林下植被对杉木林地力影响的研究*

本文研究了林下植被对杉木林地力的影响,结果表明在正常的经营水平下,林下植被生长迅速。0.7的林分郁闭度,4～5年后生物量积累达4～5 t/ha;营养元素达80～100kg/ha。丰富的林下植被能促进养分的有效化,并且在一定程度上能起到改善土壤肥力的作用,因此对防止杉木林地力衰退具有一定的意义。     

Biomass production,nutrient cycling and distribution in age-sequence Chinese fir(Cunninghamia lanceolate) plantations in subtropical China

Biomass production and nutrient(N, P, K, Ca and Mg) accumulation, distribution and cycling were quantified in young, mature and over-mature(10-, 22-, and34-year old) Chinese fir [Cunninghamia lanceolate(Lamb.) Hook] plantations in southern China. Total stand biomass of young, mature and over-mature stands was 38,104 and 138 t ha-1respectively. Biomass production increased significantly with age. Stem wood represented the highest percentage of stand biomass, accounting for 41,55 and 63 % in the young, mature and over-mature plantations respectively. Nutrients concentration was highest in live needles and branches, and lowest in stem wood. The plantations accumulated more N, followed by K, Ca, Mg,and P. Nutrient return amount, nutrient utilization efficiency, nutrient turnover time, the ratio of nutrient returnand uptake increased with stand age, which implies that young Chinese fir deplete soil nutrients to maintain growth,and efficiently utilize nutrients to decrease dependence on soil nutrients as they age. Harvesting young Chinese fir plantations would therefore lead to high nutrient loss, but prolonging the rotation length could improve soil recovery,and help sustain productivity in the long-term. Improved nutrient return through litterfall as stands get older may also be beneficial to nutrient pool recovery.     

The Use of Municipal and Pulp and Paper Sludges to Increase Production in Forestry

Because of their high nutritional content and soil conditioning properties,. municipal and pulp and paper (P&P) sludges-biosolids-can serve as soil amendments for nutritionally deurived or organically soils on forest sites. Studies conducted over the past 20 years at an experimental forest site in Western Washington, USA, have largely confined the potential of biosolids to increase the productivity of many forest lands. These studies clearly demonstrated that application of biosolids at environmentally acceptable rates will result in growth responses for both young seedlings as well as established stands. Municipal biosolids have been applied to a number of different Douglas-fir stands. Young stands applied at 47 Mg ha-1 showed an average of 72%, 14% and 2% height responses for Site Class IV, III and 11, respectively, over a 10 year period. Thinned versus unthinned 55-yeardd Douglas-fir applied with 142 dry Mg ha-l averaged 43% and 48%, respectively, for the 12 year period greater than controls. Average growth responses of 65% and 40% occurred in the 65-year-old stand for the Site Class IV and 11, respectively, from a 47 dry Mg ha1 application. Growth response resulting from application of P&P biosolids to a number of tree species has also been excellent. When properly applied, biosolids can provide an excellent alternaLive to chemical fertilizers as a means of enhancing forest production. Growth response is typically greater and lasts longer when compared to chemical fertilization. Careful consideration has to be made of the site conditions to be certain that environmental risks are minimal and losses through leaching and overland flow will not occur.     

Biomass production,nutrient cycling and distribution in age-sequence Chinese fir (<Emphasis Type="Italic">Cunninghamia lanceolate</Emphasis>) plantations in subtropical China

