Would the Nationwide Synchronized Flowering and Dieback of Sasa borealis Promote the Suppressed Forest Regeneration? = 조릿대의 전국 동시 개화 및 고사는 숲의 재생을 촉진할 것인가?

국문 초록 (Abstract)

전 세계적으로 초식, 산불체제 등의 변화로 야기된 숲 교란은 소수 종들이 숲의 하층을 독점하고 확장하게 하는 기회가 되었다. 결과적으로 특정 종이 극도로 우점해서 숲 구조와 기능에 영향을 미치는데, Royo and Rarson(2006)은 이를 ‘독점적인 하층식생(recalcitrant understory)’으로 칭했다. 대표적 예가 양치류, 대나무류, 벼과 식물, Rhododendron spp. 등 영양생장식물이다. 종다양성을 낮추고 식물 종의 재생과 생장을 억제하는 것이 주요 영향이다.
그중에서 Sasa spp.는 작은 키 대나무로 동아시아인 한국, 일본, 중국에 분포한다. 벌채와 화전과 같은 교란이 Sasa spp.의 정착과 생장에 최적인 빛 환경을 만들어서 빠른 확산을 초래한 것으로 알려져 있다. 한국에서도 화전을 비롯하여 강도 높은 숲 훼손의 기회를 이용하여 조릿대(Sasa borealis(Hack.)Makino & Shibata가 확산된 것으로 보인다. 현재 국립공원을 포함하여 전국 내륙의 숲 하층에서 조릿대가 매우 우점하고 있다. 숲 황폐기 이후 숲이 복원되어 수관층이 울폐된 상태에서도 하층의 조릿대가 우점하므로 다른 식물의 빛 이용가능성이 낮을 뿐만 아니라 지상부와 지하부의 물리적인 공간을 차지하여 숲의 종다양성을 현저하게 낮추는 문제종이다.
숲의 다양성을 증진시키기 위해서는 조릿대의 영향을 감소시킬 직접적인 사건이 필요하다. 그 방법 중 하나로 다수 개체군이 동시 개화하고 일시에 고사하는 것이다. 그럼에도 개화주기가 매우 길어 보기 드문 사건인데, 2015년을 전후로 전국에서 조릿대가 동시개화하였다. 이를 선행연구(Cho et al. 2017)로 밝혔으며, 이는 조릿대가 점유했던 숲의 재생을 연구할 수 있는 좋은 기회가 되었다. 그러나 선행 연구는 입산자의 SNS 정보를 수집한 개화 건수여서 우리나라 전역에서 실제 일어난 현상인지를 확인할 필요가 있다. 또한 조릿대 고사 이후 전국적인 규모에서 다른 식물과 조릿대 유식물의 재생 경향 및 식물의 재생을 촉진하는 주요 요인을 분석하는 것이 필요하다.
따라서 본 연구의 목적은 크게 세 가지이다. 1) SNS를 통해 수집한 조릿대 동시개화 현상이 우리나라에 전역에서 광범위하게 일어난 실제 현상인가? 이를 확인하기 위해 5개 국립공원에서 조릿대의 공간적 분포현황과 동시개화 유무 및 개화 이후 고사 동태를 분석하였다. 2) 조릿대 개화 및 고사는 다른 식물의 재생 기회가 되는가? 4개 국립공원에서 조릿대 개화 및 고사 이후 5년 뒤 재생패턴을 조사하여 초기 재생 정도와 특징, 그리고 재생에 미치는 요인들의 중요도를 분석하였다. 3) 조릿대 개화 이후 남아있는 고사체의 지상부와 지하부를 멧돼지가 제거할 시 재생을 촉진하는가? 점봉산에서 조릿대 개화, 멧돼지 섭식활동, 지상부 제거에 따른 70개 영구조사구를 설치하여 숲의 동태를 개화 후 5년간 모니터링하였다.
연구 결과, 첫째, 5개 국립공원에서 25개 경로, 133.5km를 조사결과, 신갈나무-활엽수 혼합림 임상에서 436개 조릿대 패치가 분포했다. 이중 전체 사면을 덮는 패치의 수가 75%에 달했고, 경로 출발 지점부터 산 정상까지 모두 점유하는 경우도 있었다. 즉, 조릿대가 대규모 면적으로 분포함을 확인했다. 총 51%(219개)의 패치가 개화했고, 개화한 패치의 76%는 2015년에 개화했다. 2015년을 최대로 수년 내에 우리나라 전역에서 넓은 면적의 조릿대가 개화했음을 의미한다. 개화율은 설악산국립공원이 가장 높았다. 공통적으로 미개화 패치와 비교할 때 culm의 크기가 큰 패치에서 개화했다(culm의 키 F=80.821, p <0.001, 굵기 F=58.312, p <0.001). 과거 지리산 개화 기록으로 유추했을 때, 조릿대 수명 및 개화 주기는 약 50년 내외인 것으로 추정된다.
둘째, 조릿대 개화 후 5년 뒤, 97개 plot중에서 33%는 조릿대 이외 다년생 초본의 피도가 높았으나, 51%는 조릿대가 다시 우점하며 재정착했고, 16%는 재생피도가 현저히 낮았다. 즉, 다시 조릿대가 재정착하거나 재생 피도가 낮은 경우가 절반 이상으로 많았다. 조릿대 이외 다른 식물의 재생에는 조릿대 고사체의 분해율이 가장 중요했고, 숲틈 피도가 25% 이상인 입지에서 재생피도가 크게 증가했다. 반면 조릿대 재정착에는 고도의 중요도가 높았는데, 조릿대의 생육 범위와 일치하여 1,000-1,300m에서 가장 피도가 높았다.
셋째, 멧돼지가 파헤친 곳은 목본종을 포함하여 새로운 종이 유입되면서 종다양성이 유의하게 증가했다. 관목종과 초본종의 풍부도가 증가한 반면, 조릿대 유식물의 정착은 억제되었다. 숲의 재생에 멧돼지 섭식활동이 독립적으로 영향을 미쳤으나, 조릿대 개화와 멧돼지 섭식활동의 시너지 효과가 특히 두드러졌다. 멧돼지는 조릿대 고사 이후 남아있는 고사체를 제거하고 종자 분산자로서 역할을 하는 것으로 판단된다. 그 결과 종 조성이 대조구와 가장 유사해졌다. 반면 조릿대 고사체 지상부만 제거했을 때는 오히려 조릿대 유식물의 재정착을 촉진했다.
이 연구를 종합하면, 2015년을 최대로 하는 조릿대의 전국적인 동시개화 주기와 고사현상을 밝혔으며 약 50년의 개화주기를 추정하였다. 개화 후 5년 조사 결과로서 조릿대의 재점유 경향이 우세했지만, 숲 환경이 과거와 달라졌으므로 조릿대가 과거와 같은 독점적 지위를 회복하기 어려우며 파편화된 작은 크기로 잔존할 것이다. 조릿대의 동시개화 후 고사 결과로, 기존 식생 경관에 미친 조릿대 독점의 부정적 영향의 완화와 자연 식생으로의 재생이 전망된다. 그러나 경관의 실제 변화를 파악하기 위해서는 장기생태연구가 필수적이다.

