Pinus nigra Arn.) forests in Spain and even though these forests resemble Scots pine forests in northern rocky areas, they constitute a different forest type with a contrasting historical and landscape context (e.g.
Due to lack of knowledge of the special habitat that rocky, nutrient-poor pine forests constitute and the importance of baseline information on forests with low human impact, we have examined the structure, history of human use and fire history in rocky pine forests in the High Coast Region. We have used a combination of several methods; investigation of the current forest structure, the use of historical records and biological archives (dendrochronology), which allowed us to address the following questions: 1) What characterizes the forest structure and dynamic in rocky pine forests? 2) What is the fire history in the rocky pine forests? 3) To what extent has human use in the past influenced the rocky pine forests?
The study was conducted within a 15 × 75 km area (approximately at 62.5°–63.1°N, 17.9°–18.7°E, DD) in the High Coast Region situated in Västernorrland County located in the southern boreal zone of Sweden (Fig.
In August 2014 we established three band transects at each site, resulting in total in 24 transects. We used band transects since they sample spatial heterogeneity better than circular plots. The studied forests are highly heterogeneous and exposed bedrock occurs mixed with parts of more closed forest. Transects were 10 × 100 m for living trees, but for dead wood sampling we expanded plots to 20 × 100 m to ensure a sufficient number of sampled dead wood units.
To avoid subjectivity in the placement of transects we randomized their placement by using a numbered grid that was placed over a map of the core area at each site and starting points as well as the direction (N, NE, E, SE, S, SW, W or NW) were randomly assigned, but with a minimum distance of 100 m. Within each transect, we recorded × and Y coordinates, species and diameter at breast height (DBH) for all living (stems ≥ 1.3 m high) trees. To describe the spatial distribution pattern, we calculated the distance from each tree to the nearest tree in the × direction and then computed the variance to mean ratio of these distance, i.e. a one-dimensional spatial analysis (
All snags and logs with a maximum diameter of ≥ 10cm and with their base inside a transect were included. We recorded both base- and top diameters, DBH, length and decay class. We used a four class system for decaying wood: 1 Hard dead wood – The volume of the stem consisting of > 90% hard wood, hard surface, very little impact from wood-decaying organisms; 2 Partly decayed wood – 10–25% of the stems’ volume consists of soft wood, a sheath knife goes through the surface but not through the whole sapwood; 3 Decayed wood – 26–75% of the stems volume consists of soft to very soft wood; 4 Substantially decayed wood – 75–100% of the stems volume consists of soft-very soft wood, a sheath knife can penetrate the whole stem, but a hard core can occur (
In autumn (September-November) 2015 we carried out a comprehensive search of each site for fire scars in stumps, living and dead trees. Two persons visited each site one whole day, resulting in approximately 10 search hours at each site covering the core area and the adjacent forest. Every tree with a fire scar was mapped and samples were later collected with a chainsaw. We only took partial sections whenever possible to avoid unnecessary damage. A total of 52 fire-scarred wood samples were collected and dated from eight sites. An additional six samples from dead wood sampling in 2014 and 3 samples from Skuleskogen, sampled in 2010, also had fire scars and were included, resulting in a total of 61 dated samples. More than half of the samples (33) contained scars from repeated fires and the maximum number of fires in one sample was four.
We mounted cores from living trees and cross-sections from dead trees and sanded them with increasingly fine grain size until a fine polish was achieved (down to grain size 400 for all samples and to 600 for some samples) using standard methods (
Very little written information is available that is relevant for the specific historical use of the rocky pine forests. The general history of the region is, however, relatively well documented (e.g.
Old map from one rocky pine site. Map of Vårdkallberget (VB) from 1851, which shows the classification of the nutrient poor rocky pine forests around the hill-top (marked with a triangle) as “general forest land” and the nearby settlement (marked with a plus sign). Two remnants of tar pits are marked with a star. The widest distance from east to west is approximately 2 km.
Scots pine was the dominating tree species in rocky pine forests and stands were very scattered and open; they had very little mineral soil and the ground was interspersed with bare rock and with a vegetation dominated by lichens and dwarf shrubs (Fig.
