沼泽-森林梯度上的枯萎现象导致光照供应发生变化

IF 2.7 3区 环境科学与生态学 Q2 ECOLOGY Ecosphere Pub Date : 2024-10-14 DOI:10.1002/ecs2.70021
Giovanna Nordio, Keryn Gedan, Sergio Fagherazzi
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引用次数: 0

摘要

沿海森林的生态分带受海平面上升和风暴潮事件的影响。能在中度盐碱条件下存活的成熟树木在土壤盐度超过其耐受水平时会表现出应激迹象。由于树叶灼伤、叶片损伤和落叶减少了树冠覆盖率,树冠内就会形成光隙。在森林-沼泽边缘,树冠覆盖损失最为严重;没有树冠的枯树干形成了 "幽灵森林"。树冠变薄和来自边缘的光照改变了林下植被的生长条件,促进了灌木的生长,并有利于以前受光照竞争限制的入侵物种的建立和传播。在这项研究中,我们对过渡到盐沼的沿海森林的照度和温度进行了分析。地表上方的光传感器用于测量树木和林下植被的光衰减,并观察森林-沼泽边缘树冠减少的影响。在离沼泽较远的地方,盐度较低且树木健康,浓密的树冠会减弱光照。我们估计,在生长季节,树冠平均截获了 50% 的光照。在靠近沼泽的地方,树冠变薄和树木枯死会让更多的光线从上方以及邻近的沼泽地穿透进来。森林-沼泽边缘的光线穿透(边缘效应)进一步提高了这些照度值。在这里,较高的照度可能会使葭萌植物得以扩展。在中间位置,根据灌木树冠上方和下方的照度比较,树木截取了 32% 到 49% 的光线,林下灌木 Morella cerifera 又截取了 45% 的穿透光线。从边缘也能感觉到光线的穿透。Cerifera 的存在降低了靠近土壤表面的空气温度,创造了一个凉爽的夏季小气候。树冠大小反映了树木的健康状况。树冠模式和边缘效应导致了森林-沼泽梯度上的光照分布,从而影响了林下植被的生物量。我们的结论是,在海平面上升导致的森林退缩过程中,树木的枯死会增加光照的可用性,从而有利于楠木和桉树在林下的临时蚕食。
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Shifts in light availability driven by dieback across a marsh-forest gradient

Ecological zonation in coastal forests is driven by sea level rise and storm-surge events. Mature trees that can survive moderately saline conditions show signs of stress when soil salinity increases above its tolerance levels. As leaf burn, foliar damage, and defoliation reduce tree canopy cover, light gaps form within the crown. At the forest-marsh edge, canopy cover loss is most severe; trunks of dead trees without canopies form “ghost forests.” Canopy thinning and light from the edge alter conditions for understory vegetation, promoting the growth of shrubs and facilitating establishment and spread of invasive species that were previously limited by light competition. In this research, we present an analysis of illuminance and temperature in a coastal forest transitioning to a salt marsh. Light sensors above the ground surface were used to measure light attenuation of trees and understory vegetation and to observe the effect of reduced canopies at the forest-marsh edge. Farther from the marsh, where salinity is lower and trees are healthy, dense canopies attenuate light. We estimate that during the growing season, tree canopies intercept 50% of illuminance on average. Closer to the marsh, canopy thinning, and tree death allow greater light penetration from above, as well as from the adjacent marsh. These illuminance values are further increased by light penetration from the forest-marsh edge (edge effect). Here, higher illuminance may permit Phragmites australis expansion. At intermediate locations, trees intercept between 32% and 49% of light and the understory shrub Morella cerifera intercepts a further 45% of penetrating light based on comparisons of illuminance above and below shrub canopies. Light penetration from the edge can also be felt. The presence of M. cerifera reduces the air temperature close to the soil surface, creating a cooler summer microclimate. The tree health state is reflected in the canopy size. The canopy patterns and the edge effect are responsible for light availability distribution along forest-marsh gradients, consequently affecting the understory vegetation biomass. We conclude that during forest retreat driven by sea level rise, tree dieback increases light availability favoring the temporary encroachment of Ph. australis and M. cerifera in the understory.

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来源期刊
Ecosphere
Ecosphere ECOLOGY-
CiteScore
4.70
自引率
3.70%
发文量
378
审稿时长
15 weeks
期刊介绍: The scope of Ecosphere is as broad as the science of ecology itself. The journal welcomes submissions from all sub-disciplines of ecological science, as well as interdisciplinary studies relating to ecology. The journal''s goal is to provide a rapid-publication, online-only, open-access alternative to ESA''s other journals, while maintaining the rigorous standards of peer review for which ESA publications are renowned.
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