Ishikawa Naoto F, Togashi Hiroyuki, Kato Yoshiyazu, Yoshimura Mayumi, Kohmatsu Yukihiro, Yoshimizu Chikage, Ogawa Nanako O, Ohte Nobuhito, Tokuchi Naoko, Ohkouchi Naohiko, Tayasu Ichiro
Ecology. 2016 May;97(5):1146-58. doi: 10.1890/15-1133.1.
Long-term monitoring of ecosystem succession provides baseline data for conservation and management, as well as for understanding the dynamics of underlying biogeochemical processes. We examined the effects of deforestation and subsequent afforestation of a riparian forest of Japanese cedar (Cryptomeria japonica) on stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) and natural abundances of radiocarbon (Δ¹⁴C) in stream biota in the Mt. Gomadan Experimental Forest and the Wakayama Forest Research Station, Kyoto University, central Japan. Macroinvertebrates, periphytic algae attached to rock surfaces (periphyton), and leaf litter of terrestrial plants were collected from six headwater streams with similar climate, topography, and bedrock geology, except for the stand ages of riparian forests (from 3 to 49 yr old in five stands and > 90 yr old in one reference stand). Light intensity and δ¹³C values of both periphyton and macroinvertebrates decreased synchronously with forest age in winter. A Bayesian mixing model indicates that periphyton contributions to the stream food webs are maximized in 23-yr-old forests. Except for grazers, most macroinvertebrates showed Δ¹⁴C values similar to those of terrestrial leaf litter, reflecting the influence of modern atmospheric CO₂ Δ¹⁴C values. On the other hand, the Δ¹⁴C values of both periphyton and grazers (i.e., aquatic primary consumers) were significantly lower than that of modern atmospheric CO₂, and were lowest in 23-yr-old forest stands. Previous studies show that root biomass of C. japonica peaks at 15-30 yr after planting. These evidences suggest that soil CO₂ released by root respiration and dispersed by groundwater weathers carbonate substrata, and that dissolved inorganic carbon (DIC) with low Δ¹⁴C is incorporated into stream periphyton and some macroinvertebrates. The ecological response in the studied streams to clear-cutting and replanting of Japanese cedar is much slower (~20 yr) than the chemical response (< 5 yr). More than 50 yr is required for the food web structure to completely recover from clear-cutting. The ecological delay is attributed to several biogeochemical factors, the understanding of which is critical to integrated management of forest-stream continuum and the prediction of ecosystem resilience in response to environmental change.
对生态系统演替进行长期监测可为保护和管理提供基线数据，同时有助于理解潜在生物地球化学过程的动态变化。我们在日本中部京都大学的御岳山实验林和和歌山森林研究站，研究了砍伐河岸的日本柳杉（Cryptomeria japonica）林并随后进行造林对溪流生物群中碳（δ¹³C）和氮（δ¹⁵N）的稳定同位素比率以及放射性碳（Δ¹⁴C）自然丰度的影响。从六条源头溪流中采集大型无脊椎动物、附着在岩石表面的周丛藻类（周丛生物）和陆生植物的落叶，这些溪流具有相似的气候、地形和基岩地质条件，只是河岸森林的林龄不同（五个林分的林龄为3至49年，一个参照林分的林龄大于90年）。冬季，周丛生物和大型无脊椎动物的光照强度和δ¹³C值均随森林年龄同步下降。贝叶斯混合模型表明，在23年林龄的森林中，周丛生物对溪流食物网的贡献最大。除了食草动物外，大多数大型无脊椎动物的Δ¹⁴C值与陆生落叶相似，反映出现代大气CO₂的Δ¹⁴C值的影响。另一方面，周丛生物和食草动物（即水生初级消费者）的Δ¹⁴C值均显著低于现代大气CO₂的Δ¹⁴C值，且在23年林龄的林分中最低。先前的研究表明，日本柳杉的根系生物量在种植后15至30年达到峰值。这些证据表明，根系呼吸释放并通过地下水扩散的土壤CO₂使碳酸盐基质风化，且具有低Δ¹⁴C的溶解无机碳（DIC）被纳入溪流周丛生物和一些大型无脊椎动物中。所研究溪流对日本柳杉皆伐和重新造林的生态响应比化学响应（<5年）慢得多（约20年）。食物网结构从皆伐状态完全恢复需要50多年时间。这种生态延迟归因于几个生物地球化学因素，了解这些因素对于森林 - 溪流连续体的综合管理以及预测生态系统对环境变化的恢复力至关重要。