General description of rocky forests in the High Coast Area. Photos from Fanön (FA), Gårdberget (GA) and S. Ulvön (SU), which show the topography, typical characteristics in rocky pine forests with dispersed trees and dead wood in various sizes in rocky terrain, spruce interspersed at concave surfaces and a fire-scarred pine.
The general stand structure at the eight sites was characterized by sparsely distributed trees with a mean basal area of approximately 9 m2 ha-1 and a density of 640 trees ha-1 on average (Table
General stand structure. Stand structure data for eight rocky Pinus sylvestris dominated forests in the High Coast Region in Northern Sweden. Values are means with SE in parenthesis and based on three band transects per site. Site acronyms as in Figure
Study site | GB | PB | VB | FA | GA | SU | SK | HU |
Dbh (cm), Trees ≥ 1.3 m height | 11.4 (0.6) | 9.8 (1.2) | 11.2 (0.8) | 11.3 (2.8) | 11.1 (1.0) | 12.2 (0.7) | 12.6 (0.3) | 9.3 (0.6) |
Basal area (m2 ha-1), Trees ≥ 1.3 m height | 11.0 (1.9) | 8.8 (0.9) | 10.2 (1.1) | 8.1 (2.4) | 10.2 (1.9) | 6.3 (0.8) | 10.1 (2.1) | 8.8 (0.9) |
Maximum height, Pine (m), average | 10.1 (0.67) | 7.0 (0.27) | 6.6 (0.23) | 8.4 (0.42) | 8.4 (0.45) | 6.2 (0.05) | 8.0 (0.67) | 5.5 (0.25) |
Age, Pine (yr), average ≥ 10 cm DBH | 194 (16) | 157 (10) | 182 (10) | 147 (4) | 157 (15) | 189 (21) | 156 (30) | 158 (24) |
Age, Pine (yr), maximum | 334 | 299 | 372 | 276 | 418 | 403 | 442 | 376 |
No. of living trees ha-1 ≥ 1.3 m height | 647 (94) | 713 (91) | 636 (76) | 563 (39) | 753 (234) | 363 (19) | 593 (118) | 783 (72) |
No. of living trees ha-1 ≥ 10 cm DBH | 280 (70) | 300 (15) | 297 (32) | 300 (60) | 323 (33) | 220 (6) | 303 (61) | 363 (35) |
Spatial distribution (variance to mean ratio, VMR) | 1.9* | 1.1 | 1.2 | 3.3* | 1.2 | 1.7* | 1.7* | 1.0 |
Pine, share (%) | 77 (15) | 95 (3) | 95 (1.4) | 78 (6) | 88 (11) | 92.5 (4) | 94 (1.3) | 98 (2.3) |
Spruce, share (%) | 20 (13) | 4 (2.2) | 5 (1.4) | 4 (0.2) | 9 (7) | 6 (4) | 4 (0.8) | 0 (0) |
Deciduous, share (%) | 3 (1.9) | 1 (1.1) | 0 (0) | 18 (5.8) | 3 (3.4) | 1.5 (1.5) | 2 (1.1) | 2 (2.2) |
Dead wood volume (m3 ha-1) Standing |
4.8 (1.09) | 1.0 (0.49) | 1.7 (0.31) | 1.9 (0.52) | 2.6 (1.30) | 1.9 (0.89) | 1.5 (0.76) | 0.6 (0.21) |
Downed | 3.3 (1.56) | 1.7 (0.29) | 1.6 (0.30) | 3.3 (1.14) | 2.0 (0.15) | 2.0 (0.99) | 4.0 (1.44) | 1.2 (0.52) |
Proportion dead wood, basal area (%) | 18.9 (1.91) | 13.5 (1.69) | 16.7 (2.88) | 21.7 (5.64) | 16.7 (2.64) | 26.1 (6.00) | 20.3 (8.47) | 9.9 (2.61) |
Tree-ring width based growth. The growth of living Scots pines measured as average annual tree-ring width in eight rocky Pinus sylvestris dominated forests in the High Coast Region in Northern Sweden. Values are means and SD from all trees > 10 cm DBH at the sites. Site acronyms as in Figure
Study site | GB | PB | VB | FA | GA | SU | SK | HU |
Growth (mm yr-1) | 0.53 | 0.53 | 0.58 | 0.68 | 0.56 | 0.48 | 0.55 | 0.52 |
SD | 0.21 | 0.20 | 0.29 | 0.38 | 0.26 | 0.25 | 0.24 | 0.19 |
n | 82 | 85 | 84 | 70 | 83 | 59 | 49 | 89 |
The tree diameter distribution was positively skewed with small trees (DBH ≤ 10 cm), dominating and with decreasing frequency of trees with increasing size (Fig.
