An Overview on Spruce Forests in China

The genus Picea A. Dietrich (spruce), which is a relative isolated group under evolution, belongs to Pinaceae family (Ran et al., 2006; Bobrow, 1970; Buchholz, 1929, 1931; Alvin, 1980; Mikkola, 1969). It includes 28–56 species depending on different systems of classification (Farjon, 1990; Ledig et al., 2004), most of which are in Eastern Asia, while many researchers thought that there were about 40 species in Picea genus and were only found in the north hemisphere (Budantsey, 1992, 1994; Wolfe, 1975, 1978; Tiffney and Manchester, 2001). The distribution range is from 21oN (Huanglian Mountains of Vietnam) to 70oN (Far Eastern area of Russia) (Fig. 1). Spruce forests are the main dominant vegetation in alpine coniferous forest in subtropical zone and temperate zone, and they are only found in alpine area, subalpine area and plateau from 21oN to 46oN (Li, 1995). In cold temperate zone and its adjacent regions (47oN to 57oN), spruce forests are the zonal vegetation types in boreal coniferous forest. From 57oN to 70oN, spruce forests transform from horizontal (latitudinal) zonal distribution to vertical (altitudinal) zonal distribution and from continuous distribution to discontinuous distribution.


Introduction
The genus Picea A. Dietrich (spruce), which is a relative isolated group under evolution, belongs to Pinaceae family (Ran et al., 2006;Bobrow, 1970;Buchholz, 1929Buchholz, , 1931Alvin, 1980;Mikkola, 1969). It includes 28-56 species depending on different systems of classification (Farjón, 1990;Ledig et al., 2004), most of which are in Eastern Asia, while many researchers thought that there were about 40 species in Picea genus and were only found in the north hemisphere (Budantsey, 1992(Budantsey, , 1994Wolfe, 1975Wolfe, , 1978Tiffney and Manchester, 2001). The distribution range is from 21 o N (Huanglian Mountains of Vietnam) to 70 o N (Far Eastern area of Russia) (Fig. 1). Spruce forests are the main dominant vegetation in alpine coniferous forest in subtropical zone and temperate zone, and they are only found in alpine area, subalpine area and plateau from 21 o N to 46 o N (Li, 1995). In cold temperate zone and its adjacent regions (47 o N to 57 o N), spruce forests are the zonal vegetation types in boreal coniferous forest. From 57 o N to 70 o N, spruce forests transform from horizontal (latitudinal) zonal distribution to vertical (altitudinal) zonal distribution and from continuous distribution to discontinuous distribution.  Li, 1995, Lű et al., 2004, and McKenna, 1975 (1-7. Fossil localities: 1. Eocene; 2, 3. Oligocene; 4, 5. Miocene; 6, 7. Pliocene; 8. Modern distribution) In China, the distribution range of spruce forests is very large, from Daxinganling Mountains (north) to Gaoligong Mountains (south), and Tianshan Mountains (west) to Central Mountains of Taiwan Province (east) (Fang, 1995(Fang, , 1996Fang and Liu, 1998). The spruce forests are found as long as there are site conditions of cold-temperate moisture types. In China the spruce forests belong to vertical zonal distribution with 17 species and 8 variations of Picea genus and take more than 40% of the species in the world. Furthermore, the almost all of the species are endemic in China, except for those in Daxinganling Mountains which belongs to East Siberian area and Arertai Mountains (belonging to West Siberian area). In China, spruce forests are distributed in Northeast, North, Northwest and Southwest.
In the mountains of Daxinganling, Xiaoxinganling and Changbai of Northeast China, P. koraiensis Nakai, P. jezoensis var. microsperma (Lindl. Cheng et L. K. Fu) and P. jezoensis var. komarovii (V. Vassil.) Cheng et L. K. Fu are the edificators of upland dark coniferous forests, which are extended partition of dark coniferous forests of Far East Area of Russia (Editorial Committee of Forest of China, 1997;Li, 1980;Li and Zhou, 1979 (Kuan, 1981;Sun, 2002;Wu et al., 1995). P. spinulosa (Griff.) A. Henry and P. smithiana (Wall.) Boiss. are found in moist area in Himalayas in south Tibet Autonomous Region, and they always form small pure forest or mixed forest (Kuan, 1981).
P. morrisonicola Hayata forms the dominant pure coniferous forest in Central Mountains in Taiwan, which is the only subalpine coniferous forest of the east China in subtropical zone (Liu, 1971).
Monophyly of Picea has never been debated (Wright, 1955;Prager et al., 1976;Frankis, 1988;Price, 1989;Sigurgeirsson and Szmidt, 1993), but infrageneric classification of the genus remains quite controversial (Liu, 1982;Schmidt, 1989;Farjón, 1990Farjón, , 2001Fu et al., 1999), owing to morphological convergence and parallelism (Wright, 1955), and high interspecific crossability (Ogilvie and von RudloV, 1968;Manley, 1972;Gorden, 1976;Fowler, 1983Fowler, , 1987Perron et al., 2000). In addition, little is known about phylogenetic relationships of most species, especially the geographically restricted species growing in the montane regions of southwest China (LePage, 2001). Moreover, the origin and biogeography of Picea have drawn great interest from both geologists and biologists (Wright, 1955;Aldén, 1987;Page and Hollands, 1987;LePage, 2001LePage, , 2003, but they are still far from being resolved. Spruce species are fine trees for lumbering, so researches on spruce were conducted very early in China (Editorial Committee of Vegetation of China, 1980). However, basic characteristics, flora, distribution types, and evolution relationship of the spruce species in China, and the relationship among spuce in China and abroad need more concern. There are many data about the topics above, but they are always scattered.
The aim of this study was (1) to summarize systematically the researches on spruce in China, and (2) to try to clarify the relationship among Chinese spruces, and among spruce in China and abroad.  , 1980;Zhou, 1988;Chou, 1986Chou, , 1991.

