By: Dr. Jelaine L. Gan
Reforestation efforts often rely on planting trees in degraded areas, a process that demands significant resources, including labor for planting and nurturing seedlings, as well as a steady supply of seedlings. This approach can be costly and limited by the availability of appropriate native species that support biodiversity. Fortunately, forests have natural mechanisms to regenerate if given the chance. Assisted Natural Regeneration (ANR) leverages these processes to accelerate forest recovery, with one effective strategy focusing on increasing seed dispersal to degraded areas.
The concept is straightforward: install bird perches in degraded areas near forests to attract fruit-eating birds. As these birds rest on the perches, they deposit seeds through their droppings, effectively planting the seeds of future forests. But how effective is this method?
Image: Clipping from the comic “How Birds Can Help Farms and Forests in the Philippines” by Jelaine Gan and Jessica Stutman. Read the full comic here: https://blogs.ncl.ac.uk/marionpfeifer/2024/07/19/how-birds-can-help-farms-and-forests-in-the-philippines/
Previous research on the effectiveness of bird perches for seed dispersal and seedling establishment has shown mixed results. To address this, an international team, led by Dr. Jelaine Gan from the Institute of Biology at the University of the Philippines, alongside researchers from Newcastle University, University of St Andrews (UK), and the Norwegian Institute for Nature Research, conducted a systematic review and meta-analysis, synthesizing data from multiple studies.
After thoroughly searching and screening, we reviewed 396 relevant publications. These studies identified three types of perches: artificial, semi-natural, and natural (see Figure 1). Artificial perches, typically man-made, included straight poles made of wood or PVC with horizontal or crossbar designs, as well as live fences (living trees connected with wire) and wood piles. Natural perches varied from shrubs and scattered trees in agricultural fields to tree islands and rocks. Semi-natural perches consisted of dead branches or snags propped up with support.
Figure 1: Illustrations of the three perch types (artificial, semi-natural, and natural) examined in the studies. Created using AI on Canva (Magic Studio™) based on author descriptions.
Key Findings
All three perch types—artificial, semi-natural, and natural—significantly increased the number and diversity of seeds arriving in degraded areas compared to control sites without perches. This confirms their effectiveness in enhancing seed dispersal.
However, successful forest regeneration requires more than just seed arrival; seeds must germinate and grow into seedlings. Our analysis found that only natural perches significantly boosted both seedling density and species diversity. Artificial and semi-natural perches increased seed rain but did not consistently lead to successful seedling establishment without additional interventions.
Recommendations
To maximize forest regeneration, we recommend preserving natural perches, such as shrubs and scattered trees, in agricultural landscapes. In areas lacking these features, artificial or semi-natural perches can be installed to enhance seed dispersal. To improve seedling establishment, complementary measures like soil improvement and weed control should be implemented alongside perch installation.