Categories of tree size and tree age. Summary of the distributions of diameter at breast height (DBH) (a) and age (b) (> 10 cm DBH) for living trees of pine and spruce at the eight sites combined (with mean and SD, n = 8).
All ages are present for pine but really old spruces were lacking. The oldest spruces were a maximum of 275 years old whereas pines were older; approximately 1 tree ha-1 was above 400 years old and 13 trees ha-1 were more than 300 years old. The correlation between age and DBH was generally low (R2 = 0.31 for pine and R2 = 0.11 for spruce) but due to the large sample size significant for both tree species (p < 0.001 and p < 0.05 respectively; Fig.
The amount of dead pine wood was low (average of 4.5 m3 ha-1, range: 2–8, SD = 2.0, n=8) and varied between sites, but both logs and snags were present at all sites (Table
A majority of the DW, 88%, had died during the last 200 years, which corresponds to a DW addition of approximately 2 trees per ha-1 and decade since the beginning of the 1800s. However, there were clear signs that dead wood can remain for several hundred years. The DW did not totally decay even in cases when the logs had been dead more than 300 years and we even found DW that had been dead more than 500 years (Fig.
Number of logs and snags from pine in rocky pine forests at the eight different sites (SE, n = 3) as well as the total mean (SD, n = 8). The abundance of DW is classified as standing (Snag) or horizontal (Log) (a) and also classified in decay stages (b).
Most signs of fire were found in FA where 18 fire years were detected from 12 collected fire-scarred samples (Fig.
Fires in rocky pine forests. The total number of fires at the eight sites and the average from the sites (a). All detected fires are included, regardless of the number of samples the fire was detected in. Total number of fires are also separated into centuries (b) and individual fire years and their occurrence in the number of areas, with fire years occurring at more than one site highlighted (c).
The studied rocky pine forests are characterized by a very open structure. The low density of trees can partly be explained by the scarcity of water and nutrients, as low productivity is generally connected with low basal area and openness (
Although the diameter distribution pattern in our study is descending with size, the pattern is not a typical reversed J-shaped curve, common in many undisturbed forest stands (e.g.
As well as being a sign of naturalness, the heterogeneity and patchiness of tree distribution may also be influenced by an uneven water and nutrient availability for the trees. A tree that grows where the ground consists of bare rock has a very different potential for growth than trees in a concave patch covered with mineral soil, which probably can explain why the trees grew spatially irregularly at four of the sites. The trees generally have a low growth and high variability between trees at all of the sites, indicating also heterogeneity in growth. The high variability in growth between trees clearly contributes to the limited correlation between age and DBH.
The average maximum tree height is generally low in rocky pine forests. The maximum tree height is related to height growth when the tree is young (
The presence of old trees is one of the key features of natural forests (
There are not many deciduous trees in the rocky pine forests and although birches (the most common deciduous species in the area) can tolerate rather dry conditions (
The CWD volume is very low and corresponding to levels in managed forest (
Charcoal and tar production has been common in the area a long time and the CWD quality in rocky pine forests is particularly suitable for tar production. Situated < 1 km from our sampling sites, two old remnants of tar pits have been found at one site, but there were no reported signs of old tar pits at the other seven sites. Hence, we cannot totally rule out the possibility that some CWD has been used for char and/or tar production in the studied area because these activities tend not to leave any visible traces behind.
