Abstract
Palm leaves represent one of the most important non-timber forest products in tropical and subtropical regions. Brahea aculeata is an endemic palm of northwest Mexico, whose leaves are intensively exploited for roof thatch and handcrafts. As part of a long-term defoliation experiment, we evaluated the effects of different leaf harvest on foliar and reproductive traits of adults and attributes of their progeny. We conducted a six-year manipulative experiment and applied three harvesting treatments to adults: high harvest, low harvest and no harvest (control). We recorded leaf production and size, flower and fruit production, seed germination and seedling growth. We also explored trade-offs among foliar and reproductive traits.Harvested palms exhibited drastically reduced reproductive activity, producing fewer flowers and fruits (up to 80 and 90% fewer than unharvested palms). However, individuals in both harvest treatments had larger leaves and increased leaf production rates, compared to control palms. For harvested palms, we registered first a slight increase in leaf traits and a decline in reproductive attributes. These traits showed a gradual reduction and for six period attained very low proportional values compared to control palms (~0.10), however individuals in the harvested treatments maintained the greatest leaf lengths and leaf production rates. Seed germination and seedling growth rates of progeny from harvested palms were significantly lower than control palms, with seeds from the high harvest treatment having the lowest seed production and germination rates. Relationships among leaf (size/production) and reproductive traits (flower/fruit production) were positive during the fourth year, but showed negative relationships for the fifth year suggesting a trade-off between reproduction and growth functions. Leaf harvesting in B. aculeata seems to alter patterns of resource allocation away from reproduction as reflected in a decrease in the probability of reproduction, seed number, germination, and vigor, causing a strong decrease in the reproductive success of this species. Results showed that the consequences of long-term leaf harvest not only affect harvested individuals, but also the fitness and vigor of progeny. This type of long-term studies is essential to understand the population dynamics of non-timber forest products and helps inform sustainable harvesting programs considering intensity, frequencies and periods for recovery from defoliation. Also results may help to explain how intensive and non-planned management schemes may negatively affect vital rates and long-term dynamics of populations from non-timber forest products and other components of the ecosystem.
Highlights
In the tropics and subtropics, palms are one of the most sources of non-timber forest products (NTFP, [1,2,3,4])
For the final year of the experiment (2015–2016), leaf production decreased in the harvesting treatments especially for palms subjected to High harvest with 0.29 less leaf production (Fig 1 and Table 1)
Palms in both harvested treatments initially showed increases in leaf production and leaf length, a similar response to what has been reported in most of the studies focused on evaluating the effects of defoliation on palms and has been proven or interpreted as overcompensation [8], [10], [30], [13, 14], [45, 46]
Summary
In the tropics and subtropics, palms are one of the most sources of non-timber forest products (NTFP, [1,2,3,4]). Palms provide a wide range of products including leaves, fruits, inflorescences and trunks, that are used for building material (e.g. roofs, floors), food, medicine, the production of fibers and oils, and many other cultural, subsistence or commercial purposes [5], [3], [63]. A wide range of responses to defoliation have been reported. Responses include positive (over-compensation), negative (under-compensation) or neutral (little or no difference from unharvested palms) [12,13,14], [16]. Based on the principle that resources are limited, assigning them to a single function should have negative consequences for other functions, resulting in trade-offs between vegetative and reproductive traits [16,17], [20, 21]
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