Agroforestry can contribute to an increase in tree cover in historically forested tropical landscapes with associated gains in biodiversity and ecosystem functioning, but only if established on open land instead of underneath a forest canopy. However, declines in yields with increasing shade are common across agroforestry crops, driving shade-tree removal in forest-derived agroforests and hindering tree regrowth in open-land-derived agroforests. To understand trajectories of change in tree cover in forest- and open-land-derived agroforests, and the impacts of tree cover on vanilla yields, we studied 209 vanilla agroforests along an 88-year chronosequence in Madagascar. Additionally, we used remotely sensed canopy cover data to investigate tree cover change in the agricultural landscape. We found yields to vary widely but independently of canopy cover and land-use history (forest- vs. open-land-derived), averaging at 154.6 kg ha⁻¹ year⁻¹ (SD = 186.9). Furthermore, we found that forest- and open-land-derived vanilla agroforests gained canopy cover over time, but that only open-land-derived agroforests gained canopy height. Canopy cover increased also at the landscape scale: areas in the agricultural landscape with medium initial canopy cover gained 6.4% canopy cover over 10 years, but canopy cover decreased in areas with high initial canopy cover. These opposing trends suggest tree cover rehabilitation across areas covered by vanilla agroforests, whereas remnant forest fragments in the agricultural landscape were transformed or degraded. Our results indicate that yield-neutral tree rehabilitation through open-land-derived agroforestry could, if coupled with effective forest protection, provide benefits for both ecosystem functions and agricultural production in a smallholder-dominated agricultural landscape.

农林业可以促进历史悠久的热带森林景观中树木的覆盖，并增加生物多样性和生态系统的功能，但前提是必须建立在开阔土地上而不是在林冠下。然而，在农林业中，随着遮阳的增加，单产下降尤为普遍，这促使森林衍生的农林中的遮荫树木被清除，并且阻碍了农田衍生的农林中的树木再生。为了解森林和开阔土地的农用林中树木覆盖率的变化轨迹以及树木覆盖率对香草产量的影响，我们在马达加斯加沿88年的时间序列研究了209种香草农用林。此外，我们使用了遥感的树冠覆盖数据来调查农业景观中树木的覆盖变化。^-1 年^-1（SD = 186.9）。此外，我们发现随着时间的推移，森林和开阔地的香草农林获得了冠层覆盖，但只有开阔地的农林获得了冠层高度。冠层的覆盖面也在景观尺度上增加：在农业景观中，初始冠层覆盖的区域在10年中获得了6.4％的冠层覆盖，但是在初始冠层覆盖较高的区域，冠层的覆盖率下降了。这些相反的趋势表明，在各种香草农林覆盖的地区，树木的植被得到了恢复，而农业景观中残留的森林碎片却被转化或退化了。我们的研究结果表明，如果结合有效的森林保护措施，通过开阔土地的农用林进行的中性树恢复生产可以