The most common decay stage in this study is stage 2, which is in line with other pine forests with a high degree of naturalness (
Only two of the sites had signs of past cutting. A low frequency of manmade stumps indicates a high degree of naturalness (
Surprisingly, many fires were detected in the rocky pine forests. There is not much fuel on the ground in the studied rocky pine forests, bare rock is common and trees are scattered. On the other hand, the ground surface easily becomes very dry and vegetated areas are mainly composed of reindeer lichens and dry mosses, which together with scattered dwarf shrubs potentially could carry a ground fire during dry years. Not many fires were detected before 1500. This could partly be a sampling artefact due to the limited number of fire scarred old trees and snags, but different climate and lower human population size cannot be ruled out as explanations for lower fire frequency in the beginning of our time series. Many fires happened during the 1600s, a pattern also observed by others (
There was a population increase after the Black Death plague during the 1600s and several “slash and burn” immigrants from Finland also settled down in northern Sweden during this period, which can be an explanation for more frequent fires. However, most of the ”slash and burn” farmers did not settle down along the coast area where fishing was the main livelihood but rather in the inland areas where the land was more suitable for the ”slash and burn” cultivation technique (
Most fire years were detected only in a few samples, which indicates that the fires in this area and forest type might have been small in size, but not necessarily rare events. A plausible explanation is that there are plenty of small-scale dispersal barriers for fires in this heterogenic landscape. Both bare rock and wet hollows often occur. Moist depressions, swamps and Picea abies patches often do not burn even when nearby dry patches do (
The rocky pine forests in the High Coast Region show a high degree of naturalness and possess many old-growth characteristics, e.g. presence of old trees, diverse structure and although the volume of dead wood is low, it constitutes approximately 18% of the total basal area. The dead wood is diverse with a variety of both snag and log sizes and can be present for a long time due to the slow decay rate. The diverse presence of dead wood, e.g. all decay stages represented, indicates that there is a constant supply of dead wood and that these types of forests have natural features. The high degree of naturalness is also supported by the lack of signs of human use; only a few man-made stumps have been found. All sites but one have clear signs of fires and it seems that the fires have happened quite frequently, but have been small in size. It is likely that these type of forests host a specific biota, evolved and adapted to the specific conditions that rocky pine forests constitute.