Biomass production and nutrient (N, P, K, Ca and Mg) accumulation, distribution and cycling were quantified in young, mature and over-mature (10-, 22-, and 34-year old) Chinese fir [Cunninghamia lanceolate (Lamb.) Hook] plantations in southern China. Total stand biomass of young, mature and over-mature stands was 38, 104 and 138 t ha^?1 respectively. Biomass production increased significantly with age. Stem wood represented the highest percentage of stand biomass, accounting for 41, 55 and 63 % in the young, mature and over-mature plantations respectively. Nutrients concentration was highest in live needles and branches, and lowest in stem wood. The plantations accumulated more N, followed by K, Ca, Mg, and P. Nutrient return amount, nutrient utilization efficiency, nutrient turnover time, the ratio of nutrient return and uptake increased with stand age, which implies that young Chinese fir deplete soil nutrients to maintain growth, and efficiently utilize nutrients to decrease dependence on soil nutrients as they age. Harvesting young Chinese fir plantations would therefore lead to high nutrient loss, but prolonging the rotation length could improve soil recovery, and help sustain productivity in the long-term. Improved nutrient return through litterfall as stands get older may also be beneficial to nutrient pool recovery.     

Impact of plantation forestry with teak (Tectona grandis) on the nutrient status of young alluvial soils in West Venezuela

On alluvial sandy loams in the western Llanos of Venezuela, biomass and inventories of macronutrients were determined for ten teak plantations (0.5–9 years old) and a mature forest stand which preceded them. Mean tree and stratified random sampling methods of estimating biomass are compared with regression estimates.Aboveground biomass of the mature forest averages 398 t ha^?1. The average yearly productivity of biomass per ha of the teak plantations is greater on sites with soils having higher clay contents; It was measured as 23 t (9-year-old plantation), 16 t (7 years), 10–14 t (6 years) and 7–14 t (4 years).The original ecosystem stores per ha for these sites range between 8380 and 8840 kg N (total), 4550 and 4890 kg P, 2290 and 2540 kg K, 6720 and 6850 kg Ca and 960 and 1760 kg Mg.In the mature forest most N, P and Mg is stored in the soil, whereas 70% of the K and 40–50% of the Ca is stored in the vegetation. The ecosystem K stores of the teak plantations are an average of 40% lower than in the original forest. This difference is interpreted as being due to leaching loss caused by replacement of the original forest.Using data from the literature and from this study, a nutrient budget has been calculated for the first rotation period of teak. It is predicted that substantial amounts of Ca will be removed from the site by the teak harvest. These exports may not be replenished by atmospheric inputs and soil mineral weathering, especially on the highly productive sites.     

Biodiversity of arbuscular mycorrhizal fungi in Amygdalus scoparia Spach plantations and a natural stand

The biodiversity of arbuscular mycorrhizal fungi(AMF) was surveyed in the Kolm region of Iran in three adjacent sites, a natural stand, a 10-year-old and a 15-yearold plantation of Amygdalus scoparia. To date, there have been few studies of AMF biodiversity in Iran, especially in the western forests of the country. For this study, soil and root samples were taken from A. scoparia rhizosphere soil in spring and autumn. Almost half of the root length was colonized by AMF. We identified 13 AMF species belonging to Glomeraceae, Claroideoglomeraceae or Diversisporaceae. The three plantations differed in terms of soil electrical conductivity, organic C and P. Spore density was significant correlated with P concentration. Root length colonization was correlated only with soil Ca.Species diversity and richness were significantly correlated with soil N, P, organic C and spore density. AMF diversity in 15-year-old plantations was more similar to that in the natural stand than in the 10-year-old plantation. We confirmed that a 15-year-old plantation is not similar in terms of AMF colonization to natural stands. We conclude that more than 15 years are required for AMF colonization of plantations to resemble that of natural stands.     

Simulated biomass and soil carbon of loblolly pine and cottonwood plantations across a thermal gradient in southeastern United States