다국어 초록 (Multilingual Abstract)

Forest disturbances caused by changes in herbivory and fire regimes around the world have provided an opportunity for a small number of species to monopolize and expand the understory vegetation. As a result, those species become extremely dominant and affect forest structure and function, which Royo and Rarson(2006) refer to as ‘recalcitrant understory’. Representative examples of such species are vegetative plants such as ferns, bamboos, grass, Rhododendron spp. Its main impact is to adversely affect species diversity and inhibit the regeneration and growth of plants species.
Among them, the genus Sasa is an evergreen dwarf bamboo distributed in East Asian countries, namely Korea, Japan and China. Disturbances such as deforestation and slash-and-burn are known to create an optimal light environment for the settlement and growth of this genus Sasa. Among this, Sasa borealis(Hack.)Makino & Shibata have spread in South Korea, taking the advantage of slash-and-burn and other intensive forest damage in the past. Currently, S. borealis is very dominant in the understory vegetation of forests across the country including the national parks as well. The dominance of the understory S. borealis continues even after the forest was restored to a closed forest after the deforestation period. As a result, not only the availability of light for other plants has become low, but Sasa borealis is also a problematic species that significantly lowers the species diversity of the forest by occupying physical space above and below the ground.
Therefore, direct events that reduce the impact of S. borealis are needed to promote forest diversity. One of the methods is to simultaneously flower and decline in several populations depending on the characteristics of this monocarpic S. borealis. It is a rare event that the flowering cycle is very long, but with the peak in 2015, the S. borealis bloomed simultaneously across the country. This was a good opportunity to study the regeneration of the forest occupied by S. borealis and was published in a previous report(Cho et al. 2017). However, as the previous study collected SNS information from the climbers, it is necessary to check whether S. borealis actually bloomed in South Korea. In addition, after the decline of S. borealis, it is necessary to analyze the regeneration patterns of the other plants and S. borealis seedlings on a national scale and the main factors that promote plants regeneration.
In the present study, three objectives were established. 1) Is the simultaneous flowering of S. borealis collected through SNS a real phenomenon that has occurred widely in reality in South Korea? To investigate this, the spatial distribution status of S. borealis in 5 national parks, simultaneous flowering and post-flowering dynamics were analyzed. 2) Does the simultaneous flowering and decline of S. borealis give other plants a chance to regenerate? In 4 national parks, the generation patterns of S. borealis after flowering and decline were studied, and the characteristics of early regeneration and the importance of the factors affecting regeneration were analyzed. 3) Does wild boar promote regeneration by removing the upper and lower parts of dead matter remaining after flowering? In Mt. Jeombong, 70 permanent plots were set for S. borealis flowering, wild boar rooting activities, and removal of above-ground parts to monitor forest dynamics for 5 years after flowering.
First, as a result of investigating 25 transects in 5 national parks, 436 S. borealis patches were distributed on the forest floor of Quercus mongolica-hardwood mixed forest. Among them, the number of patches covering the entire slope reached 75%, and in some cases, the entire area was occupied from the starting point to the top of the mountain. That is, it was found that S. borealis was distributed over a large area. A total of 51% (219) patches bloomed, and 76% bloomed in 2015. It means that with the peak in 2015, a large area of S. borealis patches bloomed all over the country within a few years. The flowering rate was the highest in Seorak National Park. Comparing with the non-flowering patches, flowering occurred in the patch with a larger culm size (height: F=80.821, p <0.001, diameter: F=58.312, p <0.001). Judging from the past flowering records of Mt. Jiri, it was estimated that the lifespan and flowering cycle of S. borealis are around 50 years.
Second, 5 years after S. borealis flowering, among 97 plots, 33% of the plots had high coverage of perennial herbs excluding S. borealis, but in 51%, S. borealis dominated again and resettled, whereas 16% showed a remarkably low regeneration coverage. That is, in more than half of the cases S. borealis resettled or had low regeneration coverage. For regeneration of other plants, the decomposition rate of the S. borealis dead remains was the most important, and the regeneration coverage increased significantly in sites where the forest gap coverage was more than 25%. On the other hand, elevation was an important factor for resettlement of S. borealis, which was the highest at 1,000-1,300 m and consistent with the main distribution range.
Third, species diversity increased significantly as new species, including tree species, were introduced into the areas dug by wild boars. While the abundance of shrub and herbaceous species increased, the settlement of S. borealis seedlings was suppressed. Although wild boar rooting had an independent effect on forest regeneration, the synergistic effect of S. borealis flowering and wild boar rooting was particularly remarkable. Wild boars act as seed dispersers, removing dead materials that remain after flowering. As a result, the species composition was mostly similar to that of the reference. On the other hand, when only the dead culms of S. borealis were removed, the resettlement of S. borealis seedlings was promoted.
In summary, the nationwide simultaneous flowering cycle and death phenomenon of S. borealis, which peaked in 2015, were clarified, and a flowering cycle of about 50 years was estimated. As a result of investigation for 5 years after flowering, the tendency of S. borealis to re-occupy was found to be dominant. However, since the forest environment has changed from the past, it is difficult for S. borealis to regain its monopoly position as in the past, and it this remains in fragmented small size. As a result of simultaneous flowering and decline of S. borealis, it is expected that the negative impact of the monopoly of bamboo plants on the existing vegetation landscape will be alleviated and regeneration of natural vegetation will occur. However, long-term ecological studies are essential to understand the actual changes in the landscape.