We are thankful to all landowners for allowing access to the study sites. We would like to thank for their much appreciated help in the field: Julia Hjalmarsson, Miriam Matheis, Jonas Orelund and Håkan Norberg. Thanks also for the valuable help from the County Administration in Västernorrland, especially to Pekka Bader, Jonas Salmonsson and Johan Uebel. We would also like to thank Prof. Lars Östlund for advice regarding signs of human use and for comments that improved the manuscript. Thanks to Prof. Evan Larsson for help with the master chronology and for comments that improved the manuscript. Many thanks also to Prof. Timo Kuuluvainen for comments that improved the manuscript.
Master chronology, marker years and ring widths
Abbreviations: ++ much bigger than normal; + bigger than normal; - Smaller than normal; -- much smaller than normal. All other years with ring widths are of average size. Bold years means that they are valuable marker years (unusually thin latewood = TH, unusually thick and dark latewood = DL, unusually thick latewood = B).
Year | Ring width | Year | Ring width | Year | Ring width | Year | Ring width | Year | Ring width |
---|---|---|---|---|---|---|---|---|---|
1204 | + | 1329 | + | 1464 | - | 1647 | + | 1874 | -- |
1207 | - | 1331 | + | 1466 | -- | 1648 | + | 1878 | + |
1209 | - | 1332 | + | 1468 | + | 1656 | + | 1881 | -- |
1210 | -- | 1333 | - | 1473 | -- | 1659 | -- | 1886 | + |
1212 | + | 1335 | + | 1476 | + | 1665 | + | 1888 | -- |
1213 | -- | 1339 | - | 1484 | ++ | 1666 | - | 1890 | ++ |
1214 | + | 1347 | - | 1490 | - | 1667 | - | 1891 | - |
1216 | + | 1348 | - | 1491 | + | 1673 | + | 1896 | + |
1218 | - | 1351 | - | 1494 | - | 1686 | + | 1901 | B |
1219 | - | 1353 | + | 1498 | + | 1687 | + | 1902 | -- |
1223 | + | 1357 | + | 1503 | - | 1693 | -- | 1907 | + |
1228 | + | 1358 | + | 1505 | + | 1696 | - | 1911 | - |
1229 | ++ | 1362 | - | 1506 | - | 1698 | - | 1913 | + B |
1230 | + | 1363 | - | 1508 | - | 1713 | - | 1917 | - |
1233 | -- | 1364 | + | 1509 | -- | 1723 | + | 1918 | - |
1234 | -- | 1366 | -- | 1511 | - | 1726 | - | 1922 | + |
1235 | - | 1368 | + | 1512 | + | 1736 | - | 1923 | + |
1239 | - | 1370 | - | 1513 | + | 1742 | - | 1924 | ++ |
1243 | + | 1372 | + | 1514 | - | 1747 | - | 1925 | + |
1244 | ++ | 1373 | + | 1525 | ++ | 1749 | - | 1928 | + |
1247 | + | 1376 | ++ | 1528 | + | 1752 | + | 1929 | + DL |
1252 | ++ | 1381 | + | 1531 | - | 1771 | - | 1933 | -- |
1256 | -- | 1382 | ++ | 1533 | - | 1776 | + | 1934 | - |
1259 | - | 1384 | - | 1535 | + | 1777 | ++ | 1936 | -- |
1261 | + | 1385 | - | 1538 | -- | 1778 | + | 1939 | B |
1262 | + | 1386 | - | 1541 | + | 1781 | - | 1940 | -- |
1263 | - | 1388 | -- | 1543 | - | 1786 | - | 1943 | - |
1265 | -- | 1389 | - | 1547 | + | 1792 | + | 1945 | + |
1267 | ++ | 1391 | - | 1550 | -- | 1793 | + | 1946 | + |
1268 | + | 1394 | + | 1551 | + | 1794 | B | 1947 | + |
1269 | - | 1396 | ++ | 1554 | -- | 1795 | -- | 1953 | + |
1274 | -- | 1398 | - | 1561 | ++ | 1805 | ++ | 1954 | + |
1275 | -- | 1401 | + | 1562 | + | 1806 | + | 1955 | - |
1278 | ++ | 1403 | + | 1568 | -- | 1810 | - | 1957 | ++ DL |
1279 | + | 1404 | ++ | 1572 | -- | 1816 | - | 1959 | -- |
1283 | -- | 1406 | ++ | 1578 | + | 1821 | B | 1960 | -- |
1285 | ++ | 1411 | -- | 1583 | + | 1822 | - | 1961 | - |
