Comparison of Tropical Tree Plantations with Secondary Forests of Similar Age
Comparison of Tropical Tree Plantations with Secondary Forests of Similar Age
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DOI：
10.2307/2937169
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发表时间：
1992-02
影响因子：
6.1
通讯作者：
A. Lugo
中科院分区：
文献类型：
--
作者：
A. Lugo
的结构和动态的小人工林的松树（加勒比松; 4和18.5岁，1980年）和桃花心木（Swietenia macrophylla; 17和49岁，1980年）进行了比较，对次生林林相似的年龄和生长在相似的土壤和气候条件下彼此相邻。该研究于1980年至1984年在卢基略实验森林进行。比较包括各种人口，生产和养分循环特征的立场。虽然小的未管理的人工林林下的物种数量较低，配对次生林，林下的老人工林开发高物种丰富度，包括许多本地树种。17年后，本地树种入侵人工林的上层。50年后，红木种植园林下的物种丰富度接近其配对的次生林。种植园林下具有重要的生态功能，包括高养分积累.林下植物组织，特别是凋落叶，有较高的养分浓度在松树人工林比配对次生林。林下生物量在人工林中积累了较高比例的总养分库存的立场比林下配对次生林。人工林的地上生物量和地上生物量净生产量高于成对次生林.次生林的根系密度和生物量均高于配对人工林，根系的渗透深度、根系中的养分含量和根系生长的微生境数量均高于配对人工林。相对于成对的人工林而言，这些特征可能会提高次生林迅速重新获得通过矿化作用获得的养分以及通过水文或气体途径可能损失的养分的能力。这两种森林类型都积累了养分和物质，但次生林的养分循环速度比人工林快得多，人工林倾向于储存养分。人工林有较高的落叶量和总凋落物量，凋落物与较低的养分浓度，积累更多的养分在凋落物中，分解更多的凋落物在一年的基础上，表现出更多的变化，在空间分布的凋落物质量，并有更多的月到月的变化，凋落物储量比配对次生林。凋落物的次生林，另一方面，有一个更快的养分周转比种植园凋落物，虽然人工林retranslocated更多的养分落叶前比次生林。随着种植园的增加，养分再转运量增加。人工林，特别是松树种植园，产生更多的凋落物质量每单位养分归还比成对的次生林。土壤中的总养分储存量与养分利用效率的相关性最好，估计为元素：质量比在各个隔间。养分利用效率排名不同的森林对，这取决于营养和生态系统参数进行比较。由于养分的高度再转运，尽管更大的养分“需要”产生更高的生物量，人工林对土壤的养分需求类似于成对的次生林。在测量的生态系统参数中，落叶中的营养物质与各林分土壤养分的差异相关性最好。林下物种的养分浓度似乎是全林分养分利用效率的敏感指标。该研究的一些观察结果可以归因于小型未管理人工林和次生林之间的内在差异，但许多观察结果可以用物种差异来解释（即，落叶时间），种植园年龄（即，生物量或物种的积累），或被子植物和裸子植物的相对重要性（即，营养价值（）。这项研究挑战了关于种植园和原生演替生态系统之间差异的传统教条，并强调了对所有热带树木种植园或所有天然热带森林进行概括，甚至从生态系统的一个部门推断到另一个部门的危险。
The structure and dynamics of small plantations of pine (Pinus caribaea; 4 and 18.5 yr old in 1980) and mahogany (Swietenia macrophylla; 17 and 49 yr old in 1980) were compared with those of paired secondary forest stands of similar age and growing adjacent to each other under similar edaphic and climatic conditions. The study was conducted in the Luquillo Experimental Forest between 1980 and 1984. Comparisons included a variety of demographic, production, and nutrient cycling characteristics of stands. Although the small unmanaged plantations had a lower number of species in understory than paired secondary forests, the understory of the older plantations developed high species richness, including many of native tree species. After 17 yr, native tree species invaded the overstory of plantations. After 50 years the species richness in the understory of a mahogany plantation approached that of its paired secondary forest. Plantation un- derstories had important ecological roles, including high nutrient accumulation. Understory plant tissue, particularly leaf litter, had higher nutrient concentration in pine plantations than in paired secondary forests. Understory biomass in plantations accumulated a higher proportion of the total nutrient inventory in the stand than did the understory in paired secondary forests. Plantations had higher aboveground biomass and net aboveground bio- mass production than paired secondary forests. Higher root densities and biomass were found in secondary forests as were greater depth of root penetration, higher nutrient con- centration in roots, and more microsites where roots grow, than paired plantations. These characteristics may improve the capacity of secondary forests relative to that of paired plantations to rapidly recapture nutrients that become available by mineralization and that could otherwise be lost through hydrological or gaseous pathways. Both forest types accumulated nutrients and mass, but secondary forests recirculated nutrients much faster than the plantations, which tended to store the nutrients. Plantations had higher leaf fall and total litterfall, had litterfall with lower nutrient concentrations, accumulated more nutrients in litter, decomposed more litter on an annual basis, exhibited more variation in the spatial distribution of litter mass, and had more month-to-month variation in litter storage than paired secondary forests. Litter of the secondary forests, on the other hand, had a faster nutrient turnover than plantation litter, though plantations retranslocated more nutrients before leaf fall than did secondary forests. Nutrient retranslocation increased with plantation age. Plantations, particularly pine plantations, produced more litter mass per unit nutrient return than did paired secondary forests. Total nutrient storage in soil gave the best correlation with nutrient use efficiency estimated as element: mass ratios in various compartments. Nutrient use efficiency ranked differently among forest pairs, depending upon which nutrient and ecosystem parameters were being compared. Because of high retranslocation of nutrients, and in spite of greater nutrient "need" to produce higher biomass, plantations had nutrient demands on soil similar to paired secondary forests. Among the ecosystem parameters measured, nutrients in leaf fall correlated best with differences in soil nutrients across stands. Nutrient concentrations in understory species appeared to be a sensitive indicator of whole-stand nutrient use efficiency. Some of the observations of the study could be attributed to intrinsic differences between small un- managed plantations and secondary forests, but many could be explained by species dif- ferences (i.e., timing of leaf fall), age of plantation (i.e., accumulation of biomass or species), or the relative importance of angiosperms and gymnosperms (i.e., nutritional quality of litter). The study challenges the conventional dogma with respect to differences between plantations and native successional ecosystems and underscores the dangers of generalizing about all tropical tree plantations or all natural tropical forests, or even extrapolating from one sector of the ecosystem to another.