Disturbance after Disturbance: Combined Effects of Two Successive Hurricanes on Forest Community Structure

Abstract

Our attempts to gain knowledge from studying the effects of a single windstorm might be complicated by one or more other events that pass through the same system before it recovers from prior damage. In this article, we had the opportunity to examine permanent plots affected by two consecutive catastrophic storms of comparable intensity within a short time frame (less than a decade). We compared tree damage patterns resulting from Hurricane Rita in 2005 and Hurricane Ike in 2008, which struck the same five forest plots (40 m × 50 m each; 1 ha total) established in the Big Thicket National Preserve of southeast Texas. The results showed that the post-Rita forest structure was characterized by intense damage to short, shade-tolerant stems and increased canopy openness. Hence, trees damaged by Ike were, in general, taller, more shade intolerant, and more spatially distant from their undamaged counterparts than trees damaged by Rita. These contrasting damage patterns indicate that Ike affected the plots differently to a normal windstorm occurring in isolation (after a long absence of prior windstorms). We anticipate that the cumulative, compounded effects of these two storms will potentially have long-lasting footprints on the structure and function of the study forest. The need to account for compounding disturbance interactions in forest research and management will grow, because many atmospheric scientists predict increases in both the intensity and frequency of hurricanes in conjunction with future climate change scenarios. Key Words: Big Thicket, disturbance interaction, forest structure, hurricane, spatial point pattern analysis.

我们从研究单一暴风中取得知识的尝试，可能会因为经过尚未从过往损害中回復的同一系统的一个或其他更多事件而复杂化。我们于本文中，有机会检视在短时间内（少于十年）受到两个连续且程度相当的灾难性风暴所影响的固定土地。我们比较由 2005 年瑞塔飓风和 2008 年艾克飓风所导致的三大损害模式；这两个飓风同时侵袭了德州南方大灌木丛国家保护区中设立的五大林地（各自为四十公尺乘以五十公尺；总共为一公顷）。研究结果显示，瑞塔风灾过后的森林结构，以低矮、耐阴树干的密集损害和树冠层增加的开放性为特徵。因此总体而言，受到艾克飓风侵害的树，较受到瑞塔损害的树木而言更高、更为耐阴，并且在距离上距其未受损害的对照组更远。这些对照的损害模式显示，艾克对林地的影响，与（前次风暴发生后一段长时间之后）单独发生的一般风暴并不相同。我们预期这两个风暴累积性且复杂化的影响，将有可能对于所研究的森林结构与功能产生长远的足迹。在森林研究与管理中考量复杂化的干扰互动之需求将会成长，因为诸多大气科学家预测，随着未来气候变迁局势而来的飓风强度与频率皆将有所增加。关键词：大灌木丛，扰乱互动，森林结构，飓风，空间点模式分析。

Nuestros intentos por incrementar conocimiento a partir del estudio de los efectos de una sola tormenta de viento podrían verse complicados por más de un evento que ocurra a través del mismo sistema antes de que éste se haya recuperado de daños anteriores. En este artículo, tuvimos la oportunidad de examinar lotes permanentes que fueron afectados por dos tormentas catastróficas consecutivas, de intensidad comparable, dentro de un marco temporal muy corto (menos de una década). Comparamos los patrones de daño arbóreo resultantes del Huracán Rita en 2005 y del Huracán Ike, en 2008, que golpearon los mismos cinco lotes de bosque (40m x 50m cada uno; 1 ha en total) establecidos en la Reserva Nacional del Big Thicket, en el sudeste de Texas. Los resultados mostraron que la estructura del bosque pos-Rita se caracterizó por intenso daño de los tallos cortos y tolerantes al sombrío y con creciente apertura del dosel. Se nota que los árboles dañados por Ike fueron, en general, más altos, más intolerantes al sombrío, y espacialmente más distantes de sus contrapartes indemnes, que los árboles afectados por Rita. Estos patrones de daño contrastados indican que Ike afectó los lotes de una manera diferente a una tormenta normal que ocurra en aislamiento (después de una larga ausencia de tormentas). Anticipamos que los efectos compuestos acumulativos de estas dos tormentas potencialmente dejarán más impacto duradero en la estructura y función del bosque de estudio. La necesidad de justificar las interacciones de perturbaciones compuestas en investigación y manejo de bosques aumentará debido a que muchos científicos atmosféricos predicen incrementos de los huracanes, tanto en intensidad como en frecuencia, en conjunción con futuros escenarios del cambio climático.

Palabras clave:

• análisis espacial de patrones de puntos
• Big Thicket
• estructura forestal
• huracán
• interacción de perturbaciones

Acknowledgments

The authors appreciate the help of Will Flatley, Laura Spanel-Weber, and Amanda Young in the field. Two anonymous reviewers provided valuable comments on an earlier version of this article.

Supplemental Material

Supplemental data for this article can be accessed on the publisher’s Web site. Material includes Table A.1 and Figure A.1.

Additional information

Funding

This work was supported by the Research Resettlement Fund for the new faculty of Seoul National University.

Notes on contributors

Daehyun Kim

DAEHYUN KIM is an Associate Professor in the Department of Geography at Seoul National University, Seoul 08826, South Korea. E-mail: [email protected]. His research interests include the effects of climate change on the dynamics of coastal, riparian, and forest systems and the implications of spatial autocorrelation for modeling the distribution of natural resources.

Andrew C. Millington

ANDREW C. MILLINGTON is a Professor in the College of Science and Engineering at Flinders University, Adelaide 5001, Australia. E-mail: [email protected]. His research interests include land change science, biogeography, and GIScience.

Charles W. Lafon

CHARLES W. LAFON is a Professor in the Department of Geography at Texas A&M University, College Station, TX 77843. E-mail: [email protected]. His research interests include vegetation patterns, vegetation disturbances (storms, fires, etc.), and the interactions of terrain, climate, human activities, and vegetation.