XiuPing Cui,GuoHou Liu

1.College of Resources and Environment Economy,Inner Mongolia University of Finance and Economics,Hohhot,Inner Mongolia 010051,China

2.College of Ecological and Environmental Science,Inner Mongolia Agricultural University,Hohhot,Inner Mongolia 010019,China

Study on characteristics and regeneration rules ofSalixgordejeviiin Hunshandak Sandland,China

XiuPing Cui1*,GuoHou Liu2

1.College of Resources and Environment Economy,Inner Mongolia University of Finance and Economics,Hohhot,Inner Mongolia 010051,China

2.College of Ecological and Environmental Science,Inner Mongolia Agricultural University,Hohhot,Inner Mongolia 010019,China

Salix gordejevii,a species of dune-fixing pioneer shrub in the Hunshandak Sandland in China,plays a vital role in maintenance and improvement of the local ecological environment.Salix gordejeviihas anr-type reproductive countermeasure,which means it produces large quantities of seeds that have a high germination rate but relatively low seedling viability.Our research on the seed regeneration and sprouting regeneration characteristics ofSalix gordejeviishows that its sprouting regeneration process is more productive and efficient than its seed regeneration process.At the same time,growth ofSalix gordejeviiwould decline when the drifting sand dune was fixed.To assess its sprouting regeneration process,we analyzed the number,length,and diameter of new shoots under different cutting treatments,and found significant differences based on various cutting heights and different cutting times (April vs.October).We conclude that cutting measures which take advantage of this species’ robust sprout tillering can increase the biomass of this shrub and also can improve its canopy density and its forage properties for livestock grazing,with the added benefits of improved sand-fixing and prevention of wind erosion.

Salix gordejevii;seed regeneration;sprouting regeneration;Hunshandak Sandland

1.Introduction

Plant regeneration is an important part of forest community dynamics,and seeds are the basis of most plant regeneration (Liet al.,2008).The seeds of many plant species,includingSalix gordejevii,enter the seed bank by wind diffusion and then sprout seedlings to renew plant communities;this is the dynamic process from potential population to real population (Wuet al.,2006;Wanget al.,2007;Liuet al.,2008;Panet al.,2008).In addition to natural seed regeneration,artificial regeneration can be realized by making use of plant species’ sprout tillering characteristics,and cutting is one of the main methods to achieve this.Cutting can effectively prevent some plants(mainly certain desert shrubs) from growing slowly and then dying naturally,and can promote plant growth so as to achieve regeneration (Changet al.,1997;Liet al.,2000;Yanet al.,2006).

Salix gordejeviiis the main shrub species in the soil and water conservation forests and fuelwood forests in the Hunshandak Sandland.It plays a key role in the protection and construction of the sandland ecological environment.To date,most research has focused on this plant’s physiological and ecological adaptability,morphological characteristics,habits,cultivation methods,root distribution,and canopy structure features (Changet al.,1997;Cuiet al.,2006a,b;Zhanget al.,2006;Cui and Liu,2009).Here,we studied this plant from the aspects of natural seed regeneration and artificial regeneration (cutting),and we analyze and discuss the features and rules of these two regeneration methods,aiming to provide a scientific basis for better understanding,protecting,and utilizingSalix gordejevii.

2.Natural geography of the study area

The study area is situated in Sanggendalai Town in the Zhenglan Banner in Xilinguole League,China (42°40.986′–42°41.922′N,115°57.198′–115°59.789′E).The local climate is a drought continental monsoon climate of the middle latitude temperate zone.The winters are long and cold,and the summers are short and hot.The annual average temperature is 1.7 °C,the average temperature in July is 22 °C,the average temperature in January is −21 °C,and the accumulative temperature of ≥10 °C in a year is 2,000 °C.The frost-free period is 110 days.The average annual precipitation is 355 mm.Precipitation is unevenly distributed throughout the seasons,and mainly occurs in June to August.The average annual evaporation is 1,931.4 mm.The average wind speed is 4 m/s,and the frequency of gale winds above the 8-class level is up to 90 days in a year.In spring and autumn there are frequent episodes of gale and sand-dust weather,and sandstorms occasionally occur.The predominant wind direction is northwest.The zonal soil type is chestnut soil,and its surface is always covered by sandy soil.The trees are mainlyUlmus pumilavar.Sabulosa;the shrubs are mainlySalix gordejevii,Salix microstachyavar.bordensis,Caragana microphylla,andHedysarum laeve;and the herbs are mainlyPotentilla acaulis,Cleistogenes squarrosa, andAgropyron cristatum(Liu and Wang,2005;Liuet al.,2008;Yueet al.,2008).

