马尾松-阔叶树混交异龄林生物量与生产力分配格局

Allocation pattern of biomass and productivity in the mixed uneven-aged stands of Masson's pine and hardwood species

在25年生的马尾松林下分别套种1年生火力楠、闽粤栲、苦储、格氏栲、青栲和拉氏栲幼苗，经过16a的培育后形成了郁闭的针阔混交异龄林。应用分层平均标准木收获法，建立相对生长方程，对上述6种混交林及马尾松纯林的生物量与生产力分配格局进行了研究。6个混交林的林木总生物量分别为216．41、260．06、221．92、221．65、246．13t／hm^2及201．04t／hm^2，而马尾松纯林的生物量为204．37t／hm^2；其中地上部分占81．4％～83．7％，林分之间差异较小。在混交林中，处于主林层的马尾松生物量占林分总生物量的比例为73．5％～85．4％。在各林分生物量组成中，干材生物量最大，占总生物量的56．4％～64．8％，其它组分所占的比例依次为根（16．3％～18．6％）〉枝（9．O％～16．9％）〉皮（4．9％～7．3％）〉叶（1．1％～4．3％）。生物量的空间结构在马尾松纯林和混交林之间存在明显差异，混交林中0～9m高度的生物量分配比例（67．1％）明显大于马尾松纯林（53．7％）；混交林中，在2～3m高度就出现了枝、叶的分布，而马尾松纯林中则出现在13～14m。混交林中，阔叶树根系的生物量主要集中于0～40cm土层，占根系总生物量的74％～99％，60cm以下土层则根系分布很少，而马尾松的根系则主要分布于土壤表层（0～20cm）和60cm以下土层，分别占总生物量的26％和49％。各混交林分的净初级生产力为10．60～15．25t／（hm^2·a），而马尾松纯林的生产力仅7．34t／（hm^2·a）。林分净初级生产力（NPP）与光合器官／地上部分生物量比（X1）、细根生物量／地下部分生物量比（X2）存在显著的非线形关系：NPP=5．5745＋1．1985 X1＋2．6479X2^2。在所研究的林分中，细根（d〈2mm）生物量占林分总生物量的平均比例为0．2％，但细根生产力占林分净生产力的平均比达2．9％。

One-year old seedlings of six hardwood species, Michelia macclurei, Castanopsis fissa, Castanopsis sclerophylla, Castanopsis kawakamii, Cyclobalanopsis myrsinaefolia and Castanopsis lamontii, were separately planted under the overstory of 25-year-old Masson＇s pine plantation, and developed into closed mixed stands after 16 years of management. By harvesting and measuring the average sample trees collected from the plots, a group of allometric growth equations were established to estimate the allocation patterns of biomass and net primary productivity in the above six mixed stands and also the pure Masson＇s pine plantation. The whole-tree biomasses were 216.41 t/hm^2, 260.06 t/hm^2, 221.92 t/hm^2, 221.65 t/hm^2, 246.13 t/hm^2 and 201.04 t/hm^2 , respectively, for the mixtures, and 201.04 t/hm^2 for the pure pine stand. The percent allocation to aboveground biomass was in the range of 81.4% to 83.7%, with little difference among the stand types. In the mixtures, the pine trees in the upper canopy accounted for 72.5 % -- 85.4 % of the total biomass, the lower hardwoods for 27.5 % -- 14.6 %. For all the stand types, allocation to stems was the greatest, making up 56.4%--64.8% of the sum, followed by roots （16.3%-18.6%）, branches （9.0%-- 16.9% ）, barks （4.9%-- 7.3% ）, with foliage the least （ 1.1%-- 4.3% ）. For pine trees in the mixtures, average allocation percentages to stems, barks, branches, foliage, and roots were 63.9%, 6.5%, 10.8% , 1.0% and 17.9%, respectively, but for the hardwoods 42.0%, 4.6%, 27.6%, 12.2% and 13.6%, respectively. In the mixtures, the average dead-to-living branch ratio was 0. 47, quite higher than the pure stand, suggesting the upward growth by hardwoods in the mixtures accelerated the natural pruning of the forests. The spatial pattern of the biomasses varied greatly between pure and mixed stands, with 67.1% of the total biomass being distributed in the height of 0 -- 9 meters for the mixtures, and 53.7% for the pure. In addition, the first whorl of living branches and foliage were present at the height of 2 -- 3 meters above the ground in the mixtures, but 13 -- 14 meters in the pure pine stand. In the mixtures, roots of the hardwoods were mostly distributed at the soil depth of 0 --40 cm, occupying 74%-99% of the total belowground biomass, but very sparse under 60 cm; pine roots were mainly concentrated at the depth of 0 - 20 cm and under 60 cm, making up 26% and 49% of the biomass, respectively. In the mixtures, more fine roots were distributed in the soils under 40 cm, but in the pure stand, more fine roots found in the surface soil （0- 40 cm）. The net primary productivity （NPP） was estimated to be between 10.60 and 15.25 t/（hm^2· a） for the mixtures, and 7.34 t/（hm2 ·a） for the pure. The NPP for each component of the pine trees varied with the stand types, but decreased in the order： stem 〉 foliage 〉 branch 〉 bark 〉 root. For the hardwoods except Castanopsis fissa, foliage exhibited the greatest NPP, followed by stems, branches, and roots, barks the least. Significant nonlinear relations were found between NPP and two biomass proportion parameters： the photosynthetic organs/aboveground ratio （X1） and fine roots/belowground ratio （X^2 ）, developed into a predicatable formula： NPP = 5.5745 ＋ 1. 1985 X1 ＋ 2.6479 X2^2 . In all the studied stands, fine roots （d 〈 2 mm） averagely held about 0.2% of the total biomass, but 2.9% of the NPP.