1287 | - | 1418 | -- | 1585 | + | 1827 | + | 1962 | + |
1291 | - | 1420 | -- | 1588 | -- | 1828 | + | 1969 | -- |
1293 | - | 1422 | - | 1590 | -- | 1831 | - | 1972 | + |
1296 | + | 1423 | + | 1594 | + | 1832 | -- | 1974 | + |
1297 | - | 1425 | + | 1601 | -- | 1835 | - | 1976 | -- TH |
1298 | + | 1426 | + | 1603 | - | 1840 | + | 1984 | + |
1299 | - | 1427 | + | 1606 | - | 1844 | + | 1987 | + |
1302 | -- | 1428 | + | 1611 | + | 1847 | -- | 1991 | + |
1303 | + | 1430 | - | 1615 | - | 1850 | + | 1992 | -- |
1304 | -- | 1432 | -- | 1623 | + | 1851 | + | 1997 | -- |
1305 | + | 1434 | + | 1625 | + | 1853 | -- | 2000 | + |
1307 | + | 1442 | - | 1626 | + | 1859 | TH | 2002 | - |
1309 | + | 1446 | -- | 1628 | + | 1860 | B | 2004 | + |
1312 | -- | 1451 | + | 1630 | - | 1861 | -- | 2008 | -- |
1319 | + | 1454 | + | 1631 | -- | 1862 | - | 2009 | -- |
1321 | + | 1455 | - | 1633 | - | 1866 | + | 2011 | + B |
1324 | - | 1459 | - | 1638 | + | 1868 | + | 2012 | + |
1325 | -- | 1462 | + | 1642 | - | 1869 | + | 2014 | + |
10 or more samples from 1431 | |||||||||
Total no. of samples | 248 | ||||||||
Age span | 1197–2015 | ||||||||
Total no. of years | 819 | ||||||||
Total no of rings | 56329 | ||||||||
Mean age | 227 | ||||||||
Sensitivity | 0.29 | ||||||||
Series intercorrelation | 0.505 |
Dated samples with fire scars and fire years
Site and Sample ID | Correlation with master | Pith year | Outermost ring year | Age | Year of fire1 | Year of fire2 | Year of fire3 | Year of fire4 | Sample type | Scar direction |
---|---|---|---|---|---|---|---|---|---|---|
Gropberget | ||||||||||
No fire scars detected | ||||||||||
Porsmyrberget | ||||||||||
BrandPO8 | 0,206 | 1467 | 1783 | 316 | 1702 | Dead | ||||
BrandPO12 | 0,248 | 1500 | 1990 | 490 | 1660 | 1693 | 1804 | |||
BrandPO14 | 0,614 | 1773 | 2015 | 242 | 1804 | Living | ||||
Vårdkallberget | ||||||||||
VA1d20 | 0,275 | 1230 | 1505 | 275 | 1268 | 1347 | Dead | |||
VA1d29 | 0,338 | 1671 | 1846 | 175 | 1740 | |||||
BrandVA1 | 0,454 | 1783 | 2013 | 230 | 1804 | Living | E | |||
BrandVA3 | 0,562 | 1580 | 1838 | 126 | 1835 | Dead | N | |||
BrandVA4 | 0,468 | 1661 | 2015 | 354 | 1804 or 1805 | Living | SE | |||
BrandVA5 | 0,56 | 1561 | 1854 | 293 | 1601 | 1631 | 1729 | Dead | W | |
BrandVA7 | 0,606 | 1604 | 1896 | 292 | 1601 | Stump | W | |||
BrandVA10 | 0,323 | 1574 | 1819 | 269 | 1631 | |||||
BrandVA12 | 0,273 | 1731 | 2015 | 284 | 1749 | 1923 | Living | E | ||
Fanön | ||||||||||
BrandFA1 | 0,333 | 1518 | 2015 | 497 | 1781 | Living | S | |||
BrandFA4 | 0,342 | 1494 | 1647 | 153 | 1533 | Stump | ||||
BrandFA5 | 0,163 | 1526 | 1990 | 463 | 1582 | 1640 | 1713 | 1822 | Dead | |
BrandFA6 | 0,58 | 1712 | 2015 | 303 | 1822 | Living | E | |||
BrandFA7 | 0,338 | 1435 | 1863 | 428 | 1527 | 1563 | 1693 | 1819 | Dead | E |
BrandFA8B | 0,492 | 1518 | 2004 | 486 | 1693 | 1798 | 1846 | 1910 | Dead | N |
BrandFA11 | 0,587 | 1484 | 1912 | 428 | 1590 | 1693 | 1827 (1828) | Dead | S, N | |
BrandFA12 | 0,57 | 1702 | 2015 | 313 | 1693 | 1857 | Living | Fire 1 SE, Fire 2 N | ||
BrandFA16 | 0,585 | 1599 | 1855 | 256 | 1689 | 1781 | 1822 | Dead | ||
BrandFA19 | 0,296 | 1407 | 1546 | 136 | 1500 | Dead | SW | |||
