Gheyur Gheyret, Xinjiang Normal University, discusses his article in Journal of Ecology: Tree growth phenology shifts in response to trait-based neighborhood effects in a large subtropical forest biodiversity experiment
Growth in trees is invisible to the naked eye — it happens too slowly, too quietly, measured in micrometers rather than anything you could observe directly. But across days and weeks, those tiny increments accumulate. And within a single growing season, the pace of growth is far from constant: there are bursts, pauses, and peaks. We wanted to know when those peaks arrive — and whether the neighbouring trees have anything to do with it.
In our recent study at the BEF-China experiment — the first large biodiversity experiment in a species-rich subtropical region — we asked a deceptively simple question: when during the year do trees actually grow fastest, and does the answer depend on who is standing next to them?
Listening to trees, every 30 minutes
To find out when trees are growing, we strapped automatic dendrometers onto tree trunks across a large biodiversity experiment in Jiangxi Province, southeastern China. These instruments measure changes in stem girth down to a few micrometers—every 30 minutes, day and night. Combined with monthly hand-measurements from manual dendrometer bands, we built three full years of intra-annual growth records for 2,478 trees across 35 species.
For every tree, we identified three things: when its “fast-growing phase” started, when it ended, and how high its daily growth rate peaked in between. Then we asked how these timings related to the tree’s own functional traits — its leaf and wood economy — and to the traits of its eight nearest neighbors.
Trees keep different schedules
Species with thin leaves, high specific leaf area, and high leaf phosphorus — traits that define what ecologists call the acquisitive strategy typical of many deciduous trees — began their fast-growing phase early in the season and ended it early too. Their peak daily growth rate, however, was relatively modest. Think of them as early risers: they get going before anyone else and wrap up before the heat of late summer — busy, but never especially fast at their peak.
Species at the other end of the spectrum — with denser wood and higher stomatal density per unit leaf area, a profile ecologists call the conservative strategy, common in evergreen trees — showed the opposite pattern. They were slow to get started, but once underway, their daily growth rate climbed to a notably higher peak and held on later into the season. If acquisitive trees are early risers, these are the ones who take their time warming up, build steadily, and finish strongest.
In short: some trees get going early and keep things quiet at their peak; others start late but push harder when it counts. Each follows its own internal schedule.
Your neighbors change your schedule
When we looked at each neighborhood, the results were surprising. We originally thought that diversified neighborhoods would only promote growth. But in reality, the situation is more complicated: the same neighborhood will guide each tree to grow in different directions according to their characteristics.
Acquisitive trees surrounded by neighbours that were primarily water-conserving species (those with denser wood and higher stomatal regulation) tended to delay both the start and end of their fast-growing phase. One likely reason: water-conserving neighbours use soil moisture more efficiently, keeping it available later in the season—and acquisitive trees appear to capitalize on that late-season supply. In contrast, trees with the conservative strategy started their fast-growing phase earlier and reached a higher peak daily growth rate when surrounded by neighbours spanning a wide range of functional strategies—particularly those with strong water-conserving traits.
In other words, trees appear to take turns— the timing of each species’ peak growth shifting in response to the traits of its neighbours, so that different trees peak at different moments rather than all competing for the same resources at once. Ecologists call this temporal niche complementarity—the idea that species in a diverse community reduce direct competition not just by occupying different physical spaces, but by peaking at different times. Rather than all trees racing to grow simultaneously, diversity allows them to stagger their most intensive growth, spreading the demand for light, water and nutrients across the season. This pattern appears to be a widespread feature of diverse forests: similar signals have recently emerged from dendrometer-based studies in temperate old-growth forests in Japan and in tropical forests along Afrotropical elevation gradients.
Why peak speed beats long season
When we brought everything together using a structural equation model, the strongest driver of annual growth was neither the start date nor the end date, but the peak daily growth rate. For subtropical trees, annual growth depended more on how fast they grew at their best moment than on the length of the growing season.
This has a practical implication. As climate change intensifies drought and shifts seasonal patterns, forests that contain a range of functional strategies may be better able to spread growth across the year and among species. That spread can help stabilize productivity. Mixed-species plantations designed with temporal complementarity in mind may therefore offer a way to build forests that are both more productive and more resilient.
It is also crucial to clarify the limitations of our model. Focal tree and neighborhood traits can only explain 8% to 19% of the variance of growth phenology. Most of the remaining variation is likely to reflect the complex reality of individual trees, each shaped by microclimate, soil conditions, growth history, and chance. Even so, the directional signals we captured are still consistent and perform robustly for a variety of diversity measurement methods, indicating a reasonable mechanism rather than a simple correlation.
Three years of dendrometer measurements revealed a simple phenomenon, but it made us quietly excited. Trees are not soloists. They are a forest orchestra, and the conductor sits right next door.
