| Under the background of global warming and increasingly frequent forest disturbance, the resources of broad-leaved Pinus koraiensis forest, as the top-level zonal vegetation in Northeast China, has been decreasing sharply and forest disturbance has become increasingly prominent. Based on the 9 hm2 primary broad-leaved P. koraiensis forests permanent monitoring plot at Liangshui National Natural Reserve in Xiaoxing’an Mountain of Northeast China, mainly researches are carried out in the following three aspects:(1) investigate the basic characteristics and formation-causes of large and medium-sized (an area larger than 50 m2) forest gap disturbance in 6 hm2 a typical broad-leaved P. koraiensis forest using the conventional ecological and dendrochronological methods; (2) reconstruct the disturbance history of forest gaps and explore the possible mechanisms of disturbances, the disturbance chronologies were developed respectively for P. koraiensis and Abies nephrolepis in a typical broad-leaved P. koraiensis forest of Xiaoxing’an Mountain by detecting growth release with boundary-line release criteria using the dendroecological method; (3) explore the influence of global warming (after 1980) on tree radial growth of trees in and out gaps and the response differences to warming, the ring-width chronologies of P. koraiensis and A. nephrolepis in and out of forest gaps in a typical broad-leaved P. koraiensis forest of Xiaoxing’an Mountain were developed using dendroclimatology mothd. The main results are as follows:The total 46 gaps accounted for 40.96%area with an average density of 7.67 per hm2 and an average speed of 0.08/hm2 per year. The average gap-interference frequency was 0.42%·a-1 and the interference period was about 240 years, which in line with the average life expectancy of broad-leaved Korean pine major needles- and broad-leaf species. The gaps mainly formed by a variety of methods (gaps which formed by three or more ways accounted for 67.39%). Death forms of gap-maker trees, which are mainly composed of P. koraiensis (50.2%), A. nephrolepis (9.78%), Betula costala (7.78%) as well as the part which unable to distinguished species with serious decay (10.44%), mainly are breakage at trunk base (BB.54.89%), uprooting (U,16.67%), breakage on trunk(BT,12.89%), standing death(S,10.67%) and artificial cutting(A,4.89%). The average numbers of gap-makers in each gap is 9.38 individual with a higher decay leves. The small-diameter level fallen trees are often victims of gaps formed, rather than makers. The contribution of conifers to the formation of gap is much larger than broad-leaf tree. As the majory species of gap border trees (accounted for 63.08%), P. koraiensis have an average diameter of 46.68 cm (11.4-126.5 cm) and an average height of 23.6 m (5.6-42.9 m), which is far greater than the proportion of other coniferous and deciduous trees. Among those gap-border trees, the A. nephrolepis tree has the fastest growth rate, and Picea koraiensis and Acer mono has the slowest growth rate, other species between them. The size of gaps has little effect on the species and compositions of gap-maker and-border trees, while the different define-standard of of gap-maker trees would has a significant impact on the cause of gap formation. Comprehensive variety of methods to surveys large and medium-sized gaps as well as large diameter class gap-maker tree can improve the accuracy of reconstruction interference and determine the causes of gaps. In addition, the use of hierarchical analysis method can be more reasonably to dynamic analysis the formation and development of large and medium-sized gaps occurred two or more times hurt, which is critical important to understanding the dynamic changes of gaps and processes of forest communities.The variations of percentage growth changes (GC) in P. koraiensis and A. nephrolepis at the edges of forest gap were similar to those in closed canopy. However, there are apparent differences in GC among different gaps; the forest gap disturbance and its impact varied greatly. The strong growth release in P. koraiensis occurred in the periods 1733-1738,1748-1752, 1769-1771,1798-1801,1827-1833,1841-1844,1935-1939, and 1968-1973, with significant disturbance peaks in 1752,1770,1800,1830,1842,1937, and 1970. The growth release in A. nephrolepis occurred in the periods 1889-1904,1932-1938,1938-1973, and 1986-2005, with significant disturbance peaks in 1894,1951 and 1990. The disturbances occurred at intervals of 2.0 a,3.5 a,3.8 a,7.3-7.9 a, and 9.1-18.2 a in P. koraiensis, and of 3.5-3.6 a,7.5-48.8 a, and 65-85 a in A. nephrolepis. Wind was a major mode of disturbances for producing forest gaps and resulting in tree growth releases in the primary broad-leaved P. koraiensis forest in the Xiaoxing’an Mountain. In addition, extreme temperatures could also affect the regime of tree growth release in this region. Solar activity may be another important mechanism of forest gap disturbance and tree growth release in the primary broad-leaved P. koraiensis forest; it affects the forest gap dynamics by changing local wind speed, air temperature, precipitation, and other large-scale climate patterns in the Xiaoxing’an Mountain.The annual mean ring width of P. koraiensis out of forest gaps slightly decreased after warming (1980), while it increased in forest gaps. The relationship between the radial growth of P. koraiensis out of forest gaps and temperature weakened, but it was higher in response to temperature for the trees which in forest gaps. The correlation coefficients between Palmer severity drought index (PDSI) and P. koraiensis chronologies in and out of forest gaps both changed from negative to positive after warming. For the purposes of A. nephrolepis, however, the radial growth of A. nephrolepis decreased due to forest gap disturbance. Annual mean ring width of A. nephrolepis in and out of forest gaps both decreased 50% since climate warming after 1980. The relationship between the radial growth of A. nephrolepis in and out of forest gaps and temperature was negative correlation, but it was higher in response to temperature for the trees which out of forest gaps. The negative effect of temperature from May to October on radial growth of A. nephrolepis out of forest gaps increased since 1980. The negative effect of precipitation on A. nephrolepis out of forest gaps from January to May increased since recent warming, while it changed from negatively to positively for A. nephrolepis in forest gaps. The correlation coefficients between PDSI and A. nephrolepis chronologies out of forest gaps changed from negative to positive after warming, but it happened that negative correlation replaced by significantly (p<0.05) negative correlated for A. nephrolepis which in forest gaps. Our results indicate that forest gap disturbance decreases radial growth of shaded tree species, while it has little effect on sunny tree species or slight increase of radial growth. Tree radial growth in forest gaps is more vulnerable to be affect by external environment change than that out of forest gaps. Gaps disturbances improve the adaptability of the wet and shade-tolerant species to warming in the forest gaps by making it adapt to the warm and arid environment (forest gaps environment) in advance, but has little effect on the positive species. In addition, the recent warming causes larger difference of growth-climate relationship between trees growing in and out of forest gaps. |
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