Coarse Woody Debris Of Main Forest Types At Huoditang Forest Region In The Qinling Mountains

Taking coarse woody debris(CWD) of the four main forest types(Quercus aliena var. acuteserrata, Pinus armandi, Pinus tabulaeformis and Larix principis-rupprechtii) at Huoditang forest region in the Qinling Mountains as objects, we investigated the storage, decay classes and diameter classes of CWD in the four main forest types. We measured the biomass of the living trees, shrub, herb and litter, revealed the relationship between biomass of CWD and forest in the four forest types. We also assessed α diversity in these plant communities, and its relationship to CWD. The characteristics of density, water content and temperature in logs of the four forest types were investigated, and single exponential decay model was used for estimating the decay rate. We discussed the effects on the decomposition of logs, and revealed the reason for the formation of logs. We also analyzed the change of the nutrients of logs during the decomposition process, and discussed the effects of the decomposition of logs on the soil nutrients. By measuring the respiration, temperature and water content of logs, we quantified the relationships of the respiration against the temperature and water content of logs, and examined seasonal dynamics of the respiration of logs. In addition, we estimated the annual efflux of logs, and compared the difference of the annual efflux of logs, analyzed seasonal dynamics of the annual efflux of logs. The main results are as follows:(1) The storage of CWD in the four main forest types from 2009-2014 varied in a large range, but they all increased yearly. The logs were the most common CWD component in Q. aliena var. acuteserrata, P. tabulaeformis and L. principis-rupprechtii forests, the logs and snags had approximately the same proportion in P. armandi forest. By contrast, rare CWD occurred in the form of stumps. There were large differences among 5 decay classes of CWD storage across the four forest types, Q. aliena var. acuteserrata forest had the highest CWD storage for decay class 3. For P. armandi forest, the decay class 1 occupied the largest proportion, P. tabulaeformis forest had the greatest CWD storage for decay class 2, and L. principis-rupprechtii forest had the highest CWD storage for decay classes 1 and 2. Moreover, it had large differences in different diameter classes of CWD storage across the four forest types, logs of diameter class 30~40 cm had the highest storage in Q. aliena var. acuteserrata forest(P<0.05). In P. armandi forest, logs of diameter class 20~30 cm had the highest storage(P<0.05), P. tabulaeformis forest had the greatest logs storage in diameter class 30~40 cm, and L. principis-rupprechtii forest had the largest logs storage in the smallest diameter class(10~20 cm).(2) The forest biomass increased yearly in the four forest types from 2009-2014, annual average forest biomass and arbor biomass had significantly difference among the four forest types(P<0.05), Q. aliena var. acuteserrata forest had the highest forest biomass and arbor biomass, and L. principis-rupprechtii forest had the lowest forest biomass and arbor biomass(P<0.05). There was no significant difference in shrub biomass among the three coniferous forests(P>0.05), but Q. aliena var. acuteserrata forest had the lowest shrub biomass(P<0.05). L. principis-rupprechtii forest had the highest herb biomass, and Q. aliena var. acuteserrata forest had the lowest herb biomass(P<0.05). The litter biomass in Q. aliena var. acuteserrata and P. armandi forests were significantly higher than that in P. tabulaeformis and L. principis-rupprechtii forests(P<0.05). The annual average storage of CWD was the highest in P. armandi forest, and that was the lowest in L. principis-rupprechtii forest(P<0.05). The arbor biomass was the highest among the four forest types, followed by CWD storage(P<0.05). There was a significant correlation between CWD storage and forest biomass in the four forest types(P<0.0001), but the correlation coefficient was different in forest types and species composition.(3) Diversity indexes of arbor, shrub and herb were significant difference in the four forest types(P<0.05), diversity indexes of different layers showed that herb > shrub > arbor, but the variation was different in the four forest types and four kinds of diversity index. There was a significant positive correlation among four kinds of α diversity index(P<0.05). There was also a significant positive correlation between CWD storage and plant community diversity(P<0.05), but the correlation coefficient was different in forest types, growth types(arbor, shrub and herb) and diversity indexes. The CWD storage exerted a great influence on the species richness, but it had little effect on the Pielou’s evenness index, and the CWD storage had great influence on the species diversity of herb, while it had little influence on the species diversity of arbor.