3.Research contents and methods

3.1.Survey of seed regeneration rules

In August of 2004,we selected a newly seeded,40m×60m regeneration plots ofSalix gordejeviiin the study area.Follow-up investigations were conducted in August of 2005 and 2006.We randomly selected 100 mature branches and 100 leaves without insect pests and plant diseases,and then measured a series of indexes,including the length and number of branches,the length and width of leaves,and the distribution density.By averaging the values of several measurements we calculated the relative survival rate: the relative survival rate (%) equals to the present plant density in plots divided by the plant density in the previous year.

3.2.Sprouting regeneration study

We selected a degenerated 6-year-oldSalix gordejeviiplot on a fixed sand dune for artificial sprouting regeneration research.The plot was randomly divided into three small subplots.On one of the subplots,cutting was conducted in early April;on another the cutting was conducted at the end of October;and the third subplot was left uncut as the control.Ten clumps of shrubs (having similar canopy size and branch density) on each of the first two subplots were divided into five groups and were cut to different heights of 0 cm,5 cm,10 cm,15 cm,and 20 cm.

Similar to the seed regeneration study described in Section 3.1,follow-up investigations were conducted in August of 2005 and 2006,wherein 100 mature branches and 100 leaves without insect pests and plant diseases were randomly selected to be measured for the length and number of branches,the diameter of the base,the length and width of leaves,and the distribution density.

The measurement data were subjected to variance analysis with SAS9.0 software.Only in cases where there was a significant difference,the mean difference was subjected to the paired-samples test (Duncan’s method) (Pei and Xue,1998).

4.Research results

4.1.Seed regeneration rules

Our field surveys showed thatSalix gordejeviiseeds mature in early June or so.The seeds are plump and have no disease and insect pests,and they are not fed on by animals.Salix gordejeviiseeds are small (the 1,000-seed weight is 11.48 g) and have surface pappus,so they are mainly spread by wind.Influenced by environmental factors such as soil water,sand-bury depth,and temperature,only a few of the seeds that enter the soil seed bank actually germinate and survive (Cuiet al.,2006a) (Figure 1).Soil water is the key factor influencing germination ofSalix gordejeviiseeds.Our investigation was carried out during gale and drought periods in the study region,so the viable seedlings were mainly distributed in interdune lowlands that had advantageous water conditions.

The results of our follow-up investigation into natural seed regeneration are listed in Table 1.In 2004,the leaves of the 1-year-old seedlings were relatively small,the branches were few and relatively short,and the seedling distribution density was 60 individuals per square meter.Rarely,there were other plant species distributed in the plots,only scatteredAgriophyllum pungensandBassia dasyphylla.In 2005,the average leaf length and width of the seedlings reached 75 mm and 4.5 mm,respectively;the average number of branches on each plant was 9 and the average branch length was about 50.2 cm,with the longest of 95 cm;and the seedling density was 11 individuals per square meter (a relative survival rate of only 18.3%).In 2006,the seedlings grew vigorously.The average number of branches on each plant reached 37,so the canopy size increased obviously.The average length of the seedling branches was about 210 cm,with the longest of 284 cm.Compared with the previous year,there were almost no dead seedlings in the plots,and the relative seedling survival rate reached 95%.Also,there were no other plant species in the plots.

It can be concluded that although the relative survival rate of the 2-year-old seedlings was low,the surviving seedlings grew well and exhibited vigorous growth in the third year,but only with adequate soil water and no anthropogenic destruction.This describes the natural seed regeneration process ofSalix gordejevii.

Figure 1 Spatiotemporal model of seed regeneration.Note: Solid arrows indicate the process;dotted arrows indicate impacts to the process;solid frames indicate the status of seed existence;dotted frames indicate the influencing factors.