BrandFA20 | 0,382 | 1640 | 1972 | 332 | 1640 | 1693 | 1781 | 1846 | Dead | S |
BrandFA22 | 0,343 | 1642 | 1837 | 195 | 1693 | 1781 | Living | S | ||
Gårdberget | ||||||||||
Gamlingen | 0,397 | 1419 | 2014 | 595 | 1563 | 1601 | 1631 | 1713 | Living | |
GA1dStump1A | 0,596 | 1409 | 1736 | 327 | 1438 | 1601 | Dead | |||
GA1dStump1B | 0,663 | 1465 | 1713 | 248 | 1601 | 1713 | ||||
BrandGA4 | 0,456 | 1698 | 2013 | 315 | 1713 | 1826–1827 | Living | NW | ||
BrandGA6 | 0,585 | 1436 | 2000 | 564 | 1516 | 1830 | Living | Fire 1 NW, Fire2 SW | ||
BrandGA10 | 0,306 | 1587 | 1905 | 318 | 1667 | 1830 | Living | NW | ||
BrandGAlst14 | 0,146 | 1773 | 1996 | 223 | 1830 | Dead | SE | |||
BrandGAX1 | 0,391 | 1338 | 1517 | 179 | 1378 | Dead | ||||
BrandGAX2 | 0,53 | 1582 | 1715 | 133 | 1667 | Stump | N | |||
BrandGAX3 | 0,3 | 1447 | 1723 | 276 | 1516 | 1601 or 1602 | 1667 | Dead | W | |
S. Ulvön | ||||||||||
BrandULV1 | 0,3 | 1683 | 1868 | 185 | 1729 | 1864 | Living | E | ||
BrandULV2 | 0,237 | 1745 | 2015 | 270 | 1767 | Living | E | |||
BrandULV3 | 0,484 | 1760 | 1959 | 199 | 1767 | Dead | S | |||
BrandULV4 | 0,28 | 1641 | 1991 | 350 | 1693 | Living | E | |||
BrandULV5 | 0,37 | 1725 | 2015 | 290 | 1767 | Living | NE | |||
BrandULV6 | 0,543 | 1735 | 1817 | 82 | 1794 | Living | W | |||
BrandULV7 | 0,561 | 1749 | 1925 | 176 | 1892 | Stump | S | |||
BrandULV8 | 0,423 | 1587 | 2015 | 428 | 1794 | Living | E | |||
Skule | ||||||||||
BrandSKU2 | 0,305 | 1428 | 2004 | 576 | 1781-1782 | 1840 | Living | W + E | ||
BrandSKU6 | 0,196 | 1662 | 2014 | 352 | 1693 | 1840 | Living | W | ||
BrandSKU9 | 0,396 | 1657 | 2015 | 358 | 1840 | Living | NE | |||
BrandSKUX1 | 0,225 | 1565 | 1826 | 261 | 1631 | Dead | ||||
BrandSKUX2 | 0,212 | 1295 | 1626 | 331 | 1351 | 1415 | 1510 | Dead | W | |
BrandSKUStump | 0,476 | 1796 | 161 | 1652 | 1693 or 1694 | Stump | ||||
BrandSKUStump8 | 0,451 | 1559 | 1853 | 294 | 1554 | 1631 | 1672 | Stump | W | |
T4.126 | 0,617 | 1598 | 1808 | 210 | 1642 | Dead | ||||
T5.95 | 0,338 | 1203 | 1546 | 343 | 1235 | 1263 | 1351 | 1415 | Dead | |
T6.05 | 0,484 | 1421 | 1753 | 332 | 1510 | 1631 | Dead | |||
Hummelvik | ||||||||||
HU1d02A | 0,408 | 1864 | 2006 | 142 | 1872 | Dead | ||||
BrandHU5 | 0,365 | 1546 | 1983 | 437 | 1568 or 1569 | 1668 or 1678 | 1887 | Dead | SE | |
BrandHU8 | 0,451 | 1411 | 1759 | 348 | 1458 | 1514 | 1569 | 1693 | Dead | E |
BrandHU9 | 0,201 | 1648 | 1918 | 270 | 1683 | 1872 | Dead | E | ||
BrandHUlst13 | 0,31 | 1617 | 1937 | 320 | 1721 | Dead | NW | |||
BrandHUStump1 | 0,472 | 1446 | 1725 | 279 | 1514 | 1568 (+- 1 yr) | 1630 | Stump | ||
BrandHUStump2 | 0,503 | 1469 | 1578 | 109 | 1514 | 1630 | Stump |
Fire years and interval
Fire years. The individual fire years at the different sites and the number of samples where fires were detected and the average fire interval at each site (calculated as: number of fires/(last fire year minus first fire year)). GB = Gropberget, PB = Porsmyrberget, VB = Vårdkallberget, FA = Fanön, GA = Gårdberget, SU = Southern Ulvön, SK = Skuleskogen National Park, HU = Hummelvik Nature Reserve. Gropberget (GR) did not have any signs of fire.