(4) The log temperature and water content of the four tree species were all showed monthly variation during the measuring period of 2010, 2012 and 2014, but the change was different in the four tree species. With the decomposition of the four tree species, the water content of logs all increased at linear trend, but the log temperature presented from raise to decline in P. armandi, P. tabulaeformis and L. principis-rupprechtii(4>3>5>2>1), and in Q. aliena var. acuteserrata, the log temperature rose gradually. In addition, There was a significant correlation between the water content of different decay classes of logs and the precipitation(P<0.05), but no significant correlation with relative humidity(P>0.05). Significant linear positive correlation between the log temperature at different decay classes and 10 cm soil temperature could be found, and the log temperature lagged behind the air and 10 cm soil temperature. Compared with the air temperature, 10 cm soil temperature was closer correlated with the log temperature.(5) With the decomposition of the four tree species, the log density all decreased at linear trend. The relationship between the log density and the decay time was simulated using a single exponential decay model, and the decay rate of log in Q. aliena var. acuteserrata reached the highest, 0.07064, while that in L. principis-rupprechtii fell to the lowest, 0.0316. The single exponential decay model predicted that it would take 20 and 86 years to decompose 50% and 95% of P. tabulaeformis log, 14 and 60 years to decompose 50% and 95% of P. armandi log, 10 and 42 years to decompose 50% and 95% of Q. aliena var. acuteserrata log, while 22 and 95 years to decompose 50% and 95% of L. principis-rupprechtii log.(6) With the decomposition of the four tree species, the nutrient contents of 6 elements in logs were all different, C was the highest content in the nutrient contents of 6 elements, followed by N. The C, K contents and C/N of logs in the four tree species all decreased with decaying, but the N、P、Ca and Mg contents of logs in the four tree species all increased with decaying. In addition, with the decomposition of the four tree species, the C contents of three soil layers under logs increased significantly, and the N contents of three soil layers under logs of P. armandi, P. tabulaeformis and L. principis-rupprechtii also increased significantly with decaying(P<0.05), but with the decomposition of Q. aliena var. acuteserrata, the N contents of three soil layers under logs presented from raise to decline, and then changed to be steady. With the decomposition of the four tree species, the P, K and Ca contents of three soil layers under logs had large fluctuation, but no obvious changes. The Mg contents of three soil layers under logs of the four tree species changed differently with decaying. With the increase of soil depth, the content of soil C, N and Mg under logs of the four tree species decreased significantly(P<0.05).(7) During the measuring period of 2010, 2012 and 2014, there was no significant difference in log respiration among the four tree species(P>0.05), but it had significant difference among the different decay classes(P<0.05). The log respiration at different decay classes in the three coniferous species(P. armandi, P. tabulaeformis and L. principis-rupprechtii) showed that 4>5>3>2>1, but that in Q. aliena var. acuteserrata showed that 5>4>3>2>1. The log respiration at different decay classes in the four tree species were all showed monthly variation during the measuring period of 2010, 2012 and 2014, but the change was different in the four tree species and five decay classes, the maximum log respiration was in August and the minimum value was in October. The log respiration in Q. aliena var. acuteserrata was higher than that in the three coniferous species(P. armandi, P. tabulaeformis and L. principis-rupprechtii), and the lowest value was in L. principis-rupprechtii.(8) The variation of log respiration was driven by the log temperature, and the log temperature played the most important environmental factors in the log respiration. There was a significant exponential correlation between the log respiration of different decay classes and temperature(P<0.0001), and the log temperature could explain 66% of the variability in the log respiration. The range of Q10 values of log respiration at different decay classes in the four tree species which could reflect the sensitivity of respiration to temperature changes were 1.82~3.55. According to our analysis, there was no significant difference between the log respiration and water content at different decay classes in the four tree species(P>0.05).(9) The annual efflux of logs showed seasonal variation in the four forest types, with a maximum in summer, and a minimum in winter. With the increase of year, the annual efflux of logs at different decay classes in the four forest types increased, with a minimum in 2010, and a maximum in 2014. The average annual efflux of logs was the highest in Q. aliena var. acuteserrata forest(P<0.05,70.57±7.23 g C·m-2·a-1), followed by P. tabulaeformis(52.59±4.58 g C·m-2·a-1) and P. armandi forests(51.75±4.34 g C·m-2·a-1), L. principis-rupprechtii forest had the lowest value(P<0.05,36.49±3.23 g C·m-2·a-1). The average annual efflux of logs were different among the five decay classes in the four forest types, the decay classes 3, 4 and 5 occupied 88.86% in the Q. aliena var. acuteserrata forest, the decay class 3 was the highest proportion both in P. armandi and P. tabulaeformis forests(P<0.05), accounted for 31.24% and 30.80%, respectively. There was no significant difference among the average annual efflux of logs in L. principis-rupprechtii forest at the decay classes 1, 2, 3 and 4(P>0.05), but that was the lowest at the decay class 5(P<0.05), only occupied 11.85%.