Effects of thinning on microsites and natural regeneration in a Larix olgensis plantation in mountainous regions of eastern Liaoning Province, China

In order to understand the effects of thinning on microsite conditions and natural regeneration in the larch plantation, thinning experiment was conducted in a 40-year-old Larix olgensis plantation in Qingyuan County in eastern Liaoning Province, China in 2003-2004 Five thinning treatments （0%, 10.2%, 19.8%, 29.7% and 40.3% thinned） were designed on the same site. After thinning, canopy openness and the microsite conditions such as photosynthetic photon flux density （PPFD）, soil moisture content, and soil temperature were measured in one growing season. Meanwhile, the investigation of natural regeneration was conducted at the end of the growing season. The results showed that the canopy openness increased with the increase of thinning intensities. PPFD and soil temperature and soil moisture content in different soil layers were positively relative with canopy openness after thinning. The richness of regenerating tree species did not significantly increase （p=0.30） after one growing season since thinning, but the regeneration density and frequency of tree species increased significantly （p〈0.05）. In addition, the number of regenerating tree species increased, and the increment was correlated with the characteristics of iudividual tree species. The increasing percentage of regenerating seedlings of the shade-intolerant tree species was more than that of shade-tolerant tree species. Among the investigated regeneration species, the biggest response of seedling emergency to the canopy openness was Phellodendron amurense. This paper confirmed the following conclusions： after thinning, the variety of regenerating tree species was correlative with the characteristics of regenerating tree species, and the distribution of unthinned trees and the site conditions in the investigated larch plantation were the additional factors influencing, the regeneration.

Variations in stem radii of Larix principis-rupprechtii to environmental factors at two slope locations in the Liupan Mountains,northwest China

Relationships between stem growth and climatic and edaphic factors,notably air temperatures and soil moisture for different slopes,are not completely understood.Stem radial variations were monitored at the bottom and top slope positions in a Larix principis-rupprechtii plantation during the 2017 and 2018 growing seasons.Total precipitation during the growing season in 2017 and 2018 was 566 mm and 728 mm,respectively.Stem contractions typically occurred after mid-morning followed by swelling in the late afternoon in both plots,reflecting the diurnal cycle of water uptake and loss.Trees at the two locations showed the same growth initiation(mid-May)because of the small differences in air and soil temperatures.There were no significant differences in cumulative stem radial growth between the bottom plot(1.57±0.34 mm)and the top plot(1.55±0.26 mm)in 2018.However,in 2017,the main growth period of the bottom plot ceased 17 days earlier than in the top plot,while cumulative seasonal growth of the bottom plot(1.08±0.25 mm)was significantly less than the top plot(1.54±0.43 mm).Maximum daily stem shrinkage was positively correlated with air and soil temperatures,solar radiation,vapor pressure deficits,and negatively correlated with volumetric soil moisture content.The maximum daily shrinkage reflected transpiration rates as affected by environmental factors.Daily radial stem increment was correlated with precipitation and volumetric soil moisture in both years,but with air temperatures only in 2017.The seasonal growth of L.principis-rupprechtii Mayr thus shows interannual dynamics,while precipitation constitutes a key driving factor.

STUDIES ON BIOMASS AND PRODUCTIVITY FOR DAHUIAN LARCH PLANTATIONS

The biornass and productivity for dahurian larch (Larix gmelini) plantations of four structure types were measured. The biomass of trees, understory' herb and litter was surveyed using methods of average standard tree and subsample yield respectively.The estimated total mean biomass for dahurian larch plantation communities of four structure types was 159. 445 t/hm2 and the net productivity was 12. 237 t/hm2. a.

The effects of simulated nitrogen deposition on extracellular enzyme activities of litter and soil among different-aged stands of larch

Aims Nitrogen(N)addition could affect the rate of forest litter and soil organic matter decomposition by regulating extracellular enzyme activity(EEa).The impact of N addition on EEa may differ across different age stands with different organic matter quality.We were interested in whether the impact of N addition on EEa in litter and mineral soil during the growing season was dependent on stand age of a larch plantation in North China.Methods We added three levels of N(0,20 and 50 kg N ha^(−1) year^(−1))in three age stands(11,20 and 45 years old)of Larix principis-rupprech-tii plantation in North China.We measured potential activities of β-1,4-glucosidase(b),cellobiohydrolase(Cb),β-1,4-N-acetyl-glucosaminidase(Nag)and phenol oxidase(Po)in litter(organic horizon)and mineral soil(0-10 cm)during the second growing sea-son after N amendment.We also measured C and N concentrations,microbial biomass C and N,and KCl-extractable ammonium and nitrate in both litter and mineral soil.Important Findings We observed unimodal patterns of EEa during the growing season in all three stands,consistent with the seasonal variations of soil temperature.stand age had a strong effect on EEa in both litter and mineral soil,and this effect differed between litter and mineral soil as well as between different enzymes.N addition did not significantly affect the activities of b or Cb but significantly suppressed the activity of Nag in litter.We also found stand age-specific responses of Po activity to N addition in both litter and mineral soil.N addition suppressed Po activity of the high C:N ratio litters in 20-and 45-year-old stands but had no significant effect on Po activity of the low C:N ratio litter in 11-year-old stand.moreover,N addition inhibited Po activity of the high C:N ratio soil in 20-year-old stand but had no significant impact on Po activity of the low C:N ratio soils in 11-and 45-year-old stands.overall,stand age had a greater effect on EEa in litter and mineral soil compared to 2 years of N addition.moreover,the effect of N addition on Po activity is stand age dependent,which may affect the long-term soil carbon storage in this forest.