Publication output
In this study, 1018 publications published between 1980 and 2022 were downloaded on WoS. The number of identified publications and citations were showed in Fig. 1 for the years. It was understood that the increasing trend in the number of citations was faster than the increasing trend in the number of publications. However, numbers of citation and papers were analyzed based on Wos in this study. The papers could be published or cited national journals and international/national proceedings or other scopus than seed orchards such as forest genetics. The present study did not focus on national and other international databases.
The 1018 articles have been cited a total of 13288 times. The average of number of citation was 13.05 per publication. The H-Index for the publication set was 48, indicating that 48 publications were cited at least 48 times up to searching date.
The most prolific contributors
The most prolific contributors section provided an overview of the most productive and influential contributors to the field. The most prolific five authors were listed in Table 1 according to WoS database.
Table 1
Top ten prolific authors with centrality values.
Counted | Centrality | Year | Prolific Authors |
58 | 0.02 | 1984 | Elkassaby, YA |
40 | 0.03 | 1981 | Lindgren, D |
15 | 0.01 | 2000 | Kang, KS |
9 | 0.01 | 1980 | Adams, WT |
8 | 0.02 | 1993 | Nikkanen, T |
8 | 0.01 | 1991 | Burczyk, J |
7 | 0.00 | 2012 | Lstiburek, M |
6 | 0.00 | 1985 | Skroppa, T |
6 | 0.00 | 2007 | Almqvist, C |
6 | 0.00 | 1995 | Owens, JN |
El-Kassaby was the most prolific contributor author by 58 publications in this field since 1984. The citation burst mean of authors who changed in literature with a sudden frequency during the period was given in Table 2. However, H. Liesebach from Germany was the most productive author by five papers in current trend of 2021.
The modularity value divided into nearly perfect clusters, and the mean of Silhouette value was 0.9662, suggested that the homogeneity of these clusters was sufficient. 1018 academic works were divided into 7 clusters (Table 2).
Figure 2a showed the most massive clusters. In the Cluster analysis, cluster was given according to silhouette scores started from 0. Clusters with low silhouette scores could not been shown in Table 3 and Fig. 2b.
Table 3
Cluster summary of author analysis.
Cluster ID | Size | Silhouette | Mean Year |
#0 douglas-fir seed orchard | 36 | 0.918 | 2002 |
#1 reproductive phenology | 21 | 0.997 | 1994 |
#3 individual ramet | 11 | 0.989 | 1989 |
#10 scale insect | 6 | 0.986 | 1987 |
#15 picea-abies | 5 | 1.000 | 1994 |
#16 wood production | 5 | 0.988 | 1998 |
#33 level | 4 | 0.986 | 1980 |
Clusters, 0, 1 and 3 were the largest by more than 10 members. The most active author El-kassaby was in cluster 1 (Table 3, Fig. 2). The change of clusters over time could be understood from the timeline view. According to the cluster analysis (Table 3, Fig. 2), the field of “reproductive phenology” has been studied by seed orchard or related researchers (Fig. 3). “Reproductive phenology” was one of the basic steps in establishment and managements of seed orchards. It was effective from selection to clone or families to seed harvesting.
Analysis of the countries
The network consists of 76 nodes in which each node represented countries and 206 linkages. The density of the network was 0.0723 (Table 4). Countries Network structures of visualization were showed in Fig. 4.
Table 4
Displayed the most active countries.
Counted | Centrality | Year | Countries |
186 | 0.23 | 1980 | Canada |
140 | 0.24 | 1982 | USA |
115 | 0.45 | 1986 | Sweden |
69 | 0.32 | 1986 | Australia |
60 | 0.16 | 1994 | China |
56 | 0.16 | 1988 | Finland |
38 | 0.01 | 2000 | Japan |
31 | 0.15 | 1992 | France |
30 | 0.00 | 1998 | India |
29 | 0.03 | 1998 | South Korea |
29 | 0.00 | 1986 | Poland |
24 | 0.04 | 2002 | Brazil |
24 | 0.20 | 1991 | Germany |
24 | 0.14 | 1996 | Denmark |
23 | 0.03 | 2002 | Turkey |
As seen from Table 4, the most contributors were from Canada by 186 articles, and then USA by 140 and Sweden by 115 articles. Number of articles could be also related to years and published language. International bibliometric databases were generally focused on English papers. This gave advantage to countries whose mother tongue was English.
Many materials were not published in English. Some of this would come into the database if published in USA but similar material in Sweden did not reach the database. This hit was against the forest and seed orchard rich countries such as Russia and China and many others smaller. It favored forest and seed orchard rich USA and Canada. For example, Sweden was rather English oriented and was slightly favored compared to e.g. France and Brazil. It could be said that Sweden had the highest centrality value (0.45) meant that linkage or also called base/key country for other countries. Australia, Canada, USA, China, France, Finland and Denmark were also linkage countries because of higher centrality value than 0.1 (Table 4, Fig. 4).
The strongest citation bursts of top twelve countries were given in Table 5. It was interesting that China, Brazil, and Germany had higher number of citations than expected recently. It showed that the countries mainly focused on seed orchard studies in recent years.
Modularity Q reached 0.4516. It indicated that the structure was reasonable sufficient. It meant that clusters were partially nested and not fully separated. The silhouette score showed the result validation reached 0.8706 > 0.4. Studies of the countries had mainly five clusters (Table 6, Fig. 5).
Table 6
Summary studies of clusters in countries.
