Importance of interspecific and intraspecific variation of plant functional traits: a case study in the Lalashan Forest Dynamics Plot

Master thesis at the Institute of Ecology and Evolutionary Biology, National Taiwan University (October 2021)

Author: Lee Yi-Nuo (李以諾)

Advisor: David Zelený


Knowing the community-level trait-environment relations is important for understanding how species and individuals increase their fitness under the environment, and many case studies based on the interspecific trait variation (BTV) has been published. However, recent studies argued that the intraspecific trait variation (ITV) is also important in these relations. Here, we explored the leaf trait of broadleaf trees in the subtropical montane mixed cloud forest of northern Taiwan as an example to answer the following questions: 1) which trait relates to which environmental factor in interspecific and intraspecific level, and what are the possible mechanisms of these relations? 2) what is the relative importance of BTV and ITV in these relations? The one-hectare Lalashan Forest Dynamics Plot (LFDP, 24°42′ N, 121°26′ E, elevation 1758-1782 m a.s.l.) has been established in a wind-exposed flat ridge. We surveyed all the trees with DBH ≥ 1 cm in 25 10 m × 10 m subplots within LFDP, and measured the leaf traits from 1-3 individuals of every broadleaf woody species occurring in each subplot, including leaf area, leaf thickness, relative chlorophyll content, specific leaf area, leaf dry matter content and leaf succulence. We calculated the site-specific, interspecific and intraspecific level community weighted mean (CWM), and separately linear regressed them against the environmental factors, including convexity, windwardness, conifer basal area, and soil properties. The subsequent variation partitioning was performed to obtain the relative importance of BTV and ITV in those regressions. We found many trait-environment relations occurred in the intraspecific level. In particular, the leaf thickness and succulence are positively related to the windwardness, specific leaf area is negatively and positively related to the windwardness and conifer basal area, respectively. These may indicate that the tree individuals mitigate the wind-induced physiological impact by adjusting their leaf traits, and the broadleaf trees acclimate to the shading effect by the extruded tree crown of large coniferous trees nearby. Variation partitioning reveals that the ITV can be more important in totally different trait-environment relations than the BTV. Our results support the argument that ITV is important in the trait-environment relations. Our findings also agree with the suggestion that considering both BTV and ITV may be necessary in the trait-environment studies, especially in the studies conducted in the small spatial extent (e.g., one-hectare).



研究植群的功能性狀與環境的關聯性可幫助我們了解物種及個體適應環境的機制,許多基於種間性狀變異的研究已被提出,然而最近的討論認為種內性狀變異在小空間尺度中對這些關聯性也相當重要。本研究以臺灣北部中海拔雲霧林為例進行探討,以回答:1) 闊葉樹的何種葉片功能性狀在種間與種內層級與環境因子有所關聯,並提出可能的機制;2) 種間與種內性狀變異對於這些關聯性的重要性為何? 我們在拉拉山附近的寬稜線上建置一公頃的森林動態樣區,調查了其中25個10公尺 × 10公尺小樣區中所有胸徑大於等於一公分的樹,並在每個小樣區的每種闊葉樹中挑選1-3棵測量葉片功能性狀,包含葉面積、葉厚度、比葉面積 (specific leaf area)、及葉片肉質程度。我們計算了小樣區、種間及種內層級的群落性狀加權平均 (community weighted mean),並分別與環境因子,包含迎風程度 (windwardness)、針葉樹樹基面積、及土壤性質進行線性迴歸,再進行方差分解 (variation partitioning) 以得知種間與種內性狀變異對這些迴歸的重要性。 迴歸分析發現許多植群的功能性狀與環境皆只在種內層級有關聯,特別是葉厚度和葉片肉質程度與迎風程度的正關聯性、及比葉面積與迎風程度的負關聯性、和與針葉樹樹基面積的正關聯性。這些發現或顯示了闊葉樹個體會改變其葉片性狀以減低恆風 (chronic wind) 對其生理的影響,且會對於附近大胸徑針葉樹之突出樹冠所導致的遮蔽效應有所反應。方差分解則發現種間與種內的性狀變異分別對於不同的關聯性有不同的重要性。總而言之,本研究支持了種內性狀變異相當重要的論述,且認為在植群性狀與環境關聯的研究,特別是在小空間尺度中,同時考慮種間與種內的性狀變異是必要的。