Modeling carbon allocation in trees: a search for principles

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Authors: Oskar Franklin, Jacob Johansson, Roderick C Dewar, Ulf Dieckman, Ross E Murtrie, Ake Brannstrom, Ray Dybzinski.


We review approaches to predicting carbon and nitrogen allocation in forest models in terms of their underlying assumptions and their resulting strengths and limitations. Empirical and allometric methods are easily developed and computationally efficient, but lack the power of evolution-based approaches to explain and predict multifaceted effects of environmental variability and climate change. In evolution-based methods, allocation is usually determined by maximization of a fitness proxy, either in a fixed environment, which we call optimal response (OR) models, or including the feedback of an individual's strategy on its environment (game-theoretical optimization, GTO).

Optimal response models can predict allocation in single trees and stands when there is significant competition only for one resource. Game-theoretical optimization can be used to account for additional dimensions of competition, e.g., when strong root competition boosts root allocation at the expense of wood production. However, we demonstrate that an OR model predicts similar allocation to a GTO model under the root-competitive conditions reported in free-air carbon dioxide enrichment (FACE) experiments. The most evolutionarily realistic approach is adaptive dynamics (AD) where the allocation strategy arises from eco-evolutionary dynamics of populations instead of a fitness proxy. We also discuss emerging entropy-based approaches that offer an alternative thermodynamic perspective on allocation, in which fitness proxies are replaced by entropy or entropy production. To help develop allocation models further, the value of wide-ranging datasets, such as FLUXNET, could be greatly enhanced by ancillary measurements of driving variables, such as water and soil nitrogen availability.

Model alokasi karbon pada pohon: sebuah pencarian prinsip dasar


Penelitian ini membahas tentang pendekatan yang digunakan untuk memprediksi alokasi karbon dan nitrogen dengan model hutan dengan lingkup masalah pada asumsi-asumsi dasar dan kekuatan serta keterbatasan yang dihasilkannya. Metode empiris dan alometrik memang mudah dikembangkan dan berdasarkan hitungan termasuk efisien, namun metode tersebut tidak memiliki kekuatan pendekatan berbasis evolusi yang diperlukan untuk menjelaskan dan memprediksi berbagai bentuk dan jenis dampak variabilitas lingkungan dan perubahan iklim. di dalam model berbasis evolusi, alokasi biasanya ditentukan dengan memaksimalkan sebuah 'fitness proxy', baik dalam lingkungan yang tetap, yang peneliti sebut sebagai model respon optimal (OR), atau menyertakan umpan balik strategi individu terhadap lingkungannya (game-theoretical optimization, GTO). Model respon optimal dapat memprediksi alokasi setiap pohon jika terdapat persaingan yang signifikan hanya untuk satu satu sumber daya. 'Game-theoretical optimization' dapat digunakan untuk mempelajari dimensi-dimensi pendukung persaingan, misalnya, jika persaingan akar yang kuat mendorong alokasi akar dengan mengorbankan produksi kayu. Namun demikian, peneliti membuktikan bahwa model OR memprediksi alokasi yang sama terhadap model GTO dalam kondisi 'root-competitive' yand dilaporkan di dalam eksperimen 'free-air carbon dioxide enrichment (FACE). Pendekatan realistis yang paling revolusioner adalah dinamika adaptif (AD) di mana strategi alokasi berasal dari dinamika eko-evolusioner populasi, bukan dari 'fitness proxy'. Peneliti juga membahas munculnya pendekatan-pendekatan berbasis-entropi yang menawarkan sebuah perspektif termodinamika alternatif terhadap alokasi, dimana 'fitness proxy' digantikan oleh entropi atau produksi entropi. Untuk membantu model-model alokasi lebih lanjut, nilai dataset yang lengkap, seperti FLUXNET, dapat ditingkatkan dengan ukuran variabel-variabel pendorong, misalnya ketersediaan nitrogen air dan tanah.

Kata kunci: aklimasi, strategi stabil evolusioner, keseimbangan fungsional, 'game theory', partisi, plastisitas, kedalaman tanah, teori, pertumbuhan pohon.

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