GB | PB | VB | FA | GA | SU | SK | HU | |||||||
No signs of fires | Fire year | n | Fire year | n | Fire year | n | Fire year | n | Fire year | n | Fire year | n | Fire year |
n
|
1660 ±2 yr | 1 | 1268 | 1 | 1500 | 1 | 1378 ±2 yr | 1 | 1693 | 1 | 1235 | 1 | 1514 | 3 | |
1693 | 1 | 1347 | 1 | 1527 | 1 | 1438 | 1 | 1729 | 1 | 1263 | 1 | 1569 | 3 | |
1702 | 1 | 1601 | 2 | 1533 | 1 | 1516 | 2 | 1767 | 3 | 1351 | 2 | 1630 | 2 | |
1804 | 2 | 1631 | 2 | 1563 | 1 | 1563 | 1 | 1794 | 2 | 1415 | 2 | 1668 | 1 | |
1729 | 1 | 1582 | 1 | 1601 | 4 | 1864 | 1 | 1510 | 2 | 1683 | 1 | |||
1740 | 1 | 1590 | 1 | 1631 | 1 | 1892 | 1 | 1554 | 1 | 1693 | 1 | |||
1749 | 1 | 1640 | 2 | 1667 | 3 | 1631 | 3 | 1721 | 1 | |||||
1804 | 3 | 1689 | 1 | 1713 | 4 | 1642 | 1 | 1872 | 2 | |||||
1835 | 1 | 1693 | 6 | 1830 | 4 | 1652 | 1 | 1887 | 1 | |||||
1923 | 1 | 1713 | 1 | 1672 | 1 | |||||||||
1781 | 4 | 1693 | 1 | |||||||||||
1798 | 1 | 1781 | 1 | |||||||||||
1819 | 1 | 1840 | 3 | |||||||||||
1822 | 3 | |||||||||||||
1827 | 1 | |||||||||||||
1846 | 2 | |||||||||||||
1857 | 1 | |||||||||||||
Average fire interval (yr) | 36 | 65.5 | 20.5 | 50 | 33 | 46.5 | 41.5 |
Fire years and ring widths
Abbreviations: ++, much bigger than normal; +, bigger than normal; aver, average size; -, smaller than normal; --, much smaller than normal. GB = Gropberget, PB = Porsmyrberget, VB = Vårdkallberget, FA = Fanön, GA = Gårdberget, SU = Southern Ulvön, SK = Skuleskogen National Park, HU = Hummelvik Nature Reserve.
Fire years | Site (and number of samples) | Ring width in master |
---|---|---|
1235 | SK (1) | - |
1263 | SK (1) | - |
1268 | VB (1) | + |
1347 | VB (1) | - |
1351 | SK (1+1) | - |
1378+- 2 yr | GA (1) | aver |
1415 | SK (2) | aver |
1438 | GA (1) | - |
1500 | FA (1) | aver |
1510 | SK (2) | - |
1514 | HU (3) | - |
1516 | GA (2) | aver |
1527 | FA (1) | aver |
1533 | FA (1) | - |
1554 | SK (1) | -- |
1563 | FA (1), GA (1) | aver |
1569 | HU (3) | aver |
1582 | FA (1) | aver |
1590 | FA (1) | -- |
1601 | VB (2), GA (4) | -- |
1630 | HU (2) | - |
1631 | VB (2), GA (1), SK (3) | -- |
1640 | FA (2) | - |
1642 | SK (1) | - |
1652 | SK (1) | - |
1660 ± 2 yr | PB (1) | aver (1659 --) |
1667 | GA (3) | - |
1668/1669 | HU (1) | aver |
1672 | SK (1) | aver |
1683 | HU (1) | aver |
1689 | FA (1) | aver |
1693 | FA (6), SU (1), SK (2), HU (1), PB (1) | -- |
1702 | PB (1) | aver |
1713 | GA (4), (FA (1) | - |
1721 | HU (1) | aver |
1729 | VB (1), SU (1) | - |
1740 | VB (1) | - |
1749 | VB (1) | - |
1767 | SU (3) | aver |
1781 | FA (4), SK (1) | - |
1794 | SU (2) | aver |
1798 | FA (1) | - |
1804 | VB (3), PB (2) | aver |
1819 | FA (1) | aver |
1822 | FA (3) | - |
1827/1828 | FA (1) | + |
1830 | GA (4) | - |
1835 | VB (1) | - |
1840 | SK (3) | + |
1846 | FA (2) | aver |
1857 | FA (1) | aver |
1864 | SU (1) | aver |
1872 | HU (2) | aver |
1887 | HU (1) | aver |
1892 | SU (1) | aver |
1910 | FA (1) | aver |
1923 | VB (1) | + |