Table 1 Status of natural regeneration seedlings

4.2.Sprouting regeneration rules

4.2.1 Branch growth

Our data pertaining to the number,length,and diameter ofSalix gordejeviibranches under both treatments (cutting and no cutting) are listed in Table 2.Comparison analyses disclosed significant differences in the treatments.Compared with the control plants,the number,length,and base diameter of the new branches from the cut plants all increased obviously.However,among the treatments with different cutting heights,there were no obvious differences during the same growth period (either April or October).Also,there were no obvious differences among the same cutting height treatments when the cutting times were different (April vs.October).

Table 2 Effects of cutting treatment on the number,length,and diameter of new branches

4.2.2 Leaf growth

Similar to the positive effect that cutting measure had on new branch growth,cutting also improved the leaf length and width ofSalix gordejevii(Table 3).Compared with the control plants,the average leaf length of the cut shrubs was 2.7 cm longer,and the average leaf width was 0.2 cm broader.However,there was no significant difference in their length-to-width ratio.Also,there were no obvious differences among the various cutting heights or among the cuttings that occurred at different times (April vs.October).

Table 3 Comparison of leaves under different treatments

5.Analysis and discussion

5.1.Seed regeneration

Seed dispersal and seed germination are two aspects of plant population expansion by seeds.Seed dispersal is the basis of successful seed germination,as it controls the location of seed germination.Seed germination may eventually produce new seeds and bring about new seed dispersal.However,plant population expansion is the result of the interaction of many factors,not the role of a single factor.Seed germination is the key to plant population succession and expansion.In arid desert areas,most plant seeds germinate through "opportunistic" or "cautious" mechanisms(Huang,2003).In harsh natural environmental conditions,desert plant seeds always seek the right germination opportunity,and can acclimate to grasp even more germination opportunities.Some scholars have posited the "seed dispersal strategy for avoiding competition," especially for avoiding sib competition for water and sunlight (Ellner,1987;Nilssonet al.,1994;Yutaka and Norio,2000).BecauseSalix gordejeviiproduces a large amount of small seeds with surface pappus,the seeds can be transported long distances by wind,greatly enhancing the probability of seeds falling into a microhabitat appropriate for germination.This "r-type"reproductive countermeasure (Sunet al.,1992) is characterized by a small seed size,a high germination rate,and a low seedling survival rate;it lacks a mechanism to protect new generations and it is only able to compete weakly,but its strong dispersal mechanism enables it to invade an appropriate new habitat and propagate rapidly.

5.2.Sprouting regeneration

Cutting is an effective measure for shrub regeneration and restoration.It can regenerate plants and improve the biomass,and can also improve forage characteristics for better livestock grazing ratios.Because the canopy density is significantly increased by cutting,its benefits of wind erosion prevention and sand fixation are strengthened.Also,the cut branches are suitable materials for cutting propagation,fuel,knitting,papermaking,and so forth.Thus,cutting is a primary plant management measure as well as an important way to harvest certain raw materials.For maximum production,the cutting height should be as low as possible.

Salix gordejeviihas strong sprout tillering characteristics.This property has been widely and fully utilized in the practice of forest regeneration and restoration.When old and degeneratedSalix gordejeviibushes are cut,the growth can become vigorous again.Also,the biomass does not decrease as a result of cutting because the large root system ofSalix gordejeviiwill have a deeper and wider water- and nutrient-absorbing area after cutting.

Our research results are in general agreement with those of Changet al.(1997),who concluded that the cutting effect ofSalix gordejeviiis optimal when the cutting height is lessthan 3 cm,and the effect decreases obviously when the cutting height is greater than 5 cm.However,our study showed no obvious differences among various cutting-height and cutting-time treatments.Our different conclusions may have resulted from different selections of plots,shrub age,and growth vigor.

Acknowledgments:

This project is supported by the National Natural Science Foundation of China (Grant No.30560128) and the Special Research Funds of the Doctoral Program of Higher Education(No.20070129004).

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January 12,2012 Accepted: May 2,2012

*Correspondence to: Dr.XiuPing Cui,College of Resources and Environment Economy,Inner Mongolia Finance and Economics University.No.185,North Second Ring Road,Hohhot,Inner Mongolia 010051,China.Tel: +86-471-3660196;Email: mkscxp@126.com