Changes in biomass and soil carbon with nitrogen fertilization were simulated for a 25-year loblolly pine (Pinus taeda) plantation and for three consecutive 7-year short-rotation cottonwood (Populus deltoides) stands. Simulations were conducted for 17 locations in the southeastern United States with mean annual temperatures ranging from 13.1 to 19.4 °C. The LINKAGES stand growth model, modified to include the “RothC” soil C and soil N model, simulated tree growth and soil C status. Nitrogen fertilization significantly increased cumulative cottonwood aboveground biomass in the three rotations from a site average of 106 to 272 Mg/ha in 21 years. The equivalent site averages for loblolly pine showed a significant increase from 176 and 184 Mg/ha in 25 years with fertilization. Location results, compared on the annual sum of daily mean air temperatures above 5.5 °C (growing-degree-days), showed contrasts. Loblolly pine biomass increased whereas cottonwood decreased with increasing growing-degree-days, particularly in cottonwood stands receiving N fertilization. The increment of biomass due to N addition per unit of control biomass (relative response) declined in both plantations with increase in growing-degree-days. Average soil C in loblolly pine stands increased from 24.3 to 40.4 Mg/ha in 25 years and in cottonwood soil C decreased from 14.7 to 13.7 Mg/ha after three 7-year rotations. Soil C did not decrease with increasing growing-degree-days in either plantation type suggesting that global warming may not initially affect soil C. Nitrogen fertilizer increased soil C slightly in cottonwood plantations and had no significant effect on the soil C of loblolly stands.     

How well does Kirtland's warbler management emulate the effects of natural disturbance on stand structure in Michigan jack pine forests?

Jack pine (Pinus banksiana) forests in parts of northern Lower Michigan have been managed with 30 years of extensive clearcut harvesting followed by planted stand establishment in order to maintain habitat for the endangered Kirtland's warbler (Dendroica kirtlandii). We used two, parallel chronosequences to study how this management has affected the structural development of jack pine stands relative to the historically dominant disturbance regime of stand-replacing wildfire. Each chronosequence consisted of three young stands (age range 3–6 years), three intermediate-aged stands (age range of 12–17 years) and three mature stands (age range of 39–69 years). Average stem density in young plantations (2300 stems/ha) was lower than the average for young, fire-origin stands (11,000) and varied over a much narrower range among stands (1403–2667 for plantations and 1552–24,192 in fire stands). In addition, within-stand patchiness of stem density was also much higher in the wildfire sites for young and intermediate ages. Plantation sites possessed very little dead wood at young ages (averaging 3 snags/ha and 12 m³/ha CWD) compared to young fire-origin stands (averaging 252 snags/ha and 49 m³/ha CWD). In contrast, mature plantations had similar levels of dead wood (averaging 269 snags/ha and 22 m³/ha CWD) as mature fire-origin stands (averaging 557 snags/ha and 12 m³/ha CWD). Differences between the plantation and fire-origin chronosequences were driven mainly by young- and intermediate-aged stands, whereas mature stands were typically quite similar in all structural features. Our results show clearly that forest management aimed at preserving and enhancing the population of a single endangered species results in greatly simplified habitat structure at the stand level, and suggest that this simplification is perpetuated across the landscape as well. Of particular concern are the effects of extensive harvesting and planting on the availability of snags and CWD.     

Biodiversity of arbuscular mycorrhizal fungi in <Emphasis Type="Italic">Amygdalus scoparia</Emphasis> Spach plantations and a natural stand

The biodiversity of arbuscular mycorrhizal fungi (AMF) was surveyed in the Kolm region of Iran in three adjacent sites, a natural stand, a 10-year-old and a 15-year-old plantation of Amygdalus scoparia. To date, there have been few studies of AMF biodiversity in Iran, especially in the western forests of the country. For this study, soil and root samples were taken from A. scoparia rhizosphere soil in spring and autumn. Almost half of the root length was colonized by AMF. We identified 13 AMF species belonging to Glomeraceae, Claroideoglomeraceae or Diversisporaceae. The three plantations differed in terms of soil electrical conductivity, organic C and P. Spore density was significant correlated with P concentration. Root length colonization was correlated only with soil Ca. Species diversity and richness were significantly correlated with soil N, P, organic C and spore density. AMF diversity in 15-year-old plantations was more similar to that in the natural stand than in the 10-year-old plantation. We confirmed that a 15-year-old plantation is not similar in terms of AMF colonization to natural stands. We conclude that more than 15 years are required for AMF colonization of plantations to resemble that of natural stands.