목차 (Table of Contents)

• ABSTRACT ⅰ
• CONTENTS ⅲ
• LIST OF FIGURES ⅵ
• LIST OF TABLES ⅷ
• CHAPTER Ⅰ. General Introduction 1
• 1. Distribution of Sasa spp. in East Asia and Sasa borealis in Korea 1
• 2. Spread of S. borealis by Forest Disturbances in Korea 2
• 3. Growth Characteristics and Effects on Forest 4
• 4. Synchronized Massive Flowering and Dieback 5
• 5. Aims of This Study 7
• 6. References 9
• CHAPTER Ⅱ. Distribution and synchronized massive flowering of Sasa borealis in the forests of Korean Parks 14
• 1. Introduction 14
• 2. Materials and Methods 16
• 1) Studied National Parks and Investigated Transects 16
• 2) Vegetation Survey and Data Analysis 18
• 3. Results 19
• 1) Distribution of S. borealis 19
• 2) Synchronized Massive Flowering of S. borealis 21
• 3) Synchronized Dieback Following the Flowering Events 25
• 4. Discussion 25
• 5. References 29
• CHAPTER Ⅲ. Early Regeneration of Understory Vegetation and Success Factors following Dwarf Bamboo Monocarpic Flowering in Closed Forests 33
• 1. Introduction 33
• 2. Materials and Methods 36
• 1) Study Site 36
• 2) Vegetation Survey 37
• 3) Data Analysis 41
• 3. Results 42
• 1) Early Regeneration Pattern 42
• 2) Regeneration Factors 45
• 4. Discussion 50
• 5. References 53
• CHAPTER Ⅳ. Synergistic Effect of Dwarf bamboo Flowering and Wild Boar Rooting on Forest Regeneration 58
• 1. Introduction 58
• 2. Materials and Methods 61
• 1) Study Area and Species 61
• 2) Experimental Layout and Permanent Plot Set Up 63
• 3) Vegetation Survey 65
• 4) Data Analysis 65
• 3. Results 66
• 1) Species Diversity 66
• 2) Species Composition 68
• 3) Regeneration of Tree Species 71
• 4) Reestablishment of S. borealis 74
• 4. Discussion 75
• 5. References 81
• CHAPTER Ⅴ. General Conclusions 89
• 1. S. borealis Expansion and Distribution in South Korea 89
• 2. Synchronized Flowering, Decline Cycle and Lifespan 90
• 3. Early Regeneration of Vegetation after Mass Flowering and Decline 90
• 4. Regeneration Prospects of S. borealis Distribution Areas at Landscape Level: Management Implications 92
• 국문초록 95
• Appendix 97

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