Flora characters of spruce forests in China
In different districts in China, the floristic and geographical elements of spruce forests are complex (Table 2) (Wu, 1991;Wang, 1992Wang, , 2000

Structure variation of chromosomes and evolution hierarchy
We took arm ratio as x-coordinate, and chromosome length ratio as y-coordinate. All Picea spp. were drawn as shown in (Fig. 2a, b). The change range of arm ratio is from 1.23 to 1.50, and most of species (22) are from 1.25 to 1.35. The change range of chromosome length ratio is from 1.60 to 2.12, and only 14 species are from 1.75 to 1.85 (Wang et al., 1990).
Structure variation of chromosomes of Chinese Picea spp. (Fig. 2a) is more obvious than Picea spp. found in other parts of the world (Fig. 2b).  Table 5) Some researchers (Wang et al., 1990) thought a coefficient k (Karyotypic asymmetry in both average arm ratio and ratio of longest / shortest of chromosomes) was a good index for expressing the evolution hierarchy of certain species and genus.
Where A i -average arm ratio of species (or genus), L i -chromosome length ratio of species (or genus), A max -maximum arm ratio in genus (or family), L max -maximum chromosome length ratio in genus (or family).
According to value of k of Picea spp., the evolution hierarchy of 17 Picea spp. in China (Fig.  3) and 15 Picea spp. abroad (Fig. 4) were determined.

Section grouping
In taxonomy, Picea genus in China can be divided into three sections according to their karyotypes and the coefficient k. These sections are Sect. Casicta, Sect. Omirica, and Sect. Picea. Furthermore, we can determine their evolution hierarchy as in (Fig. 5) (Ran et al., 2006;Wu, 1991).

Distribution range and niches of Picea spp. in China
The data of some Picea species (including P. koraiensis, P. jezoensis var. microsperma, P. jezoensis var. komarovii, and P. mongolica) are based on our previous field investigation. And we conducted the interpretation of TM image of some pivotal regions (including Tianshan Mountains in Xinjiang Weiwuer Autonomous Region, Hengduan Mountians in Sichuan Province and Tibet Autonomous Region, Qilian Mountains in Shaanxi Province and Gansu Province) Yang et al., 1994; Editorial Committee of Forest of China, 1997;Cen, 1996).

Grouping of distribution types
Principal Components Analysis (PCA) was performed to compress the autocorrelated metric environmental variables by creating a reduced number of compounds (principal components) that explain the observed variation of distribution type (Jolliffe, 2002; Norusšis, www.intechopen.com  1990). Only compounds that accounted for more variation than any individual variable (eigenvalue > 1) were used in the final model. A 'varimax' rotation was applied to the reserved components to redistribute the variance among factors to obtain factor scores. Fuzzy clustering was then applied to the sample scores from the PCA ordination to identify the main distribution types. The fuzzy clustering specification used 3-6 clusters, a fixed fuzziness criterion of 2 and a convergence coefficient of 0.001. Then we obtained three categories of distribution types.