Cluster ID | Size | Silhouette | Mean Year |
#0 fertility variation | 19 | 0.782 | 1998 |
#1 genetic variation | 17 | 0.947 | 2004 |
#2 south africa | 14 | 0.857 | 1998 |
#3 pinus sylvestris | 13 | 0.932 | 2005 |
#4 supporting domestication | 6 | 0.832 | 2007 |
The results of Table 6 and Fig. 5 indicated that “genetic variation” and “Pinus sylvestris” were activated/refreshed by the scientists and researchers of the countries.
Analysis of keywords
The network had 714 nodes with representing of each node a keyword, and 3962 linkages. The word “seed orchard” occurred in 234 articles followed by “growth” in 136 articles (Table 7). Network map for trends based on keywords analysis were presented in Fig. 6.
Table 7
List of top 21 key words with centrality.
Counted | Centrality | Year | Keywords | Counted | Centrality | Year | Keywords |
234 | 0.37 | 1986 | seed orchard | 30 | 0.05 | 1994 | scots pine |
136 | 0.21 | 1991 | growth | 29 | 0.08 | 1989 | picea abies |
68 | 0.13 | 1991 | population | 28 | 0.05 | 1990 | pollination |
52 | 0.08 | 1991 | douglas fir | 28 | 0.08 | 1999 | tree improvement |
51 | 0.06 | 1996 | genetic diversity | 26 | 0.02 | 1990 | pollen contamination |
48 | 0.12 | 1995 | genetic gain | 25 | 0.01 | 2002 | number |
44 | 0.07 | 1989 | selection | 24 | 0.03 | 1993 | clonal seed orchard |
43 | 0.07 | 1986 | pinus sylvestris | 24 | 0.02 | 1992 | tree |
42 | 0.07 | 1993 | genetic variation | 22 | 0.06 | 1993 | norway spruce |
40 | 0.05 | 1990 | mating system | 22 | 0.01 | 1999 | fertility variation |
39 | 0.12 | 1991 | loblolly pine | 21 | 0.03 | 1991 | cone |
38 | 0.08 | 1991 | diversity | 20 | 0.02 | 2008 | gene flow |
31 | 0.02 | 2001 | relatedness | - | - | - | - |
Actually, “key words” of the papers were mirrors of the researches. They were also guides in search literature, and inventory and classification of early studies, and direction of future studies. However, Authors generally have avoided the extraction from title to keyword. Most of the national papers were published in mother tongue with English abstract and keywords, while Bibliometric analysis focused in English and WoS papers. These were getting importance of keywords.
The strongest citation bursts of the top 21 key words were given in Table 8. Keywords of “climate change”, “management” and “growth” were active studied areas in seed orchards recently. Modularity Q reached 0.4251 by 0.7546 of silhouette score. Studies of the keywords countries had mainly five clusters (Fig. 7).
“Matting pattern” “Swedish forestry”, “fertility variation”, “Hymenoscyphus fraxineus”, “threatened pacific sandalwood” and “outbreeding depression” together with others seemed active keywords according to the time line and clusters (Fig. 7).
Data analysis by reference
There were 23275 cited references in 1018 studies on seed orchards. The network shown in Fig. 8 had a total of 1358 nodes and 4726 linkages. The top 20 articles according to their citation frequency were listed in Table 9.
Table 9
List of top ten cited reference with centrality.
# | Counted | Centrality | Year | Cited References |
1 | 23 | 0.11 | 1998 | Lindgren D, 1998, CAN J FOREST RES, V28, P276, DOI 10.1139/cjfr-28-2-276 |
2 | 22 | 0.07 | 2007 | White TL, 2007 FOREST GENETICS, V0, P0 |
3 | 22 | 0.22 | 2004 | Moriguchi Y, 2004, CAN J FOREST RES, V34, P1683, DOI 10.1139/X04-029 |
4 | 19 | 0.11 | 1984 | El-Kassaby YA, 1984, SILVAE GENET, V33, P120 |
5 | 19 | 0.04 | 2007 | Kalinowski ST, 2007, MOL ECOL, V16, P1099, DOI 10.1111/j.1365-294X.2007.03089.x |
6 | 18 | 0.23 | 1999 | Kang KS, 1999, FOREST GENETICS, V6, P191 |
7 | 16 | 0.12 | 2012 | Funda T, 2012, P21, V0, P0, DOI 10.1079/PAVSNNR20127013 |
8 | 15 | 0.08 | 1985 | Ritland K, 1985, THEOR APPL GENET, V71, P375, DOI 10.1007/BF00251176 |
9 | 15 | 0.05 | 2001 | Kang KS, 2001, NEW FOREST, V21, P17, DOI 10.1023/A:1010785222169 |
10 | 15 | 0.10 | 2003 | Kang KS, 2003, FORESTRY, V76, P329, DOI 10.1093/forestry/76.3.329 |
In Table 9, the most representative references with respect to burst strength, burst duration, and burst time were illustrated based on the results of clustering by beginning time of the burst marked in bold (Fig. 8). According to the analysis, paper of Lindgren and Mullin (1998) had the most cited references (Table 9), while paper of Funda and El-Kassaby (2012) had been actively cited references in recent years (Table 10). Additionally, Moriguchi Y’s article had also an intense citation burst recently by “Gene flow and pollen contamination in a seed orchard of Cryptomeria japonica D. Don” investigated using six microsatellite markers in their paper (Moriguch et al. 2004).
The network shown in Fig. 8a had a total of 1358 nodes and 4726 linkages. The modularity value was 0.868 meant that the network is divided into separate clusters. The mean silhouette value was 0.9603 suggested that the homogeneity of these clusters was suitable. Figure 8b shows the most massive clusters.