Abstract
Herbaceous vegetation is a major source of interference with the regeneration of woody species. This is particularly the case after forest fires, as a dense herbaceous layer usually regenerates naturally. Although the competitive effect of the herbaceous vegetation upon tree seedlings has been widely studied, there are still gaps in knowledge for management related to the effect of tree seedling age and size on the outcome of the interaction. In this study, we seek to determine the response of maritime pine (Pinus pinaster Aiton) seedlings to herbaceous competition at two different seedling ages. For that, two treatments of herbaceous competition were implemented, namely unweeded (no action around pine seedlings) and weeded (herbaceous cover removed around pine seedlings). Treatments were conducted twice (2 and 4 years after the fire), and we monitored seedling survival and growth at the end of each growing season. The treatments were implemented across three adjacent landscape units that differed in the management of burned wood and that are representative of common post-fire scenarios: no intervention, salvage logging, and an intermediate degree of intervention. Weeding increased seedling survival from 44.7% to 67.8% when seedlings were 2 years old, but had no effect for four-year-old seedlings, which showed 99% survival. Seedling growth also increased in the weeding treatment, but only slightly. Moreover, growth (and survival for two-year-old seedlings) was strongly correlated with initial seedling size, particularly in the case of two-year-old seedlings. Initial pine seedling height was strongly and positively correlated with the height of the herbaceous layer, supporting the existence of microsite features that promote plant growth above competitive effects. The results support that management actions conducive to foster post-fire pine forest restoration in this Mediterranean ecosystem should reduce herbaceous competition at early stages after fire (second or third year) and focus on larger seedlings.
Highlights
Competition with herbaceous vegetation is a major constraint for woody species recruitment, both through natural regeneration [1,2,3] and in reforestations and afforestations [4,5,6,7]
The negative effect of herbaceous cover is quite ubiquitous, and its effect may change depending on environmental conditions, a competitive interaction has been widely reported for biomes and ecosystem types as different as conifer forests [2], broadleaf forests [5,19], grasslands [6,13,20], and Mediterranean-type ecosystems [21,22]
Our study shows that the herbaceous layer interfered with the recruitment of a serotinous pine species in a burned Mediterranean ecosystem and that appropriate management can help increase species in a burned Mediterranean ecosystem and that appropriate management can help increase seedling survival and growth
Summary
Competition with herbaceous vegetation is a major constraint for woody species recruitment, both through natural regeneration [1,2,3] and in reforestations and afforestations [4,5,6,7]. Competition with herbs can be limiting for the growth and survival of woody seedlings after wildfire, which usually removes competitive tree canopies but triggers the establishment of dense herbaceous cover (e.g., [8,9,10]). The negative effect of herbaceous cover is quite ubiquitous, and its effect may change depending on environmental conditions (even turning to facilitation in some cases; [16,17,18]), a competitive interaction has been widely reported for biomes and ecosystem types as different as conifer forests [2], broadleaf forests [5,19], grasslands [6,13,20], and Mediterranean-type ecosystems [21,22]. Given that ground vegetation and tree seedlings compete for resources, any niche separation of resource use, either above or below ground, may reduce the negative effect of the competition by herbs
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