The origin of Picea genus
Severe climatic oscillations associated with glacial cycles in the arctic during the late Tertiary and throughout the Quaternary era resulted in great changes in species distribution and population structure (Böhle et al., 1996;Qian and Ricklefs, 2000;Petit et al., 2003;Hewitt, 2004;Thomas, 1965). Meanwhile, descendent sea level created land connections for intercontinental exchanges of flora and fauna, especially boreal species (Tiffney, 1985a, b;Wen, 1999;Xiang et al., 2005). Spruce, as a kind of gymnosperm, is an archaic group under evolution, although pioneer reliable fossils of Picea genus are not available so early in Oligocene (Miller, 1975(Miller, , 1977. Later in Oligocene and Miocene, fossils of Picea genus appear widely in Europe, North America and Japan (Page, 1988;Axelord, 1986Axelord, , 1976Ferguson, 1967). According to the fossils and modern distribution range, it can be concluded that ancestor of Picea genus might be a branch differentiate from Pinaceae during evolvement metaphase. But until Tertiary, ancient Picea spp. became the same as modern Picea spp.
Where does Picea genus originate from? There are many hypotheses in botanical science. Wright (1955) (Miller, 1988;Hopkins et al., 1994). Wu (1991) thought the distribution center of Picea spp. was in East Asia, particularly in Hengduan Mountains according to his research findings. Li (1995) reported that in Hengduan Mountains, Picea spp. belonged to almost all of the subgroups except for an obvious evolutional subgroup -P. pungens subgroup originated from Rocky Range. In Hengduan Mountains in western Sichuan (Sun, 2002), northern Yunnan and eastern Tibet, there are more interspecific differentiations in Picea genus. Some species from Sect. Picea (P. asperata, P. jezoensis, and so on), Sect. Casicta (P. likiangensis, P. likiangensis var. balfouriana, and so on) and Sect. Omirica (P. brachytyla, P. brachytyla var. complanata, and so on) are found there. For example, in relatively ancient subgroup -Sect. Picea, there are 30 species and 2 variations in Sect. Picea, and 13 species and 1 variation are found here, which take 43.3% of the total species of Sect. Picea. So many researchers thought Hengduan Mountain was the original center of Picea genus, at least it was one of the most important differentiated centers.
It proved has been proven according to analysis on fossils and pollens of Picea genus (Jain, 1976;Miller, 1972Miller, , 1974Miller, , 1985Schall and Pianka, 1978;Shi et al., 1998) that during the ice age in Quaternary, the forest composed of Picea spp. and Abies spp. and the two species were distributed widely in the mountains and plains of Southwest China, Northwest China, North China, East China, and Taiwan. During that time, cold-temperate coniferous forests have wider distribution range than present. It's well known that glacier activity was active in Quaternary, and vegetation zone moved in both horizontal and vertical directions. With the advance and retreat of ice sheets, species went extinct over large parts of their range, and some populations were dispersed to new locations or survived in refugia and then expanded again (Hewitt, 2000;Stewart and Lister, 2001;Abbott et al., 2000). This repeated process would on the one hand stimulate adaptation and allopatric speciation (Hewitt, 2004), whereas, on the other, provide the opportunities for hybridization between recolonized populations, even reproductively unisolated species (Abbott and Brochmann, 2003). During interglacial time, because of climate warming, some cold-temperate coniferous forests retreated to north, and others moved towards the mountains when the glacier melted, which formed the modern distribution range shrinking again and again. In Hengduan Mountains, there are more spaces and diverse habitats for cold-temperate coniferous trees moving upwards to the high environments (Sun, 2002). However, it's latitudinal is lower, so the cold-temperate coniferous species such as Picea spp. are distributed in the medium and top parts of mountains, which detached the distribution area into many parts, and some Picea spp. differentiate into many subspecies. The place became the center of geographical distribution and differentiation of Picea genus. The reticulate evolution and biological radiation resulted from climatic, ecological and geological changes broght many difficulties to the evolutionary and biogeographical studies of some taxa with long generation times, widespread distributions and low morphological divergence.

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Karyotype equation (16m+8sm) is a relative evolutional type, this type is not found in abroad Picea spp.. On the contrary, karyotype equation (24m), which is a relatively primordial chromosome, is found in them (P. sitchensis). We can conclude from karyotype structure that Chinese Picea spp. are relatively evolutional than abroad Picea spp.  Table 5. Karyotype characters of 15 spruce species abroad Hu et al. (1983) reported the differences of interspecific zymogram distances of genus Picea (Table 6). Firstly, concerning abroad Picea, P. abies is similar to the Chinese Picea, but it has long zymogram distance with P. polita. The zymogram distance between P. polita and other Picea except for P. wilsonii is long. The zymogram distance between P. pungens and other Picea except for P. schrenkiana and P. wilsonii is long. About the relationship between the Chinese Picea, the zymogram distances are short except for the following three pairs, those are P. koraiensis and P. meyeri, P. meyerii and P. crassifolia, P. wilsonii and P. likiangensis.  (Zheng and Fu, 1978). P. jezoensis distributes widely in Northeastern Asia, including Far East of Russia, Korean Peninsula, and North Japan (Ying, 1989). When it extends into Northeast China, it differentiates into some variations, such as P. jezoensis var. microsperma (in Da Xinganling Mountains, Xiao Xinganling Mountains, Zhangguangcailing Mountains) and P. jezoensis var. komarovii (in Changbai Mountains). In North China, Southwest China, and Taiwan, the Picea spp. have few connection with abroad Picea spp., so there are many China endemic species in spruce forests of these regions.